Projection on the motor cortex of thalamic neurons with pallidal input in the monkey

Summary The cortical projection areas of thalamic neurons with basal ganglia and/or cerebellar inputs were studied electrophysiologically in unanesthetized monkeys. Thalamic neurons which receive inhibition from the pallidum were found to project to the motor cortex (area 4) as well as to premotor cortex. The neurons with pallidal input and motor cortical projection were located mainly in VLo. This result indicates that the basal ganglia innervate the motor cortex through the thalamus. Thus the basal ganglia can modify the cortical output for controlling movements directly through this pathway as compared with its influence through the prefrontal and premotor cortices.     

An anatomical study of the projections from the dorsal column nuclei to the midbrain in cat

Summary The termination of the fibers from the dorsal column nuclei (DCN) to the midbrain has been investigated in the cat with the degeneration method, the anterograde horseradish peroxidase (HRP) method and autoradiography after ³H-leucine injections. The results show that the DCN project to several midbrain regions. The external nucleus of the inferior colliculus (IX) receives the heaviest projection from both the gracile and cuneate nuclei. The DCN fibers form three joint terminal zones in IX. Each terminal zone contains clusters with dense aggregations of DCN fibers. Fairly dense terminal networks are found in the posterior pretectal nucleus (PP) and the compact part of the anterior pretectal nucleus (PAc) as well. More scattered DCN fibers are present in the cuneiform nucleus (CF), the lateral part of the periaqueductal gray (PAG1), the red nucleus (NR), the nucleus of the brachium of the inferior colliculus (B), the mesencephalic reticular formation (MRF) and the intermediate and deep layers of the superior colliculus (SI, SP). The projections to all regions are mainly contralateral. Most of the few ipsilateral fibers terminate in IX.A somatotopic organization was seen in IX and NR. The gracile fibers terminate preferentially in the caudal and lateral part of IX and the cuneate ones preferentially in its rostral and medial part. In the red nucleus the gracile fibers terminate ventral to the cuneate ones. In the pretectal region there was a predominance for gracile fibers. There also appeared to be quantitative differences in the projections from various levels of the gracile nucleus, with more midbrain projecting fibers originating in the rostral than in the middle and caudal parts of the nucleus.     

Cortical cells projecting to the dorsal column nuclei of Rhesus monkeys

Summary Corticals cells projecting to the dorsal column nuclei (DCN) of Rhesus monkeys have been identified after unilateral or bilateral injection of horseradish peroxidase (HRP) into the dorsal medulla. HRP-positive neurons identifiable as the source of cortico-DCN projections were pyramidal cells in layer V whose largest diameters ranged from 12–31 m. Cortico-DCN neurons were concentrated in the trunk, fore- and hindlimb regions of area 4 and of SI, and to a lesser extent in SII. This distribution is comparable to the topographical distribution of cortico-DCN neurons in cats. However, cortico-DCN neurons in monkeys are also numerous in at least part of the supplementary motor cortex and in area 5. The results suggest that cortical neurons in several different cytoarchitectonic areas may exert direct control upon cells in the DCN and that the functional role of cortico-DCN projections ought not be viewed as a simple feedback system.Abbreviation List centr. s. central sulcus - cingul. s. cingulate sulcus - cun cuneate nucleus - ec external cuneate nucleus - FAL cytoarchitectonic area indicated as such by von Bonin and Bailey (1947) - gr gracile nucleus - hyp hypoglossal nucleus - intrap(ar) s. intraparietal sulcus - pyr pyramids - sp(in) V spinal trigeminal complex Submitted in partial fulfillment of the requirements for the Ph. D. in Neurobiology (J.A.W.), University of North Carolina at Chapel Hill, Chapel Hill, N.C. 27514     

