Regional ontogeny of a unique glutamate recognition site in rat brain: An autoradiographic study

The developmental pattern of L-[3H]glutamate binding to rat brain in the presence of saturating concentrations of unlabeled N-methyl-D-aspartate (NMDA), kainate (KA) and quisqualate (QQA) was examined in an autoradiographic assay. The unique glutamate binding site defined by this assay displayed four distinct, regionally specific patterns of development. (1) In reticular nucleus of thalamus there was an initial very high level of binding at postnatal day 1 (PND1) followed by a progressive 80% decline in binding during maturation. (2) In entorhinal cortex, a progressive 500-1100% increase in binding was seen during development. (3) In ventral posterior medial nucleus of thalamus, there was an initial transient 200-300% increase in binding, peaking at PND10, followed by a steady decline in binding. (4) In frontal cortex, binding remained relatively stable throughout development. At all stages of development, the distribution of these recognition sites was different from NMDA, KA or QQA receptors. The function of this glutamate binding site remains to be determined, but the distinct regional and temporal patterns of binding suggest that it may be important in normal development of the central nervous system.