Electrophysiological studies of the projections from the parietal association area to the cerebellar cortex

1. Responses evoked in the cerebellar cortex by stimulation of the parietal association cortex (rostral portions of the middle suprasylvian gyrus) were recorded and analysed in cats, and were compared with those by stimulation of the motor cortex (anterior sigmoid gyrus). 2. The parietal stimulation elicited early mossy fibre and late climbing fibre responses in the cerebellar cortex. The mossy fibre responses appeared at a latency of 2.0--2.5 msec and predominantly in the lateral (hemispherical) part of the contralateral cerebellum (mainly crus I, crus II and paramedian lobules). Cutting of the inferior cerebellar peduncle produced little or no influence upon the mossy fibre responses, which suggests that the mossy fibre responses are mediated chiefly by the pontine nuclei. 3. The climbing fibre responses were recorded at a latency of 17--19 msec and markedly in the contralateral intermediate and medial parts of IV--VI lobules. The responses were easily sppressed by anaesthesia and depended on the conditions of experimental animals. The unstable appearance of the responses and their longer latencies than those of the climbing fibre responses due to stimulation of the motor cortex imply indirect pathways from the parietal association cortex to the inferior olive. 4. The predominant projection of the parietal-induced mossy fibre responses to the lateral part of the cerebellum was compared with the mossy fibre projection from the motor cortex and was discussed as an important component in the cerebrocerebellar loops.     

The olivo-cerebellar system: Functional properties as revealed by harmaline-induced tremor

Summary Intracellular recording from Purkinje cells in cat cerebellar cortex demonstrated an 8–10/sec burst activity following intravenous administration of harmaline (10 mg/kg), a drug known to produce tremor at the same frequency. The burst activation of Purkinje cells was generated by large all-or-none depolarizations similar to climbing fiber (CF) excitatory postsynaptic potentials (EPSPs). Polarization of the cell membrane through the recording electrode (via a Wheatstone bridge) revealed that the all-or-none depolarization had an equilibrium potential and time course identical to the electrically evoked CF-EPSP, demonstrating directly that tremor is associated with specific activation of the CF afferent system.Interspike frequency histograms of the burst responses of Purkinje cells show that the rhythmic CF activity may continue for several hours with approximately 10% frequency scatter, the actual frequency depending on the level of anesthesia. Simultaneous extracellular recordings from Purkinje cells near the midline vermis indicated that CFs projecting to this area fire in a synchronous manner, while simultaneous recording from three Purkinje cells at different lateralities from the midline showed that the rhythmic activity is reduced in the lateral vermis and may be absent in the cerebellar hemispheres.Intra- and extracellular recordings from cerebellar nuclear cells (fastigial) disclosed a bursting type of activation following harmaline; a similar type of activity could be recorded in the reticular formation neurons and at inferior olive level. At spinal cord level, harmaline induced a repetitive and rhythmic activation of motoneurons which was not modified by dorsal root section. Cooling of the cerebellar cortex produced a definite desynchronization of the rhythmic motoneuronal firing. However, the basic 10/sec firing of the spinal cord motoneurons could still be observed. Following lesion of the inferior peduncles which interrupted the olivo-cerebellar pathway, the rhythmic activation of Purkinje cells, nuclear cells, vestibular and reticular cells and motoneurons disappeared. However, the rhythmic activity was maintained at inferior olivary level. It is suggested that harmaline acts directly on the inferior olive since in animals with low decerebration, cerebellectomy and spinal transection, rhythmic activity of the inferior olive could still be observed.The results of these experiments strongly suggest that the inferior olive is able to generate the activation of motoneurons and that such influence can only take place through the activation of the cerebellar nuclei. Possible functions of the inferior olive as a generator of fast muscular transients are discussed.     

Origin of the climbing fibers activated by glossopharyngeal nerve stimulation in the frog

The origin of climbing fibers activated by electrical stimulation of the frog's glossopharyngeal (IXth) nerve was investigated using histological and electrophysiological technique. At the molecular layer near the Purkinje cell layer, where the maximum negative cerebellar field potential could be recorded following electrical stimulation of the IXth nerve, horseradish peroxidase (HRP) was iontophoretically injected through the tip of the recording micropipette. The HRP labeled cells were seen in the contralateral inferior olive (IO). In some cases, a small number of HRP-labeled cells were seen in the ipsilateral IO. Labeled cells were not found in the other areas of the brain stem. After electrolytic lesion of the contralateral IO, the negative cerebellar field potential which would be recorded in the molecular layer following electrical stimulation of the IXth nerve had almost ceased. These results demonstrate that the climbing fibers activated by the IXth nerve stimulation have their origin in the contralateral IO.     

