Pattern of recovery following cerebellar deep nuclear lesions in monkeys

Monkeys were trained to perform simple motor habits including phasic movement and maintained limb positions before receiving bilateral lesions of the cerebellar dentate and interpositus nuclei. The frequency, relative amplitude, and duration of oscillations, measured by an accelerometer worn on the limb, varied with the limb's position, being slower and wider (ataxia) with more extended-abducted positions, faster and smaller (tremor) with more flexed-adducted postures. Changes with time showed a progressive conversion of ataxic oscillations to tremor as reflex and locomotor performance improved. At any time, limb fixation combined with phasic movement initiated the oscillations, whereas a fixed position by itself could be maintained, or a phasic movement without a fixed end point performed without tremor or ataxia. Analysis of these data suggests that the cerebellum provides a timing device for movement which matches limb fixation with phasic (usually distal) movement so that the limb fixation stops at the right moment for the phasic component to begin. The timing of these two components may have separate mediation by the interpositus (fixation) and dentate (phasic-distal) nuclei. During recovery, loss of internal feed-forward cerebellar circuits is compensated for by external feedback loops involving the dorsal root afferents and cerebral cortex.     

Glutamic acid decar☐ylase activity in micropunches of the deep cerebellar nuclei of the genetically dystonic (dt) rat

Glutamic acid decar☐ylase (GAD) activity was measured in specific divisions of the deep cerebellar nuclei of rats with an inherited dystonia. In 16-day-old dystonic rats there was a significant increase in GAD activity only in the nucleus interpositus (+26%). In 20-day-old dystonic rats GAD activity in all 3 cerebellar nuclei (fastigial, interpositus, dentate) was significantly increased compared to normal controls. The results indicate a spread of the anatomical locus of the neurochemical abnormality with time. During this period (postnatal days 16–20) there is a progressive worsening of the motor disorder in the affected animals.     

Projection from the deep cerebellar nuclei to the pedunculopontine nucleus in the squirrel monkey

Large injections of the anterograde tracer biocytin in the deep nuclei of the cerebellum of squirrel monkeys (Saimiri sciureus) led to a massive labeling of the superior cerebellar peduncle fibers which could be followed up to their major termination site in the thalamus. Along their course through the brainstem, biocytin-labeled fibers emitted fine collaterals that arborized profusely within the entire rostrocaudal extent of the pedunculopontine nucleus (PPN). These fibers were long, slightly varicose, and broke off into numerous shorter and thinner fibers whose terminal portions consisted of a few large varicosities that were often closely apposed to dendrites and cell bodies of PPN neurons. Some PPN cells that were contacted displayed immunoreactivity for choline acetyltransferase. Ultrastructural analysis revealed that synapses formed by cerebellar fibers in PPN were of the asymmetric type and occurred predominantly on dendrites of PPN neurons. Thus, beside the well established cerebellothalamic projection, our findings reveal the existence of a cerebellotegmental projection, whereby the cerebellum may influence the basal ganglia and/or the thalamus via a relay in PPN.     

Cerebellar transcranial direct current stimulation modulates the fMRI signal in the cerebellar nuclei in a simple motor task

BackgroundIn a seminal paper, Galea et al. (Modulation of cerebellar excitability by polarity-specific noninvasive direct current stimulation. 2009. J Neurosci 29, 9115–9122) showed that cerebellar transcranial direct current stimulation (ctDCS) alters cerebellar-M1 connectivity. This effect has been explained by ctDCS-related changes of excitability of the cerebellar cortex with consecutive modulation of its main output, the dentate-thalamo-cortical pathway.ObjectivesThe aim of this functional magnetic resonance imaging (fMRI) study was to provide evidence that cathodal ctDCS decreases the activity of the cerebellar cortex, resulting in increased activity of the cerebellar nuclei, whereas anodal ctDCS has the opposite effect.MethodsA total of 48 participants (female/male: 23/25, age: 23.8 ± 4.1yrs., mean ± standard deviation) performed a finger tapping task with the right hand in a 3T MRI scanner. Functional MR images were acquired prior, during and after tDCS of the right cerebellum. Participants were assigned randomly to anodal, cathodal or sham ctDCS.ResultsNo significant difference of cerebellar cortical activation was found after comparing the three modes of stimulation. On the level of the dentate nuclei, however, a significant increase of activation was detected during and after cathodal stimulation. Furthermore, dentate nuclei activation was suppressed on a trend level following anodal stimulation.ConclusionsThe present findings support the hypothesis that cathodal ctDCS leads to a disinhibition of the dentate nucleus, whereas anodal ctDCS may have the opposite effect.     

