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PubMed1983

Role of staggerer gene in determining cell number in cerebellar cortex. I. Granule cell death is an indirect consequence of staggerer gene action.

Mouse chimeras were made by aggregating two embryos at the 8-cell stage of development. These experimental mosaic animals are useful in assessing whether the effect of a mutant gene in a given cell type is direct (intrinsic) or indirect (extrinsic). The results reported are an analysis of the involvement of the staggerer gene in the phenotype of granule cell death observed in staggerer mutant mice. The ichthyosis mutation has been used as an independent cell marker. This mutation produces no known neurological defects but does cause a characteristic clumping of heterochromatin, especially in small cells. Analysis of two staggerer in equilibrium ichthyosis chimeras leads to the conclusion that staggerer granule cells, that would have died in the mutant, are rescued in the mosaic cerebella. The death of granule cells in the homozygous staggerer mutant is thus an indirect, epigenetic consequence of direct gene action in other cells. The implications and limitations of this conclusion are discussed.

Animals↗

PubMed2003

Expression of TrkB subtypes in the adult monkey cerebellar cortex.

BDNF and its specific receptor TrkB are concerned with synaptic plasticity as well as maintenance of the nervous system. TrkB has three subtypes: full-length TrkB (TK+), which has a tyrosine kinase containing intracellular domain, and two truncated TrkBs (TK-; T1 and T2), which lack tyrosine kinases. To understand the molecular interaction among these subtypes, we investigated the expression and distribution of BDNF, TK+, and T1 in the adult monkey cerebellum by single and double immunohistochemistry and Western blot analysis. We observed by single immunohistochemistry that BDNF, TK+, and T1 are distributed in almost all the somata and dendrites of Purkinje and granule cells. In the double-stained sections, three kinds of regions were observed: TK+ >T1; TK+ =T1; TK+ <T1. Moreover, three types of TrkB dimers (TK+/TK+ homodimer, TK+/TK- heterodimer, and TK-/TK- homodimer) were induced by stimulating with exogenous BDNF. These observations suggest that the functions of BDNF may be modified by interaction among subtypes of TrkB in each region of the Purkinje cells.

Animals↗

PubMed1975

Diversity of mossy fibres in the cerebellar cortex in relation to different afferent systems: an experimental electron microscopic study in the cat.

The evolution of the terminal degeneration has been compared in two systems of mossy fibres: the spinocerebellar and the pontocerebellar projections. The two systems exhibit both dense and clear types of terminal degeneration. However, there are important differences between the evolutive processes of terminal degeneration in the two systems: (i) the time course of the degenerating process is much faster for spinocerebellar than for pontocerebellar rosettes, and (ii) the glial phagocytic process accompanying the dense type of degeneration is different for the two systems. Spinocerebellar rosettes are generally removed from their glomerular central position by reactive glia, leaving fragments of the presynaptic membrane attached to their postsynaptic partner. This feature is exceptional for pontocerebellar rosettes which, in the course of their glial engulfment, leave free the postsynaptic differentiation of their former target granule cell dendrites. These differences of terminal degenerative processes have been reconciled with optical microscope observations by Brodal and Drablos1 of morphological differences between the rosettes of two different fibre systems.

Afferent Pathways↗

PubMed1994

The unipolar brush cell: a neglected neuron of the mammalian cerebellar cortex.

We describe with a variant of the Golgi method a new type of neuron that is prominently represented in the granular layer of the mammalian vestibulocerebellum but is presently neglected in all major accounts on the cerebellum. These neurons, here termed unipolar brush cells, are intermediate in size between granule cells and Golgi cells. They typically have a thin and presumably myelinated axon, and a single and stubby dendrite whose tip forms a tightly packed group of branchlets resembling a paintbrush. The branchlets often intertwine with the digitiform claws of granule cell dendrites and are occasionally approached by Golgi cell dendrites, indicating that the unipolar brush cells may share the input of the other granular layer neurons. Branchlets of neighboring unipolar brush cells converging into the same neuropil island also occur. The brush-like tip of the unipolar cell engulfs one or two mossy fiber rosettes to form an extensive synapse that appears to close recurrent loops involving the vestibular nuclei. Positive feedback in these loops could help to explain several motor responses and drive mechanisms of extended duration that are controlled by the ventral cerebellum.

Animals↗

PubMed1979

Postnatal vascular growth in the cerebellar cortex of normal and protein-deprived rats. Morphometric studies.

