EVIDENCE FOR ESTROGEN-RECEPTOR IN CELL-NUCLEI AND AXON TERMINALS WITHIN THE LATERAL HABENULA OF THE RAT - REGULATION DURING PREGNANCY

The habenular complex is involved in several estrogen-dependent reprod uctive behaviors in female rats, namely, sexual behavior, maternal beh avior, and postpartum sexual behavior. Although it is known that estro gen acts in other brain regions to mediate these behaviors, it is not known whether estrogen may also act directly on the habenular complex. To address this possibility, we examined this region for the presence of estrogen receptor (ER). This analysis was carried out in separate experiments by using in situ hybridization, immunocytochemistry at the light and electron microscopic levels, and steroid autoradiography, N eurons within the lateral habenula (LHb), but not the medial habenula, express ER mRNA, contain ER immunoreactivity (ER-ir) in their nuclei, and concentrate radiolabelled estradiol, providing strong evidence fo r the presence of functional ER in the lateral habenula. There were al so ER-ir containing punctate fibers within the LHb, which, at the elec tron microscopic level, in part, proved to be axons and presynaptic ax onal terminals. Both the level of ER-ir in cell nuclei and the density of ER-ir fibers within the LHb were regulated during the course of pr egnancy and the postpartum period, suggesting that the sensitivity of the LHb to estrogen may be altered during this time. Taken together, t hese results demonstrate that the LHb is likely a more estrogen-sensit ive region than was previously considered, and they suggest alternativ e mechanisms of action for ER. ER within the LHb may play a critical r ole in the involvement of the LHb in estrogen-dependent female reprodu ctive behaviors. (C) 1988 Wiley-Liss, Inc.