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PubMed1985

Developmental microvascular architecture of the rat cerebellar cortex.

External and internal microvascular architectures of the developing rat cerebellar cortex, from embryonic day 18 to postnatal day 14 and in adults, were studied using a cerebrovascular casting method for scanning electron-microscopic observation. The external vascularization of the developing cerebellum showed the most significant alteration in vascular morphology at the stage of intensive proliferation of matrix cells in the external granular layer (EGL) from birth to postnatal day 4. It consisted of multiple luminal protrusion of the vessels, septum formation in the lumina, and small, ring-like anastomoses. Moreover, at the end of this stage, these structures of the vessels disappeared and the subarachnoid space was filled with newly-formed microvascular networks. Thereafter, architectural change of the developing pial vessels was mainly accomplished by elongation of each contorted vessel of the network. Concerning internal vascularization, a few vessels connected with the pial vessels were observed in the cerebellar plate forming a loose, simple network in the deeper neural parenchyma before the stage of foliation began. During the period of thickening of the EGL, however, there was no alteration in vascularity of the parenchyma other than the architectural changes proportionate to the newly-formed folia. It was during the synaptogenetic stage in the internal granular layer that the earliest intraneural vascular plexuses were formed. The vascular network in the molecular layer was formed after disappearance of the EGL. These findings suggest that vascular proliferation correlated with EGL-formation pertains to the pial vessels, and not the intraneural ones, which develop after neuronal cell migration in the developing cerebellum has taken place.

Animals↗
PubMed2006

Memory trace of motor learning shifts transsynaptically from cerebellar cortex to nuclei for consolidation.

Adaptation of ocular reflexes is a prototype of motor learning. While the cerebellum is acknowledged as the critical site for motor learning, the functional differences between the cerebellar cortex and nuclei in motor memory formation are not precisely known. Two different views are proposed: one that the memory is formed within the cerebellar flocculus, and the other that the memory is formed within vestibular nuclei. Here we developed a new paradigm of long-term adaptation of mouse horizontal optokinetic response eye movements and examined the location of its memory trace. We also tested the role of flocculus and inferior olive in long-term adaptation by chronic lesion experiments. Reversible bilateral flocculus shutdown with local application of 0.5 microl-5% lidocaine extinguished the memory trace of day-long adaptation, while it very little affected the memory trace of week-long adaptation. The responsiveness of vestibular nuclei after week-long adaptation was examined by measuring the extracellular field responses to the electrical stimulation of vestibular nerve under trichloroacetaldehyde anesthesia. The amplitudes and slopes of evoked monosynaptic field response (N1) of week-long adapted mice were enhanced around the medial vestibular nucleus compared with those of control mice. Chronic flocculus or inferior olive lesions abolished both day and week-long adaptations. These results suggest that the functional memory trace of short-term adaptation is formed initially within the cerebellar cortex, and later transferred to vestibular nuclei to be consolidated to a long-term memory. Both day and week-long adaptations were markedly depressed when neural nitric oxide was pharmacologically blocked locally and when neuronal nitric oxide synthase was ablated by gene knockout, suggesting that cerebellar long-term depression underlies both acquisition and consolidation of motor memory.

Adaptation, Physiological↗
PubMed1986

Habituation rules for a theory of the cerebellar cortex.

A quantitative model of cerebellar cortical function is described with a complete formalization based on (i) the topology of cerebellar cortical neuronal network, (ii) some particular synaptic properties of cell classes in cerebellum cortex, and (iii) the dynamics of excitation in this network. For (i), a construction of functional classes around one Purkinje cell is given and their existence is discussed. For (ii), as in Marr-Albus model, the modifiability of synapses between parallel fibres and Purkinje cell is assumed. But the formalization permits to consider the consequences of such a property at the level of glomerulus (with granule cells) which is known as a complex transformation system. For (iii) habituation rules are assumed. It is shown that this method leads to some interesting properties in the functioning of cerebellar cortex. Particularly, emitting frequency along a Purkinje cell axon results from a discrimination by the system between transformed input signals and an external "noise" due to all other "contexts," and learning could be considered as the result of a conflict between a set of patterns and the transformed input signals. This model could be a basis for future numerical simulations.

