A HISTOCHEMICAL INVESTIGATION OF CHOLINESTERASES AT NEUROMUSCULAR JUNCTIONS IN MAMMALIAN AND AVIAN MUSCLE

Multiple acetylcholinesterases in Pardosa pseudoannulata brain worked collaboratively to provide protection from organophosphorus insecticides

Acetylcholinesterase (AChE) is an essential neurotransmitter hydrolase in nervous systems of animals and its number varies among species. So far, five AChEs have been identified in the natural enemy Pardosa pseudoannulata. Here we found that Ppace1, Ppace2 and Ppace5 were highly expressed in the spider brain, among which the mRNA level of Ppace5, but not Ppace1 and Ppace2, could be up-regulated by organophosphorus insecticides at their sublethal concentrations. In spider brain, the treatment by organophosphorus insecticides at the sublethal concentrations could increase total AChE activity, although high concentrations inhibited the activity. The activity that increased from the sublethal concentration pretreatment could compensate for the activity inhibition due to subsequent application of organophosphorus insecticides at lethal concentrations, and consequently reduce the mortality of spiders. PpAChE1 and PpAChE2 were highly sensitive to organophosphorus insecticides, and their activities would be strongly inhibited by the insecticides. In contrast, PpAChE5 displayed relative insensitivity towards organophosphorus insecticides, but with the highest catalytic efficiency for ACh. That meant the up-regulation of Ppace5 under insecticide exposure was important for maintaining AChE activity in spider brain, when PpAChE1 and PpAChE2 were inhibited by organophosphorus insecticides. The study demonstrated that multiple AChEs in the spider brain worked collaboratively, with part members for maintaining AChE activity and other members responding to organophosphorus inhibition, to provide protection from organophosphorus insecticides. In fields, high concentration insecticides are often applied when ineffective controls of insect pests occur due to relative-low concentration of insecticides in last round application. This application pattern of organophosphorus insecticides provides more chances for P. pseudoannulata to survive and controlling insect pests as a natural enemy.

Potential Enzymatic Targets in Alzheimer's: A Comprehensive Review

Alzheimer's, a degenerative cause of the brain cells, is called as a progressive neurodegenerative disease and appears to have a heterogeneous etiology with main emphasis on amyloid-cascade and hyperphosphorylated tau-cascade hypotheses, that are directly linked with macromolecules called enzymes such as β- & γ-secretases, colinesterases, transglutaminases, and glycogen synthase kinase (GSK-3), cyclin-dependent kinase (cdk-5), microtubule affinity-regulating kinase (MARK). The catalytic activity of the above enzymes is the result of cognitive deficits, memory impairment and synaptic dysfunction and loss, and ultimately neuronal death. However, some other enzymes also lead to these dysfunctional events when reduced to their normal activities and levels in the brain, such as α- secretase, protein kinase C, phosphatases etc; metabolized to neurotransmitters, enzymes like monoamine oxidase (MAO), catechol-O-methyltransferase (COMT) etc. or these abnormalities can occur when enzymes act by other mechanisms such as phosphodiesterase reduces brain nucleotides (cGMP and cAMP) levels, phospholipase A2: PLA2 is associated with reactive oxygen species (ROS) production etc. On therapeutic fronts, several significant clinical trials are underway by targeting different enzymes for development of new therapeutics to treat Alzheimer's, such as inhibitors for β-secretase, GSK-3, MAO, phosphodiesterase, PLA2, cholinesterases etc, modulators of α- & γ-secretase activities and activators for protein kinase C, sirtuins etc. The last decades have perceived an increasing focus on findings and search for new putative and novel enzymatic targets for Alzheimer's. Here, we review the functions, pathological roles, and worth of almost all the Alzheimer's associated enzymes that address to therapeutic strategies and preventive approaches for treatment of Alzheimer's.