Topographical organization of climbing fiber pathway from the superior colliculus to cerebellar vermal lobules VI-VII in the cat.

Topographical distribution of the climbing fiber responses induced by stimulation of the superior colliculus was investigated in the cerebellar posterior vermis (lobules VI-VII) of the cat. The climbing fiber-responsive areas were distributed longitudinally forming sagittal zones. The sagittal zones responsive to stimulation of the left and right superior colliculus were located on the side ipsilateral to the stimulation, and they were completely segregated. The sagittal zones responsive to stimulation of the caudal superior colliculus were distributed more laterally than those responsive to stimulation of the rostral superior colliculus. Study of the extracellular unit in the inferior olive demonstrated that the climbing fiber responses were relayed in the caudomedial part of the medial accessory olive contralateral to the stimulation.     

On the origin of the climbing fibers of the cerebellum. An experimental study in the cat with an autoradiographic tracing method

An autoradiographic fiber tracing method was used to determine the contribution of climbing fibers to the cerebellar cortex from the olive and other brainstem precerebellar structures. The morphological characteristics of silver grain accumulations and their location in the molecular or granular layer made it possible to distinguish clearly between climbing fibers and mossy fibers. Three injections of l-leucine were made in the olive to obtain extensive labeling. The projection thus demonstrated is completely crossed and covers large portions of all cerebellar lobules. The course of olivocerebellar fibers was described and it was stressed that some of these fibers make a long rostral loop close to the superior and middle cerebellar peduncles. Injections in the pons, including the nucleus reticularis tegmenti pontis, the lateral reticular nucleus, the spinal nucleus of the fifth nerve, the cuneate and external cuneate nuclei, the descending vestibular nucleus and the nucleus reticularis ventralis, labeled only mossy fibers.It is concluded that, in the cat, the large majority and probably all the climbing fibers originate from the inferior olive. Evidence suggesting that the inferior olive sends a collateral projection to the nucleus reticularis tegmenti pontis was also obtained.     

Regional cerebellar choline acetyltransferase activity following peduncular lesions

Summary The activity of choline acetyltransferase (ChAT) in the cerebellar lobules of the rat was determined after bilateral destruction of either the superior, middle, or inferior cerebellar peduncles. A significant, 40–60% decrease in ChAT activity occurred in all subdivisions of the cerebellum (anterior lobe, posterior lobe hemisphere, posterior lobe vermis/nodulus and flocculus/paraflocculus) following bilateral inferior peduncle lesions. In contrast, bilateral lesions of the superior or middle peduncles did not result in significant reductions of enzyme activity. These findings indicate that the cholinergic afferents to the cerebellum are contained predominantly in the inferior peduncle, from which they emerge to innervate all of the gross subdivisions of the cerebellum.Supported by NINCDS post doctoral fellowship No. 1F32NS06399-02     

Latencies of climbing fiber inputs to turtle cerebellar cortex

Responses of separate regions of rat cerebellar cortex (Cb) to inferior olive (IO) stimulation occur with the same latency despite large differences in climbing fiber (CF) lengths. Here, the olivocerebellar path of turtle was studied because its Cb is an unfoliated sheet on which measurements of latency and CF length can be made directly across its entire surface in vitro. During extracellular DC recordings at a given Cb position below the molecular layer, IO stimulation evoked a large negative field potential with a half-width duration of approximately 6.5 ms. On this response were smaller oscillations similar to complex spikes. The stimulating electrode was moved to map the IO and the CF path from the brain stem to the Cb. The contralateral brain stem region that evoked these responses was tightly circumscribed within the medulla, lateral and deep to the obex. This response remained when the brain stem was bathed in solutions that blocked synaptic transmission. The Cb response to IO stimulation had a peak latency of approximately 10 ms that was not dependent on the position of the recording electrode across the entire 8-mm rostrocaudal length of the Cb. However, for a constant Cb recording position, moving the stimulation across the midline to the ipsilateral brain stem and along the lateral wall of the fourth ventricle toward the peduncle did shorten the response latency. Therefore a synchronous Cb response to CF stimulation seems to be caused by changes in its conduction velocity within the entire cerebellar cortex but not within the brain stem.     

