FUNCTIONAL ORGANIZATION OF THE SPINO- AND CUNEOCEREBELLAR TRACTS

Excitatory inputs to four types of spinocerebellar tract neurons in the cat and the rat thoraco-lumbar spinal cord

The cerebellum receives information from the hindlimbs through several populations of spinocerebellar tract neurons. Although the role of these neurons has been established in electrophysiological experiments, the relative contribution of afferent fibres and central neurons to their excitatory input has only been estimated approximately so far. Taking advantage of differences in the immunohistochemistry of glutamatergic terminals of peripheral afferents and of central neurons (with vesicular glutamate transporters VGLUT1 or VGLUT2, respectively), we compared sources of excitatory input to four populations of spinocerebellar neurons in the thoraco-lumbar spinal cord: dorsal spinocerebellar tract neurons located in Clarke's column (ccDSCT) and in the dorsal horn (dhDSCT) and ventral spinocerebellar tract (VSCT) neurons including spinal border (SB) neurons. This was done on 22 electrophysiologically identified intracellularly labelled neurons in cats and on 80 neurons labelled by retrograde transport of cholera toxin b subunit injected into the cerebellum of rats. In both species distribution of antibodies against VGLUT1 and VGLUT2 on SB neurons (which have dominating inhibitory input from limb muscles), revealed very few VGLUT1 contacts and remarkably high numbers of VGLUT2 contacts. In VSCT neurons with excitatory afferent input, the number of VGLUT1 contacts was relatively high although VGLUT2 contacts likewise dominated, while the proportions of VGLUT1 and VGLUT2 immunoreactive terminals were the reverse on the two populations of DSCT neurons. These findings provide morphological evidence that SB neurons principally receive excitatory inputs from central neurons and provide the cerebellum with information regarding central neuronal activity.

Signals from the ventrolateral thalamus to the motor cortex during locomotion

The activity of the motor cortex during locomotion is profoundly modulated in the rhythm of strides. The source of modulation is not known. In this study we examined the activity of one of the major sources of afferent input to the motor cortex, the ventrolateral thalamus (VL). Experiments were conducted in chronically implanted cats with an extracellular single-neuron recording technique. VL neurons projecting to the motor cortex were identified by antidromic responses. During locomotion, the activity of 92% of neurons was modulated in the rhythm of strides; 67% of cells discharged one activity burst per stride, a pattern typical for the motor cortex. The characteristics of these discharges in most VL neurons appeared to be well suited to contribute to the locomotion-related activity of the motor cortex. In addition to simple locomotion, we examined VL activity during walking on a horizontal ladder, a task that requires vision for correct foot placement. Upon transition from simple to ladder locomotion, the activity of most VL neurons exhibited the same changes that have been reported for the motor cortex, i.e., an increase in the strength of stride-related modulation and shortening of the discharge duration. Five modes of integration of simple and ladder locomotion-related information were recognized in the VL. We suggest that, in addition to contributing to the locomotion-related activity in the motor cortex during simple locomotion, the VL integrates and transmits signals needed for correct foot placement on a complex terrain to the motor cortex.

A trans-spinal loop between neurones in the reticular formation and in the cerebellum

Voluntary limb movements are initiated in the brain but the neurones responsible for activating the muscles (motoneurones and interneurones) are located in the spinal cord. The spinal cord also contains neurones that provide the brain, and especially the cerebellum, with continuous information on effects of the descending commands. We show that one population of such neurones provide the cerebellum with information on how likely the brain's commands (mediated by descending reticulospinal neurones) are to be executed as planned, depending on the degree of inhibition of motoneurones. They may therefore play an important role in preventing errors in activation of motoneurones and thereby help the brain to correct its signals to the spinal cord before such errors have been committed.

Clarke's column neurons as the focus of a corticospinal corollary circuit

Proprioceptive sensory signals inform the CNS of the consequences of motor acts, but effective motor planning involves internal neural systems capable of anticipating actual sensory feedback. Just where and how predictive systems exert their influence remains poorly understood. We have explored the possibility that spinocerebellar neurons that convey proprioceptive sensory information also integrate information from cortical command systems. Analysis of the circuitry and physiology of identified dorsal spinocerebellar tract neurons located in Clarke's column mouse spinal cord reveals distinct populations of Clarke's column neurons that receive direct excitatory and/or indirect inhibitory inputs from descending corticospinal axons. The convergence of these descending inhibitory and excitatory inputs to Clarke's column neurons establishes local spinal circuits with the capacity to mark or modulate incoming proprioceptive input. Together, our genetic, anatomical, and physiological studies provide evidence that Clarke's column spinocerebellar neurons nucleate local spinal corollary circuits of relevance to motor planning and evaluation.

The role of the cerebellum in cognition and emotion: personal reflections since 1982 on the dysmetria of thought hypothesis, and its historical evolution from theory to therapy

The cognitive neuroscience of the cerebellum is now an established multidisciplinary field of investigation. This essay traces the historical evolution of this line of inquiry from an emerging field to its current status, with personal reflections over almost three decades on this journey of discovery. It pays tribute to early investigators who recognized the wider role of the cerebellum beyond motor control, traces the origins of new terms and concepts including the dysmetria of thought theory, the universal cerebellar transform, and the cerebellar cognitive affective syndrome, and places these developments within the broader context of the scientific efforts of a growing community of cerebellar cognitive neuroscientists. This account considers the converging evidence from theoretical, anatomical, physiological, clinical, and functional neuroimaging approaches that have resulted in the transition from recognizing the cerebellar incorporation into the distributed neural circuits subserving cognition and emotion, to a hopeful new era of treatment of neurocognitive and neuropsychiatric manifestations of cerebellar diseases, and to cerebellar-based interventions for psychiatric disorders.

Evidence for topographic organization in the cerebellum of motor control versus cognitive and affective processing

Patients with cerebellar damage often present with the cerebellar motor syndrome of dysmetria, dysarthria and ataxia, yet cerebellar lesions can also result in the cerebellar cognitive affective syndrome (CCAS), including executive, visual spatial, and linguistic impairments, and affective dysregulation. We have hypothesized that there is topographic organization in the human cerebellum such that the anterior lobe and lobule VIII contain the representation of the sensorimotor cerebellum; lobules VI and VII of the posterior lobe comprise the cognitive cerebellum; and the posterior vermis is the anatomical substrate of the limbic cerebellum. Here we analyze anatomical, functional neuroimaging, and clinical data to test this hypothesis. We find converging lines of evidence supporting regional organization of motor, cognitive, and limbic behaviors in the cerebellum. The cerebellar motor syndrome results when lesions involve the anterior lobe and parts of lobule VI, interrupting cerebellar communication with cerebral and spinal motor systems. Cognitive impairments occur when posterior lobe lesions affect lobules VI and VII (including Crus I, Crus II, and lobule VIIB), disrupting cerebellar modulation of cognitive loops with cerebral association cortices. Neuropsychiatric disorders manifest when vermis lesions deprive cerebro-cerebellar-limbic loops of cerebellar input. We consider this functional topography to be a consequence of the differential arrangement of connections of the cerebellum with the spinal cord, brainstem, and cerebral hemispheres, reflecting cerebellar incorporation into the distributed neural circuits subserving movement, cognition, and emotion. These observations provide testable hypotheses for future investigations.

