Differential regulation of cortical NMDA receptor subunits by sensory learning.

NMDA receptor is an important player in neuronal plasticity, including cortical reorganization. In the adult cerebral cortex, the receptor properties are regulated by relative expression of NR2A and NR2B subunits. We have previously found that 3 days of sensory conditioning, in which stimulation of whiskers was paired with a tail shock, induce NMDA-receptor-dependent expansion of metabolically labeled cortical representations of the stimulated vibrissae. Here, we examined the effect of learning-induced cortical reorganization upon expression of NR2A and NR2B NMDA receptor subunits. An increase in NR2A mRNA expression in the barrel of the "trained" row of vibrissae was observed with in situ hybridization 24 h after sensory conditioning. NR2B mRNA expression level did not change. Protein level of both regulatory subunits and obligatory NR1 subunit were examined in P2 fraction. NR2A protein level was found elevated 1 h and 24 h after the sensory conditioning, but not in controls which received only whisker stimulation, signifying that the change was associated with cortical map reorganization. NR2B protein level was transiently elevated in both trained and stimulated control groups. NR1 protein level did not change. The results show that simple sensory learning induces a change in expression of regulatory NMDA receptor subunits, indicating a potential for receptor channel properties modification.