A Small Population of Tyrosine Hydroxylase‐lmmunoreactive Neurons in the Guinea‐Pig Arcuate Nucleus Contains Progestin Receptor‐lmmunoreactivity

Abstract

We studied the co‐localization of progestin receptor‐immunoreactive (PR‐IR) cell nuclei and tyrosine hydroxylase‐immunoreactive (TH‐IR) cell bodies in guinea‐pig brain with a double antibody, immunocytochemical technique. Sections were first immunostained for estradiol‐induced PR‐IR using a peroxidase‐antiperoxidase technique with diaminobenzidine as the chromogen followed by α‐naphthol as the chromogen for TH‐IR. We examined the periventricular‐preoptic area and the arcuate nucleus, because these two sites are dense in both PR‐IR cells and TH‐IR cells (cell groups A14 and A12, respectively), and the dorsal hypothalamic Area A13, because this area contains a high density of TH‐IR cells, but few PR‐IR cells. No co‐localization was seen in the periventricular‐preoptic area or Area A13. However, a small proportion (5% to 13%) of TH‐IR cells in the arcuate nucleus was observed to have PR‐IR cell nuclei with the rostral arcuate showing the greatest concentration of co‐localized cells. In order to determine if the estradiol pretreatment required to induce PR‐IR influenced TH‐IR, TH‐IR in estradiol‐primed guinea‐pigs was compared with that of vehicle‐injected controls. This treatment did not noticeably influence the amount of TH‐IR in the arcuate nucleus. Therefore, the results of these experiments suggest that, although some of the TH‐IR neurons in the arcuate nucleus contain PR‐IR, this relationship is seen in less than 15% of the TH‐IR cells. In many cases, PR‐IR neurons were found to have TH‐IR varicosities closely associated with their cell bodies. Copyright © 1989, Wiley Blackwell. All rights reserved