The postnatal vascular growth in the cortex of vermis cerebelli folium IX of normal and pre- and postnatally protein-deprived rats was examined. The rate of increase in specific length of vessels seem to parallel the functional maturation of neurons in all cortical layers. From the first postnatal week there is a higher specific length of vessels in the Purkinje cell layer than in the adjoining parts of the molecular and granular layers. The results indicate that such differences are present also after the period of rapid vascular growth. Protein deprivation appears to affect the postnatal increase in specific length of vessels less in the Purkinje cell layer than in the granular and molecular layer where a significant reduction compared to controls was seen for the interval 7--20 days of age. At 90 days of age no significant differences were seen between control and protein-deprived rats.

Age Factors↗

PubMed1986

Localization of Thy-1 expression during postnatal development of the mouse cerebellar cortex.

Thy-1 is a cell membrane differentiation antigen with a restricted distribution in murine tissues. In both mice and rats the antigen is widely expressed in the CNS, while in the neonatal cerebellum it is expressed at very low levels. We have devised a protocol of immersion fixation by freeze-substitution that preserves both antigenicity and tissue morphology. We have stained freeze-substituted tissue sections of developing mouse cerebella with monoclonal anti-Thy-1. Thy-1 is faintly detectable at birth in Purkinje cells and in the molecular layer. The intensity in these two sites increases to a maximum at day 9; this subsequently decreases in the Purkinje cell cytoplasm until most are negative by day 21, but persists in the molecular layer into adulthood. Thy-1 is not detectable in the external granular layer and is only detectable in the glomeruli of the internal granular layer. Ascending fibre tracts are positive from day 5 onwards. The chronologic and anatomic expressions of Thy-1 are compatible with a role of Thy-1 in the generation and maintenance of synapses.

Aging↗

PubMed2001

A tryptophan-deficient corn-based diet induces plastic responses in cerebellar cortex cells of rat offspring.

Sprague-Dawley male rats, fed with a tryptophan-deficient and 8% protein corn-based diet were compared with a group of animals fed with 8% protein alone, and with a group fed with Chow Purina containing 23% protein. Retardation of Bergmann glial cell maturation and a concomitant retardation in granule cell migration were observed in the corn-fed group at 21 days. At 30 days of age, the dendrites of granule cells of both hypoproteic and corn-fed groups were larger than those of the Chow-fed animals. At 60 days of age, dendritic arborization of Purkinje cells was more profuse in both the hypoproteic and corn-fed rats compared with the Chow-fed group. This retardation in granule cell migration could be partially due to Bergmann glial cell immaturity. Consequently, several plastic and maybe compensatory events in both granule and Purkinje cells could have occurred, due to tryptophan deficiency resulting from the corn-based diet.

Animal Feed↗

PubMed1998

Metabotropic glutamate receptors are associated with non-synaptic appendages of unipolar brush cells in rat cerebellar cortex and cochlear nuclear complex.

Unipolar brush cells (UBCs) are a class of small neurons that are densely concentrated in the granular layers of the vestibulocerebellar cortex and dorsal cochlear nucleus. The UBCs form giant synapses with individual mossy fibre rosettes on the dendrioles which make up their brush formations and are provided with numerous, unusual non-synaptic appendages. In accord with the glutamatergic nature of mossy fibres, our previous post-embedding immunocytochemical studies indicated that various ionotropic glutamate receptor subunits are localized at the post-synaptic densities of the giant synapses, whereas the non-synaptic appendages are immunonegative. On the contrary, the metabotropic glutamate receptors mGluR1alpha and mGluR2/3 are situated at the non-synaptic appendages and are lacking at the post-synaptic densities. Other authors, however, have shown that antibodies to these metabotropic receptors stain both appendages and post-synaptic densities. In the present study, we have re-evaluated the distribution of metabotropic glutamate receptors in the UBCs of the cerebellum and the cochlear nuclear complex by light and electron microscopic pre-embedding immunocytochemistry with subtype-specific antibodies. We confirm that UBCs dendritic brushes are densely immunostained by antibody to mGluR1alpha particularly in the cerebellum and that antibody to mGluR2/3 labels at least a percentage of the UBC brushes in both the cerebellum and cochlear nuclei. At the ultrastructural level, it appears that mGluR1alpha and mGluR2/3 immunoreactivities are not associated with the post-synaptic densities of the giant mossy fibre-UBC synapses, but instead are concentrated on the non-synaptic appendages of the cerebellar UBCs. The non-synaptic appendages, therefore, may be an important avenue for regulating the excitability of UBCs and mediating glutamate effects on their still unknown intracellular signal transduction cascades. We also show that the pre-synaptic densities of UBC dendrodendritic junctions are mGluR2/3 positive. As previously demonstrated, antibodies to mGluR1alpha and mGluR2/3 label subsets of Golgi cells. Antibody to mGluR5 does not stain UBCs in the cerebellum and cochlear nucleus and reveals the somatodendritic compartment of Golgi cells situated in the core of the cerebellar granular layer, whilst cochlear nucleus Golgi cells are mGluR5 negative.

