The objectives of the proposed experiments are (1) to determine the selectivity for nociceptive input of the spinal inhibition descending from the brain stem, correlating the spinal inhibition with the analgesias produced by focal electrical stimulation and morphine given at selected sites in the brain stem, and (2) to clarify the organization in the brain stem of descending systems of analgesia/inhibition. Rats will be chronically implanted with 26 guage guide cannula(e), through which either a stimulating electrode or injection cannula can be passed. Both the electrodes and injection cannulae will be of identical length to permit stimulation and morphine administration at identical sites in the brain stem. The effect(s) of stimulation and morphine given in the periaqueductal gray, lateral mesencephalic reticular formation, nucleus raphe magnus, and lateral medullary reticular formation on both noxious (radiant heat, electrical C-fiber activation) and non-noxious (brush, electrical A Alpha, Beta-activation) evoked spinal neuronal activity will be quantitatively examined. At all four sites in the brain stem, morphine will be compared with stimulation. In other experiments, stimulation at one site will be compared with stimulation at another site. Significantly, prior to the electrophysiologic evaluation of spinal neurons, the analgetic efficacy of stimulation and morphine will be evaluated in several analgesiometric tests organized at different levels of the CNS to allow correlation of the analgesia produced with the descending inhibitory effects subsequently examined electrophysiologically in the same animals. The study will determine whether there exists a descending system(s) which is selectively analgetic and further our understanding of the brain stem pathways and mechanisms of spinal inhibition.
Showing the most recent 10 out of 140 publications
