Cerebellar Responses Research Articles

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.

P37.8 Cerebellar excitatory and inhibitory responses in normal subjects and patients with ataxia

P37.8 Cerebellar excitatory and inhibitory responses in normal subjects and patients with ataxia

Event-related fMRI of word classification and successful word recognition in subjects at genetically enhanced risk of schizophrenia

Verbal declarative memory is a core deficit in schizophrenia patients, seen to a lesser extent in unaffected biological relatives. Neuroimaging studies suggest volumetric differences and aberrant function in prefrontal and temporal regions in schizophrenia patients compared to controls. These deficits are also reflected in the small number of similar investigations in unaffected biological relatives. However, it is unclear the extent to which dysfunction is genetically mediated or a feature of the established illness. Event-related blood-oxygen-level-dependent (BOLD) functional magnetic resonance imaging (fMRI) was used to measure brain activation in 68 biological relatives of schizophrenia patients (of whom 27 experienced transient or isolated psychotic symptoms) and 21 controls during verbal classification and recognition. During word classification, the high-risk group showed a greater response relative to controls in the right inferior frontal gyrus. During correct recognition (relative to correct rejection), the high-risk group showed significantly greater response relative to controls in the right cerebellum. When the high-risk group was split into those with (HR+) and without (HR-) psychotic symptoms, the increased response in the right inferior frontal gyrus was only seen when the HR+ were compared to controls. The greater cerebellar response was seen when both HR groups were compared to controls. Activation increases in the right inferior frontal gyrus and cerebellum in high-risk subjects compared to controls during a relatively low-load memory task are likely to represent compensation for genetically mediated abnormalities. This is consistent with a leftward shift of the inverted 'U' load-response model of cognitive function in schizophrenia.

Correction for Roper et al., Defective cerebellar response to mitogenic Hedgehog signaling in Down’s syndrome mice

Correction for Roper et al., Defective cerebellar response to mitogenic Hedgehog signaling in Down’s syndrome mice

Defective cerebellar response to mitogenic Hedgehog signaling in Down [corrected] syndrome mice.

Trisomy 21 is the cause of Down [corrected] syndrome (DS) which is characterized by a number of phenotypes, including a brain which is small and hypocellular compared to that of euploid individuals. The cerebellum is disproportionately reduced. Ts65Dn mice are trisomic for orthologs of about half of the genes on human chromosome 21 and provide a genetic model for DS. These mice display a number of developmental anomalies analogous to those in DS, including a small cerebellum with a significantly decreased number of both granule and Purkinje cell neurons. Here we trace the origin of the granule cell deficit to precursors in early postnatal development, which show a substantially reduced mitogenic response to Hedgehog protein signaling. Purified cultures of trisomic granule cell precursors show a reduced but dose-dependent response to the Sonic hedgehog protein signal in vitro, demonstrating that this is a cell-autonomous deficit. Systemic treatment of newborn trisomic mice with a small molecule agonist of Hedgehog pathway activity increases mitosis and restores granule cell precursor populations in vivo. These results demonstrate a basis for and a potential therapeutic approach to a fundamental aspect of CNS pathology in DS.

Functional dysconnectivity in schizophrenia associated with attentional modulation of motor function

