Use of serotonin-active drugs in alcohol preference studies

Prevalence of high serotonin uptake in lymphocytes of abstinent alcoholics

An impairment in serotonergic neurotransmission may be associated with alcoholism. We recently identified a high-affinity serotonin transporter (5-HTT) in human peripheral blood lymphocytes (PBLs). Moreover, molecular analysis of RNA samples of human lymphocytes using reverse transcription, coupled with polymerase chain reaction, enabled us to confirm the expression of a 5-HTT identical to the one reported in neuronal tissues, as evidenced by hybridization and sequence analysis. In this investigation, we measured the serotonin (5-HT) uptake in PBLs of recovering alcoholics (N = 10) with long-term abstinence (2-10 years) and non-alcoholic controls (N = 10). 5-HT uptake was measured by incubating 1 x 10(7) cells of PBLs with [3H]5-HT (3-1000 nM; sp. act. 23 Ci/mmol) for 10 min at 37 degrees. The results of this preliminary study revealed that abstinent alcoholics had significantly (P < 0.01) increased uptake of 5-HT (43.6 +/- 5.70 pmol/10(7) cells) as compared with controls (23.33 +/- 2.50 pmol/10(7) cells). An enhanced uptake of 5-HT in PBLs of abstinent alcoholics agrees with previously reported observations of increased 5-HT uptake in brain and platelets of former alcoholics and their descendants. This suggested that a serotonergic mechanism may be linked to the heredity of alcoholism.

Reduced sensitivity to ethanol reward, but not ethanol aversion, in mice lacking 5-HT1B receptors

Various serotonergic receptor systems are thought to influence the motivational effects of ethanol. This experiment characterized the acquisition of ethanol-induced conditioned taste aversion and ethanol-induced conditioned place reference in mutant knockout mice lacking 5-HT1b receptors. In the taste conditioning procedure, adult homozygous knockout mice (-/-) and homozygous wild-type mice (+/+) received access to 0.2 M NaCl solution, followed immediately by intraperitoneal injection of 0 to 4 g/kg of ethanol. Ethanol produced dose-dependent conditioned taste aversion that was the same in both genotypes. In the place conditioning procedure, knockout and wild-type mice received six pairings of a tactile stimulus with ethanol (2 g/kg, i.p.). A different tactile stimulus was paired with saline. Ethanol produced increases in locomotor activity, with wild-type mice showing higher levels of ethanol-stimulated activity than knockout mice during conditioning trials 5 and 6. Wild-type mice demonstrated conditioned place preference for the ethanol-paired stimulus. In contrast, knockout mice showed no evidence of place conditioning. These results are generally consistent with an important role for serotonergic systems in ethanol reward and specifically indicate that 5-HT1b receptors are important for ethanol's rewarding effects but not for ethanol's aversive effects.

Effect of ethanol on extracellular 5-HT and glutamate in the nucleus accumbens and prefrontal cortex: comparison between the Lewis and Fischer 344 rat strains

The present study investigated the impact of systemic (i.p.) ethanol administration on extracellular levels of serotonin and glutamate in the prefrontal cortex and the nucleus accumbens in Lewis and Fischer 344 rat strains using in vivo microdialysis. At 1.0 g/kg, ethanol elicited a significant increase in nucleus accumbens-dialysate levels of both 5-HT (44% +/- 16, P = 0.002) and glutmate (90% +/- 43, P = 0.009) in Lewis rats. In Fischer rats, there was no increase in 5-HT (6% +/- 7: P = 0.5), and a trend toward an increase in glutamate (88% +/- 46: P = 0.1). The 0.5 and 2.0 g/kg doses did not result in any significant change in extracellular 5-HT or glutamate in the nucleus accumbens or prefrontal cortex of either strain. The basal levels of glutamate, in both brain regions, were significantly lower in Lewis than in Fischer 344 rats. The basal levels of 5-HT were also lower in the nucleus accumbens of Lewis rats. These findings suggest that enhanced sensitivity of the mesoaccumbens 5-HT or glutamate systems to ethanol and/or inherent low basal levels of 5-HT or glutamate activity may be associated with the predisposition to alcohol-drinking behavior seen in Lewis rats.

Abstinent alcoholics exhibit an exaggerated stress response to 2-deoxy-D-glucose challenge

Chronic excessive alcohol consumption can significantly disturb the hypothalamic control of glucose metabolism; however, the mechanism and clinical significance of this disturbance are poorly understood. We used 2-deoxy-D-glucose (2-DG), which produces intracellular glucoprivation, to compare neurochemical, physiological, and behavioral responses to glucoprivic stress between alcoholics abstinent for 3 weeks and healthy volunteers. Twenty-six male alcoholics and 15 male healthy volunteers received intravenous infusions of placebo, 12.5 mg/kg, and 25.0 mg/kg of body weight of 2-DG over 30 min on three separate days, following a random-ordered, double-blind procedure. Minimal effects were observed following administration of the 12.5 mg/kg of body weight dose of 2-DG. Following 25.0 mg/kg, alcoholics showed both exaggerated ACTH and cortisol responses and greater increases in caloric intake when compared with controls. Although anxiety, desire to consume alcohol, plasma progesterone, and sympathetic and adrenal medullary activity all increased following 2-DG, these responses did not differ between alcoholics and controls. The present findings suggest certain specificity for the exaggerated hypothalamic and adrenocortical responses to mild glucoprivic stress in 3-week-abstinent alcoholics.

