The function of cerebellar Golgi cells revisited

Computational models of neurotransmission at cerebellar synapses unveil the impact on network computation

The neuroscientific field benefits from the conjoint evolution of experimental and computational techniques, allowing for the reconstruction and simulation of complex models of neurons and synapses. Chemical synapses are characterized by presynaptic vesicle cycling, neurotransmitter diffusion, and postsynaptic receptor activation, which eventually lead to postsynaptic currents and subsequent membrane potential changes. These mechanisms have been accurately modeled for different synapses and receptor types (AMPA, NMDA, and GABA) of the cerebellar cortical network, allowing simulation of their impact on computation. Of special relevance is short-term synaptic plasticity, which generates spatiotemporal filtering in local microcircuits and controls burst transmission and information flow through the network. Here, we present how data-driven computational models recapitulate the properties of neurotransmission at cerebellar synapses. The simulation of microcircuit models is starting to reveal how diverse synaptic mechanisms shape the spatiotemporal profiles of circuit activity and computation.

The modular architecture and neurochemical patterns in the cerebellar cortex

The review deals with topical issues of the neuronal arrangement underlying basic cerebellar functions. The cerebellum and its auxiliary structures contain several hundreds of modules (so called "microzones"). Each module receives the corticopetal input specific for the lobule it belongs to and forms the topographic projection. The precision of the major input-output signal flow in the cerebellar cortex is provided by a pronounced stratification of its synaptic zones of a various origin and regular topography of its afferent connections, interneurons, and efferent neurons. There is a nice match between the anatomical and functional coordinates of the modules, whose spatial boundaries are determined by the spread of afferent excitation and local interneuron connections. The dynamic characteristics of the modules are analyzed by the example of the formation of the nitrergic neuron ensembles and cerebellar projections of corticopetal fibers. The authors discuss the cerebellar blood flow and its relation to the activity of NO/GABAergic Lugaro cells and other interneurons in the cerebellar cortex. A generalized scheme of intra- and intermodular communication is proposed.

Non-synaptic signaling from cerebellar climbing fibers modulates Golgi cell activity

Golgi cells are the principal inhibitory neurons at the input stage of the cerebellum, providing feedforward and feedback inhibition through mossy fiber and parallel fiber synapses. In vivo studies have shown that Golgi cell activity is regulated by climbing fiber stimulation, yet there is little functional or anatomical evidence for synapses between climbing fibers and Golgi cells. Here, we show that glutamate released from climbing fibers activates ionotropic and metabotropic receptors on Golgi cells through spillover-mediated transmission. The interplay of excitatory and inhibitory conductances provides flexible control over Golgi cell spiking, allowing either excitation or a biphasic sequence of excitation and inhibition following single climbing fiber stimulation. Together with prior studies of spillover transmission to molecular layer interneurons, these results reveal that climbing fibers exert control over inhibition at both the input and output layers of the cerebellar cortex.

Circadian Plasticity of Mammalian Inhibitory Interneurons

Inhibitory interneurons participate in all neuronal circuits in the mammalian brain, including the circadian clock system, and are indispensable for their effective function. Although the clock neurons have different molecular and electrical properties, their main function is the generation of circadian oscillations. Here we review the circadian plasticity of GABAergic interneurons in several areas of the mammalian brain, suprachiasmatic nucleus, neocortex, hippocampus, olfactory bulb, cerebellum, striatum, and in the retina.

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.

Anti-brain antibodies are associated with more severe cognitive and behavioral profiles in Italian children with Autism Spectrum Disorder

