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1Department of Biomedical Engineering, Case Western Reserve University, Cleveland, Ohio; and 2Department of Biomedical Engineering, Duke University, Durham, North Carolina
Submitted 20 September 2004; accepted in final form 12 December 2004
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMETHODSRESULTSDISCUSSIONGRANTSACKNOWLEDGMENTSREFERENCES |
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-chloralose monitored by blood pressure and heart rate. DP stimulation elicited bladder contractions before and after SCT but only if the bladder contained a sufficient volume of fluid (78% of the volume needed to cause distention-evoked reflex contractions). The volume dependency was mediated by a neuronal mechanism in the lumbosacral spinal cord and was not attributable to length-tension properties of the detrusor muscle. Stimulation at 2–40 Hz initiated bladder contractions, but 20–40 Hz was more effective than lower frequencies in evoking and sustaining bladder contractions for the duration of the stimulus train. Decreases in urethral sphincter activity occurred during sustained bladder contractions evoked by 20- to 40-Hz stimulation before and within 16 h after SCT. After SCT, average bladder pressure increases evoked by DP stimulation were smaller than those evoked before SCT, but in some animals, bladder pressures elicited by DP stimulation continued to increase as time after SCT increased and reached pretransection amplitudes at 8–16 h posttransection. These data confirm the presence of a spinal circuit that can mediate coordinated bladder–sphincter responses and show that afferents from the DP can activate this circuit under appropriate conditions. |
INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMETHODSRESULTSDISCUSSIONGRANTSACKNOWLEDGMENTSREFERENCES |
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, 1987). The traditional view of coordinated reflex micturition holds that it is mediated by a spinal cord–brain stem–spinal cord reflex loop initiated by input from pelvic nerve afferents signaling bladder distention (de Groat 1990). However, a recent study challenges this view by showing that stimulation of a rostral sensory branch of the pudendal nerve evoked weak micturition-like activity even after acute spinal transection (Shefchyk and Buss 1998). The present study investigated the ability of activation of afferents in the deep perineal nerve (DP), a caudal branch of the pudendal nerve (Martin et al. 1974), to evoke micturition-like activity with and without the brain stem. The results demonstrate that deep perineal afferents can evoke a spinal reflex capable of coordinated micturition-like activity and that the reflex was sensitive to bladder volume and the firing rate of deep perineal afferents.
Flow of urine through the urethra can evoke afferent firing in the deep perineal branch of the pudendal nerve (Todd 1964) and initiate bladder contraction through a spinobulbospinal reflex loop (Barrington 1931, 1941). Despite the implication that deep perineal receptors transduce fluid flow and the resulting afferent firing elicits the micturition response, the ability to induce a micturition-like response through direct stimulation of DP afferents has not been investigated. The established doctrine of the micturition cycle states that the brain stem is essential for coordinating the bladder–sphincter activity that enables micturition (Morrison 1987; Nitti and Combs 1998), but the necessity of the brain stem in the micturition pathway mediated by DP afferents cannot be evaluated until the bladder–sphincter response to direct DP activation is investigated. This study determines whether DP activation can elicit coordinated bladder–sphincter activity and if a spinal reflex exists to maintain bladder–sphincter synergy after spinal cord transection. The existence of a spinal micturition-like reflex initiated through cranial pudendal sensory nerve stimulation has been shown previously, but it was limited to 1 h postspinalization and was conducted in animals that did not exhibit distention-evoked reflex contractions (Shefchyk and Buss 1998). The present study extends the Shefchyk and Buss (1998) investigation by determining in animals responsive to bladder distention whether a urethral sensory pathway can mediate a micturition-like reflex several hours after acute spinalization.
Urethral fluid flow produces bladder contractions when the bladder contains a sufficiently large volume but not when it contains a small volume (Barrington 1931, 1941). Increases in bladder pelvic nerve activity evoked in response to electrical stimulation of the cranial pudendal sensory nerve show a similar dependency on bladder volume in animals anesthetized with -chloralose (Mazieres et al. 1997), but bladder response to electrical stimulation of the sensory nerve is not documented in the same detail as the bladder response to fluid flow (Robain et al. 2001) to allow direct comparison of the volume thresholds. The present study quantifies the volume needed for DP stimulation to elicit a bladder contraction relative to the volume required to elicit a distention-evoked reflex bladder contraction. This investigation also determines whether the volume dependency arises from detrusor length-tension properties or is neural in origin and whether the volume dependency changes after spinal transection.
