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Transient intermediate zone neurons project to the spinal cord, the superiol colliculus, and the contralateral hemisphere
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ASTROGLIAL INFLUENCES ON THE DENDRITIC MORPHOLOGY OF OLFACTORY BULB NEURONS IN VITRO. ;
rDho1.
Kitasato Univ. Sch. of Nurs., 2-l-l Kitasato, Saaamihara, Kanaaawa 228. Javan.
Glial influences on the morphology of dendrites were analyzed in mixed culture of neurons and glial cells from the neonatal rat olfactory bulb. Two types of glial cells were seen in the culture of dissociated olfactory bulb cells; astrocytes and olfactory ensheathing cells, both of which similarly supported neuronal adhesion. The number of dendritic branching was significantly higher in neurons attached on astrocytes than in those on olfactory ensheathing cells. No difference was found between two types of glial cells with respect to the length of dendritic processes from attaching neurons. These results suggest that the dendritic morphology is affected by local environments, a part of which is provided by astrocytes.
1212
91041
TRANSIENT
INTERMEDIATE
ZONE NEURONS PROJECT TO THE SPINAL CORD, S, AND THE CO NTRALATERAL HEMISPHERE. NOJYC
Japan
The developing mammalian telencephalon contains many transient neurons. Transient subplate neurons have been proposed to lay down the first axonal pathways as a scaffold for the establishment of permanent cortical projections to the thalamus, the superior colliculus, and the contralateral hemisphere in cats. The question of whether there are pioneer fibers to the spinal cord 1s a major issue in neocortical development. Here, I have searched for neurons iving rise to ioneer fibers using retrograde tracers in newborn rats. Tracers were injected into the spinal cord, t%e superior coPliculus, or the contralateral hemisphere in vivo, and a population of labeled cells were found in the lower intermediate zone (IZ) of the dorsomedral cortex where the cingulate bundle would later be formed. Rostrocaudally, labeled cells were distributed from the rostra1 ole of the cortex to the visual cortex. Cresyl violet staining of frontal sections showed an accumulation of ce Ks in a similar location corresponding to the transitional field which contains cells migrating to the cortical surface. The accumulation also corresponded to a po ulation of GABA-immunoreactive cells m the lower intermediate zone. These were MAP2-positive (microtu %le associated protein 2; neuron-s cific protein , and some of them also expressed somatostatin. The IZ neurons in the dorsomedial cortex un r erwent their Bnal round of cell division before embryonic da 14 (El4 and sent out fibers to the internal capsule before E16, disappearing from the IZ as the brain mature dy. These ch aracteristics imply that the IZ neurons pioneer the major corticofugal pathway.
STOP OF AXON GROWTH BY INHJBlTION OF Ca INFLUX IN THE SOMAS, BUT NOT THAT IN THE AXONS THEh4SELVES. K. KEINO-MASUr, I.1 AND K. TORlMITSU2, 2-m koroxaw 1 tD Iaboratorv. NTT Basic Research Laboratories. Atsugi. Japan.
1213
To examine roles of Ca influx in mediating growth of nerve fibers, axons and somas of DRG cells were independently exposed to media containing Ca-chelators or Ca-channel blockers during culture in a specially designed 2-chamber dish. Axons were viewed under a confocal laser microscope and their [Caz+]i was examined by fluorescent dye methods. Even when C$+ was absent in the medium bathing axons, they continued to grow for more than several days; they were 30 % shorter than normal axons, and their [Caz+]iwas reduced to about l/2 of normal level. While, no morphological differences were noted in the axons growing in the C&free medium. In the presence of verapamil (a Ca channel blocker) axons continued to grow for several days, without changes in morphology or in [CaZ+]i. By contrast, axons in normal medium stopped to grow when their somas were selectively exposed to Ca-free medium or verapamil-containing medium. No changes in morphology or [Caz+]iwas noted in these axons. We therefore conclude that Ca influx in the somas is essential while Ca influx in axons plays only a limited role for elongation of axons themselves.
