The neural basis of footshock analgesia: the effect of periaqueductal gray lesions and decerebration.
Previous studies have demonstrated that brief front paw shock and brief hind paw shock produce potent opiate and non-opiate analgesia, respectively. Front paw footshock-induced analgesia (FSIA) and hind paw FSIA are similar in that each is mediated by a medullospinal pathway. A question which arises is whether these opiate and non-opiate descending pathways are activated in direct response to afferent information from the spinal cord or whether indirect activation via more rostral centers is required. The first experiment examined the effect of lesions of the rostral periaqueductal gray (PAG) and caudal PAG on front paw (opiate) FSIA and hind paw (non-opiate) FSIA. In no case did PAG lesions markedly reduce the magnitude of these pain inhibitory states. Since this result raised the possibility that rostral centers may not have any major involvement in the production of these phenomena, the second experiment examined the effect of decerebration on front paw FSIA and hind paw FSIA. Decerebration effect on hind paw FSIA and, at most, produced only a very modest decrease in front paw FSIA. The fact that potent and prolonged analgesia can still be elicited after decerebration clearly demonstrates that limbic, cortical, thalamic, and rostral midbrain structures are not critical to the production of these pain inhibitory effects. Thus this work provides the first demonstration of opiate and non-opiate analgesia systems within the caudal brainstem and spinal cord which can be activated by environmental stimuli.
D000698:Analgesia; D000818:Animals; D001931:Brain Mapping; D003655:Decerebrate State / Q000503:physiopathology*; D004597:Electroshock; D004723:Endorphins / Q000502:physiology; D005552:Forelimb; D006614:Hindlimb; D008297:Male; D009434:Neural Pathways / Q000503:physiopathology; D010146:Pain / Q000503:physiopathology*; D010487:Periaqueductal Gray / Q000503:physiopathology*; D051381:Rats; D011919:Rats, Inbred Strains
D004723:Endorphins