Development of a brief ataxia rating scale (BARS) based on a modified form of the ICARS

To develop a brief ataxia rating scale (BARS) for use by movement disorder specialists and general neurologists. Current ataxia rating scales are cumbersome and not designed for clinical practice. We first modified the International Cooperative Ataxia Rating Scale (ICARS) by adding seven ataxia tests (modified ICARS, or MICARS), and observed only minimally increased scores. We then used the statistics package R to find a five-test subset in MICARS that would correlate best with the total MICARS score. This was accomplished first without constraints and then with the clinical constraint requiring one test each of Gait, Kinetic Function-Arm, Kinetic Function-Leg, Speech, and Eye Movements. We validated these clinical constraints by factor analysis. We then validated the results in a second cohort of patients; evaluated inter-rater reliability in a third cohort; and used the same data set to compare BARS with the Scale for the Assessment and Rating of Ataxia (SARA). Correlation of ICARS with the seven additional tests that when added to ICARS form MICARS was 0.88. There were 31,481 five-test subtests (48% of possible combinations) that had a correlation with total MICARS score of > or =0.90. The strongest correlation of an unconstrained five-test subset was 0.963. The clinically constrained subtest validated by factor analysis, BARS, had a correlation with MICARS-minus-BARS of 0.952. Cronbach alpha for BARS and SARA was 0.90 and 0.92 respectively; and inter-rater reliability (intraclass correlation coefficient) was 0.91 and 0.93 respectively. BARS is valid, reliable, and sufficiently fast and accurate for clinical purposes.

Cerebellar stroke without motor deficit: clinical evidence for motor and non-motor domains within the human cerebellum

OBJECTIVE

To determine whether there are non-motor regions of cerebellum in which sizeable infarcts have little or no impact on motor control.

EXPERIMENTAL PROCEDURES

We evaluated motor deficits in patients following cerebellar stroke using a modified version of the International Cooperative Ataxia Rating Scale (MICARS). Lesion location was determined using magnetic resonance imaging (MRI) and computerized axial tomography (CT). Patients were grouped by stroke location-Group I, stroke within the anterior lobe (lobules I-V); Group 2, anterior lobe and lobule VI; Group 3, posterior lobe (lobules VI-IX; including flocculonodular lobe, lobule X); Group 4, posterior lobe but excluding lobule VI (i.e. lobules VII-X); Group 5, stroke within anterior lobe plus posterior lobe.

RESULTS

Thirty-nine patients were examined 8.0+/-6.0 days following stroke. There were no Group 1 patients. As mean MICARS scores for Groups 2 through 5 differed significantly (one-way analysis of variance, F(3,35)=10.9, P=0.000 03), post hoc Tukey's least significant difference tests were used to compare individual groups. Group 2 MICARS scores (n=6; mean+/-SD, 20.2+/-6.9) differed from Group 3 (n=6; 7.2+/-3.8; P=0.01) and Group 4 (n=13; 2.5+/-2.0; P=0.000 02); Group 5 (n=14; 18.6+/-12.8) also differed from Group 3 (P=0.009) and Group 4 (P=0.000 02). There were no differences between Groups 2 and 5 (P=0.71), or between Group 3 and Group 4 (P=0.273). However, Group 3 differed from Group 4 when analyzed with a two-sample t-test unadjusted for multiple comparisons (P=0.03). Thus, the cerebellar motor syndrome resulted from stroke in the anterior lobe, but not from stroke in lobules VII-X (Groups 2 plus 5, n=20, MICARS 19.1+/-11.2, vs. Group 4; P=0.000 002). Strokes involving lobule VI produced minimal motor impairment.

CONCLUSION

These findings demonstrate that cerebellar stroke does not always result in motor impairment, and they provide clinical evidence for topographic organization of motor versus nonmotor functions in the human cerebellum.

Regional (14C) 2-deoxyglucose uptake during forelimb movements evoked by rat motor cortex stimulation: pons, cerebellum, medulla, spinal cord, muscle

Electrical stimulation of the right forelimb motor (MI) sensory (SI) cortex in normal, adult rats produced repetitive left forelimb movements. Regions of increased (14C) 2-deoxyglucose (2DG) uptake were mapped auto-radiographically during these movements. MI stimulation activated the ipsilateral reticular tegmental pontine nucleus (RTP) and the middle (rostral-caudal) third of the pontine nuclei including pyramidal (P), medial (POM), ventral (POV), and lateral (POL) pontine nuclei. The ipsilateral inferior olivary complex was activated including dorsal accessory olive (DAO), principal olive (PO), and medial accessory olive (MAO). The contralateral lateral reticular (LR) nucleus and nucleus cuneatus (CU) were activated. Lateral vermal, paravermal, and hemispheric portions of the contralateral cerebellum were also activated. Parts of vermian lobules IV, V, VI, VII, and VIII, and lobulus simplex, crus I, crus II, paramedian lobule, and copula pyramidis were activated. Granule cell layers were activated much more than molecular layers. Discrete microzones of high granule cell 2DG uptake alternated with zones of low uptake in left paramedian lobule and copula pyramidis and may correlate with the fractured cerebellar somatotopy described physiologically by Welker and his associates. Portions of the left lateral and interpositus nuclei were metabolically activated. Medial portions of laminae I-VI were activated in the dorsal horn of cervical spinal cord. The 2DG uptake was either unchanged or decreased in the ventral horn. Thoracic and lumbar spinal cord were not activated. Monsynaptic MI and SI connections to P, POM, POV, POL, RTP, DAO, PO, MAO, LR, CU, and spinal cord could account for activation of those structures. However, there are no direct MI or SI connections to the deep cerebellar nuclei, the cerebellar hemisphere, or the muscles. Activation of these structures must be due to activation of polysynaptic pathways, sensory feedback from the moving forelimb, or both. The present experiments cannot distinguish these possibilities. Comparison of the regions activated during forelimb MI stimulation (FLMIS) to those activated during vibrissae MI stimulation (VMIS) suggests that the pontine nuclei, cerebellar hemisphere, and possibly the deep cerebellar nuclei are somatotopically organized. RTP, LR, CU, and spinal cord were activated during FLMIS but were not activated during VMIS. The failure to activate the ventral horn of cervical spinal cord may be due to known inhibition of alpha-motor neurons during motor cortex stimulation.

Comparison of neuronal activities of external cuneate nucleus, spinocerebellar cortex and interpositus nucleus during passive movements of the rat's forelimb

In this paper we examined the neuronal activities of external cuneate nucleus, spinocerebellar Purkinje cells and interpositus nucleus during passive forelimb movements in anesthetized rats with the aim of identifying common or different patterns of activation across structures. By means of principal components analysis, we identified two main patterns of discharge which explained most of the dataset variance. One component characterized the movement-related activity of external cuneate and spinocerebellar cortical neurons, while the other reflected neuronal activity of the interpositus nucleus. We also found that both principal components were related to global forelimb kinematics but, while most of the variance of the activity of external cuneate cells and spinocerebellar Purkinje cells was explained by the limb axis orientation and orientation velocity, interpositus neurons' firing was best related to length and length velocity. This difference in the forelimb kinematics representation observed in external cuneate nucleus and spinocerebellar cortex compared with the interpositus nucleus is discussed with respect to the specific role that these structures may play also during active control of limb movements.

Dorsal spinocerebellar tract neurons respond to contralateral limb stepping

Proprioceptive sensory information carried by spinocerebellar tracts provides a major input to the spinocerebellum, which has an important role in coordinating motor output for posture and locomotion. Until recently it was assumed that the information transmitted by the dorsal spinocerebellar tract (DSCT) was organized to represent single muscles or single joints in the ipsilateral hindlimb. Recent studies have shown, however, that DSCT activity represents global kinematic parameters of the hindlimb. We now present evidence that the DSCT neurons are also modulated by passive step-like movements of either hindlimb, implying they receive a bilateral sensory input. About two-thirds of 78 cells studied had significant responses to movements of the contralateral limb alone and about 70% responded differently to bipedal movements than to ipsilateral movement alone. The same basic behavior was observed in anesthetized, paralyzed cats and in unanesthetized, decerebrate cats, although decerebrate cats may have had larger responses on average. The results suggest that many DSCT cells may encode information about interlimb coordination.