A photonic crystal based sensing scheme for acetylcholine and acetylcholinesterase inhibitors

A 2-layer approach towards optical sensing of acetylcholine and detection of an acetylcholinesterase inhibitor using photonic crystal sensor technology.

Structure and distribution of fibre types in the external eye muscles of the rat

Rat extraocular muscles are composed of two layers differing in muscle fibre diameter. In both layers multiply innervated fibres are found besides focally innervated ones. Significant differences in internal structure thus demand further subtyping. The global layer (predominantly larger fibres) contains 10" 'clear' fibres (multiple innervation, medium size) and a spectrum of focally innervated fibres, from small 'dark' fibres (30%, abundant mitochondria) over 'intermediate' fibres (30%) to large 'pale' fibres (30 %, few mitochondria). The orbital layer (exclusively small fibres) contains 80% focally innervated 'dark' fibres and 20% extremely small 'clear' fibres with multiple innervation. An ultrastructural characterization of the fibre types is given and possible functional implications are discussed.

Mechanisms of cardiac muscle insensitivity to a novel acetylcholinesterase inhibitor C-547

We compared the effects of the novel acetylcholinesterase (AChE) inhibitor C-547 on action potential configuration and sinus rhythm in the isolated right atrium preparation of rat with those of armin and neostigmine. Both armin (10(-7), 10(-6), and 10(-5) M) and neostigmine (10(-7), 10(-6), and 5 x 10(-6) M) produced a marked decrease in action potential duration and slowing of sinus rate. These effects were abolished by atropine and are attributable to the accumulation of acetylcholine in the myocardium. The novel selective AChE inhibitor C-547 (10(-9) to 10(-7) M), an alkylammonium derivative of 6-methyluracil, had no such effects. The inhibition constant of C-547 on cardiac AChE is 40-fold higher than that on extensor digitorum longus muscle AChE. These results suggest that C-547 might be employed to treat diseases such as myasthenia gravis or Alzheimer disease, without having unwanted effects on the heart.

Differential requirement for MuSK and dystroglycan in generating patterns of neuromuscular innervation

Vertebrates display diverse patterns of neuromuscular innervation, but little is known about how such diversity is generated. In mammals, neuromuscular junctions form predominantly at equatorial locations, giving rise to a focal innervation pattern along a central endplate band. In addition, vertebrate striated muscles exhibit two nonfocal neuromuscular patterns, myoseptal and distributed innervation. Although agrin-MuSK-rapsyn signaling is essential for the focal innervation pattern, it is unknown whether the same genetic program also controls synaptogenesis at nonfocal innervation sites. Here we show that one of three transcripts generated by the zebrafish unplugged locus, unplugged FL, encodes the zebrafish MuSK ortholog. We demonstrate that UnpFL/MuSK is critical for the assembly of focal synapses in zebrafish and that it cooperates with dystroglycan in the formation of nonfocal myoseptal and distributed synapses. Our results provide the first genetic evidence that neuromuscular synapse formation can occur in the absence of MuSK and that the combinatorial function of UnpFL/MuSK and dystroglycan generates diverse patterns of vertebrate neuromuscular innervation.

Acetylcholinesterase--new roles for an old actor

The discovery of the first neurotransmitter--acetylcholine--was soon followed by the discovery of its hydrolysing enzyme, acetylcholinesterase. The role of acetylcholinesterase in terminating acetylcholine-mediated neurotransmission made it the focus of intense research for much of the past century. But the complexity of acetylcholinesterase gene regulation and recent evidence for some of the long-suspected 'non-classical' actions of this enzyme have more recently driven a profound revolution in acetylcholinesterase research. Although our understanding of the additional roles of acetylcholinesterase is incomplete, the time is ripe to summarize the evidence on a remarkable diversity of acetylcholinesterase functions.

