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1Laboratory of Veterinary Pharmacology, College of Veterinary Medicine and BK21 Program for Veterinary Science, Seoul National University, Seoul; and 2Department of Oral Physiology and Institute of Oral Bioscience, School of Dentistry, Chonbuk National University, Jeonju, Republic of Korea
Submitted 22 May 2007; accepted in final form 17 November 2007
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMETHODSRESULTSDISCUSSIONGRANTSACKNOWLEDGMENTSREFERENCES |
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2A- and 1A/1L-adrenoceptor antagonists, respectively. ADX increased the proportion of the neurons showing the noradrenergic reduction and the extent of reduction in the IPSC frequency. The ADX-induced changes were reversed by supplementation of ADX rats with corticosterone (10-mg pellet). ADX also potentiated the noradrenergic reduction in the frequency of miniature IPSC and paired-pulse facilitation of evoked IPSC. BRL 44408 (3 µM), a 2A-adrenoceptor antagonist, blocked the noradrenergic reduction in ADX rats. Corticotropin-releasing hormone and/or vasopressin transcripts were detected in neurons displaying noradrenergic augmentation or reduction of IPSC frequency. ADX enhanced the proportion of neurons expressing corticotropin-releasing hormone. Collectively, the results suggest that depletion of corticosterone by ADX markedly potentiates the noradrenergic suppression of GABAergic transmission mediated by the 2A-adrenoceptors on the GABAergic terminals in the parvocellular neurosecretory PVN neurons. These results may provide a novel synaptic mechanism for the glucocorticoid-induced plasticity in the noradrenergic modulation of neuroendocrine function of the PVN. |
INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMETHODSRESULTSDISCUSSIONGRANTSACKNOWLEDGMENTSREFERENCES |
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; Keller-Wood and Dallman 1984; Whitnall 1993) but also by modulating neuronal inputs to the PVN in the central stress pathways (Herman et al. 2003). An important target of the glucocorticoid action is the catecholaminergic pathways from the brain stem that provide the major excitatory inputs to the PVN. The A2/C2 catecholaminergic cells in the area of the solitary tract nucleus preferentially innervate the neurons in the medial parvocellular zone and the A1/C1 cells in the rostral ventrolateral medulla innervate the parvocellular preautonomic neurons (Cunningham and Sawchenko 1988; Cunningham et al. 1990). These pathways are activated by stress (Pacak et al. 1995) and mediate the release of CRH and adrenocorticotropin through the 1-adrenoceptors (Plotsky et al. 1989; Szafarczyk et al. 1987). On the other hand, adrenalectomy (ADX) or removal of circulating corticosterone in the rat increases the stress-induced release of noradrenaline (Pacak et al. 1995) and both 2A- (Feuvrier et al. 1999) and 1B-adrenoceptor mRNA levels in the PVN (Day et al. 1999), whereas chronic stress reduces the 2A-adrenoceptor mRNA levels in selective brain regions (Meyer et al. 2000).
Another important target of glucocorticoid action is the GABAergic inputs to the PVN. The GABAergic terminals in the PVN are abundant (Decavel and van den Pol 1990) and originate mainly from the extranuclear regions, particularly the peri-PVN areas (Boudaba et al. 1996; Herman et al. 2003; Roland and Sawchenko 1993). These GABAergic inputs are considered as local relay not only for the inhibitory inputs from the hippocampus and the prefrontal cortex but also for the excitatory signals from the amygdala to the PVN (Herman and Cullinan 1997). ADX increases the number of GABAergic synapses in the CRH neurons by 55% (Miklos and Kovacs 2002) and the frequency of inhibitory postsynaptic currents (IPSCs) in the PVN neurons (Verkuyl and Joels 2003). Stress also regulates the expression of glutamate decarboxylase mRNA (Bowers et al. 1998) and 
-aminobutyric acid type A [GABA(A)] receptors (Cullinan and Wolfe 2000) and suppresses the frequency of IPSCs in the PVN (Verkuyl et al. 2005).
Noradrenaline increases the frequency of IPSCs by activating the 1-adrenoceptors on the soma, but decreases their frequency by activating the 2-adrenoceptors (Chong et al. 2004; Daftary et al. 2000; Han et al. 2002; Li et al. 2005) and 1-adrenoceptors on the terminal of GABAergic neurons (Chen et al. 2006). These receptors were further identified as 1A/1L and 2A subtypes, respectively (Chong et al. 2004). Despite the fact that glucocorticoids are known to regulate both the GABAergic and the noradrenergic inputs in the PVN, whether glucocorticoids affect the noradrenergic modulation of GABAergic transmission is largely unknown. To answer these questions, we examined the effects of noradrenaline on IPSCs recorded from the putative parvocellular neurosecretory PVN neurons in the brain slices of the sham-operated and adrenalectomized rats. Putative parvocellular neurosecretory neurons were identified based on retrograde staining (Makarenko et al. 2001; Yang et al. 2007) and electrophysiological criteria (Luther et al. 2002).
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METHODS |
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Male Sprague–Dawley rats (3–5 wk old; Samtaco, Seoul, Korea) were either bilaterally adrenalectomized (ADX group) via a dorsal approach, operated but left adrenal intact (sham-operated group), or adrenalectomized and supplemented with corticosterone (ADX-CS group) under 2% xylazine and 5% ketamine [1:3, 2 ml/kg, administered intraperitoneally (ip)] anesthesia. For the rats in the ADX-CS group, a pellet of slow-release corticosterone (10 mg) was implanted subcutaneously to the dorsal neck region (Innovative Research of America, Sarasota, FL). The experiments were carried out in accordance with the guidelines of the Laboratory Animal Care Advisory Committee of Seoul National University. The animals were housed two to three per cage under a constant temperature and humidity, on a 12-h light/dark cycle (lights on at 8:00 am), with unrestricted access to food and water or isotonic saline (0.9%) +5% sucrose (ADX rats). Trunk blood was collected at the time of brain slice preparation (10:00–14:00 h) 7–9 days after the ADX. Plasma was separated and stored at –20°C for analysis of corticosterone. The corticosterone level was determined by a radioimmunoassay (125[I] Corticosterone Kit, MP Biomedicals, Orangeburg, NY) using a gamma counter (Wallac 1470 Wizard, Turku, Finland). The lower limit of the assay sensitivity for corticosterone was 0.7 µg/dl.
