Neuromuscular junction adults

IGF I has recently been the focus of considerable interest due to its actions on motor neurons. It can prevent normal motor neuron cell death during development, reduce the loss of these cells following nerve injury and enhance axonal regeneration. In the adult, injection of IGF I results in sprouting of motor neuron terminals and increases the size of the neuromuscular junction. These and other studies suggest potential therapeutic applications of IGF I in several neurological diseases including amyotrophic lateral sclerosis and peripheral neuropathies. 

The components of C2 toxin con be isolated from culture supernatants of type C and type D Clostridium botulinum. It is important to remember that these organisms are capable of producing type C and type D botulinum neurotoxin. Although there are no documented cases of type C or type D poisoning in adults, recent work has shown that the isolated human neuromuscular junction can be poisoned by type C toxin (Coffield and Simpson, unpublished). Therefore, extreme caution should be used when handling organisms that produce neurotoxin. 

The nodal localization of SCNSA would predict that mice cannot survive without this channel. In fact, null mutants lacking this protein are paralysed and do not survive beyond one month. The timing of death may be explained by an apparent developmental switch in the type of Na + channel located at the node. Between 2 and 3 weeks of age, Na+ channels SCNIA (Na,l.l) and SCN2A (Na l. 2) can be detected at the nodes with specific antisera. In the third week of life, during the period of myelination, these channels appear to be replaced by SCNSA (Nayl.6), which is the only channel detected in nodes in adult mice (Caldwell et al 2000). Consistent with this time course, the null mutants lacking SCNSA med and med can walk at 2 weeks of age but become paralysed by 3 weeks of age. Secondary effects of the null mutations include sprouting of nerve terminals at the neuromuscular junction (Duchen Stefani 1971) and atrophy of the hind limb muscles. 

The subunit composition at the neuromuscular junction is fixed (al)2()5l)<57 in the fetal form and (al)2(/ l)(5e in the adult form. M2 from each subunit lines the... 

Two types of illness are associated with the botulinum toxin, infant and adult botulism. An adult becomes iU by eating spoiled food that contains the toxin. Infants become ill from eating the spores of the botulinum bacterium. One source of these spores comes from the ingestion of honey. Spores are not normally toxic to adults. Botulinum toxins work by binding to the presynaptic nerve terminal at the neuromuscular junction and at cholinergic autononuc sites. They then act to stop the release of acetylchloline presynaptically, thus blocking neurotransmission. 

Coniine causes death by blocking the neuromuscular junction in a manner similar to curare this results in an ascending muscular paralysis with eventual paralysis of the respiratory muscles which results in death due to lack of oxygen to the heart and brain [80]. Death can be prevented by artificial ventilation until the effects have worn off 48-72 h later. For an adult, the ingestion of more than 100 mg of coniine (approximately 6-8 fresh leaves, or a smaller dose of the seeds or root) may be fatal [70, 85],... 

One of the clinical signs associated with MeHg intoxication is a myasthenia gravis-like muscle weakness in adults (Rustam et al. 1975), a syndrome which responded well to therapy with neostigmine, a reversible acetylcholinesterase inhibitor. In this syndrome, two effects of MeHg on synaptic transmission at the neuromuscular junction were demonstrated using intracellular microelectrode recording techniques (Atchison and Narahashi 1982 Atchison et al. 1984). First, nerve-evoked, synchronous quantal release of acetylcholine (ACh) is inhibited, as indicated by a decrease in end-plate potential (EPP) amplitude. Second, spontaneous quantal release... 

Fig. 6.3 Adult neuromuscular junction with the three cells that constitute the synapse the motor neuron (i.e. nerve terminal), muscle fibre and Schwann cell. The motor neuron from the ventral horn of the spinal cord innervates the muscle. Each fibre receives only one synapse. The motor nerve loses its myelin to terminate on the muscle fibre. The nerve terminal, covered by Schwann cell, has vesicles clustered about the membrane thickenings, which are the active zones, towards its synaptic side and mitochondria and microtubules towards its other side. A synaptic gutter, made up of primary and many secondary clefts, separates the nerve from the muscle. The muscle surface is cormgated, and dense areas on the shoulders of each fold contain acetylcholine receptors. The sodium channels are present at the clefts and throughout the musele membrane (from Martyn 2005, p 863 copyright Elsevier)...

Wigston, D. J. Repeated in vivo visualization of neuromuscular junctions in adult mouse lateral gastrocnemius. J. Neurosci. 1990,10,1753-1761. 

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