Intersectin-1 enhances calcium-dependent replenishment of the readily releasable pool of synaptic vesicles during development.

Intersectin-1 (Itsn1) is a scaffold protein that plays a key role in coupling exocytosis and endocytosis of synaptic vesicles (SVs). However, it is unclear whether and how Itsn1 regulates these processes to support efficient neurotransmission during development. To address this, we examined the calyx of Held synapse in the auditory brainstem of wild-type and Itsn1 mutant mice before (immature) and after (mature) the onset of hearing. Itsn1 was present in the pre- and postsynaptic compartments at both developmental stages. Loss of function of Itsn1 did not alter presynaptic action potentials, Ca2+ entry via voltage-gated Ca2+ channels (VGCCs), transmitter release or short-term depression (STD) induced by depletion of SVs in the readily releasable pool (RRP) in either age group. Yet, fast Ca2+-dependent recovery from STD was attenuated in mature mutant synapses, while it was unchanged in immature mutant synapses. This deficit at mature synapses was rescued by introducing the DH-PH domains of Itsn1 into the presynaptic terminals. Inhibition of dynamin, which interacts with Itsn1 during endocytosis, had no effect on STD recovery. Interestingly, we found a developmental enrichment of Itsn1 near VGCCs, which may underlie the Itsn1-mediated fast replenishment of the RRP. Consequently, the absence of Itsn1 in mature synapses led to a higher failure rate of postsynaptic spiking during high-frequency synaptic transmission. Taken together, our findings suggest that Itsn1 translocation to the vicinity of VGCCs during development is crucial for accelerating Ca2+-dependent RRP replenishment and sustaining high-fidelity neurotransmission. KEY POINTS: Itsn1 is expressed in the pre- and postsynaptic compartments of the calyx of Held synapse. Developmental upregulation of vesicular glutamate transporter-1 is Itsn1 dependent. Itsn1 does not affect basal synaptic transmission at different developmental stages. Itsn1 is required for Ca2+-dependent recovery from short-term depression in mature synapses. Itsn1 mediates the recovery through its DH-PH domains, independent of its interactive partner dynamin. Itsn1 translocates to the vicinity of presynaptic Ca2+ channels during development. Itsn1 supports high-fidelity neurotransmission by enabling rapid recovery from vesicular depletion during repetitive activity.

A shedding analysis after AAV8 CNS injection revealed fragmented viral DNA without evidence of functional AAV particles in mice.

Adeno-associated viruses (AAV) are commonly used in the scientific field due to their diverse application range. However, AAV shedding, the release of virions from the host organism, can impact the safety of AAV-based approaches. An increasing number of authorities require the characterization of vector shedding in clinical trials. Recently, shedding of transduced laboratory animals has also gained attention regarding the necessary disposal measures of their waste products. However, no explicit international regulations for AAV-shedding waste exist. Generating insights into shedding dynamics becomes increasingly relevant to help authorities develop adequate regulations. To date, knowledge of AAV vector shedding in mice is very limited. Moreover, confirmation of functional shed AAV particles in mice is missing. Therefore, we examined feces, urine, and saliva of mice after CNS injection with AAV2/8. It revealed the presence of viral DNA fragments via qPCR for up to 4 days after injection. To examine AAV functionality we performed nested PCR and could not detect full-length viral genomes in any but two collected feces samples. Furthermore, a functional infection assay did not reveal evidence of intact AAV particles. Our findings are supposed to contribute murine shedding data as a foundation to help establish still lacking adequate biosafety regulations in the context of AAV shedding.

Cerebellar contribution to threat probability in a SCA6 mouse model.

Fear and anxiety have proven to be essential during the evolutionary process. However, the mechanisms involved in recognizing and categorizing threat probability (i.e. low to high) to elicit the appropriate defensive behavior are yet to be determined. In this study, we investigated the cerebellar contribution in evoking appropriate defensive escape behavior using a purely cerebellar, neurodegenerative mouse model for spinocerebellar ataxia type 6 which is caused by an expanded CAG repeat in exon 47 of the P/Q type calcium channel α1A subunit. These mice overexpress the carboxy terminus (CT) of the P/Q type calcium channel containing an expanded 27 CAG repeat specifically in cerebellar Purkinje cells (CT-longQ27PC). We found that our CT-longQ27PC mice exhibit anxiolytic behavior in the open field, elevated plus maze and light/dark place preference tests, which could be recovered with more threatening conditions such as brighter lighting, meowing sounds and an ultrasound repellent. Their innate fear to find safety in the Barnes maze and visual cliff tests was also diminished with subsequent trials, which could be partially recovered with an ultrasound repellent in the Barnes maze. However, under higher threat conditions such as in the light/dark place preference with ultrasound repellent and in the looming tests, CT-longQ27PC mice responded with higher defensive escape behaviors as controls. Moreover, CT-longQ27PC mice displayed increased levels of CT-labeled aggregates compared with controls. Together these data suggest that cerebellar degeneration by overexpression of CT-longQ27PC is sufficient to impair defensive escape responses in those mice.