Cortical and cerebellar activity of the human brain during imagined and executed unimanual and bimanual action sequences: a functional MRI study

The neural (blood oxygenation level dependent) correlates of executed and imagined finger sequences, both unimanual and bimanual, were studied in adult right-handed volunteers using functional magnetic resonance imaging (fMRI) of the entire brain. The finger to thumb opposition tasks each consisted of three conditions, two unimanual and one bimanual. Each experimental condition consisted of overt movement of the fingers in a prescribed sequence and imagery of the same task. An intricate network consisting of sensorimotor cortex, supplementary motor area (SMA), superior parietal lobule and cerebellum was identified when the tasks involved both planning and execution. During imagery alone, however, cerebellar activity was largely absent. This apparent decoupling of sensorimotor cortical and cerebellar areas during imagined movement sequences, suggests that cortico-cerebellar loops are engaged only when action sequences are both intended and realized. In line with recent models of motor control, the cerebellum may monitor cortical output and feed back corrective information to the motor cortex primarily during actual, not imagined, movements. Although parietal cortex activation occurred during both execution and imagery tasks, it was most consistently present during bimanual action sequences. The engagement of the superior parietal lobule appears to be related to the increased attention and memory resources associated, in the present instance, with coordinating difficult bimanual sequences.

Modulation of responses of feline ventral spinocerebellar tract neurons by monoamines

Ventral spinocerebellar tract neurons located in laminae V-VII of cat lumbar spinal cord were tested for the effects of ionophoretically applied monoamines and receptor selective agonists. Extracellularly recorded responses, monosynaptically evoked by group I afferents in a muscle nerve, were compared before, during, and after ionophoresis. They were analyzed with respect to changes in the number of evoked spikes and in the latency. Both serotonin (5-HT) and noradrenaline (NA) were found to facilitate responses of all neurons tested. Ionophoresis of three serotonin subtype receptor agonists (5-carboxamidotryptamine maleate, 5 methoxytryptamine HCl, and alpha-methyl 5-hydroxytryptamine) and of two NA receptor agonists (phenylephrine and isoproterenol) likewise had a facilitatory effect. However, three other 5-HT receptor agonists (8-hydroxy-dipropylaminotetraline hydrobromide), 2-methyl 5-hydroxytryptamine, and 1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane HCl and two NA receptor agonists (tizanidine and clonidine) had the opposite effect because they depressed responses of the tested neurons. These results show that information forwarded by means of the ventral spinocerebellar tract may be modulated by monoamines and that several receptor subtypes, located pre- or postsynaptically, may be involved. The results also demonstrate that transmission by means of group I muscle afferents may not only be facilitated by monoamines but also depressed by selective receptor subtype activation.

Neurons labeled from locomotor-related ventrolateral funiculus stimulus sites in the neonatal rat spinal cord

Spinal cord/brainstem preparations from 5- to 8-day-old rats, maintained in vitro, were used to determine the cells of origin and regions of termination of fibers in the superficial ventrolateral funiculus (VLF) at a site from which rhythmic locomotor-like activity can be induced. Rhythmic locomotor-like activity was recorded from lumbar ventral roots after short trains of stimuli (50 Hz for 0.5-2 seconds) delivered to the VLF. Field potential mapping revealed that single VLF stimuli elicited responses in the ipsilateral ventrolateral medulla. Tract-tracing experiments by using biocytin, pressure-injected into the VLF, showed that only a small number of brainstem neurons were labeled and these were scattered bilaterally in the ventrolateral and lateral medulla. Dense concentrations of nerve terminals were found in the lateral reticular nucleus ipsilateral to the stimulation site. Labeled spinal cord neurons included a primary population of large cells distributed bilaterally in lamina VII from T13 to L4, with peak numbers in L2 ipsilaterally and in L3 contralaterally. Intracellular recordings revealed that some L2 and L3 neurons with rhythmic responses to VLF stimulation could be activated antidromically from the VLF, with latencies of less than 1.0 msec. These observations led us to speculate that the superficial VLF carries a locomotor-related tract originating bilaterally in lumbar lamina VII and terminating in the ipsilateral medulla, including the lateral reticular nucleus. This pathway may be part of the spinoreticular or spinoreticulotectal pathway that has been described in many species, the function of which has only loosely been ascribed.

Proprioception from a spinocerebellar perspective

This review explores how proprioceptive sensory information is organized at spinal cord levels as it relates to a sense of body position and movement. The topic is considered in an historical context and develops a different framework that may be more in tune with current views of sensorimotor processing in other central nervous system structures. The dorsal spinocerebellar tract (DSCT) system is considered in detail as a model system that may be considered as an end point for the processing of proprioceptive sensory information in the spinal cord. An analysis of this system examines sensory processing at the lowest levels of synaptic connectivity with central neurons in the nervous system. The analysis leads to a framework for proprioception that involves a highly flexible network organization based in some way on whole limb kinematics. The functional organization underlying this framework originates with the biomechanical linkages in the limb that establish functional relationships among the limb segments. Afferent information from limb receptors is processed further through a distributed neural network in the spinal cord. The result is a global representation of hindlimb parameters rather than a muscle-by-muscle or joint-by-joint representation.

14C-deoxyglucose mapping of the monkey brain during reaching to visual targets

The strategies used by the macaca monkey brain in controlling the performance of a reaching movement to a visual target have been studied by the quantitative autoradiographic 14C-DG method. Experiments on visually intact monkeys reaching to a visual target indicate that V1 and V2 convey visuomotor information to the cortex of the superior temporal and parietoccipital sulci which may encode the position of the moving forelimb, and to the cortex in the ventral part and lateral bank of the intraparietal sulcus which may encode the location of the visual target. The involvement of the medial bank of the intraparietal sulcus in proprioceptive guidance of movement is also suggested on the basis of the parallel metabolic effects estimated in this region and in the forelimb representations of the primary somatosensory and motor cortices. The network including the inferior postarcuate skeletomotor and prearcuate oculomotor cortical fields and the caudal periprincipal area 46 may participate in sensory-to-motor and oculomotor-to-skeletomotor transformations, in parallel with the medial and lateral intraparietal cortices. Experiments on split brain monkeys reaching to visual targets revealed that reaching is always controlled by the hemisphere contralateral to the moving forelimb whether it is visually intact or 'blind'. Two supplementary mechanisms compensate for the 'blindness' of the hemisphere controlling the moving forelimb. First, the information about the location of the target is derived from head and eye movements and is sent to the 'blind' hemisphere via inferior parietal cortical areas, while the information about the forelimb position is derived from proprioceptive mechanisms and is sent via the somatosensory and superior parietal cortices. Second, the cerebellar hemispheric extensions of vermian lobules V, VI and VIII, ipsilateral to the moving forelimb, combine visual and oculomotor information about the target position, relayed by the 'seeing' cerebral hemisphere, with sensorimotor information concerning cortical intended and peripheral actual movements of the forelimb, and then send this integrated information back to the motor cortex of the 'blind' hemisphere, thus enabling it to guide the contralateral forelimb to the target.

GDNF, RET and GFRalpha-1-3 mRNA expression in the developing human spinal cord and ganglia

The identification of endogenous neurotrophic factors and their receptors in human spinal cord is important not only to understand development, but also in the consideration of possible future therapies for neurodegenerative disorders and trauma. Using in situ hybridization, the expression of glial cell line-derived neurotrophic factor (GDNF), neurturin (NTN), persephin (PSP), GFRalpha-1, GFRalpha-2, GFRalpha-3 and RET mRNA in human fetal spinal cord was studied. Strong GDNF mRNA hybridization signal, presumably restricted to Clarke's nucleus, was detected in the thoracic spinal cord. mRNA encoding GFRalpha-1 was expressed in the entire spinal cord gray matter with particularly high expression in the ventral horn. GFRbeta-1 was also expressed more weakly in dorsal root ganglia. NTN and persephin mRNA were not detected in either the fetal spinal cord or the dorsal root ganglia. mRNA coding for GFRalpha-2, however, was found in most cells of the spinal cord gray matter. A strong expression of GFRalpha-3 mRNA was detected in dorsal root ganglia cells and Schwann cells. The transducing receptor RET was expressed strongly in motorneurons and dorsal root ganglion neurons. We conclude that basic features concerning the role of the GDNF family of ligands and their receptors revealed in rodents applies to humans.

