Innervation and the regulation of acetylcholinesterase activity during the development of normal and dystrophic chick muscle

Incidence of acetylcholinesterase in the sarcoplasm of human and chicken muscles

Fifty-nine biopsies of human muscle, 53 of them abnormal, 6 normal, were studied for the histochemical localization of acetylcholinesterase (AChE) using frozen sections and light microscopy. In addition to AChE which was found at the myoneural and myotendon junction, specific staining was found around the periphery of many fibers from normal and abnormal muscles. Moreover, AChE activity was found to be high in the sarcoplasm of more than 10% of the fibers from 28 biopsies of abnormal muscle including cases of hemiplegia, spinal cord injury, denervation and neuropathy, infantile spinal muscle atrophy, Duchenne, limb-girdle and facioscapulohumeral dystrophies, Schwartz-Jampel syndrome and a myasthenic syndrome. Of the muscles from experimental animals examined, only the Rhesus monkey exhibited AChE around the periphery of the fibers, and only the dystrophic chicken and not the dystrophic mouse or hamster, showed extensive sarcoplasmic AChE. Histograms of muscle fiber diameters indicated that AChE in the sarcoplasm was associated with fibers of all sizes, depending on the nature of the disorder examined. Fibers containing AChE were smaller than unstained fibers in dystrophic chicken muscle. The results suggest that in the human, sarcoplasmic AChE is reversibly repressed during muscle maturation and that its mode of regulation by motor neurons is similar to that found in the chicken.

A histochemical study of cervical motor neurons and the posterior latissimus dorsi muscle in normal and dystropic chickens

A chromatolysis study, 14 to 21 days following denervation, showed the spinal cord representation of the nerve to the posterior latissimus dorsi muscle to be in the ventrolateral cell column between cervical ganglia 14 and 15. to characterize cevical neruos nt undergoing chromatolysis, histochemical stuies were done the cords of additional nondenervated animals. Staining reactions for beta-hydrocybutyrate dehydrogenase, succinic dehydrogenase and cholinesterase did not reveal any quantitative differences between motor neurons in cervical segments 14 and 15 of normal and dystrophic birds. Motor neurons are positive for beta-hydroxybutyrate dehydrogenase and succinic dehydrogenase, but the surrounding neuropil is positive for the latter only. No pseudocholinesterase activity is found in the ventral horn cells, but true cholinesterase is present in most of the neurons...

Appearance of acetylcholinesterase and creatine kinase in plasma of normal chickens after denervation

Evidence that acetylcholinesterase (AChE) activity is released from normal chick embryonic muscle fibers and from muscles of chickens with inherited muscular dystrophy suggested that denervated chick muscles, which have AChE properties similar to dystrophic muscles, would also release AChE. Bilateral denervation of the breast and wing muscles of normal chickens was followed by the appearance of AChE activity, distinguished from plasma cholinesterase by differential substrate hydrolysis, inhibitor sensitivity, and electrophoretic migration. Plasma creatine kinase (CK) activity was also elevated after denervation.

Acetylcholinesterase in singly and multiply innervated muscles of normal and dystrophic chickens. II. Effects of denervation

Neural regulation of mature normal fast twitch muscle of the chicken suppresses high activity, extrajunctional localization, and isozyme forms of acetylcholinesterase (AChE) characteristic of embryonic, denervated and dystrophic muscle. Normal adult slow tonic muscle ofthe chicken retains intermediate levels of activity and embryonic isozyme forms but not extrajunctional activity; it is not affected by muscular dystrophy. The hypothesis that neural regulation of the AChE system is lacking in slow tonic muscle and thus not affected by dystrophy was tested by denervating the fast twitch posterior latissimus dorsi and slow tonic anterior latissimus dorsi muscles of normal and dystrophic chickens. Extrajunctional AChE activity and embryonic isozyme forms increased, then declined, in both muscles. The results suggest that ocntrol of AChE is qualitatively similar in slow tonic and fast twitch muscle of the chicken.