Animals↗
PubMed1992

Gamma-radiation produces abnormal Bergmann fibers and ectopic granule cells in mouse cerebellar cortex.

Morphological changes in Bergmann glial fibers in the developing cerebellar cortex produced by exposure to gamma-rays were investigated in association with ectopic granule cells. Six-day-old mice that had been exposed to 3 Gy of gamma-radiation were killed 6 hours after exposure or at 7 through 30 days of age. Their cerebella were examined histologically and immunohistochemically for glial fibrillary acidic protein in Bergmann fibers. Extensive cell death took place in the external granular layer (EGL) of the cerebellum from 6 through 24 hours after exposure. This led to the thinning of the EGL and a decrease in the number of migrating cells in the molecular layer. The number of Bergmann cells was not decreased, but the fibers in the molecular layer were distorted; whereas, in the control these fibers were straight and perpendicular to the pial surface. The EGL began to recover 2 days after exposure, and abnormally oriented migrating cells were seen. At 17 days of age, some cell clustering was observed in the molecular layer of the irradiated cerebellum. Distortion of the Bergmann fibers was marked in regions where ectopic granule cells appeared at 30 days of age. These findings suggest that the distortion of Bergmann fibers leads to the production of ectopic granule cells after exposure to gamma-radiation.

Animals↗
PubMed1994

Calbindin D-28k immunoreactivity in the rat cerebellar cortex: age-related changes.

The present study was designed to analyze age-dependent changes in the expression of calbindin D-28k immunoreactivity in the cerebellar cortex of male Wistar rats aged 3 months (young), 12 months (adult) and 24 months (old). Calbindin D-28k immunoreactivity was localized primarily in the cytoplasm of Purkinje neurons and in the basal portion of their dendritic processes entering in the molecular layer. The expression of calbindin D-28k immunoreactivity was highest in Purkinje neurons of adult rats and lowest in Purkinje neurons of old rats. Moreover, the number of Purkinje neurons displaying calbindin D-28k immunoreactivity was decreased in aged rats. These results demonstrate the occurrence of age-related-changes in the expression of immunoreactivity of the Ca2+ binding protein calbindin D-28k in the rat cerebellar cortex. The possibility that impairment in the expression of Ca2+ binding proteins may be involved in changes of intracellular Ca2+ homeostasis reported in aging and in some neuro-degenerative disorders is discussed.

Aging↗
PubMed1989

Cytological investigations on the cerebellar cortex of sudden infant death victims.

The study was based on the hypothesis that cerebellar hypoxia may play a role in sudden infant death syndrome resulting in morphological changes of the cerebellar cortex, especially with respect to Purkinje cell density. In the morphological evaluation of the Purkinje cell layer, special consideration was additionally given to secondary alterations (i.e., macrophage and/or astrocyte reaction). A total of 12 sudden infant death syndrome cases were compared with an age- and sex-matched control group. The Purkinje cell density was evaluated by determining the number of these cells per surface unit on parasagittal sections in both hemispheres. The myelomonocytic and glial reaction was demonstrated by immunohistochemical methods using lysozyme as leukocyte and macrophage markers and glial fibrillary acidic protein as an astrocyte marker. Qualitatively, no alterations resembling a macrophage or glial cell reaction were detected in sudden infant death syndrome. No differences between the right and left cerebellar hemisphere could be established in the victims of sudden infant death syndrome nor in the controls. The number of Purkinje cells per 0.352 mm2 cortex was higher in the younger victims of sudden infant death (younger than 45 weeks of gestation) than in all matched controls. A statistically significant difference in Purkinje cell density, however, could not be established, and, especially, no indications of hypoxia were observed in the cerebellar cortex.

Cerebellar Cortex↗
PubMed1991

[Modulatory role of the cerebellar cortex during the classically conditioned nictitating membrane response in rabbit].

