Crustacean and insect neuromuscular junctions typically include numerous small synapses, each of ... more Crustacean and insect neuromuscular junctions typically include numerous small synapses, each of which usually contains one or more active zones, which possess voltage-sensitive calcium channels and are specialized for release of synaptic vesicles. Strength of transmission (the number of quantal units released per synapse by a nerve impulse) varies greatly among different endings of individuaI neurons, and from one neuron to another. Ultrastructural features of synapses account for some of the physiological differences at endings of individual neurons. The nerve terminals that release more neurotransmitter per impulse have a higher incidence of synapses with more than one active zone, and this is correlated with more calcium build-up during stimulation. However, comparison of synaptic structure in neurons with different physiological phenotypes indicates no major differences in structure that could account for their different levels of neurotransmitter release per impulse, and release per synapse differs among neurons despite similar calcium build-up in their terminals during stimulation. The evidence indicates differences in calcium sensitivity of the release process among neurons as an aspect of physiological specialization.
Frq2 and Ric8a genetically interact to modulate, through Gs-α, the release per synapse and total ... more Frq2 and Ric8a genetically interact to modulate, through Gs-α, the release per synapse and total synapse number Number of synapses (A,B,C) and intracellular recordings (D,E), (n= 8-12
Comparative biochemistry and physiology. A, Comparative physiology, 1971
Abstract 1. 1. Ultrastructural features of muscle fibres with long and short sarcomeres from a cr... more Abstract 1. 1. Ultrastructural features of muscle fibres with long and short sarcomeres from a crayfish walking leg were compared by electron microscopy. The short sarcomere fibres possessed a more extensive system of transverse tubules and diads than the long sarcomere fibres. 2. 2. The membrane resistance of both types of fibre increased when nitrate, bromide or thiocyanate was substituted for chloride in the bathing solution. 3. 3. The increase in membrane resistance was greater for the short sarcomere fibres. 4. 4. The more numerous transverse tubules and diads of the short sarcomere fibres probably provide a higher membrane anion conductance, and a greater sensitivity to the effects of anions which are less permeant than chloride.
Abstract 1. 1. The membrane and contractile characteristics of fibres in the extensor muscle of t... more Abstract 1. 1. The membrane and contractile characteristics of fibres in the extensor muscle of the crab Cancer magister Daba were investigated by intracellular electrode techniques. 2. 2. Two extreme types of fibre were found: small-diameter “tonic” fibres which contracted slowly and had sarcomeres about 10 μ long; and large-diameter “phasic’ fibres which contracted rapidly and had sarcomeres about 5 μ long. 3. 3. A few of the tonic fibres gave graded spikes when depolarized, but all-or-nothing spikes were encountered only in certain phasic fibres.
An investigation was made of the electrical and mechanical responses of Nephrops closer muscles t... more An investigation was made of the electrical and mechanical responses of Nephrops closer muscles to indirect stimulation via "fast" and "slow" motor axons. 2. Most of the proximal muscle fibres showed large "fast" p.s.p.'s in response to single stimuli, but very small "slow" electrical responses at any frequency of stimulation. Certain distal muscle fibres showed very small "fast" electrical responses, but large "slow" electrical responses when the frequency of stimulation was greater than 30/sec. Indirectly evoked electrically excitable responses occurred in both groups of muscle fibres. 3. Single stimuli applied to the "fast" axon produced a small twitch response of the muscle. Tension was developed when frequencies of stimulation greater than 30/sec were applied to the "slow" axon. 4. Throughout the muscle, directly applied depolarization produced small electrically excitable responses in some muscle fibres, and much larger responses (sometimes with a threshold) in others. 5. It was estimated that the membrane potential threshold for tension development induced by potassium chloride depolarization was 58 mV. 6. "Fast" and "slow" electrical responses exceed the estimated threshold for tension development when tension is produced by indirect stimulation.
