Changes in receptor sensitivity of the cerebral cortex and liver during chronic ethanol ingestion and withdrawal

Fluoxetine, desipramine, and the dual antidepressant milnacipran reduce alcohol self-administration and/or relapse in dependent rats

A few clinical studies have shown that dual antidepressants (serotonergic (5-HT) and noradrenergic (NE) transporter inhibitors, SNRIs) may be effective in alcoholism treatment. We studied the effect of the dual antidepressant milnacipran on ethanol operant self-administration in acutely withdrawn ethanol-dependent and in -non-dependent Wistar rats, and used fluoxetine and desipramine to dissect both 5-HT and NE components, respectively, in the effect of milnacipran. Milnacipran was also tested for relapse after protracted abstinence and on ethanol-induced (1.0 g/kg) conditioned place preference in control rats and ethanol-induced locomotor sensitization in DBA/2J female mice. Milnacipran dose dependently (5-40 mg/kg) attenuated the increased ethanol self-administration observed during early withdrawal and was more potent in preventing reinstatement in dependent rats after protracted abstinence as compared with non-dependent rats. Desipramine and fluoxetine (10 mg/kg) blocked ethanol self-administration during early withdrawal, and recovery was delayed in dependent animals, indicating a potent effect. Ethanol self-administration was also reduced 1 day after treatment with desipramine and fluoxetine but not with milnacipran. Finally, milnacipran prevented ethanol-induced place preference in ethanol-naive rats and reduced the magnitude of ethanol-induced sensitization associated with a delayed induction in mice. Desipramine (20 mg/kg) countered sensitization development and reduced its expression at 1 week after treatment; fluoxetine (10 mg/kg) reduced sensitization expression. Thus, 5-HT and NE transmissions during sensitization expression may mediate the effect of milnacipran on sensitization induction. These results support that SNRIs may have a potential use in alcoholism treatment.

Clinical neuroendocrinology and neuropharmacology of alcohol withdrawal

A number of alcohol research groups have measured anterior and posterior pituitary hormones, the endogenous opiates, CNS peptides, and putative neurotransmitters during alcohol withdrawal. The data are often complex and contradictory, though a number of themes have emerged. Activity of the hypothalamic-pituitary-adrenal axis (HPA) is increased during chronic alcohol exposure and appears to remain altered for at least 2 to 4 weeks after cessation of drinking. There is increased turnover of norepinephrine and enhanced binding of CNS adrenergic receptors. By contrast, there are decreases in CNS activity of select endogenous opiates and GABA. Other CNS compounds that may play a role in alcohol withdrawal are prolactin, thyrotropin-releasing hormone (TRH), vasopressin, cyclic 3'5'-adenosine monophophate (cAMP), Delta-sleep-inducing peptide (DSIP), and iron. Despite many studies in humans and animals, the roles of CNS dopamine and serotonin in withdrawal remain unclear. A number of peptides, including cholecystokinin (CCK), neurotensin, and bombesin, have been shown to interact with the CNS actions of alcohol and may play a role in alcohol withdrawal. Inadequate work has been performed on acetylcholine (ACh), human growth hormone (HGH) and luteinizing hormone (LH). Studies of the recently identified GABA-benzodiazepine-barbituate receptor complex indicate that this system is likely to be involved in the pathophysiology of alcohol withdrawal. Perturbation studies with corticotropin-releasing factor (CRF) and TRH (with measures of ACTH and cortisol and TSH and prolactin, respectively), may identify patients with withdrawal-related autonomic dysfunction.

[Effect of ethanol on the neurotransmitters glutamate and GABA]

The effect of chronic ethanol administration, 5 g/kg per day for 2 or 4 weeks, on the neurotransmitters glutamate and GABA was investigated in rats. An increase in GABA was found in the striatum, hippocampus, and substantia nigra, 8 or 12 h after the last ingestion of ethanol, this being masked by injection of barbiturate. In addition an increase of glutamate has been found in the examined brain areas. This is consistent with the known effect of ethanol on brain Dopa metabolism and release. Finally, the relevance of the results for the pathogenesis of withdrawal seizures and delirious states is discussed.

Pathophysiology of the alcohol withdrawal syndrome

A characteristic withdrawal syndrome appears following the interruption of chronic heavy consumption of alcoholic beverages. The pathophysiological elaborations of the various withdrawal signs and symptoms are considered. Among the unlikely, although plausible, pathophysiologic mechanisms of the tremulousness and skeletal muscle hyperreactivity of withdrawal is the accumulation or the sustained production of one or more circulating "toxic substances." Evidence consistent with such a mechanism includes the reported alleviation by dialysis of an impending withdrawal syndrome in alcoholic patients, the appearance of reflex hyperreactivity in withdrawing animals below the level of a chronic section of the spinal cord, and the time course of the appearance and disappearance of withdrawal syndromes. The various potential pathophysiological and neurochemical manifestations of the withdrawal illness are discussed--alterations in neural inhibition, in alpha-aminobutyric acid, catecholamines, acetylcholine, dopamine, prostaglandin, and in peptides. Experimental tests whereby a "toxic substance hypothesis" of withdrawal can be ruled in or out are proposed.