Functional recovery after cerebellar damage is related to GAP-43-mediated reactive responses of pre-cerebellar and deep cerebellar nuclei

Since brain injuries in adulthood are a leading cause of long-term disabilities, the development of rehabilitative strategies able to impact on functional outcomes requires detailing adaptive neurobiological responses. Functional recovery following brain insult is mainly ascribed to brain neuroplastic properties although the close linkage between neuronal plasticity and functional recovery is not yet fully clarified. The present study analyzed the reactive responses of pre-cerebellar (inferior olive, lateral reticular nucleus and pontine nuclei) and deep cerebellar nuclei after a hemicerebellectomy, considering the great plastic potential of the cerebellar system in physiological and pathological conditions. The time course of the plastic reorganization following cerebellar lesion was investigated by monitoring the Growth Associated Protein-43 (GAP-43) immunoreactivity. The time course of recovery from cerebellar symptoms was also assessed to parallel behavioral and neurobiological parameters. A key role of GAP-43 in neuronal reactive responses was evidenced. Neurons that underwent an axotomy as consequence of the right hemicerebellectomy (neurons of left inferior olive, right lateral reticular nucleus and left pontine nuclei) exhibited enhanced GAP-43 immunoreactivity and cell death. As for the not-axotomized neurons, we found enhanced GAP-43 immunoreactivity only in right pontine nuclei projecting to the spared (left) hemicerebellum. GAP-43 levels augmented also in the three deep cerebellar nuclei of the spared hemicerebellum, indicating the ponto-cerebellar circuit as crucially involved in functional recovery. Interestingly, each nucleus showed a distinct time course in GAP-43 immunoreactivity. GAP-43 levels peaked during the first post-operative week in the fastigial and interposed nuclei and after one month in the dentate nucleus. These results suggest that the earlier plastic events of the fastigial and interposed nuclei were driving compensation of the elementary features of posture and locomotion, while the later plastic events of the dentate nucleus were mediating the recovered ability to flexibly adjust the locomotor plan.     

电刺激小脑顶核防治血管性痴呆的实验研究

目的探讨电刺激小脑顶核(FNS)对血管性痴呆(VD)的防治作用.方法采用反复低血压和双侧颈总动脉阻断法建立VD大鼠模型,双侧小脑顶核植入电极进行FNS,用跳台试验、程控穿梭箱试验和神经病理学检查评价FNS对VD大鼠的防治效果.结果反复全脑缺血前2 d给予FNS 1次或缺血后即刻给予FNS治疗7 d均可明显减轻脑缺血后2周大鼠的学习和记忆障碍(P＜0.01),并使脑缺血后大脑皮层和海马神经元丢失显著减少(P＜0.01).脑缺血11周后给予FNS治疗7 d,虽不能减轻脑缺血后大脑皮层和海马神经元的丢失P＞0.05),但可明显改善大鼠的学习和记忆障碍(P＜0.05).结论FNS对VD大鼠具有明确的防治效果,但减轻缺血神经元损害可能只是其防治作用的机制之一.     

Role of the cerebellar deep nuclei in respiratory modulation

The cerebellum contains three deep nuclei, i.e., the fastigial, interposed and lateral nucleus. Recent studies demonstrate that these nuclei play different roles in respiratory modulation. Activation of fastigial nuclear neurons predominantly increases ventilation via elevation of respiratory frequency and/or tidal volume. Ablation of the fastigial nucleus did not significantly alter eupneic breathing, but did markedly attenuate the respiratory response to medium and severe hypercapnia as well as hypoxia. The fastigial nucleus contains respiratory-modulated neurons and about 25% of these neurons do not show their respiratory-related phasic activity until exposed to hypercapnia. The fastigial nucleus also contains CO2/H+ chemosensitive sites that contributed to the respiratory response to hypercapnia. Therefore, it is concluded that fastigial nuclear facilitatory influence on chemoreflexes emerges during hypercapnia via recruiting intrinsic chemoreception and respiratory-modulated neurons. Full expression of the fastigial nucleus-mediated respiratory responses depends on the integrity of the medullary gigantocellular nucleus at least partially via monosynaptic projections. Additionally, the fastigial nucleus receives inhibitory inputs primarily from Purkinje cells located in the medial vermis and recent observations indicate that simulation of these Purkinje cells inhibits respiration. As compared to chemoreflexes, fastigial nuclear role in the respiratory mechanoreflexes is not significant. The studies related to the role of the interposed and lateral nucleus in eupneic breathing are limited and the results appear controversial. However, there is evidence to show that the interposed nucleus contains respiratory-modulated neurons and is involved in coughing motor control.     

