An Experimental Study of the Course and Termination of the Projection Fibers From Cortical Areas 4 and 6 in the Cat

Abstract

Summary The axon degeneration following cortical ablation of areas 4 and 6 of the cat has been traced in serial sections impregnated by the Nauta‐Gygax method. The results obtained are as follows: 1. The motor cortex projects ipsilaterally to the caudate nucleus, the putamen, the claustrum, the amygdaloid complex, the thalamic nuclei, the subthalamic nucleus, the zona incerta, the field of Forel, the substantia nigra, the red nucleus, the central gray, and to the superior and inferior colliculi. In addition to ipsilateral projections, the motor cortex has a few projections to the contralateral subcortical centers, that is the caudate nucleus, the putamen, the claustrum, the ventral thalamic nucleus, the red nucleus, the central gray and the suparior colliculus. 2. Practically no fibers from the motor cortex reach the motor nuclei of the cranial nerves except for the nucleus ambiguus and the nucleus of the accessory nerve, both of which appear to receive only a very few fibers. On the contrary, the motor cortex projects to some sensory nuclei of the cranial nerves such as the main sensory and spinal nuclei of the trigeminal nerve, the lateral and inferior vestibular nuclei and the nucleus of the solitary tract. 3. The motor cortex sends fibers profusely to the reticular formation and the nuclei pontis, and to a lesser degree to the gracile and cuneate nuclei. 4. The corticospinal tract is composed of the crossed and uncrossed lateral pyramidal tracts, and the crossed and uncrossed ventral pyramidal tracts. The crossed lateral pyramidal tract can be traced as far as the caudal end of the spinal cord, while the uncrossed terminates at the level of the third lumbar segment. The uncrossed anterior pyramidal tract reaches the levels from the third cervical to the second thoracic segment, but the crossed ends at the level of the third cervical segment. 5. The corticospinal tract sends fibers to the dorsal horn, the nucleus dorsalis, the intermediate zone and the lateral horn, but sends scarcely any fibers to the ventral horn and the substantia gelatinosa. 6. The corticobulbar and corticospinal tracts contain more numerous ipsilateral fibers than is generally thought. Moreover, it should be mentioned that very few crossed fibers appear to recross the midline and end in the dorsal column nuclei and the dorsal horn of the operated side. 7. The projection fibers from the motor cortex are generally classified into the pyramidal and the cortical extrapyramidal tracts. However, it is regarded as impossible to distinguish morphologically between these tracts. This work was aided by grants from the Ministry of Education for Scientific Rcsearch, for which the authors wish here to express their deepest thanks.

The interpretation of the degenerative changes in the intralaminar nuclei of the thalamus.

“…In the case of the intralaminar nuclei all the necessary conditions for transneuronal degeneration are present. First, the nature of the cellular change is entirely consistent with that described in sites where the degeneration is unquestionably transneuronal; secondly, there is now good evidence from a number of studies for a substantial projection from the cerebral cortex to these nuclei (Auer, 1956;Niimi, Kishi, Miki, and Fujita, 1963;Astruc, 1964;Petras, 1964;Mehler, 1966;Kuypers, 1966) and, thirdly, although a systematic study of the organization of the corticointralaminar projection has not yet been reported, the available evidence suggests that the arrangement of the cortical afferents to the intralaminar nuclei is in agreement with the distribution of the cellular changes in these nuclei after cortical lesions.…”

Strio-pallidal projection in the monkey.

“…Their additional finding that part of the projection from the internal segment is to the centromedian nucleus is of particular interest: first, because it may provide a 'circular pathway' from the striatum to the globus pallidus and thalamus, and back to the striatum; second, because of the substantial projection to the intralaminar nuclei of the thalamus (including the centromedian nucleus) from the cerebral cortex (Auer, 1956;Niimi, Kishi, Miki, and Fujita, 1963;Astruc, 1964;Petras, 1964;Mehler, 1966;Powell and Cowan, 1966). …”

Projections from the Cerebral Cortex to the Red Nucleus of the Guinea‐pig. A Retrograde Tracing Study

“…The cortical topography of CR projections in the guinea-pig shows many analogies with other mammals in which the CR pathway has been extensively studied using both anterograde and retrograde techniques. These studies indicate that most of the projections originate from the frontal cortex, and fewer from the parietal cortex in the rat (Flumerfelt and Gwyn, 1974;Gwyn and Flumerfelt, 1974;Brown, 1974;Hicks and D'Amato, 1975;Nah and Leong, 1976;Bernays et al, 1988), opossum Martin and Fisher, 1968;King et al, 1972), cat (Rinvik and Walberg, 1963;Niimi et al, 1963;Grofova, 1964;Rinvik, 1965;Mabuchi and Kusama, 1966;Kusama eta!., 1966;Massion, 1967;Mizumo et al, 1973;Padel et al, 1973;Oka and Jinnai, 1978;Saint-Cyr, 1987) and monkey (Kuypers and Lawrence, 1967;Humphrey and Rietz, 1976;Jones and Wise, 1977;Catman-Berrevoets et al, 1979;Hartmann-von Monakow et al, 1979;Humphrey et al, 1984). Some CR fibres arising from the Cg were also demonstrated in the rat (Bernays et al, 1988) and in the monkey (Humphrey er al., 1984).…”