Journal of Neurophysiology, Vol 58, Issue 1 138-159, Copyright © 1987 by APS

ARTICLES

Spinal pathways mediating tonic, coeruleospinal, and raphe-spinal descending inhibition in the rat

S. L. Jones and G. F. Gebhart

1. The contribution of midline medullary bulbospinal neurons to descending inhibition from the locus coeruleus (LC) and the funicular trajectories of coeruleo- and raphe-spinal fibers mediating inhibition of spinal nociceptive transmission were examined in different experiments. Extracellular recordings of lumbar dorsal horn neurons were made in deeply pentobarbital-anesthetized, paralyzed rats. All units studied responded to electrical stimulation of the ipsilateral tibial nerve at intensities supramaximal to activate A-alpha-delta- and C-fibers and to mechanical and heat (50 degrees C) stimuli of the glabrous skin of the ipsilateral hind foot. Parallel studies were done in lightly pentobarbital-anesthetized rats utilizing the nociceptive tail-flick (TF) reflex. 2. To examine the contribution of bulbospinal neurons in the nucleus raphe magnus (NRM) to descending coeruleospinal inhibition, lidocaine microinjections were made into the NRM to produce a time-limited, reversible block. Lidocaine microinjections into the NRM effectively blocked NRM stimulation-produced inhibition of the TF reflex (prelidocaine stimulation thresholds were increased two to three times), but did not affect stimulation-produced inhibition from the LC. 3. In parallel electrophysiological studies, stimulation in the NRM inhibited heat-evoked dorsal horn unit activity to 31% of control, whereas stimulation in the LC/SC inhibited heat-evoked activity of the same units to 30% of control. Following NRM lidocaine microinjections, stimulation at the same intensity in the NRM no longer inhibited heat-evoked activity (93% of control), confirming the efficacy of the lidocaine block. LC stimulation-produced inhibition, however, was not affected by blockage of the NRM; heat-evoked unit activity was inhibited by LC stimulation to 39% of control. 4. The effects of ipsilateral and bilateral ventrolateral funiculus (VLF) lidocaine microinjections on spontaneous and heat-evoked unit activity were examined in other experiments. Spontaneous activity increased following ipsilateral VLF lidocaine microinjections for 13/18 units; decreases and no change in spontaneous activity were observed for three and two units, respectively. Heat-evoked unit activity was increased significantly following ipsilateral VLF lidocaine microinjections.(ABSTRACT TRUNCATED AT 400 WORDS)

This article has been cited by other articles:

				M. Warnecke, H. Oster, J.-P. Revelli, G. Alvarez-Bolado, and G. Eichele Abnormal development of the locus coeruleus in Ear2(Nr2f6)-deficient mice impairs the functionality of the forebrain clock and affects nociception Genes & Dev., March 1, 2005; 19(5): 614 - 625. [Abstract] [Full Text] [PDF]

				M. W. Luijpen, D. F. Swaab, J. A. Sergeant, and E. J. A. Scherder Effects of Transcutaneous Electrical Nerve Stimulation (TENS) on Self-Efficacy and Mood in Elderly with Mild Cognitive Impairment Neurorehabil Neural Repair, September 1, 2004; 18(3): 166 - 175. [Abstract] [PDF]

				M. Zhuo and G. F. Gebhart Modulation of Noxious and Non-Noxious Spinal Mechanical Transmission From the Rostral Medial Medulla in the Rat J Neurophysiol, December 1, 2002; 88(6): 2928 - 2941. [Abstract] [Full Text] [PDF]

				Y.-Z. Pan, D.-P. Li, S.-R. Chen, and H.-L. Pan Activation of delta -Opioid Receptors Excites Spinally Projecting Locus Coeruleus Neurons Through Inhibition of GABAergic Inputs J Neurophysiol, November 1, 2002; 88(5): 2675 - 2683. [Abstract] [Full Text] [PDF]

				B. H. Manning A Lateralized Deficit in Morphine Antinociception after Unilateral Inactivation of the Central Amygdala J. Neurosci., November 15, 1998; 18(22): 9453 - 9470. [Abstract] [Full Text] [PDF]

				O. Gall, D. Bouhassira, D. Chitour, and D. Le Bars Involvement of the Caudal Medulla in Negative Feedback Mechanisms Triggered by Spatial Summation of Nociceptive Inputs J Neurophysiol, January 1, 1998; 79(1): 304 - 311. [Abstract] [Full Text] [PDF]

				B. A. Graham, D. L. Hammond, and H. K. Proudfit Differences in the Antinociceptive Effects of Alpha-2 Adrenoceptor Agonists in Two Substrains of Sprague-Dawley Rats J. Pharmacol. Exp. Ther., November 1, 1997; 283(2): 511 - 519. [Abstract] [Full Text]

				M. O. Urban and G. F. Gebhart Characterization of Biphasic Modulation of Spinal Nociceptive Transmission by Neurotensin in the Rat Rostral Ventromedial Medulla J Neurophysiol, September 1, 1997; 78(3): 1550 - 1562. [Abstract] [Full Text] [PDF]

				M. Zhuo and G. F. Gebhart Biphasic Modulation of Spinal Nociceptive Transmission From the Medullary Raphe Nuclei in the Rat J Neurophysiol, August 1, 1997; 78(2): 746 - 758. [Abstract] [Full Text] [PDF]