Electron-microscopic, cytochemical and biochemical studies of acetylcholinesterase and butyrylcholinesterase activity in muscle of dystrophic mice

We have studied extrajunctional muscle of control and dystrophic mice by electron microscopic-cytochemistry and radiometric assay. We have found both a soluble and particulate AChE activity, which is similar proportionally in control and dystrophic muscle. The particulate AChE activity is probably due to the enzyme localized in the sarcotubular system. These sites are more numerous in muscle adjacent to the motor end-plant than in distally located extrajunctional muscle, and are increased markedly in the dystrophic mouse. Myoblasts and small muscle fibers in the dystrophic mouse also have AChE activity in the reticulum similar to fetal muscle. The soluble AChE activity identified radiometrically may represent those sites exhibiting random cytochemical end-product, such as some muscle nuclei, satellite cells, myogenic mononuclear cells in the connective tissue, and degenerating axonal boutons no longer associated with junctional folds of muscle. Enzyme activity is present in degenerating fibers, but it is randomly dispersed in the sarcoplasm rather than membrane-bound. AChE activity has not been found in debris of completely necrotic muscle. BuChE activity is higher and the number of BuChE-active sites in the sarcotubular system adjacent to the motor end-plates is greater in dystrophic muscle than in control muscle.

Myogenic defect in acetylcholinesterase regulation in muscular dystrophy of the chicken

To determine whether inherited muscular dystrophy of the chicken is neurogenic or myogenic in origin, limb buds from homozygous normal and dystrophic chick embryos were exchanged prior to muscle differentiation and innervation. Biceps muscles of hatched chicks, in which muscle of the donor was innervated by nerves of the host, were analyzed for embryonic properties of muscle acetylcholinesterase and for fiber diameter, two distinctive markers for expression of the dystrophic gene. The results indicate that muscular dystrophy of the chicken is caused by an initial biochemical lesion in the limb and its muscle rather than in its innervating nerve.

Regulation of newly synthesized acetylcholinesterase in muscle cultures treated with diisopropylfluorophosphate

Brief treatment with 0.1 mM diisopropylfluorophosphate inhibited an average of 89% of the acetylcholinesterase (EC 3.1.1.7; acetylcholine hydrolase) activity of cultures of chick embryo muscle. As long as protein synthesis occurred, an average of 78% of the activity returned within 4 hr. Newly synthesized acetylcholinesterase did not stain cytochemically, was rapidly and extensively degraded or released in the presence of 10 muM cycloheximide, and consisted mainly of low-molecular-weight forms. Acetylcholinesterase activity first appeared around the nucleus, about 4 hr after treatment with diisopropylfluorophosphate, and then spread to the rest of the cell about the time release of acetylcholinesterase was detected in the medium. With time, more and more of the enzyme was retained in the cells after treatment with cycloheximide, and the proportions of low-molecular-weight forms decreased and high-molecular-weight forms increased. The results suggest that newly synthesized acetylcholinesterase undergoes an orderly process of binding, movement, and assembly in diisopropylfluorophosphate treated, and probably also in untreated, embryo muscle fibers.

Synaptogenesis in cell cultures of neurones and myotubes from chickens with muscular dystrophy

Intracellular microelectrode recordings from chick dystrophic myotubes in cell culture reveal a capability for innervation by neurones from either dystrophic or normal embryos. Neither neuronal class differentially affects the incidence of synapse formation at neuromuscular junctions (about 75%) or at neural junctions (about 85%), the PSP frequency (about 10/sec), the maximum quantal content at neuromuscular junctions (over 70), or the resting membrane potentials of either myotubes (about - 53 mV) or neurones (about - 43 mV). In each culture conditon about 20% of nerve-muscle cell pairs exhibit bidirectional electrical coupling. Dual innervation of a muscle and nerve cell from a common presynaptic source sometimes occurs and both muscle and nerve cells probably have multiple innervation. Assuming the capability for expression in culture of genetic differences between neurones from the dystrophic and normal chick, we conclude that these differences are not significant in the regulation of synapse formation in dystrophic chick nerve-muscle cell culture.