Analysis of Spontaneous Behavior Patterns of Male Rhesus Macaques Exposed to Voluntary Ethanol Consumption Over Two-Year Period

BACKGROUND: The onset of mental disorders associated with chronic ethanol use without dependence and safe threshold for alcohol consumption remain unclear. AIM: To describe changes in the spontaneous behavior patterns of rhesus macaques in response to long-term alcohol consumption in a free-choice model. MATERIAL AND METHODS: Behavioral responses of mature male rhesus macaques were evaluated using the ethogram-based time-interval method. The study included six animals with low ethanol consumption and eight animals with high ethanol consumption. Ethanol consumption was measured prior to (baseline) and during the initiation period (62 days) and at the start and end of the phase of alcohol motivation maintenance (688 days of continuous access to 4% ethanol and water). Two 30-day withdrawal periods were completed in the middle and end of the motivation maintenance phase. Analysis of variance was conducted using the Kruskal–Wallis test. RESULTS: During the initiation phase and two motivation maintenance periods, the median ethanol consumption was 0.6, 0.5, and 0.8 g/kg/day for the low-consumption group and 1.6, 2.4, and 2.8 g/kg/day for the high-consumption group, respectively. The animals from the high-consumption group demonstrated a 9% decrease in body weight by the end of the observation period (p = 0.030). Ultrasound examination showed no hepatic or cardiac abnormalities. The baseline intergroup differences in stereotypy (p = 0.023), front-of-cage position (p = 0.023), and sitting position (p = 0.006) persisted throughout the experimental period. At the end of the motivation maintenance phase, the low-consumption group revealed a lower frequency of the slumped posture (p = 0.035). However, an increase was noted in the frequency of the front-of-cage position in the high-consumption group (76%; 60%–98% confidence interval; p = 0.006) compared to baseline (48%; 28%–63% confidence interval), which remained increased in the subsequent withdrawal period (83%; 53%–95% confidence interval; p = 0.008). CONCLUSION: The 2-year alcohol consumption of male rhesus macaques in the free-choice model induced transient and prolonged changes in the spontaneous behavior patterns of the animals.