Takahiro Futami

Morphology of single neurones in the cerebello-rubrospinal system

Axonal branching patterns of physiologically identified cerebellar nucleus neurones and rubrospinal neurones were investigated in the cat with intra-axonal injection of horseradish peroxidase and 3-dimensional reconstruction on serial sections. Axons of dentate and interpositus neurones projected to the VL nucleus of the thalamus and on their way, several axon collaterals were given off from the stem axons to the red nucleus. Axon terminals of interpositus neurones terminated as a sagittal sheet of arborizations in the red nucleus. Their terminal boutons made apparent contact with cell bodies and proximal dendrites of rubrospinal neurones. In rubrospinal axons, multiple axon collaterals were identified at different segments of the cervical spinal cord.

Synaptic organization of the cerebello-thalamo-cerebral pathway in the cat. II: Input-output organization of single thalamocortical neurons in the ventrolateral thalamus

Input-output neural organization of single thalamocortical (T-C) neurons in the ventrolateral nucleus (VL) of the thalamus was investigated using an intracellular recording technique in the anesthetized cat. Stimulation of the dentate (DN) and the interpositus (IN) nuclei produced monosynaptic unitary EPSPs of large amplitude in T-C neurons projecting to the motor cortex or area 6 over the entire mediolateral region of VL. The thalamic projections from DN and IN are very wide and there is a considerable overlap between the dentate and the interpositus projection areas in VL. And in this overlapping area, a considerable number of T-C neurons (50%) receive inputs from both DN and IN. More than 40% of T-C neurons were antidromically activated from widely separated electrodes in the motor cortex, indicating that the cortical arbolization of single T-C neurons is very wide and the number of these neurons with widely divergent projections is considerably large.

Excitatory inputs to cerebellar dentate nucleus neurons from the cerebral cortex in the cat

Summary1. In anesthetized cats, we investigated excitatory and inhibitory inputs from the cerebral cortex to dentate nucleus neurons (DNNs) and determined the pathways responsible for mediating these inputs to DNNs. 2. Intracellular recordings were made from 201 DNNs whose locations were histologically determined. These neurons were identified as efferent DNNs by their antidromic responses to stimulation of the contralateral red nucleus (RN). Stimulation of the contralateral pericruciate cortex produced excitatory postsynaptic potentials (EPSPs) followed by long-lasting inhibitory postsynaptic potentials (IPSPs) in DNNs. The most effective stimulating sites for inducing these responses were observed in the medial portion (area 6) and its adjacent middle portion (area 4) of the precruciate gyrus. Convergence of cerebral inputs from area 4 and area 6 to single DNNs was rare. 3. To determine the precerebellar nuclei responsible for mediation of the cerebral inputs to the dentate nucleus (DN), we examined the effects of stimulation of the pontine nucleus (PN), the nucleus reticularis tegmenti pontis (NRTP) and the inferior olive (IO). Systematic mapping was made in the NRTP and the PN to find effective low-threshold stimulating sites for evoking monosynaptic EPSPs in DNNs. Stimulation of either the PN or the NRTP produced monosynaptic EPSPs and polysynaptic IPSPs in DNNs. Using a conditioning-testing paradigm (a conditioning stimulus to the cerebral peduncle (CP) and a test stimulus to the PN or the NRTP) and intracellular recordings from DNNs, we tested cerebral effects on neurons in the PN and the NRTP making a monosynaptic connection with DNNs. Conditioning stimulation of the CP facilitated PN- and NRTP-induced monosynaptic EPSPs in DNNs. This spatial facilitation indicated that the excitatory inputs from the cerebral cortex to DNNs are at least partly relayed via the PN and the NRTP. 4. Stimulation of the contralateral IO produced monosynaptic EPSPs and polysynaptic IPSPs in DNNs. These monosynaptic EPSPs were facilitated by conditioning stimulation of the CP, strongly suggesting that the IO is partly responsible for mediating excitatory inputs from the cerebral cortex to the DN. A comparison was made between the latencies of IO-evoked IPSPs in DNNs and the latencies of IO-evoked complex spikes in Purkinje cells. Such a comparison indicated that the shortest-latency IPSPs evoked from the IO were not mediated via the Purkinje cells and suggested the pathway mediated by inhibitory interneurons in the DN. 5. The functional significance of the excitatory inputs from the PN and the NRTP to the DN is discussed in relation to the motor control mechanisms of the cerebellum.

