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Cellular responses of nucleus accumbens neurons to opiate‐seeking behavior: i. sustained responding during heroin self‐administration
Author(s) -
Lee RongSheng,
Criado Jose R.,
Koob George F.,
Henriksen Steven J.
Publication year - 1999
Publication title -
synapse
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.809
H-Index - 106
eISSN - 1098-2396
pISSN - 0887-4476
DOI - 10.1002/(sici)1098-2396(199907)33:1<49::aid-syn5>3.0.co;2-o
Subject(s) - nucleus accumbens , heroin , opiate , self administration , neuroscience , pharmacology , psychology , dopamine , medicine , drug , receptor
The nucleus accumbens (NAcc) has been hypothesized to be a critical component of the circuit mediating opiate‐seeking behaviors. To further explore the electrophysiological correlates of opiate‐seeking behavior, we recorded neurons in the NAcc and in the medial prefrontal cortex (mPFC) of rats trained to self‐administer heroin for at least 2 weeks. Rats were trained to lever press (FR‐1 schedule) for an intravenous (i.v.) infusion of heroin (0.06 mg/kg/injection) in an operant chamber. Spontaneous single unit activity in the NAcc and the mPFC was then recorded while animals were allowed to self‐administer heroin. Our data suggest that about 20% (8/42) of the NAcc neurons studied exhibited an inhibitory response immediately after heroin self‐administration. However, most of the NAcc neurons studied (76%; 32/42) were not affected during heroin self‐administration. In contrast, noncontingent injection of a similar dose of heroin (0.06 mg/kg/injection) had no effect on NAcc spontaneous activity (0/6). On the other hand, passive administration of higher doses of heroin (0.2–0.6/mg/kg/injection) markedly suppressed the firing rate in 46% (6/13) of the neurons studied. These effects of heroin on NAcc activity were antagonized by systemic administration of naloxone (4–6 mg/kg, i.v.). Studies characterizing the responses of mPFC neurons during heroin self‐administration showed that 40% (2/5) of the neurons tested exhibited an inhibitory effect immediately after heroin self‐administration. These data suggest that in animals well‐trained to self‐administer heroin, only a small number (20%) of the NAcc neurons studied responded to heroin self‐administration. Further research is necessary to determine whether these responses are a function of the opiate‐seeking state of the animal and the mechanism(s) responsible for these effects of heroin. Synapse 33:49–58, 1999. © 1999 Wiley‐Liss, Inc.