Distribution of ionotropic glutamate receptor subunit mRNAs in the rat hypothalamus

Abstract

The excitatory amino acid neurotransmitter glutamate participates in the control of most (and possibly all) neuroendocrine systems in the hypothalamus. This control is exerted by binding to two classes of membrane receptors, the ionotropic and metabotropic receptor families, which differ in their structure and mechanisms of signal transduction. To gain a better understanding about the precise sites of action of glutamate and the subunit compositions of the receptors involved in the glutamatergic neurotransmission in the hypothalamus and septum, in situ hybridization was used with 35S-labeled cRNA probes for the different ionotropic receptor subunits, including glutamate receptor subunits 1-4 (GluR1-GluR4), kainate-2, GluR5-GluR7, N-methyl-D-aspartate (NMDA) receptor 1 (NMDAR1), and NMDAR2A-NMDAR2D. The results showed that subunits of alpha-amino-3-hydroxy-5-methyl-4-isoxazole-propionate-preferring, kainate-preferring, and NMDA-preferring receptor subunits are distributed widely but heterogeneously and that the GluR1, GluR2, kainate-2, NMDAR1, NMDAR2A, and NMDAR2B subunits are the most abundant in the hypothalamus. Thus, GluR1 subunit mRNA was prominent in the lateral septum, preoptic area, mediobasal hypothalamus, and tuberomammillary nucleus, whereas kainate-2 subunit mRNA was abundant in the medial septum-diagonal band, median and anteroventral preoptic nuclei, and supraoptic nuclei as well as the magnocellular portion of the posterior paraventricular nucleus. Regions that contained the highest levels of NMDAR1 subunit mRNA included the septum, the median preoptic nucleus, the anteroventral periventricular nucleus, and the supraoptic and suprachiasmatic nuclei as well as the arcuate nucleus. Together, the extensive distribution of the different GluR subunit mRNAs strengthen the view that glutamate is a major excitatory neurotransmitter in the hypothalamus. The overlap in the distribution of the various subunit mRNAs suggests that many neurons can express GluR channels that belong to different families, which would allow a differential regulation of the target neurons by glutamate.

Depolarization and Neurotransmitter Regulation of Vasopressin Gene Expression in the Rat Suprachiasmatic NucleusIn Vitro

“…For this purpose, we used the c-fos gene expression as the marker of neuronal activation. Illustrations of this strategy for several of the neurotransmitters used for activation of the SCN neurons are shown in Figures 1-3. A pharmacological approach to the study of regulated gene expression in the SCN SCN neurons are known to contain various glutamate afferent inputs and receptor subunits (Eyigor et al, 2001;Hannibal, 2002), and we wanted to determine which, if any, of the various agonists could directly effect the expression initially of c-fos and subsequently VP of hnRNA in the cultured SCN slices. The data in Figure 1 illustrate the results of activation of neurons in the cultured SCNs by various glutamate-receptor ligands.…”

Neurotransmitter Regulation of Cellular Activation and Neuropeptide Gene Expression in the Paraventricular Nucleus of the Hypothalamus

“…This result was unexpected, because the PVH is known to express a variety of (mainly ionotropic) glutamate receptors (van den Pol et al, 1994;Aubry et al, 1996;Herman et al, 2000;Eyigor et al, 2001) and to receive a substantial glutamatergic innervation (van den Pol et al, 1990;van den pol, 1991). The role of glutamate in the regulation of PVH mechanisms is unsettled, and its effects on parvocellular neurosecretory neurons have not been thoroughly characterized (Oliver et al, 1996;Herman and Cullinan, 1997).…”

“…It remains to be determined to what extent local glutamate-sensitive GABAergic elements identified in our experiments actually contribute to the innervation of the PVH in general and to that of parvocellular neurosecretory neurons in particular. Current understanding of the distribution of glutamate receptors in and around the PVH is of limited value in ascertain-ing a likely site of action, because some are localized preferentially to the PVH, some to perinuclear regions, and still others distributed ubiquitously across both (Herman et al, 2000;Eyigor et al, 2001). In any event, the present findings call attention to the potential confounding influence of local circuit neurons in interpreting the effects of microinjection studies, which, in this instance, leave open to question the nature and any selectivity of glutamatergic regulation of PVH effector populations.…”

Panic-Prone State Induced in Rats with GABA Dysfunction in the Dorsomedial Hypothalamus Is Mediated by NMDA Receptors

“…Antibodies that recognize the NR1 subunit of the NMDA receptor and the GluR2 and 3 subunits of the AMPA receptor were used. We selected these antibodies because the NR1 protein (Petralia et al, 1994) and mRNA (Eyigor et al, 2001) and the GluR2 and 3 proteins (Petralia et al, 1996) and mRNA (Eyigor et al, 2001) expressions are most ubiquitous in the DMH and are equal to or greater than NR2 and GluR1 and 4 subunits. In another group of rats, which received L-AG infusions into the DMH and were responsive to intravenous sodium lactate infusions, the lactate responses were retested after acute injection of NMDA and non-NMDA antagonists into the DMH.…”