Deletion of the P/Q-type calcium channel from serotonergic neurons drives male aggression in mice.

Aggressive behavior is one of the most conserved social interactions in nature and serves as a crucial evolutionary trait. Serotonin (5-HT) plays a key role in the regulation of our emotions such as anxiety and aggression, but which molecules and mechanisms in the serotonergic system are involved in violent behavior is still unknown. In this study we show that deletion of the P/Q-type calcium channel selectively from serotonergic neurons in the dorsal raphe nuclei (DRN) augments aggressive behavior in male mice, while anxiety is not affected. These mice demonstrated increased induction of the immediate early gene c-fos and in vivo serotonergic firing activity in the DRN. The ventrolateral part of the ventromedial hypothalamus (VHMvl) is also a prominent region of the brain mediating aggression. We confirmed a monosynaptic projection from the DRN to the VHMvl and silencing these projections with an inhibitory designer receptor exclusively activated by a designer drug (DREADD) effectively reduced aggressive behavior. Overall, our findings show that deletion of the P/Q-type calcium channel from DRN neurons is sufficient to induce male aggression in mice and regulating its activity may serve as a therapeutic approach to treat violent behavior.SIGNIFICANCE STATEMENTIn this study we show that P/Q-type calcium channel is mediating aggression in serotonergic neurons from the dorsal raphe nucleus via monosynaptic projections to the ventrolateral part of the ventromedial hypothalamus. More importantly, silencing these projections reduced aggressive behavior in mice and may serve as a therapeutic approach for treating aggression in humans.

Cognitive deficits in episodic ataxia type 2 mouse models.

Episodic ataxia type 2 (EA2) is a rare autosomal dominant disorder characterized by motor incoordination, paroxysmal dystonia, vertigo, nystagmus and more recently cognitive deficits. To date over 100 mutations in the CACNA1A gene have been identified in EA2 patients leading to a loss of P/Q-type channel activity, dysfunction of cerebellar Purkinje cells and motor incoordination. To determine if the cerebellum is contributing to these cognitive deficits, we examined two different EA2 mouse models for cognition impairments where CACNA1A was removed specifically from cerebellar Purkinje or granule cells postnatally. Both mutant mouse models showed anxiolytic behavior to lighted, open areas in the open field and light/dark place preference tests but enhanced anxiousness in the novel suppressed feeding test. However, EA2 mice continued to show augmented latencies in the light/dark preference test and when the arena was divided into two dark zones in the dark/dark preference test. Moreover, increased latencies were also displayed in the novel object recognition test, indicating that EA2 mice are indecisive and anxious to explore new territories and objects and may have memory recognition deficits. Exposure to a foreign mouse led to deficiencies in attention and sniffing as well as in social and genital sniffing. These data suggest that postnatal removal of the P/Q type calcium channel from the cerebellum regulates neuronal activity involved in anxiety, memory, decision making and social interactions. Our EA2 mice will provide a model to identify the mechanisms and therapeutic agents underlying cognitive and psychiatric disorders seen in EA2 patients.

Loss of parkin causes endoplasmic reticulum calcium dyshomeostasis by upregulation of reticulocalbin 1.