Efferent fibers of the deep cerebellar nuclei in hedgehogs

Three main deep cerbellar nuclei are apparent in hedgehogs belonging to the genera Erinaceus and Hemiechinus; however, at various levels they exhibit a considerable continuity with one another. Electrolytic unilateral lesions were placed in the deep cerebellar nuclei of these hedgehogs, and additional animals were subjected to a midline incision of the cerebellum between the two fastigial nuclei. Degenerating axons were traced from the sites of lesions using the Nauta and Fink-Heimer techniques. The typical mammalian pattern is evident in the distribution of the cerebellifugal fibers of the hedgehog. Crossed and uncrossed fastigial efferent fibers are directed primarily toward vestibular nuclei and the bulbar reticular formation except for a relatively small ascending limb of the uncinate fasciculus. The brachium conjunctivum originates from the nucleus interpositus and nucleus lateralis. The efferents of these nuclei are directed rostrally to the contralateral red nucleus. Fibers passing beyond the level of the red nucleus terminate in the thalamic nuclei. Fibers from the brachium conjunctivun also supply the inferior and superior colliculi. Axons forming the descending limb of the brachium conjunctivum are divided into medial and lateral fascicles.     

Divergent effects of deep cerebellar lesions on two different conditioned somatomotor responses in rabbits

Rabbits with bilateral lesions involving either the anterior interpositus nucleus or the superior cerebellar peduncle were subjected to appetitive Pavlovian conditioning training involving repeated pairings of a 2-s tone with an intraoral pulse of water. Such training resulted in the rapid development of robust, anticipatory jaw-movement responses (JM CRs) to the tone, and, in fact, the performance levels exhibited by lesioned animals did not differ significantly from those observed in sham-operated control animals. Additional experiments involving unpaired tone/water presentations confirmed the associative character of the JM CRs. On the other hand, lesioned animals exhibited severe bilateral performance deficits when later subjected to aversive eyeblink conditioning procedures, consistent with previous findings. The present results thus suggest that the interpositus nucleus is not an essential neural substrate for the development of appetitively conditioned masticatory responses.     

Brainstem and spinal projections of the deep cerebellar nuclei in the monkey,with observations on the brainstem projections of the dorsal column nuclei

Miniature end-plate potentials (MEPPs) recorded at the neuromuscular junction were initially reported to be normally distributed and have been attributed to quantal ACh release. This quantum was later correlated with the release of the content of one clear vesicle. This is the ‘classical vesicular hypothesis’. Recent observations of subminiature end-plate potentials (s-MEPPs) and of multimodal distribution of the MEPP amplitudes have led to the formulation of a new 'multivesicular hypothesis'. It attributes the s-MEPP to the release of one vesicle and the MEPP to the simultaneous release of several vesicles at one active zone.The distribution of MEPP intervals, the evaluation of the ACh content of a vesicle and of the ACh necessary to produce a MEPP, estimates of the number of vesicles missing following repeated stimulation, and the freeze fracture studies of the active zone do not permit a definitive rejection of either hypotheses.     

Brainstem and spinal projections of the deep cerebellar nuclei in the monkey, with observations on the brainstem projections of the dorsal column nuclei

The cytoarchitecture of the ventral lateral region of the primate thalamus has been appraised in the frontal, parasagittal and horizontal planes. A morphologically distinct region, possessing a sparse and diffuse distribution of large and small neurons is identified. The region includes several nuclei previously separately named by Olszewski⁴⁵. These are nuclei VPLo, VLc, X, VLps, and some cellular extensions into the VLo nucleus. The whole zone is continuous, and it is shown that no clear separation exists between any of the previously identified sub-nuclei. Connectional grounds are given for suggesting that this region should be considered as a common cerebellar relay nucleus to motor cortex.Morphological criteria for distinguishing the cellsparse nucleus from adjacent nuclei are given. These cytological criteria provide a basis for the experimental analysis of cortical and subcortical connectivity of the ventral lateral thalamic region. Close attention was paid to the border between the VPLo nucleus and the VPLc nucleus. VPLc is separated from VPLo by a clear border, and no transitional zone can be detected in the parasagittal or horizontal planes. Previous ambiguities in the delineation of the VPLo-VPLc border probably stem from analysis in the frontal plane, in which the border is not clear.     

Representation of the tongue in the cerebellar nuclei of the monkey.

