Sex differences in the location of immunochemically defined cell populations in the mouse preoptic area/anterior hypothalamus

The preoptic area/anterior hypothalamus (POA/AH) is sexually dimorphic in many vertebrates. We have defined specific cell populations within the POA/AH using immunocytochemical markers for estrogen receptor beta (ER beta) and the R1 subunit of the GABA(B) receptor (GABA(B)R1). Our previous finding of sex differences in cell migration in this region in embryonic day 15 mice led us to examine sex differences in the location or size of chemically identified cell groups. At embryonic day 17 (E17), cells containing immunoreactive (it) ER beta in females were located more dorsal and lateral than those in males. In contrast to this positional sex difference seen at E 17, ER expression at PO and adulthood showed a sex difference in cell number and area of immunoreactivity with a higher expression of ER beta in males than females. Furthermore, in animals that were genetically deprived of gonadal and adrenal hormones by virtue of a disrupted gene coding for steroidogenic factor 1, cells containing ir ER beta followed a female phenotype for location at E 17 and a female phenotype for number of ir cells at PO regardless of genetic sex, suggesting that circulating hormones may be influencing cell position in the POA/AH. A second phenotypically identified cell group containing ir GABA(B)R1 also had a sex difference in cell positions at E17. Females expressed GABA(B)R1 in cells with a more dorsal position than in males. These results provide support for the suggestion that sex differences in cellular organization in the developing hypothalamus arise from sex differences in cell migration. (c) 2005 Elsevier B.V. All rights reserved.