Smooth and sparsely‐spined stellate cells in the visual cortex of the rat: A study using a combined golgi‐electron microscope technique

Abstract

The visual cortex of the rat was impregnated by the rapid Golgi procedure. From these preparations, smooth (spine‐free) and sparsely‐spined multipolar stellate cells with well impregnated axons were selected and drawn in the light microscope using a camera lucida. Five suitably impregnated cells were then gold‐toned and deimpregnated by removal of the silver chromate produced by the Golgi impregnation, so that they could be examined in the electron microscope to determine both their cytological features and their pre‐ and postsynaptic relationships. A sixth neuron was not deimpregnated, and was examined in the electron microscope only to evaluate the types of synapses formed by its axons terminals. Five of these cells had extensive local axonal plexus and the sixth had a plexus which was less profuse. In the electron microscope the various portions of the deimpregnated neurons were readily identified by their content of fine gold particles, and it was found that their perikarya possessed a rather dark cytoplasm containing many ribosomes. Both symmetric and asymmetric synapses were present on the perikarya, and some of the perikarya had spines. The dendrites of the cells had relatively smooth contours and contained rather closely packed microtubules. The dendrites also had both symmetric and asymmetric synapses along their shafts, with the symmetric synapses being more frequent on the proximal portions of the dendrites. The axons of the neurons were unmyelinated and all of them formed symmetric synapses with their postsynaptic partners. The synapses occurred at dilatations of the axons at both en passant and terminal boutons. Neuronal elements identified as being postsynaptic to the axon terminals of the stellate cells included the perikarya and apical dendritic shafts of pyramidal neurons, the perikarya and dendritic shafts of other stellate cells, and an axons initial segment. Reasons are given for concluding that these multipolar, smooth and sparsely‐spined stellate cells are inhibitory in function, and their relationships with some other neuronal components of the rat visual cortex are considered.