Alcohol, the reward system and dependence

Evidence is presented to show that multiple neurotransmitter systems of the brain reward systems including GABA, glutamate, dopamine, serotonin and opioid peptides are involved in alcohol reinforcement. Dependence is associated with changes in many of these same systems, but also with changes in other neurotransmitters, such as brain corticotropin releasing factor. A midbrain forebrain circuitry that involves parts of the nucleus accumbens and amygdala is hypothesized to be the focus for the neuropharmacology of alcohol reinforcement.

Fluoxetine: a spectrum of clinical applications and postulates of underlying mechanisms

The antidepressant efficacy of fluoxetine in major depression has been briefly reviewed. A brief outline of dose selection, therapeutic onset, and pharmacokinetics of fluoxetine were made. The potential use of the drug in management of various psychiatric conditions has been examined. These include obsessive-compulsive disorder and related variances, anorexia nervosa, bulimia nervosa, Tourette's syndrome, and trichotillomania. The suggested use of fluoxetine in pain relief in certain diabetics, premenstrual syndrome, and migraine headache were assessed. The reports on the use of fluoxetine in panic disorders, paraphilias, and related conditions and in the management of substance abuse, alcoholism, and cocaine abuse, were summarized and elaborated upon. A composite of preliminary reports cited in literature pertinent to the potential of fluoxetine in treatment of abusing injurious behavior, dysthymic disorder, fibrositis, postanoxicaction myoclonus, pathologic jealously, personality disorder, pseudobulbar affect, and social phobia were also reviewed. Fluoxetine pharmacological profile may be extended to cover a relative wide range of application, provided future controlled studies confirm the preliminary data found in the literature.

Involvement of the serotonergic system in ethanol intake in the rat

A two-bottle, free-choice paradigm was used to investigate the influence of the serotonergic (5-HT) system on ethanol intake in genetically heterogeneous Wistar rats. Systemic administration of the 5-HT1A agonist ipsapirone (1.25-5.0 mg/kg) caused a dose-dependent decrease in ethanol preference and intake, while the 5-HT2 antagonist ritanserin (1.25-5.0 mg/kg) and the 5-HT3 antagonists ondansetron (0.01-1.0 mg/kg) and granisetron (0.5-1.0 mg/kg) failed to alter ethanol consumption. The effect of ipsapirone treatment on ethanol intake was more pronounced in high-preferring animals than in low-preferring. A closer look at the microstructure of the rat's drinking behaviour by means of a microcomputer-controlled data acquisition system showed that ipsapirone treatment caused a significant decrease in the number of licks recorded at the ethanol-containing bottle and a decrease in the time spent at this bottle. Furthermore, ipsapirone treatment caused a significant increase in the number of breaks in licking behaviour recorded at this bottle. The drinking behaviour at the water-containing bottle was not affected by the ipsapirone treatment. Neither was the rat's eating behaviour altered by this treatment. These findings support the hypothesis that the 5-HT system is involved in the regulation of ethanol intake, with special emphasis on the involvement of the 5-HT1A receptor subtype, and may indicate that central reward-mediating mechanisms are influenced.

Brain levels of amines and amino acids in taste aversion-prone and -resistant rats

Possible biological contributions to taste aversion (TA) conditionability were explored by comparing whole-brain levels of five neurotransmitter amines and 14 common amino acids within TA-prone (TAP) and TA-resistant (TAR) rats. The selectively bred strains had been developed via 22 generations of bidirectional nonsibling matings based on susceptibility to cyclophosphamide-induced conditioned TAs. The target substances were separated by HPLC and were measured by electrochemical or fluorometric procedures. The TAP brains had higher levels of serotonin (5-HT) and lower levels of norepinephrine (NE) than TAR brains. No strain differences were found with respect to dihydroxyphenylalanine (DOPAC), dopamine (DA), or 5-hydroxyindoleacetic acid (5-HIAA). Among amino acids, TAP rats had lower levels of lysine than TARs: no other differences were detected. Therefore, higher levels of 5-HT and lower levels of NE and lysine were associated with enhanced TA conditionability. The 5-HT and NE results extend prior indications of their central neurotransmitter TA involvements. The functional role of lysine in TA or other brain functions remains obscure.