Effects of acute ethanol on β-endorphin release in the nucleus accumbens of selectively bred lines of alcohol-preferring AA and alcohol-avoiding ANA rats
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The selectively bred lines of alcohol-preferring alko alcohol (AA) and alcohol-avoiding alko nonalcohol (ANA) rats have been used to demonstrate differences in relevant neurotransmitters which could account for their difference in alcohol consumption. Studies have demonstrated differences in distinct components of the endogenous opioid system in various brain regions associated with the process of reinforcement between the AA and ANA lines of rats.
The goal of this current study was to investigate the hypotheses that the AA and ANA rats will show differences in the release of β-endorphin at the level of nucleus accumbens (NAC) and in locomotor activity in response to acute systemic administration of ethanol.
Materials and methods
AA and ANA rats were unilaterally implanted with a guide cannula to aim microdialysis probes at the level of NAC. Intraperitoneal injections of 0.0, 1.5, 2.0, and 2.5 g ethanol/kg body weight were administered. Dialysate samples were collected at 30-min intervals prior to and following the injection. Radioimmunoassay specific for β-endorphin was used to determine the dialysate β-endorphin content.
The 2.5-g/kg ethanol dose induced a transient increase in extracellular β-endorphin at the level of NAC of AA but not of ANA rats. The 2.5-g/kg ethanol dose also attenuated locomotor activity in the AA but not in the ANA rats.
The lack of an increase in the β-endorphin concentration in the NAC of ANA rats in response to ethanol may partially account for their lower alcohol consumption and lower alcohol-induced attenuation of locomotor activity compared to AA rats.
KeywordsAlcohol Nucleus accumbens Opioid peptides beta-Endorphin AA ANA Alcohol preferring Alcohol avoiding Rat lines In vivo microdialysis
Artificial cerebral spinal fluid
Analysis of variance
Blood alcohol concentration
Bovine serum albumin
Ventral tegmental area
These studies were funded through grants from the Canadian Institute of Health Research (CIHR) and the Academy of Finland. The authors would like to thank Ms. Leena Tanner-Väisänen for her technical assistance.
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