ASTROGLIAL INFLUENCES ON THE DENDRITIC MORPHOLOGY OF OLFACTORY BULB NEURONS IN VITRO. ;
rDho1.
Kitasato Univ. Sch. of Nurs., 2-l-l Kitasato, Saaamihara, Kanaaawa 228. Javan.
Glial influences on the morphology of dendrites were analyzed in mixed culture of neurons and glial cells from the neonatal rat olfactory bulb. Two types of glial cells were seen in the culture of dissociated olfactory bulb cells; astrocytes and olfactory ensheathing cells, both of which similarly supported neuronal adhesion. The number of dendritic branching was significantly higher in neurons attached on astrocytes than in those on olfactory ensheathing cells. No difference was found between two types of glial cells with respect to the length of dendritic processes from attaching neurons. These results suggest that the dendritic morphology is affected by local environments, a part of which is provided by astrocytes.
1212
91041
TRANSIENT
INTERMEDIATE
ZONE NEURONS PROJECT TO THE SPINAL CORD, S, AND THE CO NTRALATERAL HEMISPHERE. NOJYC
Japan
The developing mammalian telencephalon contains many transient neurons. Transient subplate neurons have been proposed to lay down the first axonal pathways as a scaffold for the establishment of permanent cortical projections to the thalamus, the superior colliculus, and the contralateral hemisphere in cats. The question of whether there are pioneer fibers to the spinal cord 1s a major issue in neocortical development. Here, I have searched for neurons iving rise to ioneer fibers using retrograde tracers in newborn rats. Tracers were injected into the spinal cord, t%e superior coPliculus, or the contralateral hemisphere in vivo, and a population of labeled cells were found in the lower intermediate zone (IZ) of the dorsomedral cortex where the cingulate bundle would later be formed. Rostrocaudally, labeled cells were distributed from the rostra1 ole of the cortex to the visual cortex. Cresyl violet staining of frontal sections showed an accumulation of ce Ks in a similar location corresponding to the transitional field which contains cells migrating to the cortical surface. The accumulation also corresponded to a po ulation of GABA-immunoreactive cells m the lower intermediate zone. These were MAP2-positive (microtu %le associated protein 2; neuron-s cific protein , and some of them also expressed somatostatin. The IZ neurons in the dorsomedial cortex un r erwent their Bnal round of cell division before embryonic da 14 (El4 and sent out fibers to the internal capsule before E16, disappearing from the IZ as the brain mature dy. These ch aracteristics imply that the IZ neurons pioneer the major corticofugal pathway.
STOP OF AXON GROWTH BY INHJBlTION OF Ca INFLUX IN THE SOMAS, BUT NOT THAT IN THE AXONS THEh4SELVES. K. KEINO-MASUr, I.1 AND K. TORlMITSU2, 2-m koroxaw 1 tD Iaboratorv. NTT Basic Research Laboratories. Atsugi. Japan.
1213
To examine roles of Ca influx in mediating growth of nerve fibers, axons and somas of DRG cells were independently exposed to media containing Ca-chelators or Ca-channel blockers during culture in a specially designed 2-chamber dish. Axons were viewed under a confocal laser microscope and their [Caz+]i was examined by fluorescent dye methods. Even when C$+ was absent in the medium bathing axons, they continued to grow for more than several days; they were 30 % shorter than normal axons, and their [Caz+]iwas reduced to about l/2 of normal level. While, no morphological differences were noted in the axons growing in the C&free medium. In the presence of verapamil (a Ca channel blocker) axons continued to grow for several days, without changes in morphology or in [CaZ+]i. By contrast, axons in normal medium stopped to grow when their somas were selectively exposed to Ca-free medium or verapamil-containing medium. No changes in morphology or [Caz+]iwas noted in these axons. We therefore conclude that Ca influx in the somas is essential while Ca influx in axons plays only a limited role for elongation of axons themselves.