Sex differences in behavioral taste responses to and ingestion of sucrose and NaCl solutions by rats

Abstract

Sex differences in the ingestion of food and concentrated NaCl solutions by rats have been investigated for more than a quarter of a century, though the underlying mechanism(s) and the role of reproductive hormones remain the subject of debate. We hypothesized that sex differences in the ingestion of sucrose and NaCl solutions are attributable, in part, to sex differences in taste responses/taste perception. We employed short-access, 10-s tests along with 18-h, two-bottle preference tests to examine sex differences in sensitivity to and ingestion of sucrose and NaCl solutions. To evaluate the role of estrogen, we ovariectomized (OVX) female rats and then used an estrogen-replacement schedule that mimics the pattern of fluctuation of estrogen levels in intact female rats. We observed striking sex differences in the rate of licking NaCl mixed in a dilute sucrose solution. Compared to males, OVX rats with or without estrogen licked at higher rates to more concentrated NaCl solutions, suggesting that female rats are less sensitive to concentrated NaCl solutions. Although less pronounced, we also observed sex differences in the rate of licking to sucrose, particularly at lower concentrations. Compared to males, OVX rats with or without estrogen licked less, suggesting that female rats are less sensitive to lower concentrations of sucrose. Estrogen appeared to play, at most, a small role in mediating taste responses to specific concentrations of sucrose in these testing procedures. Nonetheless, sex differences in taste responses were clear, and it seems likely that such differences underlie, in part, observed differences in ingestion.