It is not known whether there is a core abnormality that occurs in all cases of schizophrenia. The cognitive dysmetria hypothesis proposes that there is such an abnormality which is characterized cognitively by a disruption in control and coordination processes, and functionally by abnormal inter-regional connectivity within the cortico-cerebellar-thalamo-cortical circuit (CCTCC). In the current study, we used functional MRI (fMRI) to investigate these two key aspects of the hypothesis. Since patients with schizophrenia show deficits in attention which have been characterized extensively using the continuous performance task (CPT) and since functional imaging studies have also demonstrated that this task engages the CCTCC, we used this task to investigate whether two patient groups with distinct symptom profiles would show functional dysconnectivity within this network. Three groups of subjects participated in the study: healthy volunteers (n = 12), schizophrenia patients with both negative and positive symptoms (n = 11) and schizophrenia patients with primarily positive symptoms (n = 11). Patient groups were matched for age of illness onset and medication, and to the control group for age, gender and handedness. Subjects were scanned using fMRI whilst they performed a modified version of the CPT, involving both degraded and non-degraded stimuli. Stimulus degradation has been shown to produce decrements in sensitivity, which is thought to reflect increased demands on the limited capacity of visual attention. Between-group comparisons revealed that patients with schizophrenia, irrespective of symptomatology, showed attenuation of the anterior cingulate and cerebellar response to stimulus degradation in comparison with control subjects. We also observed disruptions of inter-regional brain integration in schizophrenia. A task-specific relationship between the medial superior frontal gyrus and both anterior cingulate and the cerebellum was disrupted in both patient groups in comparison with controls. In addition, patients with negative symptoms showed impaired behavioural performance, and abnormal task-related connectivity between anterior cingulate and supplementary motor area. These findings are consistent with theoretical accounts of schizophrenia as a disorder of functional integration, and with the cognitive dysmetria hypothesis, which posits a disconnection within the CCTCC as a fundamental abnormality in schizophrenia, independent of diagnostic subtype. Furthermore, these data show evidence of additional functional deficits in patients with negative symptoms, deficits which may explain the accompanying attentional impairment.

Synthesis and Characterization of 4-Methoxy-7-nitroindolinyl-d-aspartate, a Caged Compound for Selective Activation of Glutamate Transporters andN-Methyl-d-aspartate Receptors in Brain Tissue

The D-isomer of aspartate is efficiently transported by high-affinity Na(+)/K(+)-dependent glutamate transporters and is an effective ligand of N-methyl-d-aspartate (NMDA) receptors. To facilitate analysis of the regulation of these proteins in their native membranes, we synthesized a photolabile analogue of D-aspartate, 4-methoxy-7-nitroindolinyl-D-aspartate (MNI-D-aspartate). This compound was photolyzed with a quantum efficiency of 0.09 at pH 7.4. Photorelease of d-aspartate in acute hippocampal slices through brief (1 ms) UV laser illumination of MNI-d-aspartate triggered rapidly activating currents in astrocytes that were inhibited by the glutamate transporter antagonist DL-threo-beta-benzyloxyaspartic acid (TBOA), indicating that they resulted from electrogenic uptake of D-aspartate. These transporter currents exhibited a distinct tail component that was approximately 2% of the peak current, which may result from the release of K(+) into the extracellular space during counter transport. MNI-D-aspartate was neither an agonist nor an antagonist of glutamate transporters at concentrations up to 500 muM and was stable in aqueous solution for several days. Glutamate transporter currents were also elicited in Bergmann glial cells and Purkinje neurons of the cerebellum in response to photolysis of MNI-D-aspartate, indicating that this compound can be used for monitoring the occupancy and regulation of glutamate transporters in different brain regions. Photorelease of D-aspartate did not activate alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)/kainate receptors or metabotropic glutamate receptors (mGluRs) in neurons, but resulted in the selective, but transient, activation of NMDA receptors in hippocampal pyramidal neurons; MNI-D-aspartate was not an antagonist of NMDA receptors. These results indicate that MNI-D-aspartate also may be useful for studying the regulation of NMDA receptors at excitatory synapses.

Learning-related fMRI activation associated with a rotational visuo-motor transformation

The unique ability to learn transformed or altered visuo-motor relationships during motor learning (visuo-motor transformation learning) has engaged researchers for over a century. Compared to other forms of motor learning (e.g., sequence learning), little is known about plasticity in the cortical and/or subcortical systems involved. We used fMRI to isolate region-specific activation changes during the learning of a visuo-motor (joystick) task under a simple transformation (90° rotation of visual feedback). Distributed brain systems were engaged in the learning process. In particular, we found evidence of a learning-dependent transition from early activation of the posterior parietal cortex to later distributed cortico-subcortical–cerebellar responses (in the temporal and occipital cortices, basal ganglia, cerebellum and thalamus). The role of the posterior parietal cortex may relate specifically to the acquisition of the transformation, while that of the fusiform and superior temporal gyri may reflect higher level visual and visuo-spatial processing underlying consolidation. Learning-related increases in cerebellar responses are consistent with its proposed role in the acquisition of internal models of the motor apparatus. These learning-related changes suggest a role for interacting neural systems involving the co-operation of cortico-cortico, cortico-cerebellar and cortico-basal ganglia loops during visuo-motor transformation learning.