Retrograde staining and slice preparation
To label the neurosecretory PVN neurons, we anesthetized the rats with 2% xylazine and 5% ketamine (1:3, 2 ml/kg, ip), fixed to a customized hypophysectomy instrument that allows access to the pituitary through the ears. We injected a fluorescent dye, 1,1'-dioctadecyl-3,3,3',3'-tetramethylin-docarbocyanine perchlorate (DiI, 0.3 µl of 3% solution; Molecular Probes, Eugene, OR), to the pituitary stalk of the rats over a 1-min period using a 5-µl Hamilton syringe as described previously (Yang et al. 2007). After 1 or 2 days after the dye injection, coronal brain slices were prepared from male Sprague–Dawley rats (4–6 wk old) according to the methods described previously (Han et al. 2002). Briefly, brains were dissected under ether anesthesia and immersed in oxygenated (95% O2-5% CO2), ice-cold artificial cerebrospinal fluid (ACSF) for about 1 min. The brains showing dye diffusion outside the pituitary boundary were excluded. The hypothalamus was blocked with a razor, and one or two coronal hypothalamic slices (300 µm) were cut caudally to the optic chiasm with a tissue slicer (Vibratome 1000+, Vibratome, St. Louis, MO). The slices were incubated in oxygenated ACSF for 
1 h until the recordings were made at 30–32°C. The composition of the ACSF used was (in mM): 126 NaCl, 26 NaHCO3, 5 KCl, 1.2 NaH2PO4, 2.4 CaCl2, 1.2 MgCl2, and 10 glucose.
Electrophysiological recording
The whole cell currents were recorded from the PVN neurons in the coronal hypothalamic slices with the visualization of individual neurons using fluorescence microscopy with a "green" filter cube (U-MWG, Olympus, Tokyo, Japan), as reported previously (Han et al. 2002). Pipettes were pulled from borosilicate glass capillaries with a 1.7-mm diameter and a 0.5-mm wall thickness. Their open resistances ranged from 2 to 5 M
and the seal resistances ranged from 1 to 10 G. The patch pipettes were filled with a solution containing (in mM) 140 KCl, 20 HEPES, 0.5 CaCl2, 5 EGTA, and 5 MgATP (pH adjusted with KOH to 7.2). One of the slices in the incubation chamber was transferred to a recording chamber (0.7 ml) and fixed with a grid of nylon stocking threads supported by a U-shaped silver wire weight while being perfused (2 ml/min) with oxygenated (95% O2-5% CO2) ACSF at 30–33°C. Individual neurons were identified using an upright microscope with differential interference contrast (BX50WI, Olympus) for the whole cell patch recording. Electrical signals were recorded by an Axoclamp 2B amplifier (probe gain, x0.01 MU with HS-2 probe) or an Axopatch 200B. Current or voltage signals were filtered at 1 kHz and digitized at 10 kHz using an analog-digital converter (Digidata 1200) and the pClamp program (Version 8, Axon Instruments, Foster City, CA). Resting membrane potentials were corrected for the liquid junction voltage (
4.8 mV). The membrane input resistance was obtained by relating the hyperpolarizing current pulses (about –60 pA) applied to classify the cell type and the respective voltage shifts.
To determine the effect of ADX on the paired-pulse ratio (PPR) of evoked IPSCs following application of noradrenaline, electrical stimuli were applied using a bipolar tungsten electrode (World Precision Instruments, Sarasota, FL) that was placed on the region adjacent to the PVN (Li et al. 2005; Verkuyl et al. 2005). Paired stimuli (0.2 ms, 0.2–0.8 mA, and 0.2 Hz) were generated with an isolated pulse stimulator (Model 2100; A-M Systems, Carlsborg, WA) at a 100-ms interstimulus interval. The PPR was expressed as the peak amplitude ratio of the second synaptic response to the first synaptic response (P2/P1).
Identification of putative parvocellular neurosecretory neurons
DiI, a highly lipophilic fluorescent dye, was used to label PVN neurons located in both the parvocellular and magnocellular subdivisions (Fig. 1A), as reported previously (Makarenko et al. 2001; Yang et al. 2007). To identify the putative parvocellular neurosecretory PVN neurons, we initially selected a labeled neuron within the presumed parvocellular division of the slice using fluorescence (Fig. 1B) and determined the type of neuron by applying electrophysiological criteria under normal light (Fig. 1, C and D). The intranuclear location of recorded neurons was estimated based on the distance from the dorsal end of the third ventricle and shape of the translucent area of the PVN (Figs. 1E and 3C). In some neurons, we additionally measured the widths and lengths of soma before recording electrophysiological properties using a scale built within the microscope. Immediately after establishing the whole cell configuration, the type of PVN neurons was determined by applying a series of depolarizing current pulses of 250 ms with a 250-ms prepulse hyperpolarizing to approximately –100 mV (Han et al. 2002; Tasker and Dudek 1991; Fig. 1D). Neurons showing a prominent transient outward rectification were classified as type I and those showing little rectification as type II. We considered the DiI-labeled type II PVN neurons as putative parvocellular neurosecretory neurons (Luther et al. 2002). Thus type I neurons were excluded from further analyses. Figure 1E shows the distribution of some of the labeled type II neurons in the PVN. In addition, the cells were also excluded from the analyses if they did not meet the following criteria: resting membrane potential negative to –50 mV and spontaneous synaptic activity with an unstable frequency and amplitude during the control period.
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GABAergic sIPSCs were recorded in the presence of the nonselective glutamate receptor antagonists, 20 µM 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) plus 50 µM D-2-amino-5-phosphonopentanoic acid (D-AP5; Tocris Bioscience, Bristol, UK), and miniature (m)IPSCs were recorded in the presence of 1 µM tetrodotoxin (TTX), 20 µM CNQX, and 50 µM D-AP5, at a holding potential of –70 mV. Alternatively, the GABAergic postsynaptic currents were confirmed by the complete inhibition by bicuculline (20 µM), a GABA(A) receptor antagonist. The frequency, amplitude, and decay time constant of IPSCs were determined from the 3- to 5-min segments of the current records according to the methods previously described (Han et al. 2002) using a Mini Analysis Program (Version 4.0, Synaptosoft; http://www.synaptosoft.com). The effects of noradrenaline on the frequency, amplitude, and decay time constant of IPSCs are presented relative to the corresponding control values immediately before applying the drug. All data are presented as means ± SE and the number of neurons tested and analyzed is denoted by "n." Statistical comparisons were performed with the appropriate analyses, including 
2 test, unpaired and paired Student's t-tests, and ANOVA with post hoc Newman–Keuls test. A value of P < 0.05 was considered significant.