Non-uniform olivocerebellar conduction time in the vermis of the rat cerebellum

It has been proposed that the conduction velocities of cerebellar climbing fibre (olivocerebellar) axons are tuned according to length, in order to precisely fix the conduction time between the inferior olive and cerebellar cortex. Some data conflict with this view. We have re-evaluated this issue using the climbing fibre reflex. The white matter of the tip of one folium in lobule VI or VII was stimulated electrically 0.5–1 mm below the surface and recordings were made from Purkinje cells in lobules VIII and IX. Reflex evoked climbing fibre (CF) responses (33 units) were recorded at different depths from Purkinje cells found in a narrow sagittal zone of cortex as complex spikes. The responses had latencies ranging from 4.3 ms to 11.3 ms. A consistent trend was that Purkinje cell responses recorded at greater depth had shorter CF reflex latencies than those recorded more superficially, both in individual experiments and in grouped data. These data show that the CF reflex latency is not constant, but is directly proportional to the distance an action potential has to travel along a CF. These data are not consistent with tuning of CF conduction velocities to normalize olivocerebellar conduction time, but are consistent with a CF conduction velocity in the cortex of approximately 0.6 m s⁻¹. This suggests that climbing fibres projecting to different parts of the cerebellar cortex may have differences in spike conduction time of a few milliseconds, and that submillisecond precision is not an important element of the climbing fibre signal.     

Responses of a spino-olivo-cerebellar pathway in the cat

1. Surface potentials, similar to those found by earlier workers, have been recorded from the vermis of the anterior lobe of the cerebellum following stimulation of muscular, cutaneous and articular nerves of the ipsilateral hind limb. The most conspicuous component of the response consisted of a positive potential succeeded by a smaller negative potential.

2. Micro-electrode recordings showed that this component coincided both with climbing fibre responses in individual Purkinje cells, and with extracellular field potentials within the cerebellar cortex which closely resembled those found by Eccles, Llinás & Sasaki (1966) following electrical stimulation of the inferior olive.

3. Stimulation of the cerebellar surface, in the region where the responses to limb nerve stimulation were largest, led to antidromic invasion of neurones of the contralateral inferior olive. The antidromic action potentials were sometimes followed by up to three orthodromic spikes. Histological techniques were used to show that these neurones were located in the caudal parts of the dorsal and medial accessory olives.

4. Stimulation of nerves of the hind limb evoked discharges of the same neurones of the dorsal accessory olive which were antidromically invaded from the vermis of the anterior lobe. The nerves used (quadriceps, gastrocnemius-soleus, sural and the posterior nerve to the knee joint) were shown to excite heavily overlapping populations of neurones.

5. Those neurones of the medial accessory olive, which were identified antidromically from the anterior lobe vermis, were not discharged by stimulation of hind limb nerves.

6. Simultaneous recording from the surface of the anterior lobe and from the dorsal accessory olive showed that the onset of olive cell discharges occurred about 5 msec before the onset of the positive potential at the cerebellar surface.

     

Inhibition of inferior olivary transmission by mesencephalic stimulation in the cat

Cerebellar climbing fiber responses (CFRs) evoked in anesthetized cats by stimulation of peripheral nerves, contralateral inferior olive and cerebellar white matter were investigated by recording unit activity and surface field responses in anterior lobe of cerebellar cortex. When nerve and olive stimulation was preceded at long intervals (greater than 35 ms) by weak electrical stimulation of an ipsilateral mesencephalic area close to the locus coeruleus and brachium conjunctivum, CFRs could be virtually abolished in the pars intermedia but not in the vermis. White-matter evoked CFRs were not affected; thus the site of the inhibition was the inferior olive.     

