DISTRIBUTION OF AROMATASE-IMMUNOREACTIVE CELLS IN THE FOREBRAIN OF ZEBRA FINCHES (TAENIOPYGIA-GUTTATA) - IMPLICATIONS FOR THE NEURAL ACTIONOF STEROIDS AND NUCLEAR DEFINITION IN THE AVIAN HYPOTHALAMUS

Cells immunoreactive for the enzyme aromatase were localized in the fo rebrain of male zebra finches with the use of an immunocytochemistry p rocedure. Two polyclonal antibodies, one directed against human placen tal aromatase and the other directed against quail recombinant aromata se, revealed a heterogeneous distribution of the enzyme in the telence phalon, diencephalon, and mesencephalon. Staining was enhanced in some birds by the administration of the nonsteroidal aromatase inhibitor, R76713 (racemic Vorozole) prior to the perfusion of the birds as previ ously described in Japanese quail, Large numbers of cells immunoreacti ve for aromatase were found in nuclei in the preoptic region and in th e tuberal hypothalamus. A nucleus was identified in the preoptic regio n based on the high density of aromatase immunoreactive cells within i ts boundaries that appears to be homologous to the preoptic medial nuc leus (POM) described previously in Japanese quail, In several birds al ternate sections were stained for immunoreactive vasotocin, a marker o f the paraventricular nucleus (PVN), This information facilitated the clear separation of the POM in zebra finches from nuclei that are adja cent to the POM in the preoptic area-hypothalamus, such as the PVN and the ventromedial nucleus of the hypothalamus, Positively staining cel ls were also detected widely throughout the telencephalon, Cells were discerned in the medial parts of the ventral hyperstriatum and neostri atum near the lateral ventricle and in dorsal and medial parts of the hippocampus. They were most abundant in the caudal neostriatum where t hey clustered in the dorsomedial neostriatum, and as a band of cells c oursing along the dorsal edge of the lamina archistriatalis dorsalis, They were also present in high numbers in the ventrolateral aspect of the neostriatum and in the nucleus taeniae, None of the telencephalic vocal control nuclei had appreciable numbers of cells immunoreactive f or aromatase within their boundaries, with the possible exception of a group of cells that may correspond to the medial part of the magnocel lular nucleus of the neostriatum. The distribution of immunoreactive a romatase cells in the zebra finch brain is in excellent agreement with the distribution of cells expressing the mRNA for aromatase recently described in the finch telencephalon, This widespread telencephalic di stribution of cells immunoreactive for aromatase has not been describe d in non-songbird species such as the Japanese quail, the ring dove, a nd the domestic fowl. (C) 1996 John Wiley & Sons, Inc.