Functional evaluation of epilepsy-associated KCNT1 variants in multiple cellular systems reveals a predominant gain of function impact on channel properties.

Objective: Gain of function variants in the sodium-activated potassium channel KCNT1 have been associated with pediatric epilepsy disorders. Here, we systematically examine a spectrum of KCNT1 variants and establish their impact on channel function in multiple cellular systems.

Methods: KCNT1 variants identified from published reports and genetic screening of pediatric epilepsy patients were expressed in Xenopus oocytes and HEK cell lines.

Developmental synaptic regulator, TWEAK/Fn14 signaling, is a determinant of synaptic function in models of stroke and neurodegeneration.

Identifying molecular mediators of neural circuit development and/or function that contribute to circuit dysfunction when aberrantly reengaged in neurological disorders is of high importance. The role of the TWEAK/Fn14 pathway, which was recently reported to be a microglial/neuronal axis mediating synaptic refinement in experience-dependent visual development, has not been explored in synaptic function within the mature central nervous system. By combining electrophysiological and phosphoproteomic approaches, we show that TWEAK acutely dampens basal synaptic transmission and plasticity through neuronal Fn14 and impacts the phosphorylation state of pre- and postsynaptic proteins in adult mouse hippocampal slices.

Characterization of Vixotrigine, a Broad-Spectrum Voltage-Gated Sodium Channel Blocker.

Voltage-gated sodium channels (Navs) are promising targets for analgesic and antiepileptic therapies. Although specificity between Nav subtypes may be desirable to target specific neural types, such as nociceptors in pain, many broadly acting Nav inhibitors are clinically beneficial in neuropathic pain and epilepsy. Here, we present the first systematic characterization of vixotrigine, a Nav blocker.

Discovery of Vixotrigine: A Novel Use-Dependent Sodium Channel Blocker for the Treatment of Trigeminal Neuralgia.

Drugs that block voltage-gated sodium channels (Nas) have utility in treating conditions including pain, epilepsy, and cardiac arrhythmias and as anesthetics (Lancet Neurol.20109413424; Expert Opin. Ther.

Graded Arrays of Spinal and Supraspinal V2a Interneuron Subtypes Underlie Forelimb and Hindlimb Motor Control.

The spinal cord contains neural networks that enable regionally distinct motor outputs along the body axis. Nevertheless, it remains unclear how segment-specific motor computations are processed because the cardinal interneuron classes that control motor neurons appear uniform at each level of the spinal cord. V2a interneurons are essential to both forelimb and hindlimb movements, and here we identify two major types that emerge during development: type I neurons marked by high Chx10 form recurrent networks with neighboring spinal neurons and type II neurons that downregulate Chx10 and project to supraspinal structures.

Satb2 Is Required for the Development of a Spinal Exteroceptive Microcircuit that Modulates Limb Position.

Motor behaviors such as walking or withdrawing the limb from a painful stimulus rely upon integrative multimodal sensory circuitry to generate appropriate muscle activation patterns. Both the cellular components and the molecular mechanisms that instruct the assembly of the spinal sensorimotor system are poorly understood. Here we characterize the connectivity pattern of a sub-population of lamina V inhibitory sensory relay neurons marked during development by the nuclear matrix and DNA binding factor Satb2 (ISR(Satb2)).

Loss of motoneuron-specific microRNA-218 causes systemic neuromuscular failure.

Dysfunction of microRNA (miRNA) metabolism is thought to underlie diseases affecting motoneurons. One miRNA, miR-218, is abundantly and selectively expressed by developing and mature motoneurons. Here we show that mutant mice lacking miR-218 die neonatally and exhibit neuromuscular junction defects, motoneuron hyperexcitability, and progressive motoneuron cell loss, all of which are hallmarks of motoneuron diseases such as amyotrophic lateral sclerosis and spinal muscular atrophy.

Spinal Locomotor Circuits Develop Using Hierarchical Rules Based on Motorneuron Position and Identity.

The coordination of multi-muscle movements originates in the circuitry that regulates the firing patterns of spinal motorneurons. Sensory neurons rely on the musculotopic organization of motorneurons to establish orderly connections, prompting us to examine whether the intraspinal circuitry that coordinates motor activity likewise uses cell position as an internal wiring reference. We generated a motorneuron-specific GCaMP6f mouse line and employed two-photon imaging to monitor the activity of lumbar motorneurons.

Identification of a cellular node for motor control pathways.

The rich behavioral repertoire of animals is encoded in the CNS as a set of motorneuron activation patterns, also called 'motor synergies'. However, the neurons that orchestrate these motor programs as well as their cellular properties and connectivity are poorly understood. Here we identify a population of molecularly defined motor synergy encoder (MSE) neurons in the mouse spinal cord that may represent a central node in neural pathways for voluntary and reflexive movement.

Imaging spinal neuron ensembles active during locomotion with genetically encoded calcium indicators.

Advances in molecular-genetic tools for labeling neuronal subtypes, and the emerging development of robust genetic probes for neural activity, are likely to revolutionize our understanding of the functional organization of neural circuits. In principle, these tools should be able to detect activity at cellular resolution for large ensembles of identified neuron types as they participate in specific behaviors. This report describes the use of genetically encoded calcium indicators (GECIs), combined with two-photon microscopy, to characterize V1 interneurons, known to be critical for setting the duration of the step cycle.

Sensory modulation of locomotor-like membrane oscillations in Hb9-expressing interneurons.

The central pattern generator can generate locomotor-like rhythmic activity in the spinal cord in the absence of descending and peripheral inputs, but the motor pattern is regulated by feedback from peripheral sensory inputs that adjust motor outputs to external stimuli. To elucidate the possible role of Hb9-expressing interneurons (Hb9 INs) in the locomotor circuitry, we investigated whether their induced oscillatory activity is modulated by low-threshold afferents in the isolated spinal cords of neonatal Hb9:eGFP transgenic mice. Low-intensity stimulation of segmental afferents generated short-latency, monosynaptic excitatory responses in 62% of Hb9 INs.

Electrical coupling between locomotor-related excitatory interneurons in the mammalian spinal cord.

Locomotor rhythm generation is a fundamental characteristic of neural networks in the spinal cord. Identifying the synaptic interactions between neurons in the locomotor circuitry is key to our understanding of the mechanisms that underlie the production of rhythmic motor outputs. Using transgenic mice in which the homeobox gene HB9 drives the reporter green fluorescent protein (GFP), we have demonstrated that a genetically distinct cluster of Hb9/GFP-expressing interneurons (Hb9 INs) can generate locomotor-like rhythms in the newborn mouse spinal cord (Hinckley et al.