Mono- and dual-frequency fast cerebellar oscillation in mice lacking parvalbumin and/or calbindin D-28k

Cerebellar dysfunction in the mdx mouse model of Duchenne muscular dystrophy: An electrophysiological and behavioural study

Patients with Duchenne muscular dystrophy (DMD) commonly show specific cognitive deficits in addition to a severe muscle impairment caused by the absence of dystrophin expression in skeletal muscle. These cognitive deficits have been related to the absence of dystrophin in specific regions of the central nervous system, notably cerebellar Purkinje cells (PCs). Dystrophin has recently been involved in GABAA receptors clustering at postsynaptic densities, and its absence, by disrupting this clustering, leads to decreased inhibitory input to PC. We performed an in vivo electrophysiological study of the dystrophin-deficient muscular dystrophy X-linked (mdx) mouse model of DMD to compare PC firing and local field potential (LFP) in alert mdx and control C57Bl/10 mice. We found that the absence of dystrophin is associated with altered PC firing and the emergence of fast (~160-200 Hz) LFP oscillations in the cerebellar cortex of alert mdx mice. These abnormalities were not related to the disrupted expression of calcium-binding proteins in cerebellar PC. We also demonstrate that cerebellar long-term depression is altered in alert mdx mice. Finally, mdx mice displayed a force weakness, mild impairment of motor coordination and balance during behavioural tests. These findings demonstrate the existence of cerebellar dysfunction in mdx mice. A similar cerebellar dysfunction may contribute to the cognitive deficits observed in patients with DMD.

Neuroprotective effects of quercetin on the cerebellum of zinc oxide nanoparticles (ZnoNps)-exposed rats

Engineered nanomaterials induce hazardous effects at the cellular and molecular levels. We investigated different mechanisms underlying the neurotoxic potential of zinc oxide nanoparticles (ZnONPs) on cerebellar tissue and clarified the ameliorative role of Quercetin supplementation. Forty adult male albino rats were divided into control group (I), ZnONPs-exposed group (II), and ZnONPs and Quercetin group (III). Oxidative stress biomarkers (MDA & TOS), antioxidant biomarkers (SOD, GSH, GR, and TAC), serum interleukins (IL-1β, IL-6, IL-8), and tumor necrosis factor alpha (TNF-α) were measured. Serum micro-RNA (miRNA): miRNA-21-5p, miRNA-122-5p, miRNA-125b-5p, and miRNA-155-3p expression levels were quantified by real-time quantitative polymerase-chain reaction (RT-QPCR). Cerebellar tissue sections were stained with Hematoxylin & Eosin and Silver stains and examined microscopically. Expression levels of Calbindin D28k, GFAP, and BAX proteins in cerebellar tissue were detected by immunohistochemistry. Quercetin supplementation lowered oxidative stress biomarkers levels and ameliorated the antioxidant parameters that were decreased by ZnONPs. No significant differences in GR activity were detected between the study groups. ZnONPs significantly increased serum IL-1β, IL-6, IL-8, and TNF-α which were improved with Quercetin. Serum miRNA-21-5p, miRNA-122-5p, miRNA-125b-5p, and miRNA-155-p expression levels showed significant increase in ZnONPs group, while no significant difference was observed between Quercetin-treated group and control group. ZnONPs markedly impaired cerebellar tissue structure with decreased levels of calbindin D28k, increased BAX and GFAP expression. Quercetin supplementation ameliorated cerebellar tissue apoptosis, gliosis and improved calbindin levels. In conclusion: Quercetin supplementation ameliorated cerebellar neurotoxicity induced by ZnONPs at cellular and molecular basis by different studied mechanisms.Abbreviations: NPs: Nanoparticles, ROS: reactive oxygen species, ZnONPs: Zinc oxide nanoparticles, AgNPs: silver nanoparticles, BBB: blood-brain barrier, ncRNAs: Non-coding RNAs, miRNA: Micro RNA, DMSO: Dimethyl sulfoxide, LPO: lipid peroxidation, MDA: malondialdehyde, TBA: thiobarbituric acid, TOS: total oxidative status, ELISA: enzyme-linked immunosorbent assay, H2O2: hydrogen peroxide, SOD: superoxide dismutase, GR: glutathione reductase, TAC: total antioxidant capacity, IL-1: interleukin-1, TNF: tumor necrosis factor alpha, cDNA: complementary DNA, RT-QPCR: Real-time quantitative polymerase-chain reaction, ABC: Avidin biotin complex technique, DAB: 3', 3-diaminobenzidine, SPSS: Statistical Package for Social Sciences, ANOVA: One way analysis of variance, Tukey's HSD: Tukey's Honestly Significant Difference, GFAP: glial fiberillar acitic protein, iNOS: Inducible nitric oxide synthase, NO: nitric oxide, HO-1: heme oxygenase-1, Nrf2: nuclear factor erythroid 2-related factor 2, NF-B: nuclear factor-B, SCI: spinal cord injury, CB: Calbindin.

Electrophysiological alterations of the Purkinje cells and deep cerebellar neurons in a mouse model of Alzheimer disease (electrophysiology on cerebellum of AD mice)

Alzheimer's disease is histopathologically well defined by the presence of amyloid deposits and tau-related neurofibrillary tangles in crucial regions of the brain. Interest is growing in revealing and determining possible pathological markers also in the cerebellum as its involvement in cognitive functions is now well supported. Despite the central position of the Purkinje cell in the cerebellum, its electrophysiological behaviour in mouse models of Alzheimer's disease is scarce in the literature. Our first aim was here to focus on the electrophysiological behaviour of the cerebellum in awake mouse model of Alzheimer's disease (APPswe/PSEN1dE9) and the related performance on the water-maze test classically used in behavioural studies. We found prevalent signs of electrophysiological alterations in both Purkinje cells and deep cerebellar nuclei neurons which might explain the behavioural deficits reported during the water-maze test. The alterations of neurons firing were accompanied by a dual (~16 and ~228 Hz) local field potential's oscillation in the Purkinje cell layer of Alzheimer's disease mice which was concomitant to an important increase of both the simple and the complex spikes. In addition, β-amyloid deposits were present in the molecular layer of the cerebellum. These results highlight the importance of the output firing modification of the AD cerebellum that may indirectly impact the activity of its subcortical and cortical targets.

