Ipsilateral Lateral Funiculus Research Articles

A Molecular Program for Contralateral Trajectory: Rig-1 Control by LIM Homeodomain Transcription Factors

Despite increasing evidence for transcriptional control of neural connectivity, how transcription factors regulate discrete steps in axon guidance remains obscure. Projection neurons in the dorsal spinal cord relay sensory signals to higher brain centers. Some projection neurons send their axons ipsilaterally, whereas others, commissural neurons, send axons contralaterally. We show that two closely related LIM homeodomain proteins, Lhx2 and Lhx9, are expressed by a set of commissural relay neurons (dI1c neurons) and are required for the dI1c axon projection. Midline crossing by dI1c axons is lost in Lhx2/9 double mutants, a defect that results from loss of expression of Rig-1 from dI1c axons. Lhx2 binds to a conserved motif in the Rig-1 gene, suggesting that Lhx2/9 regulate directly the expression of Rig-1. Our findings reveal a link between the transcriptional programs that define neuronal subtype identity and the expression of receptors that guide distinctive aspects of their trajectory.

Development of interneurons with ipsilateral projections in embryonic rat spinal cord.

Considerable progress has been made in recent years in identifying molecules with restricted expression in mammalian spinal cord at early developmental stages. However, the significance of the different expression patterns for most of these molecules is unclear because so little is known about the development of various classes of spinal interneurons. Recently, we have characterized the development of rat spinal cord interneurons with an axon that crosses in the ventral commissure (Silos-Santiago and Snider, J. Comp. Neurol., 325:514, 1992). In the current study, we describe the morphological development of ipsilaterally projecting spinal interneurons in laminae V-VIII of the thoracic spinal cord. These neurons were labelled by retrograde lateral diffusion of DiI after crystals were placed in various locations in the embryonic thoracic cord. By E14, approximately 48 hours after the first interneurons are generated, eight different groups of ipsilateral interneurons are present in the spinal cord. By E15, these groups of ipsilateral interneurons have reached distinct locations within the gray matter. Even at this early stage, different groups of cells have elaborated characteristic dendritic arborizations. By E19, at least 17 different types of ipsilateral interneurons can be identified on the basis of location and dendritic morphology. In general, ipsilateral interneurons are located more dorsally and laterally than commissural interneurons at all stages of embryonic development. Furthermore, in comparison with commissural neurons, fewer ipsilateral interneurons have dendritic arbors with a mediolateral orientation in the transverse plane. This work demonstrates that rat embryonic spinal cord contains a large number of morphologically distinct classes of interneurons that extend axons into the ipsilateral lateral funiculus. These neurons can be distinguished from commissural neurons on the basis of location and morphology. These results, taken together with those from our previous study, provide a framework for the localization of gene expression to different classes of spinal interneurons at early developmental stages.

Behavior of upper cervical inspiratory propriospinal neurons during fictive vomiting

1. The role of upper cervical inspiratory (UCI)-modulated neurons in respiratory muscle control during vomiting was examined by recording the impulse activity of these neurons during fictive vomiting in decerebrate, paralyzed cats. Fictive vomiting was identified by a characteristic series of bursts of coactivation of phrenic and abdominal muscle nerves, elicited either by electrical stimulation of supradiaphragmatic vagal nerve afferents or by emetic drugs, which would be expected to produce expulsion of gastric contents in nonparalyzed animals. 2. Data were recorded from 43 propriospinal UCI neurons, located in the C1-C3 spinal segments near the border of the intermediate gray matter and lateral funiculus, which were antidromically activated with floating pin electrodes placed in the ipsilateral lateral funiculus, usually at T1-T3. Some cells (9/21 tested) were also activated from the upper lumbar cord (L1). During respiration, most neurons (n = 40) had an augmenting discharge pattern during inspiration. In addition, more than one-half (55%) fired tonically during the remainder of the respiratory cycle. About 40% of UCI neurons showed variations in their firing pattern during the noninspiratory portion of respiration. These latter two properties of UCI neurons were not observed in dorsal and ventral respiratory group (DRG and VRG-, respectively) bulbospinal inspiratory (I) neurons previously recorded under similar conditions. 3. During fictive vomiting, the firing pattern of most UCI neurons fell into one of three main categories. More than one-half (53%) were active in phase with bursts of phrenic discharge and were thus classified as Active-type cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Nerve cell bodies in the dorsal funiculus of the rat spinal cord