Increasing evidence suggests that astrocytes play an important role in the progression of Parkinson's disease (PD). Previous studies on our parkin knockout mouse demonstrated a higher accumulation of damaged mitochondria in astrocytes than in surrounding dopaminergic (DA) neurons, suggesting that Parkin plays a crucial role regarding their interaction during PD pathogenesis. In the current study, we examined primary mesencephalic astrocytes and neurons in a direct co-culture system and discovered that the parkin deletion causes an impaired differentiation of mesencephalic neurons. This effect required the parkin mutation in astrocytes as well as in neurons. In Valinomycin-treated parkin-deficient astrocytes, ubiquitination of Mitofusin 2 was abolished, whereas there was no significant degradation of the outer mitochondrial membrane protein Tom70. This result may explain the accumulation of damaged mitochondria in parkin-deficient astrocytes. We examined differential gene expression in the substantia nigra region of our parkin-KO mouse by RNA sequencing and identified an upregulation of the endoplasmic reticulum (ER) Ca2+ -binding protein reticulocalbin 1 (RCN1) expression, which was validated using qPCR. Immunostaining of the SN brain region revealed RCN1 expression mainly in astrocytes. Our subcellular fractionation of brain extract has shown that RCN1 is located in the ER and in mitochondria-associated membranes (MAM). Moreover, a loss of Parkin function reduced ATP-stimulated calcium-release in ER mesencephalic astrocytes that could be attenuated by siRNA-mediated RCN1 knockdown. Our results indicate that RCN1 plays an important role in ER-associated calcium dyshomeostasis caused by the loss of Parkin function in mesencephalic astrocytes, thereby highlighting the relevance of astrocyte function in PD pathomechanisms.

Controlling absence seizures from the cerebellar nuclei via activation of the Gq signaling pathway.

Absence seizures (ASs) are characterized by pathological electrographic oscillations in the cerebral cortex and thalamus, which are called spike-and-wave discharges (SWDs). Subcortical structures, such as the cerebellum, may well contribute to the emergence of ASs, but the cellular and molecular underpinnings remain poorly understood. Here we show that the genetic ablation of P/Q-type calcium channels in cerebellar granule cells (quirky) or Purkinje cells (purky) leads to recurrent SWDs with the purky model showing the more severe phenotype. The quirky mouse model showed irregular action potential firing of their cerebellar nuclei (CN) neurons as well as rhythmic firing during the wave of their SWDs. The purky model also showed irregular CN firing, in addition to a reduced firing rate and rhythmicity during the spike of the SWDs. In both models, the incidence of SWDs could be decreased by increasing CN activity via activation of the Gq-coupled designer receptor exclusively activated by designer drugs (DREADDs) or via that of the Gq-coupled metabotropic glutamate receptor 1. In contrast, the incidence of SWDs was increased by decreasing CN activity via activation of the inhibitory Gi/o-coupled DREADD. Finally, disrupting CN rhythmic firing with a closed-loop channelrhodopsin-2 stimulation protocol confirmed that ongoing SWDs can be ceased by activating CN neurons. Together, our data highlight that P/Q-type calcium channels in cerebellar granule cells and Purkinje cells can be relevant for epileptogenesis, that Gq-coupled activation of CN neurons can exert anti-epileptic effects and that precisely timed activation of the CN can be used to stop ongoing SWDs.

Cerebellum and Emotion Memory.

Fear is an important emotion for survival, and the cerebellum has been found to contribute not only to innate affective and defensive behavior, but also to learned fear responses. Acquisition and retention of fear conditioned bradycardia and freezing have been shown to depend on the integrity of the cerebellar vermis in rodents. There is a considerable number of brain imaging studies, which observe activation of the human cerebellum in fear conditioning paradigms. Different to what one may expect based on the initial cerebellar lesion studies, activations related to the learned prediction of threat go well beyond the vermis, and are most prominent in the lateral cerebellum. Different parts of the cerebellum likely contribute to learning of autonomic, motor, emotional and cognitive responses involved in classical fear conditioning. The neural operation which is performed in the various parts of the cerebellum is frequently assumed to be the same. One hypothesis is that the cerebellum acts as, or is part of, a predictive device. More recent findings will be discussed that the cerebellum may not only be involved in the processing of sensory prediction errors, but also in the processing of reward and reward prediction errors, which may play a central role in emotions and emotional learning. Current knowledge about the intrinsic learning mechanisms underlying fear memory in the cerebellum, and its connections with subcortical and cortical fear circuitry will be presented. The chapter will conclude with a discussion on how disordered cerebellar fear learning may contribute to affective disorders.

Reelin signaling modulates GABAB receptor function in the neocortex.