Circulating 45 and 62kDa antibodies targeting the cerebellum were previously associated with Autism Spectrum Disorder (ASD), lower adaptive/cognitive function and aberrant behaviors. Moreover, 37, 39 and 73kDa maternal antibodies (mAb) targeting the fetal brain were previously correlated with broad autism spectrum, irritability, abnormal brain enlargement and impaired expressive language. The present study aims towards clinically characterizing individuals with brain-targeted IgG and/or exposed to maternal antibrain antibodies in a large sample of Italian autistic children (N=355), their unaffected siblings (N=142) and mothers (N=333). The presence of patient- and mother-produced anti-brain antibodies does not confer increased risk of autism within the same sibship. However, the 45 and 62kDa antibodies are correlated with autism severity: the 45kDa Ab is associated with cognitive impairment and lower scores at the Vineland Adaptive Behavior Scales, the 62kDa Ab with motor stereotypies, while both correlate with larger head circumference (all P<0.05). On the other hand, maternal 37, 39 and 73kDa antibrain antibodies, either alone or in combination, are correlated with impaired verbal and non-verbal language development, neurodevelopmental delay and sleep/wake cycle disturbances in their autistic children (P<0.05). Presence of the 62kDa autoAb in the child is significantly associated with presence of the 39 and/or 73kDa antibodies in his/her mother. Our results confirm and extend previous observations in an ethnically distinct sample, providing further evidence of a pathomorphic role for anti-brain antibodies in autism while demonstrating their familial clustering.

Identification of an inhibitory circuit that regulates cerebellar Golgi cell activity

Here we provide evidence that revises the inhibitory circuit diagram of the cerebellar cortex. It was previously thought that Golgi cells, interneurons that are the sole source of inhibition onto granule cells, were exclusively coupled via gap junctions. Moreover, Golgi cells were believed to receive GABAergic inhibition from molecular layer interneurons (MLIs). Here we challenge these views by optogenetically activating the cerebellar circuitry to determine the timing and pharmacology of inhibition onto Golgi cells and by performing paired recordings to directly assess synaptic connectivity. In contrast to current thought, we find that Golgi cells, not MLIs, make inhibitory GABAergic synapses onto other Golgi cells. As a result, MLI feedback does not regulate the Golgi cell network, and Golgi cells are inhibited approximately 2 ms before Purkinje cells, following a mossy fiber input. Hence, Golgi cells and Purkinje cells receive unique sources of inhibition and can differentially process shared granule cell inputs.

Altered cerebellar development in nuclear receptor TAK1/ TR4 null mice is associated with deficits in GLAST(+) glia, alterations in social behavior, motor learning, startle reactivity, and microglia

Previously, deficiency in the expression of the nuclear orphan receptor TAK1 was found to be associated with delayed cerebellar granule cell migration and Purkinje cell maturation with a permanent deficit in foliation of lobules VI–VII, suggesting a role for TAK1 in cerebellum development. In this study, we confirm that TAK1-deficient (TAK1(−/−)) mice have a smaller cerebellum and exhibit a disruption of lobules VI–VII. We extended these studies and show that at postnatal day 7, TAK1(−/−) mice exhibit a delay in monolayer maturation of dysmorphic calbindin 28K-positive Purkinje cells. The astrocyte-specific glutamate transporter (GLAST) was expressed within Bergmann fibers and internal granule cell layer at significantly lower levels in the cerebellum of TAK1(−/−) mice. At PND21, Golgi-positive Purkinje cells in TAK1(−/−) mice displayed a smaller soma (18%) and shorter distance to first branch point (35%). Neuronal death was not observed in TAK1(−/−) mice at PND21; however, activated microglia were present in the cerebellum, suggestive of earlier cell death. These structural deficits in the cerebellum were not sufficient to alter motor strength, coordination, or activity levels; however, deficits in acoustic startle response, prepulse startle inhibition, and social interactions were observed. Reactions to a novel environment were inhibited in a light/dark chamber, open-field, and home-cage running wheel. TAK1(−/−) mice displayed a plateau in performance on the running wheel, suggesting a deficit in learning to coordinate performance on a motor task. These data indicate that TAK1 is an important transcriptional modulator of cerebellar development and neurodevelopmentally regulated behavior.