Neuromuscular junctions contain NP185: the multifunctional protein is located at the presynaptic site

The NP185 polypeptide (AP3) is a multifunctional component isolated from brain endocytic vesicles, which binds to tubulin and clathrin light chains, decoated vesicles, synaptic vesicles, and the synaptosomal plasma membrane (Su et al., 1991). The NP185 molecules are expressed during avian cerebellar synaptogenesis and appear to function in CNS regions rich in synaptic terminals (Perry et al., 1991). In this report we describe double-labelling experiments with avian embryonic striated muscle fibers demonstrating the exclusive presence of the brain-specific protein at the neuromuscular junction. We used indirect rhodamine immunofluorescence labeling with a monoclonal antibody (mAb-8G8) to mark the location of NP185 in muscle combined with fluorescein-alpha-bungarotoxin to mark the postsynaptic location of the acetylcholine receptors (AChRs). We show that the distribution of both NP185 and AChRs has an overall correlation, but the location of NP185 is circumscribed to presynaptic structures adjacent but not overlapping with postsynaptic structures displaying the AchRs. To confirm the identity of NP185, the molecule was extracted from both tissues, partially purified, immunoprecipitated, and identified in Western blots with the mAb 8G8. The mAb reacted with an identical 185 kD protein band purified from both tissues. Based on its properties and specific neuronal location, the NP185 molecule may function in motor nerve terminals by screening membrane proteins, identifying areas of the synaptic plasma membrane, and to anchor these elements with structural proteins for their recycling and transport within the neuronal cellular compartments.

Neuronal protein NP185 is developmentally regulated, initially expressed during synaptogenesis, and localized in synaptic terminals

Evidence is presented here that demonstrates the presence of NP185 (AP3) in neuronal cells, specifically within syn-aptic terminals of the central nervous system and in the peripheral nervous system, particularly in the neuro-muscular junction of adult chicken muscle. Biochemical results obtained in our laboratories indicate that NP185 is associated with brain synaptic vesicles, with clathrin-coated vesicles, and with the synaptosomal plasma membrane. Also, NP185 binds to tubulin and clathrin light chains and the binding is regulated by phosphorylation (Su et al., 1991). Based on these properties and the data reported here, we advance the postulate that NP185 fulfills multiple functions in synaptic terminals. One function is that of a plasma membrane docking or channel protein, another of a signaling molecule for brain vesicles to reach the synaptic terminal region, and a third is that of a recycling molecule by binding to protein components on the lipid bilayer of the synaptic plasma membrane during the process of endocytosis. In support of these premises, a thorough study of NP185 using the developing chick brain, adult mouse brain, and chicken straited muscle was begun by temporally and spatially mapping the expression and localization of NP185 in evolving and mature nerve endings. To achieve these objectives, monoclonal antibodies to NP185 were used for immunocytochemistry in tissue sections of chicken and mouse cerebella. The distribution of NP185 was compared with those of other cytoskeletal and cytoplasmic proteins of axons and synapses, namely synaptophysin, vimentin, neurofilament NF68, and the intermediate filaments of glial cells (GFAP). The data indicate that expression of NP185 temporally coincides with synaptogenesis, and that the distribution of this protein is specific for synaptic terminal buttons of the CNS and the PNS.

Reversible and reproducible in vivo staining of motor endplates by use of the acetylthiocholine-iodide method

In vivo staining of motor endplates was carried out in the anterior tibial muscle of the rat, using the acetylthiocholine-iodide staining method of Koelle and Friedenwald. A strong and distinct endplate staining was obtained after incubation in the staining solution for only one minute if the epimysium had been removed from the muscle. Staining with intact epimysium gave a less satisfactory result if the incubation time was 3 minutes, but it was excellent after incubation for 10 minutes. At re-examination 5 or 30 days later, the initial staining had disappeared in all animals, and a second staining at this time gave just as good results as on the first occasion. The inflammatory reaction in the muscle was more severe with removed epimysium than with intact epimysium, and the staining solution had a slight local toxic effect compared with 0.9% NaCl. Staining with intact epimysium should therefore be preferred if possible.

