IMMUNOHISTOCHEMICAL COLOCALIZATION OF TYROSINE-HYDROXYLASE AND ESTRADIOL RECEPTORS IN THE SHEEP ARCUATE NUCLEUS

In sheep, the arcuate nucleus contains numerous tyrosine hydroxylase (TH) and estradiol receptor (rE2) immunoreactive (IR) perikarya and it has been shown previously in this species that catecholaminergic neurons can mediate the gonadal steroid action on the reproductive function. In the present study, double immunohistochemical labelling with antibodies against TH and rE2 have been used to demonstrate the presence of rE2 in TH-IR neurons in the arcuate nucleus where the distribution of TH-IR and rE2-IR neurons overlap each other. Only less than 10% of all the r-E2-IR perikarya presented TH immunoreactivity. It was therefore hypothesized that either such a low number of double labelled neurons can support the effects of estradiol in this area or that the effect of this steroid was indirect. In the latter case it might be first mediated by beta-endorphin neurons which have been previously described in this nucleus.