Journal of Neuroscience, Vol 9, 3538-3546, Copyright © 1989 by Society for Neuroscience
Opiate influences on nucleus accumbens neuronal electrophysiology: dopamine and non-dopamine mechanisms
RL Hakan and SJ Henriksen
Department of Neuropharmacology, Research Institute of the Scripps Clinic, La Jolla, California 92037.
Single-unit recordings of nucleus accumbens septi (NAS) neurons in
halothane-anesthetized rats revealed that microinfusions of morphine into
the ventral tegmental area (VTA) primarily inhibited spontaneously active
NAS units. These inhibitory effects were reversed by alpha- flupenthixol
(s.c.), suggesting a role for dopamine (DA) in the observed opiate-induced
effect. VTA opiate microinfusions also inhibited the evoked (driven)
responses of silent cells (spontaneously inactive) in the NAS elicited by
stimulation of hippocampal afferents to the NAS. In addition, this
inhibition of driven response was reversed by naloxone (s.c.) but not by
alpha-flupenthixol, implying a VTA-mediated non-DA mechanism. Morphine
applied iontophoretically to cells within the NAS inhibited spontaneous
activity but not fimbria- driven cellular activity, suggesting that the
systemic effects of opiates on NAS activity can be mediated directly in the
NAS as well as through VTA afferents. Moreover, since VTA-induced
inhibition of fimbria-driven activity was reversed by systemic opiates,
opiates also can exert effects through other, as yet unidentified NAS
afferent systems.