THE PROCESS OF REINNERVATION IN THE DENTATE GYRUS OF ADULT-RATS - GENE-EXPRESSION BY NEURONS DURING THE PERIOD OF LESION-INDUCED GROWTH

Neurons in the hippocampal dentate gyrus are extensively reinnervated following the destruction of their normal inputs from the ipsilateral entorhinal cortex (EC). The present study evaluates gene expression by dentate granule neurons and the neurons giving rise to the sprouting connections during the period of synapse growth. Adult male rats were prepared for in situ hybridization at 2, 4, 6, 8, 10, 12, 14, 20, and 30 days following unilateral EC lesions. Sections were hybridized usin g S-35-labeled cRNA probes for mRNAs that encode proteins thought to b e important for neuronal structure and/or synapse function, including (1) mRNAs that are normally present in dendrites-the mRNAs for the hig h molecular weight microtubule-associated protein 2 (MAP2) and the alp ha-subunit of calcium/calmodulin-dependent protein kinase II (CAMII ki nase), (2) mRNAs that are upregulated in neurons that are regenerating their axons (T alpha 1 tubulin and F1/GAP43) and (3) mRNAs for protei ns that are the principal constituents of neurofilaments and microtubu les (the low molecular weight neurofilament protein NF68 and beta-tubu lin). Although there were small changes in the levels of labeling for the mRNAs that are normally present in dendrites, there were no dramat ic increases in the levels of any of the mRNAs either in dentate granu le cells or in neurons giving rise to the reinnervating fibers at any postlesion interval. These results indicate that neurons in mature ani mals can substantially remodel their synaptic terminals and their dend rites in the absence oflarge-scale changes in gene expression (at leas t as measured by steady-state mRNA levels at various time points). (C) 1995 Wiley-Liss, Inc.