Nerve cell bodies located within the white matter of the dorsal funiculus (DF neurons) have been previously observed but not described in detail. The present study examines the morphology, ontogeny, and projection of DF neurons utilizing Fluoro-Gold as a retrograde tracer, alone, and in combination with tritiated thymidine autoradiography in the spinal cord of the rat. DF neurons were consistently labelled in spinal segments T13 through L2 following injections of Fluoro-Gold into the cerebellum. The cell bodies of DF neurons were small to medium in size, fusiform to multipolar in shape, and were located on the side ipsilateral to the injection site. Cell counts revealed approximately five labelled cells per millimeter along the longitudinal axis. An examination of neurogenesis using tritiated thymidine combined with Fluoro-Gold showed that DF neurons have relatively late birthdates as do other spinocerebellar neurons of the dorsal horn. Retrograde axon tracing studies in the spinal cord using Fluoro-Gold showed that DF neurons project rostrally via the ipsilateral lateral funiculus. The significance of the presence of nerve cells in the dorsal funiculus is unclear, but judging from their location, ontogeny, and projection, DF neurons are probably derived from the same pool of neurons as those in the Nucleus dorsalis.

A group II-activated ascending tract of lumbosacral origin in the cat spinal cord.

1. Electrophysiological investigations have revealed a population of ascending tract neurones originating in the lumbosacral enlargement, with input from group II muscle afferents of the cat hindlimb. 2. Single-unit microelectrode recordings were made in the lateral funiculus at L6, from the axons of thirty-four ascending tract neurones. All of the axons were antidromically activated by stimulation of the ipsilateral lateral funiculus at Th13 and, whenever tested (eight units), at C1. 3. Conduction velocities of the axons, between the L6 and Th13 segment, ranged from 33 to 92 m s-1 (mean 61 m s-1). 4. All of the ascending tract neurones were discharged following electrical stimulation of muscle nerves at group II strength, but not by weaker stimuli in the group I range. Most of the investigated neurones were excited by group II afferents of more than one muscle nerve. In addition, a proportion of the units tested could also be discharged by cutaneous and by joint afferents. 5. Responses to natural stimuli were investigated in eighteen ascending tract neurones discharged by electrical stimulation of group II afferents in the gastrocnemius-soleus (GS) and plantaris (P1) nerves which were dissected free in continuity with their muscles. Seven units were spontaneously active. Eight units responded to isometric contraction of the GS/P1 muscles with a discharge occurring mainly on the falling phase of muscle tension. Nine units increased their discharge frequency in response to stretching of the muscles and five units responded to mechanically probing the muscles with a blunt instrument. 6. The final termination sites of this group of ascending tract neurones has yet to be determined. Initial attempts (three units) to antidromically activate the neurones from the cerebellum have been unsuccessful. Other likely areas of termination in the brain stem are considered.

The morphology and projections of dorsal horn spinocerebellar tract neurones in the cat.

