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The Effects of Microinjection of d-Amphetamine Into The N. Accumbens During the Late Maintenance Phase of an Ethanol Consumption Bout

https://doi.org/10.1016/S0091-3057(98)00263-9Get rights and content

Abstract

The microinjection of d-amphetamine into the n. accumbens of rats, prior to the start of an operant ethanol self-administration session, increases operant behavior and the amounts of ethanol presented as the reinforcer. Although this effect could result by blocking termination processes regulating a consummatory bout, it could also be a result of enhancing the stimulus control regulating the maintenance of a drinking bout. To explore this issue, rats were trained to self-administer 10% ethanol in an operant situation. Following establishment of stable behavior, they were surgically instrumented so that the n. accumbens could be microinjected with d-amphetamine during a drinking bout, without having to handle the animal. The microinjection of d-amphetamine in the rats self-administering ethanol at the late phase of the drinking bout resulted in a prolonged bout and increased self-administration. During extinction testing, a reinstatement of responding was found following the amphetamine microinjection. The data suggest the most likely action of the amphetamine microinjection was to alter stimulus control factors, which normally regulate the maintenance of drinking, thereby prolonging the bout and increasing intake.

Section snippets

Subjects

Male Long–Evans rats, weighing between 200–225 g at the start of the experiment, were housed individually in standard hanging wire cages in an AAALAC-approved vivarium with ad lib food and water always available. The vivarium was maintained on a 12 L:12 D cycle, with the lights on at 0600 h. All experimental sessions were run during the light portion of the cycle. The rats were maintained in accordance with the NIH guidelines at all phases of the experiment.

Apparatus

Self-administration sessions were

Results

Thirty rats were used in this study. Nine animals developed an infection at various times following the surgery and had to be sacrificed prior to completing the experiment, two rats failed to regain baseline ethanol self-administration after surgery and were discontinued, six rats damaged their head stage connector mounts during the experiment and had to be discontinued with only partial data collected, and three rats were found upon histological examination to have incorrect bilateral cannula

Discussion

The primary objective of this study was to determine if amphetamine microinjected into the n. accumbens during the later phases of an ethanol self-administration bout would produce an effect similar to that observed when the microinjection occurred prior to bout onset. Based on our regulatory model of ethanol bout control (10), it was hypothesized that a microinjection during the late maintenance phase would delay termination of responding and increase intake; an effect similar to that observed

Acknowledgements

This research was supported by grants AA07404 and AA00142 from the National Institute on Alcohol Abuse and Alcoholism to HHS. Special thanks to Mr. H. Seibold of EMDEC, Bellevue, WA, for his assistance in the development of the microinjection equipment.

References (18)

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