Input-output organization of reticulospinal neurones,with special reference to connexions with dorsal neck motoneurones in the cat

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.     

Effects of electrical stimulation of the thoracic spinal cord on bladder and external urethral sphincter activity in the decerebrate cat

Summary Electrical stimulation of the spinal cord above the sacral segments was used to produce coordinated micturition in the paralysed decerebrate cat. Stimulation of the superficial aspect of the dorsolateral funiculus (DLF) within the lower thoracic (T9-T13) segments produced a bladder contraction coordinated with decreased activity in the external urethral sphincter (EUS) branch of the pudendal nerve during which time fluid was expelled. In addition, a similar response was observed with DLF stimulation at the boundary of the L5/L6 segments. At the second cervical spinal segment, however, stimulation of a more lateral and ventral portion of the superficial spinal white matter was the only effective site for producing micturition. The spinal cord-evoked response was comparable to the micturition evoked by electrical stimulation of the pontine micturition centre (PMC) within the brainstem. A bilateral lesion of the dorsal columns (DC) and the dorsolateral funiculi (DLF) at the lower thoracic levels abolished reflex micturition evoked by bladder distension. However stimulation rostral to the lesion, within the PMC or thoracic DLF, continued to produce coordinated bladder and sphincter response during voiding. Stimulation caudal to the lesion produced a decrease in pudendal nerve activity but did not produce a void or bladder pressure change. This reduction in pudendal nerve activity could be abolished with a second lesion of the superficial DLF caudal to the stimulation site. It was concluded that stimulation of the thoracic dorsolateral funiculus activates both ascending and descending fibres which can influence the bladder and/or sphincter muscles. The spinal cordevoked voiding was hypothesized to be due to activation of some portion of the ascending limb of the spinobulbospinal micturition reflex loop. The decreased activity produced by stimulation of the thoracic DLF caudal to a bilateral DC/DLF subtotal cord lesion may be mediated by fibres descending in the dorsolateral funiculus. The possibility that the spinal cord stimulation antidromically activated axons of neurons having segmental collaterals capable of influencing pudendal neural activity cannot be exclused at this time.     

Reticulospinal and vestibulospinal pathways in the snake Python regius

In the present HRP study extensive reticulospinal projections and more modestly developed vestibulospinal pathways have been demonstrated in the snake Python regius. The funicular trajectories of the main reticulospinal pathways have been shown: via the lateral funiculus pass spinal projections of the nucleus reticularis superior pars lateralis, the nucleus reticularis inferior and nucleus raphes inferior; via the ventral funiculus fibers arising in the nucleus reticularis superior and nucleus reticularis medius. Spinal projections of the locus coeruleus and subcoeruleus area reach their targets via both the lateral and ventral funiculi. Two vestibulospinal pathways have been demonstrated: an ipsilateral tractus vestibulospinalis lateralis arising in the ventrolateral vestibular nucleus, and a contralateral tractus vestibulospinalis medialis from the descending and ventromedial vestibular nuclei. After HRP gel implants into the vestibular nuclear complex direct vestibulocollic projections to motoneurons in the rostral spinal cord were observed. Spinal projections from the ventral part of the nucleus reticularis inferior and the descending and ventromedial vestibular nuclei are mainly aimed at the thin "neck area" (approximately the first 50 spinal segments). This area is extensively used in such acts as orientation and prey-catching, requiring a rather delicate brain stem control.     

Dorsal column nuclei afferents in the lateral funiculus of the cat: Distribution pattern and absence of sprouting after chronic deafferentation

Summary In adult cats the successive degeneration technique has been used to demonstrate the existence and distribution pattern of lateral funicular fibers to the dorsal column nuclei (DCN) originating from the brachial and thoracic cord. In a first operation, interruption of the dorsal columns at appropriate cervical levels and of the lateral funiculus at low thoractic levels was performed. Thirteen months later, a lesion was made in the lateral funiculus at upper brachial or uppermost thoracic levels. Fiber degeneration in the DCN consequent to this second operation is not contaminated by damage to dorsal roots or by interruption of lateral funicular afferents from lumbo-sacro-coccygeal segments. All animals were sacrified 7 days after the second operation. Serial sections through the medulla oblongata, impregnated with the Fink-Heimer technique, show that fibers ascending from brachial levels in the dorsal part of the lateral funiculus reach the cuneate nucleus either by a dorsomedial route through the tegmentum or by ascending in the restiform body. Degenerated fibers distribute selectively to the rostral part, and to a lesser extent to the base, of the cuneate nucleus. Only very few fibers ascending from thoracic levels in the lateral funiculus distribute to the DCN.Abbreviation List CUN cuneate nucleus - DV dorsal motor nucleus of vagus nerve - EC external cuneate nucleus - GR gracile nucleus - HYP hypoglossal nucleus - int nucleus intercalatus - PH nucleus praepositus hypoglossi - PM paramedian nucleus - SOL solitary nucleus and tract - VEST vestibular complex - X nucleus X of Brodal and Pompeiano (1957) - Z nucleus Z of Brodal and Pompeiano (1957) - V spin spinal trigeminal nucleus     