Electrophysiologic techniques were used to determine the pattern of representation of the tongue within the cerebellar nuclei of the monkey, Macaca mulatta. The cerebellar nuclei were stimulated with bipolar, concentric electrodes, and lingual activity was recorded electromyographically from the extrinsic tongue musculature with indwelling needle electrodes. Correlative gross tongue movements were also monitored via a system of force-displacement transducers. The results indicate that the tongue is represented within each of the four cerebellar nuclei; however, the degree of representation is not equivalent. Whereas numerous stimulus sites in the fastigal and anterior interposed nuclei were effective in influencing tongue muscle activity, effective sites were limited to medial and rostral regions of the dentate nucleus and to a small central region of the posterior interposed nucleus. This particular pattern of tongue representation in the cerebellar nuclei has implications for the anatomicofunctional organization of the cerebellum for controlling other somatic motor organs.     

Inhibitory effects of cerebellar lesions on respiration in the spontaneously breathing, anesthetized cat

Acute cerebellectomy depressed spontaneous respiration in cats anesthetized with chloralose-urethane. After cerebellectomy there was an increased interbreath interval (T_TOT) accompanied by increased inspiratory and expiratory durations (T_IandT_E, respectively). However, the change of T_E exceeded that of T_I so that T_I/T_TOT decreased. Tidal volume (V_T) and mean inspiratory flow (V_T/T_I) were not affected. No respiratory variable was significantly altered when cerebellectomy was performed subsequent to bilateral vagotomy. Bilateral lesions of the rostral fastigial nuclei (FN) in cats with intact vagi also caused a reduction in ventilation due to increased T_TOT. In this case T_I and V_T/T_I increased, but V_T and T_I/T_TOT remained unchanged. Bilateral control lesions that usually included protions of the dentate nuclei did not influence respiration. The results suggest that in the anesthetized cat the cerebellum tonically excites respiratory centers controlling respiratory rate and the termination of inspiration. A part of this influence may be mediated by the rostral FN. In addition, vagal input appears to be important in the expression of the cerebellar influence on spontaneous respiration.     

Importance of the projection from the sensory to the motor cortex for recovery of motor function following partial thalamic lesion in the monkey

Motor deficits produced by thalamic lesions were studied using adult cynomolgus monkeys. Lesioned areas included n. ventralis anterior (VA), ventralis lateralis (VL), n. ventralis posterolateralis pars oralis (VPLo), pars caudalis (VPLc) n. subthalamus (STN) and n. centrum medianum (CM). When the lesion included VA, VL and VPLo, there was a cerebellar syndrome, i.e., ataxia and dysmetria. When the lesion included VPLo and VPLc, the animal was paralyzed. When the lesion included VPLo and rostral part of VPLc, there was loss of orientation in hand movement and clumsiness of finger manipulation. These motor deficits gradually disappeared within 1-2 weeks and the function recovered near to normal except for when VPLo and VPLc were totally destroyed. After recovery of motor function, the somatic sensory cortex (areas 1, 2, 3b) ipsilateral to the thalamic lesion was removed. Removal of the sensory cortex resulted in abolition of the recovered function, but when the border area between VPLo and VPLc was intact, the function recovered again. On the other hand, when the thalamic lesion included this border area, succeeding cortical lesion permanently abolished the recovered function or the reappeared function was substantially worse than that before the cortical lesion. Neuronal mechanisms subserving these differences are discussed and it is concluded that when direct sensory input to the motor cortex was interrupted by lesion of the border area between VPLo and VPLc, the lost function was compensated by reorganization of the projection from the sensory cortex to the motor cortex.     

The organization of afferents to the cerebellar cortex in the cat: Projections from the deep cerebellar nuclei

The topography of the cerebellar nucleo-cortical projection was investigated in the cat by experiments employing the horseradish peroxidase (HRP) technique or by combined HRP-autoradiographic methods. The results of the HRP studies extend previous findings showing that neurons in the deep nuclei project to the cerebellar cortex in an orderly way. Thus, it appears that the cortex of the vermis-proper receives projections fron neurons located predominately in the fastigial nucleus. Intermediate and lateral zones of mid-vermal cerebellar cortex are projected on by neurons located in the interposed and dentate nuclei. Crus II receives input from neurons located predominately in the dentate nucleus, while the paramedian lobule is projected on by neurons located in a large postero-dorsal sector of the interposed nucleus and in a smaller medial strip of the dentate nucleus. Neurons in the ventral part of the dentate nucleus and the lateral part of the interposed nucleus send fibers to the paraflocculus. The nucleo-cortical pathway to the flocculus and nodulus arises largely from a population of neurons located in a ventral region stretching from the medial border of the dentate nucleus to the lateral border of the fastigial nucleus. The results of experiments using the combined HRP-autoradiographic method show that clusters of neurons in the deep cerebellar nuclei project back to the cerebellar cortical areas from which they receive input, establishing a fairly precise feedback loop between the cerebellar cortex and deep nuclei.     