The organization of the corticonuclear and olivocerebellar climbing fiber projections to the rat cerebellar vermis: the congruence of projection zones and the zebrin pattern

The zonal organization of the corticonuclear and the olivocerebellar climbing fiber projections to the vermis of the cerebellum of the rat was compared to the pattern of zebrin-positive and zebrin-negative bands in material double-stained for zebrin II and for different anterograde tracers injected in subnuclei of the inferior olive, or retrograde tracers injected in the cerebellar and vestibular target nuclei of the Purkinje cells of the vermis. Projection zones A(1), A(X), X, B, C(X) in the vermis and A(2) (accessory A zone) and C(2) in the hemisphere were defined by their efferent corticonuclear and their afferent climbing fiber connections, and were found to share the same topographical framework with the zebrin pattern.     

Purkinje cell functions in the in vitro cerebellum isolated from neonatal rats in a block with the pons and medulla

The cerebellum dissected from neonatal rats in a block including the pons and medulla and maintained in a modified Krebs solution provides a unique preparation of brain tissue with preserved major fiber connections. Electrophysiological and optical recordings revealed that, at postnatal days 4-8 (P4-P8), Purkinje cells in the lateral portion of the cerebellum responded to the stimulation of climbing fiber afferents at the inferior olive and of parallel fibers at the posterior vermis, and that the combination of these inputs induced long-term depression. These observations and pharmacological testings indicate that certain functional features of Purkinje cells mature around P5 in the lateral portion of the cerebellum.     

Motor coding in floccular climbing fibers

The climbing fibers (CFs) that project from the dorsal cap of the inferior olive (IO) to the flocculus of the cerebellar cortex have been reported to be purely sensory, encoding "retinal slip." However, a clear oculomotor projection from the nucleus prepositus hypoglossi (NPH) to the IO has been shown. We therefore studied the sensorimotor information that is present in the CF signal. We presented rabbits with visual motion noise stimuli to break up the tight relation between instantaneous retinal slip and eye movement. Strikingly, the information about the motor behavior in the CF signal more than doubled that of the sensory component and was time-locked more tightly. The contribution of oculomotor signals was independently confirmed by analysis of spontaneous eye movements in the absence of visual input. The motor component of the CF code is essential to distinguish unexpected slip from self-generated slip, which is a prerequisite for proper oculomotor learning.     

Collateral branches of cerebellopontine axons reach the thalamus, superior colliculus, or inferior olive: a double-fluorescence and combined fluorescence-horseradish peroxidase study in the rat

Retrograde double-labeling methods that used two different fluorescent dyes or a fluorescent dye in combination with wheat germ agglutinin horseradish peroxidase were used in the rat to study the collateralization of cerebellopontine fibers to the thalamus, the superior colliculus, or the inferior olive. In cases with combined basilar pontine nuclei and thalamus injections, double-labeled neurons were located in the rostral part of the lateral cerebellar nucleus as well as within the interpositus anterior and interpositus posterior nuclei. These cells are medium to large in size and multipolar-shaped. A much smaller number of double-labeled cells was observed in the combined basilar pontine nuclei and superior colliculus injections. In these cases most of the double-labeled cells were intermediate- to large-sized and either bipolar- or multipolar-shaped. Such neurons were distributed throughout the rostrocaudal extent of the lateral cerebellar nucleus, with only a few double-labeled cells located in the interpositus anterior and posterior nuclei. Finally, in the cases with combined basilar pontine nuclei and inferior olive injections, double-labeled cells were located in interpositus anterior and posterior nuclei and the medial portion of the lateral cerebellar nucleus. The double-labeled cells were relatively small in size and most were spindle-shaped. No double-labeled cells were observed in the medial cerebellar nucleus in any of the three injection combinations. Based upon the observation of double-labeled neurons in the deep cerebellar nuclei in each of the three injection combinations involving the basilar pontine nuclei, we conclude that cerebellar projections to the basilar pons arise in part as collaterals of axons that project to the thalamus, superior colliculus, or the inferior olive.     

