Neurohistological and behavioral evidence for lordosis-inhibiting tract from lateral septum to periaqueductal gray in male rats

To verify the anatomical and functional connection of the lateral septum (L S) and periaqueductal gray (PAG) in inhibiting female sexual behavior, lord osis, in male rats, retrograde (Fluoro-Gold, FG) or anterograde (Phaseolus vulgaris-leucoagglutinin, PHA-L) tracer was injected into the PAG or LS on the right side, respectively, and FG-labeled cells or PHA-L-labeled axons i n the forebrain and mesencephalon were determined in estrogen-treated castr ated male rats. A ventral cut (VC) of the septum and a behavioral test were also conducted in some FG-injected rats. Furthermore, lordosis behavior wa s observed after chemical destruction of the septum by ibotenate. As a resu lt, the lordosis quotient (LQ) in VC males was higher than that in control males without VC. FG-labeled neuronal cell bodies were found in the ipsilat eral intermediate part of the LS in the control males but not in this area of the VC males. When neuronal cells in the intermediate part of the bilate ral LS were completely destroyed by ibotenate, the LQ was higher than that in sham-lesioned male rats. These results suggest that a direct neural conn ection of the intermediate LS to the PAG has an inhibitory role in regulati ng lordosis in male rats. In addition, neuronal cell bodies in the intermed iate LS exert an inhibitory influence. In the PHA-L experiment, labeled axo ns were seen in the ventral part of the LS, the medial forebrain bundle at the chiasmatic level, the lateral hypothalamus, the median region of the me sencephalon, and the rostral PAG in the side ipsilateral to the tracer inje ction site of the LS. Thus, these areas are thought to be involved in the p athway for lordosis-inhibition from the intermediate part of the LS to the PAG in male rats.