Current source density correlates of cerebellar Golgi and Purkinje cell responses to tactile input

The overall circuitry of the cerebellar cortex has been known for over a century, but the function of many synaptic connections remains poorly characterized in vivo. We used a one-dimensional multielectrode probe to estimate the current source density (CSD) of Crus IIa in response to perioral tactile stimuli in anesthetized rats and to correlate current sinks and sources to changes in the spike rate of corecorded Golgi and Purkinje cells. The punctate stimuli evoked two distinct early waves of excitation (at <10 and ∼ 20 ms) associated with current sinks in the granular layer. The second wave was putatively of corticopontine origin, and its associated sink was located higher in the granular layer than the first trigeminal sink. The distinctive patterns of granular-layer sinks correlated with the spike responses of corecorded Golgi cells. In general, Golgi cell spike responses could be linearly reconstructed from the CSD profile. A dip in simple-spike activity of coregistered Purkinje cells correlated with a current source deep in the molecular layer, probably generated by basket cell synapses, interspersed between sparse early sinks presumably generated by synapses from granule cells. The late (>30 ms) enhancement of simple-spike activity in Purkinje cells was characterized by the absence of simultaneous sinks in the granular layer and by the suppression of corecorded Golgi cell activity, pointing at inhibition of Golgi cells by Purkinje axon collaterals as a likely mechanism of late Purkinje cell excitation.

Schizophrenia-like GABAergic gene expression deficits in cerebellar Golgi cells from rats chronically exposed to low-dose phencyclidine

One of the most consistent findings in schizophrenia is the decreased expression of the GABA synthesizing enzymes GAD(67) and GAD(65) in specific interneuron populations. This dysfunction is observed in distributed brain regions including the prefrontal cortex, hippocampus, and cerebellum. In an effort to understand the mechanisms for this GABA deficit, we investigated the effect of the N-methyl-D-aspartate receptor (NMDAR) antagonist phencyclidine (PCP), which elicits schizophrenia-like symptoms in both humans and animal models, in a chronic, low-dose exposure paradigm. Adult rats were given PCP at a dose of 2.58 mg/kg/day i.p. for a month, after which levels of various GABAergic cell mRNAs and other neuromodulators were examined in the cerebellum by qRT-PCR. Administration of PCP decreased the expression of GAD(67), GAD(65), and the presynaptic GABA transporter GAT-1, and increased GABA(A) receptor subunits similar to those seen in patients with schizophrenia. Additionally, we found that the mRNA levels of two Golgi cell selective NMDAR subunits, NR2B and NR2D, were decreased in PCP-treated rats. Furthermore, we localized the deficits in GAD(67) expression solely to these interneurons. Slice electrophysiological studies showed that spontaneous firing of Golgi cells was reduced by acute exposure to low-dose PCP, suggesting that these neurons are particularly vulnerable to NMDA receptor antagonism. In conclusion, our results demonstrate that chronic exposure to low levels of PCP in rats mimics the GABAergic alterations reported in the cerebellum of patients with schizophrenia (Bullock et al., 2008. Am. J. Psychiatry 165, 1594-1603), further supporting the validity of this animal model.

Characteristics of responses of Golgi cells and mossy fibers to eye saccades and saccadic adaptation recorded from the posterior vermis of the cerebellum

The anatomical organization of the granular layer of the cerebellum suggests an important function for Golgi cells (GC) in the pathway conveying mossy fiber (MF) afferents to Purkinje cells. Based on such anatomic observations, early proposals have attributed a role in "gain control" for GCs, a function disputed by recent investigations, which assert that GCs instead contribute to oscillatory mechanisms. However, conclusive physiological evidence based on studies of cerebellum-dependent behavior supporting/dismissing the gain control proposition has been lacking as of yet. We addressed the possible function of this interneuron by recording the activity of a large number of both MFs and GCs during saccadic eye movements from the same cortical area of the monkey cerebellum, namely the oculomotor vermis (OMV). Our cellular identification conformed to previously established criteria, mainly to juxtacellular labeling studies correlating physiological parameters with cell morphology. Response patterns of both MFs and GCs were highly heterogeneous. MF discharges correlated linearly with eye saccade metrics and timing, showing directional preference and precise direction tuning. In contrast, GC discharges did not correlate strongly with the metrics or direction of movement. Their discharge properties were also unaffected by motor learning during saccadic adaptation. The OMV therefore receives a barrage of information about eye movements from different oculomotor areas over the MF pathway, which is not reflected in GCs. The unspecificity of GCs has important implications for the intricacies of neuronal processing in the granular layer, clearly discrediting their involvement in gain control and instead suggesting a more secluded role for these interneurons.

