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 proj ections. In the present investigation we have studied whether the exte nt 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 ar ranged in pairs and have compared the extent of the projections quanti tatively in the areas of interneuronal contact with that in the areas of neuron-to-satellite cell contact. In both species we have found tha t the projections are present over the entire perikaryal surface and t hat the overall development of the perikaryal projections is significa ntly greater in those portions of the surface in contact with satellit e cells than in the portions in contact with another neuron. On the ba sis 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 e xtrinsic influence from the microenvironment of the neuron, which may account for the quantitative differences in different domains of the p erikaryal surface.