Translational approach to understanding momentary factors associated with alcohol consumption

Sex differences in serotonergic control of rat social behaviour

RATIONALE

There is increasing evidence that enhancement of the salience of social stimuli can have a beneficial effect in managing many psychiatric conditions. There are, however, clear sex-related differences in social behaviour, including the neural mechanisms responsible for different aspects of social functions.

OBJECTIVES

We explored the role of the serotonergic system on rat social behaviour under baseline and under stressful conditions in female and male rats.

METHODS

Rats were treated with the selective serotonin transporter (SERT) inhibitor escitalopram postnatally; a procedure known to cause a long-lasting reduction of serotonergic activity. In adulthood, social behaviour was tested in a social interaction test and in ultrasonic vocalisation (USVs) recording sessions before and after yohimbine-induced stress-like state.

RESULTS

Our data demonstrated that both female and, to a lesser extent, male escitalopram treated rats, exposed to a novel social situation, had fewer social exploration events and emitted fewer frequency-modulated calls with trills, trills and step calls, suggesting that an impaired function of the serotonergic system reduced the positive valence of social interaction. In a stress-like state, 50 kHz flat calls were increased only in female rats, indicating an increased seeking of social contact. However, the number of flat calls in escitalopram treated female rats was significantly lower compared with control rats.

CONCLUSIONS

These data suggest that females may respond differently to serotonergic pharmacotherapy with respect to enhancement of beneficial effects of social support, especially in stress-related situations.

Melatonin Reduces Alcohol Drinking in Rats with Disrupted Function of the Serotonergic System

The reason for the limited treatment success of substance-use-related problems may be a causal heterogeneity of this disorder that, at least partly, is manifested as differences in substance-use motives between individuals. The aim of the present study was to assess if rats with pharmacologically induced differences in the function of the serotonergic system would respond differently to melatonin treatment compared to control rats with respect to voluntary alcohol consumption. To achieve this goal, we treated rats neonatally with the selective serotonin transporter (SERT) inhibitor escitalopram. This procedure has been reported to cause long-lasting sleep abnormalities in rodents. The study demonstrated that during adulthood, rats that had been treated with escitalopram tended to drink higher amounts of alcohol compared to control rats. Further, administration of melatonin significantly decreased the alcohol intake in escitalopram-treated animals but caused only a slight, nonsignificant reduction in the alcohol consumption by control rats. In conclusion, our data support the therapeutic potential of melatonin as a treatment for alcohol use disorder. However, interindividual differences between alcohol users may considerably modify the outcome of the melatonin treatment, whereby patients that manifest lower sleep quality due to disruption of serotonergic activity are more likely to benefit from this treatment.

The Anticonvulsant Lamotrigine Reduces Bout-Like Alcohol Drinking in Rats

We used an optical lickometer system to study drinking microstructure and effect of lamotrigine in voluntary alcohol-drinking rats. We showed that, similar to humans, animals differ by their drinking microstructure where some consume alcohol exclusively in a bout-like patterns. The study suggests that anticonvulsants, such as lamotrigine, may be one treatment strategy specifically affecting this type of drinking.

Translational approach to understanding momentary factors associated with alcohol consumption

Multiple interindividual and intra-individual factors underlie variability in drinking motives, challenging clinical translatability of animal research and limiting treatment success of substance use-related problems. Intra-individual variability refers to time-dependent continuous and discrete changes within the individual and in substance use research is studied as momentary variation in the internal states (craving, stressed, anxious, impulsive and tired) and response to external triggers (stressors, drug-associated environmental cues and social encounters). These momentary stimuli have a direct impact on behavioural decisions and may be triggers and predictors of substance consumption. They also present potential targets for real-time behavioural and pharmacological interventions. In this review, we provide an overview of the studies demonstrating different momentary risk factors associated with increased probability of alcohol drinking in humans and changes in alcohol seeking and consumption in animals. The review also provides an overview of pharmacological interventions related to every individual risk factor.