An investigation was made of the electrical and mechanical responses to direct and indirect stimu... more An investigation was made of the electrical and mechanical responses to direct and indirect stimulation in Carcinus closer muscles. 2. Three main types of muscle fibre could be distinguished on the basis of electrical responses to indirect stimulation. They were called Types A, B and C. 3. Type A muscle fibres showed large "fast" p.s.p.'s and electrically excitable membrane responses, but usually no response to "slow" axon stimulation. Type B muscle fibres showed large, slowly decaying "slow" p.s.p.'s and small or no "fast" p.s.p.'s. In Type C muscle fibres "fast" and "slow" p.s.p.'s were both present. Both were small at low frequencies of stimulation of the motor axons but increased in size with increasing frequency of stimulation. 4. The electrical properties of the membranes of the three muscle fibre types were found to differ. Type A muscle fibres had low membrane resistances, small time constants and electrically excitable membranes. Type B muscle fibres had high membrane resistances, large time constants and electrically inexcitable membranes. Type C muscle fibres had intermediate properties. The electrical responses to indirect stimulation could be largely explained in terms of the membrane properties of the fibres from which they were recorded. 5. The average membrane potential at which detectable tension was developed by the muscle in response to potassium depolarization was 55 inV. 6. Tension was developed by single directly stimulated Type C muscle fibres when the depolarization at the current-passing microelectrode was 42 mV to 58 mV. 7. During both fast and slow contractions, electrical responses can be observed which exceed the estimated membrane potential threshold for ten~,ion development.
The histological and physiological features of the deep and superficial extensor muscles in the a... more The histological and physiological features of the deep and superficial extensor muscles in the abdomen of the crayfish (Procarabarus) and rock lobster (Panulirus) were investigated. 2. The deep muscles consist entirely of rapidly contracting muscular elements which have the histological features of "phasic" muscle fibres. They have short (24 ft) sarcomeres and a uniform distribution of the myofilaments. In many cases adjacent parts in these muscles show electrotonic interaction. 3. The superficial extensor muscles contract slowly and are histologically of the "tonic" type. The sarcomeres are relatively long (9-11/D and the myofibrils are grouped in clumps. 4. From each segmental ganglion, the deep extensors receive four (rock lobster) or five (crayfish) excitor axons, and one inhibitor. Two of the excitors and the inhibitor send branches to the next posterior segment. 5. The excitor axons typically produce large electrical responses, often spikelike, for each impulse. The responses fatigue readily with repeated stimulation. Post-tetanic potentiation of electrical and mechanical responses is often seen following a train of closely spaced impulses in certain of the axons. 6. The excitor axons of the superficial extensor muscles give small junctional potentials which generally undergo facilitation with repeated stimulation and show little fatigue. 7. The muscle fibres and axons of the deep muscles are adapted for phasic contraction, whereas the corresponding elements of the superficial muscles are adapted for tonic contraction.
The opener and closer muscles of the spider crab, Chionecetes tanneri, contain thick and thin mus... more The opener and closer muscles of the spider crab, Chionecetes tanneri, contain thick and thin muscle fibres. The former have short sarcomeres and a uniformly fibrillar appearance in cross section, whereas the latter have much longer sarcomeres and are often deeply invaded by sarcolemmal elements. 2. The thick fibres often gave large spikes and fast, phasic mechanical responses to direct stimulation. 3. The thin fibres did not produce spikes, and their mechanical responses were very slow. 4. In the opener muscle, the thick fibres produced repetitive spikes when the single motor axon was stimulated at high frequencies. The thin fibres gave large, slowly decaying post-synaptic poten~als at low frequencies of stimulation. The slow mechanical response of the muscle as a whole at these frequencies was attributable to contraction of the latter fibres. 5. In the closer muscle, the thin fibres responded to stimulation of the "slow" motor axon and the "common" inhibitor axon. Membrane conductance in these fibres was markedly increased by v-aminobutyric acid. The thick fibres of the closer responded mainly to the "fast" motor axon and were relatively insensitive to stimulation of the inhibitor axon and to 7-aminobutyric acid.
