DEVELOPMENTAL AND REGIONAL EXPRESSION PATTERN OF A NOVEL NMDA RECEPTOR-LIKE SUBUNIT (NMDAR-L) IN THE RODENT BRAIN

A novel NMDA receptor-like (NMDAR-L) cDNA was isolated that contained an open reading frame coding for a predicted polypeptide of 1115 amino acids that shares similar to 27% identity with NMDA receptor subunits . In situ hybridization experiments indicated that NMDAR-L mRNA was ex pressed in the developing rodent CNS. On postnatal day 1 (P1), NMDAR-L mRNA expression was pronounced in the entorhinal cortex, the subiculu m and the thalamus, in layer V of the developing neocortex, in the sup erior and inferior colliculi, and various regions of the hindbrain, ex cluding the cerebellum. On P5, NMDAR-L mRNA was expressed in layer V o f the neocortex, in the entorhinal cortex, in the subiculum, and in th e thalamus. On P14, NMDAR-L mRNA was expressed in layers II-VI of the neocortex, in the entorhinal and piriform cortex, in the subiculum and CA1 field, and in the nucleus of the lateral olfactory tract. In the adult brain, NMDAR-L mRNA was detected predominately in the nucleus of the lateral olfactory tract. Injection of NMDAR-L cRNA into Xenopus o ocytes did not lead to the expression of homomeric glutamate-activated channels. However, coinjection of the triple combination of NMDAR-L w ith NMDAR1 and NMDAR2B cRNAs led to a striking decrease in the current magnitude compared to currents obtained after coexpression of the dou ble combination of NMDAR1 with NMDAR2B. While the function of NMDAR-L remains to be established, its developmental and regional expression p attern suggests that NMDAR-L may influence axonal outgrowth and synapt ogenesis during brain development.