Ethanol consumption by Fawn-Hooded rats following abstinence: effect of naltrexone and changes in mu-opioid receptor density.

Published

Journal Article

BACKGROUND: Relapse after abstinence can be modelled in rats using an alcohol deprivation effect (ADE) of enhanced ethanol consumption after a period of enforced abstinence from ethanol; however, not all rat strains display such an effect. We wanted to examine the effect of naltrexone on ethanol consumption by ethanol-preferring Fawn-Hooded (FH) rats using such a model. METHODS: FH rats were given continual free-choice access to a 5% ethanol solution or water (4 weeks) followed by 2 weeks of water alone. At the end of this abstinence period, osmotic minipumps were implanted subcutaneously to deliver saline (n = 4) or naltrexone (n = 4; 8.4 mg/kg/day for 4 weeks). After recovery from surgery, the rats were again given access to 5% ethanol under the same free-choice conditions (4 weeks). A third group of age-matched controls drank only water during the behavioral trial. At the end of the behavioral trial, the rats were decapitated and an autoradiographic examination was made of micro-opioid receptor density through the forebrain using the ligand [125I]FK-33824. RESULTS: First, a period of enforced abstinence from ethanol consumption caused a significant (p < 0.05) and prolonged increase in ethanol preference (+18%) and decrease in water consumption (-53%), although the volume of ethanol consumed (ml/day) did not vary, indicating an atypical ADE in this rat strain. Second, naltrexone significantly (p < 0.05) decreased ethanol consumption by the FH rats in terms of absolute amount of ethanol consumed and preference for ethanol solution, but this effect of naltrexone diminished over time, concurrent with a robust and significant elevation in micro-opioid receptor density in all brain regions examined (p < 0.05). Finally, ethanol consumption alone also upregulated micro-opioid receptor density relative to nondrinking controls in a number of brain regions, which included the nucleus accumbens (+29%) and caudate-putamen (+15%,p < 0.05), but decreased micro-opioid receptor density in other regions including the substantia nigra pars reticulata, which was suggestive of an indirect effect on micro-opioid receptors. CONCLUSIONS: The data suggest that continual long-term naltrexone treatment may not be effective in the treatment of alcoholism, possibly because of the induced increase in micro-opioid receptor density.

Full Text

Duke Authors

Cited Authors

  • Cowen, MS; Rezvani, AH; Jarrott, B; Lawrence, AJ

Published Date

  • June 1999

Published In

Volume / Issue

  • 23 / 6

Start / End Page

  • 1008 - 1014

PubMed ID

  • 10397284

Pubmed Central ID

  • 10397284

International Standard Serial Number (ISSN)

  • 0145-6008

Language

  • eng

Conference Location

  • England