Cerebellar and Striatal Implications in Autism Spectrum Disorders: From Clinical Observations to Animal Models

Autism spectrum disorders (ASD) are complex conditions that stem from a combination of genetic, epigenetic and environmental influences during early pre- and postnatal childhood. The review focuses on the cerebellum and the striatum, two structures involved in motor, sensory, cognitive and social functions altered in ASD. We summarize clinical and fundamental studies highlighting the importance of these two structures in ASD. We further discuss the relation between cellular and molecular alterations with the observed behavior at the social, cognitive, motor and gait levels. Functional correlates regarding neuronal activity are also detailed wherever possible, and sexual dimorphism is explored pointing to the need to apprehend ASD in both sexes, as findings can be dramatically different at both quantitative and qualitative levels. The review focuses also on a set of three recent papers from our laboratory where we explored motor and gait function in various genetic and environmental ASD animal models. We report that motor and gait behaviors can constitute an early and quantitative window to the disease, as they often correlate with the severity of social impairments and loss of cerebellar Purkinje cells. The review ends with suggestions as to the main obstacles that need to be surpassed before an appropriate management of the disease can be proposed.

Operant conditioning deficits and modified local field potential activities in parvalbumin-deficient mice

Altered functioning of GABAergic interneurons expressing parvalbumin (PV) in the basal ganglia-thalamo-cortical circuit are likely to be involved in several human psychiatric disorders characterized by deficits in attention and sensory gating with dysfunctional decision-making behavior. However, the contribution of these interneurons in the ability to acquire demanding learning tasks remains unclear. Here, we combine an operant conditioning task with local field potentials simultaneously recorded in several nuclei involved in reward circuits of wild-type (WT) and PV-deficient (PVKO) mice, which are characterized by changes in firing activity of PV-expressing interneurons. In comparison with WT mice, PVKO animals presented significant deficits in the acquisition of the selected learning task. Recordings from prefrontal cortex, nucleus accumbens (NAc) and hippocampus showed significant decreases of the spectral power in beta and gamma bands in PVKO compared with WT mice particularly during the performance of the operant conditioning task. From the first to the last session, at all frequency bands the spectral power in NAc tended to increase in WT and to decrease in PVKO. Results indicate that PV deficiency impairs signaling necessary for instrumental learning and the recognition of natural rewards.

Cellular, Molecular and Biochemical Impacts of Silver Nanoparticles on Rat Cerebellar Cortex

BACKGROUND

The excessive exposure to silver nanoparticles (Ag-NPs) has raised concerns about their possible risks to the human health. The brain is a highly vulnerable organ to nano-silver harmfulness. The aim of this work was to evaluate the impacts of Ag-NPs exposure on the cerebellar cortex of rats.

METHODS

Rats were assigned to: Control, vehicle control and Ag-NP-exposed groups (at doses of 10 mg and 30 mg/kg/day). Samples were processed for light and electron microscopy examinations. Immunohistochemical localization of c-Jun N-terminal kinase (JNK), nuclear factor kappa beta (NF-κB) and calbindin D28k (CB) proteins was performed. Analyses of expression of DNA damage inducible transcript 4 (Ddit4), flavin containing monooxygenase 2 (FMO2) and thioredoxin-interacting protein (Txnip) genes were done. Serum levels of inflammatory cytokines were also measured.

RESULTS

Ag-NPs enhanced apoptosis as evident by upregulation of Ddit4 gene expressions and JNK protein immune expressions. Alterations of redox homeostasis were verified by enhancement of Txnip and FMO2 gene expressions, favoring the activation of inflammatory responses by increasing NF-κB protein immune expressions and serum inflammatory mediator levels. Another cytotoxic effect was the reduction of immune expressions of the calcium regulator CB.

CONCLUSION

Ag-NPs exposure provoked biochemical, cellular and molecular changes of rat cerebellar cortex in a dose-dependent manner.

Calcium-binding proteins are altered in the cerebellum in schizophrenia

Alterations in the cortico-cerebellar-thalamic-cortical circuit might underlie the diversity of symptoms in schizophrenia. However, molecular changes in cerebellar neuronal circuits, part of this network, have not yet been fully determined. Using LC-MS/MS, we screened altered candidates in pooled grey matter of cerebellum from schizophrenia subjects who committed suicide (n = 4) and healthy individuals (n = 4). Further validation by immunoblotting of three selected candidates was performed in two cohorts comprising schizophrenia (n = 20), non-schizophrenia suicide (n = 6) and healthy controls (n = 21). We found 99 significantly altered proteins, 31 of them previously reported in other brain areas by proteomic studies. Transport function was the most enriched category, while cell communication was the most prevalent function. For validation, we selected the vacuolar proton pump subunit 1 (VPP1), from transport, and two EF-hand calcium-binding proteins, calmodulin and parvalbumin, from cell communication. All candidates showed significant changes in schizophrenia (n = 7) compared to controls (n = 7). VPP1 was altered in the non-schizophrenia suicide group and increased levels of parvalbumin were linked to antipsychotics. Further validation in an independent cohort of non-suicidal chronic schizophrenia subjects (n = 13) and non-psychiatric controls (n = 14) showed that parvalbumin was increased, while calmodulin was decreased in schizophrenia. Our findings provide evidence of calcium-binding protein dysregulation in the cerebellum in schizophrenia, suggesting an impact on normal calcium-dependent synaptic functioning of cerebellar circuits. Our study also links VPP1 to suicide behaviours, suggesting a possible impairment in vesicle neurotransmitter refilling and release in these phenotypes.

Cytosolic Ca2+ Buffers Are Inherently Ca2+ Signal Modulators

For precisely regulating intracellular Ca²⁺ signals in a time- and space-dependent manner, cells make use of various components of the "Ca²⁺ signaling toolkit," including Ca²⁺ entry and Ca²⁺ extrusion systems. A class of cytosolic Ca²⁺-binding proteins termed Ca²⁺ buffers serves as modulators of such, mostly short-lived Ca²⁺ signals. Prototypical Ca²⁺ buffers include parvalbumins (α and β isoforms), calbindin-D9k, calbindin-D28k, and calretinin. Although initially considered to function as pure Ca²⁺ buffers, that is, as intracellular Ca²⁺ signal modulators controlling the shape (amplitude, decay, spread) of Ca²⁺ signals, evidence has accumulated that calbindin-D28k and calretinin have additional Ca²⁺ sensor functions. These other functions are brought about by direct interactions with target proteins, thereby modulating their targets' function/activity. Dysregulation of Ca²⁺ buffer expression is associated with several neurologic/neurodevelopmental disorders including autism spectrum disorder (ASD) and schizophrenia. In some cases, the presence of these proteins is presumed to confer a neuroprotective effect, as evidenced in animal models of Parkinson's or Alzheimer's disease.