Afferent fiber firing rates between 2 and 40 Hz have been recorded from the deep perineal nerve during urethral fluid flow with rates from 20 to 40 Hz predominating during extended periods of flow (Todd 1964). The preponderance of the higher-frequency firing rates may suggest that the reflex is more responsive to specific interspike intervals. The bladder and pelvic nerve responses to cranial pudendal sensory nerve activation have been investigated over a range of continuous stimulation frequencies (1–50 Hz) in decerebrate animals and animals anesthetized with -chloralose (Jiang and Lindstrom 1999; Mazieres et al. 1997; Shefchyk and Buss 1998), but the relative effect of stimulation frequency on either bladder or urethral sphincter response before or after spinalization has not been reported. The present study determines whether the afferent firing rate influences the reflex response by stimulating the DP over the range of frequencies recorded during urethral fluid flow. This report also compares the capacity of different firing rates to evoke micturition-like activity after acute spinal transection.
The overall goal of this study is to investigate the existence of a spinal micturition-like reflex mediated by activation of the deep perineal nerve and to quantify the dependency of the reflex on bladder volume and the firing rate of DP fibers. The results challenge the traditional view that the brain stem is required to evoke a micturition-like response by demonstrating that the spinal circuitry can coordinate bladder–sphincter activity in response to electrical stimulation of the deep perineal nerve after the brain stem has been removed from the reflex loop.
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METHODS |
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Acute experiments were conducted on 14 adult, sexually intact male cats 3.5–5.7 kg. All animal care and experimental procedures were followed according to National Institutes of Health guidelines and were approved by the Institutional Animal Care and Use Committee of Case Western Reserve University. Anesthesia was induced with ketamine HCl (Ketaset, 35 mg/kg, intramuscularly, supplemented as required during surgical preparation). A venous catheter was inserted in the cephalic vein, and anesthesia was maintained with -chloralose [Sigma, 65 mg/kg, intravenously (iv), supplemented at 15 mg/kg]. A catheter was placed in the carotid artery to measure blood pressure. A surgical plane of anesthesia was maintained by ensuring the blood pressure was <120 mmHg and that blink and withdrawal reflexes were absent. A midline abdominal incision was made to expose the bladder; the ureters were ligated, transected proximal to the ligation, and drained externally. The bladder was cannulated with a 3.5 Fr (1.17 mm) catheter introduced with a hypodermic needle through the bladder dome, secured with a purse-string suture, and the abdominal incision was closed in layers. The urethra was occluded with a 5 Fr (1.67 mm) catheter advanced through the urethra to lie within the bladder. Body temperature was maintained between 37 and 39°C with a heating blanket; 0.9% saline with 8.4 mg/ml sodium bicarbonate and 5% dextrose added was administered iv (10–15 ml kg–1 h–1), and end tidal CO2 was maintained between 3–4% with artificial respiration. In 8 animals the spinal cord was transected after collection of data with the spinal cord intact. A laminectomy was made to expose the thoracic spinal cord at T12; lidocaine was administered on the surface of the spinal cord, and the spinal cord was elevated and transected using a scalpel. A piece of Gelfoam was inserted between ends of the spinal cord and the exposure was closed.
Recording and stimulation
A solid-state pressure transducer (Deltran DPT-100, Utah Medical Products, Midvale, UT) connected to the suprapubic catheter was used to measure bladder pressure. The pressure signal was amplified, low-pass filtered (cutoff frequency = 300 Hz), continuously recorded on a strip-chart recorder (TA11, Gould Instruments), sampled at 24 kHz, and stored on digital tape (CDAT 16 Data Recorder, Cygnus Technology, Delaware Water Gap, PA). Bladder volume was increased in 1-ml increments to determine the threshold volume (Vthr) for distention-evoked contractions and the threshold volume for bladder contractions elicited by stimulation of the DP. Accuracy of bladder volumes was determined by emptying the bladder every 1–2 h, and the bladder volumes reported were accurate to within ±2 ml.
The gluteus superficialis and gluteofemoralis muscles were partially transected and reflected laterally to expose the pudendal nerve. The ipsilateral deep perineal nerve branch was isolated and stimulated with platinum bipolar hook electrodes and a constant current stimulator (Pulsar 9 bp, FHC, Bowdoinham, ME). Stimuli were cathodic monophasic pulses with amplitude of 100–900 µA and duration of 100 µs applied as 5- to 25-s trains with a frequency between 2 and 40 Hz. The minimum current amplitude necessary to elicit bladder contractions was called threshold (DPthr) and ranged from 150 to 450 µA (n = 10 cats). The bladder contained a volume of approximately 125% of Vthr for distention-evoked bladder contractions when DPthr was determined. The electrical threshold to evoke a compound nerve action potential in the DP was measured in 2 cats by stimulating the DP and recording proximally to the stimulation site at the trunk of the ipsilateral pudendal nerve and fell in a similar range (100–300 µA). In these 2 experiments, DPthr ranged from 1.5 to 2.0 times the electrical threshold to evoke a compound nerve action potential. The data presented here were obtained at 2DPthr to 4DPthr. In 3 cats, electroneurogram (ENG) activity of fibers innervating the EUS was recorded with a tripolar cuff electrode placed on the contralateral deep perineal nerve branch. The ENG was preamplified (100x, Stanford SR560, Sunnyvale, CA) and filtered (300 Hz–10 kHz), further amplified (1,000x) and filtered (300 Hz–3 kHz, Grass P511, Quincy, MA), sampled (24-kHz sampling frequency), and stored on digital tape. The ipsilateral DP was transected distal to the stimulating electrodes to prevent direct activation of the EUS and the subsequent afferent response to the EUS ENG discharge that would be recorded by the contralateral cuff electrode.