Skilled digit movements in feline and primate--recovery after selective spinal cord lesions

Recovery of voluntary movements after partial spinal cord injury depends, in part, on a take-over of function via unlesioned pathways. Using precise forelimb movements in the cat as model, spinal pathways contributing to motor restitution have been investigated in more detail. The food-taking movement by which the cat graSPS a morsel of food with the digits and brings it to the mouth is governed by interneurones in the forelimb segments (C6-Th1) and is normally controlled via the cortico- and rubrospinal tracts. Food-taking disappears after transection of these pathways in the dorsal part of the lateral funiculus (DLF) in C5/C6, but then recovers during a period of 2-3 weeks. Experiments with double lesions showed that the recovery depends on a take-over via ipsilateral ventral systems; a ventrally descending pathway, most probably cortico-reticulospinal, and a pathway via propriospinal neurones in the C3-C4 segments. It is postulated that the recovery involves a plastic reorganization of these systems. Dexterous finger movements in the macaque monkey are generally considered to depend on the monosynaptic cortico-motoneuronal (CM) connexion, which is lacking in the cat. Such movements are abolished after pyramidotomy at the level of the trapezoid body. However, experiments with transection of the corticospinal tract in the DLF and partly ventral part of the lateral funiculus in C5, showed a fast (1-28 days) recovery of precision grip and, to some extent, independent finger movements. Deficits in preshaping during the final approach to the morsel as well as lack of force were observed. A C5 DLF lesion spares corticofugal pathways to the brainstem and upper cervical segments. It is suggested that indirect corticomotoneuronal pathways may provide for recovery of dexterous finger movements and that the role of CM pathways for such movements should be broadened to include not only the monosynaptic connexion.     

Axonal trajectories of the nucleus reticularis gigantocellularis neurons in the C2-C3 segments in cats.

Axonal trajectories in the C2-C3 segments of the nucleus reticularis gigantocellularis neurons projecting to the lower cervical cord (C-RSNs) and excited monosynaptically from cortico- and tectofugal fibers were studied by mapping thresholds of antidromic excitation and intra-axonal staining in cats. The C-RSNs descended in various sites of the spinal funiculi, and the projection area of individual cells varied with the funicular location of the stem axon. C-RSNs descending in the ventrolateral funiculus (inRSNs) projected mainly to lamina VIII-IX, those descending in the lateral funiculus (IRSNs) mainly to laminae VI-VIII, and those descending in the contralateral funiculus (coRSNs) chiefly to laminae VIII-IX on that side. It is suggested that inRSNs and coRSNs mediate disynaptic effects from cortico- and tectofugal fibers to dorsal neck motoneurons bilaterally.     

Thermosensory defects after cervical spinal cord lesions in the cat

Summary The behavioural thermosensitivity of cat paws was examined before and/or after restricted uni- and/or bilateral lesions had been made in the spinal cord between the first and fifth cervical segments. Unilateral lesions of the lateral funiculus, which involved at least its whole width at the level of the central canal, reproducibly were found to interfere with the contralateral sensitivity for temperature increases and/or decreases. No corresponding thermosensory deficiencies were found after unilateral lesions involving the ventral spinal quadrant or the dorsal funiculus. Various bilateral and combined lesions were made, but no cat ever developed thermoanaesthesia. The bilateral lesions included bilateral transections of: the middle parts of the lateral funiculi, the dorsal halves of the lateral funiculi, the dorsal funiculi, and the ventral spinal half.Most of our knowledge about peripheral behavioural thermosensitivity after spinal cord injury is based on observations of human patients, especially after anterolateral chordotomies. The present finding of contralateral thermosensory deficiencies after lesions of the middle part of the lateral funiculus fits with some of the clinical reports. The present failure to cause thermoanaesthesia, on the other hand, is inconsistent with the theory of a single ascending spinal pathway for behavioural thermo-sensitivity, which has emanated mainly from the clinical observations.     