Pharmacological Modulation of Cognitive Functions: Studies with fMRI

There is ample evidence that normal cognitive and emotional information processing is functionally dependent on the concerted activity of different interacting neurotransmitter systems. In a series of studies, we employed acute pharmacological challenge paradigms and subchronic pharmacological interventions in order to elucidate GABAergic and dopaminergic effects on functional brain imaging patterns subserving short-term working memory, learning processes and prediction uncertainty. An acute lorazepam challenge was associated with decreased cortical and subcortical activity during a 2-back working memory task. For alcohol-dependent patients, a blunted dopaminergic cerebellar response could be observed suggesting altered cerebellar GABAergic setpoints. On the other hand, fMRI activation during a prediction uncertainty task was found to be pronounced in the DLPFC after a dopaminergic methylphenidate challenge. Additionally, atypical antipsychotic drugs with a potential to enhance dopaminergic functions were associated with altered information processing not only in the PFC but also in an entire cortical-subcortical cerebellar circuitry in schizophrenic patients. Taken together, these findings indicate the regulatory capacity of both GABAergic and dopaminergic mechanisms and the existence of propagated effects involving changes in effective connectivity between segregated brain areas. Functional MRI appears to be a suitable tool to monitor the restoration of normal activation patterns during psychopharmacological interventions.

Environmental impacts on the developing CNS: CD15, NCAM-L1, and GFAP expression in rat neonates exposed to hypergravity

We have previously reported that the developing rat cerebellum is affected by hypergravity exposure. The effect is observed during a period of both granule and glial cell proliferation and neuronal migration in the cerebellum and coincides with changes in thyroid hormone levels. The present study begins to address the molecular mechanisms involved in the cerebellar response to hypergravity. Specifically, the study focuses on the expression of cerebellar proteins that are known to be directly involved in cell–cell interactions [protein expressing 3-fucosyl- N-acetyl-lactosamine antigen (CD15), neuronal cell adhesion molecule (NCAM-L1)] and those that affect cell–cell interactions indirectly [glial fibrillary acidic protein (GFAP)] in rat neonates exposed to centrifuge-produced hypergravity. Cerebellar mass and protein expression in rat neonates exposed to hypergravity (1.5 G) from gestational day (G) 11 to postnatal day (P) 30 were compared at one of six time points between P6 and P30 against rat neonates developing under normal gravity. Proteins were analyzed by quantitative western blots of cerebellar homogenates prepared from male or female neonates. Cerebellar size was most clearly reduced in male neonates on P6 and in female neonates on P9, with a significant gender difference; differences in cerebellar mass remained significant even when change in total body mass was factored in. Densitometric analysis of western blots revealed both quantitative and temporal changes in the expression of selected cerebellar proteins that coincided with changes in cerebellar mass and were gender-specific. In fact, our data indicated certain significant differences even between male and female control animals. A maximal decrease in expression of CD15 was observed in HG females on P9, coinciding with maximal change in their cerebellar mass. A shift in the time-course of NCAM-L1 expression resulted in a significant increase in NCAM-L1 in HG males on P18, an isolated time at which cerebellar mass does not significantly differ between HG and SC neonates. A maximal decrease in expression of GFAP was observed in HG males on P6, coinciding with maximal change in their cerebellar mass. Altered expression of cerebellar proteins is likely to affect a number of developmental processes and contribute to the structural and functional alterations seen in the CNS developing under altered gravity. Our data suggest that both cerebellar development and its response to gravitational manipulations differ in males and females.

