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

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