Taste responses in the parabrachial pons of male, female and pregnant rats.

Sex-related and pregnancy-related variations in taste preferences have long been known to exist in humans as well as animals. However, the neurophysiological underpinnings of these variations have not yet been described. In an effort to discover whether differences in hormonal state are reflected in the neural processing within the gustatory system, electrophysiological responses to representatives of the 4 basic taste qualities were recorded in the parabrachial nucleus of the pons (PbN) of male, diestrous female and pregnant rats. Results revealed that PbN units in female and pregnant rats showed larger responses to sweet stimuli than units in male rats. Also, a greater proportion of units in female and pregnant rats were classified as sweet-best compared with units in males. This result may correlate with the greater preference for sweet stimuli in female rats compared with males that has been reported in the behavioral literature. Analysis of response profiles with multidimensional scaling techniques showed that units that responded best to a given stimulus were placed near that stimulus for units from males, but not for units from female and pregnant rats. Hierarchical cluster analysis of response profiles suggested 3 clusters of units within each group of PbN units. Response profiles within clusters showed different types of units in male, female and pregnant rats. Collectively, these data suggest that ovarian hormones may act to alter the central processing of gustatory information. Evidence for both activational and organizational effects of ovarian hormones on the gustatory system is discussed.