In order to clarify the functional relationships between the lateral septum (LS) and the mesencephalic central gray (MCG) in regulating lordosis behavior, ovariectomized female rats received dual lesions in these two areas. In the first experiment, females with unilateral (right or left, R-MCGL or L-MCGL) or bilateral MCG (B-MCG) lesions were subjected to behavioral tests after the implantation of a Silastic tube containing estradiol. Lordosis was observed in only one B-MCGL female. In the R-MCGL and L-MCGL groups, most females displayed lordosis, but lordosis quotients (LQ) were significantly lower than that of the control group. These results suggest the importance of the MCG in lordosis regulation, and that there is no functional laterality in the MCG. In the second experiment, B-MCGL or R-MCGL females received bilateral LS lesions (LSL). The lordotic activity in the LSL + B-MCGL group was extremely low, being comparable to that of B-MCGL alone. On the other hand, in the LSL + R-MCGL females, the LQ was significantly higher than that of females with R-MCGL alone and was comparable to that of controls. Thus, the lateral septum plays an inhibitory role in regulating lordosis, but the influence of the lateral septum is not stronger than the facilitatory influence of the mesencephalic central gray, because the LSL could not recover the suppressive effect of the MCGL.
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