Two modes of cerebellar input to the parietal cortex in the cat

Summary The characteristics of cerebellar input to the parietal cortex through the ventroanterior-ventrolateral (VA-VL) complex of the thalamus were investigated in the adult cat by using combined electrophysiological and anatomical methods. Two distinct parietal regions were activated by stimulation of the cerebellar nuclei (CN). In the first region located in the depth of the bank of the ansate sulcus, stimulation of the CN induced early surface positive-deep negative potentials and late surface negative-deep positive potentials. In this cortical area, potentials of similar shape and time course were evoked at a shorter latency by stimulation of the ventrolateral part of the VA-VL complex where large negative field potentials were evoked by stimulation of the CN. After injection of the anterograde tracer Phaseolus vulgaris leucoagglutinin (PHA-L) in this part of the VA-VL complex, axon terminals of thalamocortical (TC) fibers were found in layers I, III and IV in the depth of the bank of the ansate sulcus and layers I and III in the motor cortex. In the second region located in the suprasylvian gyrus, late surface negative-deep positive potentials were evoked by stimulation of the CN and similar potentials were evoked at a shorter latency from the dorsomedial part of the VA-VL complex where large cerebellar-evoked potentials could be recorded. PHA-L injection in this thalamic region stained TC fibers and their terminals in layer I of the suprasylvian gyrus, and in layers I and III of the motor cortex. The laminar distribution of TC axon terminals in two different regions of the parietal cortex could account for the depth profiles of the cerebellar- and the thalamic-evoked potentials in each region. These results show that cerebellar information is conveyed to two separate areas in the parietal cortex by two different TC pathways.     

Spinocervical neurons and dorsal horn neurons projecting to the dorsal column nuclei through the dorsolateral fascicle: a retrograde HRP study in the cat

Summary Spinocervical cells were identified by retrograde labelling from implants of HRP in the dorsolateral fascicle after destruction of the dorsal columns. They lay in laminae III and IV throughout the cord in estimated numbers of 700, 450 and 1100 in lumbosacral enlargement, upper lumbar and thoracic cord, and brachial enlargement respectively. In the cord enlargements dendritic trees were mainly or exclusively developed dorsally, with rostrocaudal exceeding mediolateral spread, and a gradient across the dorsal horn, lateral cells showing this contrast most strongly. Dendritic spread was limited at the II/III laminar boundary. Transition occurred at the edge of the enlargements to a shape with extreme rostrocaudal elongation of perikarya and of dendritic trees in upper lumbar and thoracic segments. Axons of Spinocervical cells ascended in the most dorsal part of the fascicle, distinguishable from the larger spinocerebellar bundle lying adjacent and ventral. The initial axonal course was tortuous, with local collateral branching, the axon sometimes travelling briefly in the dorsal column. In other experiments implants were made ipsilaterally in the dorsal column nuclei after destruction of the dorsal columns. Cells were few and relatively poorly labelled, for which the reasons are discussed. Some such cells, lying in lamina IV, were similar to spinocervical tract cells and may have projected to both lateral cervical and dorsal column nuclei. Others, at the extreme lateral edge of the mid-dorsal horn, were quite different, with dendrites greatly extended rostrocaudally and primary and higher order dendrites projecting ventrally from the perikaryon.     

Connections between pericruciate cortex and the medullary reticulospinal neurons in cat: an electrophysiological study

Summary The connections between the pericruciate cortex and the medullary reticulospinal (RS) neurons were studied in anesthetized cat. Intracellular recordings were made from reticulospinal neurons and the effects of stimulating different areas of the pericruciate cortex were compared. (1) EPSPs were elicited in all the 93 neurons studied which were antidromically activated by spinal stimulation and had an IS-SD notch on the ascending limb of their antidromic spikes. According to the conduction velocity (c.v.) of the axon and the minimal EPSP latency to cortical stimulation, the neurons could be divided into two groups, i.e. fast-conducting RS neurons (FRS neurons, c.v. > 45 m/s) and slow-conducting RS neurons (SRS neurons, c.v. < 45 m/s). The minimal latencies of FRS neurons were equal to or shorter than 2 ms whereas those of SRS neurons were longer than 2 ms. (2) EPSPs with short latency (< 2 ms) could be evoked in FRS neurons by stimulating a relatively wide cortical area including the major part of precruciate area 4 and area 6, with a central area of strongest excitatory effect located in area 4 slighthly medial to the tip of the cruciate sulcus. Stimulation of the postcruciate area 4 only produced long latency EPSPs. (3) By extrapolation from the cortical and peduncular latencies and the conducting distances it was revealed that the earliest part of the minimal latency EPSPs were monosynaptically evoked in FRS neurons and were mediated by fastconducting corticobulbar fibers. (4) FRS neurons could be excited by stimuli applied to both ipsilateral and contralateral pericruciate cortex. The influence from the contralateral cortex was slightly stronger.     

