REGIONAL-ANALYSIS OF 5-HT1A RECEPTORS IN 2 SPECIES OF PEROMYSCUS

Two species of deer-mice, Peromyscus maniculatus (P. man) and Peromysc us leucopus (P. leu), were compared for differences in 5-hydroxytrypta mine1A (5-HT1A) receptor number and affinity. Both species enter into torpor; however, P. man enters spontaneous torpor with a higher freque ncy and for a longer duration than P. leu. Further, compared to P. leu a higher percentage of P. man exhibit daily torpor. Deer mice can be induced to enter torpor by a reduction in food supply, shortened photo periods, and decreasing ambient temperature. Under these conditions, P . man enters into torpor more frequently, for longer durations, and wi th a higher percentage of individuals as compared to P. leu. [H-3]8-OH -DPAT was used to label 5-HT1A brain receptors in three brain regions: the frontal cortex, brainstem, and striatum. In addition, the hypotha lamus and hippocampus were examined for 5-HT1A receptor differences; h owever, no measurable specific binding could be determined in these re gions. In the frontal cortex, the B(max) values were significantly low er in P. man compared to P. leu. There were no significant differences in the B(max) values in the striatum and brainstem between P. man and P. leu. Further, there were no significant differences in the K(d) va lues between the two species in any of the brain regions examined. The absence of any difference in receptor number or affinity in any of th e brain regions examined, except the cortex, suggests that the 5-HT1A receptor is most likely not involved in a more efficient pathway to to rpor.