Sexually dimorphic development and binding characteristics of NMDA receptors in the brain of the platyfish

This study investigated age- and gender-specific variations in properties o f the glutamate N-methyl-D-aspartate receptor (NMDAR) in a freshwater teleo st, the platyfish (Xiphophorus maculatus). Prior localization of the immuno reactive (ir)-R1 subunit of the NMDAR protein (R1) in cells of the nucleus olfactoretinalis (NOR), a primary gonadotropin-releasing hormone (GnRH)-con taining brain nucleus in the platyfish, suggests that NMDAR, as in mammals, is involved in modulation of the platyfish brain-pituitary-gonad (BPG) axi s. The current study shows that the number of cells in the NOR displaying i r-R1 is significantly increased in pubescent and mature female platyfish wh en compared to immature and senescent animals. In males, there is no signif icant change in ir-R1 expression in the NOR at any time in their lifespan. The affinity of the noncompetitive antagonist (H-3)MK-801 for the NMDAR is significantly increased in pubescent females while maximum binding of(H-3)M K-801 to the receptor reaches a significant maximum in mature females. In m ales, both MK-801 affinity and maximum binding remain unchanged throughout development. This is the first report of gender differences in the associat ion of NMDA receptors with neuroendocrine brain areas during development. I t is also the first report to suggest NMDA receptor involvement in the deve lopment of the BPG axis in a nonmammalian vertebrate. (C) 1999 Academic Pre ss.