Biology subjects

Mark, M. D.

Publications and source records attributed to Mark, M. D..

5 recordsLinked to original sources

bioRxiv2025

Multimodal characterization and optogenetic potential of the bistable Gi/o-coupled vertebrate ancient opsin from the flashlight fish Anomalops katoptron

Vertebrate ancient long opsin, or VAL opsin, is a light-sensitive protein that is found within and outside the visual system in vertebrates. In accordance with its wide distribution in the retina, brain, testis and skin, VAL is suggested to play a role in light-dependent physiological processes that are beyond vision. However, many aspects of the physiological properties and specific functions of VAL remain unclear. Here we identified and characterized the VAL opsin from the flashlight fish Anomalops katoptron (AkVAL) and show that this opsin is bistable and reversibly converts between active and inactive states by responding to cycles of green and blue/UV lights. We further show that AkVAL couples to the Gi/o pathway and controls the activity of GIRK channels in a bistable manner. In line with this, we demonstrated that AkVAL modulates neuronal activity in cerebellar Purkinje cells, where neuronal activity is reduced by UV/blue light and increased by green/red light illumination. In addition, upon the in vivo expression of AkVAL in neurons innervating body muscles of Caenorhabditis elegans the worms body movement can be bidirectionally controlled altering blue/UV and green illuminations. These data highlight the potential of AkVAL as an optogenetic tool to control cells in vitro and in vivo, in a bistable manner.

neuroscience↗

bioRxiv2023

Cerebellar a1D-adrenergic receptors mediate stress-induced dystonia in totteringtg/tg mice

Episodic ataxia type 2 (EA2) is an inherited neurological disorder, where patients suffer from chronic ataxia and severe episodes of motor dysfunction exhibited as dystonia. Despite other factors, physical and emotional stress triggers those episodes reliably in both human and mice. We used the well-established EA2 mouse model tottering to explore the cerebellar adrenergic receptor (AR) involvement in stress-induced dystonic attacks. We found that 1-ARs, but not 2-ARs, on cerebellar Purkinje cells (PCs) are activated by norepinephrine (NE) from the locus coeruleus (LC), differentially expressed and required for initiation of dystonia. Moreover, pharmacological blockade and shRNA-induced knock down of cerebellar 1D-ARs was sufficient to effectively prevent stress-induced dystonia in homozygous totteringtg/tg mice but had no impact on ataxia amelioration. In vivo recordings and live calcium (Ca2+) imaging of PCs demonstrated that 1D-AR blockade successfully protects PCs from NE-mediated erratic firing patterns through decreased release of calcium from intracellular stores, thus preventing stress-induced dystonia. Furthermore, chemogenetic inhibition of the LC-NE pathway alleviated the frequency and symptoms of stress-induced dystonia. Together, our data show the modulatory effects of NE on dystonia severity and suggest a predominant role of cerebellar 1D-ARs in the formation of stress-induced dystonia in totteringtg/tg mice and, thereby providing a potential new therapeutic target to treat stress-induced dystonia in EA2.

neuroscience↗

bioRxiv2023

Reduced cerebellar Gq-protein signaling elicits early onset spatial navigation deficits in a SCA6 mouse model

Spinocerebellar ataxia type 6 (SCA6) is a hereditary neurodegenerative disease that manifests in a late onset and progressive impairment of motor coordination, balance and speech as well as cerebellar and brainstem atrophy. It is caused by a polyglutamine expansion in the CACNA1A gene which bicistronically encodes the 1A-subunit of the P/Q-type voltage-gated calcium channel and the transcription factor 1ACT. To date, no effective treatment exists and the exact pathobiology is controversially discussed; especially the impact on cognition is poorly understood. Here, we demonstrate that SCA6 84Q mice exhibit cognitive deficits in their spatial navigation abilities. Surprisingly, spatial memory impairments develop prior to motor impairments at 5 months of age. By expressing and stimulating a Gq-protein coupled designer receptor exclusively activated by a designer drug (Gq-DREADD) in the cerebellum, we were able to counteract these spatial navigation deficits indicating that a reduced Gq-protein signaling is part of the SCA6 phenotype. Electrophysiological recordings in anaesthetized mice further revealed that Purkinje cells (PCs) of SCA6 84Q mice exhibit a disrupted spontaneous simple spike activity that precedes the development of both cognitive and motor deficits. Concurrently, PC dysfunction was further confirmed by elevated numbers of torpedoes found in the proximal axon of PCs throughout the cerebellum. Overall, our study raises awareness to survey cognitive abnormalities more carefully during clinical examination to detect the disease earlier and potentially optimize the individual treatment by enhancing PC signaling. Significance statementSCA6 is a hereditary neurological disease that is mainly characterized by the late-onset development of progressive motor deficits. Here we show, using a SCA6 mouse model, that cognitive impairments in spatial navigation are also a non-negligible feature of the disease which manifests earlier than the motor deficits. Moreover, we demonstrate that these spatial navigation deficits are caused by a reduced Gq-protein signaling in the cerebellum. Electrophysiological and histological analysis further confirmed dysfunctional PC signaling even before the onset of first symptoms. Since no effective treatment is available for SCA6 patients, early onset stimulation of PC signaling may be a new therapeutic approach.

neuroscience↗

bioRxiv2022

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

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. To investigate the relevance of Cav2.1 channel surface mobility for the input processing in the primary auditory cortex (A1) in vivo, we make use of a new optogenetic system which allows us to acutely cross-link 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. Clustering VGCCs suppresses overall sensory-evoked population activity, particularly when stimuli lead to a highly synchronized distribution of synaptic inputs. 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. Statement of SignificanceVoltage Gated Calcium Channel (VGCC) mobility plays an important role in neuronal firing dynamics. Failure of these channels to function or be regulated has been linked to migraine and ataxia. We here link the microscopic process of VGCC mobility to the mesoscopic population dynamics as a mechanism to regulate and appropriately amplify synaptic inputs of different strengths to the mouse primary auditory cortex. We also demonstrate a novel and effective technique with which VGCC function can be further explored in meso- or macroscopic scales and with behaving subjects. We believe that this is of importance to the broader scientific community in aspects of non-linear scaling in the brain, potential translational applications, and basic research on cortical mechanisms of physiological function.

neuroscience↗

bioRxiv2018

Subtraction and division of visual cortical population responses by the serotonergic system

Normalization is a fundamental operation throughout neuronal systems to adjust dynamic range. In the visual cortex various cell circuits have been identified that provide the substrate for such a canonical function, but how these circuits are orchestrated remains unclear. Here we suggest the serotonergic (5-HT) system as another player involved in normalization. 5-HT receptors of different classes are co-distributed across different cortical cell types, but their individual contribution to cortical population responses is unknown. We combined wide-field calcium imaging of primary visual cortex (V1) with optogenetic stimulation of 5-HT neurons in mice dorsal raphe nucleus (DRN) -- the major hub for widespread release of serotonin across cortex -- in combination with selective 5-HT receptor blockers. While inhibitory (5-HT1A) receptors accounted for subtractive suppression of spontaneous activity, depolarizing (5-HT2A) receptors promoted divisive suppression of response gain. Added linearly, these components led to normalization of population responses over a range of visual contrasts.

neuroscience↗