The cortico‐nigral projection in the cat an experimental study with silver impregnation methods

Abstract

Following lesions of various parts of the cerebral cortex in cats the terminal distribution of cortico-nigral fibers has been studied by means of silver impregnation methods. A modest number of cortico-nigral fibers have been traced from the gyrus proreus, the "supplementary motor" area, the "primary sensory-motor" area and the "secondary sensory" area. Lesions of the remaining regions of the cerebral cortex did not give rise to terminal degeneration in the substantia nigra. The number of cortico-nigral fibers was considerably less than expected from the data available in the literature.The cortico-nigral projection system is chiefly homolateral. A few crossed corticonigral fibers were found following lesions of the gyrus proreus or the "supplementary motor" area. The majority of the corticofugal fibers from these two cortical regions and the "secondary sensory" area terminate on the somata or the proximal dendrites of the cells in the nigra complex. Following lesions of the "primary sensorymotor" area of the cerebral cortex, terminal degenerating fibers were only seen in the neuropi1 of the substantia nigra. The findings are discussed briefly.The substantia nigra is a nuclear complex whose afferent and efferent fiber connections have been a matter of controversy and dispute for decades. However, it seems to be generally agreed that the substantia nigra in animals and man is related to the cerebral cortex, in that it receives fibers from various cortical areas (Muratoff,

Effects of Frontal Motor Cortex Ablation on the Ultrastructure of Cat Substantia Nigra

“…In a different set of experi ments where only the parietal parts of the cortex around the sulcus lateralis and sulcus ansatus were removed, we could not find any terminal degeneration, although in caudate nucleus, putamen and fundus striati (nucleus accumbens) numerous degenerated elements were found [Hassler et al 1978], Our results agree with the light microscopic findings of Rinvik [1966] and Afifi et al [1974] who show degenerating terminal fibers mainly in the medial and medio-lateral part of the nigra pars compacta. Especially after ablation of the prefrontal cortex (gyrus proreus) and the supplementary motor area degenerations were observed also in the contrala teral nigra [Rinvik, 1966]. Such a bilateral projection is now confirmed by our results.…”

Human GABAA receptors on dopaminergic neurons in the pars compacta of the substantia nigra

“…Striatonigral fibers mainly terminate in the pars reticulata, few striatal fibers also on the dendrites of SNc extending into the pars reticulata. Afferents to SNc neuronal somata projecting from cortex, globus pallidus, amygdala, hypothalamus, the raphe nuclei, and the habenula have been discussed controversially (Rinvik, 1966; Mehler, 1981; Parent et al, 1994; Parent and Hazrati, 1995). From our data, it seems possible that GABA A receptors of human SNc neurons may participate in a negative feedback by means of the accessory striatal circuit that originates from SNc dopaminergic cells, which may establish direct synaptic contacts with striatonigral projection neurons (Andén et al, 1964; Nieuwenhuys et al, 1988; Tanaka et al, 1982; Freund et al, 1984).…”

Observations on the fine structure of the substantia nigra in the cat

“…From light microscopical studies of routinely stained histological sections it has been argued that the substantia nigra in animals and man is composed of two morphologically distinct parts: the cell-rich pars compacta and the cell-poor pars reticulata (for references see Rinvik, 1966). This subdivision, furthermore, seems to gain substantial support from experimental studies on its afferent fibre connections in animals (Voneida, 1960;Szabo, 1962Szabo, , 1967Szabo, , 1969Nauta and Mehler, 1966 ;Cowan and Powell, 1966).…”