1. The morphology of dorsal horn neurones located in the mid-lumbar segments of the spinal cord and which have an axonal projection to the cerebellum has been investigated. The neurones were identified by antidromic activation from the cerebellum and by their characteristic input from group II afferents as described in the preceding paper (Edgley & Jankowska, 1988). 2. The cell bodies of the neurones were distributed across the width of the spinal cord in laminae IV and V, but particularly at the border between these laminae. Most were in the caudal half of the fourth lumbar segment (L4), caudal to Clarke's column. However, neurones of this type were encountered as far caudal as the middle of the fifth lumbar segment (L5) and as far rostral as the middle of the third lumbar segment (L3). 3. The morphology of the neurones was investigated following intracellular staining with horseradish peroxidase (HRP). Fourteen well-filled cells were recovered. They had large somata and extensive dendritic arborizations within the dorsal horn which could extend more than 2 mm rostro-caudally. The most dense arborization was in laminae III and IV, just dorsal to the cell bodies. 4. The axons of all fourteen cells could be followed well into the white matter. All of them passed into the dorsal part of the ipsilateral lateral funiculus where they ascended. All followed a similar indirect course through the grey matter. Despite careful inspection, initial axon collaterals were never found. 5. All of the neurones were antidromically activated by low-intensity electrical stimulation of the dorsolateral part of the ipsilateral lateral funiculus in the thoracic region and from the cerebellum. The conduction velocities of the axons ranged from 62 to 112 m s-1 (mean 84.2 (S.D. +/- 10.1) m s-1). 6. The axonal terminations of some neurones were investigated by mapping the most effective locations for antidromic activation from the cerebellar cortex. Most neurones were activated with lowest stimulus intensities from the rostral part of the anterior lobe. A second effective area was found in the posterior lobe, deep to the paramedian lobule. The majority of neurones were activated from both locations, suggesting that their axons branched to terminate in both areas. 7. On the basis of their projection and termination, it is proposed that the axons of these dorsal horn spinocerebellar tract neurones contribute to the dorsal spinocerebellar tract (DSCT).

Circumferential cells of the developing Rana catesbeiana lumbar spinal cord

Neural elements in the lumbar enlargement of the developing Rana catesbeiana spinal cord were labelled by placing chips of dessicated horseradish peroxidase (HRP) into various lesions of the spinal cord. Of the elements labelled in the lumbar enlargement, a population of cells circumjacent to the gray matter was seen to be distinct from all others on the basis of their morphology, position and their putative embryonic origin. One cell type not previously described was a large circumferential cell (LCC) with primary processes completely circumscribing the gray matter. The ventral process crosses the midline and ascends or descends in the ventral funiculus. The dorsal primary process was observed to extend to the midline and turn ipsilaterally in a rostro-caudal direction in the dorsal funiculus. LCC's were present at early stages of larval development (stage III, Taylor and Kollros 1946) but could not be labelled in juvenile frogs. LCC's were only observed in the lumbar enlargement and could only be labelled through HRP applications at that level. They receive abundant synaptic input from the ipsilateral lateral funiculus. Possible roles for the LCC in the early function and development of the ranid lumbar spinal cord are discussed.

ラット脊髄小脳路の脊髄および下部延髄における経路 逆行性軸索流法による研究

The spinocerebellar tract neurons and their fibers were observed throughout the spinal cord and lower medulla in the Wistar rat following injections of horseradish peroxidase (HRP) into the cerebellum.The fiber course before reaching into the periphery of the lateral funiculus was classified into three types. Type I fibers crossed contralaterally through the anterior white commissure, and then ascended obliquely in the periphery of the anterior funiculus to reach into the periphery of the lateral funiculus. These fibers mainly originated from Co-L6 (neurons in laminae V, VII, ventrolateral part of the ventral horn), L3-Tll (lamina VII neurons, spinal border cells) and C3-C1 (central cervical nucleus neurons). The fibers in Co-L6 and L3-Tll ascended obliquely for 2-4 segments to reach into the periphery of the lateral funiculus, while the fibers in C3-C1 ascended obliquely for 1-2 segments. Type II fibers entered the ipsilateral lateral funiculus through the dorsal part of the intermediate substance, and ascended obliquely for 2-9 segments in the medial part of the lateral funiculus to reach into the periphery of the lateral funiculus. The fibers of this type arose mainly from L2-T1 (neurons in lamina V, Clarke's column). Thpe III fibers entered the ipsilateral lateral funiculus from the lateral corner of the anterior horn, and ascended obliquely for 2-4 segments to reach into the periphery of the lateral funiculus. The fibers of this type mainly occurred in T3-C5 (lamina VII neurons).After reaching into the periphery of the lateral funiculus, the majority of type I fibers ascended in the ventral half of the periphery of the lateral funiculus, but the minority migrated dorsalward and ascended in the dorsal half. In the periphery of the lateral funiculus, most of type II fibers ascended in the dorsal half, but some of them ascended in the posterior part of the ventral half. Type III fibers ascended in the ventral half of the periphery of the lateral funiculus.There is a classical conception that the ventral spinocerebellar tract and dorsal spinocerebellar tract ascend through the ventral half of the lateral funiculus and through the dorsal half of it, respectively. The present results indicate that this should be modified.