Origin, course, and laterality of spinocerebellar axons in the North American opossum, Didelphis virginiana

Spinocerebellar axons have been studied extensively in placental mammals, but there have been no full reports on their origin, laterality, or spinal course in any marsupial. We have used the North American opossum (Didelphis virginiana) to obtain such information and to ask whether any spinocerebellar neurons innervate both the anterior and posterior lobes of the cerebellum through axonal collaterals. To identify spinal neurons that project to the cerebellum, we employed the retrograde transport of Fluoro-Gold (FG) from the anterior lobe, the main target of spinocerebellar axons. In some cases, cerebellar injections of FG were combined with hemisections of the rostral cervical or midthoracic spinal cord, so that laterality of spinocerebellar connections could be established. To determine whether single neurons project to both the anterior lobe and the posterior lobe, injections of Fast Blue (FB) into the anterior lobe were combined with injections of Diamidino yellow (DY) or rhodamine B dextran (RBD) into the posterior lobe, or vice versa. Following injections of FG into the anterior lobe, neurons were labeled throughout the length of the spinal cord, which differed in laminar distribution and laterality of their projections. Among other areas, neurons were labeled in the central cervical nucleus, the nucleus centrobasalis, Clarke's nucleus, the dorsal horn dorsal spinocerebellar tract area, the spinal border region, and Stilling's nucleus. When anterior lobe injections of FB were combined with injections of RBD or DY into the posterior lobe, or vice versa, some double-labeled neurons were present in all major spinocerebellar groups. Cerebellar injections of FG also retrogradely labeled spinocerebellar axons, allowing us to document their locations in the gray matter as well as within the periphery of the lateral and ventral funiculi at all spinal levels. A few spinocerebellar axons also were found in the dorsal funiculus (a dorsal column-spinocerebellar tract), which appeared to originate from neurons in the dorsal part of Clarke's nucleus from the ninth thoracic segment to the first lumbar segment. Our results indicate that spinocerebellar axons in the marsupial opossum are generally comparable in origin, course, and laterality to the same axons in the placental mammals studied to date.

Spinocerebellar Purkinje cells and rat forelimb postures: a direction-dependent activity

On anesthetized adult rats, we examined the possibility that the discharges of spinocerebellar Purkinje cells (PCs) are modulated by passive limb positioning. The rat forelimb was passively placed in four different sagittal positions while the simple spike spontaneous activity of single PCs was recorded; recordings started 5 s after the reaching of the posture and the forelimb remained at each position for at least 30 s. Although the activity of the PCs did not reflect the forelimb position, it showed hysteresis that depended in a cosine fashion on the direction of the preceding movement. This implies that the directional sensitivity of spinocerebellar PCs is persistent, since the activity levels were almost constant throughout the recording time.

Representation of multiple kinematic parameters of the cat hindlimb in spinocerebellar activity

Dorsal spinocerebellar tract (DSCT) neurons have been shown to transmit signals related to hindlimb position and movement direction in the anesthetized cat. Because both parameters may be encoded by single neurons, we examined the extent to which their representations might occur sequentially or simultaneously by recording unit activity while the hindlimb was moved passively in the sagittal plane by a robot arm. A center-out/out-center paradigm moved the foot 2 cm from a given position radially to eight positions located 45 degrees apart, holding each position for 8 s. Another paradigm moved the foot along various paths to 20 positions distributed throughout most of the limb's workspace. With each paradigm, we could assess the activity related to foot position and the direction of movement to each position. Modulation of unit activity evoked by center-out/out-center movements was determined for each 1-s postmovement interval by use of a cosine tuning model that specified modulation amplitude and preferred direction. Of 125 units tested, 82.4% were significantly modulated (P < 0.05) according to this model. We assessed the relative contributions of position and movement by taking advantage of the fact that directional modulation following out-center movements to a common position could only be related to the movement, whereas that following the center-out movements related to both position and movement. The results suggested a simultaneous modulation by these two parameters. Each cell could be characterized by a similar preferred direction for position or movement modulation and the distribution of preferred directions across cells clustered significantly along an axis close to the limb axis. When the limb axis was rotated, the unit preferred directions rotated similarly, on average. Unexpectedly, we found the activity of more than half the cells to be modulated for > or = 8 s after out-center movements, implying a persistent movement-related activity well after a movement is completed. These findings were confirmed and extended with the second paradigm by using a multivariate regression model that included terms for position, movement, and their multiplicative interaction. The activity of 81.3% of the 97 neurons tested fit the model (R2 > 0.4, P < .0001); 31.6% were modulated exclusively by foot position, and 58.2% simultaneously by both position and movement, with significant interaction. We conclude from our results that DSCT neurons may be modulated simultaneously by limb position and movement, and their preferred directions tend to align with the limb axis. The modulation is interactive such that movement modulation amplitude depends on limb position, and many cells also retain a memory trace of recent movements. The results are discussed in terms of a possible role for the DSCT in encoding limb compliance.

Visually guided reaching with the forelimb contralateral to a "blind" hemisphere in the monkey: contribution of the cerebellum

Metabolic activity was mapped in the cerebellar cortex and its major inputs and projection targets in monkeys performing visually guided reaching with the left forelimb. Normal monkeys and monkeys deprived of visual input to the right cerebral hemisphere by right optic tract section, combined in some cases with forebrain commissurotomy, were studied. We reported previously that visually guided reaching with the left forelimb activated the motor cortex of the right hemisphere equally in all these monkeys, indicating that reaching was controlled by the right hemisphere whether it was visually intact or "blind" [Savaki H.E. et al. (1993) J. Neurosci. 13, 2772-2789]. In the present study, metabolic activations were observed in the left cerebellar hemispheric extensions of vermian lobules V, VI and VIII, again regardless of whether the right hemisphere was visually intact or "blind". In intact monkeys, however, the activations were significantly smaller in the lateral than in the paravermal zone of these hemispheric extensions, whereas in tractotomized/commissurotomized monkeys the activations were equal in the two zones. The greater activations in the left lateral zone in tractotomized/commissurotomized monkeys may represent compensation in part for the visual deafferentation of the right cerebral hemisphere. Also observed were metabolic activation in the left dorsolateral pontine nucleus in tractotomized/commissurotomized monkeys and metabolic depression in the left dentate nucleus in visually intact monkeys. This pattern of results suggests the following conclusions. The activated loci in the left cerebellar cortex combine (i) visual information about the target relayed by seeing cerebral hemispheres, and (ii) sensorimotor information concerning intended and actual movements of the left forelimb relayed by the right cerebral hemisphere and the limb, respectively, and then (iii) send this integrated information back to the motor cortex of the right cerebral hemisphere, thus enabling it to guide the left forelimb to the target whether the hemisphere is visually intact or "blind".

Course of spinocerebellar axons in the ventral and lateral funiculi of the spinal cord with projections to the anterior lobe: an experimental anatomical study in the cat with retrograde tracing techniques

The fiber course of the spinocerebellar tracts in the ventral and lateral funiculi of the cat spinal cord were studied by a new approach, making cordotomies at different spinal levels or lesions of the restiform body followed by injections of HRP or WGA-HRP into the anterior cerebellar lobe. The retrogradely labeled axons showed characteristic distribution patterns related to the level and extent of the lesions. The results show the following. 1) The dorsal spinocerebellar tract (DSCT) originating ipsilaterally from the thoracic and upper lumbar segments ascends in the dorsolateral fasciculus. It undergoes a dorsal shift during its rostral course. The tract is topically arranged and passes through the restiform body. 2) The ventral spinocerebellar tract (VSCT) arising contralaterally from lower thoracic, lumbar, and more caudal segments passes via the ventral funiculus and ascends in the ventrolateral fasciculus. This tract is also topically arranged. It makes a lateral and then a dorsal shift during its ascending course. The main portion of the VSCT enters the cerebellum via the superior cerebellar peduncle. A minor portion originating from the sacrococcygeal region enters via the restiform body. 3) The spinocerebellar fibers originating ipsilaterally from the cervical enlargement ascend in the lateralmost part of the lateral funiculus in the area between the dorsolateral and ventrolateral fasciculi. These fibers form two groups, one passing through the restiform body, the other through the superior cerebellar peduncle. 4) The spinocerebellar fibers originating contralaterally from the central cervical nucleus pass through the ventral funiculus and ascend in the lateralmost part of the lateral funiculus, mainly in the ventrolateral fasciculus. Most of the fibers seem to pass through the superior cerebellar peduncle.

