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Corticospinal fibers in the raccoon
SHORT COMMUNICATIONS
195
Corticospinal fibers in the raccoon Cerebral cortical ablations made unilaterally with suction were placed in the motor cortex (area gigantopyramidalis of Brodmann) of the raccoon (Procyon lotor). The resulting fiber degeneration was studied utilizing the Nauta method. Fiber degeneration in the gray matter of cervical, ilumbosacral and coccygeal segments is: (a) abundant contralaterally in the external basilar region of the dorsal horn, the internal basilar region ventromedially and the lateral and central parts of the zona intermedia, and (b) modest in the area centralis of the ventral horn in intumescential segments, while sparser still in areas mediodorsalis and medioventralis. In the Ca and the T1 segments,sparse degenerated fibers are found among contralateral motor neurons. A parallel situation of lesser degree is encountered in sacral segments. Motor neurons were identified by the presence of chromatolysis following brachial plexus and lumbosacral plexus or sciatic nerve crushes. The proportion of degenerated fibers in motoneuronal cell groups is very small when compared with cortical fiber degeneration in the medial part of the ventral horn and more especially, the zona intermedia. Since very limited numbers of motor neurons appear to be associated with degenerated cortical fibers, it is problematical whether these fibers terminate upon the perikarya or dendrites of motor neurons or whether they terminate upon outlying dendrites of propriospinal neurons. We believe that we have consistently found degenerated fibers juxtaposed to the perikarya (Figs. 2 and 4) and dendrites of chromatolytic cells. Unlike motor cortex ablations, lesions of the raccoon's somatosensory cortex did not result in fiber degeneration among motor neurons. We have compared the motor corticospinal fiber connections of the raccoon with those of the cat and found that in the cat these fibers do not appear to cross the cytoarchitecturally defined limits of motoneuronal groups. In the raccoon, a limited infiltration of motoneuronal cell groups by degenerated cortical fibers occurs and these fibers are distributed among the dorsolaterally situated motor neurons in the Ca, T1 and sacral segments (Figs. 1-4). The findings in the raccoon were also compared with the distribution of motor corticospinal fibers in the spider and rhesus monkeys, gibbon and chimpanzee 7. In accord with earlier reports on the corticospinal fiber distribution in primates 2-4, large numbers of cortical fibers invading the motoneuronal cell groups could be identified in these species in all intumescential segments, in a distribution suggesting telmination on perikarya as well as dendrites of motor neurons. From the findings considered here it is tempting to conclude that direct corticomotoneuronal connections are absent in the cat, abundant in several species of primates, and limited in number and segmental distribution in the raccoon. It should, however, be emphasized that this conclusion refers solely to corticalfibers extending to within the boundaries of motoneuronal cell groups. No experimental finding reported thus far has eliminated the possibility that even in the cat some cortical fibers at least terminate on motoneuronal dendrites protruding well outside the perikaryal grouping 1,5,6. Any categorical statement of presence versus absence of direct cortico-motoneuronal connections must therefore be made subject to the reservation that future findings may prove the actual difference to be one of termination on motoneuronal Brain Research, 3 (1966) 195-197
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SHORT COMMUNICATIONS
Figs. 1-4. High-power photomicrographs of degenerated cortical fibers among spinal motor neurons in the raccoon. Suggestive axodendritic relationships are illustrated in Fig, I taken from the sacral spinal cord ( x 484). Arrows with bent shafts point to a large dendrite of a motor neuron; arrows with straight shafts label degenerated axonal fragments. Degenerated fibers among motor cells in the TI segment are illustrated in the other figures, along with chromatolytic motor neurons in Figs. 2 ( x 475) and 4 ( x 285).
Brain Research, 3 (1966) 195-197
SHORT COMMUNICATIONS
197
perikarya and proximal dendrites in some m a m m a l i a n forms (.primates) as against synaptic contacts only on distal dendritic segments in others (cat). The present findings suggest that the m o d e o f corticospinal fiber termination in relation to m o t o r neurons in the r a c c o o n is somewhat similar, at least qualitatively, to that observed in m a n y primates. In conclusion, corticospinal fibers originating in the m o t o r cortex o f the r a c c o o n converge in great numbers u p o n the spinal neurons in basilar regions of the dorsal horn and zona intermedia; few fibers are f o u n d in the medial part o f the ventral horn. In addition, sparse cortical efferents selectively distributed a m o n g the more caudal m o t o r neurons o f the cervical and lumbosacral intumescentia have been found. Depts. of Neuroahysiology and Experimental Surgery, Walter Reed Army Institute of Research, Washington, D.C. (U.S.A.)
