MESSENGER-RNA DISTRIBUTION WITHIN DENDRITES - RELATIONSHIP TO AFFERENT INNERVATION

The majority of neuronal mRNAs are confined to cell bodies, but a few mRNAs are present at high levels in dendrites, Here we report an initi al analysis of the relationship between afferent innervation and the d istribution of mRNA within dendritic fields. In situ hybridization tec hniques were used to compare the subcellular distribution of dendritic mRNAs in principal neurons of the hippocampal formation in vivo, The mRNA encoding the alpha subunit of calcium/calmodulin dependent protei n kinase II (CAR III kinase) was present at high levels throughout the layers that contain the dendrites of hippocampal pyramidal cells and dentate granule cells, In contrast, the mRNA encoding the high molecul ar weight microtubule-associated protein MAP2 had a more limited distr ibution, In the dentate gyrus, labeling for MAP:! was present in a dis crete band in the lamina containing proximal dendrites and decreased t o low levels in laminae containing distal dendrites, This laminar patt ern resembles the distinct terminations of the commissural/association al projection (high MAP2 labeling) and the entorhinal projection (lowe r MAP2 labeling) upon dendrites of granule cells, To determine if the differential distribution of dendritic mRNAs was regulated by either t he presence or activity of afferents, we evaluated mRNA distribution i n the dentate molecular layer following (1) removal of the entorhinal input by lesions of the entorhinal cortex or (2) prolonged delivery of potentiating stimulation to entorhinal afferents. Denervation led to modest decreases in the levels of mRNAs for both CAMII and MAP2 but di d not lead to detectable alterations in mRNA distribution. Also, prolo nged stimulation did not lead to detectable alterations in MAP2 or CAM II mRNA distribution, although such stimulation clearly elevated the e xpression of mRNA for glial fibrillary acidic protein (GFAP). (C) 1995 John Wiley and Sons, Inc.