The Journal of neuroscience : the official journal of the Society for Neuroscience, 1985
Crustacean tonic and phasic motoneurons have neuromuscular synaptic properties corresponding with... more Crustacean tonic and phasic motoneurons have neuromuscular synaptic properties corresponding with their functional requirements. Phasic axon synapses produce large excitatory postsynaptic potentials (EPSPs) which depress rapidly during repetitive activation. Tonic axon synapses generally produce smaller EPSPs which are more resistant to fatigue. To test whether nerve impulse activity of the motoneuron plays a role in the establishment of these synaptic properties, a phasic axon was tonically stimulated in vivo. The "fast" closer excitor of the crayfish claw, which normally fires few impulses, was stimulated for 2 hr/day at 5 Hz, through implanted electrodes. In young crayfish, this stimulation produced an 11-fold decrease in synaptic fatigue at the fast axon's neuromuscular synapses, as determined from measurements of EPSPs during 5 Hz stimulation of the fast axon for 30 min. In comparison with EPSPs of the contralateral control claw, the initial EPSP amplitude was 44%...
Publisher Summary This chapter focuses on some of the recent physiological and morphological work... more Publisher Summary This chapter focuses on some of the recent physiological and morphological work and modeling that is of most immediate relevance to an overview of synaptic properties and plasticity in crustacean neuromuscular junctions. The data on the acute control of synaptic transmission comes from the squid giant synapse. All important features of transmission and short-term facilitation can reasonably be accounted for on the basis of calcium entry and subsequent distribution within the terminal; there seems to be no need to propose a voltage-dependent second step for that synapse. Most of the work removed basis for this proposal in the squid synapse to a large extent. New models of calcium domains can accommodate a small degree of hysteresis in the voltage-release curves, purely on the basis of the calcium hypothesis. However good the models for the squid giant synapse are, it is not the physiological equivalent of the crustacean or vertebrate synapse. Processes such as long-term facilitation cannot be observed in the squid synapse. Other processes may also exist at the crustacean synapse and not at the squid synapse.
The histological and physiological features of the deep and superficial extensor muscles in the a... more The histological and physiological features of the deep and superficial extensor muscles in the abdomen of the crayfish (Procarabarus) and rock lobster (Panulirus) were investigated. 2. The deep muscles consist entirely of rapidly contracting muscular elements which have the histological features of "phasic" muscle fibres. They have short (24 ft) sarcomeres and a uniform distribution of the myofilaments. In many cases adjacent parts in these muscles show electrotonic interaction. 3. The superficial extensor muscles contract slowly and are histologically of the "tonic" type. The sarcomeres are relatively long (9-11/D and the myofibrils are grouped in clumps. 4. From each segmental ganglion, the deep extensors receive four (rock lobster) or five (crayfish) excitor axons, and one inhibitor. Two of the excitors and the inhibitor send branches to the next posterior segment. 5. The excitor axons typically produce large electrical responses, often spikelike, for each impulse. The responses fatigue readily with repeated stimulation. Post-tetanic potentiation of electrical and mechanical responses is often seen following a train of closely spaced impulses in certain of the axons. 6. The excitor axons of the superficial extensor muscles give small junctional potentials which generally undergo facilitation with repeated stimulation and show little fatigue. 7. The muscle fibres and axons of the deep muscles are adapted for phasic contraction, whereas the corresponding elements of the superficial muscles are adapted for tonic contraction.
An investigation was made of the electrical and mechanical responses of Nephrops closer muscles t... more An investigation was made of the electrical and mechanical responses of Nephrops closer muscles to indirect stimulation via "fast" and "slow" motor axons. 2. Most of the proximal muscle fibres showed large "fast" p.s.p.'s in response to single stimuli, but very small "slow" electrical responses at any frequency of stimulation. Certain distal muscle fibres showed very small "fast" electrical responses, but large "slow" electrical responses when the frequency of stimulation was greater than 30/sec. Indirectly evoked electrically excitable responses occurred in both groups of muscle fibres. 3. Single stimuli applied to the "fast" axon produced a small twitch response of the muscle. Tension was developed when frequencies of stimulation greater than 30/sec were applied to the "slow" axon. 4. Throughout the muscle, directly applied depolarization produced small electrically excitable responses in some muscle fibres, and much larger responses (sometimes with a threshold) in others. 5. It was estimated that the membrane potential threshold for tension development induced by potassium chloride depolarization was 58 mV. 6. "Fast" and "slow" electrical responses exceed the estimated threshold for tension development when tension is produced by indirect stimulation.