Reelin is a protein that is best known for its role in controlling neuronal layer formation in the developing cortex. Here, we studied its role for post-natal cortical network function, which is poorly explored. To preclude early cortical migration defects caused by Reelin deficiency, we used a conditional Reelin knock-out (RelncKO ) mouse, and induced Reelin deficiency post-natally. Induced Reelin deficiency caused hyperexcitability of the neocortical network in vitro and ex vivo. Blocking Reelin binding to its receptors ApoER2 and VLDLR resulted in a similar effect. Hyperexcitability in RelncKO organotypic slice cultures could be rescued by co-culture with wild-type organotypic slice cultures. Moreover, the GABAB receptor (GABAB R) agonist baclofen failed to activate and the antagonist CGP35348 failed to block GABAB Rs in RelncKO mice. Immunolabeling of RelncKO cortical slices revealed a reduction in GABAB R1 and GABAB R2 surface expression at the plasma membrane and western blot of RelncKO cortical tissue revealed decreased phosphorylation of the GABAB R2 subunit at serine 892 and increased phosphorylation at serine 783, reflecting receptor deactivation and proteolysis. These data show a role of Reelin in controlling early network activity, by modulating GABAB R function. Cover Image for this issue: https://doi.org/10.1111/jnc.15054.

Adult loss of Cacna1a in mice recapitulates childhood absence epilepsy by distinct thalamic bursting mechanisms.

Inborn errors of CACNA1A-encoded P/Q-type calcium channels impair synaptic transmission, producing early and lifelong neurological deficits, including childhood absence epilepsy, ataxia and dystonia. Whether these impairments owe their pathologies to defective channel function during the critical period for thalamic network stabilization in immature brain remains unclear. Here we show that mice with tamoxifen-induced adult-onset ablation of P/Q channel alpha subunit (iKOp/q) display identical patterns of dysfunction, replicating the inborn loss-of-function phenotypes and, therefore demonstrate that these neurological defects do not rely upon developmental abnormality. Unexpectedly, unlike the inborn model, the adult-onset pattern of excitability changes believed to be pathogenic within the thalamic network is non-canonical. Specifically, adult ablation of P/Q channels does not promote Cacna1g-mediated burst firing or T-type calcium current (IT) in the thalamocortical relay neurons; however, burst firing in thalamocortical relay neurons remains essential as iKOp/q mice generated on a Cacna1g deleted background show substantially diminished seizure generation. Moreover, in thalamic reticular nucleus neurons, burst firing is impaired accompanied by attenuated IT. Interestingly, inborn deletion of thalamic reticular nucleus-enriched, human childhood absence epilepsy-linked gene Cacna1h in iKOp/q mice reduces thalamic reticular nucleus burst firing and promotes rather than reduces seizure, indicating an epileptogenic role for loss-of-function Cacna1h gene variants reported in human childhood absence epilepsy cases. Together, our results demonstrate that P/Q channels remain critical for maintaining normal thalamocortical oscillations and motor control in the adult brain, and suggest that the developmental plasticity of membrane currents regulating pathological rhythmicity is both degenerate and age-dependent.

Lipoprotein receptor loss in forebrain radial glia results in neurological deficits and severe seizures.

The Alzheimer disease-associated multifunctional low-density lipoprotein receptor-related protein-1 is expressed in the brain. Recent studies uncovered a role of this receptor for the appropriate functioning of neural stem cells, oligodendrocytes, and neurons. The constitutive knock-out (KO) of the receptor is embryonically lethal. To unravel the receptors' role in the developing brain we generated a mouse mutant by specifically targeting radial glia stem cells of the dorsal telencephalon. The low-density lipoprotein receptor-related protein-1 lineage-restricted KO female and male mice, in contrast to available models, developed a severe neurological phenotype with generalized seizures during early postnatal development. The mechanism leading to a buildup of hyperexcitability and emergence of seizures was traced to a failure in adequate astrocyte development and deteriorated postsynaptic density integrity. The detected impairments in the astrocytic lineage: precocious maturation, reactive gliosis, abolished tissue plasminogen activator uptake, and loss of functionality emphasize the importance of this glial cell type for synaptic signaling in the developing brain. Together, the obtained results highlight the relevance of astrocytic low-density lipoprotein receptor-related protein-1 for glutamatergic signaling in the context of neuron-glia interactions and stage this receptor as a contributing factor for epilepsy.

Lamprey Parapinopsin ("UVLamP"): a Bistable UV-Sensitive Optogenetic Switch for Ultrafast Control of GPCR Pathways.

