Spatio-temporal pattern of N-methyl-D-aspartate receptor NR1 mRNA expression during postnatal development of visual structures of the rat brain.

N-methyl-D-aspartate (NMDA) excitatory amino acid receptors (NMDAR) play a pivotal role in various physiological and pathological responses of the central nervous system (CNS), including such phenomena of neuronal plasticity as cortical development. Hence, it could be suggested that expression of genes coding for NMDAR components can be differentially regulated throughout the development. To test this notion we analyzed with in situ hybridization mRNA levels of NMDAR subunit designated as NR1, during time of development (1-6 weeks postnatally) spanning the critical period of functional formation of major visual structures of the rat brain, namely visual cortex (VC), superior colliculus (SC), and lateral geniculate nucleus (LGN). The highest levels of NR1 mRNA were found in the VC and SC at the onset of the critical period, i.e., 21 days postnatally, whereas in the LGN a tendency toward a similar pattern of expression was observed. Analysis of spatial distribution of NR1 mRNA in the SC and VC revealed that an adult-like laminar pattern of expression was also achieved between 14 and 21 days postnatally. This pattern of expression corroborates with developmentally regulated changes in an overall density of cell bodies in these areas.