Long-Term Blockade of Nociceptive Na1.7 Channels Is Analgesic in Rat Models of Knee Arthritis.

The voltage gated sodium channels (Na) 1.7, 1.8, and 1.

Mice Heterozygous for the Sodium Channel Scn8a (Nav1.6) Have Reduced Inflammatory Responses During EAE and Following LPS Challenge.

Voltage gated sodium (Nav) channels contribute to axonal damage following demyelination in experimental autoimmune encephalomyelitis (EAE), a rodent model of multiple sclerosis (MS). The Nav1.6 isoform has been implicated as a primary contributor in this process.

Voltage-gated sodium channel-dependent retroaxonal modulation of photoreceptor function during post-natal development in mice.

Juvenile (postnatal day 16) mice lacking Na 1.6 channels (null-mutant Scn8a ) have reduced photoreceptor function, which is unexpected given that Na channels have not been detected in mouse photoreceptors and do not contribute appreciably to photoreceptor function in adults. We demonstrate that acute block of Na channels with intravitreal TTX in juvenile (P16) wild-type mice has no effect on photoreceptor function.

Nav1.6 promotes inflammation and neuronal degeneration in a mouse model of multiple sclerosis.

Background: In multiple sclerosis (MS) and in the experimental autoimmune encephalomyelitis (EAE) model of MS, the Nav1.6 voltage-gated sodium (Nav) channel isoform has been implicated as a primary contributor to axonal degeneration. Following demyelination Nav1.

Contribution of Na1.8 sodium channels to retinal function.

We examined the contribution of the sodium channel isoform Na1.8 to retinal function using the specific blocker A803467. We found that A803467 has little influence on the electroretinogram (ERG) a- and b-waves, but significantly reduces the oscillatory potentials (OPs) to 40-60% of their original amplitude, with significant changes in implicit time in the rod-driven range.

Dopamine modulation of rod pathway signaling by suppression of GABAC feedback to rod-driven depolarizing bipolar cells.

Reducing signal gain in the highly sensitive rod pathway prevents saturation as background light levels increase, allowing the dark-adapted retina to encode stimuli over a range of background luminances. Dopamine release is increased during light adaptation and is generally accepted to suppress rod signaling in light-adapted retinas. However, recent research has suggested that dopamine, acting through D1 receptors, could additionally produce a sensitization of the rod pathway in dim light conditions via gamma-aminobutyric acid (GABA) type C receptors.

Glial reaction in the spinal cord of the degenerating muscle mouse (Scn8a (dmu)).

The glial reaction was investigated in the spinal cord of the degenerating muscle (dmu) mouse, which harbours a null mutation in the voltage-gated sodium channel gene Scn8a and does not produce functional Nav1.6 channel. Glial fibrillary acidic protein (GFAP)- and Iba1-immunoreactivity were detected in numerous cells throughout the spinal cord of wild type mice.

D1 dopamine receptors modulate cone ON bipolar cell Nav channels to control daily rhythms in photopic vision.

In amphibians, voltage-gated sodium (Nav) channels in cone ON bipolar cells (ON-CBC) amplify cone signals in the dark and in mesopic background light. However, during light adaptation, dopamine, acting through D1 receptors (D1R), suppresses Nav channels and therefore act as a gain control mechanism. Curiously in rodents, Nav channel contributions to the ON-CBC-generated light-adapted electroretinogram (ERG) b-wave appear to exist even in fully light-adapted conditions.

Contribution of retinal ganglion cells to the mouse electroretinogram.

Purpose: To quantify the direct contribution of retinal ganglion cells (RGCs) on individual components of the mouse electroretinogram (ERG).

Methods: Dark- and light-adapted ERGs from mice 8 to 12 weeks after optic nerve transection (ONTx, n=14) were analyzed through stimulus response curves for a- and b-waves, oscillatory potentials (OPs), positive and negative scotopic threshold response (p/n STR), and the photopic negative response (PhNR) and compared with unoperated and sham-operated controls, as well as to eyes treated with 6-cyano-7-nitroquinoxaline-2,3-dion (CNQX).

