Yoshihiro Matsuda

Tetrodotoxin sensitivity and Ca component of action potentials of mouse dorsal root ganglion cells cultured in vitro.

In the mouse dorsal root ganglia cultured in vitro, neurons were classified into 3 groups according to the responses of their action potentials to tetrodotoxin (TTX) and removal of Na ions from bathing medium: (1) the neurons whose action potentials were not affected by TTX by TTX (10(-6) - 10 (-5)g/ml) and which generated Ca-dependent regenerative responses under Na-free condition, (2) the neurons whose spike potentials were resistant to TTX but failed to survive in Na-free saline and (3) the neurons whose action potentials were suppressed by TTX(10(-8)g/ml) as well as Na removal. The mean duration of spike and after-hyperpolarization was longest in the first group of the neurons and shortest in the third, probably reflecting the difference in the contribution of Ca currents to action potentials. The unresponsiveness of the neurons to TTX was shown to be due to the insensitivity of Na as well as Ca components of action potentials to the toxin. It was discussed that the occurrence of TTX-resistant action potentials to the toxin. It was discussed that the occurrence of TTX-resistant action might be related to the neuronal development.

Electrophysiological studies on cerebello-cerebral projections in the cat

Summary1.Cerebello-cerebral projections were electrophysiologically investigated in cats under light Nembutal anaesthesia. Marked responses were produced by stimulation of the interpositus and the lateral nucleus of the cerebellum not only in the pericruciate but also in the suprasylvian cortical areas, both areas being contralateral to the cerebellar nuclei stimulated. Medial nucleus stimulation set up little or no response in the cerebral cortex.2.The previous electrophysiological study on thalamo-cortical (T-C) projections showed two different kinds of responses in the cortex due presumably to two different T-C projection systems, i. e., deep and superficial T-C responses (see Sasaki et al., 1970). According to laminar field potential analysis, the response in the pericruciate area is characterized by a deep T-C response which is often followed by a superficial T-C response, whereas the response in the parietal cortex consists of a pure superficial T-C response. Intracellular potential changes in cortical neurones elicited by cerebellar nucleus stimulation were consistent with the results of laminar field potential analysis.3.Comparison between laminar field potentials in the same cortex produced by thalamic and cerebellar nucleus stimulation suggests that the response in the pericruciate cortex is mediated by the ventral lateral nucleus and that the response in the parietal cortex is relayed by the ventral anterior nucleus of the thalamus.

Electrophysiological studies of the projections from the parietal association area to the cerebellar cortex

Summary1.Responses evoked in the cerebellar cortex by stimulation of the parietal association cortex (rostral portions of the middle suprasylvian gyrus) were recorded and analysed in cats, and were compared with those by stimulation of the motor cortex (anterior sigmoid gyrus).2.The parietal stimulation elicited early mossy fibre and late climbing fibre responses in the cerebellar cortex. The mossy fibre responses appeared at a latency of 2.0–2.5 msec and predominantly in the lateral (hemispherical) part of the contralateral cerebellum (mainly crus I, crus II and paramedian lobules). Cutting of the inferior cerebellar peduncle produced little or no influence upon the mossy fibre responses, which suggests that the mossy fibre responses are mediated chiefly by the pontine nuclei.3.The climbing fibre responses were recorded at a latency of 17–19 msec and markedly in the contralateral intermediate and medial parts of IV–VI lobules. The responses were easily suppressed by anaesthesia and depended on the conditions of experimental animals. The unstable appearance of the responses and their longer latencies than those of the climbing fibre responses due to stimulation of the motor cortex imply indirect pathways from the parietal association cortex to the inferior olive.4.The predominant projection of the parietal-induced mossy fibre responses to the lateral part of the cerebellum was compared with the mossy fibre projection from the motor cortex and was discussed as an important component in the cerebrocerebellar loops.

On the cerebello-thalamo-cerebral pathway for the parietal cortex.