Intracellular recordings from rat thalamic VL neurons: a study combined with intracellular staining

Summary Intracellular recordings from thalamic neurons receiving cerebellar inputs were performed under urethane anesthesia in the rat. A total of 64 neurons were recorded intracellularly with micropipettes filled with 4% biocytin solution (dissolved in 0.5 M K-acetate), and cerebellar-induced EPSPs (CN-EPSPs), the membrane resistance and firing properties were analyzed with intracellular current injections. The mean latency of CN-EPSPs was 1.9 ± 0.8 ms and the mean input resistance measured in 10 neurons was 17.6 ± 5.0 M. Thirty-two out of 35 stained neurons were analysed morphologically; 28 of these neurons were located in the VL, and 26 received CN-EPSPs. Their somata were round or polygonal in shape and the mean size was 22.5 × 15.2 m. They had radially extending spinous dendrites, and the mean radii of the dendritic fields were 214.7 m in the frontal and 171.4 m in the sagittal planes. These morphological features were similar to those observed in the sensory relay nucleus of the thalamus.     

Movement-related activity of thalamic neurons with input from the globus pallidus and projection to the motor cortex in the monkey

Summary Thalamic neurons projecting to the arm area of the motor cortex were identified by their antidromic response to stimulation of that area in two awake monkeys. Neurons were further identified as receiving inputs from the cerebellar nuclei or the internal segment of the globus pallidus by excitatory or inhibitory response to stimulation of these nuclei. Most (33/34) of the thalamic neurons in the cerebello-thalamo-cortical projection and more than half (12/18) of those in the pallido-thalamocortical projection changed their firing rate on the leverlifting hand movement in the reaction-time task. A considerable number of neurons of both groups (14/23 and 3/10) changed their firing rate prior to the onset of the earliest EMG. These findings agree with the model that activities of pallidal as well as cerebellar nuclear neurons related to motor control are transmitted to the motor cortex through the thalamus.     

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     

Short-latency peripheral inputs to thalamic neurones projecting to the motor cortex in the monkey

Summary One hundred seventy-five neurones in the n.ventroposterior lateralis (VPL) and n.ventralis lateralis (VL) in the thalamus of anaesthetised monkeys have been tested antidromically for projection to the cortex and for somatosensory input from the contralateral arm.Using bipolar stimulation of the cortical surface, 113 thalamic neurones were successfully identified as antidromically driven from the hand area of the postcentral gyrus (48 neurones) or from the hand area of the precentral gyrus (65 neurones). All but one of these 113 neurones could only be antidromically discharged from the postcentral cortex or from the precentral cortex, and not from both. Most had antidromic latencies between 0.5 and 1.5 ms.Twenty-five/sixty-five precentrally projecting neurones and 45/48 postcentrally projecting neurones were activated by stimulation of the contralateral median or radial nerves. Both groups responded at short latency (4–8 ms) and many were activated by low-threshold shocks (0.8–1.3 T) and had restricted receptive fields on the hand. Precentrally projecting neurones responded most powerfully to joint movement or deep pressure, and some of these neurones were also responsive to cutaneous stimuli.Precentrally projecting neurones with peripheral inputs were all found in the oral subdivision of the VPL (the VPL_o). The properties of these neurones suggest that they may be partly responsible for rapid somatosensory input to the motor cortex.     

Neurons of the pretectal area convey spinal input to the motor thalamus of the cat

Summary The aim of this study was to corroborate lesioning work (Mackel and Noda 1989), suggesting the pretectal area of the rostral midbrain acts as a relay between the spinal cord and the ventrolateral (VL) nucleus of the thalamus. For this purpose, extracellular recordings were made from neurons in the pretectal area which were antidromically activated by stimulation in the rostral thalamus, particularly in VL. The neurons were tested for input from the dorsal columns of the spinal cord, the dorsal column nuclei, and the ventral quadrant of the spinal cord. Latencies of the antidromic responses ranged between 0.6 and 3.0 ms (median 1.0 ms): no differences in latencies were associated with either location of the neurons in the pretectal area or with the site of their thalamic projection. Orthodromic responses to stimulation of ascending pathways were seen in the majority of neurons throughout the pretectal area sampled. Latencies of orthodromic responses varied considerably, with ranges of 0.9–9 ms, 6–20 ms, and 2.5–20 ms upon stimulating the dorsal column nuclei, dorsal columns, and ventrolateral quadrant, respectively. The shortest-latency responses to stimulation of the dorsal column nuclei or of the ventral quadrant were likely to be monosynaptic. Temporal and spatial facilitation of the responses to ascending input were common. The data show that neurons of the pretectal area are capable of relaying somatosensory input ascending from the spinal cord to the rostral thalamus. It is suggested that the pretectofugal output to VL converges with cerebellar input in VL neurons and becomes incorporated in cerebello-cerebral interactions and, ultimately, the control of movement.     