The distribution pattern of boutons of muscle spindle group 11 afferents in relation to the homonymous motor column in the cat

Using a retrograde tracer technique with horseradish peroxidase (HRP) attempts were made to determine the origins of reticulospinal tracts and their funicular trajectories.Reticulospinal tracts originating from the mesencephalic reticular formation (RF) were composed of: (1) descending projections arising from the cluster of cells located just lateral to the periaqueductal gray that course in the anterior funiculus (AF) and ventral part of the lateral funiculus (LF) with ipsilateral predominance; and (2) projections from the cluster of cells located dorsal to the brachium conjunctivum that course in the ipsilateral LF. Origins of the ponpine reticulospinal tracts arising from the n. reticularis pontis oralis (Poo) have been divided into three parts: (1) medial one-third; (2) middle; and (3) ventrolateral. The axons from the medial part descend ipsilaterally via the medial part of the AF, while the axons from the ventrolateral part of the Poo give rise to diffuse descending projections in the AF and LF. The middle part of the Poo has been further subdivided into: (1) dorsal part that gives rise to spinal projections ipsilaterally in the ventrolateral funiculus (VLF); and (2) ventral, particularly its upper part, whose axons descend bilaterally via the DLF. Origins of reticulospinal tracts from the n. reticularis pontis caudalis (Poc) could be divided into three parts: (1) medial; (2) dorsolateral; and (3) ventrolateral. The medial part of the Poc is a source of axons via the medial part of the ipsilateral AF, while the ventrolateral part of the nucleus is a source of axons via the contralateral LF. The spinal projections from the dorsolateral part of the Poc appears to course diffusely in the AF and LF, but with DLF predominance. The n. reticularis gigantocellularis (Gc) was found to be a main medullary source of the spinal projections in the ipsilateral AF, while n. reticularis magnocellularis (Mc) is the major source of the fibers coursing ipsilaterally in the VLF. The most medial part of the Mc descends ipsilaterally via the medial part of the AF, while the ventrolateral part of the nucleus together with the n. reticularis lateralis of Meessen and Olszewski descends ipsilaterally via the DLF. It has also been found that the axons from the n. reticularis paramedianus pass via both the AF and LF with ipsilateral predominance, while the n. reticularis dorsalis and ventralis course via the LF with ipsilateral predominance.

Spinal projections from the lower brain stem in the cat as demonstrated by the horseradish peroxidase technique. I. Origins of the reticulospinal tracts and their funicular trajectories

Using a retrograde tracer technique with horseradish peroxidase (HRP) attempts were made to determine the origins of reticulospinal tracts and their funicular trajectories. Reticulospinal tracts originating from the mesencephalic reticular formation (RF) were composed of: (1) descending projections arising from the cluster of cells located just lateral to the periaqueductal gray that course in the anterior funiculus (AF) and ventral part of the lateral funiculus (LF) with ipsilateral predominance; and (2) projections from the cluster of cells located dorsal to the brachium conjunctivum that course in the ipsilateral LF. Origins of the ponpine reticulospinal tracts arising from the n. reticularis pontis oralis (Poo) have been divided into three parts: (1) medial one-third; (2) middle; and (3) ventrolateral. The axons from the medial part descend ipsilaterally via the medial part of the AF, while the axons from the ventrolateral part of the Poo give rise to diffuse descending projections in the AF and LF. The middle part of the Poo has been further subdivided into: (1) dorsal part that gives rise to spinal projections ipsilaterally in the ventrolateral funiculus (VLF); and (2) ventral, particularly its upper part, whose axons descend bilaterally via the DLF. Origins of reticulospinal tracts from the n. reticularis pontis caudalis (Poc) could be divided into three parts: (1) medial; (2) dorsolateral; and (3) ventrolateral. The medial part of the Poc is a source of axons via the medial part of the ipsilateral AF, while the ventrolateral part of the nucleus is a source of axons via the contralateral LF. The spinal projections from the dorsolateral part of the Poc appears to course diffusely in the AF and LF, but with DLF predominance. The n. reticularis gigantocellularis (Gc) was found to be a main medullary source of the spinal projections in the ipsilateral AF, while n. reticularis magnocellularis (Mc) is the major source of the fibers coursing ipsilaterally in the VLF. The most medial part of the Mc descends ipsilaterally via the medial part of the AF, while the ventrolateral part of the nucleus together with the n. reticularis lateralis of Meessen and Olszewski descends ipsilaterally via the DLF. It has also been found that the axons from the n. reticularis paramedianus pass via both the AF and LF with ipsilateral predominance, while the n. reticularis dorsalis and ventralis course via the LF with ipsilateral predominance.