Animals↗

PubMedDate not supplied

No parallel fiber volleys in the cerebellar cortex: evidence from cross-correlation analysis between Purkinje cells in a computer model and in recordings from anesthetized rats.

Purkinje cells aligned on the medio-lateral axis share a large proportion of their approximately 175,000 parallel fiber inputs. This arrangement has led to the hypothesis that movement timing is coded in the cerebellum by beams of synchronously active parallel fibers. In computer simulations I show that such synchronous activation leads to a narrow spike cross-correlation between pairs of Purkinje cells. This peak was completely absent when shared parallel fiber input was active in an asynchronous mode. To determine the presence of synchronous parallel fiber beams in vivo I recorded from pairs of Purkinje cells in crus IIa of anesthetized rats. I found a complete absence of precise spike synchronization, even when both cells were strongly modulated in their spike rate by trains of air-puff stimuli to the face. These results indicate that Purkinje cell spiking is not controlled by volleys of synchronous parallel fiber inputs in the conditions examined. Instead, the data support a model by which granule cells primarily control Purkinje cell spiking via dynamic population rate changes.

Action Potentials↗

PubMed1980

Scanning electron microscopy of human cerebellar cortex.

Scanning electron microscopy and cryofracture technique were applied to study neuronal architecture and synaptic connections of the human cerebellum. Samples were processed according to the technique of Humphreys et al. (1975) with minor modifications. The granule cells exhibit unbranched filiform axons and coniform dendritic processes. The latter show typical claw-like endings making "gearing type" synaptic contacts with mossy fiber rosettes. The unattached mossy rosettes appear as solid club-like structures. Some fractographs show individual granule cells, Golgi neurons and glomerular islands. The climbing fibers and their Scheibel's collaterals were also characterized. In the Purkinje layer the surface fracture was produced at the level of the Bergmann glial cells, which are selectively removed, allowing us to visualize the rough surface of Purkinje cells and the supra- and infraganglionic plexuses of basket cell axons which appeared as entangled threads. In the molecular layer the three-dimensional configuration of the Purkinje secondary and tertiary dendritic branches was obtained. The filiform parallel fibers make cruciform synaptic contacts with the Purkinje dendritic spines. The appearance of stellate neuronal somata closely resembled that of the granule cells. The subpial terminals of Bergmann fibers appeared attached to the exterior of the folia forming the rough surfaced external glial limiting membrane.

Adolescent↗

PubMed1988

Mode of induction of long-term depression at parallel fibre--Purkinje cell synapses in rabbit cerebellar cortex.

In a superficial folium of the dorsal paraflocculus of high decerebrate rabbits, extracellular unitary spikes were recorded from a Purkinje cell, while two parallel fibre beams impinging onto that Purkinje cell were separately stimulated in the molecular layer. Climbing fibre afferents were stimulated at the contralateral inferior olive. Quisqualate was ionophoretically applied to the dendrite of the Purkinje cell intersecting one of the stimulated parallel fibre beams (test beam). Long-term depression (longer than 45 min) occurred in Purkinje cell responsiveness to the test beam, but not to the other beam (control beam), when quisqualate was applied for 4 min in conjunction with 2 Hz stimulation of climbing fibres. This effect was completely abolished by simultaneous application of a glutamate blocker, kynurenate, during conjunctive quisqualate-climbing fibre stimulation. Application of quisqualate alone caused a small degree of depression in parallel fibre-Purkinje cell transmission. This effect was abolished when spontaneous activity of climbing fibres was blocked by injection of tetrodotoxin or lidocaine to the contralateral inferior olive, and therefore was due to conjunction of quisqualate with spontaneous climbing fibre inputs that normally occurred at 0.5-1.2 Hz. These findings suggest that the occurrence of long-term depression is strictly dependent on conjunction of climbing fibre activity with quisqualate receptor activation.

Action Potentials↗

PubMed1985

On the role of taurine in the cerebellar cortex: a reappraisal.