Single-cell reverse transcription–polymerase chain reaction (RT-PCR)
The single-cell RT-PCR was performed as described previously with minor modifications (Di et al. 2003; Glasgow et al. 1999; Yang et al. 2007). Briefly, the cytoplasm of neuron was gently aspirated under visual control into a patch-clamp recording electrode, with care taken not to aspirate the nucleus. The contents of the electrode were subsequently dissipated into a microtube containing (in µl): 2.9 of diethyl pyrocarbonate–treated water, 0.7 of bovine serum albumin, 0.7 of random hexamer (100 ng/µl), and 0.7 of RNaseOUT (40 U/µl). After aspiration of the neuron, the microtube including cytoplasm was either stored at –70 °C or immediately used for RT. Single-strand cDNA was synthesized from the cellular mRNA using Superscript III. All reagents except random hexamer (Promega, Madison, WI) were obtained from Invitrogen (Carlsbad, CA).
PCR amplification was carried out using a fraction of the single-cell cDNA as a template. Reaction components were as follows: 1 µM each primer, 12.5 µl of 2 x buffer (GoTaq Green Master Mix; Promega), 1 µl of dimethyl sulfoxide, and 4 µl of the cDNA template made from the single-cell RT reaction. The thermal cycling program, set at 94 °C for 40 s, 60 °C for 40 s, and 72 °C for 1 min, consisted of 50 cycles. The primer pairs used (Bioneer, Daejeon, South Korea) were: CRH (M54987 [GenBank] ), 5'-AAC TCA GAG CCC AAG TAC GTT GAG-3' and 5'-TCA CCC ATG CGG ATC AGA ATC-3' (355 bp); VP (X59496 [GenBank] ), 5'-CCT CAC CTC TGC CTG CTA CTT-3' and 5'-GGG GGC GAT GGC TCA GTA GAC-3' (440 bp); and glyceraldehyde 3-phosphate dehydrogenase (GAPDH, X02231 [GenBank] ), 5'-GGA CAT TGT TGC CAT CAA CGC-3' and 5'-ATG AGC CCT TCC ACG ATG CCA AAG-3' (245 bp).
Negative controls for contamination from the extraneous and genomic DNA were run for every batch of neurons by omitting the reverse transcriptase or replacing the cellular template with water. All the PCR products were purified using a PCR purification kit (Qiagen, Hilden, Germany) and the purified products were sequenced with gene-specific primers to confirm the amplified sequences. DNA sequencing was performed at the National Instrumentation Center for Environmental Management at Seoul National University.
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RESULTS |
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TOPABSTRACTINTRODUCTIONMETHODSRESULTSDISCUSSIONGRANTSACKNOWLEDGMENTSREFERENCES |
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), and expressed the mRNA of CRH and/or VP in 8 of 20 neurons tested (data not shown). The resting membrane potential and input resistance of labeled type II PVN neurons were, respectively, –58.5 ± 1.12 mV and 497 ± 30 M (n = 33) in the sham-operated rats and –58 ± 1.2 mV and 529 ± 32 M (n = 19) in the ADX rats. The width and length of the soma were 7.5 ± 0.22 and 17 ± 0.80 µm (n = 22) in the sham-operated rats and 7.8 ± 0.27 and 17.4 ± 0.43 µm (n = 17) in the ADX rats. These observations indicate that the DiI-labeled type II PVN neurons are likely to represent the parvocellular neurosecretory neurons in the PVN. Noradrenergic modulation of sIPSCs in parvocellular neurosecretory PVN neurons
The labeled type II PVN neurons showed rich spontaneous (s)IPSCs at the resting state. The mean baseline frequency, amplitude, and decay time constant of the sIPSCs were, respectively, 3.2 ± 0.45 Hz, 83.7 ± 7.9 pA, and 9.1 ± 0.38 ms (n = 28). Noradrenaline (100 µM, 2 min) either reduced or augmented the frequency of sIPSCs (Fig. 2, A and B). The effects of noradrenaline on the sIPSC frequency were induced in <2 min after initiation of the bath application and reversed to the baseline level after a washout period of about 20 min. The cumulative probability plots of the interevent intervals of sIPSCs further demonstrate that noradrenaline shifted the curve either to the right in the neurons showing a noradrenergic reduction (Fig. 2C) or to the left in the neurons showing a noradrenergic augmentation in the sIPSC frequency (Fig. 2D). Of the 28 type II neurons recorded, 13 (46%) showed noradrenergic reduction in the sIPSC frequency, whereas the rest (54%) showed noradrenergic augmentation in the sIPSC frequency (Fig. 2E). Noradrenaline decreased the frequency by half (from 3.45 ± 0.61 to 1.63 ± 0.32 Hz, P < 0.01, n = 13) in the neurons showing the noradrenergic reduction, but increased the frequency by 2.1-fold (from 2.8 ± 0.68 to 5.22 ± 1.18 Hz; P < 0.01, n = 15) in the neurons showing the noradrenergic augmentation in the sIPSC frequency. In contrast to the modulation of the sIPSC frequency, noradrenaline did not alter the amplitude or decay time constant of the sIPSCs recorded from the neuron groups showing either noradrenergic reduction or augmentation in the sIPSC frequency (data not shown). These results are consistent with previous reports on pooled parvocellular PVN neurons (Chong et al. 2004; Han et al. 2002). Based on earlier reports, we further determined whether the noradrenergic augmentation and reduction of the sIPSC frequency in neurosecretory parvocellular neurons are also mediated by 1A/1L- and 2A-adrenoceptor subtypes, respectively (Fig. 2). In 4 of 5 neurons displaying noradrenergic reduction, the effect of noradrenaline was blocked with 3 µM 2-[(4,5-dihydro-1H-imidazol-2-yl)methyl[rsqb[-2,3-dihydro- 1-methyl-1H-isoindole maleate (BRL 44408), an 2A-adrenoceptor antagonist (Fig. 2F). In 5 of 6 neurons showing noradrenergic augmentation, the effect of noradrenaline was blocked with 1 µM prazosin, an 1L/1A-adrenoceptor antagonist (Fig. 2G). BRL 44408 (3 µM) did not affect the noradrenergic augmentation of sIPSC frequency (n = 3). These results collectively indicate that noradrenaline can either decrease or increase GABAergic inhibitory transmission in parvocellular neurosecretory PVN neurons via 2A- and 1L/1A-adrenoceptors, respectively.
