Deafferentation-induced c- fos gene expression in subthalamic nucleus and substantia nigra reticulata is reduced by non-NMDA receptor antagonist

Abstract

Molecular events underlying the mechanism by which brain injury elicits delayed transneuronal degeneration ofneurons remote from the site of initial injury are not well understood. In rats, acute injury of the caudate nucleus (CN) and globus pallidus (GP) by local injection of excitotoxic ibotenic acid (IA) or by transient forebrain ischemia resulted in delayed cell death of neurons in the substantia nigra reticulata (SNr). To elucidate the involvement of glutamate receptor mediated hyperactivity of neurons produced by loss of inhibitory inputs in this delayed degeneration of SNr neurons, the region-specific expression of an immediate early gene, c- fos, and the effect of glutamate receptor antagonists on the c- fos expression were examined by using immunocytochemical and in situ hybridization analysis. Following unilateral IA-injection into the CN and GP, a robust expression of c- fos mRNA and Fos protein was induced specifically in neurons of both subthalamic nucleus (STN) and SNr deafferented by the IA-lesions 36 h after IA-injection. The delayed expression of Fos-protein in S,Nr neurons lasted for 48 h longer than that in STN neurons. Following unilateral IA-injection confined to the CN, an intense but short-term expression of Fos-protein was exhibited only in neurons of the deafferented SNr. c- fos mRNA and Fos protein were not expressed in neurons of the substantia nigra compacta at any time points examined. The induction of c fos mRNA and Fos protein in neurons of the: STN and SNr following IA-lesions of the CN and GP was reduced markedly by non-NMDA receptor antagonist (GYKI52466), but not by NMDA receptor antagonist (MK-801). The region-specific c fos expression implies that deprivation of inhibitory afferents (disinhibition) due to destruction of presynaptic neurons can induce increased activity of postsynaptic neurons. The effect of GYK152466 on the c- fos gene expression in neurons of the deafferented STN and SNr suggests that activation of non-NMDA receptors may be involved in a pathophysiological cascade for the transneuronal degeneration of SNr neurons.