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Controlled regulation of synaptic nicotinic acetylcholine receptors (AChRs) and acetylcholinesterase (AChE), together with maintenance of a dynamic balance between them, is a requirement for proper function of cholinergic synapses. In the present study we assessed whether pathological changes in AChR perturb this balance, and whether such changes can be corrected. We studied the influence of AChR loss, caused by experimental autoimmune myasthenia gravis (EAMG), on muscle AChE, as well as the reciprocal effect of an antisense targeted towards AChE on both AChR and AChE at the neuromuscular synapse. The extensor digitorum longus (EDL) muscles of EAMG Lewis rats were isolated, and AChE levels and isoform compositions were examined. Although AChE levels in the muscles of healthy and EAMG rats were similar, marked changes were observed in isoform composition. Healthy EDL muscles contained globular (G(1,2) , G(4) ) and asymmetric (primarily A(12) ) isoforms. G(1,2) -AChE was significantly reduced in EAMG muscles, whereas both G(4) - and A(12) -AChE remained unchanged. Treatment of EAMG rats with the antisense EN101 resulted in decreased total muscle AChE, with recovery in G(1,2) and reduction in A(12) -AChE. AChE/AChR ratios were determined at the neuromuscular junctions (NMJ). The decrease in AChR levels that occurred as the disease progressed resulted in a dramatic increase in this ratio, and a significant recovery towards normal ratios occurred after EN101 treatment. This improvement was primarily due to increased synaptic AChR content. Our findings emphasise the tight connection between AChR and AChE at the myasthenic NMJ, and the importance of the AChE/AChR ratio in maintaining the required cholinergic balance., (© 2012 The Authors. European Journal of Neuroscience © 2012 Federation of European Neuroscience Societies and Blackwell Publishing Ltd.)

During the course of experimental autoimmune encephalomyelitis, a massive loss of motor and sensitive function occurs, which has been classically attributed to the demyelination process. In rats, the clinical signs disappear within 5 days following complete tetraplegia, indicating that demyelination might not be the only cause for the rapid evolution of the disease. The present work investigated the occurrence of experimental autoimmune encephalomyelitis-induced changes of the synaptic covering of spinal motoneurons during exacerbation and after remission. The terminals were typed with transmission electron microscopy as C-, F- and S-type. Immunohistochemical analysis of synaptophysin, glial fibrillary acidic protein and the microglia/macrophage marker F4/80 were also used in order to draw a correlation between the synaptic changes and the glial reaction. The ultrastructural analysis showed that, during exacerbation, there was a strong retraction of both F- and S-type terminals. In this sense, both the covering as well as the length of the remaining terminals suffered great reductions. However, the retracted terminals rapidly returned to apposition, although the mean length remained shorter. A certain level of sprouting may have occurred as, after remission, the number of F-terminals was greater than in the control group. The immunohistochemical analysis showed that the peak of synaptic loss was coincident with an increased macro- and microglial reaction. Our results suggest that the major changes occurring in the spinal cord network during the time course of the disease may contribute significantly to the origin of the clinical signs as well as help to explain their rapid recovery.