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To study the effects of corticosterone on the noradrenergic modulation of GABAergic transmission, the circulating corticosterone was depleted by ADX or restored by implanting a corticosterone pellet after ADX (ADX-CS). The plasma corticosterone levels were 13.1 ± 2.83 µg/dl in the sham-operated rats (n = 7), below the detection limit (0.7 µg/dl) in the ADX rats (n = 13) and 3.5 ± 0.56 µg/dl in the ADX-CS rats (n = 14). The frequency of sIPSC in ADX rats was 6.19 ± 1.06 Hz, about twice that in sham-operated rats (3.2 ± 0.45 Hz, P < 0.05). The elevation of sIPSC frequency was not observed in ADX-CS rats receiving a corticosterone supplement (2.83 ± 0.66 Hz in ADX-CS rats vs. 3.2 ± 0.45 Hz in sham-operated rats, P = 0.3). ADX did not alter either the amplitude or the decay time constant (P > 0.2).
An obvious finding on the neurons from ADX rats was a significant increase in the proportion of the neurons showing the noradrenergic reduction in the sIPSC frequency. In the neurons from ADX rats, the proportion of neurons showing the noradrenergic reduction in the sIPSC frequency increased by twofold (from 46% in the sham-operated rats to 89% in ADX rats), but decreased the proportion of neurons showing the noradrenergic augmentation to one fifth (from 54% in the sham-operated rats to 11% in ADX rats; P < 0.01, 2 test; Fig. 3A). In addition, the extent of noradrenergic reduction in the sIPSC frequency was also significantly larger in the ADX rats. The noradrenergic reduction in the frequency of sIPSCs was, respectively, 74 ± 4.5 and 49 ± 5.3% in the neurons from ADX and sham-operated rats (P < 0.05; Fig. 3B). Such ADX-induced changes in the noradrenergic reduction were not observed in the ADX-CS rats supplemented with corticosterone (10-mg pellet). As illustrated in Fig. 3C, most of the labeled neurons examined were located in the mediodorsal parvocellular part of the PVN, but there was no obvious segregation between the two neuron groups showing noradrenergic augmentation and reduction of sIPSC frequency. Taken together, these results suggest that depletion of corticosterone by ADX markedly potentiates the noradrenergic suppression of GABAergic transmission in the parvocellular neurosecretory PVN neurons.
Effects of ADX on noradrenergic modulation of mIPSCs
To determine whether the noradrenergic suppression of GABAergic transmission is due to a direct effect of noradrenaline on the GABAergic terminals, we examined the effect of noradrenaline on the mIPSCs recorded in the presence of TTX (1 µM), a Na+ channel blocker that blocks neuronal firing (Fig. 4). In a similar manner to that observed in the sIPSC, the frequency of mIPSC in the ADX rats was significantly higher than that in the sham-operated rats (7.1 ± 1.85 Hz, n = 6 vs. 2.81 ± 0.67 Hz, n = 7; P < 0.05). However, the amplitude and decay time constant of mIPSCs were not different between the ADX and sham-operated rats (96.7 ± 15.8 vs. 100 ± 20.2 pA, P > 0.05; 7.13 ± 0.63 vs. 7.69 ± 0.65 ms, P > 0.05).
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Effect of ADX on paired-pulse ratio of evoked IPSCs
Our earlier observation (Fig. 4) indicates that noradrenaline depresses the GABAergic transmission through a presynaptic action, either by affecting the release probability of GABA or by changing the number of functional GABAergic synapses. To further identify the presynaptic mechanism of the noradrenergic suppression of GABAergic transmission, we examined the effect of noradrenaline on the paired-pulse ratio (PPR) recorded from DiI-labeled type II PVN neurons showing noradrenergic reduction in the IPSC frequency. Prior to the application of noradrenaline, neurons showed weak paired-pulse facilitation and PPR values were similar between the sham-operated and ADX rats (1.06 ± 0.04 in sham-operated, n = 6, vs. 1.15 ± 0.03 in ADX, n = 6; P > 0.05 by ANOVA with a post hoc Newman–Keuls test). Bath application of noradrenaline (100 µM) caused a significant reduction in the amplitude of the first evoked IPSC in both sham-operated (39 ± 5%, n = 6; P < 0.05) and ADX rats (47 ± 3%, n = 6; P < 0.05 by Student's t-test; Fig. 5A). The extent of noradrenergic reduction was larger in ADX rats, but differences were not statistically significant (39 ± 5 vs. 47 ± 3%, P > 0.05). Furthermore, noradrenaline significantly enhanced the PPR in cells from both sham-operated (from 1.06 ± 0.04 to 1.45 ± 0.06, n = 6; P < 0.001) and ADX rats (from 1.15 ± 0.03 to 1.98 ± 0.11, n = 6; P < 0.001). ADX potentiated the noradrenaline-induced increase in PPR (1.45 ± 0.06 in sham-operated vs. 1.98 ± 0.11 in ADX rats; P < 0.01 by ANOVA with a post hoc Newman–Keuls test). The extent of the noradrenaline-induced increase in PPR was significantly larger in the ADX rats (172 ± 9.8%), compared with their sham-operated counterparts (137 ± 3%, P < 0.05 by Student's t-test; Fig. 5B).
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Figure 6 shows that BRL 44408, a selective antagonist of 2A-adrenoceptors (pA2 = 8.0; Alexander et al. 2001) blocked the noradrenaline-induced reduction in the sIPSC frequency in the type II neurons of the ADX rats. The time course histograms of sIPSC frequency and current records before and after applying noradrenaline show that BRL 44408 (3 µM) reversibly blocked the noradrenergic reduction (Fig. 6, A and B). BRL 44408 itself did not affect the sIPSC frequency. Similar results were observed in six of six type II neurons from the ADX rats (n = 4) that showed the noradrenergic reduction in the sIPSC frequency (Fig. 6C). In these neurons, noradrenaline decreased the sIPSC frequency to 34% of that observed in the control (4.44 ± 1.58 Hz, P < 0.01), but failed to reduce the sIPSC frequency in the presence of BRL 44408 (P = 0.772). This result suggests that 2A-adrenoceptors also mediate the noradrenergic suppression of GABAergic transmission in the parvocellular neurosecretory PVN neurons of the ADX rats.
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CRH and VP from the neurosecretory parvocellular neurons are the major stimulators of the hypothalamic-pituitary-adrenal (HPA) axis. Using the single-cell RT-PCR technique (Di et al. 2003; Glasgow et al. 1999; Yang et al. 2007), we further examined the effects of ADX on the expression of these peptides in parvocellular neurosecretory PVN neurons and correlations between the effects of noradrenaline on sIPSC and peptide expression. In sham-operated rats, of the 19 neurons showing noradrenergic augmentation in sIPSC frequency, 2 expressed both peptides, 2 expressed CRH, and 3 expressed VP (Fig. 7A). Among another 19 neurons showing noradrenergic reduction in sIPSC frequency, 2 expressed both peptides, 1 expressed CRH, and 4 expressed VP, respectively (Fig. 7B). In ADX rats, of the 14 neurons showing noradrenergic reduction, 3 expressed both peptides, 2 expressed CRH, and 1 expressed VP (Fig. 7C). Our results demonstrate that expression of CRH, but not VP, is significantly enhanced in ADX rats (18%, 7 of 38 cells in sham-operated vs. 36%, 5 of 14 cells in ADX; P < 0.05 by 2 test). The results also indicate that noradrenergic modulation of GABAergic transmission is not correlated with expression of CRH and/or VP in neurosecretory parvocellular PVN neurons.
