Perikaryal projections of spinal ganglion neurons: quantitative differences between membrane domains in contact with different microenvironments.

The perikarya of spinal ganglion neurons display numerous slender projections. In the present investigation we have studied whether the extent of these projections is uniform over the entire perikaryal surface or whether there is a difference between the regions of the perikaryon in contact with different microenvironments. In spinal ganglia of the rat and the lizard we have analysed about 200 neuronal cell bodies arranged in pairs and have compared the extent of the projections quantitatively in the areas of interneuronal contact with that in the areas of neuron-to-satellite cell contact. In both species we have found that the projections are present over the entire perikaryal surface and that the overall development of the perikaryal projections is significantly greater in those portions of the surface in contact with satellite cells than in the portions in contact with another neuron. On the basis of these observations we conclude that the outgrowth of perikaryal projections is an intrinsic property of the nerve cell body which is manifested over the entire perikaryal surface; there is, however, an extrinsic influence from the microenvironment of the neuron, which may account for the quantitative differences in different domains of the perikaryal surface.