Differential regulation of the NMDA receptor by acute and sub-chronic phencyclidine administration in the developing rat

Neurodegeneration induced by the NMDA receptor antagonist, phencyclidine (PCP), has been used to model the pathogenesis of schizophrenia in the developing rat. Acute and sub-chronic administration of PCP in perinatal rats results in different patterns of neurodegeneration. The potential role of an alteration in the membrane expression of NMDA receptors in PCP-induced degeneration is unknown. Acute PCP treatment on postnatal day 7 increased membrane levels of both NMDA receptor subunit 1 (NR1) and NMDA receptor subunit 2B (NR2B) proteins in the frontal cortex; conversely, NR1 and NR2B protein levels in the endoplasmic reticulum fraction were decreased. Acute PCP administration also resulted in increased membrane cortical protein levels of post-synaptic density-95, as well as the activation of calpain, which paralleled the observed increase in membrane expression of NR1 and NR2B. Further, administration of the calpain inhibitor, MDL28170, prevented PCP-induced up-regulation of NR1 and NR2B. On the other hand, sub-chronic PCP treatment on postnatal days 7, 9 and 11 caused an increase in NR1 and NR2A expression, which was accompanied by an increase in both NR1 and NR2A in the endoplasmic reticulum fraction. Sub-chronic PCP administration did not alter levels of post-synaptic density-95 and had no effect on activation of calpain. These data suggest that increased trafficking accounts for up-regulation of cortical NR1/NR2B subunits following acute PCP administration, while increased protein synthesis likely accounts for the increased expression of NR1/NR2A following sub-chronic PCP treatment of the developing rat. These results are discussed in the context of the differential neurodegeneration caused by acute and subchronic PCP administration in the developing rat brain.