Classical conditioning of the rabbit nictitating membrane(NM) response was accomplished by standard delay procedure of paired tone (CS) and airpuff (US) stimuli. Upon reaching a criterion of 90% conditioned responses (CRs) in 3 consecutive blocks, an electrolytic lesion was made at the hemicerebellar VI cortical lobule on the training side. Results showed that the learned response of the dentate-interpositus (D-I) nuclei and the conditioned NM response were completely or almost completely eliminated without affecting the unconditioned response. However, cerebellar cortical lesion performed on animals being over 1 week overtrained produced no effect on CRs and the learned response of the D-I nuclei. Meanwhile, the spontaneous activity of the D-I nuclei during consolidation reduced in frequency as a result of the cortical lesion at the early stage of learning. Our findings indicate that the cerebellar cortex plays a modulatory role in the generation of the conditioned NM response and the development of the learned response of the D-I nuclei at an early stage of learning. With consolidation, the D-I nuclei become free of control from the cerebellar cortex and serve as the essential component of the memory trace for this model system.

Animals↗
PubMed2005

Unipolar brush cells--a new type of excitatory interneuron in the cerebellar cortex and cochlear nuclei of the brainstem.

Published data and the authors' own studies on the morphology, neurochemical specialization, and spatial organization of unipolar brush neurons (UBN) in the cerebellar cortex and cochlear nuclei of the brainstem are reviewed. UBN represent an exclusive category of excitatory interneurons, with a single dendrite which forms a compact branching with a shape reminiscent of that of a brush in its terminal segment. These cells are characterized by an uneven distribution in the granular layer of the cerebellum, being located mainly in its vestibular zones. UBN synthesize glutamate, calretinin, and metabotropic and ionotropic glutamate receptors. The dendritic brush of UBN form giant synapses with the rosettes of glutamatergic and cholinergic mossy afferent fibers. UBN axons form an intracortical system of mossy fibers which, forming rosettes and glomeruli, make contact with the dendrites of other UBN and granule cells. In the circuits of interneuronal communications, UBN can be regarded as an intermediate component, amplifying the excitatory effects of mossy afferent fibers on granule cells in the cerebellar cortex and cochlear nuclei of the brainstem.

Animals↗
PubMed1982

Changes in extracellular potassium and calcium in rat cerebellar cortex related to local inhibition of the sodium pump.

Extracellular K+, Ca2+, and Na+ ([K+]e, [Ca2+]e, [Na+]e) were recorded with ion selective microelectrodes in the cerebellar cortex of urethane-anesthetized rats. Superfusion of the cerebellum with artificial cerebrospinal fluid containing K-strophanthidin (10(-6)-10(-4) mol/l) or other cardioactive steroids, known to be inhibitors of the sodium/potassium pump, had the following effects: elevation of resting [K+]e, reduction of poststimulus K+-undershoots, decrease of resting [Ca2+]e and [Na+]e. For instance, at 3 X 10(-5) mol/l K-strophanthidin within the superfusion solution (the unknown intracerebellar concentration being certainly much smaller), [K+]e was elevated up to 130% and [Ca2+]e reduced to 70% of their resting values. Iontophoretic K+-pulses were enhanced in amplitude at the same time. Control experiments with iontophoretic TMA application demonstrated that the glycoside effects were not due (or in higher concentrations only partly due) to shrinkage of the extracellular fluid volume. When tetrodotoxin (10(-7) mol/l) or Mn2+ (1-3 mmol/l) were additionally superfused, K-strophanthidin effects were qualitatively similar, though quantitatively smaller. This indicates that part of the effects were indirect via neuronal activity evoked by the blockade of the sodium pump. The experiments show that reduction of sodium pump activity in cerebellar cortex has rapid and serious consequences on the distribution of potassium and calcium in the extracellular space, resulting in an alteration of neuronal circuit excitability.

Animals↗
PubMed1976

Improved histological localization of GABA-transaminase activity in rat cerebellar cortex after aldehyde fixation.

A method for the chemical fixation of the enzyme GABA-transaminase in nervous tissue is described. It is shown that after perfusion with a formaldehyde/glutaraldehyde fixative, activity of the enzyme in cerebellar cortex is demonstrable whilst cellular morphology is preserved. Results from the improved technique have shown new sites of GABA-transaminase activity in cerebellar cortex. In view of these results a special function for glial cells in this area of brain has been suggested.

