Anatomical Development of the Cerebellothalamic Tract in Embryonic Mice.

The main connection from cerebellum to cerebrum is formed by cerebellar nuclei axons that synapse in the thalamus. Apart from its role in coordinating sensorimotor integration in the adult brain, the cerebello-thalamic tract (CbT) has also been implicated in developmental disorders, such as autism spectrum disorders. Although the development of the cerebellum, thalamus and cerebral cortex have been studied, there is no detailed description of the ontogeny of the mammalian CbT. Here we investigated the development of the CbT at embryonic stages using transgenic Ntsr1-Cre/Ai14 mice and in utero electroporation of wild type mice. Wide-field, confocal and 3D light-sheet microscopy of immunohistochemical stainings showed that CbT fibers arrive in the prethalamus between E14.5 and E15.5, but only invade the thalamus after E16.5. We quantified the spread of CbT fibers throughout the various thalamic nuclei and found that at E17.5 and E18.5 the ventrolateral, ventromedial and parafascicular nuclei, but also the mediodorsal and posterior complex, become increasingly innervated. Several CbT fiber varicosities express vesicular glutamate transporter type 2 at E18.5, indicating cerebello-thalamic synapses. Our results provide the first quantitative data on the developing murine CbT, which provides guidance for future investigations of the impact that cerebellum has on thalamo-cortical networks during development.

Activity of Cerebellar Nuclei Neurons Correlates with ZebrinII Identity of Their Purkinje Cell Afferents.

Purkinje cells (PCs) in the cerebellar cortex can be divided into at least two main subpopulations: one subpopulation that prominently expresses ZebrinII (Z+), and shows a relatively low simple spike firing rate, and another that hardly expresses ZebrinII (Z-) and shows higher baseline firing rates. Likewise, the complex spike responses of PCs, which are evoked by climbing fiber inputs and thus reflect the activity of the inferior olive (IO), show the same dichotomy. However, it is not known whether the target neurons of PCs in the cerebellar nuclei (CN) maintain this bimodal distribution. Electrophysiological recordings in awake adult mice show that the rate of action potential firing of CN neurons that receive input from Z+ PCs was consistently lower than that of CN neurons innervated by Z- PCs. Similar in vivo recordings in juvenile and adolescent mice indicated that the firing frequency of CN neurons correlates to the ZebrinII identity of the PC afferents in adult, but not postnatal stages. Finally, the spontaneous action potential firing pattern of adult CN neurons recorded in vitro revealed no significant differences in intrinsic pacemaking activity between ZebrinII identities. Our findings indicate that all three main components of the olivocerebellar loop, i.e., PCs, IO neurons and CN neurons, operate at a higher rate in the Z- modules.

Single-pulse stimulation of cerebellar nuclei stops epileptic thalamic activity.

BACKGROUND: Epileptic (absence) seizures in the cerebral cortex can be stopped by pharmacological and optogenetic stimulation of the cerebellar nuclei (CN) neurons that innervate the thalamus. However, it is unclear how such stimulation can modify underlying thalamo-cortical oscillations. HYPOTHESIS: Here we tested whether rhythmic synchronized thalamo-cortical activity during absence seizures can be desynchronized by single-pulse optogenetic stimulation of CN neurons to stop seizure activity. METHODS: We performed simultaneous thalamic single-cell and electrocorticographical recordings in awake tottering mice, a genetic model of absence epilepsy, to investigate the rhythmicity and synchronicity. Furthermore, we tested interictally the impact of single-pulse optogenetic CN stimulation on thalamic and cortical recordings. RESULTS: We show that thalamic firing is highly rhythmic and synchronized with cortical spike-and-wave discharges during absence seizures and that this phase-locked activity can be desynchronized upon single-pulse optogenetic stimulation of CN neurons. Notably, this stimulation of CN neurons was more effective in stopping seizures than direct, focal stimulation of groups of afferents innervating the thalamus. During interictal periods, CN stimulation evoked reliable but heterogeneous responses in thalamic cells in that they could show an increase or decrease in firing rate at various latencies, bi-phasic responses with an initial excitatory and subsequent inhibitory response, or no response at all. CONCLUSION: Our data indicate that stimulation of CN neurons and their fibers in thalamus evokes differential effects in its downstream pathways and desynchronizes phase-locked thalamic neuronal firing during seizures, revealing a neurobiological mechanism that may explain how cerebellar stimulation can stop seizures.

