Purkinje cell | EPFL Graph Search

Purkinje cells, or Purkinje neurons, are a class of GABAergic inhibitory neurons located in the cerebellum. They are named after their discoverer, Czech anatomist Jan Evangelista Purkyně, who characterized the cells in 1839. These cells are some of the largest neurons in the human brain (Betz cells being the largest), with an intricately elaborate dendritic arbor, characterized by a large number of dendritic spines. Purkinje cells are found within the Purkinje layer in the cerebellum. Purkinje cells are aligned like dominos stacked one in front of the other. Their large dendritic arbors form nearly two-dimensional layers through which parallel fibers from the deeper-layers pass. These parallel fibers make relatively weaker excitatory (glutamatergic) synapses to spines in the Purkinje cell dendrite, whereas climbing fibers originating from the inferior olivary nucleus in the medulla provide very powerful excitatory input to the proximal dendrites and cell soma. Parallel fibers pass orthogonally through the Purkinje neuron's dendritic arbor, with up to 200,000 parallel fibers forming a Granule-cell-Purkinje-cell synapse with a single Purkinje cell. Each Purkinje cell receives approximately 500 climbing fiber synapses, all originating from a single climbing fiber. Both basket and stellate cells (found in the cerebellar molecular layer) provide inhibitory (GABAergic) input to the Purkinje cell, with basket cells synapsing on the Purkinje cell axon initial segment and stellate cells onto the dendrites. Purkinje cells send inhibitory projections to the deep cerebellar nuclei, and constitute the sole output of all motor coordination in the cerebellar cortex. The Purkinje layer of the cerebellum, which contains the cell bodies of the Purkinje cells and Bergmann glia, express a large number of unique genes. Purkinje-specific gene markers were also proposed by comparing the transcriptome of Purkinje-deficient mice with that of wild-type mice.

Multi-Modal Optical Imaging of the Cerebellum in Animals

Graham Knott, Ludovico Silvestri

Thanks to their flexibility, optical techniques could be the key to explore anatomy, plasticity, and functionality of the cerebellum. As an example, an in vivo analysis of the dynamic remodeling of cerebellar axons by nonlinear microscopy can provide fundamental insights of the mechanism that promotes neuronal regeneration. Several studies showed that damaged climbing fibers are capable of regrowing also in adult animals. The investigation of the time-lapse dynamics of degeneration and regeneration of these axons within their complex environment can be performed by time-lapse two-photon fluorescence (TPF) imaging in vivo. Here, we show that single axonal branches can be dissected by laser axotomy, thus avoiding collateral damage to the adjacent dendrite and the formation of a persistent glial scar. Despite the very small denervated area, the injured axons consistently reshaped the connectivity with surrounding neurons and sprouted new branches through the intact surroundings. Correlative light and electron microscopy revealed that the sprouted branch contains large numbers of vesicles, with varicosities in the close vicinity of Purkinje dendrites. By using an RNA interference approach, we found that downregulating GAP-43 causes a significant increase in the turnover of presynaptic boutons and hampers the generation of reactive sprouts. Further, we report how nonlinear microscopy in combination with novel voltage sensitive dyes or transgenic mice allow optical registrations of action potential across a population of neurons opening promising prospective in understanding brain functionality. Finally, we describe novel implementations of light-sheet microscopy to resolve neuronal anatomy in whole cerebellum with cellular resolution. The understanding gained from these complementary optical methods may provide a deeper comprehension of the cerebellum.

Springer2016

Altered neocortical microcircuitry in the valproic acid rat model of autism

Tania Rinaldi

Autism is a wide-spectrum disorder with early childhood onset, affecting general cognitive capabilities and, in particular, complex information processing. Although interesting directions of research start to appear, the precise causes of the disorder and the resulting brain alterations have not been elucidated yet. The goal of this research project is to get a better understanding of the neocortical microcircuitry alterations in autism, using the valproic acid (VPA) rat model of autism. Exposure to VPA can cause several teratogenic effects, including autism in human if exposure occurs during the third week of gestation. Previous studies explored the results of prenatal VPA exposure in rats and found similar gross abnormalities to those in autism, such as diminished number of Purkinje cells. Behavioural studies further showed that a number of core symptoms, such as impairment in social interactions and higher sensitivity to sensory stimulation, are also present in the VPA-treated rats. We examined the postnatal effects of embryonic exposure to VPA on the microcircuitry properties of juvenile rat neocortex using in vitro electrophysiology. We found that prenatal VPA injection causes a significant increase of more than 50% of the local connectivity formed by pyramidal neurons of the somatosensory cortex, and that the neocortical network becomes hyper-reactive to external stimuli. We identify two possible compensatory mechanisms that may follow the observed hyperconnectivity: reduced excitability of pyramidal neurons and a decreased magnitude for individual synaptic connections. We also illustrate how NMDA receptors are significantly enhanced in the rat model and how this enhancement is associated with an increased plasticity in the neocortex. Both the somatosensorial and prefrontal cortex exhibit increased plasticity, suggesting a general enhanced plasticity in the brains of VPA-exposed rats. In addition, we show that multi-electrode array stimulation of the lateral amygdala reveals a hyper-reactive amygdala with increased synaptic plasticity. These alterations may account for some of the core symptoms in autism spectrum disorders. For example, hyperconnectivity could underlie symptoms such as aberrant reactions to sensory stimulation and altered attention. Also, the enhancement of NMDA mediated transmission and increased plasticity could explain the unusual learning and memory capabilities of some autistic children. Finally, we propose that the hyper-reactive and hyper-plastic amygdala underlies abnormal fear processing in this animal model of autism. We further speculate that abnormal fear processing could be a core pathology in autism which may give rise to behavioural symptoms, such as impairments in social interactions and resistance to rehabilitation.

EPFL2006

Altered neocortical microcircuitry in the valproic acid rat model of autism

Tania Rinaldi

EPFL2006