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DISCUSSION |
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). The findings are also in good agreement with previous reports showing an elevated neuronal activity in the parvocellular PVN neurons of the ADX rats after restraint (Fevurly and Spencer 2004; Imaki et al. 1995; Roske et al. 2002) or hypovolemia (Tanimura and Watts 2000). Since ADX also augments the stress-induced release of noradrenaline (Pacak et al. 1995), corticosterone may collaborate with the noradrenergic system in regulation of the release of PVN peptides such as CRH and VP. This idea is further supported by the recent study showing that ADX increases neuronal excitability by altering the pattern and frequency as well as the noradrenergic modulation of spontaneous action potentials in the neurosecretory parvocellular PVN neurons (Yang et al. 2007). Thus our findings provide experimental evidences for a presynaptic mechanism of catecholaminergic excitation in the regulation of the HPA axis (Pacak et al. 1995; Plotsky 1987; Szafarczyk et al. 1987) and indicate that the noradrenergic modulation of GABAergic transmission is under a tonic control of glucocorticoid.
The ADX-induced increase in the proportion of neurons showing noradrenergic reduction in IPSC frequency is likely due to up-regulation or sensitization of presynaptic 2A-adrenoceptors mediating the noradrenergic reduction in IPSC frequency in unidentified (Chong et al. 2004; Han et al. 2002) and presympathetic parvocellular PVN neurons (Li et al. 2005). In parvocellular neurosecretory PVN neurons, BRL 44408, but not tetrodotoxin, blocked the noradrenergic suppression of GABAergic transmission, indicating that presynaptic 2A-adrenoceptors mediate this process. This evidence is reinforced by the finding that ADX significantly increased the paired-pulse facilitation induced by noradrenaline and decreased the frequency of mIPSCs without changing the amplitude and decay kinetics. The data additionally suggest that noradrenaline decreases the release probability of GABA (Wilcox and Dichter 1994). In view of the finding that 2A-adrenoceptors or their mRNA levels are down-regulated by chronic stress or glucocorticoids (Feuvrier et al. 1999; Flugge 1999), it is likely that ADX-induced depletion of circulating corticosterone causes up-regulation of 2A-adrenoceptors and enhancement of tissue sensitivity to noradrenaline (Bourne and Zastrow 2004). Further studies are required to clarify whether the up-regulation of presynaptic 2A-adrenoceptors is associated with the increase in the number of GABAergic synapses in ADX rats (Miklos and Kovacs 2002).
In addition to 2A-adrenoceptors, noradrenaline can enhance the frequency of IPSCs in the PVN via 1-adrenoceptors on the soma (Han et al. 2002; Chong et al. 2004) or reduce frequency via 1-adrenoceptors on the axonal terminal of GABAergic neurons (Chen et al. 2006). Therefore down-regulation of 1-adrenoceptors on the soma of GABAergic neurons (Feuvrier et al. 1999) or up-regulation of 1-adrenoceptors on the GABAergic terminal (Day et al. 1999) may promote the ADX-induced increase in the proportion of neurons showing noradrenergic reduction of IPSC frequency. However, it is unlikely that 1-adrenoceptors on the soma of presynaptic GABAergic neurons are important in mediating ADX-induced changes in the noradrenergic modulation of GABAergic transmission, since the results obtained using TTX and paired-pulse stimulation (Figs. 4 and 5) strongly suggest a significant role of presynaptic adrenoceptors. Moreover, 1-adrenoceptors on the GABAergic terminal do not appear to play a key role in the noradrenergic suppression of GABAergic transmission, since the reduction in sIPSC frequency was completely blocked by a 2A-adrenoceptor antagonist (Figs. 3 and 6).
Molecular mechanisms for the noradrenergic inhibition of GABAergic transmission may involve the suppression of voltage-gated Ca2+ channels and activation of inwardly rectifying K+ channels via stimulation of 2A-adrenoceptors (Bylund 1995). Another possible mechanism for potentiation of the noradrenergic suppression observed in the PVN is a change in downstream events, such as G proteins (Okuhara et al. 1997; Saito et al. 1989) that mediate the intracellular signal transduction pathways of multiple neurotransmitter systems, including 2A-adrenoceptors (Chabre et al. 1994). A third possible mechanism involves alterations in retrograde signaling systems, such as nitric oxide (Bains and Ferguson 1997; Li et al. 2002; Stern et al. 2001) and endocannabinoids (Di et al. 2003, 2005) that regulate GABAergic synaptic transmission. Further studies are required to determine whether activation of 2A-adrenoceptors can influence these messenger systems in the PVN. Our results collectively indicate that circulating corticosterone can control inhibitory inputs to parvocellular neurosecretory PVN neurons by inversely regulating 2A-adrenoceptors at the GABAergic terminals on neurosecretory parvocellular PVN neurons.
The ADX-induced increase in the baseline frequency of IPSC observed in neurosecretory parvocellular PVN neurons further confirms previous data obtained with pooled parvocellular neurons (Verkuyl and Joels 2003). This ADX-induced augmentation could be attributed to an increase in the number of GABAergic synapses or neurotransmitter release probability. Our observation that ADX does not alter the paired-pulse ratio of evoked IPSCs indicates that the release probability of GABA is not affected, supporting the theory of an increase in the number of GABAergic synapses in the ADX (Miklos and Kovacs 2002). However, the results are not consistent with the findings that ADX increases the neuronal excitability (Kasai et al. 1988; Yang et al. 2007) and the fos-like immunoreactivity in the PVN (Jacobson et al. 1990). Therefore the significance of ADX-induced augmentation in GABAergic transmission should be assessed together with the changes in other factors such as the excitatory synaptic inputs and the intrinsic properties of the PVN neurons.