Electrical coupling mediates tunable low-frequency oscillations and resonance in the cerebellar Golgi cell network

Tonic motor control involves oscillatory synchronization of activity at low frequency (5-30 Hz) throughout the sensorimotor system, including cerebellar areas. We investigated the mechanisms underpinning cerebellar oscillations. We found that Golgi interneurons, which gate information transfer in the cerebellar cortex input layer, are extensively coupled through electrical synapses. When depolarized in vitro, these neurons displayed low-frequency oscillatory synchronization, imposing rhythmic inhibition onto granule cells. Combining experiments and modeling, we show that electrical transmission of the spike afterhyperpolarization is the essential component for oscillatory population synchronization. Rhythmic firing arises in spite of strong heterogeneities, is frequency tuned by the mean excitatory input to Golgi cells, and displays pronounced resonance when the modeled network is driven by oscillating inputs. In vivo, unitary Golgi cell activity was found to synchronize with low-frequency LFP oscillations occurring during quiet waking. These results suggest a major role for Golgi cells in coordinating cerebellar sensorimotor integration during oscillatory interactions.

Detection of autoantibodies to neural cells of the cerebellum in the plasma of subjects with autism spectrum disorders

Autism spectrum disorders (ASD) are a group of heterogeneous, behaviorally defined disorders characterized by disturbances in social interaction and communication, often with repetitive and stereotyped behavior. Previous studies have described the presence of antibodies to various neural proteins in autistic individuals as well as post-mortem evidence of neuropathology in the cerebellum. We examined plasma from children with ASD, as well as age-matched typically developing controls, for antibodies directed against human cerebellar protein extracts using Western blot analysis. In addition, the presence of cerebellar specific antibodies was assessed by immunohistochemical staining of sections from Macaca fascicularis monkey cerebellum. Western blot analysis revealed that 13/63 (21%) of subjects with ASD possessed antibodies that demonstrated specific reactivity to a cerebellar protein with an apparent molecular weight of approximately 52 kDa compared with only 1/63 (2%) of the typically developing controls (p=0.0010). Intense immunoreactivity, to what was determined morphologically to be the Golgi cell of the cerebellum, was noted for 7/34 (21%) of subjects with ASD, compared with 0/23 of the typically developing controls. Furthermore, there was a strong association between the presence of antibodies reactive to the 52 kDa protein by Western blot with positive immunohistochemical staining of cerebellar Golgi cells in the ASD group (r=0.76; p=0.001) but not controls. These studies suggest that when compared with age-matched typically developing controls, children with ASD exhibit a differential antibody response to specific cells located in the cerebellum and this response may be associated with a protein of approximately 52 kDa.

Characterization in vivo of bilaterally branching pontocerebellar mossy fibre to Golgi cell inputs in the rat cerebellum

Golgi cells regulate the flow of information from mossy fibres to the cerebellar cortex, through a mix of feedback and feedforward inhibitory actions on granule cells. The aim of the current study was to examine mossy fibre input to Golgi cells, in order to assess their impact on switching Golgi cells into feedforward behaviour. In urethane-anaesthetized rats, extracellular recordings were made from Golgi cells in Crus II (n = 18). Spikes were evoked in all Golgi cells by microstimulation within the contralateral hemispheral cortex, via branches of mossy fibres that terminate in both cerebellar hemispheres. The latencies of these responses were very short, consistent with a monosynaptic mossy fibre contact [average onset latency 2.3 +/- 0.1 ms (SEM)]. The same stimuli had no measurable effect on spike responses of nearby Purkinje cells (n = 12). Systematic mapping in the contralateral cerebellar hemisphere (Crus Ib, IIa, IIb and the paramedian lobule) usually revealed one low-intensity stimulus 'hotspot' (12-35 microA) from which short-latency spikes could be evoked in an individual Golgi cell. Microinjections of red and green retrograde tracers (latex beads, approximately 50-150 nL injection volume) made at the recording site and the stimulation hotspot resulted in double-labelled neurons within the pontine nuclei. Overall, this suggests that subsets of pontine neurons supply mossy fibres that branch to both hemispheres, some of which directly target Golgi cells. Such an arrangement may provide a common feedforward inhibitory link to temporally couple activity on both sides of the cerebellum during behaviour.