The length-tension properties of the detrusor muscle were determined in 3 cats by stimulating the whole sacral roots, both S1 and S2 simultaneously, over a range of bladder volumes and measuring the resulting bladder pressure. Stimuli were cathodic monophasic pulses with amplitude of 2 mA and duration of 100 µs applied as 5-s trains with a frequency of 20 Hz, based on parameters previously shown to be effective in eliciting maximal bladder pressures (Grill et al. 1999).
The feasibility of voiding was determined in 3 animals (2 cats pre-SCT and 1 cat post-SCT) after unilateral transection of the DP and stimulation of the ipsilateral proximal stump to avoid direct activation of the EUS muscle. The bladder was filled at 1 ml/min and the urethral catheter was removed before voiding. Stimuli were cathodic monophasic pulses with amplitude of 2DPthr to 4DPthr and duration of 100 µs applied as 30- to 120-s trains with a frequency of 33 Hz, based on parameters found to be effective in eliciting maximal sustained bladder pressures without increases in EUS ENG activity. At the conclusion of each experiment the animal was killed by an overdose of sodium pentobarbital, and the anatomy was verified by tracing the nerves proximally and distally.
Off-line analysis of bladder pressure and electroneurogram
Data were analyzed using custom routines in MATLAB (The MathWorks, Natick, MA). Bladder responses to deep perineal nerve stimulation were assessed by measuring changes in bladder pressures (Fig. 1). The analysis considered a bladder contraction to be evoked if the pressure increased over a threshold pressure (Pth) defined as
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Distribution of experiments
Responses to DP stimulation were investigated in a total of 14 cats pre-SCT and 8 cats post-SCT. The bladder volume dependency of the bladder pressure response to DP stimulation was investigated in 13 spinal-intact cats. The relationship between the volume threshold (Vthr) for bladder contractions evoked by DP stimulation and the Vthr for distention-evoked contractions was investigated in 6 cats before SCT, and in 4 of the 6 cats the volume thresholds were examined in small (1-ml) increments before and after SCT. In 3 cats, the bladder pressure changes generated by sacral nerve root stimulation, DP stimulation, and distention-evoked reflex contractions were evaluated in 3-ml intervals. The bladder pressure response to the frequency at which the DP was stimulated was examined in 8 cats before SCT and in 6 of those 8 cats after SCT. Both bladder pressure and EUS ENG response to DP stimulation were measured in 3 cats before and after SCT. The DP was transected and stimulated proximal and distal to the cut in 3 cats pre-SCT and in 1 cat post-SCT. Voiding was validated in 3 cats: 2 cats before SCT and 1 cat after SCT.
Statistical analysis
Statistical analysis of bladder pressures and deep perineal ENG was performed using paired t-test or ANOVA followed by Tukey–Kramer post hoc test. Analysis of bladder and EUS ENG activity characteristics was performed using Kruskal–Wallis test followed by nonparametric pairwise comparison based on Bonferroni inequalities (Gibbons 1993) because the data were not normally distributed. Values are expressed as means ± SDs.
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RESULTS |
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Micturition reflex evoked by deep perineal nerve stimulation in spinally intact cats
VOLUME DEPENDENCY OF THE REFLEX.
DP stimulation evoked bladder contractions only when the bladder contained more than a minimum threshold volume (Vthr). Figure 2 shows the bladder pressure responses to DP stimulation and bladder distention at different bladder volumes. The bladder was filled in increments and between each 1-ml bolus of saline, the DP was stimulated. In this example, DP stimulation first elicited a sustained contraction when bladder volume was increased to 16 ml (DP Vthr). The saline bolus first caused a distention-evoked reflex contraction, characterized by slow oscillation of the bladder pressure during the contraction, when the bladder volume was increased to 24 ml (distention-evoked Vthr). Volume thresholds varied among cats, but Vthr for contractions evoked by DP stimulation (7 ± 6 ml; 1 to 18 ml; n = 6 cats in which the volume thresholds were investigated in intervals 
3 ml) was always less than the Vthr for distention-evoked reflex contraction (10 ± 8; 2 to 24 ml; n = 6 cats). DP stimulation elicited contractions at 78 ± 17% of the volume required for the saline bolus to evoke a contraction (n = 4 cats in which the volume thresholds were investigated in 1-ml intervals).