Since the rat brains were examined on the 7th day after ADX, it is unlikely that the changes in the GABAergic transmission or its noradrenergic modulation were due to the removal of the fast and nongenomic effects of glucocorticoids (Di et al. 2003; Keller-Wood and Dallman 1984). Of the two types of corticosteroid receptors that mediate the classical genomic effects of glucocorticoids, corticosterone can preferentially occupy the mineralocorticoid receptors (MRs; Kd 0.5 nM)) at concentrations <3 µg/dl, but can occupy both the MR and glucocorticoid receptors (GRs; Kd 2.5–5 nM) at higher levels such as during stress or during the diurnal peak of pituitary activity (half-maximal occupation at 25 µg/dl; Dallman 1993; Reul and de Kloet 1985). In this study, the potentiation in noradrenergic suppression of GABAergic transmission was reversed by a low corticosterone replacement (10 mg) that maintained circulating corticosterone at about 3.5 µg/dl, at which concentration most MRs are occupied, but most GRs are unoccupied (Reul and de Kloet 1985). It has been shown that the same dose of corticosterone replacement (10 mg) reverses the ADX-induced burst firing pattern and potentiation of noradrenergic excitation (Yang et al. 2007) and the ADX-induced increase in 1B-adrenoceptors mRNA to the control in the PVN (Day et al. 1999). Recent studies also have demonstrated that PVN neurons express MRs (Han et al. 2005) and 11β-hydroxysteroid dehydrogenase type II, which rapidly converts corticosterone to an inactive metabolite, thus allows much less abundant aldosterone to bind to MRs (Zhang et al. 2006). All these highlight the significance of MRs in the PVN of ADX rats. Further studies are needed to determine the subtype of corticosteroid receptors mediating the ADX-induced changes in the PVN.
Functional significance of potentiation of noradrenergic suppression in the PVN
Previous studies showed that noradrenergic inhibition of GABAergic transmission is mediated by 2A-adrenoceptors in the pooled PVN neurons (Chong et al. 2004; Han et al. 2002) and in the preautonomic PVN neurons projecting to the spinal cord (Li et al. 2005). The present study further demonstrates that ADX potentiates the 2A-adrenoceptor–mediated noradrenergic suppression of GABAergic transmission in parvocellular neurosecretory PVN neurons and that this circuit can be a pivotal target for the action of glucocorticoid negative feedback.
It is rather unexpected that the proportions of PVN neurons showing noradrenergic reduction and augmentation in spontaneous IPSCs are not different between the pooled (Chong et al. 2004; Han et al. 2002) and neurosecretory type II PVN neurons. Furthermore, the present study reveals that neurosecretory type II PVN neurons expressing mRNA of CRH, VP, or both peptides are subject to regulation of both noradrenergic reduction and augmentation of IPSC frequency. These findings suggest that the 1A/1L-adrenoceptor–mediated augmentation and 2A-adrenoceptor–mediated reduction of IPSC frequency constitute a common pattern of noradrenergic modulation in PVN neurons, regardless of the peptide phenotype and projection (Chong et al. 2004; Han et al. 2002; Li et al. 2005).
GABAergic inputs to the PVN originate from the peri-PVN region as well as hypothalamic and telencephalic nuclei, including the dorsomedial and medial preoptic nuclei and the bed nucleus of stria terminalis (Herman et al. 2003). The peri-PVN GABAergic cells relay the glutamatergic inputs from the hippocampus and cortex, resulting in suppression of the HPA responses to stressful stimuli (Diorio et al. 1993; Figueiredo et al. 2003) as well as GABAergic inputs from the amygdala, which increase the HPA responses by disinhibition (Swanson and Petrovich 1998). Therefore potentiation of the noradrenergic suppression of GABAergic transmission at low levels of circulating glucocorticoids such as in ADX rats would limit the inhibitory inputs from the hippocampus and cortex, but enhance the excitatory inputs from the amygdala. Further study is needed to determine whether the noradrenergic disinhibition of GABAergic transmission is diminished in the PVN at high levels of glucocorticoids such as in the rats under stress. Functionally, the circuit also provides a novel mechanism for an interaction between the brain stem noradrenergic signals for systemic/interoceptive stressors (e.g., hypoxia, ether, or cardiovascular and immune stimuli) and the GABAergic signals for the inhibitory inputs from the limbic system nuclei for processive/exteroceptive stressors (e.g., restraint, fear conditioning, or exposure to a novel environment; Dayas et al. 2001; Herman et al. 2003; Sawchenko et al. 2000).
In conclusion, we have shown that when the resting corticosterone is depleted by ADX, the noradrenergic suppression of GABAergic transmission is potentiated in the parvocellular neurosecretory PVN neurons, and that such noradrenergic suppression is due to a reduction in release probability at the axon terminals of GABAergic neurons via 2A-adrenoceptors. The results suggest that the glucocorticoids can control the excitability of the parvocellular neurosecretory neurons by collaborating with the noradrenergic system in regulation of the strength of GABAergic transmission in the PVN.
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Address for reprint requests and other correspondence: P. D. Ryu, San 56-1 Sillim-Dong, Kwanak-Gu, College of Veterinary Medicine, Seoul National University, Seoul, 151-742 Republic of Korea (E-mail: pdryu{at}snu.ac.kr)
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Bains JS, Ferguson AV. Nitric oxide regulates NMDA-driven GABAergic inputs to type I neurones of the rat paraventricular nucleus. J Physiol 499: 733–746, 1997.
Boudaba C, Szabo K, Tasker JG. Physiological mapping of local inhibitory inputs to the hypothalamic paraventricular nucleus. J Neurosci 16: 7151–7160, 1996.
Bourne HR, von Zastrow M. Drug receptors and pharmacodynamics. In: Basic and Clinical Pharmacology, edited by Katzung BG. New York: McGraw-Hill, 2004, p. 11–33.
Bowers G, Cullinan WE, Herman JP. Region-specific regulation of glutamic acid decarboxylase (GAD) mRNA expression in central stress circuits. J Neurosci 18: 5938–5947, 1998.
Bylund DB. Pharmacological characteristics of alpha-2 adrenergic receptor subtypes. Ann NY Acad Sci 763: 1–7, 1995.[Medline]
Chabre O, Conklin BR, Brandon S, Bourne HR, Limbird LE. Coupling of the alpha 2A-adrenergic receptor to multiple G-proteins. A simple approach for estimating receptor-G-protein coupling efficiency in a transient expression system. J Biol Chem 269: 5730–5734, 1994.
Chen Q, Li DP, Pan HL. Presynaptic alpha1 adrenergic receptors differentially regulate synaptic glutamate and GABA release to hypothalamic presympathetic neurons. J Pharmacol Exp Ther 316: 733–742, 2006.
