Immunocytochemical localization of ionotropic glutamate receptors subunitsin the adult quail forebrain

The excitatory amino acid glutamate is implicated in the central control of many neuroendocrine and behavioral processes. The ionotropic glutamate rec eptors are usually divided into the N-methyl-D-aspartate (NMDA) and non-NMD A (kainate and AMPA) subtypes. Subunits of these receptors have been cloned in a few mammalian species. Information available in birds is more limited . In quail, we recently demonstrated that glutamate agonists (kainate, AMPA , and NMDA) rapidly (within minutes) and reversibly decrease in vitro aroma tase activity like several other manipulations affecting intracellular HCa2 + pools. Aromatase catalyzes the conversion of androgens into estrogens whi ch is a limiting step in the control by testosterone of many behavioral and physiologic processes. Therefore, glutamate could control estrogen product ion in the brain, but the anatomic substrate supporting this effect is poor ly understood. In quail, aromatase is mainly localized in the preoptic-hypo thalamic-limbic system. We visualized here the distribution of the major io notropic glutamate receptors in quail by immunocytochemical methods by usin g commercial primary antibodies raised against rat glutamate receptor 1 and receptors 2-3 (GluR1, GluR2/3: AMPA subtype, Chemicon, CA), rat glutamate receptors 5-7 (GluR5-7: kainate subtype, Pharmingen, CA), and rat NMDA rece ptors (NMDAR1, Pharmingen, CA). Dense and specific signals were obtained wi th all antibodies. The four types of receptors are broadly distributed in t he brain, and, in particular, immunoreactive cells are identified within th e major aromatase cell groups located in the medial preoptic nucleus, ventr omedial hypothalamus, nucleus striae terminalis, and nucleus taeniae. Dense specific populations of glutamate receptor-immunoreactive cells are also p resent with a receptor subtype-specific distribution in broad areas of the telencephalon. The distribution of glutamate receptors, therefore, is consi stent with the idea that these receptors could be located at the surface of aromatase-containing cells and mediate the rapid regulation of aromatase a ctivity in a direct manlier. J. Comp. Neurol. 428: 577-608, 2000. (C) 2000 Wiley-Liss, Inc.