Optogenetics uses light-sensitive proteins, so-called optogenetic tools, for highly precise spatiotemporal control of cellular states and signals. The major limitations of such tools include the overlap of excitation spectra, phototoxicity, and lack of sensitivity. The protein characterized in this study, the Japanese lamprey parapinopsin, which we named UVLamP, is a promising optogenetic tool to overcome these limitations. Using a hybrid strategy combining molecular, cellular, electrophysiological, and computational methods we elucidated a structural model of the dark state and probed the optogenetic potential of UVLamP. Interestingly, it is the first described bistable vertebrate opsin that has a charged amino acid interacting with the Schiff base in the dark state, that has no relevance for its photoreaction. UVLamP is a bistable UV-sensitive opsin that allows for precise and sustained optogenetic control of G protein-coupled receptor (GPCR) pathways and can be switched on, but more importantly also off within milliseconds via lowintensity short light pulses. UVLamP exhibits an extremely narrow excitation spectrum in the UV range allowing for sustained activation of the Gi/o pathway with a millisecond UV light pulse. Its sustained pathway activation can be switched off, surprisingly also with a millisecond blue light pulse, minimizing phototoxicity. Thus, UVLamP serves as a minimally invasive, narrow-bandwidth probe for controlling the Gi/o pathway, allowing for combinatorial use with multiple optogenetic tools or sensors. Because UVLamP activated Gi/o signals are generally inhibitory and decrease cellular activity, it has tremendous potential for health-related applications such as relieving pain, blocking seizures, and delaying neurodegeneration.

Design of an Ultrafast G Protein Switch Based on a Mouse Melanopsin Variant.

The primary goal of optogenetics is the light-controlled noninvasive and specific manipulation of various cellular processes. Herein, we present a hybrid strategy for targeted protein engineering combining computational techniques with electrophysiological and UV/visible spectroscopic experiments. We validated our concept for channelrhodopsin-2 and applied it to modify the less-well-studied vertebrate opsin melanopsin. Melanopsin is a promising optogenetic tool that functions as a selective molecular light switch for G protein-coupled receptor pathways. Thus, we constructed a model of the melanopsin Gq protein complex and predicted an absorption maximum shift of the Y211F variant. This variant displays a narrow blue-shifted action spectrum and twofold faster deactivation kinetics compared to wild-type melanopsin on G protein-coupled inward rectifying K+ (GIRK) channels in HEK293 cells. Furthermore, we verified the in vivo activity and optogenetic potential for the variant in mice. Thus, we propose that our developed concept will be generally applicable to designing optogenetic tools.

Isolated P/Q Calcium Channel Deletion in Layer VI Corticothalamic Neurons Generates Absence Epilepsy.

Generalized spike-wave seizures involving abnormal synchronization of cortical and underlying thalamic circuitry represent a major category of childhood epilepsy. Inborn errors of Cacna1a, the P/Q-type voltage-gated calcium channel α subunit gene, expressed throughout the brain destabilize corticothalamic rhythmicity and produce this phenotype. To determine the minimal cellular lesion required for this network disturbance, we used neurotensin receptor 1 (Ntsr1) cre-driver mice to ablate floxed Cacna1a in layer VI pyramidal neurons, which supply the sole descending cortical synaptic input to thalamocortical relay cells and reticular interneurons and activate intrathalamic circuits. Targeted Cacna1a ablation in layer VI cells resulted in mice that display a robust spontaneous spike-wave absence seizure phenotype accompanied by behavioral arrest and inhibited by ethosuximide. To verify the selectivity of the molecular lesion, we determined that P/Q subunit proteins were reduced in corticothalamic relay neuron terminal zones, and confirmed that P/Q-mediated glutamate release was reduced at these synapses. Spike-triggered exocytosis was preserved by N-type calcium channel rescue, demonstrating that evoked release at layer VI terminals relies on both P/Q and N-type channels. Whereas intrinsic excitability of the P/Q channel depleted layer VI neurons was unaltered, T-type calcium currents in the postsynaptic thalamic relay and reticular cells were dramatically elevated, favoring rebound bursting and seizure generation. We find that an early P/Q-type release defect, limited to synapses of a single cell-type within the thalamocortical circuit, is sufficient to remodel synchronized firing behavior and produce a stable generalized epilepsy phenotype. SIGNIFICANCE STATEMENT: This study dissects a critical component of the corticothalamic circuit in spike-wave epilepsy and identifies the developmental importance of P/Q-type calcium channel-mediated presynaptic glutamate release at layer VI pyramidal neuron terminals. Genetic ablation of Cacna1a in layer VI neurons produced synchronous spike-wave discharges in the cortex and thalamus that were inhibited by ethosuximide. These mice also displayed N-type calcium channel compensation at descending thalamic synapses, and consistent with other spike-wave models increased low-threshold T-type calcium currents within postsynaptic thalamic relay and reticular neurons. These results demonstrate, for the first time, that preventing the developmental homeostatic switch from loose to tightly coupled synaptic release at a single class of deep layer cortical excitatory output neurons results in generalized spike-wave epilepsy.

