Role of caloric homeostasis and reward in alcohol intake in Syrian golden hamsters

Abstract

The Syrian golden hamster drinks alcohol readily, but only achieves moderate blood alcohol levels, and does not go through withdrawal from alcohol. Because the hamster is a model of caloric homeostasis, both caloric content and reward value may contribute to the hamster's alcohol consumption. The current study examines alcohol consumption in the hamster when a caloric or non-caloric sweet solution is concurrently available and caloric intake in the hamster before, during, and after exposure to either: alcohol, sucrose or saccharin. In Experiments 1 and 2, hamsters were given access to alcohol (15% v/v) and water; once alcohol consumption steadied, a bottle containing an ascending concentration of sucrose (99–614 mM) or saccharin (2–10 mM), or water was added. In Experiment 3, hamsters were given access to alcohol (15% v/v), sucrose (614 mM), saccharin (4 mM), or a second water bottle for 14 days. After the second bottle was removed, measurements continued for 14 days. Sucrose exposure suppressed alcohol consumption at concentrations lower in calories than the alcohol solution. Saccharin exposure failed to suppress alcohol consumption. Exposure to sucrose and alcohol but not saccharin decreased food intake. Decreased alcohol consumption in response to a caloric sweetener and decreased food intake during alcohol exposure support that alcohol consumption by the hamster is mediated by caloric content. However, suppression of alcohol intake by a sucrose solution of lower caloric content and the equivalent intake of individual alcohol, sucrose and saccharin solutions support a role for reward value in alcohol consumption.

Introduction

The Syrian golden hamster (Mesocricetus auratus) has been used as a research model for studies of alcohol intake [1], [2], [3], [4], [5], but also of gustation [6] and caloric balancing [7]. The hamster readily consumes solutions of 15–30% alcohol [2], solutions of 50–450 mM sucrose [7] and solutions of 1–3 mM saccharin [6], and prefers these solutions to water. Previous studies have suggested that the golden hamster may consume alcohol for both its caloric content and its pharmacological effects. Although the effects of pharmacological interventions on alcohol intake in the hamster are similar to those seen in other alcohol-preferring rodents, the hamster's pattern of alcohol consumption differs from that seen in these other rodent models. Specifically, the golden hamster is a model of moderate alcohol drinking — it tends to drink alcohol at a steady rate during its waking period, but achieves only moderate blood alcohol levels (approximately 2 mM) [8], [9] and fails to exhibit signs of physiological withdrawal following cessation of chronic alcohol drinking [10].

We have used the hamster as an animal model of co-occurring schizophrenia and alcohol abuse in studies of the effects of antipsychotic drugs on alcohol consumption. The golden hamster has strong predictive validity for the ability of antipsychotics to decrease alcohol consumption in patients with schizophrenia; the atypical antipsychotic clozapine decreases alcohol intake in both hamsters [1], [3] and humans [11], while the typical antipsychotic haloperidol fails to decrease alcohol intake in either [3], [11]. However, in order to understand the effects of pharmacological treatments on alcohol intake in the hamster, we need to understand the factors underlying the hamster's consumption of alcohol.

To test whether caloric content is a more significant factor than reward value in the consumption of alcohol and other rewarding fluids by the golden hamster, the current studies examine changes in alcohol intake and food intake when an additional palatable fluid – either the caloric sweetener sucrose or the non-caloric sweetener saccharin – is made available. In addition, to determine whether the hamster maintains caloric homeostasis during exposure to each reward, we examine changes in food intake and total caloric intake prior to, during, and after cessation of free access to alcohol, sucrose or saccharin.