4-Aminobutyrate Transaminase↗
PubMed1992

Differential Ca2+ binding properties in the human cerebellar cortex: distribution of parvalbumin and calbindin D-28k immunoreactivity.

The distribution of the Ca(2+)-binding proteins parvalbumin (PV) and calbindin D-28k (CaBP) was investigated in the human cerebellar cortex. Purkinje cells contain both PV and CaBP. PV but not CaBP stains stellate and basket cells in the molecular layer. In the granular layer Golgi neurons can be subdivided into a majority, devoid of both Ca(2+)-binding proteins, and a scanty population which appears to be PV- and CaBP-immunoreactive. Thus GABAergic neurons in the human cerebellar cortex show selective differences in their Ca(2+)-binding properties, and these differences might reflect a heterogeneity in the processing of Ca(2+)-mediated events.

Aged↗
PubMed1992

Type II corticosteroid receptor-like immunoreactivity in the rat cerebellar cortex: differential regulation by corticosterone.

Type II corticosteroid receptor-like immunoreactivity (type II-ir) was localized at the light- and electron-microscopic levels in the rat cerebellar cortex using BUGR2 monoclonal antibody. In intact rats, type II-ir was observed in the nuclei of basket, stellate, Golgi and Purkinje cells. After 1 week of adrenalectomy, type II-ir was barely resolvable in basket, stellate, Golgi and most Purkinje cells. Vermal Purkinje cells showed intense nuclear and cytoplasmic type II-ir. After 4 weeks of adrenalectomy, type II-ir was markedly reduced in most vermal Purkinje cells, however a few in lobules 1-3 and 9 and 10 retained diffuse immunoreactivity. Acute treatment with corticosterone restored nuclear type II-ir to basket, stellate, Golgi and Purkinje cells in the cerebellar hemispheres, flocculi and paraflocculi. In the vermis most Purkinje cells showed nuclear type II-ir following corticosterone treatment. Diffuse type II-ir was, however, retained in a few Purkinje cells in vermal lobules 1-3, 9 and 10. The distribution of GABA-like immunoreactivity (GABA-ir) in the cerebellar cortex was not altered by adrenalectomy or acute corticosterone treatment. 30-60% of type II-ir Purkinje cells in intact rats were GABA-ir. In adrenalectomized and corticosterone-treated rats, a similar proportion of type II-ir Purkinje cells were GABA-ir. The differential regulation of neuronal type II-ir in the cerebellum by corticosterone may account for some of the known effects of glucocorticoids on motor coordination.

Adrenal Glands↗
PubMed2005

Effects of prenatal paraquat and mancozeb exposure on amino acid synaptic transmission in developing mouse cerebellar cortex.

The goal of this study was to analyze the effects of prenatal exposure to the pesticides paraquat (PQ) and mancozeb (MZ) on the development of synaptic transmission in mouse cerebellar cortex. Pregnant NMRI mice were treated with either saline, 10 mg/kg PQ, 30 mg/kg MZ or the combination of PQ + MZ, between gestational days 12 (E12) and E20. Variation in the levels of amino acid neurotransmitters was determined by HPLC, between postnatal day 1 (P1) and P30. Motor coordination was assessed by locomotor activity evaluation of control and experimental pups at P14, P21 and P30. Significant reductions in the levels of excitatory neurotransmitters, aspartate and glutamate, were observed in PQ-, MZ- or combined PQ + MZ-exposed pups, with respect to control, during peak periods of excitatory innervation of Purkinje cells: between P2-P5 and P11-P15. However, at P30, lower aspartate contents, in contrast with increased glutamate levels, were detected in all experimental groups. During the first two postnatal weeks, delays in GABA and glycine ontogenesis were observed in PQ- and PQ + MZ-exposed pups, whereas notable decrements in GABA and glycine levels were seen in PQ + MZ-exposed animals. Decreased taurine contents were detected at P3 and P11 in PQ- and PQ + MZ-exposed mice. Pups in different experimental groups all showed hyperactivity at P14 and then exhibited reduced locomotor activity at P30. Taken together, our results indicate that prenatal exposure to either PQ or MZ or the combination of both could alter the chronology and magnitude of synaptic transmission in developing mouse cerebellar cortex.

