Sexually dimorphic distribution of Kiss1 neurons in the bed nucleus of the stria terminalis.

Kiss1 neurons play a crucial role in reproductive function and are found in distinct brain regions, including the bed nucleus of the stria terminalis (BNST). However, the sexual dimorphism of Kiss1 neurons in the BNST and their projections has not been fully characterized. This study examined the distribution and projections of Kiss1 neurons in the anterior (aBNST) and principal (prBNST) regions of the BNST in male and female Kiss1-Cre and Kiss1-Cre; tdTomato^loxP/+ mice. Neuroanatomical analysis and tracing experiments were conducted to quantify Kiss1 neurons and map their projections. Males had approximately a threefold higher number of Kiss1 neurons in the prBNST than females, while no significant sex difference was observed in the aBNST. Viral tracing experiments revealed sexually dimorphic projections of Kiss1^adBNST neurons, with females displaying more diverse projections to various brain regions involved in reproduction and social behaviors. Kiss1^prBNST neurons project exclusively to the zona incerta and adBNST in both sexes, while females exhibited additional projections to the RP3V and PVH. The sexually dimorphic distribution and projections of Kiss1^BNST neurons suggest their potential role in modulating sex-specific behaviors and neuroendocrine functions. This neuroanatomical sexual dimorphism may contribute to sex differences in social and reproductive behaviors associated with BNST function, providing new insights into the neural basis of sex-specific behaviors and reproductive regulation.