Messages conveyed by spinocerebellar pathways during scratching in the cat. I. Activity of neurons of the lateral reticular nucleus

(1) Signals transmitted to the cerebellum by the spino-reticulocerebellar pathway (SRCP) during scratching were studied. For this purpose, the activity of neurons of the lateral reticular nucleus (LRN), which are the last-order neurons of the SRCP, was recorded during scratching in thalamic cats. Scratching was evoked by stimulation of the pinna. LRN neurons were identified antidromically by stimulation of the hindlimb area in the cerebellar anterior lobe. In most experiments, animals were immobilized with Flaxedil, and stimulation of the pinna resulted in fictitious scratching 16, i.e., in periodical reciprocal activity of flexor and extensor motoneurons typical of actual scratching. (2) During both actual and fictitious scratching, the discharge frequency of LRN neurons was rhythmically modulated in relation with the scratch cycle. Most LRN neurons fired in short high-frequency bursts of spikes which coincided (completely or partly) with the extensor phase of the cycle. In this respect the SRCP differs from the ventral spinocerebellar tract (VSCT) which is maximally active in the flexor phase of the cycle 7. (3) The firing pattern of LRN neurons during fictitious scratching was similar to that during actual scratching. Therefore, the rhythmical burst firing of LRN neurons is determined mainly by the central mechanisms and not by the rhythmical sensory input. (4) Rhythmical modulation of LRN neurons disappeared after transection of the ipsilateral lateral funiculus of the spinal cord in which spinoreticular fibers are located. On the other hand, considerable reduction of rhythmical activity in descending brainstem-spinal pathways after contralateral hemisection of the spinal cord did not affect the discharge pattern of LRN neurons. These two facts indicate that the SRCP conveys mainly messages about activity of the central spinal mechanisms, and that influences of supraspinal motor centers on LRN neurons and on spinoreticular neurons are of minor importance. (5) Axonal terminations of LRN neurons are distributed rather evenly over the hindlimb area in the anterior lobe of the cerebellum. Therefore, messages about the events, which happen within the spinal cord in the vicinity of the extensor phase of the cycle, arrive at every point of the hindlimb area.

Synaptic activation of thoracic interneurons by reticulospinal fibers of the lateral funiculus

Synaptic responses of different functional groups of interneurons in segments T10 and T11 to stimulation of the ipsilateral and contralateral medullary reticular formation were investigated in anesthetized cats with only the ipsilateral lateral funiculus remaining intact. Activation of reticulospinal fibers of the lateral funiculus with conduction velocities of 30–100 m/sec was shown to induce short-latency and, in particular, monosynptic EPSPs in all types of cells tested: in interneurons excited by group Ia muscle afferents, in cells activated only by high-threshold cutaneous and muscle afferents (afferents of the flexor reflex), in cells activated mainly by descending systems, and, to a lesser degree, in neurons connected with low-threshold cutaneous afferents. These cell populations are located mainly in the central and lateral parts of Rexed's lamina VII. Most neurons in laminae I–V of the dorsal horn, except six cells located in the superficial layers of the dorsal horn, received no reticulofugal influences. The functional organization of connections of the lateral reticulospinal tract with spinal neurons is discussed and compared with the analogous organization of the medial reticulospinal tract, and also of the "lateral" (cortico- and rubrospinal) descending systems.

