Diffusion tensor tractography for the dorsal spinocerebellar tract in the human brain.

Using diffusion tensor tractography, we attempted to investigate and identify the anatomy of the dorsal spinocerebellar tract (SCT) in the human brain. We recruited 26 healthy volunteers. The dorsal SCT was determined by selection of fibers passing through three regions of interest. We found that all dorsal SCTs terminated in the ipsilateral cerebellum; in contrast, in 25 (48%) of 52 hemispheres, the dorsal SCT crossed into the contralateral hemisphere via the vermis of the anterior lobe.

Three-dimensional microsurgical anatomy of cerebellar peduncles.

The microsurgical anatomy of cerebellar peduncles and their relationships with neighbouring fasciculi were investigated by using a fibre dissection technique. As the dissection progressed, photographs of each progressive layer were obtained and stereoscopic images were created using the 3D anaglyphic method. These findings provided the anatomical basis for a conceptual division of cerebellar peduncles into segments. The middle cerebellar peduncle (MCP) was divided into two segments: cisternal and intracerebellar segments. The inferior cerebellar peduncle (ICP) was divided into three segments: cisternal, ventricular and intracerebellar segments. The superior cerebellar peduncle (SCP) was divided into three segments: intracerebellar, intermediate and intrategmental segments. The fibre dissection technique disclosed a constant course of peduncular fibres inside the white core of the cerebellum. The pontocerebellar fibres of the MCP pass over and laterally to the bundles of the ICP and SCP. The centripetal fibres of the ICP wrap around the radiation of the SCP and the dentate nucleus, directed towards the cortex of the vermis. The centrifugal bundle of the SCP ascends towards the mesencephalon where it sinks passing below the fibres the lateral lemniscus. The knowledge gained by studying the intrinsic anatomy of the cerebellum is useful to accomplish appropriate surgical planning and, ultimately, to understand the repercussions of surgical procedures on the white matter tracts in this region.

Laterality of spinocerebellar neurons in the chicken spinal cord.

The aim in this study is to elucidate the laterality of chicken spinocerebellar (SC) neurons that originate from the caudal cervical to caudal lumbosacral spinal cord. SC neurons in the spinal segment (SS) 17-20 consisted of a mixture of crossed and uncrossed axons. SC neurons in the more cranial and caudal SS than SS 17-20 (transitional zone) were generally uncrossed and crossed, respectively. In the transitional zone, SC neurons in spinal border cells and ventral border cells of the ventral horn changed dramatically from an uncrossed to a crossed type between SS 17 and SS 18. Chicken SC neurons are markedly different in laterality from mammalian SC neurons.

Fluorescence mapping of afferent topography in three dimensions.

Neural circuits are organized into complex topographic maps. Although several neuroanatomical and genetic tools are available for studying circuit architecture, a limited number of methods exist for reliably revealing the global patterning of multiple topographic projections. Here we used wheat germ agglutinin (WGA) conjugated to Alexa 555 and 488 for dual color fluorescent mapping of parasagittal spinocerebellar topography in three dimensions. Using tissue section and wholemount imaging we show that WGA-Alexa tracers have three main characteristics that make them ideal tools for analyses of neural projection topography. First, the intense brightness of Alexa fluorophores allows multi-color imaging of patterned afferent projections in wholemount preparations. Second, WGA-Alexa tracers robustly label the entire trajectory of developing and adult projections. Third, long tracts such as the adult spinocerebellar tract can be traced in less than 6 h. Moreover, using WGA-Alexa tracers we resolved a level of complexity in the compartmentalized topography of the spinocerebellar projection map that has never before been appreciated. In summary, we introduce versatile tracers for rapidly labeling multiple topographic projections in three dimensions and uncover wiring complexities in the spinocerebellar map.

Trajectories in the spinal cord and the mediolateral spread in the cerebellar cortex of spinocerebellar fibers from the unilateral lumbosacral enlargement in the chicken.

