Expression levels of Egr-1 and Nur77 proteins in mouse brain are increased by withdrawal of nicotine

Several reports on different in vitro and in vivo models have revealed neuroprotective effects afforded by nicotine treatment. Nicotine is a cognitive enhancer that acts by increasing vigilance and improving learning and memory. We previously reported that nicotine withdrawal up-regulated transcription of some immediately early genes (IEGs), apoptosis-related genes, and signal transduction-related genes in cultures of pheochromocytoma PC12 cells, which are of neuronal lineage (Ichino et al., 1999; Ichino et al., 2002; Yamada et al., 2005). Especially, nicotine withdrawal increased the levels of Bag-1, Rab2, Hsp70, and Raf1 proteins in the cerebral cortex, hippocampus, and striatum in vivo in mice. Egr-1 and Nur77 protein levels were dramatically increased by nicotine withdrawal. (Yamada et al., 2006). Also, there is a study that analyzed the expression of mRNAs by in situ hybridization using a rat genome array after acute intermittent nicotine treatment and found that some mRNA levels of them (Nr4a1, Egr-1 and Egr-2) are significantly up-regulated in the rat cerebral cortex and hippocampal regions (Belluardo et al., 2005). In the present study, we aimed at further elucidating the effects of nicotine withdrawal on the expression of the upstream proteins of IEGs in the brain of mice after chronic administration of nicotine. We observed significant increases in the protein levels of Egr-1 and Nur77 in the specific regions and in specific cells in the mouse brain by Western blot analysis and by immunohistochemistry. The present results suggest that such changes may also occur in the brain of smokers during abstaining from smoking and may be related to some of their symptoms of nicotine withdrawal.