Development of the mature distribution of synapses on fibres in the frog sartorius muscle

Most of the fibres in mature frog sartorius muscle possess two or more synapses separated by up to one-third the length of the muscle. The aim of the present work was to determine how the relative distances between these synapses changes during development in the frog (Limnodynastes tasmaniansis), as the fibres increase in length from 2 mm (stage 56) to 20 mm (1 year postmetamorphosis). At the earliest stage investigated (fibres 2.0-4.0 mm in length; stages 56-57) about 80% of the fibres were innervated at two endplates. The percentage of fibres with two endplates then remained approximately constant with further development. The polyneuronal innervation of endplates was almost eliminated by stage 57. Muscle fibres with two endplates had each situated on average about one-third the length of the fibre from a tendinous insertion; these relative positions did not change throughout development. Thus the distance between endplates increased linearly with an increase in fibre length. The size of terminals and the complexity of their branching also increased continually throughout development, independently of the location of the terminals on the fibres. The observations suggest that the distance between terminals increases during development because of the intercalation of new plasma membrane and basal lamina associated with the increase in length and diameter of fibres.

Structure of tendon organs of the rat after neonatal de-efferentation

The number, size and structure of tendon organs were examined in leg muscles of the rat 3-19 weeks after de-efferentation performed in newborn animals by removal of the lumbosacral spinal cord. After this operation, tendon organs differentiated and grew in disused muscles and were innervated by primary sensory neurons, the dorsal roots of which had been disrupted. Three weeks after de-efferentation extensor digitorum longus muscles contained 14.1 +/- 1.0 (mean +/- standard error) and soleus muscles had 14.2 +/- 1.6 tendon organs, which corresponds to the mean number of tendon organs in the respective control muscles. The mean size of tendon organs was, however, changed. Tendon organs became on the average by 53% longer and by 35% thinner in de-efferented extensor digitorum longus muscles that were prolonged due to immobilization, as compared with shorter and wider tendon organs in de-efferented soleus muscle that remained in the shortened position. The ultrastructural differentiation of tendon organs was completed after the operation as under normal conditions. Thus it can be concluded that elimination of muscle function during the period of postnatal development indirectly affects the mean size of these receptors, but does not otherwise interfere with their morphogenesis.

Acetylcholinesterase and acetylcholine receptor histochemistry on end plate regions, myotendinous junctions, and sarcolemma in the axial musculature of three teleost fish species

In this paper we describe a rapid procedure for the identification of motor end plates in fish. We demonstrated the presence of acetylcholine receptors by means of an immune fluorescence technique with alpha-bungarotoxin. Koelle's thiocholine method was used to localize acetylcholinesterase (AChE) activity. Under carefully controlled conditions the AChE activity and the anti-alpha-bungarotoxin fluorescence showed an equal distribution. This means that in the study of motor innervation in fish the AChE reaction can be used to stain only the motor end plates, leaving the AChE rich preterminal axons unstained. Comparison of the AChE reaction pattern with the distribution of binding sites for antibodies raised against neurofilament protein revealed that in end plate regions high concentrations of AChE are only present in axons and end plates. The myotendinous junctions also possess a high receptor density and enzyme activity. A low enzymatic activity was found at the non-junctional periphery of white muscle fibres. This activity probably resides in the sarcolemma. No non-specific cholinesterase activity was found. From light microscopical analysis it appeared that a single end plate may innervate 2 adjacent muscle fibres. This was affirmed by ultrastructural observations. The dual innervation suggests that, in fish, motor units have a limited distribution through the myotome.

