ESTROGEN-CONCENTRATING CELLS WITHIN CELL GROUPS OF THE MEDIAL PREOPTIC AREA - SEX-DIFFERENCES AND COLOCALIZATION WITH GALANIN-IMMUNOREACTIVE CELLS

Male and female Tats have approximately equal numbers of estrogen(E)-concentrating cells within the medial preoptic area (MPOA). Several cell groups within this brain region are sexually dimorphic, however, and these groups may have sexually different numbers of E-containing cells; this, in turn, may reflect sex differences in neural-regulated functions. In order to study this possibility, the distribution of E-concentrating cells was determined using estrogen autoradiography. Except for the lateral portion of the medial preoptic nucleus (MPN1), the density of E-concentrating cells was 3-5-times higher within the most medially situated cell groups of the female than the male, i.e., within the anteroventral periventricular nucleus (AVPv), periventricular preoptic area (PVPO), medial portion of the medial preoptic nucleus (MPNm), and its central portion (MPNc). In addition, we determined whether E-concentrating cells also express the neuropeptide, galanin. An average of 13% of the E-concentrating cells were galanin positive, which represented 15% of the galanin-immunoreactive population. These results demonstrate a frank and dramatic sex difference in the distribution of E-concentrating cells within sexually dimorphic regions of the MPOA, and also suggest that an interaction between galanin and gonadal steroids may be an important means by which cells within the MPOA regulate reproductive function.