Neuronal nitric oxide synthase is permanently decreased in the cerebellum of rats subjected to chronic neonatal blockade of N-methyl-D-aspartate receptors.

Pharmacological blockade of the (NMDA) receptor at critical stages of brain development may have long-lasting effects on brain chemistry and on animal behavior. We report here experiments in which the competitive NMDA receptor antagonist CGP 39551 was administered to rat pups from postnatal day 7 (P7) to P18. The stage of treatment was selected to primarily target the cerebellum, whose granule cells undergo post-mitotic migration and establishment of synaptic connections during this period. We focused our study on the long-term consequences of CGP 39551 treatment on the neuronal isoform of nitric oxide synthase (nNOS) since nNOS is highly expressed in the cerebellum and it is functionally linked to the NMDA receptor. Treated rats exhibited a long-lasting (up to P70) decrease in the intensity of nNOS immunocytochemical staining in the cerebellar cortex accompanied by a decrement of calcium-dependent NOS catalytic activity. A comparable decrease of enzyme activity was measured in the cerebral cortex, but not in the hippocampus, of adult rats. Other neurochemical markers (glutamatergic, gabaergic, purinergic) and glutamine synthetase were unchanged, while a cholinergic marker was slightly increased in the cerebellum of CGP 39551 treated animals. Taken together these data show that blockade of NMDA receptor during the critical period of formation and stabilization of neuronal circuits preferentially affects long-term nNOS expression and catalytic activity in the cerebellum.