CNS development under altered gravity: cerebellar glial and neuronal protein expression in rat neonates exposed to hypergravity

The future of space exploration depends on a solid understanding of the developmental process under microgravity, specifically in relation to the central nervous system (CNS). We have previously employed a hypergravity paradigm to assess the impact of altered gravity on the developing rat cerebellum [Exp. Biol. Med. 226 (2000) 790]. The present study addresses the molecular mechanisms involved in the cerebellar response to hypergravity. Specifically, the study focuses on the expression of selected glial and neuronal cerebellar proteins in rat neonates exposed to hypergravity (1.5 G) from embryonic day (E)11 to postnatal day (P)6 or P9 (the time of maximal cerebellar changes) comparing them against their expression in rat neonates developing under normal gravity. Proteins were analyzed by quantitative Western blots of cerebellar homogenates; RNA analysis was performed in the same samples using quantitative PCR. Densitometric analysis of Western blots suggested a reduction in glial (glial acidic protein, GFAP) and neuronal (neuronal cell adhesion moiecule, NCAM-L1, synaptophysin) proteins, but the changes in individual cerebellar proteins in hypergravity-exposed neonates appeared both age- and gender-specific. RNA analysis suggested a reduction in GFAP and synaptophysin mRNAs on P6. These data suggest that exposure to hypergravity may interfere with the expression of selected cerebellar proteins. These changes in protein expression may be involved in mediating the effect of hypergravity on the developing rat cerebellum.

Muscle afferent inputs from the hand activate human cerebellum sequentially through parallel and climbing fiber systems.

Spatio-temporal response characteristics of the human cerebellum to median nerve stimulation (MNS) were studied with the use of a whole-head magnetoencephalographic (MEG) system covering the cerebellum and upper cervical spine. Neuromagnetic responses from the cerebellum were recorded following electric stimulation of the right median nerve in 12 subjects. In 6 out of 12 subjects, the responses to the left median nerve and to the right index or middle finger stimulation were also recorded. The medial part of the cerebellum (spinocerebellum) was activated by MNS. In contrast, there were no responses from the cerebellum to the finger stimulation, suggesting that muscle afferent inputs are the source of cerebellar activation for MNS. The cerebellar responses consisted of 3 or 4 components of alternating polarity within 90 ms post-stimulus: the current direction for the first component was from the depth to the surface of the anterior lobe. From the timing and current direction, we speculate that the 4 components reflect, respectively, (1) excitatory postsynaptic potentials (EPSPs) of granule cells, (2) Purkinje cell EPSPs at the distal dendrites driven by parallel fibers, (3) Purkinje cell EPSPs at the soma and the proximal dendrites mediated by climbing fibers and (4) second Purkinje cell EPSPs at the distal dendrites driven by parallel fibers. We first visualized serial activation of the human spinocerebellum following MNS noninvasively with MEG.

Cerebellar responses during anticipation of noxious stimuli in subjects recovered from depression. Functional magnetic resonance imaging study.

Subjects recovered from depression have a substantial risk for recurrence of depression, suggesting persistent abnormalities in brain activity. To test whether women recovered from depression show abnormal brain activity in functional magnetic resonance imaging (fMRI) during a conditioning paradigm with a noxious pain stimulus. Ten unmedicated women who had recovered from major depression and eight healthy control women each received either noxious hot or non-noxious warm stimuli, the onset of which was signalled by a specific coloured light during 3-tesla echo planar imaging-based fMRI. Similar patterns of brain activation were found during painful stimulation for both patients and healthy controls. However, relative to healthy controls, subjects recovered from depression showed a reduced response in the cerebellum during anticipation of the noxious stimulus compared with anticipation of the non-noxious stimulus. Our data suggest that abnormal cerebellar function could be a marker of vulnerability to recurrent depression. This could provide a new target for therapeutic interventions.