Cerebellar Golgi cells in the rat receive multimodal convergent peripheral inputs via the lateral funiculus of the spinal cord

We recently showed that the activity of cerebellar Golgi cells can be powerfully modulated by stimulation of peripheral afferents, in a pattern different to local Purkinje cells. Here we have examined the pathways underlying these responses. Graded electrical stimulation of muscle and cutaneous nerves revealed that long-lasting depressions and short-lasting excitations of Golgi cells were evoked by stimulation of cutaneous nerves at stimulus intensities that activated large mechanoreceptive afferents, and grew as additional afferents were recruited. In contrast, none of the neurones responded to stimulation of muscle nerves at intensities that activated group I afferents, although about half responded with long-lasting depressions, but not excitations, to stimuli that recruited group II and III afferents. Selective lesions of the spinal dorsal columns did not affect either of these types of response. After lesions of one lateral funiculus in the lumbar cord the responses evoked by stimulation of the hindlimb contralateral to the lesion were reduced or abolished, leaving responses evoked by ipsilateral hindlimb afferents unaltered. Since both ipsi- and contralateral afferents generate responses in Golgi cells, the convergence from the two sides must occur supraspinally. It is difficult to reconcile these properties with any of the direct spinocerebellar pathways or spinoreticulocerebellar pathways that have been described. Instead, it is likely that the responses are evoked via the multimodal 'wide dynamic range' neurones of the anterolateral system. Golgi cell activity may thus be powerfully enhanced or depressed during arousal via the anterolateral system.

Different responses of rat cerebellar Purkinje cells and Golgi cells evoked by widespread convergent sensory inputs

While the synaptic properties of Golgi cell-mediated inhibition of granule cells are well studied, less is known of the afferent inputs to Golgi cells so their role in information processing remains unclear. We investigated the responses of cerebellar cortical Golgi cells and Purkinje cells in Crus I and II of the posterior lobe cerebellar hemisphere to activation of peripheral afferents in vivo, using anaesthetized rats. Recordings were made from 70 Golgi cells and 76 Purkinje cells. Purkinje cells were identified by the presence of climbing fibre responses. Golgi cells were identified by both spontaneous firing pattern and response properties, and identification was confirmed using juxtacellular labelling of single neurones (n = 16). Purkinje cells in Crus II showed continuous firing at relatively high rates (25-60 Hz) and stimulation of peripheral afferents rarely evoked substantial responses. The most common response was a modest, long-latency, long-lasting increase in simple spike output. By comparison, the most common response evoked in Golgi cells by the same stimuli was a long-latency, long-lasting depression of firing, found in approximately 70% of the Golgi cells tested. The onsets of Golgi cell depressions had shorter latencies than the Purkinje cell excitations. Brief, short-latency excitations and reductions in firing were also evoked in some Golgi cells, and rarely in Purkinje cells, but in most cases long-lasting depressions were the only significant change in spike firing. Golgi cell responses could be evoked using air puff or tactile stimuli and under four different anaesthetic regimens. Long-lasting responses in both neurone types could be evoked from wide receptive fields, in many cases including distal afferents from all four limbs, as well as from trigeminal afferents. These Golgi cell responses are not consistent with the conventional feedback inhibition or 'gain control' models of Golgi cell function. They suggest instead that cerebellar cortical activity can be powerfully modulated by the general level of peripheral afferent activation from much of the body. On this basis, Golgi cells may act as a context-specific gate on transmission through the mossy fibre-granule cell pathway.