J.M. PETRAS RALPH A. W. LEHMAN
1 CHAMBERS,W. W., AND LtU, C.-N., Cortico-spinal tract of the cat. An attempt to correlate the pattern of degeneration with deficits in reflex activity following neocortical lesions, J. coma. Neurol., 108 (1957) 23-55. 2 KuYV~Rs,H. G. J. M., Some projections from the peri-central cortex to the pons and lower brain stem in monkey and chimpanzee, J. coma. Neurol., 110 (1958) 221-255. 3 KOYPERS,H. G. J. M., The descending pathways to the spinal cord, their anatomy and function. In J. C. ECCLESANDJ. P. SCHADI~(Eds.), Organization of the Spinal Cord, Progress in Brain Research~ Vol. 11, Elsevier, Amsterdam, 1964, pp. 178-202. 4 LItI, C.-N., ANDCHAMaERS,W. W., An experimental study oft he corticospinal system in the monkey (Macaca mulatta). The spinal pathways and preterminal distribution of degenerating fibers following discrete lesions of the pre- and postcentral gyri and bulbar pyramid, J comp. Neurol., 123 (1964) 257-284. 5 NYBERG-HANSEN,R., AND BRODAL,A., Sites of termination of corticospinal fibers in the cat. An experimental study with silver impregnation methods, J. coma. Neurol., 120 (1963) 369-391. 6 PETRAS,J. M., The descending pathways and terminal distribution of cortical, tectal and tegmental fibers to the spinal cord in the cat, Anat. Rec., 145 (1963) 271. 7 PETRAS,J. M., Corticospinal fiber connections in spider and rhesus monkeys, gibbon and chimpanzee: some preliminary notes, Anat. Rec., 154 (1966) 402. (Received August 12th, 1966)
Brain Research, 3 (1966) 195-197
195
Corticospinal fibers in the raccoon Cerebral cortical ablations made unilaterally with suction were placed in the motor cortex (area gigantopyramidalis of Brodmann) of the raccoon (Procyon lotor). The resulting fiber degeneration was studied utilizing the Nauta method. Fiber degeneration in the gray matter of cervical, ilumbosacral and coccygeal segments is: (a) abundant contralaterally in the external basilar region of the dorsal horn, the internal basilar region ventromedially and the lateral and central parts of the zona intermedia, and (b) modest in the area centralis of the ventral horn in intumescential segments, while sparser still in areas mediodorsalis and medioventralis. In the Ca and the T1 segments,sparse degenerated fibers are found among contralateral motor neurons. A parallel situation of lesser degree is encountered in sacral segments. Motor neurons were identified by the presence of chromatolysis following brachial plexus and lumbosacral plexus or sciatic nerve crushes. The proportion of degenerated fibers in motoneuronal cell groups is very small when compared with cortical fiber degeneration in the medial part of the ventral horn and more especially, the zona intermedia. Since very limited numbers of motor neurons appear to be associated with degenerated cortical fibers, it is problematical whether these fibers terminate upon the perikarya or dendrites of motor neurons or whether they terminate upon outlying dendrites of propriospinal neurons. We believe that we have consistently found degenerated fibers juxtaposed to the perikarya (Figs. 2 and 4) and dendrites of chromatolytic cells. Unlike motor cortex ablations, lesions of the raccoon's somatosensory cortex did not result in fiber degeneration among motor neurons. We have compared the motor corticospinal fiber connections of the raccoon with those of the cat and found that in the cat these fibers do not appear to cross the cytoarchitecturally defined limits of motoneuronal groups. In the raccoon, a limited infiltration of motoneuronal cell groups by degenerated cortical fibers occurs and these fibers are distributed among the dorsolaterally situated motor neurons in the Ca, T1 and sacral segments (Figs. 1-4). The findings in the raccoon were also compared with the distribution of motor corticospinal fibers in the spider and rhesus monkeys, gibbon and chimpanzee 7. In accord with earlier reports on the corticospinal fiber distribution in primates 2-4, large numbers of cortical fibers invading the motoneuronal cell groups could be identified