Reproductive behavior in the female rat depends largely on the actions of estrogen on the brain. Because estrogen does not induce female-typical behavior in castrated male rats, the sex-specific behavioral pattern is not determined by the various sex hormones secreted by their gonads, but by different sensitivity of the brain to sex hormones. One of the brain structures that is sensitive to estrogen and exhibits distinctive sex difference in the rat is the preoptic area (POA).Sexual differentiation of the rat POA is also a sex hormone-dependent event during the perinatal period, and may represent developmental regulation of the brain that operates independent of genetic predisposition.
An understanding of the brain mechanism that integrates reproductive behavior is of great importance, because this would reveal neural substrates needed for higher brain functions such as emotion and motivation. Several simple components, which occur sequentially as a result of interaction with males, constitute female rat reproductive behavior. Females initiate copulation by showing proceptive behavior or soliciting. The consummatory phase of copulation is characterized by the display of the lordosis reflex, the major receptive behavior. The POA stands out because neuronal links for both proceptive and receptive components have been identified to originate in this structure.