Grafts of fetal central nervous system tissue rescue axotomized Clarke's nucleus neurons in adult and neonatal operates

Many conditions are thought to contribute to neuron death after axotomy, including immaturity of the cell at the time of injury, inability to reestablish or maintain target contact, and dependence on trophic factors produced by targets. Exogenous application of neurotrophic factors and transplants of peripheral nerve and embryonic central nervous system (CNS) tissue temporarily rescue axotomized CNS neurons, but permanent rescue may require transplants that are normal targets of the injured neurons. We examined the requirements for survival of axotomized Clarke's nucleus (CN) neurons. Two months after hemisection of the spinal cord at the T8 segment, there was an ipsilateral 30% loss of neurons at the L1 segment in adult operates and a 40% loss in neonates. Transplants of embryonic spinal cord, cerebellum, and neocortex inserted into the T8 segment at the time of hemisection prevented virtually all of the cell death in both adults and neonates, but transplants of embryonic striatum were ineffective. None of the grafts prevented the somal atrophy of CN neurons caused by axotomy. Retrograde transport of fluoro-gold from the cerebellum demonstrated that 33% of all CN neurons at L1 project to the cerebellum, 50% of these died following a T8 hemisection, but all these projection neurons were rescued by a transplant of embryonic spinal cord. These results suggest that the rescue of axotomized CN neurons is relatively specific for the normal target areas of these neurons, but this specificity is not absolute and may depend on the distribution and synthesis of particular neurotrophic agents.

Sensory integration by the dorsal spinocerebellar tract circuitry

Monosynaptic connections from sensory receptors to the dorsal spinocerebellar tract are believed to have a significant role in the transmission of sensory information to the cerebellum. However, predominant polysynaptic connections with highly convergent afferent input suggest a functional organization based on integrated sensory representations. We explored this possibility by examining the responses of dorsal spinocerebellar tract neurons to inputs from muscle receptors. We compared results from two sets of experiments designed to activate receptors in the gastrocnemius-soleus muscles. In one set (135 cells) we stimulated muscle receptors by stretching the isolated muscles and in the other set (194 cells) the muscle receptors were activated by passive foot flexion, which concurrently activated cutaneous and joint receptors as well. Population responses of the spinocerebellar neurons were quite different for the two types of stimuli. Foot flexion elicited long-latency excitatory responses in a majority (53%) of the cells, while muscle stretch elicited a large fraction of early peaking excitatory responses (28%) and inhibitory responses (38%). The long-latency responses to flexion could not be accounted for by specific cutaneous inputs or by possible delayed reflex contractions. We concluded that both types of population response resulted from the muscle stretch and therefore the responses of dorsal spinocerebellar tract cells to these stimuli do not simply reflect the activity in specific classes of sensory receptors.

Terminal distribution of mossy fibers traversing the superior cerebellar peduncle in the mouse

The carbocyanine membrane probe DiI was applied to cut fibers of the superior cerebellar peduncle in the fixed brains of adult mice. Labeled mossy fibers in the cerebellar cortex formed rosettes only in the most superficial aspect of the granular layer, just beneath the Purkinje cell layer. These results provide evidence for a functional division of the cerebellar granular layer into horizontal laminae, in addition to the commonly recognized lobular and sagittal divisions of the cerebellar cortex.

Intraoperative recordings of spinal somatosensory evoked potentials to tibial nerve and sural nerve stimulation

Somatosensory evoked potentials (SSEPs) to stimulation of the tibial nerve at the knee (TN-K) and ankle (TN-A), and the sural nerve at the ankle (SN-A), were recorded from 3 or 4 spinal levels during surgery for scoliosis in 11 neurologically normal subjects. With stimulation of all 3 nerves, the propagation velocity along the spine was nonlinear: it was faster over cauda equina and midthoracic cord than over caudal spinal cord. Over the mid-thoracic cord, TN-K SSEP propagation was faster than that of TN-A and SN-A SSEPs, whereas over the caudal spinal cord these values were similar on stimulation of all 3 nerves. These data suggest that fast conducting second order afferent fiber systems contribute to spinal cord SSEPs evoked by stimulating both mixed and cutaneous peripheral nerves.

Spinocerebellar projections from spinal border cells in the cat as studied by anterograde transport of wheat germ agglutinin-horseradish peroxidase

The cerebellar projections of spinal border cells, which give rise to crossed ascending axons, were studied in the lower lumbar segments by the anterograde transport of wheat germ agglutinin conjugated to horseradish peroxidase (WGA-HRP) in the cat. Prior to the injections, the spinal cord was lesioned rostral and ipsilateral to the WGA-HRP injections to eliminate labeling of the ipsilaterally ascending axons. Following injections of WGA-HRP into the L4-L6 segments, labeled terminals were seen in sublobules Ib-Vf of the anterior lobe, sublobules VIf-VIe, lobule VIII, the paramedian lobule, and crus II. More than 90% of the total number of labeled terminals were in the anterior lobe; the projections were predominantly ipsilateral to their cells of origin (about 90% or more labeled terminals of the total number in each of sublobules IIb-Va). Many labeled terminals were seen ipsilaterally in sublobules IIb (11.1-17.5% of the total number), IIIa (11.7-12.9%), IIIb (16.1-17.6%), IVa (8.8-10.8%), IVb (6.2-10.5%), and Va (9.7-10.3%). In the posterior lobe, labeled terminals were numerous only in sublobule C of the ipsilateral paramedian lobule (2.7-4.9%). The projection fields in the horizontal plane of the lobules were reconstructed from a series of cross-sections through each lobule. In the anterior lobe, labeled terminals were distributed in four major areas. In sublobules IIa-IVa, area 1 was located between 1.0 and 2.0 mm lateral to the midline in zones B-C1 of Voogd; area 2, between 2.0 and 3.0 mm lateral to the midline in zones C1-C2; area 3, between 3.0 and 4.0 mm in zones C2-C3; and area 4, lateral to 4.0 mm from the midline in zone C3. These areas extended apicobasally in the apical to middle parts of the lobules. On the rostral side of sublobule C1 of the ipsilateral paramedian lobule, the projection areas extended in the entire apicobasal and the mediolateral axis of the sublobule, except in the most lateral part. The present results suggest that the SBCs project to specific areas in the cerebellar lobules.

c-fos expression and (14C) 2-deoxyglucose uptake in the caudal cerebellum of the rat during motor/sensory cortex stimulation