Circadian Analysis of the Mouse Cerebellum Proteome

The cerebellum contains a circadian clock, generating internal temporal signals. The daily oscillations of cerebellar proteins were investigated in mice using a large-scale two-dimensional difference in gel electrophoresis (2D-DIGE). Analysis of 2D-DIGE gels highlighted the rhythmic variation in the intensity of 27/588 protein spots (5%) over 24 h based on cosinor regression. Notably, the rhythmic expression of most abundant cerebellar proteins was clustered in two main phases (i.e., midday and midnight), leading to bimodal distribution. Only six proteins identified here to be rhythmic in the cerebellum are also known to oscillate in the suprachiasmatic nuclei, including two proteins involved in the synapse activity (Synapsin 2 [SYN2] and vesicle-fusing ATPase [NSF]), two others participating in carbohydrate metabolism (triosephosphate isomerase (TPI1] and alpha-enolase [ENO1]), Glutamine synthetase (GLUL), as well as Tubulin alpha (TUBA4A). Most oscillating cerebellar proteins were not previously identified in circadian proteomic analyses of any tissue. Strikingly, the daily accumulation of mitochondrial proteins was clustered to the mid-resting phase, as previously observed for distinct mitochondrial proteins in the liver. Moreover, a number of rhythmic proteins, such as SYN2, NSF and TPI1, were associated with non-rhythmic mRNAs, indicating widespread post-transcriptional control in cerebellar oscillations. Thus, this study highlights extensive rhythmic aspects of the cerebellar proteome.

Purkinje cell BKchannel ablation induces abnormal rhythm in deep cerebellar nuclei and prevents LTD

Purkinje cells (PC) control deep cerebellar nuclei (DCN), which in turn inhibit inferior olive nucleus, closing a positive feedback loop via climbing fibers. PC highly express potassium BK channels but their contribution to the olivo-cerebellar loop is not clear. Using multiple-unit recordings in alert mice we found in that selective deletion of BK channels in PC induces a decrease in their simple spike firing with a beta-range bursting pattern and fast intraburst frequency (~200 Hz). To determine the impact of this abnormal rhythm on the olivo-cerebellar loop we analyzed simultaneous rhythmicity in different cerebellar structures. We found that this abnormal PC rhythmicity is transmitted to DCN neurons with no effect on their mean firing frequency. Long term depression at the parallel-PC synapses was altered and the intra-burst complex spike spikelets frequency was increased without modification of the mean complex spike frequency in BK-PC^−/− mice. We argue that the ataxia present in these conditional knockout mice could be explained by rhythmic disruptions transmitted from mutant PC to DCN but not by rate code modification only. This suggests a neuronal mechanism for ataxia with possible implications for human disease.

Beta-gamma burst stimulations of the inferior olive induce high-frequency oscillations in the deep cerebellar nuclei

The cerebellum displays various sorts of rhythmic activities covering both low- and high-frequency oscillations. These cerebellar high-frequency oscillations were observed in the cerebellar cortex. Here, we hypothesised that not only is the cerebellar cortex a generator of high-frequency oscillations but also that the deep cerebellar nuclei may also play a similar role. Thus, we analysed local field potentials and single-unit activities in the deep cerebellar nuclei before, during and after electric stimulation in the inferior olive of awake mice. A high-frequency oscillation of 350 Hz triggered by the stimulation of the inferior olive, within the beta-gamma range, was observed in the deep cerebellar nuclei. The amplitude and frequency of the oscillation were independent of the frequency of stimulation. This oscillation emerged during the period of stimulation and persisted after the end of the stimulation. The oscillation coincided with the inhibition of deep cerebellar neurons. As the inhibition of the deep cerebellar nuclei is related to inhibitory inputs from Purkinje cells, we speculate that the oscillation represents the unmasking of the synchronous activation of another subtype of deep cerebellar neuronal subtype, devoid of GABA receptors and under the direct control of the climbing fibres from the inferior olive. Still, the mechanism sustaining this oscillation remains to be deciphered. Our study sheds new light on the role of the olivo-cerebellar loop as the final output control of the intercerebellar circuitry.

Oscillations, Timing, Plasticity, and Learning in the Cerebellum

The highly stereotyped, crystal-like architecture of the cerebellum has long served as a basis for hypotheses with regard to the function(s) that it subserves. Historically, most clinical observations and experimental work have focused on the involvement of the cerebellum in motor control, with particular emphasis on coordination and learning. Two main models have been suggested to account for cerebellar functioning. According to Llinás's theory, the cerebellum acts as a control machine that uses the rhythmic activity of the inferior olive to synchronize Purkinje cell populations for fine-tuning of coordination. In contrast, the Ito-Marr-Albus theory views the cerebellum as a motor learning machine that heuristically refines synaptic weights of the Purkinje cell based on error signals coming from the inferior olive. Here, we review the role of timing of neuronal events, oscillatory behavior, and synaptic and non-synaptic influences in functional plasticity that can be recorded in awake animals in various physiological and pathological models in a perspective that also includes non-motor aspects of cerebellar function. We discuss organizational levels from genes through intracellular signaling, synaptic network to system and behavior, as well as processes from signal production and processing to memory, delegation, and actual learning. We suggest an integrative concept for control and learning based on articulated oscillation templates.

BK Channels in the Central Nervous System

Large conductance Ca(2+)- and voltage-activated K(+) (BK) channels are widely distributed in the postnatal central nervous system (CNS). BK channels play a pleiotropic role in regulating the activity of brain and spinal cord neural circuits by providing a negative feedback mechanism for local increases in intracellular Ca(2+) concentrations. In neurons, they regulate the timing and duration of K(+) influx such that they can either increase or decrease firing depending on the cellular context, and they can suppress neurotransmitter release from presynaptic terminals. In addition, BK channels located in astrocytes and arterial myocytes modulate cerebral blood flow. Not surprisingly, both loss and gain of BK channel function have been associated with CNS disorders such as epilepsy, ataxia, mental retardation, and chronic pain. On the other hand, the neuroprotective role played by BK channels in a number of pathological situations could potentially be leveraged to correct neurological dysfunction.

Reduction in parvalbumin expression not loss of the parvalbumin-expressing GABA interneuron subpopulation in genetic parvalbumin and shank mouse models of autism

BACKGROUND

A reduction of the number of parvalbumin (PV)-immunoreactive (PV(+)) GABAergic interneurons or a decrease in PV immunoreactivity was reported in several mouse models of autism spectrum disorders (ASD). This includes Shank mutant mice, with SHANK being one of the most important gene families mutated in human ASD. Similar findings were obtained in heterozygous (PV+/-) mice for the Pvalb gene, which display a robust ASD-like phenotype. Here, we addressed the question whether the observed reduction in PV immunoreactivity was the result of a decrease in PV expression levels and/or loss of the PV-expressing GABA interneuron subpopulation hereafter called "Pvalb neurons". The two alternatives have important implications as they likely result in opposing effects on the excitation/inhibition balance, with decreased PV expression resulting in enhanced inhibition, but loss of the Pvalb neuron subpopulation in reduced inhibition.

