Alcohol withdrawal-induced changes in brain biogenic amines in mice: influence of the genotype

Monoaminergic changes associated with audiogenic seizures in ethanol-dependent rats

1. A previous report demonstrated the efficacy of combining dopaminergic and serotonergic agonists in suppressing audiogenic seizures induced in ethanol-dependent rats undergoing withdrawal. Moreover, an increase in dopamine and a reduction in serotonin levels in the striatum were associated with such seizures. 2. The present study was designed to examine neurochemical changes in the striatum associated with repeated episodes of ethanol withdrawal seizures in untreated ethanol-dependent rats as well as in those treated with amphetamine and fenfluramine in combination. 3. Ethanol-dependent rats undergoing audiogenic seizures exhibited an increase in striatal dopamine and a reduction in striatal serotonin as compared to control and ethanol-dependent rats not undergoing seizures. Amphetamine and fenfluramine in combination effectively suppressed the audiogenic seizures by reversing the neurochemical changes in the striatum in ethanol-dependent rats. However, increased dopamine but decreased serotonin levels in the striatum were observed in rats undergoing one episode of ethanol withdrawal, but not in those experiencing multiple episodes of ethanol withdrawal. 4. Thus, alterations in striatal dopamine and serotonin levels were, at best, necessary but not sufficient to predispose audiogenic seizure susceptibility in ethanol-dependent rats.

Dopaminergic and serotonergic alterations in the rat brain during ethanol withdrawal: association with behavioral signs

Changes in dopaminergic and serotonergic levels and metabolites in cerebral cortex, corpus striatum and hippocampus were investigated during the first 6-h of withdrawal in ethanol-dependent Wistar rats. Ethanol was given by a liquid diet for 21 days. The concentration of ethanol was 7.2% (v/v) for the last 15 days of the exposure. After 2, 4 and 6 h of ethanol withdrawal, and after audiogenic stimulus (100 dB for 60 s) at 6 h of ethanol withdrawal, various brain regions were assayed for levels of dopamine (DA), DOPAC, HVA, serotonin (5-HT) and 5-HIAA. Behavioral signs of ethanol withdrawal and blood ethanol levels were also evaluated in other parallel groups of ethanol-dependent rats. Significant decreases in 5-HT levels and significant increases in HVA levels in striatum were found during the first 6 h of ethanol withdrawal and after the audiogenic seizures. In hippocampus, 5-HIAA levels were significantly reduced after 2 h of ethanol withdrawal and after the audiogenic seizures. 5-HIAA levels significantly increased after 2 h of ethanol withdrawal in cerebral cortex. Significant increases in both DA and 5-HT levels were also found in cerebral cortex after the audiogenic seizures. The results suggest that the levels of DA, 5-HT and their metabolites are altered by ethanol withdrawal. Furthermore, this may suggest that DA and 5-HT may be involved in the first 6 h of ethanol withdrawal syndrome in rats.

Alterations in serotonin1B (5HT1B) receptor subtypes in the brain of ethanol-treated rats

The effects of acute or chronic ethanol treatment and of withdrawal (24 h) after chronic ethanol treatment on 5HT1B receptor subtypes in different regions of the rat brain were investigated. Male Sprague-Dawley rats were fed the ethanol (9% v/v)-containing Lieber-DeCarli liquid diet or the control liquid diet for 1 day in the acute study and for 15 days in the chronic study. The ethanol-withdrawn group received the Lieber-DeCarli control liquid diet instead of the ethanol diet on the 15th night. Ethanol-withdrawn rats after 15 days of ethanol treatment were rated for withdrawal symptoms (e.g. hyperactivity, piloerection, squealing, and enhanced startle reflex) and were found to exhibit such symptoms after 24 h of ethanol withdrawal. The rats were decapitated, and cortices, cerebelli, striata, and hippocampi were separated for measurement of 5HT1B receptors by receptor binding techniques using 125I-cyanopindolol (CYP) as the ligand. It was observed that acute ethanol treatment had no significant effect on the maximum number of binding sites (Bmax) or the apparent dissociation constant (KD) of 5HT1B receptor binding sites in the various brain regions. On the other hand, chronic ethanol treatment produced a significant increase in Bmax of 125I-CYP binding to 5HT1B receptors in the rat cortex and hippocampus, which remained increased after 24 h of ethanol withdrawal. In contrast, in the striatum and the cerebellum of chronic ethanol-treated and withdrawn rats, the 5HT1B binding parameters (Bmax and KD) were unchanged. These results suggest the possible involvement of cortical and hippocampal 5HT1B receptors in ethanol dependence.