The excitatory synaptic action of climbing fibres on the Purkinje cells of the cerebellum

1. A single climbing fibre makes an extraordinarily extensive synaptic contact with the dendrites of a Purkinje cell. Investigation of this synaptic mechanism in the cerebellum of the cat has been based on the discovery by Szentagothai & Rajkovits (1959) that the climbing fibres have their cells of origin in the contralateral inferior olive.2. Stimulation in the accessory olive selectively excites fibres that have a powerful synaptic excitatory action on Purkinje cells in the contralateral vermis, evoking a repetitive spike discharge of 5-7 msec duration. Almost invariably this response had an all-or-nothing character. In every respect it corresponds with the synaptic action that is to be expected from climbing fibres.3. Intracellular recording from Purkinje cells reveals that this climbing fibre stimulation evokes a large unitary depolarization with an initial spike and later partial spike responses superimposed on a sustained depolarization.4. Typical climbing fibre responses can be excited, but in a much less selective manner, by stimulation of the olive-cerebellar pathway in the region of the fastigial nucleus, there being often a preceding antidromic spike potential of the Purkinje cell under observation.5. Impaled Purkinje cells rapidly deteriorate with loss of all spike discharge, the climbing fibre response being then reduced to an excitatory post-synaptic potential. This potential shows that stimulation of the inferior olive may evoke two or more discharges at about 2 msec intervals in the same climbing fibre. The complexity of neuronal connexions in the inferior olive is also indicated by the considerable latency range in responses.6. A further complication is that, with stimulation in the region of the fastigial nucleus, the initial direct climbing fibre response is often followed by a reflex discharge, presumably from the inferior olive, which resembles the responses produced by inferior olive stimulation in being often repetitive.7. Typical climbing fibre responses have been evoked by peripheral nerve stimulation and frequently occur spontaneously.8. An account is given of the way in which the responses evoked by climbing fibres in the individual Purkinje cells can account for the potential fields that an inferior olive stimulus evokes on the surface and through the depth of the cerebellar cortex.9. By the application of currents through the recording intracellular electrode it has been possible to effect large changes in the excitatory post-synaptic potential produced by a climbing fibre, it being diminished and even reversed with depolarizing currents and greatly increased by hyperpolarizing currents.     

应用GQI技术对小脑髓质的初步研究

目的　应用基于GQI的弥散成像方法,对小脑的纤维束进行重建和显示,为小脑疾病的影像诊断进行解剖学和技术上的探索。  方法　首先把10例脑连接组项目的磁共振弥散数据导入DSI-studio软件,然后依次用该软件中的GQI（Generalized Q-sampling imaging）成像技术和流线算法（streamline algorithm）对与小脑有关的纤维束进行重建和显示。  结果　（1）在DSI-studio软件的二维和三维界面中显示了小脑三对脚的位置和交叉情况;（2）显示了小脑3对脚与脊髓、延髓、脑桥、中脑、端脑等的连接情况及其主要纤维成分。  结论　应用GQI技术可以对小脑白质进行重建和显示,为小脑疾病的影像学诊断提供技术和结构学上的帮助。     

Functional organization of the vestibular input to the anterior and posterior cerebellar vermis of cat

1. Responses evoked by electrical stimulation (auditory division of the VIIIth nerve sectioned chronically) and natural stimulation of the vestibular apparatus were recorded in the anterior and posterior cerebellar vermis of cats anesthetized with Ketamine or Nembutal. Under Ketamine the functional state of the cerebellar cortex was similar to that of the decerebrate or encéphale isolé preparation. 2. Vestibular-evoked responses were found bilaterally throughout the vermis (lob. I-X) and parts of pars intermedia and were, for the most part, mediated via the mossy fiber-granule cell pathway although natural stimulation occasionally evoked climbing fiber responses in Purkinje cells. 3. Lesion and stimulation experiments suggested that the polysynaptic potentials recorded in the dorsal folia of the anterior and parts of posterior vermis were mediated, at least in part, by the lateral reticular nucleus. Potentials recorded in the deeper folia often had shorter latencies and were probably mediated by primary and/or secondary vestibular fibers. Studies with horseradish peroxidase (injections in lob. V and VI) supported these notions. 4. An analysis of Purkinje cell responses to sinusoidal rotation and steps of angular acceleration or velocity indicated that P-cells in these regions signalled angular head velocity in the mid-frequency range. Single canal responses as well as multi-canal convergent P-cell responses were found. Purkinje cells also responded to static head displacement.     

