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Results for “Cerebellar Cortex”

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At least 541 records · Page 30Linked to original sources
PubMed1995

Connections to cerebellar cortex (Larsell's HVI) in the rabbit: a WGA-HRP study with implications for classical eyeblink conditioning.

Conditioned eyeblink responses are presumably learned in the cerebellum and relayed to motoneurons by way of the red nucleus. Projections from the red nucleus to cerebellar cortex (Larsell's lobule HVI) could be important for shaping temporally adaptive features of the conditioned response. Rabbits that had pipettes containing wheat germ agglutinated horseradish peroxidase (WGA-HRP) implanted unilaterally into HVI showed retrograde labeling of neurons within subregions of the contralateral red nucleus implicated in eyeblink conditioning by lesioning and recording studies. Retrogradely labeled neurons were also observed in the pontine nuclei, inferior olive, and spinal trigeminal nucleus pars oralis. Projections to HVI provide a possible neural substrate for implementing time-derivative computational models of learning in the cerebellum. Time-derivative models are capable of describing the timing and topography of conditioned responses.

Animals↗
PubMed1995

Calcitonin gene-related peptide modulates neuronal activity in the mammalian cerebellar cortex.

Calcitonin gene related peptide (CGRP) has been localized within specific populations of mossy fibers in the cat's cerebellar cortex. The intent of the present study was to determine the physiological role of this peptide in cerebellar circuitry. CGRP was iontophoretically applied and its effects on spontaneous, amino acid-induced, and synaptically-mediated activity were recorded. In addition, interactions between CGRP and serotonin (5HT), another neuromodulator in cerebellar circuitry, also were analyzed. The findings of this study reveal that the primary effect of CGRP is to suppress spontaneous and excitatory amino acid-induced activity. However, CGRP has a more potent effect in suppressing aspartate- and quisqualate-induce activity as compared to that elicited by glutamate. CGRP slowed or completely blocked synaptic activity mediated by stimulation of the inferior cerebellar peduncle. Finally, the individual suppressive effects of 5HT and CGRP were potentiated when both were applied simultaneously. However, the potentiation was greater when the neuron was exposed to 5HT before CGRP was applied. In summary, the presence of CGRP in selected populations of mossy fibers, together with serotoninergic afferents, decreases the responsiveness of Purkinje cells to excitatory amino acids as well as synaptically-driven activity. Thus, activation of an afferent system to the cerebellum can elicit distinct effects on different populations of neurons that are dependent on the microenvironment of the cell at a particular point in time.

Amino Acids↗
PubMed1977

Time of origin and distribution of a new cell type in the rat cerebellar cortex.

A new cell type was identified in the granular layer of the rat cerebellum. It has a lightly staining nucleus with a nucleolus, it is spherical in shape and is larger than granule cells and smaller than Golgi cells. These pale cells are preferentially concentrated in the nodulus, the ventral uvula, the lingula, the flocculus, and parts of the paraflocculus. According to autoradiographic (3H-thymidine) evidence, over 60% of these pale cells are formed on embryonic days 19 and 20, and their production comes to an end soon after birth, prior to the differentiation of granule cells. The possible relation of pale cells to vestibular afferents of the cerebellar cortex is discussed.

Animals↗
PubMed1986

Golgi-electron microscopic study of sprouting endothelial cells in the neonatal rat cerebellar cortex.

Intraparenchymal postnatal development of the CNS vasculature proceeds by a process of vascular 'budding' or 'sprouting' from existing endothelial cells and elongation of these immature vessels. A modified Golgi technique combined with gold toning and deimpregnation was used to identify and characterize sprouting endothelial cells in the neonatal rat cerebellar cortex with light and electron microscopy. Sprouting endothelial cells were the terminal endothelial cells of immature, developing blood vessels and they had characteristic morphologic features. The most distinctive feature was an array of tentacular processes (0.1-0.2 micron in diameter and ca. 20 microns in length) which radiated from the apex of these cells in the presumed direction of vessel growth. Cytoskeletal microtubules and microfilaments were the characteristic organelles of these tentacles. Sprouting endothelial cells were thin (1-3 microns in diameter). lacked a vessel lumen and basement membrane, had abundant cytoplasmic organelles and a prominent nucleus and were closely associated with the subterminal endothelial cell without interendothelial gaps. The developing blood vessels had a blood-brain barrier which excluded intravenously injected colloidal carbon from the neuropil.

Animals↗
PubMed1999

On the role of anatomy in learning by the cerebellar cortex.

