Stimulation-produced analgesia and its cross-tolerance between dorsal and ventral PAG loci.
This study explored the development of tolerance to brain stimulation-produced analgesia in both dorsal and ventral periaqueductal gray (PAG) sites and the development of cross-tolerance between naloxone-reversible and non-reversible sites. Cross-tolerance was produced from non-naloxone-reversible sites to naloxone-reversible sites (NNR-NR) and from naloxone-reversible sites to non-naloxone-reversible sites (NR-NNR). The following conclusions can be drawn from the present study: (1) the descending pain inhibitory systems within the PAG do not operate in isolation of each other since cross-tolerance to chronic stimulation can be produced between systems; (2) the interaction between the two systems is apparently bi-directional in that cross-tolerance was produced from naloxone-reversible to non-reversible sites and vice versa; and (3) the interaction may be the result of a co-activation of opioid and non-opioid systems produced by electrical stimulation or by a co-utilization of a common neuronal substrate. It is speculated that serotonin is a neurotransmitter involved in the mechanism of convergence.
Nichols
D S
DS
Department of Psychology, Ohio State University, Columbus, OH U.S.A. Department of Psychology, University of Alabama, Tuscaloosa, AL 35487-0348 U.S.A.
Thorn
B E
BE
D000698:Analgesia / Q000379:methods*; D000818:Animals; D004361:Drug Tolerance; D004599:Electric Stimulation Therapy; D009270:Naloxone / Q000494:pharmacology; D010487:Periaqueductal Gray; D051381:Rats
D009270:Naloxone