The termination of spinomesencephalic fibers in cat

Summary The projections to the midbrain from the spinal cord have been investigated in the cat with the degeneration technique and by using horseradish peroxidase (HRP) as an anterograde tracer. Two types of spinal cord lesions were performed: 1) Cordotomies at cervical or thoracic levels transecting the ventral and lateral funiculi. 2) Transections of the ventral, ventrolateral, dorsolateral or dorsal funiculus, respectively, at cervical levels. In the anterograde tracing experiments HRP was injected into the spinal cord at cervical, lumbar or sacral levels.The results show large projections to the lateral and ventrolateral parts of the periaqueductal gray (PAG1), the posterior pretectal nucleus (PP) and the nucleus of Darkschewitsch (D). More moderate projections go to the medial division of the periaqueductal gray (PAGm), the cuneiform nucleus (CF), the mesencephalic reticular formation (MRF), lateral part of the deep layer of the superio colliculus (SP) and magnocellular medial geniculate nucleus (GMmc), while scattered spinal fibers are present in the dorsal part of the periaqueductal gray (PAGd), the external inferior collicular nucleus (IX), the intermediate layer of the superior colliculus (SI), the lateral part of the red nucleus (NR) and in the Edinger-Westphal portion of the oculomotor nucleus (3). In addition a few fibers are present in the interstitial nucleus of Cajal (CA) and anterior pretectal nucleus (PAc).The results indicate that at midcervical levels most of the spinomesencephalic fibers ascend in the ventral funiculus, with only a moderate fraction ascending in the ventral half of the lateral funiculus. Almost no fibers ascend in the dorso-lateral funiculus and none appear to pass in the dorsal funiculus.No distinct somatotopic pattern was found in the spinomesencephalic projections, but more fibers from cervicobrachial segments terminate in the rostral than in the caudal parts of the terminal fields in PAG, CF, SP and IX, while the lumbar fibers were more numberous in the caudal parts. PP seems to receive spinal fibers mainly from the caudal half of the cord.     

An evoked potential study of spinal pathways projecting to the cerebral somatosensory areas in the dog

Summary Evoked potentials from stimulation of the hindlimbs were recorded in the cerebral somatosensory areas of dogs using Nembutal anaesthesia. Various transections of the low thoracic spinal cord were made in order to determine the pathways projecting to these areas. The shortest latency cortical activation was obtained via two pathways: the dorsal column pathway and the spinocervical tract which is located in the dorsomedial part of the lateral funiculus (DLF). Cortical activation after longer latency was obtained via ventral pathways in both the contralateral and ipsilateral spinal halves. The cortical potentials elicited by adequate (hair) stimuli depended mainly on transmission via the dorsal column and DLF pathways.     

Reimplantation of avulsed lumbosacral ventral roots in the rat ameliorates injury-induced degeneration of primary afferent axon collaterals in the spinal dorsal columns

Injuries to the cauda equina/conus medullaris portion of the spinal cord can result in motor, sensory, and autonomic dysfunction, and neuropathic pain. In rats, unilateral avulsion of the motor efferents from the lumbosacral spinal cord results in at-level allodynia, along with a corresponding glial and inflammatory response in the dorsal horn of the spinal cord segments immediately rostral to the lesion. Here, we investigated the fate of intramedullary primary sensory projections following a motor efferent lesion. The lumbosacral (L6 and S1) ventral roots were unilaterally avulsed from the rat spinal cord (VRA; n=9). A second experimental group had the avulsed roots acutely reimplanted into the lateral funiculus (Imp; n=5), as this neural repair strategy is neuroprotective, and promotes the functional reinnervation of peripheral targets. A laminectomy-only group served as controls (Lam; n=7). At 8 weeks post-lesion, immunohistochemical examination showed a 42% reduction (P<0.001) in the number of RT97-positive axons in the ascending tracts of the dorsal funiculus of the L4-5 spinal segment in VRA rats. Evidence for degenerating myelin was also present. Reimplantation of the avulsed roots ameliorated axon and myelin degeneration. Axons in the descending dorsal corticospinal tract were unaffected in all groups, suggesting a specificity of this lesion for spinal primary sensory afferents. These results show for the first time that a lesion restricted to motor roots can induce the degeneration of intramedullary sensory afferents. Importantly, reimplantation of the lesioned motor roots ameliorated sensory axon degeneration. These data further support the therapeutic potential for reimplantation of avulsed ventral roots following trauma to the cauda equina/conus medullaris.     