An investigation was made of the electrical and mechanical responses to direct and indirect stimu... more An investigation was made of the electrical and mechanical responses to direct and indirect stimulation in Carcinus closer muscles. 2. Three main types of muscle fibre could be distinguished on the basis of electrical responses to indirect stimulation. They were called Types A, B and C. 3. Type A muscle fibres showed large "fast" p.s.p.'s and electrically excitable membrane responses, but usually no response to "slow" axon stimulation. Type B muscle fibres showed large, slowly decaying "slow" p.s.p.'s and small or no "fast" p.s.p.'s. In Type C muscle fibres "fast" and "slow" p.s.p.'s were both present. Both were small at low frequencies of stimulation of the motor axons but increased in size with increasing frequency of stimulation. 4. The electrical properties of the membranes of the three muscle fibre types were found to differ. Type A muscle fibres had low membrane resistances, small time constants and electrically excitable membranes. Type B muscle fibres had high membrane resistances, large time constants and electrically inexcitable membranes. Type C muscle fibres had intermediate properties. The electrical responses to indirect stimulation could be largely explained in terms of the membrane properties of the fibres from which they were recorded. 5. The average membrane potential at which detectable tension was developed by the muscle in response to potassium depolarization was 55 inV. 6. Tension was developed by single directly stimulated Type C muscle fibres when the depolarization at the current-passing microelectrode was 42 mV to 58 mV. 7. During both fast and slow contractions, electrical responses can be observed which exceed the estimated membrane potential threshold for ten~,ion development.
We have identified EMS-induced mutations in Drosophila Miro (dMiro), an atypical mitochondrial GT... more We have identified EMS-induced mutations in Drosophila Miro (dMiro), an atypical mitochondrial GTPase that is orthologous to human Miro (hMiro). Mutant dmiro animals exhibit defects in locomotion and die prematurely. Mitochondria in dmiro mutant muscles and neurons are abnormally distributed. Instead of being transported into axons and dendrites, mitochondria accumulate in parallel rows in neuronal somata. Mutant neuromuscular junctions (NMJs) lack presynaptic mitochondria, but neurotransmitter release and acute Ca2+ buffering is only impaired during prolonged stimulation. Neuronal, but not muscular, expression of dMiro in dmiro mutants restored viability, transport of mitochondria to NMJs, the structure of synaptic boutons, the organization of presynaptic microtubules, and the size of postsynaptic muscles. In addition, gain of dMiro function causes an abnormal accumulation of mitochondria in distal synaptic boutons of NMJs. Together, our findings suggest that dMiro is required for controlling anterograde transport of mitochondria and their proper distribution within nerve terminals.
International Review of Neurobiology - INT REV NEUROBIOL, 1986
Publisher Summary This chapter focuses on some of the recent physiological and morphological work... more Publisher Summary This chapter focuses on some of the recent physiological and morphological work and modeling that is of most immediate relevance to an overview of synaptic properties and plasticity in crustacean neuromuscular junctions. The data on the acute control of synaptic transmission comes from the squid giant synapse. All important features of transmission and short-term facilitation can reasonably be accounted for on the basis of calcium entry and subsequent distribution within the terminal; there seems to be no need to propose a voltage-dependent second step for that synapse. Most of the work removed basis for this proposal in the squid synapse to a large extent. New models of calcium domains can accommodate a small degree of hysteresis in the voltage-release curves, purely on the basis of the calcium hypothesis. However good the models for the squid giant synapse are, it is not the physiological equivalent of the crustacean or vertebrate synapse. Processes such as long-term facilitation cannot be observed in the squid synapse. Other processes may also exist at the crustacean synapse and not at the squid synapse.