Vestibular projections to the spinal cord: the morphology of single vestibulospinal axons.

The three-dimensional distribution of LVST and MVST axons was examined in the cat cervical spinal cord using an intra-axonal staining method. LVST and MVST axons were electrophysiologically identified by their responses to stimulation of the vestibular nucleus, bilateral vestibular primary afferents, the LVST and the MVST were stained with injection of HRP. The axonal trajectory was reconstructed from serial histological sections. LVST axons were found to have multiple axon collaterals in the cervical cord. The maximum number of the identified collaterals for one neuron was 7. These collaterals were observed in either LVST axons terminating at the cervical cord or those projecting below Th2. The rostro-caudal extension of terminals for each collateral was very restricted (mean = 760 μm) and much narrower than intercollateral intervals (mean = 1470 μm). In the gray matter, collaterals ramified successively, pursued a delta-like path, and terminated mainly in lamina VIII and in the medial part of lamina VII and many boutons made apparent contact with the cell bodies and the proximal dendrites of motoneurons in the ventromedial nucleus. Some terminals were also distributed to the ventrolateral part of lamina VII adjacent to lamina IX. One group of LVST axons projected to lamina IX in the lateral ventral horn and terminated on large neurons there, probably motoneurons of forelimb muscles. MVST axons had one to seven axon collaterals at C1–C3 within the range of the stained axon. Stem axons ran in the ventromedial funiculus and primary collaterals arose from them at right angles. Each collateral had a very nar-row rostrocaudal spread as in LVST axons. Terminals were distributed in laminae VIII and IX, including the ventromedial nucleus, the spinal accessory nucleus, and the commissural nucleus. Many terminals seemed to make contact with retrogradely labelled motoneurons of neck muscles. Both crossed and uncrossed MVST axons had these characteristics.

Synaptic organization of the cerebello-thalamo-cerebral pathway in the cat. III. Cerebellar input to corticofugal neurons destined for different subcortical nuclei in areas 4 and 6

To analyze the cerebellar effects on corticofugal neurons destined for different subcortical nuclei, intracellular recordings were made from corticofugal neurons in areas 4 and 6 of the cat. Corticonuclear neurons to the red nucleus (RN) and the pontine nucleus (PN), and pyramidal tract neurons (PTNs) with collaterals to these nuclei were identified by their antidromic responses to the stimulation of these nuclei and the pyramid. Three types of RN-projecting neurons (corticorubral neurons (CRNs), corticopontine neurons (CPNs) with a collateral to the RN and PTNs with a collateral to the RN) and two types of PN-projecting neurons (CPNs and PTNs with a collateral to the PN) were differentiated. Furthermore, these corticofugal neurons were classified as fast and slow neurons on the basis of a critical axonal conduction velocity of 20 m/s. About 80% of 98 RN-projecting neurons in area 4 were PTNs, and among the rest, CPNs were more common than CRNs. A similar tendency of the frequency distribution of 37 RN-projecting neurons was also observed in area 6. In area 4, about 70% of 158 PN-projecting neurons were PTNs (80 fast and 30 slow PTNs) and the rest were CPNs, while in area 6, only 35% of 99 PN-projecting neurons were PTNs (10 fast and 25 slow PTNs). Among the CPNs in areas 4 and 6, slow CPNs were more frequently encountered. Cerebellar effects on these identified corticofugal neurons were investigated, using electrical stimulation of the brachium conjunctivum (BC). In both areas 4 and 6, a substantial number of fast conducting CRNs, CPNs and PTNs projecting to the RN or the PN received short-latency (predominantly disynaptic), large-amplitude EPSPs from the BC, and a considerable number of slow conducting neurons to the RN and/or the PN received longer-latency, smaller-amplitude EPSPs from the BC.

