Abstract
In the United States, obesity has reached epidemic proportions, with approximately 64 percent of the population considered overweight. Despite the fact that men and women are equally likely to be overweight, women who are overweight are more likely to be obese than are men who are overweight. High fat consumption contributes significantly to obesity and the preference for high fat food is linked to the palatability of high fat foods. Thus, it seems likely that sex differences in obesity may reflect differences in fat intake that may, in turn, be related to differences in the perception of fat taste. Surprisingly, little research has examined the taste of fat and even less research has examined sex differences in fat taste. Previous research from our lab showed that male and female rats have different licking responses to linoleic acid (LA), a component of dietary fat. Therefore, the following experiments were designed to determine whether this sex difference is associated with differences in the detection of LA. In addition, the role of the chorda tympani nerve (CT), a gustatory sensory nerve, in fat taste detection and transduction was examined as an initial examination of how sensory information related to fat taste is transmitted to the brain.
The obtained results show that female rats have a lower detection threshold for LA (2.75 uM) than do male rats (11 uM). Bilateral transections of the chorda tympani nerve (CTX) shift the detection threshold for LA in both male and female rats to the same concentration (22 uM). Thus, the observation that CT- intact female rats have a lower detection threshold for LA than do male rats and that the magnitude of the shift in this detection threshold after CTX is greater in female rats suggests that CT input may play a greater role in LA detection in female rats. To evaluate this possibility, we recorded whole nerve electrophysiological responses from the CT in male and female rats. Contrary to expectations, the CT was completely unresponsive to a broad range of LA concentrations, despite responding typically to NaCl and QHCl in either male or female rats. Together, these results indicate that the increased LA preference by female rats may be attributable to an increased sensitivity to LA. Although behavioral tests clearly show that the CT is important in LA detection in female and male rats, at present, the exact role of the CT remains unknown.
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