Cortical projection of giant neostriatal neurons in the cat. Light and electron microscopic horseradish peroxidase study

Abstract

Following voluminous injections of horseradish peroxidase (HRP) in various neocortical fields, a small number of labeled large neurons are observed ipsilaterally in the putamen, striatal ponticuli, caudate nucleus, and nucleus accumbens septi. The bulk of the corticopetal cells are found in the putamen and in the striatal ponticuli. A more significant number of labeled neurons is encountered following injections in auditory and sensorimotor cortex, followed by the prefrontal and premotor cortex, very few cells project to the visual cortex. Ultrastructurally, the large HRP-labeled neurons display an eccentrically located, indented nucleus, abundant granular endoplasmic reticulum forming Nissl bodies, well developed Golgi zones, and numerous dense bodies. The simultaneous demonstration of retrogradely transported HRP and acetylcholinesterase (AChE) suggest that the large neurons are presumably cholinergic. These results provide evidence that at least some of the giant striatal neurons are efferent cells. The coincidence of cytological, histochemical, and hodological criteria invite the speculation that the giant corticopetal neostriatal neurons might be related to the magnocellular cholinergic groups of the basal forebrain (especially the Ch4 group).