Summary1.The cerebello-thalamo-cerebral projection system mediating the cerebellar-induced “superficial thalamo-cortical (T-C) response” (the basic type of the so-called recruiting response) to the anterior part of the middle suprasylvian gyrus was investigated electrophysiologically. Responses of thalamic neurones to stimulation of the cerebral cortex and the cerebellar nucleus (medial, interpositus and lateral) were recorded by microelectrodes.2.In the anterior portions of the ventral thalamic nuclear complex, presumably in and/or around the ventral anterior (VA) nucleus, there were found neurones responding antidromically to stimulation of the suprasylvian cortex and orthodromically to that of the interpositus and the lateral nucleus of the cerebellum. They were called P neurones. The neurones responding antidromically to stimulation of the anterior sigmoid cortex and orthodromically to that of the cerebellar nuclei located mostly caudo ventrolateral to the place of P neurones, presumably in and/or around the ventral lateral (VL) nucleus. These were called F neurones.3.The cerebellar excitation of P neurones was estimated on its latency to be monosynaptic and was usually followed by an inhibition lasting for more than 100 msec. Large unitary EPSPs were sometimes noted in P neurones on cerebellar stimulation as well as spontaneously. It was concluded that P neurones constitute the direct T-C projection system mediating the superficial T-C response (e. g., recruiting response) to the parietal cortex.

Neurons of the motor cortex projecting commonly on the caudate nucleus and the lower brain stem in the cat

The cortico-caudate projections due to collateral axons of cortico-spinal and/or cortico-bulbar fibers were explored. In 34 cats, 59 neurons in the motor cortex were extracellularly identified to be antidromically activated by stimulation of the caudate nucleus (Cd). Thirty four neurons responded antidromically only to Cd-stimulation, and they were irresponsive to thalamic stimulation. Contrarily, 25 neurons responded antidromically not only to Cd-stimulation but also to stimulation of the cerebral peduncle and/or the medullary pyramid. 40% of the latter were orthodromically activated by thalamic stimulations. They were considered to be important in coordinating the cerebellum and the basal ganglia system.

Responses of pontocerebellar neurones to stimulation of the parietal association and the frontal motor cortices

The corticopontine projections from the parietal association cortex (the anterior portion of the middle suprasylvian gyrus) were electrophysiologically investigated and compared with those from the frontal motor cortex (the anterior sigmoid gyrus) in cats under light Nembutal anaesthesia. It was indicated by field potential study that the pontine nucleus (PN) neurones receive a significant amount of the direct corticopontine fibres from both the parietal and frontal cortical areas. In extracellular unitary study, out of 107 PN neurones identified by antidromic activation due to the brachium pontis stimulation, 33 responded with firings to stimulation of the parietal association area and 64 to the frontal motor area. Only 10 of them were excited by both parietal and frontal stimulations, but they were not estimated to receive the dual monosynaptic projections from both cortical areas. There were found data suggesting that the pontocerebellar neurones with faster conduction velocities respond at shorter latencies to the cortical stimulation and those with slower conduction velocities fire at longer latencies on the cortical stimulation. No remarkable difference was observed between the topographical localization of the PN neurones receiving the projection fibres from the parietal association and the frontal motor cortical areas. It was concluded that a vast majority of the pontocerebellar neurones possibly receive monosynaptic contacts differentially with the corticopontine fibres originating from the parietal association and the frontal motor areas.

Thalamo-cortical projections for recruiting responses and spindling-like responses in the parietal cortex.

Summary1.The thalamic neurones sending their axons to the parietal association cortex (middle suprasylvian gyrus) and receiving monosynaptic excitation from the cerebellar (interpositus or lateral) nucleus were recorded with microelectrodes extracellularly and intracellularly around the anterior ventral (VA) nucleus of the thalamus in cats. Such thalamic neurones are known to carry exclusively the impulses responsible for superficial thalamo-cortical (T-C) responses in the parietal cortex, being called superficial T-C neurones (see Sasaki et al., 1972a, b).2.Repetitive (6–9/sec) stimulation of the centrum medianum-parafascicular complex (CM) or the intralaminar nuclei (IL) of the thalamus elicited grouped spike discharges of the neurone in synchronization with the recruiting responses in the parietal cortex. The grouped discharges usually preceded the respective cortical responses by several milliseconds. Numbers of the spikes in the grouped discharges increased and decreased as the recruiting responses waxed and waned on the repetitive stimulation.3.The superficial T-C neurones also showed similar grouped discharges in synchronization with spindling-like, surface-negative cortical responses which occurred spontaneously or were evoked by single thalamic stimulation.4.It was concluded that the superficial T-C neurones can convey impulses for recruiting responses and spindling-like responses from the thalamus directly to the cerebral cortex. They are supposed to constitute the final T-C pathway of the neuronal circuits of the recruiting system, i.e., non-specific T-C projection system.