Temporal characteristics of tactile stimuli influence the response profile of cerebellar Golgi cells

An increasing number of studies have investigated the effect of stimulation parameters on neuronal response properties. Here, we describe the effect of temporal characteristics of tactile stimuli, more specifically the stimulation frequency and duration, on the response profile of simultaneously recorded cerebellar and cerebral cortical units in ketamine-xylazine anaesthetized rats. Long stimulus durations (>50 ms) elicited ON and OFF excitatory components in response to the stimulus onset and offset respectively, in both the cortex and the cerebellum. Golgi cells responded on average 7.5 ms later to the stimulus withdrawal than to the stimulus onset. Furthermore, the corticopontine OFF responses in the cerebellum and OFF responses in the cortex showed congruent latency decreases and amplitude increases for longer stimulus durations (50-200 ms). Decreasing the stimulus frequency similarly affected the latency and amplitude of the responses for inter-stimuli intervals shorter than 200 ms. In view of these results, we speculate that the stimulus offset is regarded as a novel input, because both paradigms resulted in similar response amplitude and latency modifications. Finally, the results suggest that a 100-200 ms time window can be of particular importance for cerebellar processing of information in the somatosensory system.

Computation of inverse functions in a model of cerebellar and reflex pathways allows to control a mobile mechanical segment

The command and control of limb movements by the cerebellar and reflex pathways are modeled by means of a circuit whose structure is deduced from functional constraints. One constraint is that fast limb movements must be accurate although they cannot be continuously controlled in closed loop by use of sensory signals. Thus, the pathways which process the motor orders must contain approximate inverse functions of the bio-mechanical functions of the limb and of the muscles. This can be achieved by means of parallel feedback loops, whose pattern turns out to be comparable to the anatomy of the cerebellar pathways. They contain neural networks able to anticipate the motor consequences of the motor orders, modeled by artificial neural networks whose connectivity is similar to that of the cerebellar cortex. These networks learn the direct biomechanical functions of the limbs and muscles by means of a supervised learning process. Teaching signals calculated from motor errors are sent to the learning sites, as, in the cerebellum, complex spikes issued from the inferior olive are conveyed to the Purkinje cells by climbing fibers. Learning rules are deduced by a differential calculation, as classical gradient rules, and they account for the long term depression which takes place in the dendritic arborizations of the Purkinje cells. Another constraint is that reflexes must not impede voluntary movements while remaining at any instant ready to oppose perturbations. Therefore, efferent copies of the motor orders are sent to the interneurones of the reflexes, where they cancel the sensory-motor consequences of the voluntary movements. After learning, the model is able to drive accurately, both in velocity and position, angular movements of a rod actuated by two pneumatic McKibben muscles. Reflexes comparable to the myotatic and tendinous reflexes, and stabilizing reactions comparable to the cerebellar sensory-motor reactions, reduce efficiently the effects of perturbing torques. These results allow to link the behavioral concepts of the equilibrium-point "lambda model" [J Motor Behav 18 (1986) 17] with anatomical and physiological features: gains of reflexes and sensori-motor reactions set the slope of the "invariant characteristic," and efferent copies set the "threshold of the stretch reflex." Thus, mathematical and physical laws account for the raison d'etre of the inhibitory nature of Purkinje cells and for the conspicuous anatomical pattern of the cerebellar pathways. These properties of these pathways allow to perform approximate inverse calculations after learning of direct functions, and insure also the coordination of voluntary and reflex motor orders.

Alcohol-Induced Neurodegeneration: When, Where and Why?

