Biomedical subjects

M Shimo-oku

Publications and source records attributed to M Shimo-oku.

15 recordsLinked to original sources

PubMed1991

[Optic neuritis].

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Evoked Potentials, Visual↗

PubMed1991

[The distribution of actin on cultured oligodendrocytes from rat optic nerve].

Two types of cultured oligodendrocytes (OLs) from rat optic nerve were analyzed for the distribution of actin, a major contractile protein, using immunocytochemistry. Type 1 OLs showed extensive network of processes and type 2 OLs showed elaborate membranous expansion along an extensive network. Actin was diffusely stained on an extensive network of processes in type 1 OLs and on the distal portion of membranous expansion in type 2 OLs, but some oligodendrocytes were not stained. It was demonstrated that the distribution of actin in type 1 OLs and type 2 OLs varied with development in oligodendrocyte differentiation and maturation. Our results suggest that undifferentiated and immature oligodendrocytes display remarkable cell movement to search for target axons, and differentiated and mature oligodendrocytes do not require cell movement when myelination has finished. In conclusion, it is considered that actin plays an important role in myelinogenesis.

Actins↗

PubMed1990

The isolation of cultured oligodendrocytes from rat optic nerve.

Oligodendrocytes, the myelin-forming cells of the central nervous system, were cultured from newborn rat optic nerve employing a modified method of McCarthy and DeVellis, and cultured oligodendrocytes were analyzed for characteristic morphology and maturation events by phase contrast, MBP immunofluorescent and scanning electron microscopy. Two types of oligodendrocytes, type 1 OLs and type 2 OLs, on poly-L-lysine-coated dishes were obtained. Type 1 OLs showed extensive networks of processes and type 2 OLs elaborated membranous expansion along extensive networks, and it was demonstrated that type 2 OLs developed from type 1 OLs by phase contrast-microscopic observation. By scanning electron-microscopic observation, membrane structure in type 2 OLs clearly corresponded to membranous expansion. Our results suggest that type 1 OLs and type 2 OLs are in the different states of the myelinogenesis, and that membranous expansion and membrane structure in type 2 OLs correspond to myelin membrane.

Animals↗

PubMed1990

Cervical afferent pathway to inferior oblique motoneuron in the cat.

The neuronal pathway implicated in the vertical cervico-ocular reflex (COR) was investigated electrophysiologically in chloralose anesthetized cats. The effect of bilateral C2 dorsal root afferent stimulation on inferior oblique motoneurons (IO-MN) was investigated by intracellular recording. Control disynaptic excitatory postsynaptic potentials elicited in IO-MNs following stimulation of the contralateral anterior semicircular canal nerve (ACN) were invariably facilitated by conditioning stimulation to both ipsilateral and contralateral C2 dorsal roots (DR) in all motoneurons tested. This result indicates that inputs from the C2 DR of both sides and the contralateral ACN converge onto secondary vestibular neurons ('common interneurons') which project directly to the IO-MN. Common interneurons mediating vestibular and cervical excitation to the IO-MNs were studied in the vestibular nuclei on the side opposite to the motoneurons by extracellular recording. Nineteen vestibular neurons were identified as common interneurons; they were distributed in the caudal half of the lateral nucleus and the rostral half of the descending nucleus. The present experiment provides electrophysiological evidence of the projection of upper cervical afferents to the ipsilateral vestibular nuclei. The difference in neuronal organization between the horizontal and vertical COR is also briefly discussed.

Action Potentials↗

PubMed1990

[Responses in extraocular muscles from magnetic stimulation of the cat brain].

In 12 adult cats, pulsed magnetic stimuli were applied to the scalp, with the center of the stimulating coil over the interparietal bone. Recordings were obtained from the superior rectus, lateral rectus and inferior oblique muscles with concentric needle electrodes. In all cats, single muscle action potentials were recorded easily in all the muscles examined with latencies of 3.2-37.5 ms (mean 15.6ms). These responses disappeared after intravenous administration of pancuronium bromide. Furthermore, the elicited action potentials in the inferior oblique muscles disappeared by amputation of the inferior oblique branch of the oculomotor nerve. In some motor units, stronger stimuli shortened the latency of the responses. In most units, however, stimulus intensity did not influence the latency of responses over a wide range. The mean latency (15.6ms) is coincident with the latency of cortical spike potentials preceding voluntary saccades. This remarkable coincidence suggests that our pulsed magnetic stimuli have a very strong possibility of generation of human saccades. Thus, magnetic stimulation of the scalp may provide further information relevant to the normal operation of the oculomotor system.

Animals↗

PubMed1988

Common interneurones mediating cortical and tectal excitation of abducens motoneurones in the cat.

Tectal and cortical effects on abducens motoneurones were examined with intracellular recording techniques in cats under chloralose anaesthesia. Abducens motoneurones exhibited disynaptic EPSPs after stimulation of the contralateral superior colliculus and cerebral peduncle. The tectal disynaptic EPSPs were observed invariably in all motoneurones tested, while the peduncular EPSPs were observed only in 40% of motoneurones after stimulation of the contralateral cerebral peduncle. However, the tectal disynaptic EPSPs were consistently facilitated by conditioning peduncular stimulation in all motoneurones tested. These results indicated that the disynaptic excitatory tecto-abducens and cortico-abducens pathways shared common premotor interneurones. The common interneurones which mediated the tectal and cortical disynaptic excitation of abducens motoneurones were explored in the pons. These interneurones were identified by the criteria that they were fired monosynaptically from both the tectum and the cerebral peduncle and were activated antidromically from the abducens nucleus. Systematic threshold mapping for the antidromic activation in and around the abducens nucleus indicated that they gave off many collateral branches in the nucleus. Such neurones were found in the nucleus reticularis pontis caudalis, being distributed in the area extending 0.8-3 mm rostral to the rostral pole of the abducens nucleus, 1.3-2.7 mm deep from the dorsal surface of the brain stem, and 0.8-1.8 mm lateral from the midline. The present experiments strongly suggest that a group of neurones in the paramedian pontine reticular formation make direct excitatory connexions with abducens motoneurones and play a role of common interneurones that transmit both tectal and cortical commands.

Abducens Nerve↗

PubMed1988

Influence of visual deprivation on the visual and oculomotor system: acetylcholinesterase activity in oculomotor neurons.

The effects of visual deprivation (dark-rearing) on neurons in both the visual and oculomotor systems of black mice were studied using morphologic and histochemical techniques. In the neurons of the dorsal nucleus of the lateral geniculate body, the cytoplasm of dark-reared mice was less developed and the cytoplasm/nucleus ratio was significantly smaller in the dark-reared mice than in the controls. In contrast, large motoneurons in the oculomotor nucleus did not show any ultrastructural changes and the cytoplasm/nucleus ratio was normal. However, in large motoneurons of dark-reared mice, acetylcholinesterase (AChE)-positive areas were scattered in the cytoplasm, and the ratio of the AChE-positive areas to the cytoplasm area was significantly smaller than that in the controls.

Acetylcholinesterase↗

PubMed1988