The basilar pontine gray in the adult monkey (Macaca mulatta): A Golgi Study

Abstract

In Golgi preparations of the adult monkey(Macaca mulatta) two types of neurons are distinguished in the pontine gray: (1) larger neurons which impregnate most frequently and(2) smaller neurons which impregnate rarely. The former are judged to be projection neurons with myelinated axons because only the initial segments of their axons impregnate, while the latter are judged to be intrinsic neurons since they appear to participate only in the local circuitry of the pontine gray. The projection neurons show a variety of sizes and shapes and are the equivalent of the large, medium and small neurons that Ramón y Cajal ('09) illustrated in the pons of the 5-day-old infant. Their cell bodies are rounded, polygonal, triangular, egg-, pear-, and spindle-shaped. Some have somatic spines. Usually four to seven dendrites issue from the cell body and as they branch they attenuate. The dendrites have knobby, nodular protuberances which give them a gnarled appearance. Also the dendrites have a few scattered spines. In most instances the dendrites have a wavy recurring pattern. Neurons pressed against the corticospinal, corticopontine fiber bundles frequently have elongated cell bodies and the dendrites sprouting from them form tight, brush-like arrays. The intrinsic neurons have small ellipsoid or pear-shaped cell bodies and two to three long dendrites, which do not taper. In some impregnations short axons issuing from the cell body were found and in other impregnations several widely separated, short axon-like processes were found on dendrites. A striking feature of the intrinsic neurons is the presence of stalked dendritic appendages bearing one or more bulbous bodies, 1 to 3 microns in diameter. The intrinsic neurons in no way resemble the hairy or mossy cells with short axis cylinders that Ramón y Cajal ('09) described in the pons of the 5-day-old infant. The latter were not found in the present material.