This manuscript reviews the proceedings of a symposium organized by Drs. Antonio Noronha and Fulton Crews presented at the 2003 Research Society on Alcoholism meeting. The purpose of the symposium was to examine recent findings on when alcohol induced brain damage occurs, e.g., during intoxication and/or during alcohol withdrawal. Further studies investigate specific brain regions (where) and the mechanisms (why) of alcoholic neurodegeneration. The presentations were (1) Characterization of Synaptic Loss in Cerebella of Mature and Senescent Rats after Lengthy Chronic Ethanol Consumption, (2) Ethanol Withdrawal Both Causes Neurotoxicity and Inhibits Neuronal Recovery Processes in Rat Organotypic Hippocampal Cultures, (3) Binge Drinking-Induced Brain Damage: Genetic and Age Related Effects, (4) Binge Ethanol-Induced Brain Damage: Involvement of Edema, Arachidonic Acid and Tissue Necrosis Factor alpha (TNFalpha), and (5) Cyclic AMP Cascade, Stem Cells and Ethanol. Taken together these studies suggest that alcoholic neurodegeneration occurs through multiple mechanisms and in multiple brain regions both during intoxication and withdrawal.

Distribution of calcium-binding proteins in the cerebellum

Calcium plays a fundamental role in the cell as second messenger and is principally regulated by calcium-binding proteins. Although these proteins share in common their ability to bind calcium, they belong to different subfamilies. They present, in general, specific developmental and distribution patterns. Most Purkinje cells express the fast and slow calcium buffer proteins calbindin-D28k and parvalbumin, whereas basket, stellate and Golgi cells the slow buffer parvalbumin only. They are, almost all, calretinin negative. Granule, Lugaro and unipolar brush cells present an opposite immunoreactivity profile, most of them being calretinin positive while lacking calbindin-D28k and parvalbumin. The developmental pattern of appearance of these proteins seems to follow the maturation of neurons. Calbindin-D28k appears early, shortly after cessation of mitosis when neurons become ready to start migration and differentiation while parvalbumin is expressed later in parallel with an increase in neuronal activity. The other proteins are generally detected later. During development, some of these proteins, like calretinin, are transiently expressed in specific cellular subpopulations. The function of these proteins is not fully understood, although strong evidence supports a prominent role in physiological settings with altered calcium concentrations. These proteins regulate and are regulated by intracellular calcium level. For example, they may directly or indirectly enable sensitization or desensitization of calcium channels, and may further block calcium entry into the cells, like the calcium-sensor proteins, that have been shown to be potent and specific modulators of ion channels, which may allow for feedback control of current function and hence signaling. The absence of calcium buffer proteins results in marked abnormalities in cell firing; with alterations in simple and complex spikes or transformation of depressing synapses into facilitating synapses. Calcium-binding protein implication in resistance to degeneration is still a controversial issue. Neurons rich in calcium-binding proteins, especially calbindin-D28k and parvalbumin, seem to be relatively resistant to degeneration in a variety of acute and chronic disorders. However other data support that an absence of calcium-binding proteins may also have a neuroprotective effect. It is not unlikely that neurons may face a dual action mechanism where a decrease in calcium-binding proteins has a first short-term beneficial effect while it becomes detrimental for the cell over the long term.

Peripheral stimuli excite coronal beams of Golgi cells in rat cerebellar cortex

Cerebellar granule cells constitute the largest neurone population of the brain. Their axons run as parallel fibres along the coronal axis, and the one-dimensional spread of excitation that is expected to result from this arrangement is a key assumption of theories of cerebellar function. In many studies using various techniques, however, it was not possible to evoke such a beam-like propagation of excitation with natural stimuli. We recorded, in Crus I and II of anaesthetised rats, pairs of Golgi cells aligned along the parallel fibre axis and synchronising spontaneously. Each pair was subjected to two stimulation protocols: punctate and semi-continuous. Local punctate facial stimulation evoked distinct fast and late responses of variable strength and latency (fast: 4.0-10.2 ms; late: 13.6-22.7 ms). Semi-continuous stimulation with a brush increased the firing rate, and modified the precision and phase of synchronisation. Differences between a pair in response strength and phase to brush stimulation correlated strongly with the difference in latency to punctate stimulation. These observations were reproduced in a model of the granular layer. The stimulus activated a central patch of mossy fibres, and Golgi cells received short- and long-range excitation from mossy and parallel fibres, respectively. The strength and latency of the punctate response of a model Golgi cell were found to vary with its position, reflecting a systematic change in the contribution of mossy and parallel fibres to its excitation with distance from the activated patch. During brush stimulation, model Golgi cells inside the patch fired more precisely synchronised, whereas the other Golgi cells responded with a lag proportional to their distance from the patch, thereby reproducing the experimentally observed changes in synchronisation. Taken together with the previously reported large receptive fields of Golgi cells and with their spontaneous synchronisation, the variable, position-dependent latency of evoked Golgi cell responses indicates a beam-like spread of excitation along the parallel fibres in rat cerebellar cortex.

