POSTNATAL CHANGES IN NMDAR1 SUBUNIT EXPRESSION IN THE RAT TRIGEMINAL PATHWAY TO BARREL FIELD CORTEX

N-methyl-D-aspartate (NMDA) type glutamate receptors are constituted o f one obligatory subunit (NR1), expressed as eight splice variants, co mbined with one or more of four NMDAR2 subunits. Polyclonal antibodies were produced to an N-terminal domain of the NR1 subunit that recogni ze all eight splice variants. The antibody was used to localize NR1 in the trigeminal pathway to barrel field cortex in rats. The distributi on and density of NR1 changes between birth (postnatal day 0 = P-0) an d P-360. The trigeminal nuclei already contain a high level of NR1 imm unoreactivity on the day of birth. The ventral posterior lateral, vent ral posterior medial, and posterior nucleus, medial division, thalamic nuclei show fluctuations in NR1 immunoreactivity levels, starting at birth with moderate densities in neuropil which decrease at P-7, and p eak again in neuronal cell bodies as well as the:neuropil at P-21. In the cortex, the density of NR1 in layer VI fluctuates with low points at P-7 and P-40. Superficial cortical layers I, II, and III reach adul t levels at P-14 and remain high. NR1 levels decrease sharply in layer TV just prior to P-40 and then slowly recover over the next 3 months to stabilize at moderate levels in the adult. In addition to neuronal expression there is a transient high level of labeling in glial cells with a peak density of staining at P-21. The results emphasize that NR 1 subunit expression is finely regulated in rat somatic sensory pathwa ys for periods as long as 7-8 weeks after birth in the barrel field co rtex. (C) 1996 Wiley-Liss, Inc.