Tonic suppression of reflex transmission in low spinal cats

Summary Transmission in various spinal hindlimb reflex pathways arising from muscle, cutaneous and joint afferents, was investigated in acute low spinal (Th10) cats before and after lesions at more caudal levels in the lumbar segments. Lesions of the ipsilateral dorsolateral funiculus (DLF) resulted in increased mono- and polysynaptic ventral root discharges. With conditioning of monosynaptic reflexes it was demonstrated that the DLF lesion enhanced transmission in reflex pathways from group II and III muscle afferents. The DLF lesion also resulted in increased dorsal root potentials from cutaneous, joint and group III muscle afferents. These reflex enhancements could not be obtained with lesions rostral to L2, but developed with lesions in L2 and to some extent in L3, but no further effect was obtained by adding lesions caudal to L3. Ventral extension of the DLF lesion gave hardly any increase of reflex transmission. It is postulated that the investigated reflex pathways may be tonically inhibited in the acute low spinal state by propriospinal neurones with cell bodies in the L2–L3 segments and with axons descending in the dorsolateral funiculus.Abbreviations LF Lateral funiculus - DLF dorsolateral funiculus - FRA flexor reflex afferents - DRP dorsal root potential - PAD primary afferent depolarization - PBSt Nerves: posterior biceps and semitendinosus - ABSm anterior biceps and semimembranosus - Sur sural - G-S gastrocnemius and soleus - Pl plantaris - FDHL flexor digitorum and hallucis longus - j posterior knee joint - DP deep peroneus - SP superficial peroneus - Sart sartorius - Q quadriceps     

Effects from the sensorimotor cortex on the spinal cord in cats with transected pyramids

Summary Effects of stimulation of the sensorimotor cortex on activity of the lumbosacral cord were studied in pyramidotomized cats. The following actions initiated by corticofugal volleys were found: 1. postsynaptic effects on motoneurones, mainly excitatory in flexor motoneurones and inhibitory or excitatory in extensor motoneurones, 2. facilitation of spinal reflexes to motoneurones at an interneuronal level, 3. depolarization of presynaptic terminals of group Ib and cutaneous fibres. The latencies of the earliest cortical effects on motoneurones as indicated by modification of monosynaptic reflexes or PSPs were 9–12 msec. Experiments with lesions of different spinal tracts suggest that the effects on motoneurones are mediated mainly by pathways in the ventral part of the lateral funiculus (probably reticulospinal), the facilitation of reflex transmission by pathways in the dorsal part of the lateral funiculus (probably rubrospinal) and primary afferent depolarization by both the former and the latter pathways. The strongest cortical effects were evoked by stimulation of an area around the postcruciate dimple.JBRO-Fellow     

Pathways mediating descending control of spinal nociceptive transmission from the nuclei locus coeruleus (LC) and raphe magnus (NRM) in the cat

Summary We have previously reported that electrical stimulation in LC or NRM when tested on the activity of a multireceptive neurone in the spinal cord produced similar inhibitory actions. The present study aimed to define the pathways that mediate this descending inhibitory action in the spinal cord by pharmacological means and by making surgical lesions in the spinal cord or NRM. Attempts to differentiate pathways pharmacologically did not succeed since the i.v. administration of the 5-HT antagonists, methysergide and cinnanserin failed to antagonise descending inhibition evoked from either NRM or LC. Lesions involving a part or whole of the ipsilateral ventral quadrant reduced the inhibition produced from LC to a greater extent than that from NRM in 24 multireceptive neurones. In seven of these neurones stimulation in LC was without any effect after the lesion. In 23 multireceptive neurones recorded after making lesions that spared the ipsilateral ventral quadrant the effects of LC stimulation were unchanged. NRM effectiveness was reduced by an ipsilateral dorsolateral funiculus (DLF) lesion but required a bilateral DLF lesion for an almost complete abolition. Similar results were obtained when the effect of the various lesions were studied on the dorsal root potentials (DRPs) generated from LC or NRM. Lesions in the midline raphe complex, that included NRM, did not block the inhibitory action of LC stimulation. The inhibition produced from both these nuclei was additive whereas excitation was not. We conclude that LC actions in the spinal cord are mediated primarily through a pathway in the ipsilateral ventral quadrant whereas those from NRM are mediated through bilateral projections in DLF. Furthermore, although NRM plays no part in mediating LC actions and separate and independent pathways mediate their spinal action yet these apparently independent pathways have plenty of scope for interaction in the dorsal horn of the spinal cord itself.     

