Library

Notes: Summary Spinocerebellar 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.

Notes: Summary Extracellular 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.

Notes: Summary Excitation of dorsal neck motoneurones evoked by electrical stimulation of primary trigeminal afferents in the Gasserian ganglion has been investigated with intracellular recording from α-motoneurones in the cat. Single stimulation in the Gasserian ganglion ipsi-and contralateral to the recording side evoked excitatory postsynaptic potentials (EPSPs) in motoneurones innervating the lateral head flexor muscle splenius (SPL) and the head elevator muscles biventer cervicis and complexus (BCC). The gasserian EPSPs were composed of early and late components which gave the EPSPs a hump-like shape. A short train of stimuli, consisting of two to three volleys, evoked temporal facilitation of both the early and late EPSP components. The latencies of the gasserian EPSPs ranged from 1.6 to 3.6 ms in SPL motoneurones and from 1.6 to 5.8 ms among BCC motoneurones. A rather similar latency distribution between 1.6 and 2.4 ms was found for ipsi- and contralateral EPSPs in SPL and BCC motoneurones, which is compatible with a minimal disynaptic linkage between primary trigeminal afferents and neck motoneurones. Systematic transections of the ipsi- and contralateral trigeminal tracts were performed in the brain stem between 3 and 12 mm rostral to the level of obex. The results demonstrate that both the ipsi- and contralateral disynaptic and late gasserian EPSPs can be mediated via trigeminospinal neurones which take their origin in the nucleus trigeminalis spinalis oralis. Transection of the midline showed that the contralateral trigeminospinal neurones cross in the brain stem. Systematic tracking in and around the ipsilateral trigeminal nuclei demonstrated that the axons of ipsilateral trigeminospinal neurones descend just medial to and/or in the medial part of the nucleus. Spinal cord lesions revealed a location of the axons of the ipsilateral trigeminospinal neurones in the lateral and ventral funiculi. Interaction between the ipsi- and contralateral gasserian EPSPs showed complete summation of the disynaptic EPSP component, while the late components were occluded by about 45%. These results show that the disynaptic EPSPs are mediated by separate trigeminospinal neurones from the ipsi- and contralateral side, while about half of the late EPSPs are mediated by common neurones which receive strong bilateral excitation from commissural neurones in the trigeminal nuclei. Spatial facilitation was found in the late gasserian EPSP but not in the disynaptic gasserian EPSP by conditioning stimulation of cortico- and tectofugal fibres. Disynaptic pyramidal and tectal EPSPs, which are mediated by reticulospinal neurones, were facilitated by a single stimulation in the gasserian ganglion at an optimal interval of 2 ms. It is suggested that primary trigeminal afferents can excite the reticulospinal neurones via a disynaptic trigeminoreticular pathway.

Notes: Summary 1.The somatic location and axonal projections of inhibitory vestibular nucleus neurons activated by the horizontal semicircular canal nerve (HCN) were studied in anesthetized cats. Cats were anesthetized with ketamine hydrochloride and pentobarbital sodium. 2.Intracellular recordings were obtained from 11 neck extensor motoneurons which were identified by antidromic activation from the dosai rami (DR) in the C1 segment. Stimulation of the ipsilateral (i-) HCN and the ipsilateral abducens (AB) nucleus evoked IPSPs in the motoneurons. These IPSPs were fully or partially occluded when they were evoked simultaneously. 3. Intracellular recordings were obtained from 8 AB motoneurons. Stimulation of the i-HCN and the i-C1DR motoneuron pool evoked IPSPs in the AB motoneurons. These IPSPs were also partially occluded when they were evoked simultaneously, which implied that some HCN-activated neurons inhibit both i-AB motoneurons and ipsilateral neck motoneurons. 4. Unit activity was extracellularly recorded from 30 vestibular neurons that were activated monosynaptically by i-HCN stimulation. Their axonal projections were determined by stimulating the i-AB nucleus and the i-C1DR motoneuron pool. Eight neurons were activated by both stimuli, and were termed vestibulooculo-collic (VOC) neurons. Their axonal branching was examined by means of local stimulation in and around the i-AB nucleus and the i-C1DR motoneuron pool. Eighteen neurons were antidromically activated from the i-C1DR motoneuron pool but not from the i-AB nucleus. These were termed vestibulo-collic (VC) neurons. Four neurons were activated from the i-AB nucleus but not from the ventral funiculus in the C1 segment, and were termed vestibulo-ocular (VO) neurons. The HCN-activated inhibitory neurons were mostly localized in the rostroventral part of the medial vestibular nucleus. 5. Horseradish peroxidase (HRP) was injected iontophoretically into descending axons of 2 HCN-activated inhibitory VOC neurons which were identified by stimulation of the i-HCN and the i-AB nucleus. Axon collaterals were ramified from a stem axon in the ventral funiculus, and entered the gray matter and spread in the laminae VIII and IX. Terminal boutons were distributed over the medial and the ventromedial parts of the vental horn in the C1 segment.