in these species in all intumescential segments, in a distribution suggesting telmination on perikarya as well as dendrites of motor neurons. From the findings considered here it is tempting to conclude that direct corticomotoneuronal connections are absent in the cat, abundant in several species of primates, and limited in number and segmental distribution in the raccoon. It should, however, be emphasized that this conclusion refers solely to corticalfibers extending to within the boundaries of motoneuronal cell groups. No experimental finding reported thus far has eliminated the possibility that even in the cat some cortical fibers at least terminate on motoneuronal dendrites protruding well outside the perikaryal grouping 1,5,6. Any categorical statement of presence versus absence of direct cortico-motoneuronal connections must therefore be made subject to the reservation that future findings may prove the actual difference to be one of termination on motoneuronal Brain Research, 3 (1966) 195-197
196
SHORT COMMUNICATIONS
Figs. 1-4. High-power photomicrographs of degenerated cortical fibers among spinal motor neurons in the raccoon. Suggestive axodendritic relationships are illustrated in Fig, I taken from the sacral spinal cord ( x 484). Arrows with bent shafts point to a large dendrite of a motor neuron; arrows with straight shafts label degenerated axonal fragments. Degenerated fibers among motor cells in the TI segment are illustrated in the other figures, along with chromatolytic motor neurons in Figs. 2 ( x 475) and 4 ( x 285).
Brain Research, 3 (1966) 195-197
SHORT COMMUNICATIONS
197
perikarya and proximal dendrites in some m a m m a l i a n forms (.primates) as against synaptic contacts only on distal dendritic segments in others (cat). The present findings suggest that the m o d e o f corticospinal fiber termination in relation to m o t o r neurons in the r a c c o o n is somewhat similar, at least qualitatively, to that observed in m a n y primates. In conclusion, corticospinal fibers originating in the m o t o r cortex o f the r a c c o o n converge in great numbers u p o n the spinal neurons in basilar regions of the dorsal horn and zona intermedia; few fibers are f o u n d in the medial part o f the ventral horn. In addition, sparse cortical efferents selectively distributed a m o n g the more caudal m o t o r neurons o f the cervical and lumbosacral intumescentia have been found. Depts. of Neuroahysiology and Experimental Surgery, Walter Reed Army Institute of Research, Washington, D.C. (U.S.A.)
J.M. PETRAS RALPH A. W. LEHMAN
1 CHAMBERS,W. W., AND LtU, C.-N., Cortico-spinal tract of the cat. An attempt to correlate the pattern of degeneration with deficits in reflex activity following neocortical lesions, J. coma. Neurol., 108 (1957) 23-55. 2 KuYV~Rs,H. G. J. M., Some projections from the peri-central cortex to the pons and lower brain stem in monkey and chimpanzee, J. coma. Neurol., 110 (1958) 221-255. 3 KOYPERS,H. G. J. M., The descending pathways to the spinal cord, their anatomy and function. In J. C. ECCLESANDJ. P. SCHADI~(Eds.), Organization of the Spinal Cord, Progress in Brain Research~ Vol. 11, Elsevier, Amsterdam, 1964, pp. 178-202. 4 LItI, C.-N., ANDCHAMaERS,W. W., An experimental study oft he corticospinal system in the monkey (Macaca mulatta). The spinal pathways and preterminal distribution of degenerating fibers following discrete lesions of the pre- and postcentral gyri and bulbar pyramid, J comp. Neurol., 123 (1964) 257-284. 5 NYBERG-HANSEN,R., AND BRODAL,A., Sites of termination of corticospinal fibers in the cat. An experimental study with silver impregnation methods, J. coma. Neurol., 120 (1963) 369-391. 6 PETRAS,J. M., The descending pathways and terminal distribution of cortical, tectal and tegmental fibers to the spinal cord in the cat, Anat. Rec., 145 (1963) 271. 7 PETRAS,J. M., Corticospinal fiber connections in spider and rhesus monkeys, gibbon and chimpanzee: some preliminary notes, Anat. Rec., 154 (1966) 402. (Received August 12th, 1966)
Brain Research, 3 (1966) 195-197