Certain amino acids are now widely accepted as constituting one of the major groups of neurotransmitters in the mammalian central nervous system. However, although the available data suggest that taurine may well be involved in central synaptic transmission, its precise neurohumoral role in many areas is still poorly understood. Some of the prerequisites for the identification of chemical transmitters have been fulfilled by taurine in various central structures, including the cerebellum, but data are still inconclusive concerning its possible role either as a classical neurotransmitter or as a modulator of neuronal excitability. The synaptic role of taurine in the cerebellum is supported by: 1) its high levels associate with the synaptic fraction, 2) the identification of a high-affinity uptake mechanism, 3) its inhibitory effects exerted upon Purkinje cells, and 4) the calcium-dependence of its stimulus-induced release. However, the criterion of identity of action has not been demonstrated and a specific taurine receptor has not yet been identified. Furthermore, the observed calcium-dependence of taurine efflux may be explained as a secondary result of the release of endogenous glutamate by an inhibitory feed-back mechanism acting through autoreceptors. Therefore, although the present data support a possible involvement of taurine in central neurotransmission, its precise synaptic role remains to be established.

Action Potentials↗

PubMed1988

The glutamate receptor subtype mediating parallel fibre-Purkinje cell transmission in rabbit cerebellar cortex.

Responses of Purkinje cells to parallel fibre stimulation and to ionophoretically applied glutamate agonists, L-glutamate, L-aspartate, quisqualate, kainate and N-methyl-D-aspartate (NMDA), were extracellularly recorded in a superficial folium of the dorsal paraflocculus of high-decerebrate rabbits. NMDA caused an inhibition of simple spike discharge from Purkinje cells. 2-Amino-5-phosphonovalerate (APV), a selective NMDA receptor antagonist, effectively antagonized this inhibition. However, APV did not antagonize the excitation of Purkinje cells caused by quisqualate or parallel fibre stimulation. By contrast, both kynurenate and gamma-D-glutamylglycine (gamma-DGG) effectively antagonized the excitation of Purkinje cells by parallel fibre stimulation in a dose-dependent manner. Both kynurenate and gamma-DGG also antagonized the excitation of Purkinje cells caused by quisqualate, L-glutamate, L-aspartate or kainate. However, the antagonism was more prominent to L-aspartate and kainate than to quisqualate and L-glutamate. Quisqualate response was antagonized to an extent comparable with the response to parallel fibre stimulation. These results indicate that the receptor for the neurotransmitter at parallel fibre-Purkinje cell synapses is of quisqualate-specific type. The present data are consistent with the evidence that L-glutamate is the endogenous transmitter at these synapses.

2-Amino-5-phosphonovalerate↗

PubMed2005

NADPH-consuming enzymes correlate with glucose-6-phosphate dehydrogenase in Purkinje cells: an immunohistochemical and enzyme histochemical study of the rat cerebellar cortex.

In cerebellum of the adult rat, glucose-6-phosphate dehydrogenase (G6PD) activity is particularly localized in Purkinje cells, showing lower activity in the molecular and granule cell layers. G6PD is the first and rate-limiting step of the hexose monophosphate shunt (HMS), which has the physiological role of providing NADPH for reductive biosynthesis and detoxifying reactions. In this study, we searched for a possible correlation between G6PD and other NADPH-consuming enzymes, such as NADPH-cytochrome P450 reductase (P450R), glutathione reductase (GR) and NADPH-diaphorase (NADPH-d). This study was performed by means of immunohistochemistry and enzyme histochemistry followed by quantitative densitometric and confocal laser scanning microscopic analyses. Our results demonstrated that G6PD, P450R and GR have a similar distribution pattern characterized by the highest concentration of these enzymes in the somata of Purkinje cells, and by lower concentrations in the molecular and the granule cell layers. Moreover, in Purkinje cells, G6PD colocalized with both P450R and GR. NADPH-d activity showed a different distribution pattern when compared to the other enzymes, revealing the highest activity in the molecular layer and the lowest in Purkinje cells. Our results suggest a coordinated regulative mechanism of G6PD, P450R and GR based on the request of NADPH or on specific transcription factors.

Analysis of Variance↗

PubMed1984

Alterations in the postnatal development of the cerebellar cortex due to zinc deficiency. II. Impaired maturation of Purkinje cells.

Zinc deficiency during the first 3 postnatal weeks retarded the maturation of Purkinje cells. The dendrites of the Purkinje cells of 21-day-old zinc-deficient (ZD) rats were reduced in size and had fewer branches. Somatic processes were found in 24% of the Purkinje cells of ZD animals. Only 3% of the Purkinje cells of normal animals had somatic processes. A basal polysomal mass in the Purkinje cells of 21-day-old ZD rats indicated that zinc deficiency impaired the cytoplasmic maturation of Purkinje cells. The development of the glial envestment of the dendrites and the maturation of climbing fibers also were retarded. Pair-fed controls were studied to control for the effects of inanition in the ZD dams. In the pups of pair-fed dams, undernutrition slightly impaired the growth of the dendrites but produced few qualitative changes in the maturation of the soma and climbing fibers. Somatic processes were found on 10% of the Purkinje cells of pair-fed animals. Thus, the findings in the ZD animals were not only caused by the decreased maternal food consumption but by zinc deficiency. The retarded maturation of Purkinje cells was related to the altered metabolism of Purkinje cells and to effects secondary to decreased numbers of parallel fibers.

