Littermate pairs of male Long-Evans hooded rats, reared in social groups from weaning, were placed in either a complex or an isolated environment for 12 weeks beginning at 145 days of age. Fifteen Golgi-Cox stained neurons of each cell type-layer III pyramidal, layer IV stellate, and layer V pyramidal apical dendrites-were traced with the aid of a camera lucida from six littermate pairs. Both apical oblique branches and basilar terminal dendrites of layer III pyramidal neurons were significantly longer in animals exposed to the complex environment. In layer IV stellates, there was a significant increase in the number of first order dendrites after the complex environment as well as a tendency toward longer terminal branches which was significant for fifth-order branches. No differences in either length or number were seen in the layer V apical obliques. This study demonstrates that adult visual cortex neurons do change after exposure to differential environments, but that changes are not seen in every cell population.
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