Direct projections from thalamic intralaminar nuclei to extra-striate visual cortex in the cat traced with Horseradish peroxidase

Summary Thalamic projections to the visual cortex were investigated using the Horseradish peroxidase tracing technique. Besides confirmation of a distinct origin of thalamic projections to striate and extra-striate visual cortex, afferents of the intralaminar nuclei (ILN) to visual cortex were demonstrated. These projections of ILN were shown to be specific in that they terminate in areas 18, 19 and Clare Bishop but not area 17. The coupling of these intralaminar projections on to the extra-striate visual system is considered with respect to orientation of gaze.     

Cortical neurons projecting to the pontine nuclei in the cat. An experimental study with the horseradish peroxidase technique

Summary Horseradish peroxidase (HRP) injections in various portions of the cat pontine nuclei resulted in retrograde labeling of neurons in layer V of the ipsilateral cerebral cortex.Corticopontine neurons, pyramidal in type, have been found to be labeled in the entire cortex, confirming the previous findings of anterograde degeneration studies. Most (91%) of the labeled cells were 14–26 m in diameter (mean 19.4±4.5 m SD). Small (10–20 m) and medium (20–40 m) cells represent 51.5% and 47.7%, respectively, of the total number of the labeled neurons. The populations of the neurons of various sizes were almost identical in different cortical areas, and were different from the populations of corticoreticular and corticospinal cells.Corticopontine cells were well labeled in experimental cases of 3-days' survival time, confirming the topographical organization established previously by degeneration studies for this projection system. However, in cases of shorter survival time (20–27 h), the number of labeled neurons was very small.The relative paucity of labeled Corticopontine neurons in the sigmoid and lateral gyri is discussed with reference to other cortical descending neurons (e.g., the corticotectal, corticoreticular and corticospinal) which have hitherto been identified morphologically as well as physiologically.Abbreviations AL gyrus lateralis anterior - ASigm gyrus sigmoideus anterior - ASup gyrus suprasylvius anterior - Br.p. brachium pontis - Cor gyrus coronalis - L left - L.m. lemniscus medialis - MEct gyrus ectosylvius medius - MSup gyrus suprasylvius medius - N.dl. nucleus dorsolateralis - N.l. nucleus lateralis - N.m. nucleus medianus - N.p. nucleus peduncularis - N.pm. nucleus paramedianus - N.r.t. nucleus reticularis tegmenti pontis - N.v. nucleus ventralis - Ped corticospinal and corticopontine fibers in cerebral peduncle - PSigm gyrus sigmoideus posterior - R right     

The corticothalamic projection from the gyrus proreus and the medial wall of the rostral hemisphere in the cat an experimental study with silver impregnation methods

Summary The corticothalamic projections from the gyrus proreus and the medial wall of the rostral hemisphere have been studied in the cat with the silver method of Nauta. The gyrus proreus projects upon the following nuclei (for abbreviations, see list on page 133), ipsilateral R, VA, VM, VL, MD, Pc, CL, CM, Pf, VPM, VPMpc. VPI and to the contralateral principal nucleus of the trigeminal nerve. The medial wall of the rostral hemisphere projects bilaterally upon R, VA, VM, VL, MD, Pc, CL, CM, Pf, VPM, VPMpc, VPI, VPL, the dorsal column nuclei and the principal nucleus of the trigeminal nerve. The ipsilateral thalamic projection is more abundant than the contralateral. The latter appears to increase in amount as the lesion is placed successively more ventrally on the medial wall of the rostral hemisphere. Some degenerating fibers cross in the corpus callosum and descend in the contralateral internal capsule but the majority cross in the dorsal part of the anterior commissure and reach the medial aspect of the anterior limb of the contralateral internal capsule. A somatotopical organization of the medial wall of the rostral hemisphere has been demonstrated. The rostrocaudal part projects upon the ipsilateral VPL lateralis (VPLl) and nucleus cuneatus and the contralateral nucleus gracilis and VPL medialis (VPLm). The caudal part of this cortical area sends fibers bilaterally to VPM, VPMpc, and the principal nucleus of the trigeminal nerve. The intermediate part, which also includes agranular cortex on the medial wall, projects upon ispsilateral VPLm and nucleus gracilis and upon contralateral VPLl and nucleus cuneatus. — The fibers to the ventro-basal complex, dorsal column nuclei and the principal nucleus of the trigeminal nerve are rather thick. The corticofugal fibers to the other thalamic nuclei are quite thin. — The findings are discussed in light of relevant anatomical and physiological observations in the literature and special emphasis has been laid on reported observations on the supplementary motor area.     