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). The magnitudes of the pressures during sustained contractions were dependent on the frequency of stimulation (P < 0.005) (Fig. 5); however, there were no significant differences between any 2 stimulation frequencies (post hoc paired comparisons, Tukey–Kramer).
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)]. Stimulation at 33 Hz produced no significant change in EUS ENG in 2 cats (P > 0.05 for each cat; paired t-test of EUS ENG before stimulation and during the stimulation-evoked bladder contraction, n = 18 and 21 comparisons in respective cats) (Fig. 6A) and produced a decrease in EUS ENG in 1 cat (P < 0.01; paired t-test, n = 20 comparisons). Stimulation at 2 Hz produced an increase in EUS ENG in 2 cats (P < 0.001 for each cat; paired t-test, n = 10 and 11 comparisons in respective cats) (Fig. 6B) and produced no significant change in EUS ENG in 1 cat (P > 0.05; paired t-test, n = 8 comparisons). Thus high-frequency stimulation was less likely to evoke EUS ENG discharges than low-frequency stimulation irrespective of the bladder response.
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AFFERENT FIBER STIMULATION PRODUCED VOIDING. After transection of the DP nerve, stimulation proximal to the cut continued to elicit bladder contractions, whereas stimulation distal to the cut produced no contractions (Fig. 7) (n = 3 of 3 cats), demonstrating that the reflex was mediated by an afferent pathway. To confirm that the bladder contraction and reduction in EUS activity evoked by DP afferent stimulation were indeed a micturition reflex, voiding was measured in 2 cats after transecting the deep perineal nerve and stimulating proximal to the cut. After removing the urethral catheter, stimulation of the proximal DP stump voided 63 ± 20% of the bladder’s volume (n = 3 trials across 2 cats) and distention-evoked reflex bladder contractions voided 32 ± 3% of the bladder’s volume (n = 4 trials across 2 cats). DP stimulation voided at least as much volume as distention-evoked reflex contractions (P = 0.05; Mann–Whitney test of volume voided by DP stimulation to volume voided by distention-evoked reflex contraction).
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After acute SCT at T12, bladder distention in the absence of DP stimulation failed to elicit reflex bladder contractions, but stimulation of DP afferents generated bladder contractions after SCT in all 8 SCT cats. Immediately after SCT (0–30 min), stimulation failed to elicit an increase in bladder pressure. However, the amplitude of post-SCT contractions increased with time after spinalization and in 3 cats, the contractions returned nearly to their prespinalization magnitude by 8 h post-SCT (Fig. 8). In another 4 cats, the bladder response did not return fully to pre-SCT magnitude over the times investigated, and 1 cat died less than 5 h after SCT (Fig. 9).
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PROBABILITY OF DEEP PERINEAL STIMULATION EVOKING A BLADDER CONTRACTION INCREASED AFTER SCT. After SCT, the character of the pressure responses still varied according to the frequency at which the DP was stimulated (P < 0.005). Stimulation at 33 Hz produced the greatest percentage of sustained contractions, and 2 Hz produced the lowest percentage (Fig. 10). Post-SCT, all frequencies were more likely to evoke a bladder contraction than they were before SCT, and the ability of each frequency to evoke a sustained contraction also increased (Fig. 10). As before SCT, the magnitudes of the sustained contraction pressure varied according to the frequency (P < 0.05) (Fig. 11), but there were no significant differences in the magnitude of bladder pressures produced by any 2 frequencies post-SCT (post hoc paired comparisons, Tukey–Kramer).
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AFFERENT FIBER STIMULATION PRODUCED VOIDING AFTER SPINALIZATION. After transection of the DP nerve in one SCT cat, stimulation proximal to the cut continued to elicit bladder contractions, whereas stimulation distal to the cut did not produce contractions. After removing the urethral catheter, stimulation of the proximal DP voided 65 ± 8% of the bladder’s volume (n = 4 trials within 1 cat). This was comparable to DP stimulation–evoked voiding before SCT (63 ± 20%).