Convergent inputs from the dentate and the interpositus nuclei to pyramidal tract neurons in the motor cortex

Effects of stimulation of the cerebellar nuclei were investigated by intracellular recordings from fast and slow pyramidal tract neurons and thalamocortical neurons in the cat. The present study demonstrated that: (1) the interpositus and the dentate nuclei excite PTNs in the motor cortex; (2) single pyramidal tract neurons receive convergent inputs from both nuclei, and (3) the convergence of the inputs from both nuclei occurs at the level of the ventrolateral nucleus of the thalamus.

Chapter 19 Synaptic organization of the vestibulo-collic pathways from six semicircular canals to motoneurons of different neck muscles

The pattern of inputs from six semicircular canals to neck motoneurons was investigated by stimulating six ampullary nerves electrically and recording intracellular potentials from motoneurons of the rectus capitis dorsalis (RD), the complexus (COMP) and the obliquus capitis caudalis (OCA) muscles at the upper cervical cord of the cat. RD and COMP motoneurons received disynaptic excitation from bilateral anterior and contralateral horizontal ampullary nerves and disynaptic inhibition from bilateral posterior and ipsilateral horizontal ampullary nerves. OCA motoneurons received excitation from ipsilateral vertical and contralateral horizontal ampullary nerves and inhibition from contralateral vertical and ipsilateral horizontal ampullary nerves. Ipsilateral disynaptic inhibitory postsynaptic potentials and contralateral disynaptic excitatory postsynaptic potentials to these motoneurons were mediated by the medial longitudinal fasciculus (MLF) and the other postsynaptic potentials by the extra-MLF pathways. The results indicated that motoneurons of a neck muscle have its own characteristic pattern of inputs from six semicircular canals.

Input-Output Organization of the Ventrolateral Nucleus of the Thalamus

Input-output organization of the ventrolateral nucleus (VL) of the thalamus was analyzed electrophysiologically and morphologically at the single cell level. Virtually all pyramidal tract neurons in the motor cortex and area 6 received convergent inputs from the dentate (DN) and the interpositus (IN) nuclei and about 60% of thalamocortical (TC) neurons received convergent inputs from both the DN and the IN. Anterograde labelling following focal injection of Phaseolus vulgaris leukoagglutinin and intracellular staining of TC axons showed that the terminals in layer III tended to aggregate into patches about 1-1.5 mm wide in a frontal plane, which were arranged in longitudinal strips about 2-5 mm long in a rostrocaudal direction.

Chapter 11 Functional significance of excitatory projections from the precerebellar nuclei to interpositus and dentate nucleus neurons for mediating motor, premotor and parietal cortical inputs

Publisher Summary This chapter presents two possible models of the input-output organization of the cerebellar nucleus. The present findings suggest that excitatory inputs from the cerebral cortex to the cerebellar nucleus via the pontine nucleus; the nucleus reticularis tegmenti pontis and the inferior olive could at least partly contribute to the increase of activity of cerebellar nuclear neurons at the onset of movement. Deep cerebellar nucleus neurons give rise to output fibers that convey excitatory signals to their targets. Efferent neurons in the dentate nucleus (DN) and interpositus nucleus (IN) exert excitatory influences on the red nucleus and the motor cortex via the ventrolateral nucleus of the thalamus. Cerebral influences on neurons in the DN are investigated with intracellular recordings from dentate nucleus neurons (DNNs) in nembutal-anesthetized cats by stimulating the cerebral cortex and the cerebral peduncle. The chapter shows that inputs from the cerebral cortex are conveyed to efferent DNNs and interpositus nucleus neurons (INNs) by way of several parallel pathways.

Four Convergent Patterns of Input from the Six Semicircular Canals to Motoneurons of Different Neck Muscles in the Upper Cervical Cord

This study was performed to investigate the pattern of input and the pathways from the six semicircular canals to motoneurons of various neck muscles in anesthetized cats. Intracellular postsynaptic potentials from neck motoneurons were recorded in response to electrical stimulation of the six ampullary nerves. The results showed that motoneurons of a particular neck muscle have a homogeneous convergent pattern of input from the six semicircular canals; there are four patterns of input from the six semicircular canals to motoneurons of various neck muscles; and the trisynaptic connection between the semicircular canal nerves and neck motoneurons was identified in addition to the disynaptic connection.