Snake and spider toxins induce a rapid recovery of function of botulinum neurotoxin paralysed neuromuscular junction

Botulinum neurotoxins (BoNTs) and some animal neurotoxins (-Bungarotoxin, -Btx, from elapid snakes and -Latrotoxin, -Ltx, from black widow spiders) are pre-synaptic neurotoxins that paralyse motor axon terminals with similar clinical outcomes in patients. However, their mechanism of action is different, leading to a largely-different duration of neuromuscular junction (NMJ) blockade. BoNTs induce a long-lasting paralysis without nerve terminal degeneration acting via proteolytic cleavage of SNARE proteins, whereas animal neurotoxins cause an acute and complete degeneration of motor axon terminals, followed by a rapid recovery. In this study, the injection of animal neurotoxins in mice muscles previously paralyzed by BoNT/A or /B accelerates the recovery of neurotransmission, as assessed by electrophysiology and morphological analysis. This result provides a proof of principle that, by causing the complete degeneration, reabsorption, and regeneration of a paralysed nerve terminal, one could favour the recovery of function of a biochemically- or genetically-altered motor axon terminal. These observations might be relevant to dying-back neuropathies, where pathological changes first occur at the neuromuscular junction and then progress proximally toward the cell body

Glial TDP-43 regulates axon wrapping, GluRIIA clustering and fly motility by autonomous and non-autonomous mechanisms

Alterations in the glial function of TDP-43 are becoming increasingly associated with the neurological symptoms observed in Amyotrophic Lateral Sclerosis (ALS), however, the physiological role of this protein in the glia or the mechanisms that may lead to neurodegeneration are unknown. To address these issues, we modulated the expression levels of TDP-43 in the Drosophila glia and found that the protein was required to regulate the subcellular wrapping of motoneuron axons, promote synaptic growth and the formation of glutamate receptor clusters at the neuromuscular junctions. Interestingly, we determined that the glutamate transporter EAAT1 mediated the regulatory functions of TDP-43 in the glia and demonstrated that genetic or pharmacological compensations of EAAT1 activity were sufficient to modulate glutamate receptor clustering and locomotive behaviors in flies. The data uncovers autonomous and non-autonomous functions of TDP-43 in the glia and suggests new experimentally based therapeutic strategies in ALS

Arg206 of SNAP-25 is essential for neuroexocytosis at the Drosophila melanogaster neuromuscular junction

An analysis of SNAP-25 isoform sequences indicates that there is a highly conserved arginine residue (198 in vertebrates, 206 in the genus Drosophila ) within the C-terminal region, which is cleaved by botulinum neurotoxin A, with consequent blockade of neuroexocytosis. The possibility that it may play an important role in the function of the neuroexocytosis machinery was tested at neuromuscular junctions of Drosophila melanogaster larvae expressing SNAP-25 in which Arg206 had been replaced by alanine. Electrophysiological recordings of spontaneous and evoked neurotransmitter release under different conditions as well as testing for the assembly of the SNARE complex indicate that this residue, which is at the P 1 ′ position of the botulinum neurotoxin A cleavage site, plays an essential role in neuroexocytosis. Computer graphic modelling suggests that this arginine residue mediates protein–protein contacts within a rosette of SNARE complexes that assembles to mediate the fusion of synaptic vesicles with the presynaptic plasma membrane

CXCL12/SDF-1 from perisynaptic Schwann cells promotes regeneration of injured motor axonterminals

The neuromuscular junction has retained through evolution the capacity to regenerate after damage, but little is known on the inter-cellular signals involved in its functional recovery from trauma, autoimmune attacks, or neurotoxins. We report here that CXCL12, also abbreviated as stromal-derived factor-1 (SDF-1), is produced specifically by perisynaptic Schwann cells following motor axon terminal degeneration induced by -latrotoxin. CXCL12 acts via binding to the neuronal CXCR4 receptor. A CXCL12-neutralizing antibody or a specific CXCR4 inhibitor strongly delays recovery from motor neuron degeneration invivo. Recombinant CXCL12 invivo accelerates neurotransmission rescue upon damage and very effectively stimulates the axon growth of spinal cord motor neurons invitro. These findings indicate that the CXCL12-CXCR4 axis plays an important role in the regeneration of the neuromuscular junction after motor axon injury. The present results have important implications in the effort to find therapeutics and protocols to improve recovery of function after different forms of motor axon terminal damage

CXCL12α/SDF‐1 from perisynaptic Schwann cells promotes regeneration of injured motor axon terminals

The neuromuscular junction has retained through evolution the capacity to regenerate after damage, but little is known on the inter‐cellular signals involved in its functional recovery from trauma, autoimmune attacks, or neurotoxins. We report here that CXCL12α, also abbreviated as stromal‐derived factor‐1 (SDF‐1), is produced specifically by perisynaptic Schwann cells following motor axon terminal degeneration induced by α‐latrotoxin. CXCL12α acts via binding to the neuronal CXCR4 receptor. A CXCL12α‐neutralizing antibody or a specific CXCR4 inhibitor strongly delays recovery from motor neuron degeneration in vivo. Recombinant CXCL12α in vivo accelerates neurotransmission rescue upon damage and very effectively stimulates the axon growth of spinal cord motor neurons in vitro. These findings indicate that the CXCL12α‐CXCR4 axis plays an important role in the regeneration of the neuromuscular junction after motor axon injury. The present results have important implications in the effort to find therapeutics and protocols to improve recovery of function after different forms of motor axon terminal damage

Ewald’s role among the pioneers of otoneurology

Julius Richard Ewald was an eminent physiologist who first proposed the hydrodynamic theory of stimulation of the semicircular canals of the vestibular labyrinth. Among otoneurologists, he is remembered for the laws that take his name. The first establishes that the direction of endolymphatic flow is consensual to the direction of the slow phase of the vestibulo-oculomotor nystagmus. The second says that ampullopetal endolymphatic flow produces a stronger response than ampullofugal flow in the horizontal canal. The third law is an upgrade of the second one: ampullofugal flow produces a stronger response than ampullopetal flow in the vertical canals

The regenerating muscle as an experimental model for the study of factors which affect muscle differentiation or adaptation

Bupivacaine-induced regeneration was studied in the rat soleus muscle in the presence or absence of innervation, in the presence of tetrodotoxin (TTX)-induced block of nerve impulse conduction, and/or in the presence of vinblastine-induced block of nerve axoplasmic flow. Part of experiments were carried out on tenotomized muscles. Regenerated muscles were analysed for myosin heavy chain (MHC) composition 14 days after bupivacaine injection. In TTX-paralysed-regenerated muscles type 1 and type 2A MHC isoforms were not expressed. In denervated-regenerated muscles type 1 isoform was lacking, while all fast isoforms (2A, 2B, 2X) were expressed. Tenotomy alone increased type 2A fibres, but did not modify the effects of surgical or functional denervation. Vinblastine-block caused up-regulation of 2A isoform expression in non-tenotomized muscles. The results confirm the essential role played by neuromotor impulses for type 1 and type 2A isoform expression. They also support the hypothesis that axoplasmic flow carries some chemical factor inhibiting 2A isoform expression