Up-regulation of opiate receptors following chronic naloxone treatment in aged rats.
The present study assessed whether there are age-dependent differences in up-regulation of opiate receptors following chronic naloxone treatment in mature (3 months) and aged (27 months) male Wistar rats. Half of each age group were implanted subdermally with slow-release naloxone pellets for 10 days, and half were given sham surgery. Twenty-four hours after pellet removal, the rats were decapitated and various CNS areas including spinal cord, hindbrain, midbrain, diencephalon, hippocampus, striatum, olfactory tubercles/nucleus accumbens and prefrontal cortex were dissected and assayed for [3H]naloxone binding. The results indicated that aged rats had fewer opiate receptors in the spinal cord, midbrain, striatum, and olfactory tubercle/nucleus accumbens. Despite this age-related decline in opiate receptors, aged rats showed an up-regulation response similar to mature rats in all areas except the hippocampus of the left hemisphere, where they showed enhanced up-regulation relative to mature rats. The maintained plasticity of the opioid system contrasts with findings in other receptors systems where age-related impairments of antagonist-induced up-regulation have been reported.
Neisewander
J L
JL
Department of Psychology, University of Kentucky, Lexington 40506.
Nonneman
A J
AJ
McDougall
S A
SA
Bardo
M T
MT
D000375:Aging / Q000378:metabolism*; D000818:Animals; D001665:Binding Sites; D002490:Central Nervous System / Q000378:metabolism*; D008297:Male; D009270:Naloxone / Q000008:administration & dosage / Q000494:pharmacology*; D051381:Rats; D011957:Receptors, Opioid / Q000032:analysis / Q000187:drug effects*
D011957:Receptors, Opioid; D009270:Naloxone