Spinocerebellar (SC) neurons in the lumbosacral enlargement (LSE) give rise mainly to crossed fibers and generally terminate in parasagittal bands in the granular layer of the chicken cerebellar cortex. However, parasagittal bands for mossy fiber terminals have not always been clear in some cerebellar folia. The present study aimed at (1) observing the course in the spinal cord of the spinocerebellar tracts (SCTs), (2) confirming whether SC fibers originating from the unilateral LSE terminate in parasagittal bands, and (3) elucidating the relationship between the ventral and lateral funicular parts of the SCTs in the cervical enlargement (CE) using anterograde and retrograde labeling methods. The SCTs were located in the medial part of the ventral funiculi in spinal segment (SS) 27, the full width of the ventral funiculi in SS 22, the lateral and ventral funiculi in SS 14 and in the lateral funiculi from SS 10 rostralward. Projection areas in the cerebellar cortex of SC fibers were studied following unilateral injections of WGA-HRP into the LSE. As a result, SC fibers from the LSE terminated bilaterally in parasagittal bands of folia II-VI and IXc. Labeled terminals in the injected side were similar in number to those in the other side in folia II-IV and IXc and more than those in the other side in folia V and VI. Following ablation of the left (contralateral) lateral funiculus of the CE, the same tracer was injected into the right (ipsilateral) LSE or into the anterior or posterior cerebellar lobe. As a result, anterogradely labeled SC fibers passing through the ventral funiculus in the CE mainly terminated in the contralateral cerebellar cortex in folia II, III and IV, and in the ipsilateral cerebellar cortex in folia V, VI and IX. Following ablation of the unilateral lateral funiculus, retrogradely labeled neurons in the contralateral LSE were found in all SC neuron groups showing marked reduction in number. Thus, the ventral and lateral funicular parts of the SCTs in the CE were not pathways for specific SC neuron groups but different in projection areas.

Spinocerebellar projections from the cervical and lumbosacral enlargements in the chicken spinal cord.

In birds, spinocerebellar (SC) projections to the cerebellar cortex have not been understood well. We examined SC fiber terminal fields originating from the cervical and lumbosacral enlargements (CE and LSE, respectively) in the chicken. SC fiber terminals show parasagittal bands in the granular layer. Labeled terminals from the CE were distributed primarily in folia II-V and IX. Parasagittal bands of labeled terminals from the CE were not clearly separated in folia II and III but were clearly separated in folia IV and V. In folium IX, labeled terminals were diffusely distributed in all subfolia with no evidence of banding. The numbers of bands were 5 in folium II, 12 in folium III and 7 in folia IV and V at maximum. Labeled terminals from the LSE were distributed primarily in folia II-VI and IX. Labeled terminals from the LSE were arranged in 4 bands in folium II and in 8 bands in folium III at maximum. Parasagittal bands from the LSE in folia IV and V were not clearly separated. In folium VI, the numbers of parasagittal bands was 6 at maximum. In folium IX, labeled terminals were mainly found in subfolium IXc forming 6-8 parasagittal bands. There were more parasagittal bands of labeled terminals from the CE than from the LSE. The topography of SC fiber terminals from the CE was different from that of SC fiber terminals from the LSE.

Evoked potentials elicited on the cerebellar cortex by electrical stimulation of the rat spinocerebellar tract.

BACKGROUND: In the current study, as a first step to develop a monitoring method of cerebellar functions, we tried to record evoked potentials on the cerebellar cortex by electrical stimulation of the rat SCT, which is located in the Inf-CPed. METHODS: The experimental study was performed on rats. Unilateral muscular contractions of quadriceps femoris muscle were elicited by electrical stimulation. The evoked potentials were recorded from the surface of the ipsilateral cerebellum and the contralateral primary sensory cortex. RESULTS: The highly reproducible potentials obtained from the ipsilateral cerebellar hemisphere were named SCEP. The SCEP exhibited one negative peak with a latency of 11.7 +/- 0.3 milliseconds (N(11)). Short-latency somatosensory evoked potential was recorded from the contralateral primary sensory cortex with a latency of 19.1 +/- 0.6 milliseconds. Coagulation of the ipsilateral Inf-CPed caused disappearance or marked reduction of the SCEP N(11), but it did not change the SSEP. On the other hand, sectioning of the ipsilateral dorsal column resulted in the disappearance of the SSEP, but it did not affect the SCEP N(11). CONCLUSIONS: Reproducible SCEP was recorded from the rat cerebellar hemisphere by electrical stimulation of the quadriceps femoris muscle. We posit that the SCEP differs from the SSEP, which ascends via the dorsal column, and that it is conducted by the dorsal SCT located in the Inf-CPed. Our results suggest that it may be possible to detect the dysfunction of the Inf-CPed electrophysiologically by using SCEP.