Segregation of lemniscal inputs and motor cortex outputs in cat ventral thalamic nuclei: application of a novel technique

Summary A double labeling method that permits accurate delineation of the terminals of medial lemniscal fibers was used to determine whether thalamic neurons projecting to motor cortex in the cat are in a position to be contacted by such terminals. Thalamic neurons in the VL nucleus were retrogradely labeled by injections of fluorogold placed in the cytoarchitectonically defined area 4, while lemniscal axons and their terminal boutons were anterogradely labeled, in a Golgi-like manner, from injections of Fast Blue placed under physiological control in different parts of the contralateral dorsal column nuclei. In additional experiments, spinothalamic fibers were similarly labeled by injections of Fast Blue in the spinal cord. The results reveal that there is no significant overlap in the distributions of lemniscal terminals and motor cortex-projecting neurons and that no somata or proximal dendrites of motor cortex-projecting neurons are in a position to receive lemniscal terminals. Spinothalamic terminals, on the other hand, end in clusters around motor cortex-projecting neurons in the VL nucleus as well as in other nuclei and are a more likely route for short latency somatosensory inputs to the motor cortex.Abbreviations AD anterodorsal nucleus - AM anteromedial nucleus - AP area postrema - AV anteroventral nucleus - C cuneate nucleus - CeM central medial nucleus - CL central lateral nucleus - CM centre médian nucleus - EC external cuneate nucleus - G gracile nucleus - L limitans nucleus - LD lateral dorsal nucleus - LP lateral posterior nucleus - MGM magnocellular medial geniculate nucleus - MD mediodorsal nucleus - MTT mamillothalamic tract - MV medioventral nucleus - Pc paracentral nucleus - Pf parafascicular nucleus - Po posterior nuclei - R reticular nucleus - RF fasciculus retroflexus - S solitary nucleus - SG suprageniculate nucleus - T spinal trigeminal nucleus - VA ventral anterior nucleus - VIN vestibular nuclei - VL ventral lateral nucleus - VMb basal ventral medial nucleus - VMp principal ventral medial nucleus - VPL ventral posterior lateral nucleus - VPM ventral posterior medial nucleus - ZI zona incerta - 1,2,3a,3b,4 fields of cerebral cortex - C4, C5, C6 spinal cord segments - 5SP,5ST spinal trigeminal nucleus and tract - 10, 12 vagal and hypoglossal nuclei     

The mode of synaptic activation of pyramidal neurons in the cat primary somatosensory cortex: an intracellular HRP study

Summary A total of 141 pyramidal neurons in the cat primary somatosensory cortex (SI) were recorded intracellularly under Nembutal anesthesia (7 in layer II, 43 in layer III, 8 in layer IV, 58 in layer V and 25 in layer VI). Most neurons were identified by intracellular staining with HRP, though some layer V pyramidal neurons were identified only electrophysiologically with antidromic activation of medullary pyramid (PT) or pontine nuclear (PN) stimulation. Excitatory synaptic potentials (EPSPs) were analyzed with stimulation of the superficial radial nerve (SR), the ventral posterolateral nucleus (VPL) in the thalamus and the thalamic radiation (WM). The pyramidal neurons in layers III and IV received EPSPs at the shortest latency: 9.1±2.1 ms (Mean+S.D.) for SR and 1.6±0.7 ms for VPL stimulation. Layer II pyramidal neurons also responded at a short latency to VPL stimulation (1.7±0.5 ms), though their mean latencies for SR-induced EPSPs were relatively longer (10.6±1.9 ms). The mean latencies were much longer in layers V and VI pyramidal neurons (10.2±2.4 ms and 2.9±1.5 ms in layer V pyramidal neurons and 9.9±2.5 ms and 2.8±1.6 ms in layer VI pyramidal ones, respectively for SR and VPL stimulation). The comparison of the latencies between VPL and WM stimulation indicates that most layer III–IV pyramidal neurons and some pyramidal cells in layers II, V and VI received monosynaptic inputs from VPL. These findings are consistent with morphological data on the laminar distribution of thalamocortical fibers, i.e., thalamocortical fibers terminate mainly in the deeper part of layers III and IV with some collaterals in layers V, VI and II-I. The time-sequences of the latencies of VPL-EPSPs indicate that corticocortical and/or transcallosal neurons (pyramidal neurons in layers II and III) fire first and are followed by firing of the output neurons projecting to the subcortical structures (pyramidal neurons in layers V and VI).     

