Immunocytochemical localization of ionotropic glutamate receptors subunits in the adult quail forebrain

Abstract

The excitatory amino acid glutamate is implicated in the central control of many neuroendocrine and behavioral processes. The ionotropic glutamate receptors are usually divided into the N-methyl-D-aspartate (NMDA) and non-NMDA (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 aromatase activity like several other manipulations affecting intracellular HCa(2+) pools. Aromatase catalyzes the conversion of androgens into estrogens which is a limiting step in the control by testosterone of many behavioral and physiologic processes. Therefore, glutamate could control estrogen production in the brain, but the anatomic substrate supporting this effect is poorly understood. In quail, aromatase is mainly localized in the preoptic-hypothalamic-limbic system. We visualized here the distribution of the major ionotropic glutamate receptors in quail by immunocytochemical methods by using 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 receptors (NMDAR1, Pharmingen, CA). Dense and specific signals were obtained with all antibodies. The four types of receptors are broadly distributed in the brain, and, in particular, immunoreactive cells are identified within the major aromatase cell groups located in the medial preoptic nucleus, ventromedial hypothalamus, nucleus striae terminalis, and nucleus taeniae. Dense specific populations of glutamate receptor-immunoreactive cells are also present with a receptor subtype-specific distribution in broad areas of the telencephalon. The distribution of glutamate receptors, therefore, is consistent with the idea that these receptors could be located at the surface of aromatase-containing cells and mediate the rapid regulation of aromatase activity in a direct manner.

Glutamate released in the preoptic area during sexual behavior controls local estrogen synthesis in male quail

“…In this paper, we therefore wanted to investigate whether the rapid changes in AA observed after copulation are mediated by endogenous glutamate release. This hypothesis was supported by the following lines of evidence: (1) glutamate receptors are expressed in regions of the avian brain containing aromatase cells (Cornil et al, 2000 ; Saldanha et al, 2004), (2) quail preoptic aromatase cells are sensitive to AMPA, kainate and NMDA in vitro (Cornil et al, 2004), (3) glutamate is released in rat medial preoptic area (MPOA) during sexual behavior (Dominguez et al, 2006) and (4) one study in zebra finches demonstrated that infusion of glutamate in an auditory telencephalic region containing aromatase leads to a transient decrease of estradiol concentration (Remage-Healey et al, 2008). …”

Rapid effects of aromatase inhibition on male reproductive behaviors in Japanese quail

“…These changes in aromatase activity can be induced by the activation of glutamate or dopamine receptors (Balthazart, Baillien, and Ball, 2002;Balthazart et al, 2003). Since glutamate and dopamine inputs and receptors are present in the preoptic area (Absil, Das, Ball, Casto, and Balthazart, 1992;Bailhache and Balthazart, 1993;Ball, Casto, and Balthazart, 1995;Balthazart and Absil, 1997;Cornil, Foidart, Minet, and Balthazart, 2000) and these receptors are expressed at the surface of aromatase cells themselves (Cornil, Seutin, Motte, and Balthazart, 2004c), it is therefore likely that afferent inputs related to a variety of environmental changes are able to rapidly affect estrogen production in the preoptic area.…”

Immunohistochemical localization of AMPA-type glutamate receptor subunits in the nucleus of the Edinger-Westphal in embryonic chick

“…The primary antibody concentrations were: GluR1 [1:100], GluR2/3 [1:250], and GluR4 [1:100]. According to manufacturer information and published studies, the immunogens for the GluR1, GluR2/3 and GluR 4 antisera show ≥85% homology to the corresponding avian sequences [6,22]. Western blot analysis in mammals and diverse avian species has shown these antisera selectively detect proteins of the predicted size for each GluR subunit [4,6,20,25,30].…”

“…According to manufacturer information and published studies, the immunogens for the GluR1, GluR2/3 and GluR 4 antisera show ≥85% homology to the corresponding avian sequences [6,22]. Western blot analysis in mammals and diverse avian species has shown these antisera selectively detect proteins of the predicted size for each GluR subunit [4,6,20,25,30]. Moreover, blocked controls show the specificity of these antisera in mammals and birds [21], and in the case of GluR2/3 specificity is supported by the concordance in distribution between immunolabeling and GluR2 in situ hybridization [27].…”

“…Finally, it is possible that another glutamate receptor, kainate (KA), is present in chick EW neurons. KA receptors are abundant in the avian CNS [6,19], and prior studies by others have shown that KA-evoked currents transiently mediate excitatory transmission in chick lumbar motoneurons early in development [19]. …”