Anatomical and physiological foundations of cerebellar information processing.

A coordinated movement is easy to recognize, but we know little about how it is achieved. In search of the neural basis of coordination, we present a model of spinocerebellar interactions in which the structure-functional organizing principle is a division of the cerebellum into discrete microcomplexes. Each microcomplex is the recipient of a specific motor error signal - that is, a signal that conveys information about an inappropriate movement. These signals are encoded by spinal reflex circuits and conveyed to the cerebellar cortex through climbing fibre afferents. This organization reveals salient features of cerebellar information processing, but also highlights the importance of systems level analysis for a fuller understanding of the neural mechanisms that underlie behaviour.

Compartmentation of the reeler cerebellum: segregation and overlap of spinocerebellar and secondary vestibulocerebellar fibers and their target cells.

The cerebellum of the reeler mutant mouse has an abnormal organization; its single lobule is composed of a severely hypogranular cortex and a central cerebellar mass (CCM) consisting of Purkinje cell clusters intermixing with the cerebellar nuclei. As such the reeler represents an excellent model in which to examine the effect of the abnormal distribution of cerebellar cells on afferent-target relationships. To this effect we studied the organization of the spinocerebellar and secondary vestibulocerebellar afferent projections in homozygous reeler mice (rl/rl) using anterograde tracing techniques. Spinal cord injections resulted in labeled spinocerebellar mossy fiber rosettes in specific anterior and posterior regions of the cerebellar cortex. Some vestiges of parasagittal organization may be present in the anterior projection area. Within the CCM, labeled fibers appeared to terminate on distinct groups of Purkinje cells. Thus, the spinocerebellar mossy fibers seem to form both normal and heterologous synapses in the reeler cerebellum. Secondary vestibular injections resulted in both retrograde and anterograde labeling. Retrograde labeling was seen in clusters of Purkinje cells and cerebellar nuclear cells; anterograde labeling was distributed in the white matter and in specific regions of the anterior and posterior cortex of the cerebellum. The labeled spinocerebellar and secondary vestibulocerebellar afferents overlapped in the anterior region but in the posterior region the vestibulocerebellar termination area was ventral to the spinocerebellar area. An area devoid of labeled terminals was also observed ventral to the posterior secondary vestibulocerebellar termination field. Using calretinin immunostaining it was determined that this area contains unipolar brush cells, a cell type found primarily in the vestibulocerebellum of normal mice. Our data indicate that despite of the lack of known landmarks (fissures, lobules) the spinocerebellar and vestibulocerebellar afferent projections in the reeler cerebellum do not distribute randomly but have specific target regions, and the position of these regions, relative to each other, appears to be conserved. Two caveats to this were the finding of overlapping terminal fields of these afferents in the anterior region, and a posteroventral region that contains unipolar brush cells yet is devoid of secondary vestibulocerebellar afferents. The distribution of Purkinje cells and cerebellar nuclear cells is not random either; those that give rise to cerebellovestibular efferents form distinct groups within the central cerebellar mass.

State-related inhibition by GABA and glycine of transmission in Clarke's column.

During the state of active sleep (AS), Clarke's column dorsal spinocerebellar tract (DSCT) neurons undergo a marked reduction in their spontaneous and excitatory amino acid (EAA)-evoked responses. The present study was performed to examine the magnitude, consistency of AS-specific suppression, and potential role of classical inhibitory amino acids GABA and glycine (GLY) in mediating this phenomenon. AS-specific suppression of DSCT neurons, expressed as the reduction in mean spontaneous firing rate during AS versus the preceding episode of wakefulness, was compared across three consecutive sleep cycles (SC), each consisting of wakefulness (W), AS, and awakening from AS (RW). Spontaneous spike rate did not differ during W or RW between SC1, SC2, and SC3. AS-specific suppression of spontaneous firing rate was found to be consistent and measured 40.3, 31.5, and 41.6% in SC1, SC2, and SC3, respectively, indicating that such inhibition is marked and stable for pharmacological analyses. Microiontophoretic experiments were performed in which the magnitude of AS-specific suppression of spontaneous spike activity was measured over three consecutive SCs: SC1-control (no drug), SC2-test (drug), and SC3-recovery (no drug). The magnitude of AS-specific suppression during SC2-test measured only 11.7 or 14.6% in the presence of GABA(A) antagonist bicuculline (BIC) or GLY antagonist strychnine (STY), respectively. Coadministration of BIC and STY abolished AS-specific suppression. AS-specific suppression of EAA-evoked DSCT spike activity was also abolished in SC2-test after BIC or STY, respectively. We conclude that GABA and GLY mediate behavioral state-specific inhibition of ascending sensory transmission via Clarke's column DSCT neurons.

