Neural control of sexually dimorphic behaviors

Abstract

All sexually reproducing animals exhibit gender differences in behavior. Such sexual dimorphisms in behavior are most obvious in stereotyped displays that enhance reproductive success such as mating, aggression, and parental care. Sexually dimorphic behaviors are a consequence of a sexually differentiated nervous system, and recent studies in fruit flies and mice reveal novel insights into the neural mechanisms that control these behaviors. In the main, these include a diverse array of novel sex differences in the nervous system, surprisingly modular control of various stereotyped dimorphic behavioral routines, and unanticipated sensory and central modulation of mating. We start with a brief overview to provide the appropriate conceptual framework so that the advances made by the newer studies discussed subsequently can be fully appreciated. We restrict our review to reporting progress in understanding the basis of mating and aggression in fruit flies and mice.

Figure 1

Sensory and central control of sexually dimorphic behaviors. Both flies and mice respond to pheromones that trigger or inhibit particular behaviors. In fruit flies, pheromones are sensed by olfactory neurons as well as by gustatory neurons. In mice, volatile pheromones are sensed by the main olfactory epithelium (MOE) and non-volatile pheromones by the vomeronasal organ (VNO). In fruit flies, various components of male courtship are controlled by specific populations of Fru_M neurons. Activation of P1, P2b, or pIP10 neurons elicits the initiation of courtship behavior, while Fru_M ventral nerve cord neurons (dPR1, vPR6, vMS11) control specific elements of courtship song. In mice, gonadal sex hormones control the sexually dimorphic expression of many genes which regulate specific components of sex-typical behaviors. The VMHvl appears to contain neurons that inhibit male mating and activate male aggression. All neuronal clusters shown are bilateral but are depicted on one side for clarity.

Figure 2

Sex determination and differentiation of the nervous system in fruit flies and mice. Sex determination in fruit flies is cell-autonomous, and sexually dimorphic behaviors are controlled by neurons expressing sex-specific splice forms of Dsx and Fru. In mice, the sex-determination pathway directs the differentiation of the bipotential gonad into ovaries or testes. Gonadal sex steroids and their cognate receptors control the sexual differentiation of nervous system and the expression of sex-typical behaviors in the adult.