Chong W, Li LH, Lee K, Lee MH, Park JB, Ryu PD. Subtypes of alpha1- and alpha2-adrenoceptors mediating noradrenergic modulation of spontaneous inhibitory postsynaptic currents in the hypothalamic paraventricular nucleus. J Neuroendocrinol 16: 450–457, 2004.[CrossRef][Web of Science][Medline]
Cole RL, Sawchenko PE. Neurotransmitter regulation of cellular activation and neuropeptide gene expression in the paraventricular nucleus of the hypothalamus. J Neurosci 22: 959–969, 2002.
Cullinan WE, Wolfe TJ. Chronic stress regulates levels of mRNA transcripts encoding beta subunits of the GABA(A) receptor in the rat stress axis. Brain Res 887: 118–124, 2000.[CrossRef][Web of Science][Medline]
Cunningham ET Jr, Bohn MC, Sawchenko PE. Organization of adrenergic inputs to the paraventricular and supraoptic nuclei of the hypothalamus in the rat. J Comp Neurol 292: 651–667, 1990.[CrossRef][Web of Science][Medline]
Cunningham ET Jr, Sawchenko PE. Anatomical specificity of noradrenergic inputs to the paraventricular and supraoptic nuclei of the rat hypothalamus. J Comp Neurol 274: 60–76, 1988.[CrossRef][Web of Science][Medline]
Daftary SS, Boudaba C, Tasker JG. Noradrenergic regulation of parvocellular neurons in the rat hypothalamic paraventricular nucleus. Neuroscience 96: 743–751, 2000.[CrossRef][Web of Science][Medline]
Dallman MF. Stress update. Adaptations of the hypothalamic-pituitary-adrenal axis to chronic stress. Trends Endocrinol Metab 4: 62–69, 1993.[CrossRef][Web of Science][Medline]
Day HEW, Campeau S, Watson SJ, Akil H. Expression of alpha(1b) adrenoceptor mRNA in corticotropin-releasing hormone-containing cells of the rat hypothalamus and its regulation by corticosterone. J Neurosci 19: 10098–10106, 1999.
Dayas CV, Buller KM, Crane JW, Xu Y, Day TA. Stressor categorization: acute physical and psychological stressors elicit distinctive recruitment patterns in the amygdala and in medullary noradrenergic cell groups. Eur J Neurosci 14: 1143–1152, 2001.[CrossRef][Web of Science][Medline]
Decavel C, van den Pol AN. GABA: a dominant neurotransmitter in the hypothalamus. J Comp Neurol 302: 1019–1037, 1990.[CrossRef][Web of Science][Medline]
Di S, Malcher-Lopes R, Halmos KC, Tasker JG. Nongenomic glucocorticoid inhibition via endocannabinoid release in the hypothalamus: a fast feedback mechanism. J Neurosci 23: 4850–4857, 2003.
Di S, Malcher-Lopes R, Marcheselli VL, Bazan NG, Tasker JG. Rapid glucocorticoid-mediated endocannabinoid release and opposing regulation of glutamate and gamma-aminobutyric acid inputs to hypothalamic magnocellular neurons. Endocrinology 146: 4292–4301, 2005.
Diorio D, Viau V, Meaney MJ. The role of the medial prefrontal cortex (cingulate gyrus) in the regulation of hypothalamic-pituitary-adrenal responses to stress. J Neurosci 13: 3839–3847, 1993.[Abstract]
Feuvrier E, Aubert M, Malaval F, Szafarczyk A, Gaillet S. Opposite regulation by glucocorticoids of the alpha 1B- and alpha 2A-adrenoreceptor mRNA levels in rat cultured anterior hypothalamic slices. Neurosci Lett 271: 121–125, 1999.[CrossRef][Web of Science][Medline]
Fevurly RD, Spencer RL. Fos expression is selectively and differentially regulated by endogenous glucocorticoids in the paraventricular nucleus of the hypothalamus and the dentate gyrus. J Neuroendocrinol 16: 970–979, 2004.[CrossRef][Web of Science][Medline]
Figueiredo HF, Bodie BL, Tauchi M, Dolgas CM, Herman JP. Stress integration after acute and chronic predator stress: differential activation of central stress circuitry and sensitization of the hypothalamo-pituitary-adrenocortical axis. Endocrinology 144: 5249–5258, 2003.
Flugge G. Effects of cortisol on brain alpha2-adrenoceptors: potential role in stress. Neurosci Biobehav Rev 23: 949–956, 1999.[CrossRef][Web of Science][Medline]
Glasgow E, Kusano K, Chin H, Mezey É, Young WS 3rd, Gainer H. Single cell reverse transcription-polymerase chain reaction analysis of rat supraoptic magnocellular neurons: neuropeptide phenotypes and high voltage-gated calcium channel subtypes. Endocrinology 140: 5391–5401, 1999.
Han F, Ozawa H, Matsuda K, Nishi M, Kawata M. Colocalization of mineralocorticoid receptor and glucocorticoid receptor in the hippocampus and hypothalamus. Neurosci Res 51: 371–381, 2005.[CrossRef][Web of Science][Medline]
Han SK, Chong W, Li LH, Lee IS, Murase K, Ryu PD. Noradrenaline excites and inhibits GABAergic transmission in parvocellular neurons of rat hypothalamic paraventricular nucleus. J Neurophysiol 87: 2287–2296, 2002.
Herman JP, Cullinan WE. Neurocircuitry of stress: central control of the hypothalamo-pituitary-adrenocortical axis. Trends Neurosci 20: 78–84, 1997.[CrossRef][Web of Science][Medline]
Herman JP, Figueiredo H, Mueller NK, Ulrich-Lai Y, Ostrander MM, Choi DC, Cullinan WE. Central mechanisms of stress integration: hierarchical circuitry controlling hypothalamo-pituitary-adrenocortical responsiveness. Front Neuroendocrinol 24: 151–180, 2003.[CrossRef][Web of Science][Medline]
Imaki T, Xiao-Quan W, Shibasaki T, Yamada K, Harada S, Chikada N, Naruse M, Demura H. Stress-induced activation of neuronal activity and corticotropin-releasing factor gene expression in the paraventricular nucleus is modulated by glucocorticoids in rats. J Clin Invest 96: 231–238, 1995.[Web of Science][Medline]
Jacobson L. Hypothalamic-pituitary-adrenocortical axis regulation. Endocrinol Metab Clin North Am 34: 271–292, 2005.[CrossRef][Web of Science][Medline]
Jacobson L, Sharp FR, Dallman MF. Induction of fos-like immunoreactivity in hypothalamic corticotropin-releasing factor neurons after adrenalectomy in the rat. Endocrinology 126: 1709–1719, 1990.