Fos, the protein product of the c-fos gene, is induced in neurons in response to a variety of stimuli. In order to see if Fos could be used to map activity in the brain, the pattern of Fos staining was compared to the pattern of (14C) 2-deoxyglucose (2DG) uptake in the seventh and eighth lobules of the cerebellum during electrical stimulation of the cerebral cortex. Electrical stimulation of hindlimb motor/sensory cortex of awake rats increased 2DG uptake in the contralateral and ipsilateral cerebellum. The largest increases occurred in granule cell patches in the contralateral copula pyramidis (Cop P) and pyramis (P), the hemispheric and vermal portions of the eighth cerebellar lobule, respectively. The granule cell patches formed parasagittal bands that extended short distances mediolaterally, and extended long distances anteroposteriorly over much of the Cop P. Forelimb motor/sensory cortex stimulation increased 2DG uptake bilaterally in the seventh, paramedian (PM) cerebellar lobule. The greatest increases occurred in the granule cell layer contralateral to the stimulation. These and the above results generally agree with classical studies that localize forelimb on the seventh lobule anterior to the hindlimb on the eighth lobule. However, hindlimb cortical stimulation activated parts of the PM, and forelimb cortical stimulation activated portions of the rostral Cop P. In general, nonoverlapping portions of Cop P and PM were activated during the two types of cortical stimulation. These results are consistent with a fractured somatotopy (Welker and Shambes, '85) in which nonadjacent body parts are consistently represented in adjacent granule cell patches on each lobule, with the fractured somatotopy being different for every lobule. No region of cerebellum expressed Fos in unstimulated, electrode implanted, control subjects. However, following 15 minutes of electrical stimulation of hindlimb cortex, Fos was expressed 4 hours later in patches of granule cell nuclei in Cop P and P. These patches of Fos immunostained granule cells occurred in similar locations in Cop P to the patches of highest glucose metabolism observed with the 2DG method. Zones of Purkinje cell nuclei also expressed Fos. These Purkinje cell zones were often directly over similar sized granule cell patches in P. In the hemisphere however, the zones of Purkinje cells in ventrolateral Cop P expressing Fos only partially overlapped underlying granule cell patches that expressed Fos. Moreover, Fos was not unduced in any Purkinje cells adjacent to the Fos- stained granule cell patch in dorsolateral Cop P.(ABSTRACT TRUNCATED AT 400 WORDS)

Spinocerebellar projections from the upper lumbar segments in the cat, as studied by anterograde transport of wheat germ agglutinin-horseradish peroxidase

The projection fields of the dorsal spinocerebellar tract (DSCT) arising from Clarke's column, marginal neurons of Clarke's column, and lamina V neurons in the upper lumbar segments were studied by the anterograde transport of wheat germ agglutinin conjugated to horseradish peroxidase (WGA-HRP) in the cat. To label only these neuron groups with uncrossed ascending axons, the spinal cord was lesioned rostral and contralateral to the WGA-HRP injections. Following injections of WGA-HRP into the L1-L4 segments, labeled terminals were seen in sublobules Ia-VIc and VIIb-VIIIb, the simple lobule, the paramedian lobule, and the dorsal paraflocculus. About 70-80% and 20-30% of the total number of labeled terminals were in the anterior and the posterior lobe, respectively; the projections were predominantly ipsilateral to the cells of origin (about 87% or more labeled terminals of the total number in each of sublobules IIb-Va). The labeled terminals were abundant in sublobule IIb (6-11%), lobule III (12-27%), and sublobules IVa (14-17%) and IVb (14-21%). In the mediolateral extent of the lobules in the anterior lobe, the labeled terminals were most numerous between 1.1 and 3.0 mm lateral to the midline (45-75% of the total number of labeled terminals on the ipsilateral side). In the posterior lobe labeled terminals were numerous in sublobule VIIIb (13.6%) and sublobule C of the paramedian lobule (15-19%). The projection fields in the horizontal plane of the lobules were reconstructed from a series of cross sections through each lobule. In the anterior lobe the labeled terminals were distributed in eight major areas. In sublobules IIb-III, areas 1-3 were located within 1.0 mm of the midline in zone A of Voogd; areas 4-6, between 1.0 and 2.5 mm lateral to the midline in zones B-C1; and areas 7 and 8, lateral to 3.0 mm from the midline in zones C2 and C3. Areas 1-6 extended apicobasally in the middle part of the lobules. In sublobule VIIIb projections were confined to three longitudinal areas whereas in the paramedian lobule the projection areas were less distinct. The projection pattern of the lumbar DSCT was different from that of the thoracic DSCT reported previously. In the anterior lobe the thoracic DSCT projects to five areas in the medial (zone A) and the lateral part (zone B) of the vermis and to four areas in the intermediate region of the hemisphere (zones C1-C3).

Central distribution of cervical primary afferents in the rat, with emphasis on proprioceptive projections to vestibular, perihypoglossal, and upper thoracic spinal nuclei

The projections of primary afferents from rostral cervical segments to the brainstem and the spinal cord of the rat were investigated by using anterograde and transganglionic transport techniques. Projections from whole spinal ganglia were compared with those from single nerves carrying only exteroceptive or proprioceptive fibers. Injections of horseradish peroxidase (HRP) or wheat germ agglutinin-horseradish peroxidase conjugate (WGA-HRP) were performed into dorsal root ganglia C2, C3, and C4. Free HRP was applied to the cut dorsal rami C2 and C3, greater occipital nerve, sternomastoid nerve, and to the C1/2 anastomosis, which contains afferents from suboccipital muscles and the atlanto-occipital joint. WGA-HRP injections into ganglia C7 and L5 were performed for comparative purposes. Injections of WGA-HRP or free HRP into rostral cervical dorsal root ganglia and HRP application to C2 and C3 dorsal rami produced labeling in dorsal and ventral horns at the level of entrance, the central cervical nucleus, and in external and main cuneate nuclei. From axons ascending to pontine and descending to upper thoracic spinal levels, medial collaterals were distributed to medial and descending vestibular, perihypoglossal and solitary nuclei, and the intermediate zone and Clarke's nucleus dorsalis in the spinal cord. Lateral collaterals projected mainly to the trigeminal subnucleus interpolaris and to lateral spinal laminae IV and V. Results from HRP application to single peripheral nerves indicated that medial collaterals were almost exclusively proprioceptive, whereas lateral collaterals were largely exteroceptive with a contribution from suboccipital proprioceptive fibers. WGA-HRP injections into dorsal root ganglia C7 and L5 failed to produce significant labeling within vestibular and periphypoglossal nuclei, although they demonstrated classical projection sites within the brainstem and spinal cord. The consistent collateralisation pattern of rostral cervical afferents along their whole rostrocaudal course enables them to contact a variety of precerebellar, vestibulospinal, and preoculomotor neurons. These connections reflect the well-known significance of proprioceptive neck afferents for the control of posture, head position, and eye movements.

Activity of dorsal spinocerebellar tract neurones in the thoracic spinal cord in relation to respiratory movement

The discharges of 22 antidromically identified dorsal spinocerebellar tract (DSCT) neurones, whose activity was modulated in phase with the spontaneous respiratory cycle, were recorded in the lower thoracic segments of anaesthetized cats. Out of them, 16 neurones increased in their firing rate during the inspiratory phase and 6 during the expiratory phase. When the animal was paralysed and artificially ventilated, rhythmic activity of DSCT neurones was locked to the respiratory pump cycle. Once the artificial ventilation was stopped, no modulation was found even though rhythmic activity of the phrenic nerve discharges still remained. The same results were obtained in vagotomized cats. These results indicate that some thoracic DSCT neurones convey information of peripheral events in the chest wall during respiratory movement.

Modulation of rhythmic function in the posterior midbrain

Recordings of single unit activity in the posterior midbrain of the cat were carried out in the "fictive spontaneous locomotion" preparation. Neuronal activity was studied in relation to the onset, alternation and termination of cyclic hindlimb neurographic activity in the precollicular-postmammillary transected animal. Histochemical identification of pedunculopontine (nicotinamide adenine dinuceotide phosphate-diaphorase positive) neurons allowed the localization of recording sites in relation to this nucleus. Neurons located in the area of the cuneiform nucleus dorsal to the pedunculopontine nucleus were found to be related preferentially to cyclic (bursting) neurographic activity, while neurons in the area of the pedunculopontine were found to be related preferentially to the onset ("on") or termination ("off") of cycling episodes. Different populations of cells in the area appeared to be related to the frequency of alternation (bursting) compared with the duration of the cyclic episodes (on/off). While the area of the cuneiform-pedunculopontine nucleus has been found to be equivalent to the mesencephalic locomotor region, the same area has been found to be related to other rhythmic activities (e.g. respiratory, masticatory, sleep cycle, pressor, vesico-motor, etc.). A hypothesis is proposed to account for the weight of evidence implicating the same region in a host of distinct rhythmic activities. This hypothesis suggest that an oscillatory reverberation between cholinergic (pedunculopontine, laterodorsal tegmental nuclei) and aminergic (locus coeruleus, substantia nigra) centers is responsible for generating the various function-related "frequencies" (bursting) or "states" (on/off) of activity.

