Defective habituation to nociceptive stimulation in alcohol-avoiding ANA rats

The alcohol-preferring AA and alcohol-avoiding ANA rats: neurobiology of the regulation of alcohol drinking

The AA (alko, alcohol) and ANA (alko, non-alcohol) rat lines were among the earliest rodent lines produced by bidirectional selection for ethanol preference. The purpose of this review is to highlight the strategies for understanding the neurobiological factors underlying differential alcohol-drinking behavior in these lines. Most early work evaluated functioning of the major neurotransmitter systems implicated in drug reward in the lines. No consistent line differences were found in the dopaminergic system either under baseline conditions or after ethanol challenges. However, increased opioidergic tone in the ventral striatum and a deficiency in endocannabinoid signaling in the prefrontal cortex of AA rats may comprise mechanisms leading to increased ethanol consumption. Because complex behaviors, such as ethanol drinking, are not likely to be controlled by single factors, system-oriented molecular-profiling strategies have been used recently. Microarray based expression analysis of AA and ANA brains and novel data-mining strategies provide a system biological view that allows us to formulate a hypothesis on the mechanism underlying selection for ethanol preference. Two main factors appear active in the selection: a recruitment of signal transduction networks, including mitogen-activated protein kinases and calcium pathways and involving transcription factors such as Creb, Myc and Max, to mediate ethanol reinforcement and plasticity. The second factor acts on the mitochondrion and most likely provides metabolic flexibility for alternative substrate utilization in the presence of low amounts of ethanol.

Brain regional mu-opioid receptor function in rat lines selected for differences in alcohol preference

It has been suggested that opioid peptides play a role in the reinforcing effects of alcohol. The present study was designed to examine the function of the mu-opioid receptor system in rat lines selectively bred for alcohol preference (AA [Alko, Alcohol] rat line) and alcohol avoidance (ANA [Alko, Non-Alcohol] rat line). The functional coupling of mu-opioid receptors to G proteins was determined autoradiographically using Tyr-D-Ala-Gly-N(Me)Phe-Gly-ol-enkephalin-stimulated [35S]GTPgammaS binding in brain cryostat sections. The binding was significantly increased in the striatal patches and substantia nigra reticulata of the AA rats in comparison with that of the ANA rats. Within the AA rat line, there was a significant positive correlation between 3 mg/kg morphine-induced locomotor activity and activation of G-proteins in the substantia nigra compacta and nucleus accumbens core. These results of the selective breeding experiment suggest that brain region-specific differences in mu-opioid receptor function may correlate with innate differences in alcohol preference.

Neurobiological processes in alcohol addiction

This article represents the proceedings of a symposium at the ISBRA Meeting in Yokohama, Japan. The chairs were A. D. Lê and K. Kiianmaa. The presentations were (1) Alcohol reward and aversion, by C. L. Cunningham; (2) The role of sensitization of neuronal mechanisms in ethanol self-administration, by J. A. Engel, M. Ericson, and B. Söderpalm; (3) Alcohol self-administration in dependent animals: Neurobiological mechanisms, by G. F. Koob, A. J. Roberts, and F. Weiss; (4) Stress and relapse to alcohol, by A. D. Lê; (5) Alcohol-preferring AA and alcohol-avoiding ANA rats differ in locomotor activation induced by repeated morphine injections, by P. Hyytiä, S. Janhunen, J. Mikkola, P. Bäckström, and K. Kiianmaa; and (6) Initial sensitivity and acute functional tolerance to the hypnotic effects of ethanol in mice genetically selected for mild and severe ethanol withdrawal convulsions, by I. Ponomarev and J. C. Crabbe.