METHODS

Stereology was used to determine the number of Pvalb neurons in ASD-associated brain regions including the medial prefrontal cortex, somatosensory cortex and striatum of PV-/-, PV+/-, Shank1-/- and Shank3B-/- mice. As a second marker for the identification of Pvalb neurons, we used Vicia Villosa Agglutinin (VVA), a lectin recognizing the specific extracellular matrix enwrapping Pvalb neurons. PV protein and Pvalb mRNA levels were determined quantitatively by Western blot analyses and qRT-PCR, respectively.

RESULTS

Our analyses of total cell numbers in different brain regions indicated that the observed "reduction of PV(+) neurons" was in all cases, i.e., in PV+/-, Shank1-/- and Shank3B-/- mice, due to a reduction in Pvalb mRNA and PV protein, without any indication of neuronal cell decrease/loss of Pvalb neurons evidenced by the unaltered numbers of VVA(+) neurons.

CONCLUSIONS

Our findings suggest that the PV system might represent a convergent downstream endpoint for some forms of ASD, with the excitation/inhibition balance shifted towards enhanced inhibition due to the down-regulation of PV being a promising target for future pharmacological interventions. Testing whether approaches aimed at restoring normal PV protein expression levels and/or Pvalb neuron function might reverse ASD-relevant phenotypes in mice appears therefore warranted and may pave the way for novel therapeutic treatment strategies.

EF-hand protein Ca2+ buffers regulate Ca2+ influx and exocytosis in sensory hair cells

EF-hand Ca(2+)-binding proteins are thought to shape the spatiotemporal properties of cellular Ca(2+) signaling and are prominently expressed in sensory hair cells in the ear. Here, we combined genetic disruption of parvalbumin-α, calbindin-D28k, and calretinin in mice with patch-clamp recording, in vivo physiology, and mathematical modeling to study their role in Ca(2+) signaling, exocytosis, and sound encoding at the synapses of inner hair cells (IHCs). IHCs lacking all three proteins showed excessive exocytosis during prolonged depolarizations, despite enhanced Ca(2+)-dependent inactivation of their Ca(2+) current. Exocytosis of readily releasable vesicles remained unchanged, in accordance with the estimated tight spatial coupling of Ca(2+) channels and release sites (effective "coupling distance" of 17 nm). Substitution experiments with synthetic Ca(2+) chelators indicated the presence of endogenous Ca(2+) buffers equivalent to 1 mM synthetic Ca(2+)-binding sites, approximately half of them with kinetics as fast as 1,2-Bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (BAPTA). Synaptic sound encoding was largely unaltered, suggesting that excess exocytosis occurs extrasynaptically. We conclude that EF-hand Ca(2+) buffers regulate presynaptic IHC function for metabolically efficient sound coding.

Disruption of the LTD dialogue between the cerebellum and the cortex in Angelman syndrome model: a timing hypothesis

Angelman syndrome (AS) is a genetic neurodevelopmental disorder in which cerebellar functioning impairment has been documented despite the absence of gross structural abnormalities. Characteristically, a spontaneous 160 Hz oscillation emerges in the Purkinje cells network of the Ube3a (m-/p+) Angelman mouse model. This abnormal oscillation is induced by enhanced Purkinje cell rhythmicity and hypersynchrony along the parallel fiber beam. We present a pathophysiological hypothesis for the neurophysiology underlying major aspects of the clinical phenotype of AS, including cognitive, language and motor deficits, involving long-range connection between the cerebellar and the cortical networks. This hypothesis states that the alteration of the cerebellar rhythmic activity impinges cerebellar long-term depression (LTD) plasticity, which in turn alters the LTD plasticity in the cerebral cortex. This hypothesis was based on preliminary experiments using electrical stimulation of the whiskers pad performed in alert mice showing that after a 8 Hz LTD-inducing protocol, the cerebellar LTD accompanied by a delayed response in the wild type (WT) mice is missing in Ube3a (m-/p+) mice and that the LTD induced in the barrel cortex following the same peripheral stimulation in wild mice is reversed into a LTP in the Ube3a (m-/p+) mice. The control exerted by the cerebellum on the excitation vs. inhibition balance in the cerebral cortex and possible role played by the timing plasticity of the Purkinje cell LTD on the spike-timing dependent plasticity (STDP) of the pyramidal neurons are discussed in the context of the present hypothesis.

Subcellular structural plasticity caused by the absence of the fast Ca(2+) buffer calbindin D-28k in recurrent collaterals of cerebellar Purkinje neurons

Purkinje cells (PC) control spike timing of neighboring PC by their recurrent axon collaterals. These synapses underlie fast cerebellar oscillations and are characterized by a strong facilitation within a time window of <20 ms during paired-pulse protocols. PC express high levels of the fast Ca(2+) buffer protein calbindin D-28k (CB). As expected from the absence of a fast Ca(2+) buffer, presynaptic action potential-evoked [Ca(2+)]i transients were previously shown to be bigger in PC boutons of young (second postnatal week) CB-/- mice, yet IPSC mean amplitudes remained unaltered in connected CB-/- PC. Since PC spine morphology is altered in adult CB-/- mice (longer necks, larger spine head volume), we summoned that morphological compensation/adaptation mechanisms might also be induced in CB-/- PC axon collaterals including boutons. In these mice, biocytin-filled PC reconstructions revealed that the number of axonal varicosities per PC axon collateral was augmented, mostly confined to the granule cell layer. Additionally, the volume of individual boutons was increased, evidenced from z-stacks of confocal images. EM analysis of PC-PC synapses revealed an enhancement in active zone (AZ) length by approximately 23%, paralleled by a higher number of docked vesicles per AZ in CB-/- boutons. Moreover, synaptic cleft width was larger in CB-/- (23.8 ± 0.43 nm) compared to wild type (21.17 ± 0.39 nm) synapses. We propose that the morphological changes, i.e., the larger bouton volume, the enhanced AZ length and the higher number of docked vesicles, in combination with the increase in synaptic cleft width likely modifies the GABA release properties at this synapse in CB-/- mice. We view these changes as adaptation/homeostatic mechanisms to likely maintain characteristics of synaptic transmission in the absence of the fast Ca(2+) buffer CB. Our study provides further evidence on the functioning of the Ca(2+) homeostasome.

