Effect of Ethanol Drinking on the Gene Expression of Opioid Receptors, Enkephalinase, and Angiotensin-Converting Enzyme in Two Inbred Mice Strains

Abstract

There is convincing evidence that genetic factors contribute to the predisposition to alcoholism. In this respect, alcohol-preferring (like C57BL/6 mice) and alcohol-avoiding lines (like DBA/2 mice) of animals served as models in the search for neurobiological substrates of excessive ethanol consumption. One of the systems that is thought to be associated with the incidence of alcoholism is the endogenous opioid system. In the first experiment, basal mRNA levels of mu- and delta-opioid receptors, and of opioid-degrading enzymes enkephalinase (neutral endopeptidase 24.11; NEP) and angiotensin-converting enzyme (ACE) in the brain regions of C57BL/6 and DBA/2 mice did not reveal genetically determined differences in these parameters between the two strains. Furthermore, in the brain regions studied, the corresponding enzyme activities of NEP and ACE did not differ significantly between the lines of mice, except for a higher NEP activity in the striatum and olfactory bulb of DBA/2 mice (p < 0.01). In the second experiment, C57BL/6 and DBA/2 mice were offered a free choice between water and 10% ethanol solution for 4 weeks and were killed thereafter; from another group, ethanol was removed for 3 days and from a third group ethanol was removed for 3 weeks before killing. In the striatum, a highly significant increase in the ACE mRNA amount was detected after 3 weeks of removal of ethanol in C57BL/6 mice, whereas in DBA/2 mice the delta-opioid receptor mRNA level was increased at this time when compared with the corresponding ethanol treatment group. The most striking changes were seen in the hypothalamus, where mu-opioid receptor, ACE, and NEP mRNA amounts markedly decreased after ethanol treatment in both strains. Thus, chronic ethanol intake caused significant changes in the gene expression of distinct components of the endogenous opioid system. These findings further underline an involvement of the opioid system in the effects of ethanol.

Endogenous opioids as substrates for ethanol intake in the neonatal rat: The impact of prenatal ethanol exposure on the opioid family in the early postnatal period

“…Nevertheless, PAE effects on mRNA did not necessarily reflect these same alcohol-dependent reductions in protein. Consistent with other assessments of ethanol's effects on opioid gene expression (e.g., [46] and [47]), changes in mRNA produced by the prenatal treatment do not necessarily reflect alterations in protein for the same factors. Because there is a large divergence in the results obtained with mRNA and protein, it is especially difficult to interpret the ultimate consequence of ethanol's effects on the opioid system.…”

Reward Processing by the Opioid System in the Brain

“…Chronic exposure to ethanol did not change delta transcripts in the striatum (337, 411) or HPT (411) of these animals. Interestingly, 3 wk after the cessation of ethanol consumption, delta receptor transcripts were increased in the striatum of alcohol-avoiding but not -preferring mice (411). No modification of the expression level of delta receptors was observed in the NAc and olfactory bulbs after chronic cocaine (17).…”

“…In some studies, levels of mu receptor mRNA were assessed before or after ethanol consumption in mice and rats selected on the basis of ethanol preference. Basal levels of mu receptor transcripts were similar between preferring and nonpreferring strains in the HPT and striatum (52, 141, 411) as well as in the NAc, hippocampus (HPC), frontal cortex (FrCx), but not inferior colliculus, where higher levels were observed in alcohol-preferring animals (141). Following chronic ethanol, mu receptor transcripts were unchanged in the striatum of both strains (337, 411), but decreased in the HPT, an effect still measurable up to 3 wk after cessation of ethanol consumption, specifically in the alcohol-preferring animals (411).…”

“…As for mu receptors, delta receptor mRNA levels under basal conditions were similar in the striatum of both alcohol-preferring and alcohol-avoiding strains of mice (411). Chronic exposure to ethanol did not change delta transcripts in the striatum (337, 411) or HPT (411) of these animals.…”

AT1 receptor blockade increases cardiac bradykinin via neutral endopeptidase after induction of myocardial infarction in rats

“…BK was quantitated by a specific RIA, as described previously (6). The antiserum displayed a 36% cross-reactivity to T-kinin and had no affinity to smaller kinin fragments such as [1][2][3][4][5][6][7][8]…”