Ethanol self-administration restores withdrawal-associated deficiencies in accumbal dopamine and 5-hydroxytryptamine release in dependent rats

Basal forebrain dopamine (DA) and 5-HT neurotransmission has been implicated in the mediation of the acute reinforcing actions of ethanol. Neuroadaptation theories predict that compensatory changes in neurochemical systems that are activated by alcohol acutely may underlie symptoms of withdrawal after chronic administration. To test this hypothesis, the release of DA and 5-HT was monitored by microdialysis in the nucleus accumbens of dependent male Wistar rats at the end of a 3-5 week ethanol (8.7% w/v) liquid diet regimen, during 8 hr of withdrawal, and during renewed availability of ethanol involving (1) the opportunity to operantly self-administer ethanol (10% w/v) for 60 min, followed by (2) unlimited access to the ethanol-liquid diet. Results were compared to control groups pair-fed with ethanol-free liquid diet and trained to self-administer either ethanol or water. In nondependent rats, operant ethanol self-administration increased both DA and 5-HT release in the NAC. Withdrawal from the chronic ethanol diet produced a progressive suppression in the release of these transmitters over the 8 hr withdrawal period. Self-administration of ethanol reinstated and maintained DA release at prewithdrawal levels but failed to completely restore 5-HT efflux. 5-HT levels recovered rapidly, however, within 1 hr of reexposure to ethanol liquid diet. These findings suggest that deficits in accumbal monoamine release may contribute to the negative affective consequences ethanol withdrawal and, thereby, motivate ethanol-seeking behavior in dependent subjects.

Serotonin and alcohol intake, abuse, and dependence: findings of animal studies

Despite a relatively large body of literature on the role of the neurotransmitter serotonin (5-hydroxytryptamine, or 5-HT) in the regulation of alcohol intake, the functional significance of serotonergic neurotransmission and its relationship to alcohol intake, abuse, and dependence remains to be fully elucidated. In part two of this review, the experimental (animal) data is summarized along two lines: the effects of serotonergic manipulations on the intake of alcohol, and the effects of acute and chronic alcohol intake, as well as the withdrawal of chronic alcohol, on the serotonergic system. It is concluded that serotonin mediates ethanol intake as a part of its larger role in behavior modulation, such that increases in serotonergic functioning decrease ethanol intake, and decreased serotonergic functioning increases ethanol intake. Ethanol produces transient increases in serotonergic functioning that activate the mesolimbic dopaminergic reward system. The results are discussed in light of recent theories describing the regulatory role of serotonin in general behavior.

Urinary elimination of salsolinol enantiomers in alcoholics

The analysis of the urine from 6 chronic alcoholics showed that (R)- and (S)-salsolinol were detectable in 4 subjects, the R enantiomer was only found in one and that both enantiomers were under the limit of detection in another one. 1,2-Dehydrosalsolinol was present in the urine of all of them. There was no correlation between the presence of alcohol in blood upon admission to the hospital and that of either salsolinol enantiomer in urine In a previous study (Strolin Benedetti et al., 1989 b), both salsolinol enantiomers were found in the urine of 3 out of 6 healthy subjects, possibly in relation with regular intake of alcoholic beverages. The content in (R)- and (S)-salsolinol was determined in the same 3 subjects after deprivation of alcohol for 24 h. Under these conditions, only (R)-salsolinol was detected in urine and this also after ingestion of 50 g of alcohol (500 ml Chianti). The possible involvement of the non-physiological enantiomer of salsolinol in alcohol addiction deserves further study.