Distribution of cerebellar-induced responses in the cerebral cortex.

Abstract Distribution of responses in the cerebral cortex elicited by stimulation of cerebellar nuclei was investigated in cats lightly anesthetized with Nembutal. Stimulation of the interpositus nucleus produced more marked responses than that of the lateral nucleus but no distinguishable difference was noted between the localizations of responses in the cerebral cortex elicited by stimulating these nuclei. Medical nucleus stimulation set up little or no response in the cortex. Therefore, effects of stimulating the interpositus nucleus were mainly presented in this report. Cerebellar-evoked responses could be recorded from two regions in the cortex, frontal motor and parietal association areas; both were contralateral to the cerebellar nuclei stimulated. In the frontal cortex, the responses composed mainly of the deep thalamocortical (T-C) response were distributed in the exposed area of the anterior sigmoid gyrus, the deeply folded cruciate cortex, and a part of the exposed area of the posterior sigmoid gyrus. In the parietal cortex, the superficial T-C responses appeared in the middle suprasylvian cortex, a rostral part of the lateral gyrus, and its extension to the mesial cortex.

Induction of myelin-associated glycoprotein expression through neuron–oligodendrocyte contact

The role of neurons on expression of myelin-associated glycoprotein (MAG) in oligodendrocytes and oligodendroglial differentiation was examined. Primary cultures of oligodendrocytes prepared from neonatal mouse brains were co-cultured with neuronal cells derived from embryonal carcinoma P19 cells. The levels of MAG mRNAs following this co-culture were determined by reverse transcription (RT)-PCR. In oligodendrocytes co-cultured in direct contact with P19-derived neurons, the levels of MAG mRNAs, particularly that of the L-type isoform, were markedly higher than those in cultures without any neuronal cells. On the other hand, when the P19-derived neurons were present, but not in direct contact, no significant induction of MAG expression was found, though oligodendrocytes appeared to mature morphologically. The L-MAG expression was also stimulated when just the neuronal cell membrane fraction was added, which implies that there might be some effecter(s) in the cell membrane which are possibly exerting a signal transduction for myelin formation. These results suggest that morphological differentiation and functional maturation of oligodendrocytes are due to independent factors. The former is caused by some humoral factor(s) liberated from neuronal cells, while the latter resulted from cellular contact with neuronal cells.

Effects of stimulation of the midbrain reticular formation upon thalamo-cortical neurones responsible for cortical recruiting responses

Summary1.In lightly nembutalized cats, effects of high frequency (60–100/sec) repetitive stimulation of the midbrain reticular formation (RF) were tested upon the thalamo-cortical (T-C) neurones which project from the anterior ventral (VA) nucleus of the thalamus and its vicinities to the parietal association cortex and convey impulses responsible for cortical recruiting and spindling-like responses.2.Tonic maintained or rhythmic grouped firings of the T-C neurones recorded as extracellular units with microelectrode in the thalamus were in the majority suppressed by high frequency RF stimulation during and often for a short time after the stimulation, and they showed later tonic discharges for many seconds or minutes. Intracellular recording from the T-C neurones revealed hyperpolarizing potential changes corresponding to the suppression on high frequency RF stimulation. Field potential analysis in the VA nucleus indicated that the hyperpolarization is ascribed at least in part to IPSPs elicited in the T-C neurones. Responses in some other types of thalamic neurones to the RF stimulation were exemplified to be compared and related with those of the T-C neurones.3.Desynchronization of the parietal electrocorticogram coincided with the suppression of the T-C neurones and lasted for the time of the later tonic discharges, which contrasted with the rhythmic grouped discharges of the T-C neurones in association with recruiting and spindling-like responses of the cortex. Relations between the thalamo-cortical recruiting system and the ascending reticular activating system were discussed.