Shigeto Sasaki

Cerebellar projection and input organizations of the spinocerebellar tract arising from the central cervical nucleus in the cat

The central cervical nucleus (CCN) has now been identified as consisting of cells of origin of a spinocerebellar tract by the retrograde labeling technique using horseradish peroxidase2,6,10,14. Anatomically, the CCN has been recognized as a separate cell group from the surroundings, existing at C1-C4, and to receive dorsal root fibres mainly of the cervical segmentsZ,5,8,11-13. The present study has been undertaken to physiologically characterize this new spinocerebellar tract with respect to its input and output organizations. Adult cats anaesthetized with Nembutal (30 mg/kg, i.p., and an additional 5-20 mg/kg, i.v.), immobilized with gallamine triethiodide and artificially ventilated were used for experiments. A glass capillary microelectrode (2 M potassium citrate) was inserted into the region of CCN through the dorsal column at C2-C4 segments to record from neurones activated antidromically from the white matter of the cerebellar anterior lobe with a negative pulse (0.2 msec duration) of less than 200 FA. The criteria for antidromic nature of the excitation were the same as described previously 4. The ipsilateral (to recording side) C2-C8 dorsal roots, peripheral nerve branches of the C2-C4 dorsal rami, various forelimb nerves, and the bilateral eighth nerves and the medial longitudinal fasciculus(MLF)were stimulated to explore synaptic inputs to the recorded neurones. After experiments the sites of cell recording in the cord and of stimulation in the cerebellum were determined histologically (cf. ref. 4). Spinocerebellar tract neurones identified as above were encountered in the region 0.3-0.8 mm lateral f rom the midline and 2.5-3.8 mm deep from the dorsal surface of the C2-C4 segments, where the CCN was located. In the centre of this region, cerebellar stimulation often evoked compound, antidromic field potentials consisting of several unitary spikes, which recruited with increase of stimulus strength (Fig. l A), indicating the existence of a cluster of spinocerebellar neurones. The sites of spinocerebellar neurones recorded in one animal at C2 are shown on a representative transverse plane in Fig. lB. As this was the case, most neurones were situated in the

Neck muscle afferent input to spinocerebellar tract cells of the central cervical nucleus in the cat

SummaryExtracellular and intracellular recordings were made from spinocerebellar tract neurones of the central cervical nucleus (CCN) in C1–C3 segments of the anaesthetized cat. These neurones were identified by antidromic activation from the cerebellar peduncle. Stimulation of the ipsilateral dorsal root elicited extracellular spikes or EPSPs with a monosynaptic latency in almost all CCN neurones in the same segment (segmental input). Late excitatory effects were also observed in about one third of CCN neurones. The monosynaptic EPSP was occasionally followed by an IPSP. The excitatory input from the dorsal root to CCN neurones was extended over several segments for some CCN neurons (extrasegmental input). Monosynaptic excitation was evoked in CCN neurones after stimulation of dorsal neck muscle nerves as well; i.e. splenius (SPL), biventer cervicis and complexus (BCC), rectus capitus dorsalis, and obliquus capitus caudalis. Thresholds for this excitation were near the threshold of the nerve, suggesting that it originated from group I fibres. The component of excitation added after strong stimulation of neck muscle nerves would be attributed to group II fibres. When a CCN neurone received excitatory input from the nerve of one muscle, it was generally not affected by stimulation of other nerves in the same segment. Such muscle specificity of segmental input was the principal pattern of connexion of neck muscle afferents with CCN neurones. In some cases, however, excitatory convergence from SPL and BCC nerves onto single CCN neurones or excitation from the SPL nerve and inhibition from the BCC nerve were also observed. Nearly half of the CCN neurones received input from one muscle nerve of the same segment and not from the afferent of the same muscle of different segments, indicating a segment specificity of input. In the remaining CCN neurones, weaker excitatory effects were induced from afferents of different segments as well. In such extrasegmental effects, inputs to CCN neurones from caudal segments predominated in frequency over those from rostral segments. The origin of extrasegmental input was generally confined to the same muscle. Low threshold muscle afferents from the SPL and BCC were intraaxonally stained with HRP. The collaterals of the stained fibre distributed branchlets and terminals to the CCN, laminae VII, VIII, and motor nuclei. Two fibres responding to local muscle prodding or stretch showed a similar morphology. The findings indicated that muscle spindle afferents from primary endings projected to the CCN.