Consensus Paper: Experimental Neurostimulation of the Cerebellum.

The cerebellum is best known for its role in controlling motor behaviors. However, recent work supports the view that it also influences non-motor behaviors. The contribution of the cerebellum towards different brain functions is underscored by its involvement in a diverse and increasing number of neurological and neuropsychiatric conditions including ataxia, dystonia, essential tremor, Parkinson's disease (PD), epilepsy, stroke, multiple sclerosis, autism spectrum disorders, dyslexia, attention deficit hyperactivity disorder (ADHD), and schizophrenia. Although there are no cures for these conditions, cerebellar stimulation is quickly gaining attention for symptomatic alleviation, as cerebellar circuitry has arisen as a promising target for invasive and non-invasive neuromodulation. This consensus paper brings together experts from the fields of neurophysiology, neurology, and neurosurgery to discuss recent efforts in using the cerebellum as a therapeutic intervention. We report on the most advanced techniques for manipulating cerebellar circuits in humans and animal models and define key hurdles and questions for moving forward.

Activation of the DNA damage response in vivo in synucleinopathy models of Parkinson's disease.

The involvement of DNA damage and repair in aging processes is well established. Aging is an unequivocal risk factor for chronic neurodegenerative diseases, underscoring the relevance of investigations into the role that DNA alterations may have in the pathogenesis of these diseases. Consistently, even moderate impairment of DNA repair systems facilitates the onset of pathological features typical of PD that include derangement of the dopaminergic system, mitochondrial dysfunction, and alpha-synuclein stress. The latter establishes a connection between reduced DNA repair capacity and a cardinal feature of PD, alpha-synuclein pathology. It remains to be determined, however, whether alpha-synuclein stress activates in vivo the canonical signaling cascade associated with DNA damage, which is centered on the kinase ATM and substrates such as γH2Ax and 53BP1. Addressing these issues would shed light on age-related mechanisms impinging upon PD pathogenesis and neurodegeneration in particular. We analyzed two different synucleinopathy PD mouse models based either on intranigral delivery of AAV-expressing human alpha-synuclein, or intrastriatal injection of human alpha-synuclein pre-formed fibrils. In both cases, we detected a significant increase in γH2AX and 53BP1 foci, and in phospho-ATM immunoreactivity in dopaminergic neurons, which collectively indicate DNA damage and activation of the DNA damage response. Mechanistic experiments in cell cultures indicate that activation of the DNA damage response is caused, at least in part, by pro-oxidant species because it is prevented by exogenous or endogenous antioxidants, which also rescue mitochondrial anomalies caused by proteotoxic alpha-synuclein. These in vivo and in vitro findings reveal that the cellular stress mediated by alpha-synuclein-a pathological hallmark in PD-elicits DNA damage and activates the DNA damage response. The toxic cascade leading to DNA damage involves oxidant stress and mitochondrial dysfunction The data underscore the importance of DNA quality control for preservation of neuronal integrity and protection against neurodegenerative processes.

Differentiating Cerebellar Impact on Thalamic Nuclei.

The cerebellum plays a role in coordination of movements and non-motor functions. Cerebellar nuclei (CN) axons connect to various parts of the thalamo-cortical network, but detailed information on the characteristics of cerebello-thalamic connections is lacking. Here, we assessed the cerebellar input to the ventrolateral (VL), ventromedial (VM), and centrolateral (CL) thalamus. Confocal and electron microscopy showed an increased density and size of CN axon terminals in VL compared to VM or CL. Electrophysiological recordings in vitro revealed that optogenetic CN stimulation resulted in enhanced charge transfer and action potential firing in VL neurons compared to VM or CL neurons, despite that the paired-pulse ratio was not significantly different. Together, these findings indicate that the impact of CN input onto neurons of different thalamic nuclei varies substantially, which highlights the possibility that cerebellar output differentially controls various parts of the thalamo-cortical network.