Spatial sampling by dendritic trees in visual cortex

Kittens were reared in vertically or horizontally striped cylinders. After rearing exposures of 400-500 h, responses of single neurons were determined as a function of orientation of a square wave grating stimulus. These data suggest that the rearing environment did alter orientation preference in some of the kittens. The visual cortices of the stripe-reared kittens and of control kittens were impregnated according to a Golgi-Cox method. Dendrites of layer IV stellate cells were tracked and analyzed in three dimensions by a computer-microscope. Four methods of analyzing the spatial distribution of dendrites are described and discussed. Two methods previously described in the literature^9,31 were not sufficiently sensitive to detect any differences among kittens exposed to vertical or horizontal stripes or to a control environment. Two newly developed methods were able to provide initial evidence for rearing effects on dendritic trees in visual cortex. The more detailed of these new methods describes the angular location of dendritic segments, with respect to standard brain axes, as a function of distance from the cell body. Data obtained by means of this method of dendritic angular distribution (DAD) plots suggests a number of conclusions. Rearing animals in a striped environment may influence the way in which dendrites of layer IV stellate cells of visual cortex distribute themselves in the neuropil. The effect of selective rearing on dendritic distribution does not appear to extend back to those portions of the dendritic tree closest to the cell body. This influence of rearing in a selective environment may be explained by hypothesizing that during development dendrites distribute themselves in ways that tend to maximize the effects of spatio-temporal summation for the postsynaptic neurons.