Sex difference in dendritic development of the sexually dimorphic nucleus of the preoptic area in the rat.

Sex differences in the growth and dendritic development of neurons in the sexually dimorphic nucleus of the preoptic area were examined with quantitative Golgi techniques during early postnatal life in rats. Neuronal size and dendritic extent were found to increase more in males than in females during the first 10 postnatal days, while the numbers of primary and terminal dendrites were similar in the two sexes. The onset of greater dendritic growth in males occurs just after the volume of the nucleus begins to exhibit sexual dimorphism, between 24 and 26 days after fertilization. Growth of dendrites in this region may be related to the presence of sex hormones during the critical period of sexual brain differentiation.