Laterality of the spinocerebellar axons and location of cells projecting to anterior or posterior cerebellum in the chicken spinal cord.

In the cervical and lumbosacral enlargements of the chicken, there are seven spinocerebellar nuclei, the Clarke's column, the spinal border cells, the ventral margin of the ventral horn of both enlargements, and the ventral marginal nucleus in the lumbosacral enlargement. In the present study, we investigated the laterality of spinocerebellar tract axons and the distribution of the spinocerebellar tract neurons projecting into the anterior or posterior part of the cerebellum in these seven nuclei by retrograde transport of wheat germ agglutinin-horseradish peroxidase. The spinocerebellar tract neurons with uncrossed axons were found in the cervical Clarke's column and the cervical spinal border cells, and with crossed ones in the lumbar Clarke's column, lumbar spinal border cells, lumbar lamina IX included in the ventral margin of the ventral horn of the lumbosacral enlargement, and the ventral marginal nucleus. The ventral margin of the ventral horn of the cervical enlargement and lumbar lamina VIII included in the ventral margin of the ventral horn of the lumbosacral enlargement issued spinocerebellar tract axons bilaterally. The spinocerebellar tract neurons of the lumbar spinal border cells and lumbar lamina IX projected to the anterior part of the cerebellum only. And those of the other nuclei projected to both the anterior and posterior parts.

Ascending spinal systems in the fish, Prionotus carolinus.

The fin rays of the pectoral fin of the sea robins (teleostei) are specialized chemosensory organs heavily invested with solitary chemoreceptor cells innervated only by spinal nerves. The rostral spinal cord of these animals is marked by accessory spinal lobes which are unique enlargements of the dorsal horn of the rostral spinal segments receiving input from the fin ray nerves. Horseradish peroxidase (HRP) and 1,1;-dioctadecyl-3,3,3', 3'-tetramethylindocarbocyanine perchlorate (diI) were used as anterograde and retrograde tracers to examine the connectivity of these accessory lobes and the associated ascending spinal systems in the sea robin, Prionotus carolinus. The majority of dorsal root fibers terminate within the accessory lobes at or nearby their level of entrance into the spinal cord. A few dorsal root axons turn rostrally in the dorsolateral fasciculus to terminate in the lateral funicular complex situated at the spinomedullary junction. The lateral funicular complex also receives a heavy projection from the ipsilateral accessory lobes. In addition, it contains a few large neurons that project back onto the accessory lobes. Injections of either diI or HRP into the lateral funicular complex label fibers of the medial lemniscus which crosses the midline in the caudal medulla to ascend along the ventral margin of the contralateral rhombencephalon. Within the medulla, fibers leave the medial lemniscus to terminate in the inferior olive and in the ventrolateral medullary reticular formation. Upon reaching the midbrain, the medial lemniscus turns dorsally to terminate heavily in a lateral division of the torus semicircularis, in the ventral optic tectum, and in the lateral subnucleus of the nuc. preglomerulosus of the thalamus. Lesser projections also reach the posterior periventricular portion of the posterior tubercle with a few fibers terminating along the ventral, posterior margin of the ventromedial (VM) nucleus of the thalamus. The restricted projection to the ventral tectum is noteworthy in that this part of the tectum maintains the representation of the ventral visual field, that is, the area in which the fin rays lie. A prominent spinocerebellar system is also evident. Both direct and indirect spinocerebellar fibers can be followed through the dorsolateral fasciculus, with or without relay in the lateral funicular nucleus and terminating in a restricted portion of the granule cell layer of the ipsilateral corpus cerebelli. The similarities in connectivity of the spinal cord between the sea robins and other vertebrates are striking. It is especially notable because sea robins utilize the chemosensory input from the fin rays to localize food in the environment. Thus, although these fish use their spinal chemosense as other fishes use their external taste systems, the spinal chemosense apparently relies on the medial lemniscal system to guide this chemically driven feeding behavior.