The lateral reticular nucleus in the cat. V. Does collateral activation from the dorsal spinocerebellar tract occur?

1. The assertion made by Burton, Bloedel and Gregory (1971) that neurones in the mLRN (major portion of lateral reticular nucleus comprising its parvi- and magnocellular parts) receive collateral excitation from the dorsal spinocerebellar tract (DSCT) has been tested. The activation of mLRN neurones on stimulation of limb nerves was studied in preparations with the spinal cord interrupted at C3 sparing only the dorsal part of the ipsilateral lateral funiculus (iDLF preparations), only the ipsilateral ventral quadrant (iVQ preparations), or only the ipsilateral lateral and ventral funiculi (iLFVF preparations). 2. In iDLF preparations (with the DSCT intact) stimulation of limb nerves evoked responses in only occasional mLRN neurones. These responses could be attributed to activation from some dorsally located fibres belonging to the bilateral ventral flexor reflex tract (bVFRT) and to activation from a previously unknown path activated after a long latency from ipsilateral forelimb and hindlimb afferents. 3. In iLFVF preparations (with the DSCT intact) and iVQ preparations (with the DSCT interrupted) most mLRN neurones responsed to limb nerve stimulation. The responses in two preparations were similar and could be attributed largely or exclusively to activation from the bVFRT. 4 It is concluded that the DSCT does not activate any major group of mLRN neurones.

The lateral reticular nucleus in the cat IV. Activation from dorsal funiculus and trigeminal afferents

1. The activation of neurones in the mLRN (major portion of lateral reticular nucleus comprising its parvi- and magnocellular parts) be a spinal path ascending in the dorsal funiculus (DF) and by trigeminal afferents has been studied. 2. Stimulation of the DF at C3 activated about one half of the mLRN neurones. The latencies were 2-28 ms. In experiments with the spinal cord interrupted at C3 except for the DF it was shown that cutaneous and high threshold muscle afferents in mainly forelimb nerves were effective. The latencies of the responses to nerve stimulation were 8-27 ms. 3. Stimulation of trigeminal afferents evoked a response in about one third of the mLRN neurones. The latencies were 2-27 ms. 4. Activation from the DF- and trigeminal paths occurred often in the same mLRN neurones and the neurones activated from the two paths had a similar location in the nucleus and a similar termination in the cerebellar cortex. 5. The DF- and trigeminal paths had similar properties. Activation was evoked from both ipsilateral and contralateral nerves. Fast adapting hair receptors were commonly effective. 6. Evidence is presented indicating that the DF- and trigeminal paths share a common final path to the mLRN neurones which is formed by brain stem interneurones intercalated between the DF- and trigeminal nuclei and the mLRN. It is suggested that these interneurones represent a supraspinal motor centre. 7. Activation from the DF- and trigeminal paths occurred with unequal frequency among groups of mLRN neurones activated from different spinal paths ascending in the ipsilateral lateral funiculus (cf. Clendenin et al., 1974a).

The lateral reticular nucleus in the cat. I. Mossy fibre distribution in cerebellar cortex.

1. The areas of the cerebellar cortex receiving fibres from the mLRN (major portion of the lateral reticular nucleus comprising its parvi- and magnocellular parts) were determined by identifying the low-threshold spots on the cerebellar surface from which 286 mLRN neurones could be antidromically activated. 2. The mLRN fibres terminate bilaterally in the anterior lobe and pyramis, and ipsilaterally in the paramedian lobule. Some fibres terminate also in the rostral part of lobule VI but hardly any in other parts of the cortex. It follows that the mLRN projects almost exclusively to the classical spinal receiving areas. 3. Neurones in the parvi- and magnocellular parts project to similar cortical areas. 4. Two regions in the mLRN were distinguished on the basis of their different projection areas. Region A, a dorsolateral portion of the magnocellular part, projects to the ipsilateral parts intermedia of the anterior lobe and the ipsilateral paramedian lobule. Region B, a ventral portion of the parvi- and magnocellular parts, projects bilaterally to the pars intermedia and vermis of the anterior lobe and sparsely to the pyramis. 5. Neurones throughout the parvi- and magnocellular parts receive monosynaptic excitation from fibres ascending in the ventral part of the ipsilateral lateral funiculus.

