Chemosignals and hormones in the neural control of mammalian sexual behavior

• Odors guide steroid-dependent pre- and peri-copulatory behavior in both sexes.
• Steroids act at all levels of main and accessory olfactory systems.
• Parallel chemosensory and hormone-sensitive sub-regions within behavior circuit.
• MA–BNST interactions control chemoinvestigation in males but not females.
• MA–MPOA/VMH interactions control copulatory initiation in males/females.

Males and females of most mammalian species depend on chemosignals to find, attract and evaluate mates and, in most cases, these appetitive sexual behaviors are strongly modulated by activational and organizational effects of sex steroids. The neural circuit underlying chemosensory-mediated pre- and peri-copulatory behavior involves the medial amygdala (MA), the bed nucleus of the stria terminalis (BNST), medial preoptic area (MPOA) and ventromedial hypothalamus (VMH), each area being subdivided into interconnected chemoreceptive and hormone-sensitive zones. For males, MA–BNST connections mediate chemoinvestigation whereas the MA–MPOA pathway regulates copulatory initiation. For females, MA–MPOA/BNST connections also control aspects of precopulatory behavior whereas MA–VMH projections control both precopulatory and copulatory behavior. Significant gaps in understanding remain, including the role of VMH in male behavior and MPOA in female appetitive behavior, the function of cortical amygdala, the underlying chemical architecture of this circuit and sex differences in hormonal and neurochemical regulation of precopulatory behavior.