Neuronal oscillations in Golgi cells and Purkinje cells are accompanied by decreases in Shannon information entropy

Neuronal oscillations have been shown to contribute to the function of the cerebral cortex by coordinating the neuronal activities of distant cortical regions via a temporal synchronization of neuronal discharge patterns. This can occur regardless whether these regions are linked by cortico-cortical pathways or not. Less is known concerning the role of neuronal oscillations in the cerebellum. Golgi cells and Purkinje cells are both principal cell types in the cerebellum. Purkinje cells are the sole output cells of the cerebellar cortex while Golgi cells contribute to information processing at the input stage of the cerebellar cortex. Both cell types have large cell bodies, as well as dendritic structures, that can generate large currents. The discharge patterns of both these cell types also exhibit oscillations. In view of the massive afferent information conveyed by the mossy fiber-granule cell system to different and distant areas of the cerebellar cortex, it is relevant to inquire the role of cerebellar neuronal oscillations in information processing. In this study, we compared the discharge patterns of Golgi cells and Purkinje cells in conscious rats and in rats anesthetized with urethane. We assessed neuronal oscillations by analyzing the regularity in the timing of individual spikes within a spike train by using autocorrelograms and fast-Fourier transform. We measured the differences in neuronal oscillations and the amount of information content in a spike train (defined by Shannon entropy processed per unit time) in rats under anesthesia and in conscious, awake rats. Our findings indicated that anesthesia caused more prominent neuronal oscillations in both Golgi cells and Purkinje cells accompanied by decreases in Shannon information entropy in their spike trains.

Calbindin-D28K immunoreactivity in the human cerebellar cortex

Calbindin-D28k (CB) is a calcium-binding protein largely distributed in the cerebellum of various species of vertebrates. As regards the human cerebellar cortex, precise data on the distribution of CB have not yet been reported. Aim of the present work was to analyze the distribution of CB in postmortem samples of human cerebellar cortex using light microscopy immunohistochemical techniques. Immunoreactivity to CB was detected within neuronal bodies and processes distributed in all cortex layers. In the molecular layer, the immunoreactivity was observed in subpopulations of stellate and basket neurons. In the Purkinje neuron layer, the immunoreactivity was observed in practically all the Purkinje neurons. In the granular layer, the immunoreactivity was observed in subpopulations of granules, of Golgi neurons, and also of other types of large neurons (candelabrum, Lugaro neurons, etc.). Immunoreactivity to CB was also observed in axon terminals distributed throughout the cortex according to layer-specific patterns of distribution. The qualitative and quantitative patterns of distribution of CB showed no difference among the different lobes of the cerebellar cortex. This study reports that CB is expressed by different neuron types, both inhibitory (GABAergic) and excitatory (glutamatergic), involved in both intrinsic and extrinsic circuits of the human cerebellar cortex. The study provides further insights on the functional role of CB and on the neuronal types of the cerebellar cortex in which it is expressed.

Translational approach to behavioral learning: lessons from cerebellar plasticity

The role of cerebellar plasticity has been increasingly recognized in learning. The privileged relationship between the cerebellum and the inferior olive offers an ideal circuit for attempting to integrate the numerous evidences of neuronal plasticity into a translational perspective. The high learning capacity of the Purkinje cells specifically controlled by the climbing fiber represents a major element within the feed-forward and feedback loops of the cerebellar cortex. Reciprocally connected with the basal ganglia and multimodal cerebral domains, this cerebellar network may realize fundamental functions in a wide range of behaviors. This review will outline the current understanding of three main experimental paradigms largely used for revealing cerebellar functions in behavioral learning: (1) the vestibuloocular reflex and smooth pursuit control, (2) the eyeblink conditioning, and (3) the sensory envelope plasticity. For each of these experimental conditions, we have critically revisited the chain of causalities linking together neural circuits, neural signals, and plasticity mechanisms, giving preference to behaving or alert animal physiology. Namely, recent experimental approaches mixing neural units and local field potentials recordings have demonstrated a spike timing dependent plasticity by which the cerebellum remains at a strategic crossroad for deciphering fundamental and translational mechanisms from cellular to network levels.

The effect of parvalbumin deficiency on the acoustic startle response and prepulse inhibition in mice

The strength of the acoustic startle response (ASR) to short bursts of broadband noise or tone pips (4, 8 and 16 kHz) and the prepulse inhibition (PPI) of the ASR elicited by prepulse tones (4, 8 and 16 kHz) were measured in parvalbumin-deficient (PV-/-) mice and in age-matched PV+/+ mice as controls. Hearing thresholds as determined from recordings of auditory brainstem responses were found to be similar in both genotypes. The ASRs to broadband noise and tones of low and middle frequencies were stronger than the ASRs in response to high-frequency tones in both groups. In PV-/- mice, we observed smaller ASR amplitudes in response to relatively weak startling stimuli (80-90 dB sound pressure level (SPL)) of either broadband noise or 8-kHz tones compared to those recorded in PV+/+ mice. For these startling stimuli, PV-/- mice had higher ASR thresholds and longer ASR latencies. PPI of the ASR in PV-/- mice was less effective than in PV+/+ mice, for all tested prepulse frequencies (4, 8 or 16 kHz) at 70 dB SPL. Our findings demonstrate no effect of PV deficiency on hearing thresholds in PV-/- mice. However, the frequency-specific differences in the ASR and the significant reduction of PPI of ASR likely reflect specific changes of neuronal circuits, mainly inhibitory, in the auditory centers in PV-deficient mice.

Loss of DARPP-32 and calbindin in multiple system atrophy

We evaluated the immunohistochemical intensities of α-synuclein, phosphorylated α-synuclein (p-syn), dopamine- and cAMP-regulated phosphoprotein of 32 kDa (DARPP-32), calbindin-D 28k, calpain-cleaved carboxy-terminal 150-kDa spectrin fragment, and tyrosine hydroxylase in multiple system atrophy (MSA). The caudate head, anterior putamen, posterior putamen, substantia nigra, pontine nucleus, and cerebellar cortex from six MSA brains, six age-matched disease control brains (amyotrophic lateral sclerosis), and five control brains were processed for immunostaining by standard methods. Immunostaining for α-synuclein, p-syn, or both was increased in all areas examined in oligodendrocytes in MSA. Immunostaining for DARPP-32 and calbindin-D 28k was most prominently decreased in the posterior putamen, where neuronal loss was most prominent. Immunostaining for DARPP-32 and calbindin-D 28k was also diminished in the anterior putamen and caudate head, where neuronal loss was less prominent or absent. Calbindin immunostaining was also decreased in the dorsal tier of the substantia nigra and cerebellar cortex. Loss of immunostaining for DARPP-32 and calbindin-D 28k compared with that of neurons indicates calcium toxicity and disturbance of the phosphorylated state of proteins as relatively early events in the pathogenesis of MSA.