Comparison of response properties of dorsal and ventral spinocerebellar tract neurons to a physiological stimulus

The response characteristics of dorsal spinocerebellar tract (DSCT) neurons and ventral spinocerebellar tract (VSCT) neurons to the cutaneous inputs applied to footpads were studied in the cat. Three different wave forms were used: step displacement of varying amplitudes (0.1-3.5 mm); constant amplitude ramps with different slopes (5-120 mm/s); and constant amplitude sinusoidal displacements of varying frequencies (1-20 Hz). Both DSCT and VSCT neurons responded phasically to cutaneous stimuli of different wave forms. The phasic responses were related to both the amplitude and velocity of the peripheral stimulus. However, the responses of DSCT neurons were graded over only a very narrow, low range of stimulus intensities, whereas the responses of VSCT neurons were graded over a larger range of skin indentation up to 3 mm. Only the DSCT neurons exhibited some length sensitivity to ramp stimuli, and only DSCT neurons were activated repetitively by periodic stimuli. These results suggest both DSCT and VSCT can transmit exteroceptive information but respond selectively to different features of these stimuli.

Quantitative ultrastructural stereology of synapses in nucleus dorsalis after a peripheral nerve injury at birth

Utilizing recent techniques in quantitative stereology, this investigation studied the synaptology of nucleus dorsalis (Clarke's column) in 12-week-old rats whose sciatic nerves were crushed in the 1st postnatal day. Four morphometric variables were analyzed at the levels of L1 and L3 spinal cord segments: total surface area of synaptic contact zones per unit volume (SV), total length of synaptic contact zones per unit area (LA), average length of synaptic membrane (L), and numerical density of synapses per unit volume (NV). The original raw data were corrected for Holmes's effect. The results indicated that peripheral nerve crush at birth induced a transganglionic change in central sensory terminals with a loss of numerous synapses. A significant loss (P less than 0.001) of about 32% in the SV and LA and a significant loss (P less than 0.001) of about 36% in the NV were observed on the experimental side. There was no preferential loss of synapses in either segment. The mean synaptic membrane length showed no significant difference between the control and experimental sides. The control values of the four morphometric variables calculated for L3 were lower than those calculated for L1. The loss of synapses after a peripheral nerve lesion was probably due to the loss of sensory neurons and their central processes, but there were other possibilities.

Time course of mossy fiber degeneration following pontine ablation in the rat

The normal ultrastructure of mossy fiber terminals within the ansiform lobule of the rat was investigated in parasagittal sections of the cerebellar cortex. Four types of mossy fiber varicosities (simple and complex dispersed, simple and complex clustered) were distinguished on the basis of the presence or absence of clublike excrescences and the concentration of synaptic vesicles within the cortical zone of the terminal. Removal of the pontocerebellar input to the contralateral cerebellar hemisphere was performed electrolytically. Such lesions, when placed in the basilar pontine gray using a dorsal approach, resulted in the degeneration of nearly the entire population of mossy fiber varicosities within the contralateral ansiform lobule. As early as 3 days following pontine ablation, degenerative changes were observed within the synaptic portions of the mossy fibers. Two distinct axonal reactions were apparent within this population of degenerating varicosities. A small population of mossy fiber varicosities (12%) of the simple clustered variety underwent a rapid course of electron-dense degeneration, which was complete by the fifth day. These mossy fiber varicosities were very susceptible to phagocytosis by reactive glial elements. The second group which consisted of simple (60%) and complex (26%) varieties of dispersed terminals, underwent a very slow course of electron-dense degeneration. Reactive glial cells were rarely found in association with this second group of degenerating varicosities. As a result, most glomeruli were found to contain debris from degenerating mossy fiber varicosities throughout the first 57 days following pontine lesions. The majority of the cerebellar glomeruli, however, were denervated by 80 days.

Effect of stimulus intensity on subcortical and cortical somatosensory evoked potentials by posterior tibial nerve stimulation

The effects of stimulus intensity on subcortical and cortical somatosensory evoked potentials (SEPs) to posterior tibial nerve (PTN) stimulation were studied in 16 normal controls. Stimulus intensity was evaluated as a function of sensory threshold (S). Motor threshold (M) varied between 1 S and 2 S. The amplitude of N18 (afferent volley immediately before it enters the spinal canal) increased approximately linearly up to at least 4.5 S. N20 (dorsal cord potential) also demonstrated a linear increase up to at least 4 S but the rate of increase was significantly smaller. All central components (subcortical brain-stem components P27 and N30, and cortical components N1 and P2) showed an even smaller rate of increase which was non-linear and reached a plateau at 3 S. The relatively higher rate of increase of N18 as compared with N20 was most probably due to the recording of sensory impulses plus antidromic impulses in motor fibers. The smaller rate of increase and early saturation of all the central components compared with N20 suggests that of all the afferent fibers generating N20 only the low threshold fibers participate in the generation of more central components. Stimulus intensities of 3 S are recommended for clinical studies of the central SEPs to PTN stimulation.

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

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

The splenius capitis muscle of the rat, architecture and histochemistry, afferent and efferent innervation as compared with that of the quadriceps muscle

The splenius muscle of the rat was investigated with regard to its structure and innervation. The latter was compared with that of the quadriceps muscle. The results can be summarized as follows: The splenius muscles of both sides form a bipennate muscle plate connecting the occipital bone with the spinous process of the second thoracic vertebra. The lateral parts of both muscles are attached directly to this prominent bony process, whereas the medial parts end in a median raphe which forms a tendinous cranial extension of the second thoracic vertebra. This tendinous extension, showing no connection to the cervical vertebrae, serves also for the attachment of acromio-trapezius muscle fibers. The lateral part of the splenius muscle is divided into two parts by a tendinous intersection. The splenius muscle consists mainly of fast twitch fibers: 55% were characterized as IIB and 40% as IIA fibers by histochemical demonstration of myosin ATPase-activity. A high content of muscle spindles--57 spindles per gram of muscle tissue--was found. Comparing several aspects of the innervation of the splenius to that of the quadriceps muscle, the following results could be obtained: The ratio of motor end plate size to muscle fiber volume is significantly higher in the splenius than in the quadriceps muscle. As demonstrated by transganglionary HRP-transport, the main part of labeled splenius afferents to the spinal cord terminates in the central cervical nucleus. Quadriceps afferents, entering the lower thoracic and upper lumbar segments, mainly end in the area of Clarke's column. Several labeled fibers descend to the sixth lumbar and first sacral segments, where they terminate in the area of Stilling's nucleus. A group of primary afferents from both muscles--most probably III- and IV-afferents--projects to the dorsal laminae of the dorsal horn; terminals from the splenius are accumulated in the lateral parts of these laminae, whereas those of the quadriceps are more concentrated in the medial areas. Within the brain stem, most afferents from the splenius terminate in the external cuneate nucleus. Most of the quadriceps afferents course to the gracile nucleus. Terminals from both muscle nerves were found in the area of the spinal vestibular nucleus. In conclusion, the most conspicuous results were: 1) Besides the segmental projection to the dorsal horn there is an almost exclusive projection of splenius primary afferents to relay nuclei to the cerebellum. 2) The relatively high ratio: end plate size/muscle fiber volume, which is characteristic of finely adjusting muscles.(ABSTRACT TRUNCATED AT 400 WORDS)

Activity of cerebellar Purkinje cells during fictitious scratch reflex in the cat

The activity of Purkinje cells (PCs) was recorded in the anterior lobe (the vermis and pars intermedia) and in the paramedian lobule of the cerebellum during the fictitious scratch reflex in thalamic cats immobilized with Flaxedil. In the anterior lobe, the activity of many PCs was rhythmically modulated in relation to the scratch cycle: they generated bursts of impulses separated by periods of silence. Different PCs were active in different phases of the scratch cycle. In many cases the discharge modulation was irregular: the burst duration and the discharge rate in the burst varied considerably in subsequent cycles. The rhythmical activity of PCs was determined by modulation of the frequency of 'simple spikes' reflecting the mossy fiber input. Generation of 'complex spikes' reflecting the climbing fiber input in most PCs was not related with the scratch rhythm. In the paramedian lobule, rhythmical modulation of PCs was practically absent. Rhythmical modulation of PCs in immobilized cats is determined by signals coming from the central spinal mechanism of scratching via the ventral spinocerebellar tract (VSCT) and the spinoreticulocerebellar pathway (SRCP). Results of separate transections of these pathways demonstrated that the VSCT plays the crucial role in modulating the PCs.