Inducing inflammation following subacute spinal cord injury in female rats: A double-edged sword to promote motor recovery

The inflammatory response following spinal cord injury is associated with increased tissue damage and impaired functional recovery. However, inflammation can also promote plasticity and the secretion of growth-promoting substances. Previously we have shown that inducing inflammation with a systemic injection of lipopolysaccharide in the chronic (8 weeks) stage of spinal cord injury enhances neuronal sprouting and the efficacy of rehabilitative training in rats. Here, we tested whether administration of lipopolysaccharide in female rats in the subacute (10 days) stage of spinal cord injury would have a similar effect. Since the lesioned environment is already in a pro-inflammatory state at this earlier time after injury, we hypothesized that triggering a second immune response may not be beneficial for recovery. Contrary to our hypothesis, we found that eliciting an inflammatory response 10 days after spinal cord injury enhanced the recovery of the ipsilesional forelimb in rehabilitative training. Compared to rats that received rehabilitative training without treatment, rats that received systemic lipopolysaccharide showed restored motor function without the use of compensatory strategies that translated beyond the trained task. Furthermore, lipopolysaccharide treatment paradoxically promoted the resolution of chronic neuroinflammation around the lesion site. Unfortunately, re-triggering a systemic immune response after spinal cord injury also resulted in a long-term increase in anxiety-like behaviour.     

Quantitative examination of the deep cerebellar nuclei in the staggerer mutant mouse

Quantitative morphological techniques have revealed several new aspects of the action of the Staggerer mutant gene. Staggerer is an autosomal recessive gene which causes ataxia and severe malformation of the cerebellar cortex in mice. The Purkinje cells of the cerebellar cortex are small, abnormal in morphology and reduced in numbers. The close synaptic and developmental relationship of Purkinje cells with the cells of the deep cerebellar nuclei (dcn) lead us to look for effects of the Staggerer mutation on the dcn neurons.The volume of the deep nuclear region is shrunken in Staggerer and there is a reduction in the volume of the white matter. These findings account for the reduced wet weights and protein concentration found by Roffler-Tarlov and Sidman²⁰. In contrast to the cells of the cortex, where 75% of the medium-to-large neurons are missing, the number of cells present in Staggerer dcn is identical to wild-type. The dcn neurons are not completely spared, however. Measurements of cross-sectional cell area revealed a 30% shrinkage of neurons in Staggerer dcn. The most likely interpretation of previous work and the current findings is that the Staggerer gene acts early in development but exerts its effects directly only on those derivatives of the ventricular zone in the roof of the fourth ventricle which are destined to become Purkinje and Golgi cells.     

Behavioural recovery following transplantation of substantia nigra in rats subjected to 6-OHDA lesions of the nigrostriatal pathway. II. Bilateral lesions

Rats with a unilateral transplant of embryonic substantia nigra, placed in a cortical cavity overlying the caudate-putamen, were compared with control animals on a range of behavioral tests following bilateral 6-OHDA lesions of the ascending dopaminergic nigrostriatal pathway. Tests designed to reveal behavioural asymmetry--such as spontaneous, tail-pinch and amphetamine-induced rotation, sensorimotor orientation, and side preference in a T-maze--revealed that the rats with bilateral 6-OHDA lesions and a unilateral transplant are similar to unilaterally lesioned animals with one intact nigrostriatal pathway. Both transplanted and bilaterally lesioned control rats became spontaneously akinetic after the second 6-OHDA lesion. This akinesia could be reversed by a low dose of amphetamine (0.5 mg/kg) in the transplanted but not in the non-transplanted control rats. The attenuated effects of apomorphine and L-DOPA on activity and rotation suggest that the nigral transplant produced a partial reversal of receptor supersensitivity following the 6-OHDA lesion on the same side as the transplant. However, other effects of the bilateral 6-OHDA lesion, including the development of aphagia, adipsia and akinesia, were not reversed by the presence of the transplant. The transplants were shown by fluorescence histochemistry to have densely reinnervated the dorsal parts of the denervated caudateputamen on the side ipsilateral to the transplant. The results show that intracortical nigral grafts reinnervating parts of the dorsal caudate-putamen can reverse some, but not all, functional impairments associated with bilateral destruction of the nigrostriatal pathway.