Preoptic aromatase cells project to the mesencephalic central gray in the male Japanese quail (Coturnix japonica)

Previous tract-tracing studies demonstrated the existence of projections fr om the medial preoptic nucleus (POM) to the mesencephalic central gray (GCt ) in quail. GCt contains a significant number of aromatase-immunoreactive ( ARO-jr) fibers and punctate structures, but no ARO-ir cells are present in this region. The origin of the ARO-ir fibers of the GCt was investigated he re by retrograde tract-tracing combined with immunocytochemistry for aromat ase. Following injection of fluorescent microspheres. in GCt, retrogradely labeled cells were found in a large number of hypothalamic and mesencephali c areas and in particular within the three main groups of ARO-ir cells loca ted in the POM, the ventromedial nucleus of the hypothalamus, and the bed n ucleus striae terminalis. Labeling of these cells for aromatase by immunocy tochemistry demonstrated, however, that aromatase-positive retrogradely lab eled cells are observed almost exclusively within the POM. Double-labeled c ells were abundant in both the rostra[ and caudal parts of the POM and thei r number was apparently not affected by the location of the injection site within GCt. At both rostro-caudal levels of the POM, ARO-Ir retrogradely la beled cells were, however, more frequent in the lateral than in the medial POM. These data indicate that ARO-ir neurons located in the lateral part of the POM may control the premotor aspects of male copulatory behavior throu gh their projection to GCt and suggest that GCt activity could be affected by estrogens released from the terminals of these ARO-Ir neurons. (C) 2001 Academic Press.