The opener and closer muscles of the spider crab, Chionecetes tanneri, contain thick and thin mus... more The opener and closer muscles of the spider crab, Chionecetes tanneri, contain thick and thin muscle fibres. The former have short sarcomeres and a uniformly fibrillar appearance in cross section, whereas the latter have much longer sarcomeres and are often deeply invaded by sarcolemmal elements. 2. The thick fibres often gave large spikes and fast, phasic mechanical responses to direct stimulation. 3. The thin fibres did not produce spikes, and their mechanical responses were very slow. 4. In the opener muscle, the thick fibres produced repetitive spikes when the single motor axon was stimulated at high frequencies. The thin fibres gave large, slowly decaying post-synaptic poten~als at low frequencies of stimulation. The slow mechanical response of the muscle as a whole at these frequencies was attributable to contraction of the latter fibres. 5. In the closer muscle, the thin fibres responded to stimulation of the "slow" motor axon and the "common" inhibitor axon. Membrane conductance in these fibres was markedly increased by v-aminobutyric acid. The thick fibres of the closer responded mainly to the "fast" motor axon and were relatively insensitive to stimulation of the inhibitor axon and to 7-aminobutyric acid.
Crustacean tonic and phasic motoneurons have neuromuscular synaptic properties corresponding with... more Crustacean tonic and phasic motoneurons have neuromuscular synaptic properties corresponding with their functional requirements. Phasic axon synapses produce large excitatory postsynaptic potentials (EPSPs) which depress rapidly during repetitive activation. Tonic axon synapses generally produce smaller EPSPs which are more resistant to fatigue. To test whether nerve impulse activity of the motoneuron plays a role in the establishment of these synaptic properties, a phasic axon was tonically stimulated in vivo. The "fast" closer excitor of the crayfish claw, which normally fires few impulses, was stimulated for 2 hr/ day at 5 Hz, through implanted electrodes. In young crayfish, this stimulation produced an 11-fold decrease in synaptic fatigue at the fast axon's neuromuscular synapses, as determined from measurements of EPSPs during 5 Hz stimulation of the fast axon for 30 min. In comparison with EPSPs of the contralateral control claw, the initial EPSP amplitude was 4...
Crustacean and insect neuromuscular junctions typically include numerous small synapses, each of ... more Crustacean and insect neuromuscular junctions typically include numerous small synapses, each of which usually contains one or more active zones, which possess voltage-sensitive calcium channels and are specialized for release of synaptic vesicles. Strength of transmission (the number of quantal units released per synapse by a nerve impulse) varies greatly among different endings of individuaI neurons, and from one neuron to another. Ultrastructural features of synapses account for some of the physiological differences at endings of individual neurons. The nerve terminals that release more neurotransmitter per impulse have a higher incidence of synapses with more than one active zone, and this is correlated with more calcium build-up during stimulation. However, comparison of synaptic structure in neurons with different physiological phenotypes indicates no major differences in structure that could account for their different levels of neurotransmitter release per impulse, and release per synapse differs among neurons despite similar calcium build-up in their terminals during stimulation. The evidence indicates differences in calcium sensitivity of the release process among neurons as an aspect of physiological specialization.
Frq2 and Ric8a genetically interact to modulate, through Gs-α, the release per synapse and total ... more Frq2 and Ric8a genetically interact to modulate, through Gs-α, the release per synapse and total synapse number Number of synapses (A,B,C) and intracellular recordings (D,E), (n= 8-12
Comparative biochemistry and physiology. A, Comparative physiology, 1971
Abstract 1. 1. Ultrastructural features of muscle fibres with long and short sarcomeres from a cr... more Abstract 1. 1. Ultrastructural features of muscle fibres with long and short sarcomeres from a crayfish walking leg were compared by electron microscopy. The short sarcomere fibres possessed a more extensive system of transverse tubules and diads than the long sarcomere fibres. 2. 2. The membrane resistance of both types of fibre increased when nitrate, bromide or thiocyanate was substituted for chloride in the bathing solution. 3. 3. The increase in membrane resistance was greater for the short sarcomere fibres. 4. 4. The more numerous transverse tubules and diads of the short sarcomere fibres probably provide a higher membrane anion conductance, and a greater sensitivity to the effects of anions which are less permeant than chloride.