Cerebellar cortex: computation by extrasynaptic inhibition?

In the cerebellar cortex, inhibitory inputs to granule cells exhibit prominent tonic and spillover components resulting from the activation of extrasynaptic receptors. A recent study shows how extrasynaptic inhibition affects information flow through cerebellar cortex.

Morphological and neurochemical differentiation of large granular layer interneurons in the adult rat cerebellum

The granular layer of the cerebellar cortex consists of densely packed neuronal cells, classified into granule cells and large interneurons. In this study, we provide a comparative survey of large granular layer interneurons in the adult rat cerebellum based on both morphological and neurochemical criteria. To this end, double immunofluorescence histochemistry was performed by combining antibodies against the cytoplasmic antigen Rat-303, calretinin, the metabotropic glutamate receptor mGluR2 and somatostatin. Based on Rat-303/calretinin double immunohistochemistry, three distinct populations of large granular layer interneurons could be discerned: cells immunopositive for Rat-303, calretinin or both. Rat-303 or calretinin single-labeled cells represented Golgi cells and unipolar brush cells, respectively. Rat-303/calretinin double-labeled cells located just underneath the Purkinje cell layer represented Lugaro cells. Morphometrical analysis distinguished two populations of Rat-303-positive Golgi cells according to their location: vermis versus hemisphere. Immunostaining for the metabotropic glutamate receptor mGluR2 combined with Rat-303 or calretinin revealed that the majority of Golgi cells (about 90%) appeared to be mGluR2 positive. Lugaro cells were mGluR2 negative. In addition, a limited population of large polymorphous interneurons in the depth of the granular layer with morphological features resembling Golgi cells also displayed Rat-303/calretinin immunoreactivity and were mGluR2 negative. Double immunohistochemistry for Rat-303 and somatostatin revealed three populations of labeled cells in the depth of the granular layer. Besides double-labeled Golgi cells, Rat-303 or somatostatin single-labeled cells were present. Based on mGluR2/somatostatin and calretinin/somatostatin double immunostainings, Rat-303 single-labeled cells were found to correspond to Rat-303/calretinin-positive, mGluR2-negative Golgi-like cells, while the identity of somatostatin single-labeled cells remained unclear. The data presented in this article elaborate previous reports on the morphological and neurochemical differentiation of large interneurons in the rat cerebellar granular layer. In addition, they indicate that the current classification of these cells into Golgi cells, Lugaro cells and unipolar brush cells does not describe the observed neurochemical heterogeneity.

Decreased benzodiazepine receptor density in the cerebellum of early blind human subjects

As a first approach to study the effect of early visual deprivation in the GABA-ergic inhibitory system, the distribution of benzodiazepine receptors (BZR) was accurately estimated using [11C]flumazenil ([11C]FMZ). Measurements were carried out in five subjects who became blind early in life and in five sighted control subjects. The interactions between [11C]FMZ and BZR were described using a non-linear compartmental analysis which permitted to estimate the BZR synaptic density independently of other model parameters. The distribution of BZR in the visual areas and other cortical regions of blind subjects was qualitatively and quantitatively similar to that of controls. However, the BZR density in the cerebellum was significantly lower in blind than in control subjects (P<0.01). Our findings suggest that modifications of the cerebellar neural circuitry may be concomitant to the already observed compensatory reorganization in cerebral areas of blind subjects.