Estrogen induces ultrastructural changes in progesterone receptor-containing GABA neurons of the primate hypothalamus.

Estrogen affects gonadotrophin levels and sex behavior in monkeys. This action could be via inhibitory GABA-ergic neurons in the hypothalamus. We tested for direct estrogen actions on such neurons. Seven days after ovariectomy (OVX) or OVX + estrogen treatment (10 mg estradiol valerate in 1 ml sesame oil s.c. on the day of OVX), light- and electron-microscopic double immunostaining procedures were used for simultaneous visualization of immunoreactivity for progesterone receptors (PR) and glutamic acid decarboxylase (GAD), and to detect ultrastructural changes in PR-containing neurons in the arcuate and ventromedial hypothalamic nuclei of colchicine- and noncolchicine-treated African green monkeys (Cercopithecus aethiops). Immunoreactivity for PR was found only in cell nuclei, and estrogen treatment enhanced the intensity of the immunostaining: in estrogen-treated monkeys in the arcuate nucleus 62%, while in the ventromedial nucleus 42% of the neurons contained PR-immunoreactive nuclei. All of the PR-containing neurons were immunopositive for GAD in colchicine-pretreated monkeys. OVX induced whorl body formation, while estrogen treatment of OVX animals resulted in a large number of nematosomes. While all of the whorl bodies and the majority of nematosomes were observed in PR-immunopositive GAD neurons, nematosomes were also found in non-PR-containing GAD-immunoreactive cells.