Innervation of avian latissimus dorsi muscles and axonal outgrowth pattern in the posterior latissimus dorsi motor nerve during embryonic development

The distribution of the innervation to the anterior latissimus dorsi (ALD) and posterior latissimus dorsi (PLD) muscles of the chicken are described on the day of hatching and 6 weeks later using electron microscopy. In the ALD muscle, there are 5,000 muscle fibres and 374,000 endplates supplied by about 169 skeletomotor axons; in the PLD muscle, there are 12,000 focally innervated muscle fibers supplied by about 20 skeletomotor axons. On the cell surface of the muscle fibers the mean total subsynaptic area contacted by each motor axon is comparable in the ALD and PLD muscles. The growth pattern of the axons in the PLD motor nerve was described from the ninth day in ovo up to 6 weeks after hatching. The axons arrive in the PLD muscle in two successive waves: first, the large somatic axons which are already present before the ninth day in ovo and second, the small autonomic axons which continue to accumulate until hatching. The total number of somatic axons decreases from the ninth day until the hatching day when it reaches its definitive value. This decrease takes place during a period when the numbers of myofibers and of endplates dramatically increase, and it coincides with the axonal segregation by the Schwann cells. The myelination of the axons starts on the 15th day in ovo and is essentially complete upon hatching. Despite the decreasing number of somatic axons in the PLD nerve, the decrease in number of nerve endings per PLD endplate and the increasing number of PLD endplates per PLD muscle, it was found that between the 16th day in ovo and 6 weeks after hatching the mean number of axonal branches per PLD motor axon does not decrease.

Medullary proprioceptive neurons from extraocular muscles in the pigeon identified with horseradish peroxidase

Three to five microliters of 50% HRP in saline was injected along a central axis into one of the 6 extraocular muscles in each of 18 adult pigeons. The brain was fixed and serially sectioned 16-20 h postinjection and the HRP reacted with tetramethylbenzidine (TMB). HRP-labeled proprioceptive neurons were located in the ipsilateral nucleus descendens nervi trigemini (TTD) for all muscle injections. The labeled neurons were further subdivided into two groups based on size and shape. In each experiment the number of labeled proprioceptive cells relative to the number of labeled motoneurons ranged between 4.9 and 15.5%. There were no labeled cells in the trigeminal mesencephalic nucleus or contralateral TTD. The study suggests that at least partial afferent (proprioceptive) innervation of the extraocular muscles in the pigeon derived from neurons in the ipsilateral TTD.

Acetylcholine receptors in singly and multiply innervated skeletal muscle fibres of the chicken during development

1. The properties of acetylcholine (ACh) receptors of the singly innervated posterior latissimus dorsi (PLD) and the multiply innervated anterior latissimus dorsi (ALD) muscles of the chicken were investigated. Studies were made on chicks from 17 days in ovo to 14 weeks after hatching. Focal extracellular recordings and intracellular recordings in voltage clamped fibres were made. 2. Peak amplitudes of miniature end-plate currents (m.e.p.c.s) of the two muscles were not significantly different. The time constants of decay (tau D) were similar in both muscles, although tau D in the PLD was generally smaller than in the ALD (usually by less than 25%). M.e.p.c. decays in both muscles were well described by a single exponential. 3. The conductance (gamma) and average lifetime (tau N) of end-plate channels activated by ionophoretically applied ACh were calculated from records of current fluctuations. Noise spectra were well fitted by a single Lorentzian function. Values obtained in PLD did not differ significantly from those obtained in the ALD. There was not difference in the ACh null potential. 4. The voltage and temperature sensitivities of the ACh-activated channels in both muscle types were very similar. 5. With age there was a slight decrease in tau D: from about 6 to 5 msec in the PLD and from about 7 to 5 msec in the ALD (at -40 mV). The change in tau N with age was even less marked. However, during development, gamma almost doubled in both muscles, increasing from about 20 to 35 pS. 6. The results provide no evidence for the hypothesis that the different pattern of innervation causes marked differences in the ACh-activated channels of singly and multiply innervated muscles.

