Identification of glutamate receptor subtype mRNAs in gonadotropin-releasing hormone neurons in rat brain

Abstract

The aims of the present study were to determine: 1. If glutamate neurites can provide input to gonadotropin-releasing hormone (GnRH) neurons; 2. Which glutamate receptor subtype mRNAs are expressed in GnRH neurons; and 3. If GnRH neurons synthesize kainate 2 receptor (KA(2)) protein. Immunohistochemical double stainings for GnRH and glutamate or for GnRH and KA(2)-receptor protein were applied to rat brain sections containing the medial septum-diagonal band and preoptic area or the median eminence; in addition, dualin situ hybridization studies were carried out with digoxygenin-labeled cRNA probes encoding GnRH in combination with(35)S-labeled cRNA probes encoding the glutamate receptor subtypes GluR(1-4), KA(2), NMDA R(1), or NMDA R(2A-D). The results show that GnRH neurons are surrounded by glutaminergic neurites, which form puncta-like close appositions with the GnRH perikarya, and that an extensive overlap exists in the distribution of GnRH-positive axon terminals and glutaminergic neurites in the median eminence. Similarly, KA(2)-receptor immunoreactivity is present in the perikarya of many GnRH neurons and in their axon terminals in the median eminence. Dualin situ hybridization experiments show that about 32% of all digoxygenin-labeled GnRH neurons also contain KA(2)-receptor mRNA, 17% contain NMDA R(2A) mRNA, 8% contain NMDR R(1), whereas <5% of the GnRH neurons express measurable amounts of GluR(1-4) or NMDAR(2B-D) mRNA. The results suggest that glutaminergic neurons innervate the GnRH neuronal system directly through activation of KA(2) receptors on GnRH neurons, whereas the effects of AMPA and NMDA on GnRH release are likely to be exerted indirectly through interneurons.

Increase in In Vivo Glutamate Release in the Mediobasal Hypothalamus During Progesterone-Enhanced LH Surge in Estrogen-Primed Ovariectomized Rats.

“…The MBH has been well demonstrated to contain EAA receptors according to studies using immunocytochemistry [14,15], in situ hybridization [15,22], and binding assay [23,24]. Moreover, glutamate stimulates in vitro LHRH release from the ARC-ME fragments [16].…”

“…ity of LHRH neurons terminate. This is because the MBH has been demonstrated to be one of the major action sites of EAAs to stimulate LHRH release according to immunohistochemical studies [14,15] or an in vitro study showing the stimulatory effect of EAA on LHRH release from the arcuate nucleus-median eminence (ARC-ME) fragments [16]. Although a previous study reported that EAA release in the MBH does not increase during LH surges induced by E 2 treatment alone in OVX rats [17], it remains to be determined if EAAs increase during progesterone-enhanced LH surges in E 2 -treated OVX rats.…”

Multimodal Influence of Estrogen upon Gonadotropin-Releasing Hormone Neurons

“…223). Only small subpopulations of GnRH neurons in the rat have been reported to express NMDA and/or kainate receptors (228,229), and terminals containing glutamate have been demonstrated to synapse on GnRH neurons in the monkey (230). Neurons throughout the preoptic area and hypothalamus, including the AVPv, have been shown to express all three types of ionotropic excitatory amino acid receptors (223,231,232).…”

Expression of Glutamate Receptor Subunit mRNAs in Gonadotropin-Releasing Hormone Neurons during the Sexual Maturation of the Female Rat

“…to a lesser extent, by kainate receptors. However, it has been shown previously that less than 5% of GnRH neurons contain NMDAR1 mRNA [ 16,25,26] which encodes the common required subunit for a func tioning NMDA heteromeric glutamate receptor [27], al though recently the presence of NMDAR 1 immunoreactivity in certain GnRH neurons was reported [28]. In stead.…”

“…We have previously shown that GnRH neurons ex press several different glutamate receptor subunit mRNAs [16]. In the adult female rat, a subset of GnRH neurons expresses the kainate-preferring glutamate recep tor subunit KA2 (32% of GnRH neurons) or the NMDApreferring subunit NMDAR2A ( 17% of GnRH neurons).…”