Taste reactivity in alcohol-preferring AA and alcohol-avoiding ANA rats

Alcohol-preferring rats (Alko alcohol or AA) were tested for taste reactivity to water, sucrose, quinine, and a range of alcohol concentrations (5-40%) both before and after a period of continuous alcohol access. The alcohol-avoiding line of rats (Alko nonalcohol or ANA) was also tested for comparison. It was found that AA rats displayed greater ingestive reactivity to alcohol compared to ANA rats both before and after a three-week period of continuous access to 10% alcohol (during which time AA rats drank significantly more alcohol than ANA rats). AA rats also made significantly more ingestive responses to a 0.3 M sucrose solution and a 0.0005 M quinine solution. Differences between AA rats and ANA rats in aversive reactivity appeared only after the alcohol consumption tests; AA rats made significantly fewer aversive responses to the 30% and 40% concentrations after continuous alcohol access. AA rats also made significantly more aversive responses to the quinine solution. The results suggest that line differences between AA rats and ANA rats in the reactivity response to alcohol solutions have been selected in association with the original selection phenotype of alcohol consumption.

Brain opioid receptor binding of [3H]CTOP and [3H]naltrindole in alcohol-preferring AA and alcohol-avoiding ANA rats

We compared mu- and delta-opioid receptor distributions between the brains of alcohol-preferring Alko, Alcohol (AA) and alcohol-avoiding Alko, Non-Alcohol (ANA) rat lines, using autoradiography on brain sections with mu- and delta-opioid receptor antagonist ligands [3H]CTOP and [3H]naltrindole, respectively. The labeling patterns of the ligands were consistent with the known opioid receptor distributions in both rat lines and no major genetic differences were found between the lines. However, the binding density of mu- and delta-opioid receptors differed slightly in several brain areas: in the AA brain sections, limbic areas, such as hippocampus and amygdala, showed decreased mu- and delta-opioid receptor binding, whereas the striatal patches were larger and the substantia nigra showed higher binding density of the mu-receptors compared to the ANA sections. The small differences observed between the rat lines could be due to adaptations to altered endogenous opioid peptide levels or neural circuits, and associated with the differences in alcohol drinking or other behaviors.

Intravenous heroin and ethanol self-administration by alcohol-preferring AA and alcohol-avoiding ANA rats

The alcohol-preferring AA rats have previously been shown to drink more solution containing the opioid etonitazene than the alcohol-avoiding ANA rats. The present experiments were initiated to see whether the line difference in opioid and alcohol intake would persist if an intravenous (i.v.) route of self-administration is used. Following establishment of stable heroin responding (0.03 mg/kg per infusion), AA and ANA rats were first subjected to three within-session dose-response determinations during which they were allowed to respond for ascending heroin doses (0.0075, 0.015, 0.03, and 0.06 mg/kg per infusion) and then to one progressive-ratio schedule session. AA rats obtained more heroin infusions than ANAs during the first acquisition sessions but there were no significant differences between the lines either in their baseline heroin responding, across the ascending within-session doses, or on the progressive ratio probe. When, after additional heroin baseline sessions, ethanol (1.0 mg/kg per infusion) was substituted for heroin, AA rats initially increased their responding and showed stable rates for responding across ascending ethanol doses (2.0 and 4.0 mg/kg), whereas ANAs declined below their heroin baseline. These findings give evidence for only an initial line difference in i.v. opiate self-administration but for a sustained difference in i.v. ethanol self-administration, thus suggesting that the differential alcohol drinking of the AA and ANA rats is dependent at least partly on non-oral factors.

Endogenous opiates: 1995

This article is the eighteenth installment of our annual review of research concerning the opiate system. It includes articles published during 1995 reporting the behavioral effects of the opiate peptides and antagonists, excluding the purely analgesic effects. The specific topics covered this year include stress: tolerance and dependence; eating; drinking; gastrointestinal, renal, and hepatic function; mental illness and mood; learning, memory, and reward; cardiovascular responses; respiration and thermoregulation; seizures and other neurological disorders; electrical-related activity; general activity and locomotion; sex, pregnancy, and development; immunological responses; and other behaviors.