Rapid degeneration of developing rat Pacinian corpuscles after denervation

The effect of denervation upon the development of Pacinian corpuscles was investigated in the crural interosseous membrane of the rat during the early postnatal period. When the sciatic nerve was transected in 1-day-old rats, further development of immature Pacinian corpuscles was arrested and their structure rapidly disintegrated. In the main cluster of corpuscles, Pacinian axon terminals degenerated within 12 h after the operation and were phagocytised by the inner core cells. Subsequently large dense inclusion bodies and vacuoles with dense debris appeared in the inner core and capsule, and cell autolysis and pyknosis ensued from the 2nd day onwards. The debris of degenerated cells was removed by macrophages and the disintegration of individual corpuscles was completed 2-5 days after nerve section. Normal interosseous membranes of 2-6-day-old rats contained 54.9 +/- 1.2 (+/- S.E.) Pacinian corpuscles, as revealed by staining for cholinesterase. The total days after denervation, dropped to 38% on day 3, decreased further to 15% on day 4 and reached zero values on day 5 after nerve section. The experiments demonstrate that the postnatal development and growth of the non-nervous components of Pacinian corpuscles is completely dependent upon the neuronal induction exerted by sensory axon terminals.

A histochemical method for gross demonstration of motor end plates

The thiocholine-ferricyanide method of Karnovsky and Roots for histochemical demonstration of cholinesterases has been applied to whole fetal and neonatal mice and chicks for the visualization of motor end plate patterns in superficial muscles or deeper muscles exposed by dissection.

Species variation in the distribution of cholinesterases in the ovary of the plains viscacha, cat, ferret, rabbit, rat, guinea-pig and roe deer

Sections of ovary from plains viscacha, cat, ferret, rabbit, rat, guinea-pig and roe deer have been histochemically processed to demonstrate acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE) in nervous and non-nervous tissue. The effects of different reproductive states on enzyme activity were observed in some animals. AChE-containing nerves were sparse in rabbit and rat but plentiful in cat and roe deer. Nerves containing BuChE were not detectable in ferret or guinea-pig and were rare in cat. Species variations in the activity and type of enzyme were also found in non-neuronal tissues. Some blood vessels in the ovaries of guinea-pig and viscacha contained AChE. No other species showed a reaction for AChE in non-neuronal stromal tissue but BuChE was present at this site in all animals except rat. Granulosa cells reacted for AChE only in cat and rabbit while luteal cells were reactive in cat, rabbit and roe deer. Some BuChE activity was present in granulosa and or luteal cells in all species except roe deer. In rat, BuChE activity in luteal cells increased during pregnancy and the early phase of pseudopregnancy. The difficulty of assigning a function to ovarian cholinesterases is discussed.

Development of neuromuscular junctions of fast and slow muscles in the chick embryo: a light and electron microscopic study

The morphogenesis of neuromuscular injections (NMJ) was studied by electron microscopy in fast posterior and slow anterior latissimus dorsi muscles (PLD and ALD) of chick embryos. In 8 day embryos, the NMJ is already established in both types. In PLD at this stage, individual axons completely ensheathed by Schwann cell processes form NMJs with myotubes, whereas in ALD axon terminal lie adjacent to (and not separated by Schwann cell processes from) naked axons which are components of a nerve bundle. At 11-15 days, the number of profiles of axon terminals at each endplate increases in both PLD and ALD. In PLD, individual axon terminals are ensheathed by Schwann cells and often branch. In ALD, several axon terminals become ensheathed as a group by processes of a Schwann cell, along with a small number of adjacent naked axons. The individual axon terminals were confirmed by analysis of serial sections to originate from different preterminal axons. Thus, the increase in number of axon terminals in PLD may be due to extensive terminal branching, whereas in ALD it may be due to the arrival of other nerve fibres. From 16 days, each axon terminal in an endplate of ALD becomes individually ensheathed by Schwann cell processes. However, the property of polyneuronal innervation in each endplate is retained even in the adult muscle. The junctional sarcoplasm protrudes to separate individual axon terminals at certain developmental stages: the protuberances are thinner and more numerous in ALD than in PLD at 15-16 days. It is concluded that NMJ morphogenesis differs between PLD and ALD and that the differences reside mainly on the neuronal side.

