Effects of the combined administration of the 5-HT3 antagonist MDL 72222 and ethanol on conditioning in the periadolescent and adult rat

The 5-HT3 receptor antagonist, ondansetron, blocks the development and expression of ethanol-induced locomotor sensitization in mice

Manipulation of the serotonergic system has been shown to alter ethanol sensitization. Ondansetron is a 5-HT3 receptor antagonist, reported to attenuate cocaine and methamphetamine-induced behavioral sensitization, but no reports are available on its role in ethanol-induced behavioral sensitization. Therefore, an attempt has been made to assess this issue by using an earlier used animal model of ethanol-induced locomotor sensitization. Results indicated that ondansetron (0.25-1.0 mg/kg, subcutaneously) given before the challenge dose of ethanol (2.4 g/kg, intraperitoneally) injection, significantly and dose dependently attenuated the expression of sensitization. In addition, ondansetron (1.0 mg/kg, subcutaneously) given before ethanol injection on days 1, 4, 7, and 10 significantly blocked the development (days 1, 4, 7, and 10), and expression (day 15) of sensitization to the locomotor stimulant effect of ethanol injection. Ondansetron had no effect per se on locomotor activity and did not affect blood ethanol levels. Therefore, the results raise the possibility that ondansetron blocked the development and expression of ethanol-induced locomotor sensitization by acting on 5-HT3 receptors.

The role of 5-HT3 receptors in drug abuse and as a target for pharmacotherapy

Alcohol and drug abuse continue to be a major public health problem in the United States and other industrialized nations. Extensive preclinical research indicates the mesolimbic dopamine (DA) pathway and associated regions mediate the rewarding and reinforcing effects of drugs of abuse and natural rewards, such as food and sex. The serotonergic (5-HT) system, in concert with others neurotransmitter systems, plays a key role in modulating neuronal systems within the mesolimbic pathway. A substantial portion of this modulation is mediated by activity at the 5-HT3 receptor. The 5-HT3 receptor is unique among the 5-HT receptors in that it directly gates an ion channel inducing rapid depolarization that, in turn, causes the release of neurotransmitters and/or peptides. Preclinical findings indicate that antagonism of the 5-HT3 receptor in the ventral tegmental area, nucleus accumbens or amygdala reduces alcohol self-administration and/or alcohol-associated effects. Less is known about the effects of 5-HT3 receptor activity on the self-administration of other drugs of abuse or their associated effects. Clinical findings parallel the preclinical findings such that antagonism of the 5-HT3 receptor reduces alcohol consumption and some of its subjective effects. This review provides an overview of the structure, function, and pharmacology of 5-HT3 receptors, the role of these receptors in regulating DA neurotransmission in mesolimbic brain areas, and discusses data from animal and human studies implicating 5-HT3 receptors as targets for the development of new pharmacological agents to treat addictions.

Fear conditioning is impaired in adult rats by ethanol doses that do not affect periadolescents

Adolescent rats and humans exhibit physiological, behavioral, and cognitive differences compared to their adult counterparts. These differences are apparent also in reactions to psychoactive drugs, such as ethanol. Recent studies have shown that though less sensitive to several behavioral indices of intoxication by ethanol, adolescent rats are more sensitive to the cognition-impairing effects of ethanol. Ethanol's effects, in the present experiment, were assessed in terms of a fear conditioning test not previously used in comparison of adult and adolescent Sprague-Dawley albino rats. Separate groups of both ages were given intraperitoneal (i.p.) ethanol before or after tone-shock conditioning. This task features a hippocampus-independent component, learned freezing to a tone, and a hippocampus-dependent component, learned freezing to context. Post-training ethanol had no effect on retention in either age, but pre-acquisition ethanol impaired adult learning more than adolescent learning, as indexed by the expression of fear at the test. Blood alcohol was equivalent in adolescents and adults at a dose that produced cognitive discrepancies. Unlike other reports, these experiments demonstrate that adolescents may not be more sensitive to ethanol's effects in all cases of learning.

Effects of 5-HT3, D1 and D2 receptor antagonists on ethanol- and cocaine-induced locomotion

The effects of acute treatment with 5-HT3 receptor antagonists, ondansetron and ICS 205-930, on the stimulation of activity induced by ethanol-and cocaine were examined. Ethanol (1.8 or 2 g/kg i.p.) or cocaine (15 mg/kg i.p.) produced a significant increase in locomotor activity (LMA) in DBA/2N mice. Pretreatment with ondansetron or ICS 205-930, in doses ranging from 0.001 to 0.1 mg/kg (s.c), did not modify ethanol or cocaine induced stimulation of activity. In contrast, pretreatment with a 10 micrograms/kg dose of either SCH 23390 or spiperone, a D1 and D2 dopamine (DA) receptor antagonist respectively, completely antagonized the stimulation of LMA induced by ethanol. Similar dose of SCH23390, but not spiperone, blocked the stimulation of activity induced by cocaine. These results indicate that D1 but not D 2 DA receptors play a significant role in cocaine induced hyperactivity whereas both D1 and D2 are involved the locomotor activating effects of ethanol.

Mechanisms of alcohol abuse and alcoholism in adolescents: a case for developing animal models

This paper reviews the ontogeny of neurotransmitter systems and neuropharmacological challenge within transmitter systems and discusses the actions of alcohol on such systems during the juvenile through adolescent periods. To place the animal research within the context of human development, an attempt is made to first examine some fundamental principles of developmental research as they relate to the adolescent period. Evidence presented from animal studies indicates that unique neurochemical and behavioral changes are occurring during postnatal development, including adolescence, that could mediate the response to alcohol. The limited number of studies on the neurochemical and behavioral response to alcohol during adolescence has employed rats and has been restricted by the relatively brief adolescent period in that species. While one alternative is to use primates, it is suggested that innovative behavioral paradigms be developed for adolescent animals in other species to study behaviors such as alcohol self-administration or alcohol stimulus discrimination. It is also suggested that existing behavioral models that are more easily adapted to younger age ranges (e.g., conditioned place preference, conditioned taste aversion, thermal response to ethanol) be extended to make ontogenetic comparisons through adolescence and adulthood. This may further our understanding of alcohol's immediate consequences during each maturational stage and, more important, the contribution of early alcohol exposure to excessive drinking and abnormal cognitive and social functioning during subsequent stages of development.