Abstract 1. 1. The membrane and contractile characteristics of fibres in the extensor muscle of t... more Abstract 1. 1. The membrane and contractile characteristics of fibres in the extensor muscle of the crab Cancer magister Daba were investigated by intracellular electrode techniques. 2. 2. Two extreme types of fibre were found: small-diameter “tonic” fibres which contracted slowly and had sarcomeres about 10 μ long; and large-diameter “phasic’ fibres which contracted rapidly and had sarcomeres about 5 μ long. 3. 3. A few of the tonic fibres gave graded spikes when depolarized, but all-or-nothing spikes were encountered only in certain phasic fibres.
An investigation was made of the electrical and mechanical responses of Nephrops closer muscles t... more An investigation was made of the electrical and mechanical responses of Nephrops closer muscles to indirect stimulation via "fast" and "slow" motor axons. 2. Most of the proximal muscle fibres showed large "fast" p.s.p.'s in response to single stimuli, but very small "slow" electrical responses at any frequency of stimulation. Certain distal muscle fibres showed very small "fast" electrical responses, but large "slow" electrical responses when the frequency of stimulation was greater than 30/sec. Indirectly evoked electrically excitable responses occurred in both groups of muscle fibres. 3. Single stimuli applied to the "fast" axon produced a small twitch response of the muscle. Tension was developed when frequencies of stimulation greater than 30/sec were applied to the "slow" axon. 4. Throughout the muscle, directly applied depolarization produced small electrically excitable responses in some muscle fibres, and much larger responses (sometimes with a threshold) in others. 5. It was estimated that the membrane potential threshold for tension development induced by potassium chloride depolarization was 58 mV. 6. "Fast" and "slow" electrical responses exceed the estimated threshold for tension development when tension is produced by indirect stimulation.
An investigation was made of the electrical and mechanical responses to direct and indirect stimu... more An investigation was made of the electrical and mechanical responses to direct and indirect stimulation in Carcinus closer muscles. 2. Three main types of muscle fibre could be distinguished on the basis of electrical responses to indirect stimulation. They were called Types A, B and C. 3. Type A muscle fibres showed large "fast" p.s.p.'s and electrically excitable membrane responses, but usually no response to "slow" axon stimulation. Type B muscle fibres showed large, slowly decaying "slow" p.s.p.'s and small or no "fast" p.s.p.'s. In Type C muscle fibres "fast" and "slow" p.s.p.'s were both present. Both were small at low frequencies of stimulation of the motor axons but increased in size with increasing frequency of stimulation. 4. The electrical properties of the membranes of the three muscle fibre types were found to differ. Type A muscle fibres had low membrane resistances, small time constants and electrically excitable membranes. Type B muscle fibres had high membrane resistances, large time constants and electrically inexcitable membranes. Type C muscle fibres had intermediate properties. The electrical responses to indirect stimulation could be largely explained in terms of the membrane properties of the fibres from which they were recorded. 5. The average membrane potential at which detectable tension was developed by the muscle in response to potassium depolarization was 55 inV. 6. Tension was developed by single directly stimulated Type C muscle fibres when the depolarization at the current-passing microelectrode was 42 mV to 58 mV. 7. During both fast and slow contractions, electrical responses can be observed which exceed the estimated membrane potential threshold for ten~,ion development.