A histochemical study of cholinesterases in arm and forearm muscles of the pigeon and fowl

Various arm and forearm muscles of the pigeon and fowl were studied histochemically. Fibres of the muscles from both birds hydrolysed acetyl, butyryl and propionyl thiocholine iodide. With the exception of M. brachialis, all the fibres of the muscles had "en plaque" motor end plates. M. brachialis had "en grappe" endings on all its fibres. The possibility of M. brachialis being a physiologically "slow" muscle is discussed.

Developmental aspects of the innervation of skeletal muscle fibers in the chick embryo

The M. complexus in the chick, commonly called the hatching muscle, undergoes conspicuous growth during the latter stages of embryonic development. Myogenesis of this muscle was compared to that of M. biceps femoris with regard to development of types of muscle fiber and their innervation. In both muscles beta fibers are of relatively uniform size and show little growth in diameter between 12 days of development and hatching; alpha fibers develop continuously and display a wide range of diameters at all stages. Initial thickenings on the sarcolemma of beta fibers where axons are closely approximate were first observed at 10 days of development in both muscles. In both muscles beta fibers are innervated prior to alpha fibers. Terminal axon networks bridge intercellular spaces and contact beta fibers in different myogenic clusters. alpha fibers that develop on the surface membrane of beta fibers exhibit focal thickenings of the membrane and some cell projections that are directed toward axon-beta fiber contacts. These changes occurred only in alpha fibers of M. complexus. At 14 days of embryogenesis, the processes of synaptogenesis and of myelin formation are less advanced in M. biceps femoris than in M. complexus. At this stage alpha fibers were observed to be innervated in M. complexus, but not yet in M. biceps femoris. Each beta fiber was observed to be encircled by several preterminal axons. It is concluded that the earlier development of M. complexus is correlated with an equally early development of nerve-muscle interactions.

Dystrophic chicken muscle: altered synaptic acetylcholinesterase

Individual motor endplates in the skeletal muscles of chickens genetically homozygous for muscular dystrophy have been compared with those in normal chickens. Measurements were made there, by specific autoradiographic techniques, of the numbers of total cholinesterase-like molecules and of acetylcholinesterase molecules. The acetylcholinesterase is distinctly decreased at the endplates in dystrophic muscles. The various data available on these muscles are compatible with the concept that a neural factor which determines the synaptic acetylcholinesterase, along with a number of other characters in the muscle cell, is defective in this disorder.

The formation of synapses in reinnervated and cross-reinnervated adult avian muscle

1. A study has been made of the formation of synapses in spontaneously reinnervated and cross-reinnervated anterior latissimus dorsi (ALD) and posterior latissimus dorsi (PLD) muscles of adult fowls.2. Denervated ALD and PLD muscle fibres have a uniform and high sensitivity to iontophoretically applied acetylcholine (ACh). During early reinnervation the sensitivity distribution to ACh of the ALD muscle fibres begins to return to normal before synaptic potentials can be evoked. The normal ACh sensitivity distribution of PLD muscle fibres is also restored after reinnervation. After cross-reinnervation of the ALD and PLD muscles the ACh sensitivity distribution of many of the muscle fibres is again restored to normal.3. Reinnervating and cross-reinnervating ALD nerve terminals showed a greater than normal degree of facilitation of transmitter release when a test impulse was applied at various intervals after a conditioning impulse. Cross-reinnervating PLD nerve terminals showed facilitation of transmitter release rather than the normal depression in a conditioning-test impulse sequence.4. The distribution of nerve terminals over the surface of spontaneously reinnervated and cross-reinnervated ALD and PLD muscle fibres has been determined from an examination of the sensitivity distribution to applied ACh, the graded versus all-or-none nature of the evoked potential and the distribution of cholinesterase stained synapses.5. The results suggest that the innervation pattern of individual ALD and PLD muscle fibres is restored both after spontaneous reinnervation and cross-reinnervation.