Notes: Summary 1. Projections of reticulospinal neurones (RSNs) in the nucleus reticularis pontis caudalis (N.r.p.c.) to dorsal neck motoneurones supplying splenius (SPL, lateral head flexor) and biventer cervicis and complexus (BCC, head elevator) muscles were studied in the cat anaesthetized with pentobarbiturate or α-chloralose. 2. Threshold mapping for evoking antidromic spikes revealed that most of RSNs tested projecting down to brachial segments but not to lumbar segments (C-RSNs) gave off collaterals to the gray matter of the upper spinal cord in C2–C3 segments. 3. Spike triggered averaging showed that negative field potentials were evoked after firing of a single C-RSN (single fibre focal synaptic potentials, FSPs) in the region of C2–C3 where large antidromic field potentials from nerves supplying SPL or BCC muscles were evoked. The single fibre FSPs ranged between 1 and 10 μV in amplitude and had latencies between 0.7 and 1.2 ms from the onset of the triggering spike. In most cases, a presynaptic spike preceded the negative potential by 0.3 ms. These results indicated that C-RSNs project to the SPL or BCC motor nucleus. 4. Spike triggered averaging of postsynaptic potentials revealed EPSPs (single fibre EPSPs) in 36 dorsal neck motoneurones, predominantly in SPL (25) and less in BCC (11) motoneurones, evoked from 15 C-RSNs. The amplitude of the single fibre EPSPs ranged from 5 to 310 μV, and had latencies of 0.8–2.0 ms from the onset of the triggering spikes of C-RSNs, or 0.3–0.5 ms from the presynaptic spike when recorded. The results indicated monosynaptic excitatory connexions of C-RSNs to dorsal neck motoneurones. 5. Single fibre EPSPs from a C-RSN were usually recorded from either BCC or SPL motoneurones but not from both types of motoneurones, when tested in many motoneurones. This showed that connexions of C-RSNs with dorsal neck motoneurones were muscle specific. 6. RSNs projecting down to the lumbar segment (L-RSN) also showed branching in C2–C3 segments. Excitatory monosynaptic connexion of L-RSNs with neck motoneurones were demonstrated by recording single fibre postsynaptic population potentials (p.s.p.p.s.) from the C2 ventral root perfused with sucrose. The probability of evoking monosynaptic single fibre p.s.p.p.s. was less (19%) than for C-RSNs (59%).

Notes: Summary Dorsal neck motoneurones receive disynaptic tectal and pyramidal EPSPs via common reticulospinal neurones (RSNs). This study was aimed at identification of the RSNs projecting directly to neck motoneurones and mediating these EPSPs. 1. Stimulation of the tectum and the cerebral peduncle evoked monosynaptic descending volleys in the spinal cord, which were chiefly mediated by reticulospinal neurones in the pons and the medulla. Systematic tracking of the C3 and C7 segments was made to locate descending volleys in the spinal funiculi. The tectal monosynaptic volley was largest in the medial part of the ventral funiculus and decreased gradually as the recording electrode was moved to the lateral part of the ventral funiculus and the lateral funiculus. In contrast, the peduncle-evoked monosynaptic volley was distributed rather evenly in the ventral funiculus and the ventral half of the lateral funiculus. 2. Differences in funicular distribution of the two descending volleys suggest the existence of subgroups of RSNs which differed in strength of inputs from the two descending fibre systems and in the funicular location of descending axons. 3. The RSNs were classified into the following four groups; (1) mRSNs which descended in the medial part of the ventral funiculus, (2) in RSNs which descended in the ventrolateral funiculus, (3) 1RSNs which descended in the dorsal 2/3 of the lateral funiculus and (4) coRSNs which descended in the contralateral funiculi. The mRSNs were located in a fairly localized region corresponding to the nucleus reticularis pontis caudalis (N.r.p.c.), while inRSNs, 1RSNs and coRSNs were mainly in the nucleus reticularis gigantocellularis (N.r.g.), in the nucleus reticularis magnocellularis (N.r.m.) and in the nucleus reticularis ventralis (N.r.v.). RSNs were further divided into three types depending on the levels of projection. L-RSNs projected to the lumbar spinal segments. C-RSNs descended to the C6–C7 spinal segment but not to the lumbar segments. N-RSNs projected to the C3 but not to the C6–C7 segments. 4. Stimulation of the tectum and the cerebral peduncle produced monosynaptic negative field potentials in the medial two thirds of the reticular formation in the pons and medulla. Tectal field potentials were largest in the N.r.p.c. and the rostral part of the N.r.g., while pyramidal field potentials were largest in the N.r.g. Correspondingly, RSNs in the N.r.p.c. (mRSNs) received larger monosynaptic EPSPs from tectal than from pyramidal volleys, while RSNs in the N.r.g. (in-, 1- and coRSNs) received stronger input from the peduncle than from the tectum. 5. Stimulation of the C7 ventral but not the lateral funiculus evoked monosynaptic EPSPs on all the dorsal neck motoneurones tested. Stimulation of the L1 segment only produced monosynaptic EPSPs in 35% of the motoneurones. The L1 evoked EPSPs were much smaller than C7 evoked EPSPs. 6. The C7 evoked EPSPs (C7 EPSP) showed complete occlusion (collision) with the tectal or pyramidal disynaptic EPSPs. Similar results were obtained with L1 EPSPs. These results indicate that tectal and pyramidal disynaptic EPSPs in dorsal neck motoneurones were mediated chiefly by C-mRSNs and C-inRSNs and partly by L-RSNs.