Regional analysis of 5-HT 1A receptors in two species of Peromyscus

Abstract

Two species of deer-mice, Peromyscus maniculatus (P. man) and Peromyscus leucopus (P. leu), were compared for differences in 5-hydroxytryptamine 1A (5-HT 1A) receptor number and affinity. Both species enter into torpor; however, P. man enters spontaneous torpor with a higher frequency 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 photoperiods, and decreasing ambient temperature. Under these conditions, P. man enters into torpor more frequently, for longer durations, and with a higher percentage of individuals as compared to P. leu. [ 3H]8-OH-DPAT was used to label 5-HT 1A brain receptors in three brain regions: the frontal cortex, brainstem, and striatum. In addition, the hypothalamus and hippocampus were examined for 5-HT 1A receptor differences; however, no measurable specific binding could be determined in these regions. In the frontal cortex, the B max values were significantly lower 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 values between the two species in any of the brain regions examined. The absence of any difference in receptor number or affinity in any of the brain regions examined, except the cortex, suggests that the 5-HT 1A receptor is most likely not involved in a more efficient pathway to torpor.