Cortifugal influences on dorsal column nuclei: an electrophysiological study in the rat using the cortical spreading depression technique

Summary The sign and duration of corticofugal effects on the extracellularly recorded spontaneous activity of cuneate and gracile neurons were examined by means of the cortical spreading depresion technique (CSD). Among the 40 units studied 22 showed changes in their spontaneous firing rate during the passage of a CSD. Changes were of either short (5–20 s) or long (>20–140 s) duration. Increases and decreases in activity, as well as sequences of both types of alteration were observed. Short duration changes were more frequent and much more pronounced than those of long duration. From their time course and intensity the short duration effects seem to be related to the brief high frequency cortical neuron discharge that precedes the cortical silence due to CSD, whereas the long lasting effects seem related to the cortical block. It is concluded that the most important corticofugal effects on gracile and cuneate neurons are phasic in nature and the sensorimotor cortical regions were found to be responsible for these influences.During this work R. Giuffrida was supported by a fellowship from the European Science Foundation (1984)     

Convergence of cortico- and cuneopontine projections onto components of the pontocerebellar system in the rat: an anatomical and electrophysiological study

Summary Previous studies in the rat have demonstrated that corresponding peripheral tactile and somatosensory cortical inputs converge within the granule cell layer of various cerebellar lobules and further that descending corticopontine projections from the forelimb sensory cortex (FLSCx) partially overlap with the projection zones of ascending basilar pontine afferents from nucleus cuneatus (NC). The present study employed anatomical and electrophysiological procedures to determine whether cortical and dorsal column nuclear afferent projections converge on pontine neurons that, in turn, provide mossy fiber input to the granule cell layer of the paramedian lobule (PML), i. e., that portion of the rodent cerebellum shown to receive forelimb peripheral inputs. The combination of the orthograde and retrograde axonal transport of horseradish peroxidase (HRP) conjugated to wheat germ agglutinin (WGA) was used light microscopically to demonstrate that orthogradely labeled projections from injections of the FLSCx and NC converged with ponto-paramedian projection neurons that were retrogradely labeled from injections of the PML. These studies were also repeated in conjunction with ablations of either the FLSCx or NC which resulted in the ultrastructural identification of degenerating, as well as WGA-HRP labeled axonal boutons of these pontine afferent projections thus confirming that such projections actually formed synaptic contacts with the retrogradely labeled pontoparamedian projection neurons. Single unit recording analyses of neurons in the ventromedial region of the basilar pons following combined electrical stimulation of various regions of the sensorimotor cortex and the contralateral body surface indicated that approximately 40% of all cells recorded responded to electrical stimulation of corresponding regions of the cortex and periphery, particularly the FLSCx and the forepaw. Natural cutaneous stimuli applied to the forepaw that also elicited responses in these same groups of basilar pontine neurons and were associated with relatively small receptive fields. Taken together, these observations indicate that the previously observed convergence of peripheral and somatosensory cortical inputs within the granule cell layer of the cerebellar cortex may be at least partially organized at the level of the basilar pons.     

Relations between the ventrolateral nucleus and the motor cortex in the cat

Summary In cats anesthetized with chloralose, a topographic study of the relations between the ventrolateral nucleus and the precruciate cortex has been performed. It has revealed a mediolateral topography inside the ventrolateral nucleus such that the medial neurones project to area 6 and the more lateral ones to area 4. Postsynaptic spikes were evoked in ventrolateral nucleus by stimulation of the precruciate cortex, with the same topography. The postsynaptic spikes are usually preceeded by an antidromic spike. The possible action of the cerebellum on axial musculature by way of the ventrolateral nucleus and the motor cortex is discussed.