Keeping Our Calcium in Balance to Maintain Our Balance.

Calcium is a key signaling molecule and ion involved in a variety of diverse processes in our central nervous system (CNS) which include gene expression, synaptic transmission and plasticity, neuronal excitability and cell maintenance. Proper control of calcium signaling is not only vital for neuronal physiology but also cell survival. Mutations in fundamental channels, transporters and second messenger proteins involved in orchestrating the balance of our calcium homeostasis can lead to severe neurodegenerative disorders, such as Spinocerebellar (SCA) and Episodic (EA) ataxias. Hereditary ataxias make up a remarkably diverse group of neurological disorders clinically characterized by gait ataxia, nystagmus, dysarthria, trunk and limb ataxia and often atrophy of the cerebellum. The largest family of hereditary ataxias is SCAs which consists of a growing family of 42 members. A relatively smaller family of 8 members compose the EAs. The gene mutations responsible for half of the EA members and over 35 of the SCA subtypes have been identified, and several have been found to be responsible for cerebellar atrophy, abnormal intracellular calcium levels, dysregulation of Purkinje cell pacemaking, altered cerebellar synaptic transmission and/or ataxia in mouse models. Although the genetic diversity and affected cellular pathways of hereditary ataxias are broad, one common theme amongst these genes is their effects on maintaining calcium balance in primarily the cerebellum. There is emerging evidence that the pathogenesis of hereditary ataxias may be caused by imbalances in intracellular calcium due to genetic mutations in calcium-mediating proteins. In this review we will discuss the current evidence supporting the role of deranged calcium as the culprit to neurodegenerative diseases with a primary focus on SCAs and EAs.

Spinocerebellar ataxia type 6 protein aggregates cause deficits in motor learning and cerebellar plasticity.

Spinocerebellar ataxia type 6 (SCA6) is linked to poly-glutamine (polyQ) within the C terminus (CT) of the pore-forming subunits of P/Q-type Ca(2+) channels (Cav2.1) and is characterized by CT protein aggregates found in cerebellar Purkinje cells (PCs). One hypothesis regarding SCA6 disease is that a CT fragment of the Cav2.1 channel, which is detected specifically in cytosolic and nuclear fractions in SCA6 patients, is associated with the SCA6 pathogenesis. To test this hypothesis, we expressed P/Q-type channel protein fragments from two different human CT splice variants, as predicted from SCA6 patients, in PCs of mice using viral and transgenic approaches. These splice variants represent a short (CT-short without polyQs) and a long (CT-long with 27 polyQs) CT fragment. Our results show that the different splice variants of the CTs differentially distribute within PCs, i.e., the short CTs reveal predominantly nuclear inclusions, whereas the long CTs prominently reveal both nuclear and cytoplasmic aggregates. Postnatal expression of CTs in PCs in mice reveals that only CT-long causes SCA6-like symptoms, i.e., deficits in eyeblink conditioning (EBC), ataxia, and PC degeneration. The physiological phenotypes associated specifically with the long CT fragment can be explained by an impairment of LTD and LTP at the parallel fiber-to-PC synapse and alteration in spontaneous PC activity. Thus, our results suggest that the polyQ carrying the CT fragment of the P/Q-type channel is sufficient to cause SCA6 pathogenesis in mice and identifies EBC as a new diagnostic strategy to evaluate Ca(2+) channel-mediated human diseases.

Postnatal loss of P/Q-type channels confined to rhombic-lip-derived neurons alters synaptic transmission at the parallel fiber to purkinje cell synapse and replicates genomic Cacna1a mutation phenotype of ataxia and seizures in mice.