Phosphorylation of c-Cbl protooncogene product following ethanol administration in rat cerebellum: possible involvement of Fyn kinase

We have previously shown that ethanol administration results in tyrosine phosphorylation of the 130 kDa protein in rat brain, and identified the protein as Cas, the crk-associated src substrate. In the present study, we demonstrate that Cbl of a 120 kDa protein is also tyrosine-phosphorylated in the cerebellum in response to ethanol administration. We also investigated whether Fyn kinase was involved in ethanol-induced Cbl phosphorylation. Immunoprecipitation experiments showed that the amount of coimmunoprecipitated Fyn kinase with an anti-Cbl antibody increased in extracts from ethanol-administered rats compared to those from saline-administered rats. Exogenous Fyn kinase was shown to phosphorylate on tyrosine residue(s) of Cbl from the cerebellum in vitro. Furthermore, Fyn kinase and Cbl were demonstrated immunohistochemically to be coexpressed in white matter in the cerebellum. These findings indicate that Cbl is tyrosine-phosphorylated in rat cerebellum in response to ethanol administration, and also raise the possibility that Fyn kinase may be involved in the process.

Differential role for the striatum and cerebellum in response to novel movements using a motor learning paradigm

The aim of this pilot study was to examine the role of the striatum and cerebellum in the adaptation to a novel movement within a sequence of practiced movements using a motor learning paradigm. The performance of patients in the early or advanced stages of Parkinson's disease (PD) and of patients with damage to the cerebellum (CE) was compared, respectively to a group of aged and young matched controls on an adapted version of the Mirror-Tracing Test. In this task, subjects were required to trace a series of complex figures in two conditions: (1) a Practiced condition, in which the figures were composed of the juxtaposition of three simple designs that were extensively practiced before; and (2) a Mixed condition in which triads were created by replacing the last simple figure of the triads in the Practiced condition by a new simple figure that had never been traced individually before. Results showed that all clinical groups were slower than controls at tracing the Practiced triads. Most interestingly, however, only patients in the advanced stages of PD showed increased completion time to trace the triads in the Mixed condition. This suggests that a bilateral striatal dysfunction affects the ability to adapt to a novel motion within a sequence of practiced movements. Although exploratory, these results support a functional dissociation between the striatum and cerebellum in acquiring visuomotor skilled behaviors.

Effects of aluminium exposure on brain glutamate and GABA systems: an experimental study in rats

It has been postulated that the neurotoxic effects of aluminium could be mediated through glutamate, an excitatory amino acid. Hence the effects of aluminium administration (at a dose of 4.2 mg/kg body weight daily as aluminium chloride, hexahydrate, intraperitoneally, for 4 weeks) on glutamate and γ-amino butyrate (GABA), an inhibitory amino acid, and related enzyme activities in different regions of the brain were studied in albino rats. The glutamate level increased significantly in the cerebrum, thalamic area, midbrain–hippocampal region and cerebellum in response to in vivo aluminium exposure. The aluminium insult also caused significant increases in glutamate α-decarboxylase activity in all the brain regions. However, on aluminium insult, the GABA content was not significantly changed except in the thalamic area, where it was elevated. On the contrary, the GABA-T activities of all the regions were reduced significantly in all regions except the midbrain–hippocampal region. However, the succinic semi-aldehyde content of all brain regions increased, often significantly. The aluminium-induced modification of the enzyme activities may be either due to the direct impact of aluminium or due to aluminium-induced changes in the cellular environment. The aluminium-induced differential regional accumulation of glutamate or other alterations in enzymes of the glutamate–GABA system may be one of the causes of aluminium-induced neurotoxicity.

Neuroimaging evidence implicating cerebellum in the experience of hypercapnia and hunger for air.