A novel site of synaptic relay for climbing fibre pathways relaying signals from the motor cortex to the cerebellar cortical C1 zone

The climbing fibre projection from the motor cortex to the cerebellar cortical C1 zone in the posterior lobe of the rat cerebellum was investigated using a combination of physiological, anatomical and neuropharmacological techniques. Electrical stimulation of the ipsilateral fore- or hindimbs or somatotopically corresponding parts of the contralateral motor cortex evoked climbing fibre field potentials at the same cerebellar recording sites. Forelimb-related responses were located in the C1 zone in the paramedian lobule or lobulus simplex and hindlimb-related responses were located in the C1 zone in the copula pyramidis. Microinjections of anterograde axonal tracer (Fluoro-Ruby or Fluoro-Emerald) were made into the fore- or hindlimb parts of the motor cortex where stimulation evoked the largest cerebellar responses. After a survival period of 7–10 days, the neuraxis was examined for anterograde labelling. No terminal labelling was ever found in the inferior olive, but labelled terminals were consistently found in a well-localized site in the dorso-medial medulla, ventral to the gracile nucleus, termed the matrix region. Pharmacological inactivation of the matrix region (2 mm caudal to the obex) selectively reduced transmission in descending (cerebro-olivocerebellar) but not ascending (spino-olivocerebellar) paths targeting fore- or hindlimb-receiving parts of the C1 zone. Transmission in spino-olivocerebellar paths was either unaffected, or in some cases increased. The identification of a novel pre-olivary relay in cerebro-olivocerebellar paths originating from fore- and hindlimb motor cortex has implications for the regulation of transmission in climbing fibre pathways during voluntary movements and motor learning.     

Imaging parallel fiber and climbing fiber responses and their short-term interactions in the mouse cerebellar cortex in vivo

A major question in the study of cerebellar cortical function is how parallel fiber and climbing fiber inputs interact to shape information processing. Emphasis has been placed on the long-term effects due to conjunctive stimulation of climbing fibers and parallel fibers. Much less emphasis has been placed on short-term interactions and their spatial nature. To address this question the responses to parallel fiber and climbing fiber inputs and their short-term interaction were characterized using optical imaging with Neutral Red in the anesthetized mouse in vivo. Electrical stimulation of the cerebellar surface evoked an increase in fluorescence consisting of a transverse optical beam. The linear relationship between the optical responses and stimulus parameters, high spatial resolution and close coupling to the electrophysiological recordings show the utility of this imaging methodology. The majority of the optical response was due to activation of postsynaptic alpha-amino-3-hydroxyl-5-methyl-4-isoxazole propionate (AMPA) and metabotropic glutamate receptors with a minor contribution from the presynaptic parallel fibers. Stimulation of the inferior olive evoked parasagittal bands that were abolished by blocking AMPA glutamate receptors. Conjunctive stimulation of the cerebellar surface and inferior olive resulted in inhibition of the climbing fiber evoked optical responses. This lateral inhibition of the parasagittal bands extended out from both sides of an activated parallel fiber beam and was mediated by GABA(A) but not GABA(B) receptors. One hypothesized role for lateral inhibition of this type is to spatially focus the interactions between parallel fiber and climbing fiber input on Purkinje cells. In summary optical imaging with Neutral Red permitted visualization of cerebellar cortical responses to parallel fiber and climbing fiber activation. The GABA(A) dependent lateral inhibition of the climbing fiber evoked parasagittal bands by parallel fiber stimulation shows that cerebellar interneurons play a short-term role in shaping the responses of Purkinje cells to climbing fiber input.     

Classical conditioning of the nictitating membrane response of the rabbit

The nictitating membrane response (NMR) of 20 rabbits was conditioned to light and white noise conditional stimuli (CSs) using a periorbital shock unconditional stimulus (US). Unilateral lesions of the cerebellar cortex, sparing the underlying deep nuclei, were then made. Small lesions of cerebellar cortical lobule HVI abolished conditioning on the side of the lesion to both CSs leaving unconditional responses to the US intact. Larger lesions of the posterior lobe which spared HVI did not impair NMR conditioning. We conclude that cerebellar lobule HVI is essential for NMR conditioning in the rabbit. Degeneration following critical lesions of HVI was seen in a restricted region of the inferior olive - the medial part of the dorsal accessory olive and the adjoining medial part of the dorsal leaf of the principal olive. This region of the olive provides somatosensory information from the face to HVI. We suggest that HVI receives information related to the US via climbing fibres from the olive and CS information via mossy fibres from the pontine nuclei. The critical changes underlying NMR conditioning may be the association of these two inputs at the Purkinje cells of cortical lobule HVI.