Lesions of the preoptic area facilitate lordosis behavior in male and female guinea pigs.

Male and female guinea pigs received radiofrequency lesions in the medial preoptic area (MPOA). Animals were gonadectomized, treated with estrogen and progesterone, and tested for the occurrence of the lordosis response to manual stimulation. Females with MPOA lesions exhibited enhanced lordosis behavior, shorter latencies to heat, longer duration of heat and longer maximum lordosis duration than sham control females. In males with MPOA lesions, the lordosis response could be elicited by manual stimulation, in contrast to no response in the sham control males. Furthermore, MPOA-lesioned males were insensitive to the inhibitory effects of progesterone on lordosis behavior, while MPOA-lesioned females were as sensitive as sham controls to the inhibitory effects of progesterone. The results suggest that a neural mechanism resides within the MPOA which inhibits the occurrence of lordosis behavior in both male and female guinea pigs and which is not involved in a sexual dimorphism in responsiveness to progesterone.