The calcium-binding protein parvalbumin modulates the firing 1 properties of the reticular thalamic nucleus bursting neurons

The reticular thalamic nucleus (RTN) of the mouse is characterized by an overwhelming majority of GABAergic neurons receiving afferences from both the thalamus and the cerebral cortex and sending projections mainly on thalamocortical neurons. The RTN neurons express high levels of the "slow Ca(2+) buffer" parvalbumin (PV) and are characterized by low-threshold Ca(2+) currents, I(T). We performed extracellular recordings in ketamine/xylazine anesthetized mice in the rostromedial portion of the RTN. In the RTN of wild-type and PV knockout (PVKO) mice we distinguished four types of neurons characterized on the basis of their firing pattern: irregular firing (type I), medium bursting (type II), long bursting (type III), and tonically firing (type IV). Compared with wild-type mice, we observed in the PVKOs the medium bursting (type II) more frequently than the long bursting type and longer interspike intervals within the burst without affecting the number of spikes. This suggests that PV may affect the firing properties of RTN neurons via a mechanism associated with the kinetics of burst discharges. Ca(v)3.2 channels, which mediate the I(T) currents, were more localized to the somatic plasma membrane of RTN neurons in PVKO mice, whereas Ca(v)3.3 expression was similar in both genotypes. The immunoelectron microscopy analysis showed that Ca(v)3.2 channels were localized at active axosomatic synapses, thus suggesting that the differential localization of Ca(v)3.2 in the PVKOs may affect bursting dynamics. Cross-correlation analysis of simultaneously recorded neurons from the same electrode tip showed that about one-third of the cell pairs tended to fire synchronously in both genotypes, independent of PV expression. In summary, PV deficiency does not affect the functional connectivity between RTN neurons but affects the distribution of Ca(v)3.2 channels and the dynamics of burst discharges of RTN cells, which in turn regulate the activity in the thalamocortical circuit.

Functional integration of calcium regulatory mechanisms at Purkinje neuron synapses

Cerebellar Purkinje neurons receive synaptic inputs from three different sources: the excitatory parallel fibre and climbing fibre synapses as well as the inhibitory synapses from molecular layer stellate and basket cells. These three synaptic systems use distinct mechanisms in order to generate Ca(2+) signals that are specialized for specific modes of neurotransmitter release and post-synaptic signal integration. In this review, we first describe the repertoire of Ca(2+) regulatory mechanisms that generate and regulate the amplitude and timing of Ca(2+) fluxes during synaptic transmission and then explore how these mechanisms interact to generate the unique functional properties of each of the Purkinje neuron synapses.

Purkinje cell dysfunction and loss in a knock-in mouse model of Huntington disease

Huntington Disease (HD) is an autosomal dominant neurological disorder characterized by motor, psychiatric and cognitive disturbances. Recent evidence indicates that the viability and function of cerebellar Purkinje cells (PCs) are compromised in an aggressive mouse model of HD. Here we investigate whether this is also the case in the HdhQ200 knock-in mouse model of HD. Using quantitative-real time-PCR and immunofluorescence, we observed a loss of the PC marker and calcium buffer calbindin in 50week-old symptomatic mice. Reductions were also observed in parvalbumin and glutamic acid decarboxylase protein expression, most markedly in the molecular cell layer. Stereological analysis revealed an overall reduction in the PC population in HdhQ200/Q200 mice by nearly 40%, and loose patch electrophysiology of remaining PCs indicated a reduction in firing rate in HD mice compared to control littermates. Taken together, these data demonstrate that PC survival and function are compromised in a mouse model of adult-onset HD and suggest that further experiments should investigate the contribution of PC death and dysfunction to HD-associated motor impairment.

The arcuate nucleus of the C57BL/6J mouse hindbrain is a displaced part of the inferior olive

The arcuate nucleus is a prominent cell group in the human hindbrain, characterized by its position on the pial surface of the pyramid. It is considered to be a precerebellar nucleus and has been implicated in the pathology of several disorders of respiration. An arcuate nucleus has not been convincingly demonstrated in other mammals, but we have found a similarly positioned nucleus in the C57BL/6J mouse. The mouse arcuate nucleus consists of a variable group of neurons lying on the pial surface of the pyramid. The nucleus is continuous with the ventrolateral part of the principal nucleus of the inferior olive and both groups are calbindin positive. At first we thought that this mouse nucleus was homologous with the human arcuate nucleus, but we have discovered that the neurons of the human nucleus are calbindin negative, and are therefore not olivary in nature. We have compared the mouse arcuate neurons with those of the inferior olive in terms of molecular markers and cerebellar projection. The neurons of the arcuate nucleus and of the inferior olive share three major characteristics: they both contain neurons utilizing glutamate, serotonin or acetylcholine as neurotransmitters; they both project to the contralateral cerebellum, and they both express a number of genes not present in the major mossy fiber issuing precerebellar nuclei. Most importantly, both cell groups express calbindin in an area of the ventral hindbrain almost completely devoid of calbindin-positive cells. We conclude that the neurons of the hindbrain mouse arcuate nucleus are a displaced part of the inferior olive, possibly separated by the caudal growth of the pyramidal tract during development. The arcuate nucleus reported in the C57BL/6J mouse can therefore be regarded as a subgroup of the rostral inferior olive, closely allied with the ventral tier of the principal nucleus.

Sex differences in the cerebellum and frontal cortex: roles of estrogen receptor alpha and sex chromosome genes

Most neurobehavioral diseases are sexually dimorphic in their incidence, and sex differences in the brain may be key for understanding and treating these diseases. Calbindin (Calb) D28K is used as a biomarker for the well-studied sexually dimorphic nucleus, a hypothalamic structure that is larger in males than in females. In the current study weanling C56BL/6J mice were used to examine sex differences in the Calb protein and message focusing on regions outside of the hypothalamus. A robust sex difference was found in Calb in the frontal cortex (FC) and cerebellum (CB; specifically in Purkinje cells); mRNA and protein were higher in females than in males. Using 2 mouse lines, i.e. one with a complete deletion of estrogen receptor alpha (ERα) and the other with uncoupled gonads and sex chromosomes, we probed the mechanisms that underlie sexual dimorphisms. In the FC, deletion of ERα reduced Calb1 mRNA in females compared to males. In addition, females with XY sex chromosomes had levels of Calb1 equal to those of males. Thus, both ERα and the sex chromosome complement regulate Calb1 in the FC. In the CB, ERα knockout mice of both sexes had reduced Calb1 mRNA, yet sex differences were retained. However, the sex chromosome complement, regardless of gonadal sex, dictated Calb1 mRNA levels. Mice with XX chromosomes had significantly greater Calb1 than did XY mice. This is the first study demonstrating that sex chromosome genes are a driving force producing sex differences in the CB and FC, which are neuoranatomical regions involved in many normal functions and in neurobehavioral diseases.