Kasai M, Yamashita H. Inhibition by cortisol of neurons in the paraventricular nucleus of the hypothalamus in adrenalectomized rats: an in vitro study. Neurosci Lett 91: 59–64, 1988.[CrossRef][Web of Science][Medline]
Keller-Wood ME, Dallman MF. Corticosteroid inhibition of ACTH secretion. Endocr Rev 5: 1–24, 1984.
Li DP, Atnip LM, Chen SR, Pan HL. Regulation of synaptic inputs to paraventricular-spinal output neurons by alpha2 adrenergic receptors. J Neurophysiol 93: 393–402, 2005.
Li DP, Chen SR, Pan HL. Nitric oxide inhibits spinally projecting paraventricular neurons through potentiation of presynaptic GABA release. J Neurophysiol 88: 2664–2674, 2002.
Luther JA, Daftary SS, Boudaba C, Gould GC, Halmos KC, Tasker JG. Neurosecretory and non-neurosecretory parvocellular neurones of the hypothalamic paraventricular nucleus express distinct electrophysiological properties. J Neuroendocrinol 14: 929–932, 2002.[CrossRef][Web of Science][Medline]
Makarenko IG, Ugrumov MV, Calas A. Axonal projections from the hypothalamus to the median eminence in rats during ontogenesis: DiI tracing study. Anat Embryol 204: 239–252, 2001.[CrossRef][Medline]
Meyer H, Palchaudhuri M, Scheinin M, Flugge G. Regulation of alpha(2A)-adrenoceptor expression by chronic stress in neurons of the brain stem. Brain Res 880: 147–158, 2000.[CrossRef][Web of Science][Medline]
Miklos IH, Kovacs KJ. GABAergic innervation of corticotropin-releasing hormone (CRH)-secreting parvocellular neurons and its plasticity as demonstrated by quantitative immunoelectron microscopy. Neuroscience 113: 581–592, 2002.[CrossRef][Web of Science][Medline]
Okuhara DY, Beck SG, Muma NA. Corticosterone alters G protein alpha-subunit levels in the rat hippocampus. Brain Res 745: 144–151, 1997.[CrossRef][Web of Science][Medline]
Pacak K, Palkovits M, Kopin IJ, Goldstein DS. Stress-induced norepinephrine release in the hypothalamic paraventricular nucleus and pituitary-adrenocortical and sympathoadrenal activity: in vivo microdialysis studies. Front Neuroendocrinol 16: 89–150, 1995.[CrossRef][Web of Science][Medline]
Plotsky PM. Facilitation of immunoreactive corticotropin-releasing factor secretion into the hypophysial-portal circulation after activation of catecholaminergic pathways or central norepinephrine injection. Endocrinology 121: 924–930, 1987.
Plotsky PM, Cunningham ET Jr, Widmaier EP. Catecholaminergic modulation of corticotropin-releasing factor and adrenocorticotropin secretion. Endocr Rev 10: 437–458, 1989.
Reul JM, de Kloet ER. Two receptor systems for corticosterone in rat brain: microdistribution and differential occupation. Endocrinology 117: 2505–2511, 1985.
Roland BL, Sawchenko PE. Local origins of some GABAergic projections to the paraventricular and supraoptic nuclei of the hypothalamus in the rat. J Comp Neurol 332: 123–143, 1993.[CrossRef][Web of Science][Medline]
Roske I, Hughes ME, Newson P, Oehme P, Chahl LA. Effect of chronic intermittent immobilization stress on Fos-like immunoreactivity in rat brain and adrenal medulla. Stress 5: 277–283, 2002.[Medline]
Saito N, Guitart X, Hayward M, Tallman JF, Duman RS, Nestler EJ. Corticosterone differentially regulates the expression of Gs alpha and Gi alpha messenger RNA and protein in rat cerebral cortex. Proc Natl Acad Sci USA 86: 3906–3910, 1989.
Sawchenko PE, Li HY, Ericsson A. Circuits and mechanisms governing hypothalamic responses to stress: a tale of two paradigms. Prog Brain Res 122: 61–78, 2000.[Web of Science][Medline]
Stern JE, Ludwig M. NO inhibits supraoptic oxytocin and vasopressin neurons via activation of GABAergic synaptic inputs. Am J Physiol Regul Integr Comp Physiol 280: R1815–R1822, 2001.
Swanson LW, Petrovich GD. What is the amygdala? Trends Neurosci 21: 323–331, 1998.[CrossRef][Web of Science][Medline]
Szafarczyk A, Malaval F, Laurent A, Gibaud R, Assenmacher I. Further evidence for a central stimulatory action of catecholamines on adrenocorticotropin release in the rat. Endocrinology 121: 883–892, 1987.
Tanimura SM, Watts AG. Adrenalectomy dramatically modifies the dynamics of neuropeptide and c-fos gene responses to stress in the hypothalamic paraventricular nucleus. J Neuroendocrinol 12: 715–722, 2000.[CrossRef][Web of Science][Medline]
Tasker JG, Dudek FE. Electrophysiological properties of neurones in the region of the paraventricular nucleus in slices of rat hypothalamus. J Physiol 434: 271–293, 1991.
Verkuyl JM, Joels M. Effect of adrenalectomy on miniature inhibitory postsynaptic currents in the paraventricular nucleus of the hypothalamus. J Neurophysiol 89: 237–245, 2003.
Verkuyl JM, Karst H, Joels M. GABAergic transmission in the rat paraventricular nucleus of the hypothalamus is suppressed by corticosterone and stress. Eur J Neurosci 21: 113–121, 2005.[CrossRef][Web of Science][Medline]
Whitnall MH. Regulation of the hypothalamic corticotrophin-releasing hormone neurosecretory system. Prog Neurobiol 40: 573–629, 1993.[Web of Science][Medline]
Wilcox KS, Dichter MA. Paired pulse depression in cultured hippocampal neurons is due to a presynaptic mechanism independent of GABAB autoreceptor activation. J Neurosci 14: 1775–1788, 1994.[Abstract]
Yang JH, Li LH, Lee S, Jo IH, Lee SY, Ryu PD. Effects of adrenalectomy on the excitability of neurosecretory parvocellular neurones in the hypothalamic paraventricular nucleus. J Neuroendocrinol 19: 293–301, 2007.[CrossRef][Web of Science][Medline]
Zhang ZH, Kang YM, Yu Y, Wei SG, Schmidt TJ, Johnson AK, Felder RB. 11β-Hydroxysteroid dehydrogenase type 2 activity in hypothalamic paraventricular nucleus modulates sympathetic excitation. Hypertension 48: 127–133, 2006.
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