Effect of p-chlorophenylalanine on brain monoamines and behaviour during ethanol withdrawal in mice

The effects of chronic ethanol self-administration on hippocampal serotonin transporter density in monkeys

Evidence for an interaction between alcohol consumption and the serotonin system has been observed repeatedly in both humans and animal models yet the specific relationship between the two remains unclear. Research has focused primarily on the serotonin transporter (SERT) due in part to its role in regulating extracellular levels of serotonin. The hippocampal formation is heavily innervated by ascending serotonin fibers and is a major component of the neurocircuitry involved in mediating the reinforcing effects of alcohol. The current study investigated the effects of chronic ethanol self-administration on hippocampal SERT in a layer and field specific manner using a monkey model of human alcohol consumption. [(3)H]Citalopram was used to measure hippocampal SERT density in male cynomolgus macaques that voluntarily self-administered ethanol for 18 months. Hippocampal [(3)H]citalopram binding was less dense in ethanol drinkers than in controls, with the greatest effect observed in the molecular layer of the dentate gyrus. SERT density was not correlated with measures of ethanol consumption or blood ethanol concentrations, suggesting the possibility that a threshold level of consumption had been met. The lower hippocampal SERT density observed suggests that chronic ethanol consumption is associated with altered serotonergic modulation of hippocampal neurotransmission.

Effects of chronic ethanol treatment on the in vitro biosynthesis of pro-opiomelanocortin and its posttranslational processing to beta-endorphin in the intermediate lobe of the rat pituitary

Chronic treatment of rats with 15% (vol/vol) ethanol in tap water as their only source of liquid over a period of 3 weeks resulted in a strong decrease by almost 50% in tissue levels and in vitro release of immunoreactive beta-endorphin of the neurointermediate pituitary. Moreover, the in vitro incorporation of [3H]phenylalanine into peptides of the neurointermediate pituitary, immunoprecipitable with beta-endorphin antiserum, was found to be decreased by more than 30%. Analysis of beta-endorphin-related peptides on sodium dodecyl sulfate-polyacrylamide gel electrophoresis revealed that chronic ethanol treatment reduced the in vitro biosynthesis of the beta-endorphin precursor pro-opiomelanocortin. This ethanol-induced effect was combined with a retardation in the time course of the posttranslational processing of the precursor into beta-endorphin. Thus, chronic ethanol treatment may influence the activity of enzymes which process the opioid peptide precursor pro-opiomelanocortin, leading to a decreased formation of the final secretory product beta-endorphin.

Differential effects of acute and chronic ethanol treatment on particular opioid peptide systems in discrete regions of rat brain and pituitary

Acute ethanol treatment induced a significant increase in the tissue levels of immunoreactive (ir-) Met-enkephalin in hypothalamus, striatum and midbrain, but not in hippocampus. Levels of ir-dynorphin, ir-alpha-neo-endorphin and ir-beta-endorphin were not found to be significantly altered in brain and pituitary. Chronic ethanol treatment (by the use of ethanol liquid diet) resulted in a more than 50% decrease of the tissue levels of ir-dynorphin and ir-alpha-neo-endorphin in hypothalamus and hippocampus, while both peptides remained unchanged in midbrain, striatum, adenohypophysis and neurointermediate pituitary. In contrast, ir-met-enkephalin was decreased in striatum and hypothalamus, but unaffected in midbrain and hippocampus. Levels or ir-beta-endorphin remained unchanged in the brain and in the pituitary. However, the de novo biosynthesis of beta-endorphin and its prohormones beta-lipotropin and pro-opiomelanocortin was increased in the intermediate pituitary and to an even more pronounced degree, in the adenohypophysis, after chronic treatment of rats with ethanol liquid diet, nevertheless, the amounts of opiate-active beta-endorphin were found to be reduced in both lobes of the pituitary: In the adenohypophysis, this was due to a retardation of the enzymatic processing of beta-endorphin from its precursor beta-lipotropin, while in the intermediate pituitary the alpha-N-acetylation of beta-endorphin to opiate-inactive alpha-N-acetyl-beta-endorphin was stimulated. In conclusion, acute and chronic ethanol treatment caused selective alterations on different opioid peptide systems within distinct areas of the rat brain and pituitary.

Effects of 6-hydroxydopamine or 5,7-dihydroxy-tryptamine on the development of physical dependence on ethanol

Infant rats, treated intracisternally with 6-hydroxydopamine or 5,7-dihydroxytryptamine, alone or in combination with desmethylimipramine or pargyline, at 5 to 7 days of age, had significant specific depletions of brain norepinephrine, dopamine, both of these amines, or serotonin at 2.5 months of age. Despite apparent long-term depletions of brain biogenic amines, susceptibility to audiogenically-induced seizures following chronic ethanol withdrawal in these animals was similar to that of controls. Amine-depleted rats also displayed spontaneous withdrawal-induced tremors, spastic motor activity and irritability. The interpretation of these preliminary findings with regard to the proposed role of the biogenic amines in the development of physical dependence on ethanol is discussed.

Enhancement of ethonol-induced withdrawal convulsions by blockade of 5-hydroxytryptamine receptors

Male Swiss-Webster mice were made physically dependent on ethanol using the ethanol vapour inhalation technique. Animals pretreated with methysergide, a known 5-hydroxytryptamine receptor blocking agent, had significantly greater alcohol-induced withdrawal convulsions than saline pretreated controls. These findings suggest that the reduction of 5-HT at receptor sites may result in the augmentation of the withdrawal convulsions.

Ethanol-induced regional and dose-response differences in multiple-unit activity in rabbits

Multiple-unit activity (MUA), recorded simultaneously from many brain areas, was used to detect the existence ahd location of "target sites" for ethanol action in rabbits with chronically implanted electrodes in 14 areas. Each of 12 rabbits received intraperitoneal injection of 300, 600, 900, and 1200 mg/kg of 20% ETOH and a saline control injection given in random order with at least a 4-day interval between injections. Large amounts of MUA data, recorded continuously for a 2-min pre-injection control period and a 15-min post-injection period, were quantified by a sensitive and unique technique. MUA changes did not correlate with alcohol-induced changes in the corresponding EEG for the same locus. Whereas visual inspection of the EEG did not disclose any regional differences in response to ethanol, both temporal and topographical differences in ethanol effect on MUA were observed. There were 14 histologically verified brain areas with adequate sample size for statistical evaluation of MUA response. At high doses, all brain areas were affected. Included among the brain areas which were least affected by low doseas were the caudate nucleus, septum, fornix, and medial forebrain bundle. Those areas that met the criteria for target sites of responding quickly (less than 5 min) to low doses (300 mg/kg) were: cerebellar cortex, cerebral cortex, hippocampus, lateral and medial geniculate nuclei, midbrain reticular formation, and pyriform cortex. In conjunction with the preliminary study [Brain Res. 70, 361 (1974], the data indicate that the most ethanolsensitive tissue is found in the various kinds of cortex, cerebellar and cerebral (both paleocortex and neocortex).

Biogenic amines and head twitches in mice during ethanol withdrawal

After chronic administration of ethanol to mice by the intragastric route head twitches occur as part of the ethanol withdrawal syndrome. Treatments which reduce brain 5-hydroxytryptamine or increase brain noradrenaline inhibited ethanol withdrawal head twitches, whereas treatments which increase brain 5-hydroxytryptamine or reduce brain noradrenaline were capable of inducing head twitches in control animals.