Ataxia, episodic dyskinesia, and thalamocortical seizures are associated with an inherited loss of P/Q-type voltage-gated Ca(2+) channel function. P/Q-type channels are widely expressed throughout the neuraxis, obscuring identification of the critical networks underlying these complex neurological disorders. We showed recently that the conditional postnatal loss of P/Q-type channels in cerebellar Purkinje cells (PCs) in mice (purky) leads to these aberrant phenotypes, suggesting that intrinsic alteration in PC output is a sufficient pathogenic factor for disease initiation. The question arises whether P/Q-type channel deletion confined to a single upstream cerebellar synapse might induce the pathophysiological abnormality of genomically inherited P/Q-type channel disorders. PCs integrate two excitatory inputs, climbing fibers from inferior olive and parallel fibers (PFs) from granule cells (GCs) that receive mossy fiber (MF) input derived from precerebellar nuclei. In this study, we introduce a new mouse model with a selective knock-out of P/Q-type channels in rhombic-lip-derived neurons including the PF and MF pathways (quirky). We found that in quirky mice, PF-PC synaptic transmission is reduced during low-frequency stimulation. Using focal light stimulation of GCs that express optogenetic light-sensitive channels, channelrhodopsin-2, we found that modulation of PC firing via GC input is reduced in quirky mice. Phenotypic analysis revealed that quirky mice display ataxia, dyskinesia, and absence epilepsy. These results suggest that developmental alteration of patterned input confined to only one of the main afferent cerebellar excitatory synaptic pathways has a significant role in generating the neurological phenotype associated with the global genomic loss of P/Q-type channel function.

Phenotypic analysis of ataxia in spinocerebellar ataxia type 6 mice using DeepLabCut.

This study emphasizes the benefits of open-source software such as DeepLabCut (DLC) and R to automate, customize and enhance data analysis of motor behavior. We recorded 2 different spinocerebellar ataxia type 6 mouse models while performing the classic beamwalk test, tracked multiple body parts using the markerless pose-estimation software DLC and analyzed the tracked data using self-written scripts in the programming language R. The beamwalk analysis script (BAS) counts and classifies minor and major hindpaw slips with an 83% accuracy compared to manual scoring. Nose, belly and tail positions relative to the beam, as well as the angle at the tail base relative to the nose and tail tip were determined to characterize motor deficits in greater detail. Our results found distinct ataxic abnormalities such as an increase in major left hindpaw slips and a lower belly and tail position in both SCA6 ataxic mouse models compared to control mice at 18 months of age. Furthermore, a more detailed analysis of various body parts relative to the beam revealed an overall lower body position in the SCA684Q compared to the CT-longQ27PC mouse line at 18 months of age, indicating a more severe ataxic deficit in the SCA684Q group.

Inhibiting presynaptic calcium channel motility in the auditory cortex suppresses synchronized input processing.

Introduction: The emergent coherent population activity from thousands of stochastic neurons in the brain is believed to constitute a key neuronal mechanism for salient processing of external stimuli and its link to internal states like attention and perception. In the sensory cortex, functional cell assemblies are formed by recurrent excitation and inhibitory influences. The stochastic dynamics of each cell involved is largely orchestrated by presynaptic CAV2.1 voltage-gated calcium channels (VGCCs). Cav2.1 VGCCs initiate the release of neurotransmitters from the presynaptic compartment and are therefore able to add variability into synaptic transmission which can be partly explained by their mobile organization around docked vesicles. Methods: To investigate the relevance of Cav2.1 channel surface motility for the input processing in the primary auditory cortex (A1) in vivo, we make use of a new optogenetic system which allows for acute, reversable cross-linking Cav2.1 VGCCs via a photo-cross-linkable cryptochrome mutant, CRY2olig. In order to map neuronal activity across all cortical layers of the A1, we performed laminar current-source density (CSD) recordings with varying auditory stimulus sets in transgenic mice with a citrine tag on the N-terminus of the VGCCs. Results: Clustering VGCCs suppresses overall sensory-evoked population activity, particularly when stimuli lead to a highly synchronized distribution of synaptic inputs. Discussion: Our findings reveal the importance of membrane dynamics of presynaptic calcium channels for sensory encoding by dynamically adjusting network activity across a wide range of synaptic input strength.