Aging↗

PubMed1989

Dendritic development of Purkinje and granule cells in the cerebellar cortex of rats treated postnatally with alpha-difluoromethylornithine.

Postnatal administration of alpha-difluoromethylornithine (DFMO), an irreversible inhibitor of ornithine decarboxylase (ODC), is known to curtail replication of granule cells in the cerebellum of the rat, but its effects on post-proliferative neurons is unknown. This Golgi study assessed the influence of daily postnatal injections of DFMO on dendritic development of the Purkinje and granule cells. Although the overall appearance of the Purkinje cells was normal, DFMO affected morphogenesis by causing: 1) a reduction in somatic growth, 2) an elongation of the primary dendrite, 3) a lengthening of the distance between the soma and the pial surface, 4) a reduction in the number of tertiary dendrites, and 5) a disruption of the distribution of the tertiary branches. Many of these effects of DFMO may be mediated via the reduction of granule cells rather than representing a direct effect on dendritogenesis. In addition to reducing the number of granule cells, the distribution and morphology of these cells in the DFMO-treated rats were severely affected. Many granule cells did not complete their migration and remained trapped in the molecular layer, and many of those trapped had greatly elongated dendrites that extended into the internal granule cell layer. These results suggest that ornithine decarboxylase is involved in the postproliferative processes of neuronal migration and differentiation.

Animals↗

PubMed1991

Physiological interactions between enkephalin and excitatory amino acids in the cerebellar cortex of the opossum Didelphis marsupialis virginiana.

The opiate peptide enkephalin has been immunohistochemically localized within specific populations of climbing fibers and mossy fibers in the opossum's cerebellum. The intention of the present study was to determine the physiological effects of this peptide on Purkinje cell activity as well as to examine interactions between this peptide and the excitatory amino acids glutamate and aspartate. Iontophoretic application of enkephalin onto Purkinje cells in the posterior lobe vermis and adjacent hemisphere suppressed activity in nine of 16 (56%) spontaneously active units. Enkephalin increased the spontaneous activity of one unit and had no effect on six (38%) of the units. In addition, this peptide blocked the excitatory effects elicited by iontophoretic application of glutamate in 34 of 35 (97%) units tested and of aspartate in all cases. Enkephalin had no effect on one cell activated by glutamate. Simultaneous application of naloxone, a nonspecific opiate receptor antagonist, did not block the suppressive effects of enkephalin. Rather, there was a potentiation of suppressive responses as compared to that seen when each is applied alone. The results suggest that classically defined excitatory afferent projections to the cerebellum may be capable of both exciting and suppressing the activity of their target neurons. The excitatory action is likely mediated by an amino acid, whereas the release of the peptide enkephalin results in a decrease in unit activity. Further, it appears that enkephalin mediates its suppressive effect through mechanisms that are not mediated by opioid receptors.

Animals↗

PubMed2004

Cell proliferation correlates with the postconceptual and not with the postnatal age in the hippocampal dentate gyrus, temporal neocortex and cerebellar cortex of preterm infants.

BACKGROUND: In previous studies, lower IQ scores and educational difficulties of preterm children were correlated with the reduced size of several brain areas, including the cerebellum and the hippocampus. The most plausible reason for reduction would be the reduced cell formation following premature birth. However, no data are available about the rate of postnatal cell proliferation in the different brain areas of preterms. METHODS: Cytoarchitectonics and cell proliferation were examined in the cerebellum, hippocampal formation and temporal neocortex of preterm infants who lived for several weeks or months. Cell proliferation was detected with Ki-67 immunostaining and proliferating cells were identified with vimentin as glial and with CD31 and periodic acid-Schiff (PAS) reaction as endothelial elements. RESULTS: The rate of cell formation and the width of the cytoarchitectonic layers of the cerebellum of preterm infants corresponded to that of the age-matched controls. In the hippocampal dentate gyrus, the rate of cell formation and the density of proliferating cells were slightly higher in the preterm infants than in the full-term age-matched controls. Endothelial cell proliferation and the surface area of the capillaries were larger in the dentate gyrus of preterms than in age-matched controls. CONCLUSION: Rate of cell proliferation that correlates with the postconceptual age is not reduced in preterms, therefore the reduced size of the cerebellum and hippocampal formation is unlikely to be the result of decreased cell formation.

Aging↗