Recent neuroimaging and neurological data implicate cerebellum in nonmotor sensory, cognitive, vegetative, and affective functions. The present study assessed cerebellar responses when the urge to breathe is stimulated by inhaled CO(2). Ventilation changes follow arterial blood partial pressure CO(2) changes sensed by the medullary ventral respiratory group (VRG) and hypothalamus, entraining changes in midbrain, pons, thalamus, limbic, paralimbic, and insular regions. Nearly all these areas are known to connect anatomically with the cerebellum. Using positron emission tomography, we measured regional brain blood flow during acute CO(2)-induced breathlessness in humans. Separable physiological and subjective effects (air hunger) were assessed by comparisons with various respiratory control conditions. The conjoint physiological effects of hypercapnia and the consequent air hunger produced strong bilateral, near-midline activations of the cerebellum in anterior quadrangular, central, and lingula lobules, and in many areas of posterior quadrangular, tonsil, biventer, declive, and inferior semilunar lobules. The primal emotion of air hunger, dissociated from hypercapnia, activated midline regions of the central lobule. The distributed activity across the cerebellum is similar to that for thirst, hunger, and their satiation. Four possible interpretations of cerebellar function(s) here are that: it subserves implicit intentions to access air; it provides predictive internal models about the consequences of CO(2) inhalation; it modulates emotional responses; and that while some cerebellar regions monitor sensory acquisition in the VRG (CO(2) concentration), others influence VRG to adjust respiratory rate to optimize partial pressure CO(2), and others still monitor and optimize the acquisition of other sensory data in service of air hunger aroused vigilance.

Differential Contributions of Motor Cortex, Basal Ganglia, and Cerebellum to Speech Motor Control: Effects of Syllable Repetition Rate Evaluated by fMRI

In order to delineate the neuroanatomical correlates of speech motor control, functional magnetic resonance imaging was performed during silent repetitions of the syllable “ta” at three different rates (2.5, 4.0, and 5.5 Hz). Spatial extent and magnitude of hemodynamic responses at the level of the motor cortex showed a positive correlation to production frequencies. As concerns the basal ganglia, the lower rates (2.5 and 4.0 Hz) gave rise to higher magnitudes of activation within the left putamen as compared to the 5.5 Hz condition. In contrast, cerebellar responses were rather restricted to fast performance (4.0 and 5.5 Hz) and exhibited a shift in caudal direction during 5.5 as compared to 4.0 Hz. These findings corroborate the suggestion of a differential impact of various cortical and subcortical areas on speech motor control.

Serotonergic Modulation of Ethanol‐Induced Electrophysiological Depression in Young and Aged Rats

Ethanol (EtOH)-induced electrophysiological depressions in cerebellar Purkinje neurons have been shown to be potentiated by exogenously applied serotonin (5HT). In this study, we determined whether this modulatory action can be activated by endogenous release from presynaptic serotonergic terminals, and whether such a response is altered by age or rat strain. Extracellular 5HT levels in cerebellar cortex were measured in real time by in vivo chronoamperometry, by using Nafion-coated carbon fiber electrodes, in anesthetized young (3-5 months old) or aged (18-24 months old) Sprague Dawley and Fischer 344 rats. Some animals were prelesioned with 5,7 dihydroxytryptamine (5,7 DHT). Single unit electrophysiological activity was recorded from cerebellar Purkinje neurons. Serotonin or its presynaptic antagonist methiothepin was applied directly to cerebellar neurons through multibarrel pipettes. Local application of methiothepin dose-dependently induced 5HT overflow in young Sprague Dawley and Fisher 344 rats. Methiothepin-induced 5HT release was decreased significantly in aged or 5,7 DHT-lesioned rats. Local application of methiothepin or 5HT potentiated EtOH-induced electrophysiological depression of Purkinje neurons in young animals of both strains. Methiothepin-potentiated, EtOH-elicited neuronal inhibition was reduced greatly in aged or 5,7 DHT-lesioned rats. Serotonin-facilitated EtOH responses were reduced in the aged Sprague Dawley rats. EtOH-induced electrophysiological responses in cerebellum can be facilitated by endogenous 5HT release by using a 5HT autoreceptor antagonist. Such actions are attenuated in aged rats perhaps through a presynaptic serotonergic mechanism.

Anticipatory cerebellar responses during somatosensory omission in man

Anticipatory cerebellar responses during somatosensory omission in man