Cytosolic Ca2+ buffers

"Ca(2+) buffers," a class of cytosolic Ca(2+)-binding proteins, act as modulators of short-lived intracellular Ca(2+) signals; they affect both the temporal and spatial aspects of these transient increases in [Ca(2+)](i). Examples of Ca(2+) buffers include parvalbumins (α and β isoforms), calbindin-D9k, calbindin-D28k, and calretinin. Besides their proven Ca(2+) buffer function, some might additionally have Ca(2+) sensor functions. Ca(2+) buffers have to be viewed as one of the components implicated in the precise regulation of Ca(2+) signaling and Ca(2+) homeostasis. Each cell is equipped with proteins, including Ca(2+) channels, transporters, and pumps that, together with the Ca(2+) buffers, shape the intracellular Ca(2+) signals. All of these molecules are not only functionally coupled, but their expression is likely to be regulated in a Ca(2+)-dependent manner to maintain normal Ca(2+) signaling, even in the absence or malfunctioning of one of the components.

Developmental and age-related changes of peptidylarginine deiminase 2 in the mouse brain

Peptidylarginine deiminases (PADs) are a group of posttranslational modification enzymes that citrullinate (deiminate) protein arginine residues in a Ca(2+)-dependent manner. Enzymatic citrullination abolishes positive charges of native protein molecules, inevitably causing significant alterations in their structure and functions. Among the five isoforms of PADs, PAD2 and PAD4 are proved occupants of the central nervous system (CNS), and especially PAD2 is a main PAD enzyme expressed in the CNS. We previously reported that abnormal protein citrullination by PAD2 has been closely associated with the pathogenesis of neurodegenerative disorders such as Alzheimer's disease and prion disease. Protein citrullination in these patients is thought to play a role during the initiation and/or progression of disease. However, the contribution of changes in PAD2 levels, and consequent citrullination, during developmental and aging processes remained unclear. Therefore, we used quantitative real-time RT-PCR, Western blot analysis, and immunohistochemical methods to measure PAD2 expression and localization in the brain during those processes. PAD2 mRNA expression was detected in the brains of mice as early as embryonic day 15, and its expression in cerebral cortex, hippocampus, and cerebellum increased significantly as the animals aged from 3 to 30 months old. No citrullinated proteins were detected during that period. Moreover, we found here, for the first time, that PAD2 localized specifically in the neuronal cells of the cerebral cortex and Purkinje cells of the cerebellum. These findings indicate that, despite PAD2's normally inactive status, it becomes active and citrullinates cellular proteins, but only when the intracellular Ca(2+) balance is upset during neurodegenerative changes.

Spatiotemporal patterns of electrocorticographic very fast oscillations (> 80 Hz) consistent with a network model based on electrical coupling between principal neurons

PURPOSE

We sought to characterize spatial and temporal patterns of electrocorticography (ECoG) very fast oscillations (> ∼80 Hz, VFOs) prior to seizures in human frontotemporal neocortex, and to develop a testable network model of these patterns.

METHODS

ECoG data were recorded with subdural grids from two preoperative patients with seizures of frontal lobe onset in an epilepsy monitoring unit. VFOs were recorded from rat neocortical slices. A "cellular automaton" model of network oscillations was developed, extending ideas of Traub et al. (Neuroscience, 92, 1999, 407) and Lewis & Rinzel (Network: Comput Neural Syst, 11, 2000, 299); this model is based on postulated electrical coupling between pyramidal cell axons.

RESULTS

Layer 5 of rat neocortex, in vitro, can generate VFOs when chemical synapses are blocked. Human epileptic neocortex, in situ, produces preseizure VFOs characterized by the sudden appearance of "blobs" of activity that evolve into spreading wavefronts. When wavefronts meet, they coalesce and propagate perpendicularly but never pass through each other. This type of pattern has been described by Lewis & Rinzel in cellular automaton models with spatially localized connectivity, and is demonstrated here with 120,000- to 5,760,000-cell models. We provide a formula for estimating VFO period from structural parameters and estimate the spatial scale of the connectivity.

DISCUSSION

These data provide further evidence, albeit indirect, that preseizure VFOs are generated by networks of pyramidal neurons coupled by gap junctions, each predominantly confined to pairs of neurons having somata separated by < ∼1-2 mm. Plausible antiepileptic targets are tissue mechanisms, such as pH regulation, that influence gap-junction conductance.

BK channels control cerebellar Purkinje and Golgi cell rhythmicity in vivo

Calcium signaling plays a central role in normal CNS functioning and dysfunction. As cerebellar Purkinje cells express the major regulatory elements of calcium control and represent the sole integrative output of the cerebellar cortex, changes in neural activity- and calcium-mediated membrane properties of these cells are expected to provide important insights into both intrinsic and network physiology of the cerebellum. We studied the electrophysiological behavior of Purkinje cells in genetically engineered alert mice that do not express BK calcium-activated potassium channels and in wild-type mice with pharmacological BK inactivation. We confirmed BK expression in Purkinje cells and also demonstrated it in Golgi cells. We demonstrated that either genetic or pharmacological BK inactivation leads to ataxia and to the emergence of a beta oscillatory field potential in the cerebellar cortex. This oscillation is correlated with enhanced rhythmicity and synchronicity of both Purkinje and Golgi cells. We hypothesize that the temporal coding modification of the spike firing of both Purkinje and Golgi cells leads to the pharmacologically or genetically induced ataxia.

Compensatory regulation of Cav2.1 Ca2+ channels in cerebellar Purkinje neurons lacking parvalbumin and calbindin D-28k

Ca(v)2.1 channels regulate Ca(2+) signaling and excitability of cerebellar Purkinje neurons. These channels undergo a dual feedback regulation by incoming Ca(2+) ions, Ca(2+)-dependent facilitation and inactivation. Endogenous Ca(2+)-buffering proteins, such as parvalbumin (PV) and calbindin D-28k (CB), are highly expressed in Purkinje neurons and therefore may influence Ca(v)2.1 regulation by Ca(2+). To test this, we compared Ca(v)2.1 properties in dissociated Purkinje neurons from wild-type (WT) mice and those lacking both PV and CB (PV/CB(-/-)). Unexpectedly, P-type currents in WT and PV/CB(-/-) neurons differed in a way that was inconsistent with a role of PV and CB in acute modulation of Ca(2+) feedback to Ca(v)2.1. Ca(v)2.1 currents in PV/CB(-/-) neurons exhibited increased voltage-dependent inactivation, which could be traced to decreased expression of the auxiliary Ca(v)beta(2a) subunit compared with WT neurons. Although Ca(v)2.1 channels are required for normal pacemaking of Purkinje neurons, spontaneous action potentials were not different in WT and PV/CB(-/-) neurons. Increased inactivation due to molecular switching of Ca(v)2.1 beta-subunits may preserve normal activity-dependent Ca(2+) signals in the absence of Ca(2+)-buffering proteins in PV/CB(-/-) Purkinje neurons.

