Biomedical subjects
Publications and source records attributed to A Kanemitsu.
We studied corticofugal projections to the motoneurons with Nauta-Gygax's technique in a patient with cerebral infarction of both hemispheres. Motoneurons in the brainstem motor nuclei and spinal anterior horns seem to receive direct cortical projections, except for the oculomotor and abducens nuclei and Onuf's nucleus in the sacral cord.
The time of origin of Purkinje cells and deep cerebellar neurons was studied by 3H-thymidine autoradiography in chick embryos which received isotope at stages 17 to 29 and which were sacrificed at stage 36. These neurons originated throughout stages 17 to 27. Neurons of each cerebellar nucleus originated throughout these stages, so that histogenetically the cerebellar nuclei could be regarded as a single cell mass. Large neurons originated at stage 17, medium sized ones at stages 19 to 21, and small ones after stage 23. Purkinje cells aggregated at stage 36 to form a row of cell clusters under the external granular layer. These cell clusters were more or less labeled in the embryos which received isotope at stages 17 to 21, while unlabeled cell clusters were observed in the embryos which received isotope after stage 23. These unlabeled cell clusters showed 4 longitudinal bands in the lateral cerebellar cortex. In the embryo which received isotope at stage 27, Purkinje cells in the pars intermedius and lateralis were almost unlabeled, whereas in the vermis and the lobus flocconodularis, a fairly large number of labeled Purkinje cells were still observed. Purkinje cells were all medium sized regardless of their time of origin.
The early formation of neuronal connections in the cervical cord of chick embryos at stages 17 to 31 was studied by observing axonal courses with Golgi preparations and the distribution of synapses with electron microscopy. The results are summarized as follow: 1. Synaptic contacts between spinal interneurons and ipsilateral as well as contralateral motor neurons first develop at stage 22. The early central pathways from the dorsal root to the ventral root may be formed at stage 25 with intervention of interneurons of the primordial dorsal horn, which is composed of neurons of the zona spongiosa and the nucleus proprius of the dorsal horn, and at stage 27 with the intervention of interneurons of the zona intermedia, the nucleus proprius of the ventral horn and the primordial dorsal horn as well. 2. These polysynaptic, bilateral central pathways appear to be established just before the arrival of supraspinal descending fibres at the cervical cord, and one or two days before the formation of ipsilateral monosynaptic spinal reflex arch. 3. These early spinal central pathways are connected by synapses with spherical synaptic vesicles, and almost all of these synapses are of the axo-dendritic type and located in the spinal white matter.
Our previous study with 3H-thymidine autoradiography showed that neurons of the zona spongiosa, the nucleus proprius of the dorsal horn, the zona intermedia and the ventralhorn differentiated earlier than those of the substantia gelatinosa and the neck and the base of the dorsal horn, and that neurons of the substantia gelatinosa which were the last to differentiate reached their final position at stage 36 (Fig. 1). In the upper cervical cord of chick embryos at stage 36 when all spinal neurons finished cell migration and the cytoarchitecture similar to that of the cat spinal cord (Rexed, 1952) could be recognized (cf. Figs. 1, 3B), we studied the distribution of synapses by the electron microphotomontage (Fig. 3 A) and the morphology of axon collaterals coming from the white matter by the Golgi method (Fig. 4), in order to examine i) which spinal neurons have synaptic contacts at this stage and ii) what part of the axon collateral makes synaptic contacts. In the white matter, synapses were numerous around the gray matter and they were few in the peripheral part along the external surface of the cord. The paucity of synapses in the peripheral part was explained by a finding that dendrites reaching the external surface of the cord were few in number at this stage (cf. Fig. 3 C). In the gray matter, synapses were more numerous and denser in the zona intermedia and the ventral horn than in the dorsal horn.(ABSTRACT TRUNCATED AT 250 WORDS)
From stages 24 to 45 of the chick embryo, the longest dendrite of each interneuron in the zona intermedia was measured in the upper cervical cord prepared by the Golgi method, the measuring being done exclusively on the large neurons at each stage to follow the dendritic growth of neurons homogeneous in their time of origin. The longest dendrite grew at a rate of 92-184 micron per day at stage 24, and thereafter its growth rate gradually slowed down to 4 micron per day at stage 36. Already at stage 27, the interneurons located deep in the mantle layer reached with their longest dendrite the marginal layer which was the site of synaptic contact in early developmental stages. Thus, the initial rapid growth of the dendrite could be regarded as highly effective for the early formation of synaptic contact.
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