A Golgi analysis of the primate globus pallidus. I. Inconstant processes of large neurons, other neuronal types, and afferent axons.

The present paper is a Golgi study, with high-power lenses, of the primate globus pallidus. Two kinds of inconstant processes of large neurons are first described: complex endings and thin processes. Complex endings are thick apparatuses terminally located on dendrites having many appendages of various types. Contacts were observed not only between striatal axons and these complex endings but also between complex endings and the soma, dendritic stems, dendritic portions or complex endings of other large pallidal neurons. Thin processes were usually beaded, very thin, and arose from any part of the dendritic tree. Contacts were seen between them and soma or dendrites of other large neurons. These thin processes were very similar to initial axonal collaterals and together constitute a common pool of processes. Complex endings and thin processes were essentially observed in the lateral nucleus of the pallidum where they apparently are evenly distributed inside the nucleus but randomly distributed on individual neurons. Two neuronal types other than large pallidal neurons were isolated: the smallest were considered to be local circuit neurons, while intermediate-sized neurons might be the origin of a particular efference. Many striatal axons gave no branches over long distances and collaterals were of two types and most frequently were short (less than 50 micron). Larger axonal arborization were rarely encountered. In addition to parallel contacts, numerous very short ones were observed. All these contacts between striatal axons and dendrites of large pallidal neurons seem to be irregularly distributed.