A Ca(2+)-binding protein with numerous roles and uses: parvalbumin in molecular biology and physiology

Parvalbumins (PVs) are acidic, intracellular Ca(2+)-binding proteins of low molecular weight. They are associated with several Ca(2+)-mediated cellular activities and physiological processes. It has been suggested that PV might function as a "Ca2+ shuttle" transporting Ca2+ from troponin-C (TnC) to the sarcoplasmic reticulum (SR) Ca2+ pump during muscle relaxation. Thus, PV may contribute to the performance of rapid, phasic movements by accelerating the contraction-relaxation cycle of fast-twitch muscle fibers. Interestingly, PVs promote the generation of power stroke in fish by speeding up the rate of relaxation and thus provide impetus to attain maximal sustainable speeds. However, immunological monitoring of diverse tissues demonstrated that PVs are also present in non-muscle cells. The axoplasmic transport and various intracellular secretory mechanisms including the endocrine secretions seem to be controlled by the Ca2+ regulation machinery. Any defect in the Ca2+ handling apparatus may cause several clinical problems; for instance, PV deficiency alters the neuronal activity, a key mechanism leading to epileptic seizures. Moreover, atypical relaxation of the heart results in diastolic dysfunction, which is a major cause of heart failure predominantly among the aged people. PV may offer a unique potential to correct defective relaxation in energetically compromised failing hearts through PV gene transfer. Consequently, PV gene transfer may present a new therapeutic approach to correct cellular disturbances in Ca2+ signaling pathways of diseased organs. Hence, PVs appear to be amazingly useful candidate proteins regulating a variety of cellular functions through action on Ca2+ flux management.

Model of very fast (> 75 Hz) network oscillations generated by electrical coupling between the proximal axons of cerebellar Purkinje cells

Very fast oscillations (VFO; > 75 Hz) occur transiently in vivo, in the cerebellum of mice genetically modified to model Angelman syndrome, and in a mouse model of fetal alcohol syndrome. We recently reported VFO in slices of mouse cerebellar cortex (Crus I and II of ansiform and paramedian lobules), either in association with gamma oscillations (approximately 40 Hz, evoked by nicotine) or in isolation [evoked by nicotine in combination with gamma-aminobutyric acid (GABA)(A) receptor blockade]. The experimental data suggest a role for electrical coupling between Purkinje cells (blockade of VFO by drugs reducing gap junction conductance and spikelets in some Purkinje cells); and the data suggest the specific involvement of Purkinje cell axons (because of field oscillation maxima in the granular layer). We show here that a detailed network model (1000 multicompartment Purkinje cells) replicates the experimental data when gap junctions are located on the proximal axons of Purkinje cells, provided sufficient spontaneous firing is present. Unlike other VFO models, most somatic spikelets do not correspond to axonal spikes in the parent axon, but reflect spikes in electrically coupled axons. The model predicts gating of VFO frequency by g(Na) inactivation, and experiments prolonging this inactivation time constant, with beta-pompilidotoxin, are consistent with this prediction. The model also predicts that cerebellar VFO can be explained as an electrically coupled system of axons that are not intrinsic oscillators: the electrically uncoupled cells do not individually oscillate (in the model) and axonal firing rates are much lower in the uncoupled state than in the coupled state.

The origin of the complex spike in cerebellar Purkinje cells

Activation of the climbing fiber input powerfully excites cerebellar Purkinje cells via hundreds of widespread dendritic synapses, triggering dendritic spikes as well as a characteristic high-frequency burst of somatic spikes known as the complex spike. To investigate the relationship between dendritic spikes and the spikelets within the somatic complex spike, and to evaluate the importance of the dendritic distribution of climbing fiber synapses, we made simultaneous somatic and dendritic patch-clamp recordings from Purkinje cells in cerebellar slices. Injection of large climbing fiber-like synaptic conductances at the soma using dynamic clamp was sufficient to reproduce the complex spike, independently of dendritic spikes, indicating that neither a dendritic synaptic distribution nor dendritic spikes are required. Furthermore, we found that dendritic spikes are not directly linked to spikelets in the complex spike, and that each dendritic spike is associated with only 0.24 +/- 0.09 extra somatic spikelets. Rather, we demonstrate that dendritic spikes regulate the pause in firing that follows the complex spike. Finally, using dual somatic and axonal recording, we show that all spikelets in the complex spike are axonally generated. Thus, complex spike generation proceeds relatively independently of dendritic spikes, reflecting the dual functional role of climbing fiber input: triggering plasticity at dendritic synapses and generating a distinct output signal in the axon. The encoding of dendritic spiking by the post-complex spike pause provides a novel computational function for dendritic spikes, which could serve to link these two roles at the level of the target neurons in the deep cerebellar nuclei.

Purkinje cell dysfunction and alteration of long-term synaptic plasticity in fetal alcohol syndrome

In cerebellum and other brain regions, neuronal cell death because of ethanol consumption by the mother is thought to be the leading cause of neurological deficits in the offspring. However, little is known about how surviving cells function. We studied cerebellar Purkinje cells in vivo and in vitro to determine whether function of these cells was altered after prenatal ethanol exposure. We observed that Purkinje cells that were prenatally exposed to ethanol presented decreased voltage-gated calcium currents because of a decreased expression of the gamma-isoform of protein kinase C. Long-term depression at the parallel fiber-Purkinje cell synapse in the cerebellum was converted into long-term potentiation. This likely explains the dramatic increase in Purkinje cell firing and the rapid oscillations of local field potential observed in alert fetal alcohol syndrome mice. Our data strongly suggest that reversal of long-term synaptic plasticity and increased firing rates of Purkinje cells in vivo are major contributors to the ataxia and motor learning deficits observed in fetal alcohol syndrome. Our results show that calcium-related neuronal dysfunction is central to the pathogenesis of the neurological manifestations of fetal alcohol syndrome and suggest new methods for treatment of this disorder.

Physiology of epithelial Ca2+ and Mg2+ transport

Ca2+ and Mg2+ are essential ions in a wide variety of cellular processes and form a major constituent of bone. It is, therefore, essential that the balance of these ions is strictly maintained. In the last decade, major breakthrough discoveries have vastly expanded our knowledge of the mechanisms underlying epithelial Ca2+ and Mg2+ transport. The genetic defects underlying various disorders with altered Ca2+ and/or Mg2+ handling have been determined. Recently, this yielded the molecular identification of TRPM6 as the gatekeeper of epithelial Mg2+ transport. Furthermore, expression cloning strategies have elucidated two novel members of the transient receptor potential family, TRPV5 and TRPV6, as pivotal ion channels determining transcellular Ca2+ transport. These two channels are regulated by a variety of factors, some historically strongly linked to Ca2+ homeostasis, others identified in a more serendipitous manner. Herein we review the processes of epithelial Ca2+ and Mg2+ transport, the molecular mechanisms involved, and the various forms of regulation.