Terminations of reticulospinal fibers originating from the gigantocellular reticular formation in the mouse spinal cord

The present study investigated the projections of the gigantocellular reticular nucleus (Gi) and its neighbors—the dorsal paragigantocellular reticular nucleus (DPGi), the alpha/ventral part of the gigantocellular reticular nucleus (GiA/V), and the lateral paragigantocellular reticular nucleus (LPGi)—to the mouse spinal cord by injecting the anterograde tracer biotinylated dextran amine (BDA) into the Gi, DPGi, GiA/GiV, and LPGi. The Gi projected to the entire spinal cord bilaterally with an ipsilateral predominance. Its fibers traveled in both the ventral and lateral funiculi with a greater presence in the ventral funiculus. As the fibers descended in the spinal cord, their density in the lateral funiculus increased. The terminals were present mainly in laminae 7–10 with a dorsolateral expansion caudally. In the lumbar and sacral cord, a considerable number of terminals were also present in laminae 5 and 6. Contralateral fibers shared a similar pattern to their ipsilateral counterparts and some fibers were seen to cross the midline. Fibers arising from the DPGi were similarly distributed in the spinal cord except that there was no dorsolateral expansion in the lumbar and sacral segments and there were fewer fiber terminals. Fibers arising from GiA/V predominantly traveled in the ventral and lateral funiculi ipsilaterally. Ipsilaterally, the density of fibers in the ventral funiculus decreased along the rostrocaudal axis, whereas the density of fibers in the lateral funiculus increased. They terminate mainly in the medial ventral horn and lamina 10 with a smaller number of fibers in the dorsal horn. Fibers arising from the LPGi traveled in both the ventral and lateral funiculi and the density of these fibers in the ventral and lateral funiculi decreased dramatically in the lumbar and sacral segments. Their terminals were present in the ventral horn with a large portion of them terminating in the motor neuron columns. The present study is the first demonstration of the termination pattern of fibers arising from the Gi, DPGi, GiA/GiV, and LPGi in the mouse spinal cord. It provides an anatomical foundation for those who are conducting spinal cord injury and locomotion related research.     

The red nucleus and the rubrospinal projection in the mouse

We studied the organization and spinal projection of the mouse red nucleus with a range of techniques (Nissl stain, immunofluorescence, retrograde tracer injections into the spinal cord, anterograde tracer injections into the red nucleus, and in situ hybridization) and counted the number of neurons in the red nucleus (3,200.9 ± 230.8). We found that the rubrospinal neurons were mainly located in the parvicellular region of the red nucleus, more lateral in the rostral part and more medial in the caudal part. Labeled neurons were least common in the rostral and caudal most parts of the red nucleus. Neurons projecting to the cervical cord were predominantly dorsomedially placed and neurons projecting to the lumbar cord were predominantly ventrolaterally placed. Immunofluorescence staining with SMI-32 antibody showed that ~60% of SMI-32-positive neurons were cervical cord-projecting neurons and 24% were lumbar cord-projecting neurons. SMI-32-positive neurons were mainly located in the caudomedial part of the red nucleus. A study of vGluT2 expression showed that the number and location of glutamatergic neurons matched with those of the rubrospinal neurons. In the anterograde tracing experiments, rubrospinal fibers travelled in the dorsal portion of the lateral funiculus, between the lateral spinal nucleus and the calretinin-positive fibers of the lateral funiculus. Rubrospinal fibers terminated in contralateral laminae 5, 6, and the dorsal part of lamina 7 at all spinal cord levels. A few fibers could be seen next to the neurons in the dorsolateral part of lamina 9 at levels of C8–T1 (hand motor neurons) and L5–L6 (foot motor neurons), which is consistent with a view that rubrospinal fibers may play a role in distal limb movement in rodents.     

