Odor regulates the expression of the mitogen-activated protein kinase phosphatase gene hVH-5 in bilateral entorhinal cortex-lesioned rats

Since it is known that several immediate early genes are induced by olfacto ry stimuli, we determined whether an olfactory stimulus also induces the ex pression of the mitogen-activated protein kinase (MAPK) phosphatase gene hV H-5 (homologue of vaccinia virus H1 phosphatase gene, clone 5), a member of a novel class of immediate early genes encoding dual-specificity protein p hosphatases. The expression was studied by in situ hybridization in differe nt brain structures involved in odor processing, in control and bilateral e ntorhinal cortex (EC) lesioned rats. EC-lesion did not significantly affect hVH-5 gene expression in the glomerular cell layer of the olfactory bulb ( OB), while odor stimulation induced it in both control and EC-lesioned grou ps. In contrast, odor-induced expression of hVH-5 gene in mitral/granular c ell layers was only evident after lesion of the EC. Similar results were ob tained in the piriform cortex (PCx), a structure intimately connected to th e mitral cell layer. In the CA1 hippocampal subfield, odor stimulation indu ced hVH-5 gene expression in both control and EC-lesioned animals, the incr ease being potentiated in lesioned rats. CA3 and dentate gyrus exhibited a similar pattern of gene expression, the odor stimulating gene expression in both control and lesioned groups. The amygdala (Am) displayed no significa nt change. It appears that through the induction of a MAPK phosphatase, the EC controls MAPK activities differently after odor stimulation in OB, PCx and hippocampus (Hip). The results illustrate: the notion that odor represe ntation in the brain requires plastic modifications at both anatomical and functional levels. (C) 2000 Elsevier Science B.V. All rights reserved.