The Neck and Labyrinthine Influences on Cervical Spinocerebellar Tract Neurones of the Central Cervical Nucleus in the Cat

Publisher Summary This chapter investigates the cerebellar projection areas and the input to the spinocerebellar tract (SCT) originating from the central cervical nucleus (CCN) by electrophysiologically in the cat. The CCN-spinocerebellar tract has now been identified as (1) receiving synaptic inputs from both the neck and the labyrinths, and (2) projecting to the vermis of the anterior lobe and to the posterior lobe. Experiments indicate that the input from the neck to CCN-SCT cells is primarily of joint origin probably from the same afferents which initiate tonic neck reflexes, influence extraocular motoneurones, and project to the flocculus. Wilson et al. have shown that the joint afferent impulses are relayed by neurones of Brodal and Pompeianos group x; the latter neurones do not receive input from the labyrinth in contrast with the CCN cells, the majority of which are co-excited by impulses from both the neck and vestibular afferents.

A physiological study of identification, axonal course and cerebellar projection of spinocerebellar tract cells in the central cervical nucleus of the cat.

SummarySpinocerebellar tract (SCT) neurones in and around the central cervical nucleus (CCN) were physiologically identified by antidromic activation of these cells on stimulation of the cerebellum. Among the Spinocerebellar tract cells thus identified, those ascending the contralateral spinal funiculi were found in the CCN and ventralwards, whereas those ascending the ipsilateral funiculi existed mostly dorsal to the CCN partly overlapping with crossed cells in the nucleus. Mapping sites from which CCN cells were antidromically activated showed that axons of the CCN-SCT cross at the same segment, ascend the ventral funiculus initially, the lateral funiculus at rostral C1 and the lateral border of the medulla to reach the cerebellar peduncle, enter the cerebellum mainly via the restiform body but possibly also via the superior peduncle. Systematic mapping of stimulation within the cerebellum indicated that the CCNSCT projects to the medial part of the anterior lobe and the posterior lobe bilaterally. Projection to lobules I–II was found in almost all CCN-SCT cells examined. Three fourths of CCN-SCT cells projected to the posterior lobe, as revealed by less extensive mapping. Mapping of axonal regions of the same single CCN-SCT cells showed that they project multifocally in the cerebellum, where projection to lobules I–II was common and that to other areas varied with individual cells. Conduction velocites decreased within the cerebellum probably as the result of repeated branching. Mossy fibre responses evoked on stimulation of the C2 dorsal root in cats with the transected dorsal funiculi were shown to be mediated mostly via the CCN-SCT. Mapping the field potential showed that the response was by far the largest in lobules I–II. This suggested that the terminals provided by the CCN-SCT are the densest in these lobules.

Axonal trajectory of single group Ia and Ib fibers in the cat spinal cord

Abstract Intracellular staining with HRP of physiologically identified group Ia and Ib afferent fibers in the adult cat lumbosacral cord revealed that group Ia and Ib fibers take a similar course in the dorsal funiculus, but the collaterals emerging from them show a different topographical distribution and a different mode of branching in the gray matter. Ia collaterals terminate in laminae VI, VII, IX, and sometimes VIII, whereas Ib collaterals terminate only in lamina VI, or both VI and IX. In lamina IX, two large motor-type neurons received terminations of both Ia and Ib fibers at the same time.

A Role of Neck Afferents on Vestibulocollic Reflex Elicited by Dynamic Labyrinthine Stimulation

Publisher Summary From the frequency response analysis of the vestibulocollic reflex, the existence of a neural integrator was suggested in the pathway between vestibular nucleus neurons and neck motoneurones. The pathways participating in this integration are still unknown. This chapter presents a study on vestibular-induced neck movement (vestibulocollic reflex) with the frequency response method in decerebrate cats. The horizontal semicircular canal was stimulated by sinusoidal oscillation of the turntable. Recordings were made from single motor units or compound EMGs of dorsal neck muscles. Motor units were classified into two groups on the basis of their maximum firing rate: HF (high frequency) and LF (low frequency) units. HF units had a larger gain than LF units. The phase lag of the motor units relative to angular acceleration was about 140°at a frequency range from 0.05 to 0.2 Hz and the gain was decreased at a slope of about 40 dB/decade at a frequency range from 0.01 to 0.4 Hz. A positive correlation was observed between the phase lag and the gain of each motor units.The gain of compound EMG responses depended on the spontaneous activity. When the spontaneous activity was low or too high, the gain was small. There was an intermediate spontaneous activity level at which the gain became maximal.