Electrical properties and acetylcholine sensitivity of singly and multiply innervated avian muscle fibers

Membrane constants and distribution of acetylcholine (ACh) receptors were determined for multiply innervated fibers of the anterior latissimus dorsi (ALD) and singly innervated fibers of the posterior latissimus dorsi (PLD) muscles of 3-6 month old chickens. The values of the various membrane constants were: length constant, 1.78 mm (mean) in ALD, 0.68 mm in PLD; time constant, 35 msec in ALD, 3.7 msec in PLD; transverse membrane resistance, 4388 ohm cm(2) in ALD, 561 ohm cm(2) in PLD; and membrane capacitance, 8.2 microF/cm(2) in ALD, 7.0 microF/cm(2) in PLD. Peaks of ACh sensitivity occurred at intervals of ca. 740 micro on ALD fibers with a low sensitivity remaining between peaks. Only one peak of ACh sensitivity was detected on PLD fibers. The maximum ACh sensitivity found was 5 +/- 4 mv/ncoul for fibers of the ALD and 77 +/- 60 mv/ncoul for fibers of the PLD. The distance over which this sensitivity fell to 0.1 was ca. 225 micro in the ALD and 140 micro in the PLD. The membranes of these two muscle fiber types differ widely regarding some electrical properties and the disposition of ACh-sensitive receptor sites.

A quantitative study of cholinesterase in myoneural junctions from rat and guinea-pig extraocular muscles

1. Cholinesterase staining of rat and guinea-pig extraocular muscle shows focally and multiply innervated fibres.2. The distribution of cholinesterase activities in the populations of focal endings (from singly innervated fibres) and fine motor endings (from multiply innervated fibres) was determined by a sensitive radiochemical method.3. Focal endings had a greater cholinesterase activity than fine motor endings.4. It is suggested that this difference in enzyme activities is related to the functional difference between twitch and slow fibres in extraocular muscle.

Fast and slow muscles of the chick after nerve cross-union

1. The multiply innervated anterior latissimus dorsi (ALD) and the focally innervated posterior latissimus dorsi (PLD) muscles of the chick were investigated 2-18 months after nerve cross-union.2. The fast PLD muscle re-innervated by the slow muscle nerve became supplied with ;en grappe' end-plates and responded to a single nerve volley with local potentials only. Control PLD muscles re-innervated by the original nerve, had ;en plaque' end-plates and responded to a single nerve volley by synchronous action potentials in the same way as normal muscles.3. In the slow ALD muscle re-innervated with the ;mixed' PLD nerve, the type of innervation and of electromyographic response remained practically unchanged, with the exception of transplanted ALD muscles supplied with PLD nerves where, in addition to local responses, propagated action potentials were registered electromyographically in response to single nerve volleys.4. ALD muscles of young chickens re-innervated both with an implanted purely fast muscle nerve and with the regenerated original nerve, had two types of innervation: ;en plaque' end-plates around the nerve implant, and multiple ;en grappe' end-plates in areas supplied with the ALD nerve. Accordingly, propagated action potentials were registered in response to single nerve volleys in regions near the implant, whereas local potentials were recorded in areas with original innervation.5. Contraction velocity was not substantially altered in PLD and ALD muscles after nerve cross-union.6. No changes were observed in the fine structure of muscle fibres in extrajunctional regions.

A combined method for demonstrating the cholinesterase activity and the nervous structure of mammalian peripheral motor endings in teased preparations

Both the neural and subneural components of mammalian peripheral motor endings in teased preparations have been shown by a new method which combines a silver method with a cholinesterase technique. The significant application of this method to the study of the motor terminals is suggested.

Acetylcholinesterase at muscle-tendon junctions during postnatal development in rats

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