Animals↗
PubMed2002

Temporal organization of activity in the cerebellar cortex: a manifesto for synchrony.

The issues of temporal coding and the temporal organization of activity have aroused a great deal of interest in sensory systems, cortex, thalamus, and hippocampus. Strangely, despite the important timing roles attributed to the cerebellum, little consideration has been given to the organization of activity within the cerebellar circuitry. In fact, there is evidence of a remarkable temporal patterning of activity in even the earliest cerebellar recordings. The evidence for the existence of high-frequency oscillations in the cerebellar cortex is reviewed and possible mechanisms are discussed; one involves the synchrony of parallel fiber inputs to Purkinje cells. It is shown how synchronous and oscillatory activity can enable extremely precise timing and also how they can maximize the information storage capacity of the cerebellar cortex.

Action Potentials↗
PubMed1994

The candelabrum cell: a new interneuron in the cerebellar cortex.

A new cell type is described in silver-impregnated sections of the rat cerebellar cortex, uniformly distributed through all the cerebellar folia. The soma is rather small, roughly pyriform, vertically oriented, and squeezed, in a sandwich-like manner, between the Purkinje cell somata. One or two thick dendrites arise from the upper pole of the cell body and course through the entire molecular layer, dividing into a few, slightly oblique, branches that can reach the pia mater. These dendrites are covered with irregularly distributed spines. Some more slender dendrites emerge from the lower part of the cell body, or from the proximal trunk of a molecular dendrite, and spread tortuously for a short distance in the upper granular layer. A thick initial segment emerges directly from the soma or from the proximal portion of a dendrite, the axon winding then horizontally through or just above the Purkinje cell layer. During this horizontal course it gives off vertically oriented beaded branches ascending through the major part of the molecular layer. These branches, rather closely spaced, occupy different parasagittal planes, separated by about 10 to 30 microns. This axonal arborisation can thus be compared with a candelabrum. The peculiar three-dimensional spread of the axonal collaterals suggests a functional relationship between these branches and the dendritic trunks of neighbouring Purkinje cells. A comparative analysis of the morphological differences between this candelabrum interneuron and the other corticocerebellar interneurons found in the vicinity of the ganglionic layer confirms the specificity of this new cell class.

Animals↗
PubMed2002

Analysis of the function of GABA(B) receptors on inhibitory afferent neurons of Purkinje cells in the cerebellar cortex of the rat.

Purkinje cells, the output neurons of the cerebellar cortex, receive inhibitory input from basket, stellate and neighbouring Purkinje cells. The aim of the present study was to clarify the role of GABAB receptors on neurons giving inhibitory input to Purkinje cells. In sagittal slices prepared from the cerebellar vermis of the rat, the GABAB receptor agonist baclofen lowered the frequency and amplitude of spontaneous inhibitory postsynaptic currents (IPSCs) recorded in Purkinje cells. These effects were prevented by the GABAB receptor antagonist CGP 55845. Two mechanisms were involved in the depression of the inhibitory input to Purkinje cells. The first mechanism was suppression of the firing of basket, stellate and Purkinje cells. The second mechanism was presynaptic inhibition of GABA release from terminals of the afferent axons. This was indicated by the finding that baclofen decreased the amplitude of IPSCs occurring in Purkinje cells synchronously with action potentials recorded in basket cells. A further support for the presynaptic inhibition is the observation that baclofen decreased the amplitude of autoreceptor currents which are due to activation of GABAA autoreceptors at axon terminals of basket cells by synaptically released GABA. The presynaptic inhibition was partly due to direct inhibition of the vesicular release mechanism, because baclofen lowered the frequency of miniature IPSCs recorded in Purkinje cells in the presence of cadmium and in the presence of tetrodotoxin plus ionomycin. The results show that activation of GABAB receptors decreased GABAA receptor-mediated synaptic input to cerebellar Purkinje cells both by lowering the firing rate of the inhibitory input neurons and by inhibiting GABA release from their axon terminals with a presynaptic mechanism.

Animals↗