Microanalysis of ethanol self-administration: estrous cycle phase-related changes in consumption patterns.

Background: Female rodent and reproductive cycle-related patterns in ethanol consumption have been identified grossly, but the regulatory processes that underlie these patterns remain to be clarified. The evaluation of consummatory bout dynamics may be useful in determining the effects of a changing endogenous state (ovarian hormone fluctuations) on ethanol consumption patterns. This study assessed the microstructural components of ethanol intake patterns across the estrus cycle.

Methods: Cumulative licking of 13 female Long-Evans rats was recorded during continuous access (22 hr/day) to 10% ethanol and tap water solutions throughout a 10 week period. Drinking bouts were defined as 20 or more successive licks separated by less than a 60 sec pause. Vaginal smears were obtained daily from each rat between 1100 and 1130 hr to assess estrus cycle phase. ANOVAs were conducted to evaluate estrus cycle effects on consumption pattern parameters.

Results: Total daily ethanol intakes were unaffected by estrus cycle phase. Ethanol bout frequency was significantly greater during proestrus compared with all other phases, whereas ethanol bout sizes were significantly attenuated during proestrus compared with estrus and diestrus. Experience with ethanol was associated with a significant decline in bout frequency and a significant elevation in bout size across all cycle phases, which indicated that initiation of ethanol self-administration occurred over time. A significant main effect of hour and a cycle phase by hour interaction were found for the temporal distribution of ethanol lick responses throughout the estrus cycle, and a progressive shift in lick patterns evolved between estrus and the subsequent proestrus.

Conclusions: The estrus cycle phase-related changes in the microstructural components of ethanol intake suggest that female rats experience periods of altered sensitivity to the neurobiological and reinforcing effects of ethanol. Furthermore, these findings implicate cyclical fluctuations in ovarian hormones and other neuromodulators in the regulation of ethanol consumption patterns throughout the estrus cycle of the female rat.