Vestibular nerve input to neck and shoulder regions of lateral cuneate nucleus

Axonal transport of tritiated leucine by the vestibular nerve was observed in regions of the ipsilateral lateral cuneate nucleus (LCN) that were determined electrophysiologically to receive somatosensory input from the neck and shoulder and to respond to electrical stimulation of the vestibular nerve. Regions of the LCN receiving input from more distal musculature did not receive vestibular input.

Cross-correlation analysis of the response of units in the dorsal spinocerebellar tract (DSCT) to muscle stretch and contraction

Activity of DSCT units was cross-correlated with stimuli evoking gastrocnemius-soleus muscle stretch or contraction in order to investigate the muscle receptor input to DSCT. The most potent stimulus was generally muscle contraction, and the most common response one of inhibition. The similarity in response of many units to stretch, contraction and nerve simulation suggests that Golgi tendon organs are prominent source of input to DSCT, and that much of this input is inhibitory.

Afferent projections of the rat major occipital nerve studied by transganglionic transport of HRP

The central projection fields of cutaneous neurons of the rat's major occipital nerve have been investigated using the method of transganglionic transport of horseradish peroxidase (HRP), with tetramethylbenzidine according to Mesulam (1978) as the chromogen. Furthermore, the course of the nerve, diameter distribution of myelinated axons, and diameter distribution of HRP-labeled perikarya of spinal ganglion cells belonging to this nerve, diameter distribution of myelinated axons, and diameter distribution of HRP-labeled perikarya of spinal ganglion cells belonging to this nerve have been studied. Following HRP application to the proximal stump of the cut nerve, labeled structures were found ipsilaterally in the cervical spinal cord and in the medulla oblongata. In the spinal cord, reaction product was mainly concentrated in the lateral parts of laminae I-III of the dorsal horn in segments C2 and C3. In C1, primary afferent terminals were more sparsely distributed and restricted to laminae I and II. Reaction product was also seen in the tract of Lissauer in segments C1-C4. In the medulla oblongata HRP labeled structures were observed in the medial cuneate nucleus, in the rostral part of the external cuneate nucleus, and in the nucleus of the spinal tract of the trigeminal nerve. A possible somatotopic arrangement of central terminals of cutaneous neurons within the cervical dorsal horn, as well as differences between the projection fields of muscle and skin afferents within the upper cervical cord and caudal medulla are discussed.

Afferent projections from the rat longus capitis muscle studied by transganglionic transport of HRP

Using the method of transganglionic transport of horseradish peroxidase (HRP) according to Mesulam (1978), the course and central terminations of the afferents from the longus capitis muscle were studied in the rat. Application of HRP to the cut muscle nerves was followed by heavy labeling of a considerable number of cell bodies of different sizes in the spinal ganglia C2 and C3. The labeled central processes follow two distinct main routes: one to the external cuneate nucleus, which is known to project ipsilaterally to the cerebellum, the other to the central cervical nucleus (CCN) of the spinal cord. The latter nucleus contains dense arborizations and terminals of muscle afferents in close relationship to medium sized cells which project contralaterally to the cerebellum. This could be shown in double labeling experiments with HRP as a tracer for primary afferents and Nuclear yellow for the cerebellar pathway. The labeled area of CCN extends from the fourth cervical segment up to the medulla oblongata where it lies laterally adjacent to the hypoglossal nucleus, though clearly separated from the latter. In the cervical part of CCN, dendrites of neck muscle motoneurons arborize within the area of afferent terminals. Besides the external cuneate and the central cervical nuclei, afferent projections were seen in lamina X, partly in close contact with the central canal, and in more lateral areas of lamina VII. In contrast to results from studies on other neck muscles, no reaction product was observed in dorsal horn laminae I-VI.

The silent period in the stretch response of Ia-activated dorsal spino-cerebellar tract neurons to sinusoidal muscle stretch in cats

By means of extracellular recordings of action potentials the stretch responses of single neurons of Clarke's column were analysed. The neurons were monosynaptically activated from Ia afferents of both ipsilateral gastrocnemius muscles. When stretch cycles of more than 0.2 mm amplitude and frequencies above 2 Hz were applied to the gastrocnemius muscles, the discharging was found to cease during the period of stretch release, whereas the average discharge rate was found to increase. In the frequency range between 0.1 and 10 Hz a sinewave of stretch frequency - the response sinewave - fitted to the non-zero bins of cycle histograms described the stretch response at small and large amplitudes equally well. The amount of increase in the average firing rate corresponded quite well to the portion of the response sinewave below the zero discharge rate. This indicates that the occurrance of discharge pauses and the relation of the average discharge rate to frequency and amplitude of stretch can be described successfully by a half-wave rectification of the response at zero discharge rate. If one regards the shape of cycle histograms to be a nearly sinusoidal modulation plus a non-linear clipping at zero the application of linear systems analysis is worthwhile in describing the response not only at very small amplitudes but in the whole range of muscle stretch.

Convergence of muscle spindle afferents on single neurons of the cat dorsal spino-cerebellar tract and their synaptic efficacy

By means of tungsten microelectrodes, action potentials from axons within the dorsal spino-cerebellar tract (DSCT) and from muscle spindle afferents were recorded. A quantitative study was performed in monomuscular DSCT neurons which were excited predominantly by Ia fibers originating in the gastrocnemius muscles. In some experiments single Ia fibers were stimulated electrically while the impulse sequence of a DSCT neuron postsynaptic to the respective afferent fiber was recorded. The gastrocnemius DSCT neurons receive excitatory inputs from 10-18 Ia muscle spindle afferents. The efficacy of each of these inputs is very similar. Thus the neuronal activation decreased approximately linearly with the number of the excitatory afferents cut. Cross-correlograms between the impulse sequence of a Ia gastrocnemius muscle spindle afferent and a DSCT neuron postsynaptic to it exhibited an increased discharge probability of the DSCT neuron from 3-4 ms to 10 ms after the Ia action potential. With increasing impulse rates of the Ia afferent fibers, the excitatory efficacy of the single action potential decreased, but the overall excitation increased with the presynaptic discharge frequency, according to a hyperbolic function. This effect was tested by electrical stimulation of a single Ia axon exciting the DSCT neuron recorded. Interval histograms computed from DSCT neuron impulse trains at steady stretch conditions were predominantly monomodal. They can be well approximated by a Gaussian distribution. The coefficient of variation was independent of the mean activity. At impulse rates above 25 imp X s-1 a negative correlation between successive intervals was observed in first order joint interval diagrams. With an increasing mean discharge rate this correlation (expressed as the serial linear correlation coefficient of the first order r1,2) became stronger up to--0.62 at 90 imp X s-1. Only in a few neurons did the higher order linear correlation coefficients deviate significantly from zero. In 15% of the observed histograms double discharging (mean interval 3-5 ms) produced bimodal distributions. Under steady-state conditions the response of Ia-activated DSCT cells are linearly related to muscle stretch within a middle range of extensions. The differences between Ia impulse pattern and DSCT neuron impulse pattern at steady stretch are discussed. The number of large dendrites of the principal cells in the nucleus dorsalis (Clarke's column) corresponds to the number of excitatory afferent muscle fibers. It is assumed that each excitatory Ia axon sends one axon collateral to the DSCT neuron, forming a climbing type terminal mainly on one of the large dendrites of a DSCT cell.