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DISCUSSION |
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TOPABSTRACTINTRODUCTIONMETHODSRESULTSDISCUSSIONGRANTSACKNOWLEDGMENTSREFERENCES |
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). The reflex pathways between deep perineal afferents and bladder and sphincter efferents must lie caudal to T12 because the reflex persisted after acute spinalization. The existence of a spinal micturition reflex activated by coincident activity in bladder stretch receptors and DP afferents supports the existence of a micturition pathway not involving the brain stem. Somatic DP and visceral pathways converge within the marginal zone, intermediate gray, and dorsal gray commissure of sacral segments S1 and S2 (Roppolo et al. 1985; Thor et al. 1989), regions containing putative interneurons known to be active during micturition-like activity and pudendal nerve stimulation in animals with an intact neuraxis (Grill et al. 1998). Neurons in these regions may mediate the spinal micturition-like reflex elicited through activation of DP afferents. Limitations of the present study
Experiments were conducted in cats anesthetized with -chloralose because it interferes less with autonomic function that other anesthetics and maintains spinal reflexes (Balis and Monroe 1964; Bonvento et al. 1994). The bladder pressures elicited by DP stimulation in the present study were similar to pressures elicited by distention-evoked bladder contractions in cats anesthetized with -chloralose (Rudy et al. 1991), but slightly less than pressures elicited by bladder distention and urethral sensory nerve stimulation in decerebrate cats (Rudy et al. 1991; Shefchyk and Buss 1998). Anesthesia may also affect the coordination between the bladder and the external urethral sphincter, and -chloralose caused dyssynergic contraction of the bladder and EUS during distention-evoked micturition (Rudy et al. 1991), whereas Angel et al. (1994) showed synergic EUS relaxation and bladder contraction with -chloralose. In the present study the EUS ENG activity during distention-evoked bladder contractions was observed to be synergic in some instances and dyssynergic in others. However, synergy between the bladder and EUS was observed every time DP stimulation evoked a sustained contraction before SCT, and was also observed in all animals within 16 h post-SCT in this study. Thus DP stimulation evoked a synergic micturition-like response despite the tendency of -chloralose to induce dyssynergia in previously synergic preparations.
The present study was limited to acute measurements before and 16 h after spinal transection, and it did not investigate the properties of the reflex after chronic spinal cord injury (SCI). Spinal shock was not assessed directly, but the time course of the recovery of the bladder’s response to DP stimulation suggests that spinal shock initially depressed the bladder’s response and as the animals recovered, the bladder response to DP stimulation increased (Fig. 9) (Hassouna et al. 1992; Zvara et al. 1998). In chronic SCI, plasticity in neural and muscle properties leads to hyperreflexia, bladder–sphincter dyssynergia, and bladder hypertrophy (de Groat et al. 1981; Krenz and Weaver 1998), and these changes could alter the properties of the reflex in chronic SCI. However, a similar reflex, mediated by pudendal afferents in the proximal urethra, is present in persons with chronic SCI (Gustafson et al. 2004).
Bladder response was dependent on bladder volume
Deep perineal nerve afferent stimulation produced bladder contractions at high bladder volumes but not at lower volumes, analogous to the effects produced by urethral fluid flow (Barrington 1931, 1941). When bladder volume was high, fluid flow through the urethra elicited a bladder contraction and conversely, when bladder volume was low, fluid flowing through the urethra inhibited bladder activity (Garry et al. 1959). The volume threshold to evoke bladder contractions by DP stimulation was 78 ± 17% of the volume threshold for distention-evoked contractions, and urethral fluid flow evoked bladder contractions at bladder volumes 65 ± 17% of the volume required to evoke contractions with rapid infusion of saline into the bladder (Robain et al. 2001). Similarly, electrical stimulation of the urethral sensory nerve elicited excitation of bladder preganglionic parasympathetic neurons only if the bladder contained a sufficient volume (Mazieres et al. 1997), and an excitatory bladder response to urethral sensory nerve stimulation was observed at large bladder volumes (Shefchyk and Buss 1998). In humans intraurethral stimulation produced bladder contractions only when the bladder contained a sufficient volume (Gustafson et al. 2004).
The differences between pressures evoked by DP stimulation and sacral root stimulation at low bladder volumes demonstrate that the length-tension properties did not account for the absence of sustained bladder contractions evoked by DP stimulation at low bladder volumes (Fig. 3). This difference in bladder response to efferent and afferent stimulation demonstrates that the reflex is modulated by the bladder volume and that the bladder volume threshold results from a neural mechanism. The volume dependency may be mediated by convergence of deep perineal and bladder stretch afferents within the spinal micturition circuitry (Morgan et al. 1981; Roppolo et al. 1985), and must exist in the lumbosacral spinal cord because the volume dependency was preserved after acute spinal cord transection at T12.
Bladder response to deep perineal nerve stimulation was dependent on frequency
Higher-frequency stimulation (20–40 Hz) elicited sustained bladder contractions more consistently than lower-frequency stimulation (2–10 Hz). Deep perineal nerve stimulation presumably activated afferents from fluid flow receptors in the region of the EUS (Talaat 1937; Todd 1964), and the frequency dependency of the electrically evoked reflex is consistent with recordings of afferent fibers in the pudendal nerve showing peak firing rates between 20 and 40 Hz during fluid flow through the urethra (Todd 1964). Spinalization increased the percentage of stimuli that elicit sustained bladder contractions at all stimulation frequencies (Fig. 10). The increase in sustained contractions after SCT may arise from the decrease in the minimum volume necessary for DP stimulation to elicit bladder contractions or from removal of descending inhibitory inputs (Holstege et al. 1986).
