Gene expression in developing rat hippocampal pyramidal neurons appears independent of mossy fiber innervation

In the rat, neonatal gamma-irradiation of the hippocampus induces a selecti ve destruction of dentate granule cells and prevents the development of the mossy fiber-CA3 pyramidal cell connection. In the absence of mossy fiber input, the CA3 pyramidal neurons exhibit morp hological alterations and rats deprived of dentate granule cells fail to de velop kainate-induced epileptic activity in the CA3 pyramidal neurons. Neon atal elimination of the granule cells also impairs learning and memory task s in adult rats. In the present work, we assessed by in situ hybridization and semi-quantitative RT-PCR, whether in the pyramidal layers, the absence of mossy fiber input alters the expression of a number of genes involved in activity-dependent signal transduction, in GABAergic neurotransmitter sign aling and in neurite development via microtubule organization. Surprisingly , we show that the expression and the developmentally regulated alternative splicing of the genes we examined in the developing hippocampus are not al tered in the pyramidal neurons, whether the dentate granule afferents are p resent or absent. Our results suggest that in the CA3 pyramidal layer, the developmental expression patterns of the mRNAs we studied are independent o f extrinsic cues provided by mossy fiber input. (C) 1999 Published by Elsev ier Science Ltd. All rights reserved.