The axonal pathways of spinal neurons in the cat.

AbstractThe axonal pathways of spinal neurons were studied in the cat using Ramón y Cajal's silver method.The cells of the ventral group of the nucleus supraspinalis contribute to the ventral roots of C1 and the cells of the dorsal group send their axons to the contralateral ventral funiculus. The cells of lamina VII send their axons to the ipsilateral lateral or ventrolateral funiculus. The subnucleus ventralis of the nucleus medullae oblongatae centralis sends axons to the lateral funiculus or to the ventral roots of C1. The cells of lamina V send their axons to the lateral funiculus and the contralateral ventral funiculus. The cells of lamina VII send their axons to the ipsilateral lateral funiculus and to the contralateral ventral funiculus. Numbers of spinal border cells were were observed in lamina IX at the level of the cervical and lumbar enlargement. It was found that the cell groups which were classified cytoarchitectonically contained numbers of different types of cells as judged by their axonal pathways.

The projection of splanchnic afferents on the cerebellum of the cat.

1. The projections of the ipsilateral and contralateral splanchnic nerves on the cerebellum were studied in cats under sodium thiopentone anaesthesia.2. The splanchnic nerves were electrically stimulated. Evoked potentials and single unit discharges were recorded by means of 2.5 M-NaCl-filled glass micropipettes. A responsive region was found in the intermediate cortex of lobules Vb to f of the anterior lobe.3. The Agammadelta fibres of the splanchnic nerve had a bilateral cerebellar representation. The Abeta fibres were represented only on the ipsilateral side.4. At the level of the upper cervical spinal cord, fibres from the ipsilateral splanchnic nerve were conveyed in both the dorsal and lateral funiculi; fibres from the contralateral nerve were restricted to the ipsilateral lateral funiculus.5. On the basis of the characteristic potential fields generated in the cerebellar cortex, it is concluded that the majority of the splanchnic afferents studied terminate in the cerebellum as climbing fibres. A few responses of short latency may have been due to a mossy fibre input.6. In interaction experiments, a conditioning stimulus to one splanchnic nerve depressed the response to stimulation of the other nerve for up to 80-100 msec, the effect being most pronounced at 40-50 msec. During this period, spontaneous activity of the cerebellar unit was also suppressed.7. The organization of the splanchnic pathways to the cerebellum and their terminal connexions are discussed.

The origin, course and termination of corticospinal fibers in the slow loris, Nycticebus coucang (boddaert).

AbstractThe origin and distribution of corticospinal fibers in the slow loris (Nycticebus coucang) were studied with the aid of the Nauta‐Gygax technique following selected ablations of portions of the left cerebral cortex. Reconstruction of the cortical area which contributes to the corticospinal tract reveals a “motor” area which approximates that of Perodicticus, another lorisiform lemur, mapped by electrophysiological methods. Degenerated corticospinal fibers found in the contralateral lateral funiculus were traced caudally to sacral segments. A small number of degenerated fibers were also found in the ipsilateral lateral funiculus as far caudally as the lumbar cord. Preterminal fiber degeneration was most abundant in the contralateral dorsal horn and zona intermedia. Similar, but less abundant, degeneration was found in the contralateral ventral horn. Some degenerating fibers re‐crossed through the dorsal and ventral gray commissures to the ipsilateral gray matter where preterminal fiber degeneration was most abundant in the medial portions of the ventral horn. Degenerating corticospinal fibers could be seen among the large, laterally‐placed cells of the contralateral ventral horn.