Urethral sphincter response to deep perineal stimulation is related to bladder response
Activation of deep perineal afferents initiated and sustained a synergic micturition-like reflex including a sustained bladder contraction and an absence of increased urethral sphincter ENG. These results confirm and expand on previous studies showing a decrease in the electromyographic activity of the urethral sphincter evoked by pudendal nerve stimulation during a bladder contraction before and after spinalization (Rampal and Mignard 1975a,b).
At the onset of stimulation, the EUS ENG increased and then either returned to baseline or below as bladder pressure rose (Fig. 6A) or remained elevated above baseline if bladder pressure did not increase (Fig. 6B). The initial increase in EUS ENG activity before bladder contraction and the decrease in EUS ENG activity concomitant with bladder contraction are consistent with the response evoked by stimulation of the rostral urethral sensory branch of the pudendal nerve (Shefchyk and Buss 1998), and similar to the biphasic EUS ENG response evoked by high-frequency stimulation of pelvic detrusor nerve afferents after spinalization (Bradley and Teague 1972). Typically, no bladder contraction was elicited by low-frequency DP stimulation and the EUS activity remained elevated above baseline for the duration of stimulation. The frequency dependency of the EUS ENG response is supported by earlier findings that activation of DP afferents with stimulation frequencies <20 Hz evoked an increase in contralateral EUS ENG activity, whereas frequencies >20 Hz did not (Bradley and Teague 1972). In the present study, the sphincter activity appeared more closely linked to bladder activity than to stimulation frequency because high-frequency stimulation would occasionally elicit an increase in EUS ENG but only if a bladder contraction was not evoked.
The spinal reflex was mediated by activation of deep perineal afferents
The results of nerve transection demonstrated that the reflex was activated through afferent fibers (Fig. 7). Bladder and sphincter activity may also have been influenced by retrograde activation of pudendal motoneurons. About half of EUS motoneurons have recurrent axon collaterals that terminate in or around Onuf’s nucleus and lamina VIII in sacral levels S1 and S2 (Sasaki 1994). The axon collaterals terminating within Onuf’s nucleus could modify the activity of ipsilateral EUS motoneurons but would not influence the analysis of EUS ENG data because activity was recorded from the contralateral DP. The collaterals terminating in lamina VIII could synapse onto putative interneurons and ultimately modify the activity of both EUS motoneurons and the preganglionic neurons innervating the bladder detrusor muscle.
Stimulation of deep perineal afferents elicits micturition
Bladder emptying achieved by stimulation of the deep perineal nerve afferents was approximately twice as effective as bladder emptying achieved by distention-evoked bladder contractions in -chloralose–anesthetized cats. The difference in voiding efficacy is consistent with the conclusion that DP stimulation elicits synergic bladder contraction and sphincter relaxation facilitating bladder evacuation, whereas distention-evoked bladder contractions evoke dyssynergic sphincter contractions obstructing voiding under the influence of -chloralose (Rudy et al. 1991; Thor and Katofiasc 1995). The increased voiding percentages produced by DP stimulation also may be related to the capacity of DP stimulation to evoke bladder contractions at lower volumes than bladder distention (Figs. 2 and 3). The volume remaining after DP stimulation may be the result of bladder volume decreasing below Vthr for DP stimulation–evoked bladder contractions or -chloralose–induced decreased bladder pressures (Rudy et al. 1991) or both. This lumbosacral reflex loop, shown to decrease urethral sphincter ENG activity and initiate sustained bladder contractions producing micturition, has clinical relevance for the development of a neural prosthesis to restore bladder emptying in persons with spinal cord injury.
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ACKNOWLEDGMENTS |
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FOOTNOTES |
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Address for reprint requests and other correspondence: W. M. Grill, Department of Biomedical Engineering, Duke University, Box 90281, Durham, NC 27708-0281 (E-mail: warren.grill{at}duke.edu)
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REFERENCES |
|---|
|
TOPABSTRACTINTRODUCTIONMETHODSRESULTSDISCUSSIONGRANTSACKNOWLEDGMENTSREFERENCES |
|---|
Balis G and Monroe RR. The pharmacology of chloralose: a review. Pharmacologia 6: 1–30, 1964.
Barrington FJF. The component reflexes of micturition in the cat, Parts I and II. Brain 54: 177–188, 1931.
Barrington FJF. The component reflexes of micturition in the cat, Part III. Brain 64: 239–243, 1941.