Results: We confirmed in mice that CNQX intravitreal injection reduced the scotopic a-wave amplitude at high flash strength, confirming a post-receptoral contribution to the a-wave.

Voltage-gated sodium channels contribute to the b-wave of the rodent electroretinogram by mediating input to rod bipolar cell GABA(c) receptors.

Voltage-gated sodium (Nav) channels are known to augment cone bipolar cell light responses, increasing the electroretinogram (ERG) b-wave in response to stimulus strengths above the cone threshold. However previous in vivo studies on a number of animal models have not found a role for Nav channels in augmenting the b-wave in scotopic conditions below the cone threshold. We recorded ERGs from mice and rats using a series of TTX concentrations and tested retinal output to ensure complete Nav channel block.

Reduced Retinal Function in the Absence of Na(v)1.6.

Background: Mice with a function-blocking mutation in the Scn8a gene that encodes Na(v)1.6, a voltage-gated sodium channel (VGSC) isoform normally found in several types of retinal neurons, have previously been found to display a profoundly abnormal dark adapted flash electroretinogram. However the retinal function of these mice in light adapted conditions has not been studied.

Increase of CGRP expression in motor endplates within fore and hind limb muscles of the degenerating muscle mouse (Scn8a(dmu)).

The distribution of calcitonin gene-related peptide (CGRP) was examined in skeletal muscles of fore and hind limb as well as in oral and cranio-facial regions of the degenerating muscle (dmu) mouse, which harbours a null mutation in the voltage-gated sodium channel gene Scn8a. In limb, oral and cranio-facial muscles of wild type mice, only a few motor endplates contained CGRP-immunoreactivity. However, many CGRP-immunoreactive motor endplates appeared in the triceps brachii muscle, the biceps brachii muscle, the brachialis muscle, and the gastrocnemius muscle of dmu mice.

Increase of c-Fos and c-Jun expression in spinal and cranial motoneurons of the degenerating muscle mouse (Scn8a(dmu)).

The degenerating muscle (dmu) mouse harbors a loss-of-function mutation in the Scn8a gene, which encodes the alpha subunit of the voltage-gated sodium channel (VGSC) Na(V)1.6. The distribution of c-Fos and c-Jun was examined in spinal and cranial motoneurons of the dmu mouse.

Hypomorphic Smn knockdown C2C12 myoblasts reveal intrinsic defects in myoblast fusion and myotube morphology.

Dosage of the survival motor neuron (SMN) protein has been directly correlated with the severity of disease in patients diagnosed with spinal muscular atrophy (SMA). It is also clear that SMA is a neurodegenerative disorder characterized by the degeneration of the alpha-motor neurons in the anterior horn of the spinal cord and atrophy of the associated skeletal muscle. What is more controversial is whether it is neuronal and/or muscle-cell-autonomous defects that are responsible for the disease per se.

Physiological maturation of photoreceptors depends on the voltage-gated sodium channel NaV1.6 (Scn8a).

Voltage-gated sodium channels (VGSCs) ensure the saltatory propagation of action potentials along axons by acting as signal amplifiers at the nodes of Ranvier. In the retina, activity mediated by VGSCs is important for the refinement of the retinotectal map. Here, we conducted a full-field electroretinogram (ERG) study on mice null for the sodium channel NaV1.

Dystroglycan is not required for localization of dystrophin, syntrophin, and neuronal nitric-oxide synthase at the sarcolemma but regulates integrin alpha 7B expression and caveolin-3 distribution.

Dystroglycan is part of the dystrophin-associated protein complex, which joins laminin in the extracellular matrix to dystrophin within the subsarcolemmal cytoskeleton. We have investigated how mutations in the components of the laminin-dystroglycan-dystrophin axis affect the organization and expression of dystrophin-associated proteins by comparing mice mutant for merosin (alpha(2)-laminin, dy), dystrophin (mdx), and dystroglycan (Dag1) using immunohistochemistry and immunoblots. We report that syntrophin and neuronal nitric-oxide synthase are depleted in muscle fibers lacking both dystrophin and dystroglycan.