The spinal route of sympatho-inhibitory pathways descending from the medulla oblongata

1. The effect of making discrete lesions in the cervical spinal cord on the brainstem elicited inhibition of a spinal somato-sympathetic reflex response has been studied in anaesthetized cats. 2. Electrical stimulation within three areas of the medulla caused an inhibition of the spinal component of the reflex response elicited in thoracic white rami communicantes by stimulation of intercostal nerves. The three medullary areas studied were the ventrolateral medulla and the caudal rephe nucleus, from where bulbospinal monoamine neurones originate, and the ventromedial reticular formation. 3. The inhibitory effects of stimulation in the ventrolateral medulla and raphe nucleus were abolished by the destruction of parts of the ipsilateral dorsolateral funiculus of the cervical spinal cord, whereas the inhibition produced by ventromedial reticular formation stimulation was abolished by lesions which included part of the ventral quadrant of the cord. 4. The time course of the inhibitory effects of electrical stimulation of descending sympatho-inhibitory tracts in the cervical spinal cord was studied in unanaesthetized decerebrate cats spinalized at C1. Inhibition obtained from the dorsolateral funiculus characteristically had a longer time to onset than inhibition obtained from the ventrolateral and ventral funiculi.     

Properties of utricular nerve-activated vestibulospinal neurons in cats

The axonal pathway, conduction velocities, and locations of the cell bodies of utricular nerve-activated vestibulospinal neurons were studied in decerebrated or anesthetized cats using the collision test of orthodromic and antidromic spikes. For orthodromic stimulation, bipolar tungsten electrodes were placed on the utricular nerve and the other vestibular nerve branches were transected. Monopolar tungsten electrodes were positioned on both sides of the upper cervical segments (C2–4), caudal end of the cervical enlargement (C7-T1), and from the lower thoracic to the upper lumbar segments (T12-L3) and were used for antidromic stimulation of the spinal cord. Another monopolar electrode was also placed in the oculomotor nucleus to study whether utricular nerve-activated vestibulospinal neurons have ascending branches to the oculomotor nucleus. Of the 173 vestibular neurons orthodromically activated by the stimulation of the utricular nerve, 46 were second-order vestibulospinal neurons and 5 were third-order neurons. The majority of the utricular nerve-activated vestibulospinal neurons were located in the rostral part of the descending vestibular nucleus and the caudal part of the ventral lateral nucleus. Seventy-three percent of the utricular nerve-activated vestibulospinal neurons descended through the ipsilateral lateral vestibulospinal tract. Approximately 80% of these neurons reached the cervicothoracic junction, but a few reached the upper lumbar spinal cord. Twenty-seven percent of the utricular nerve-activated vestibulospinal neurons descended through the medial vestibulospinal tract or the contralateral vestibulospinal tracts. Those axons terminated mainly in the upper cervical segments. Almost none of the utricular nerve-activated vestibular neurons had ascending branches to the oculomotor nucleus.     

Tissue calcium levels following spinal cord transection in rats

Adult rats were subjected to midthoracic spinal cord transections. Three segments of spinal cord, each approximately 5 mm in length, were removed from each animal at intervals from 5 min to 48 h postlesion; one from the lesion site and one each immediately rostral and caudal to the transection. Total tissue calcium concentrations ([Ca]t) for each spinal cord segment were determined using atomic absorption spectrophotometry and compared to control segments from untransected animals. [Ca]t levels in the segment at the lesion site was significantly elevated above control values at 30 min post-lesion, but decreased to control levels by 1 h. All other segments remained at control levels for the duration of the postlesion period. The rapid rise and fall of [Ca]t at the lesion site differs from spinal cord contusion studies in which [Ca]t remains at elevated levels for extended periods. It is postulated that the "open" transection injury permits the rapid clearance of calcium from the injury site.     

Location and somatotopic organization of the cells of origin of the spino-cervical tract

Summary The locations of the cell bodies of origin of a pathway ascending in the dorsal part of the lateral funiculus of the cat spinal cord were mapped. It is presumed that the pathway is the spino-cervical tract. The locations of the neurons were determined by recording the antidromic action potentials in the lumbosacral enlargement evoked by stimulation of their axons at the third cervical segment, and then histologically reconstructing the recording sites. The cells were found to be scattered throughout laminae 4–6 of the dorsal horn, although most were in laminae 4 and 5. The conduction velocities of the axons ranged from 7 to 90 m/sec (mean 44 m/sec). A somatotopic relationship was observed between the locations of the cells within the dorsal horn and the distributions of their peripheral receptive fields. This somatotopic organization was oriented with respect to rostrocaudal and dorso-ventral axes as determined for the adult hindlimb by reference to its fetal development. The axes become distorted during development, but are still recognizable in the adult. Cells receiving afferent input from skin derived from rostral portions of the limb, including the medial surface of the adult foot, are located rostrally in the cord. The caudal limb, which includes the lateral surface of the foot in the adult, is represented caudally in the spinal cord. The dorsal limb or extensor surface projects to the lateral part of the dorsal horn, while the ventral limb or flexor surface is represented medially.