Brain transections differentially alter lordosis and ear wiggling of 6-day-old rats

Six-day-old male and female rats display lordosis and ear wiggling in response to tactile stimulation of the flanks and rump, without priming by exogenous estrogen. The involvement of various brain regions in these behaviors, which resemble components of adult female sexual behavior, was examined by making acute transections along the neuraxis from the olfactory tract to the medulla in 6-day-old rats. Four to 5 hr after the transection procedure, pups were tested for lordosis and ear wiggling. Lordosis was severely reduced or eliminated in pups with cuts through the hindbrain or diencephalon (above the level of the mammillary bodies) but was relatively unaffected by cuts through the posterior hypothalamus and rostral tegmentum and by cuts rostral to the anterior hypothalamus. Ear wiggling was disrupted by transections throughout the hindbrain and was facilitated only in females by transections throughout the forebrain (anterior to the mammillary bodies). These data suggest that facilitation from the hypothalamus is required for lordosis in the infant rat and the forebrain inhibitory systems for ear wiggling are functional in female infants by 6 days of age. Similarities and differences between the neural control of lordosis and ear wiggling in infant and adult rats suggest that the infant sex-like behaviors may be precursors of adult female sexual behavior.