The dorsal raphe nucleus: a re-evaluation of its proposed role in opiate analgesia systems.
Previous studies have concluded that (a) electrical stimulation in the periaqueductal gray/dorsal raphe nucleus (PAG/DRN) region specifically produces either non-opiate or opiate forms of antinociception dependent upon the dorsoventral level of stimulation and (b) the 'opiate' form of stimulation-produced analgesia (SPA) arising from the ventral PAG/DRN region shows cross-tolerance with opiate forms of footshock analgesia, implying common neural substrates. This latter conclusion in turn implies that SPA elicited from the ventral PAG/DRN region would be expected to be antagonized by scopolamine, since this muscarinic cholinergic antagonist blocks opiate footshock analgesia. The present study demonstrates instead that neither 10 mg/kg naloxone nor 10 mg/kg scopolamine had any effect on SPA elicited from sites histologically verified to lie within the presumptive 'opiate' ventral PAG/DRN region. These data bring into question both the site specificity of opiate SPA and the common mediation of ventral PAG/DRN SPA and opiate forms of footshock analgesia.
Klatt
D S
DS
Department of Animal Physiology, University of California, Davis 95616.
Guinan
M J
MJ
Culhane
E S
ES
Carstens
E
E
Watkins
L R
LR
D000698:Analgesia; D000818:Animals; D004558:Electric Stimulation; D004723:Endorphins / Q000502:physiology*; D008297:Male; D010146:Pain / Q000503:physiopathology*; D010487:Periaqueductal Gray / Q000502:physiology; D011903:Raphe Nuclei / Q000502:physiology*; D051381:Rats; D011919:Rats, Inbred Strains
D004723:Endorphins