Bonvento G, Charbonne R, Correze J, Borredon J, Seylaz J, and Lacombe P. Is alpha-chloralose plus halothane induction a suitable anesthetic regimen for cerebrovascular research. Brain Res 665: 213–221, 1994.[CrossRef][Web of Science][Medline]
Bradley W and Teague CT. Electrophysiology of pelvic and pudendal nerves in the cat. Exp Neurol 35: 378–393, 1972.[CrossRef][Web of Science][Medline]
Buss R and Shefchyk SJ. Excitability changes in sacral afferents innervating the urethra, perineum and hindlimb skin of the cat during micturition. J Physiol 514: 593–607, 1999.
de Groat W, Araki I, Vizzard M, Yoshiyama M, Yoshimura N, Sugaya K, et al. Developmental and injury induced plasticity in the micturition reflex pathway. Behav Brain Res 92: 127–140, 1998.[CrossRef][Web of Science][Medline]
de Groat W, Nadelhaft I, Milne R, Booth A, Morgan C, and Thor K. Organization of the sacral parasympathetic reflex pathways to the urinary bladder and large intestine. J Auton Nerv Syst 3: 135–160, 1981.[CrossRef][Web of Science][Medline]
de Groat WC. Central neural control of the lower urinary tract. Ciba Found Symp 151: 27–44, discussion 44, 1990.[Medline]
Garry RC, Roberts TD, and Todd JK. Reflexes involving the external urethral sphincter in the cat. J Physiol 149: 653–665, 1959.
Gibbons JD. Nonparametric Statistics: An Introduction. Newbury Park, CA: Sage, 1993.
Grill W, Bhadra N, and Wang B. Bladder and urethral pressures evoked by microstimulation of the sacral spinal cord in cats. Brain Res 836: 19–30, 1999.[CrossRef][Web of Science][Medline]
Grill W, Wang B, Hadziefendic S, and Haxhiu MA. Identification of the spinal neural network involved in coordination of micturition in the male cat. Brain Res 796: 150–160, 1998.[CrossRef][Web of Science][Medline]
Gustafson K, Creasey G, and Grill WM. A urethral afferent mediated excitatory bladder reflex exists in humans. Neurosci Lett 360: 9–12, 2004.[CrossRef][Web of Science][Medline]
Hassouna M, Li J, Sawan M, Duval F, Latt R, and Elhilali MM. Effect of early bladder stimulation on spinal shock: experimental approach. Urology 40: 563–573, 1992.[CrossRef][Web of Science][Medline]
Holstege G, Griffiths D, de Wall H, and Dalm E. Anatomical and physiological observations on supraspinal control of bladder and urethral sphincter muscles in the cat. J Comp Neurol 250: 449–461, 1986.[CrossRef][Web of Science][Medline]
Holstege G and Tan J. Supraspinal control of motoneurons innervating the striated muscles of the pelvic floor including urethral and anal sphincters in the cat. Brain 110: 1323–1344, 1987.
Jiang C and Lindstrom S. Prolonged enhancement of the micturition reflex in the cat by repetitive stimulation of bladder afferents. J Physiol 517: 599–605, 1999.
Krenz N and Weaver LC. Sprouting of primary afferent fibers after spinal cord transection in the rat. Neuroscience 85: 443–458, 1998.[CrossRef][Web of Science][Medline]
Martin W, Fletcher T, and Bradley WE. Innervation of feline perineal musculature. Anat Rec 180: 15–29, 1974.[CrossRef][Medline]
Mazieres L, Jiang C, and Lindstrom S. Bladder parasympathetic response to electrical stimulation of urethral afferents in the cat. Neurol Urodynam 16: 471–472, 1997.
Morgan C, Nadelhaft I, and de Groat WC. The distribution of visceral primary afferents from the pelvic nerve to Lissauer’s tract and the spinal gray matter and its relationship to the sacral parasympathetic nucleus. J Comp Neurol 201: 415–440, 1981.[CrossRef][Web of Science][Medline]
Morrison JFB. Reflex control of the lower urinary tract. In: The Physiology of the Lower Urinary Tract, edited by Torrens M and Morrison JFB. New York: Springer-Verlag, 1987.
Nitti VW and Combs AJ. Appendix: neurophysiology of urine storage and micturition. In: Practical Urodynamics, edited by Nitti VW. Philadelphia, PA: Saunders, 1998, p. 23–26.
