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MK‐801–induced expression of Fos protein family members in the rat retrosplenial granular cortex

The N‐methyl‐d‐aspartate (NMDA) receptor antagonist MK‐801 has been shown to induce an acute Fos and Fos‐related antigen (Fra) expression in the rat retrosplenial granular cortex (RSG), but the exact composition of the Fos protein family and their individual dynamic alterations are unknown. We examined this issue using immunocytochemistry and Western blot analysis with two antibodies that recognize, respectively, Fos and all the identified members of Fos protein family. Immunocytochemistry detected a rapid and transient expression of Fos proteins in some RSG neurons and a delayed and prolonged expression of Fra proteins in most RSG neurons following a single systemic MK‐801 injection (1 mg/kg). Multiple MK‐801 injections (i.e., ten consecutive injections once every other day; 1 mg/kg) produced a moderate Fra expression but failed to induce detectable Fos expression. Western blot analysis further showed a transient expression of 72‐kDa Fos proteins following a single MK‐801 injection and a prolonged expression of 46‐ and 43‐kDa Fra proteins after either a single or multiple MK‐801 administration. The delayed onset and prolonged expression of these Fra proteins suggest that they may be ΔFosB. The possible relevance of these results to clinical psychotomimetic effects of the NMDA receptor antagonists phencyclidine and ketamine is discussed. J. Neurosci. Res. 57:719–729, 1999. © 1999 Wiley‐Liss, Inc.