Firing Patterns of Single Nucleus Accumbens Neurons during Intravenous Cocaine Self-Administration Sessions
Neuropharmacological studies of drug-taking behavior in laboratory animals suggest that drug actions on the nucleus accumbens (NAcc) are integrally involved in drug taking and addiction. Chronic extracellular recording techniques have been used in recent years to record the activity of single nucleus accumbens (NAcc) neurons of rats during intravenous cocaine self-administration sessions. These studies have shown that NAcc neurons exhibit a variety of firing patterns during drug-taking sessions. A large percentage of neurons show firing patterns that mirror changes in drug level and that may therefore be pharmacological. A subset of those neurons exhibit an additional change in firing that appears to be nonpharmacological and that may code various aspects of the behavior and stimulus events associated with drug seeking. The firing patterns that appear pharmacological are consistent with the conclusion that self-administered cocaine inhibits a majority of accumbal neurons. In contrast, the changes in firing most closely associated with the actual occurrence of drug self-infusion behavior consist of increases in firing rate. The latter firing patterns are similar in appearance to phasic firing patterns associated with operant behavior reinforced by natural reinforcers. Drug reinforcement and addiction are hypothesized to be mediated by drug actions on neurons that normally control instrumental behavior. The firing patterns described in this chapter are thus prototypic of what might be expected of neurons that contribute importantly to drug taking and addiction.
Key wordsdrug addiction cocaine rat nucleus accumbens neurophysiology
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