Rampal G and Mignard P. Organization of the nervous control of urethral sphincter. A study in the anaesthetized cat with intact central nervous system. Pfluegers Arch 353: 21–31, 1975a.[CrossRef][Web of Science][Medline]
Rampal G and Mignard P. Behaviour of the urethral striated sphincter and of the bladder in the chronic spinal cat. Implications at the central nervous system level. Pfluegers Arch 353: 33–42, 1975b.[CrossRef][Web of Science][Medline]
Robain G, Combrisson H, and Mazieres L. Bladder response to urethral flow in the awake ewe. Neurourol Urodyn 20: 641–649, 2001.[CrossRef][Web of Science][Medline]
Roppolo J, Nadelhaft I, and de Groat WC. The organization of pudendal motoneurons and primary afferent projections in the spinal cord of the rhesus monkey revealed by horseradish peroxidase. J Comp Neurol 234: 475–488, 1985.[CrossRef][Web of Science][Medline]
Rudy D, Downie J, and McAndrew JD. alpha-Chloralose alters autonomic reflex function of the lower urinary tract. Am J Physiol Regul Integr Comp Physiol 261: R1560–R1567, 1991.
Sasaki M. Morphological analysis of external urethral and external anal sphincter motoneurones of cat. J Comp Neurol 349: 269–287, 1994.[CrossRef][Web of Science][Medline]
Sato A, Sato Y, Shimada F, and Torigata Y. Changes in vesical function produced by cutaneous stimulation in rats. Brain Res 94: 465–474, 1975.[CrossRef][Web of Science][Medline]
Sato A, Sato Y, Sugimoto H, and Tervi N. Reflex changes in the urinary bladder after mechanical and thermal stimulation of the skin at various segmental levels in cats. Neuroscience 2: 111–117, 1977.[CrossRef][Web of Science][Medline]
Shefchyk S and Buss RR. Urethral pudendal afferent-evoked bladder and sphincter reflexes in decerebrate and acute spinal cats. Neurosci Lett 244: 137–140, 1998.[CrossRef][Web of Science][Medline]
Talaat M. Afferent impulses in the nerves supplying the urinary bladder. J Physiol 89: 1–13, 1937.
Thor K, Morgan C, Nadelhaft I, Houston M, and De Groat WC. Organization of afferent and efferent pathways in the pudendal nerve of the female cat. J Comp Neurol 288: 263–279, 1989.[CrossRef][Web of Science][Medline]
Thor KB and Katofiasc MA. Effects of duloxetine, a combined serotonin and norepinephrine reuptake inhibitor, on central neural control of lower urinary tract function in the chloralose anesthetized female cat. J. Pharmacol Exp Ther 274: 1014–1024, 1995.
Todd JK. Afferent impulses in the pudendal nerves of the cat. Q J Exp Physiol Cogn Med Sci 49: 258–267, 1964.
Zvara P, Sahi S, and Hassouna MM. An animal model for the neuromodulation of neurogenic bladder dysfunction. Br J Urol 82: 267–271, 1998.[CrossRef][Web of Science][Medline]
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16 ml, DP stimulation produced sustained contractions of increasingly larger magnitudes denoted by black bars in A, B, and C. At 
), DP stimulation (
), and distention-evoked reflex contractions (
) as a function of bladder volume. Bladder pressures evoked by DP stimulation were significantly (*P < 0.001) lower than pressures evoked by sacral nerve root stimulation at low bladder volumes (3 and 6 ml) but not at higher volumes (9 and 12 ml). Bladder pressures evoked by DP stimulation were significantly (*P < 0.001) greater than pressures elicited by distention-evoked reflex contractions at a midrange bladder volume (9 ml) but not at lower volumes (3 and 6 ml) or a higher volume (12 ml). Bladder pressures evoked by sacral nerve root stimulation were significantly greater than pressures elicited by distention-evoked contractions at low to midrange bladder volumes (3, 6, and 9 ml) but not at a higher volume (12 ml). Therefore the volume dependency of the bladder response to DP stimulation did not depend only on the length-tension properties of the detrusor muscle and was therefore mediated by a neural mechanism. All DP stimulation amplitudes were between 2DPthr and 4DPthr, and the DP was stimulated at 33 Hz. S1 and S2 nerve roots were stimulated at 20 Hz and 2 mA. Numbers in the symbols represent the number of trials. Statistical significance (*P < 0.001) was determined by 2-way ANOVA of the null hypothesis that bladder pressure was independent of stimulus type for all bladder volumes, across 3 cats. Significant difference among bladder pressures was determined by post hoc paired comparisons (Tukey–Kramer).
), but returned to baseline as bladder pressure increased. EUS ENG activity remained within prestimulus baseline activity plus 1 SD ("T" in ENG trace: the base of the "T" is the mean, and the horizontal bar forming the top of the "T" represents the +1 SD level) for the duration of the bladder contraction. B: EUS ENG activity increased during DP stimulation at 2 Hz and remained above +1 SD of the prestimulus baseline ENG for the duration of the bladder contraction. Stimuli were 20-s trains of 100 µs, 900-µA pulses, and bladder volume was above threshold for distention-evoked reflex contractions.