The properties due to the location of neurons, synapses, and possibly even synaptic channels, in neuron networks are still unknown. Our preliminary results suggest that not only the interconnections but also the relative positions of the different elements in the network are of importance in the learning process in the cerebellar cortex. We have used neural field equations to investigate the mechanisms of learning in the hierarchical neural network. The numerical resolution of these equations reveals two important properties: (i) The hierarchical structure of this network has the expected effect on learning because the flow of information at the neuronal level is controlled by the heterosynaptic effect through the synaptic density-connectivity function, i.e. the action potential field variable is controlled by the synaptic efficacy field variable at different points of the neuron. (ii) The geometry of the system involves different velocities of propagation along different fibers, i.e. different delays between cells, and thus has a stabilizing effect on the dynamics, allowing the Purkinje output to reach a given value. The field model proposed should be useful in the study of the spatial properties of hierarchical biological systems.

Cerebellar Cortex↗
PubMed2006

Expression of Toll-like receptor 3 in the human cerebellar cortex in rabies, herpes simplex encephalitis, and other neurological diseases.

There is recent in vitro evidence that human neurons express the innate immune response receptor, Toll-like receptor-3 (TLR-3), and that expression is enhanced in viral infections. The authors examined the immunohistochemical expression of TLR-3 in the cerebellar cortex of postmortem human brains. Purkinje cells were found to express TLR-3 in all cases of rabies (4 of 4) and herpes simplex encephalitis (2 of 2) as well as in cases of amyotrophic lateral sclerosis (1 of 2), stroke (1 of 2), and Alzheimer's disease (3 of 3). In cases of viral infection, direct viral infection was not necessary for enhanced neuronal TLR-3 expression, suggesting that soluble factors likely play an important role in inducing TLR-3 expression. In addition to neurons, occasional Bergmann glia expressed TLR-3 in some cases. This study has provided evidence that human brain neurons can express TLR-3 in vivo and suggests that neurons may play an important role in initiating an inflammatory reaction in a variety of neurological diseases.

Adolescent↗
PubMed1985

[Cerebellar cortex: simulation of recurrent collateral inhibition by means of a neuronal automata assembly. II. Temporal modulation and informational content].

A quantitative evaluation of the information content exhibited by a neuronal automata assembly coupled by collateral inhibitory--type rules was undertaken on the results of a computer simulation of this partial model of the cerebellar cortex. By comparison with an uncoupled array the model exhibited two main properties: A markovian type of behavior appears in the functioning of the system in as much as the appearance of a given state is strongly and exclusively correlated to the immediately preceding one. This behavior leads to a decrease in the entropy of the system. This implies that the informational content of the efferent "activity" is significantly higher than that of the afferent one.

Cerebellar Cortex↗
PubMed1990

Synapse-to-neuron ratios in rat cerebellar cortex following lengthy periods of undernutrition.

Black and white hooded Lister rats were undernourished for various times up to 150 days of age; some of them were nutritionally rehabilitated from 75 days. Undernourished rats weighed significantly less than well-fed controls at all ages studied. After embedding in resin, sections of cerebellar cortex were cut and examined at the light and electron microscopical levels using traditional morphometric methods. Undernourished rats showed significant deficits in synapse-to-neuron ratio, compared with controls, at 21 days of age. This deficit disappeared by 75 days despite continued undernutrition. Indeed, there was no alteration in this ratio even when undernutrition was extended up to 150 days even though the ratio for the controls decreased after that period. Rats undernourished from birth to 75 days and subsequently rehabilitated to 150 days had significantly more synapses per neuron than controls. The functional sequelae of these morphological changes remain unknown.

Age Factors↗
PubMed1996

Expression and subcellular distribution of glutamate receptor subunits 2/3 in the developing cerebellar cortex.

The expression and subcellular location of glutamate receptor subunits 2&3 was investigated in the developing postnatal cerebellum. Immunoblotting revealed that glutamate receptor subunits 2/3 is expressed in an identical pattern of immunoreactive bands of approximately 108 kDa from postnatal day zero to adult animals. Light microscopy showed that within the cerebellar cortex, GluR 2/3 immunoreactivity was essentially confined to Purkinje neurons. Strong immunostaining could be observed at postnatal days 1-3 within Purkinje cell bodies and primary dendrites. With ongoing development, the cell body and an increasingly elaborate dendritic tree was outlined by immunoreaction product. In adult animals, staining of Purkinje cell dendrites was patchy, and staining intensity of the cell body, in particular, was greatly reduced. Ultrastructural analysis revealed that during early postnatal development, immunoreaction product was localized to the cell membrane, but was not confined to postsynaptic densities. From the second postnatal week, glutamate receptor subunits 2/3 immunoreactivity was largely restricted to postsynaptic densities. These observations reveal a developmentally regulated refinement of the subcellular distribution of defining subunits of the AMPA-type glutamate receptor. The presence of membrane bond receptors prior to the formation of synapses also provides a rationale for the known transmitter-mediated modulation of Purkinje cell dendritogenesis.

Age Factors↗