The histological and physiological features of the deep and superficial extensor muscles in the a... more The histological and physiological features of the deep and superficial extensor muscles in the abdomen of the crayfish (Procarabarus) and rock lobster (Panulirus) were investigated. 2. The deep muscles consist entirely of rapidly contracting muscular elements which have the histological features of "phasic" muscle fibres. They have short (24 ft) sarcomeres and a uniform distribution of the myofilaments. In many cases adjacent parts in these muscles show electrotonic interaction. 3. The superficial extensor muscles contract slowly and are histologically of the "tonic" type. The sarcomeres are relatively long (9-11/D and the myofibrils are grouped in clumps. 4. From each segmental ganglion, the deep extensors receive four (rock lobster) or five (crayfish) excitor axons, and one inhibitor. Two of the excitors and the inhibitor send branches to the next posterior segment. 5. The excitor axons typically produce large electrical responses, often spikelike, for each impulse. The responses fatigue readily with repeated stimulation. Post-tetanic potentiation of electrical and mechanical responses is often seen following a train of closely spaced impulses in certain of the axons. 6. The excitor axons of the superficial extensor muscles give small junctional potentials which generally undergo facilitation with repeated stimulation and show little fatigue. 7. The muscle fibres and axons of the deep muscles are adapted for phasic contraction, whereas the corresponding elements of the superficial muscles are adapted for tonic contraction.
The opener and closer muscles of the spider crab, Chionecetes tanneri, contain thick and thin mus... more The opener and closer muscles of the spider crab, Chionecetes tanneri, contain thick and thin muscle fibres. The former have short sarcomeres and a uniformly fibrillar appearance in cross section, whereas the latter have much longer sarcomeres and are often deeply invaded by sarcolemmal elements. 2. The thick fibres often gave large spikes and fast, phasic mechanical responses to direct stimulation. 3. The thin fibres did not produce spikes, and their mechanical responses were very slow. 4. In the opener muscle, the thick fibres produced repetitive spikes when the single motor axon was stimulated at high frequencies. The thin fibres gave large, slowly decaying post-synaptic poten~als at low frequencies of stimulation. The slow mechanical response of the muscle as a whole at these frequencies was attributable to contraction of the latter fibres. 5. In the closer muscle, the thin fibres responded to stimulation of the "slow" motor axon and the "common" inhibitor axon. Membrane conductance in these fibres was markedly increased by v-aminobutyric acid. The thick fibres of the closer responded mainly to the "fast" motor axon and were relatively insensitive to stimulation of the inhibitor axon and to 7-aminobutyric acid.
The Journal of neuroscience : the official journal of the Society for Neuroscience, 1985
Crustacean tonic and phasic motoneurons have neuromuscular synaptic properties corresponding with... more Crustacean tonic and phasic motoneurons have neuromuscular synaptic properties corresponding with their functional requirements. Phasic axon synapses produce large excitatory postsynaptic potentials (EPSPs) which depress rapidly during repetitive activation. Tonic axon synapses generally produce smaller EPSPs which are more resistant to fatigue. To test whether nerve impulse activity of the motoneuron plays a role in the establishment of these synaptic properties, a phasic axon was tonically stimulated in vivo. The "fast" closer excitor of the crayfish claw, which normally fires few impulses, was stimulated for 2 hr/day at 5 Hz, through implanted electrodes. In young crayfish, this stimulation produced an 11-fold decrease in synaptic fatigue at the fast axon's neuromuscular synapses, as determined from measurements of EPSPs during 5 Hz stimulation of the fast axon for 30 min. In comparison with EPSPs of the contralateral control claw, the initial EPSP amplitude was 44%...
Publisher Summary This chapter focuses on some of the recent physiological and morphological work... more Publisher Summary This chapter focuses on some of the recent physiological and morphological work and modeling that is of most immediate relevance to an overview of synaptic properties and plasticity in crustacean neuromuscular junctions. The data on the acute control of synaptic transmission comes from the squid giant synapse. All important features of transmission and short-term facilitation can reasonably be accounted for on the basis of calcium entry and subsequent distribution within the terminal; there seems to be no need to propose a voltage-dependent second step for that synapse. Most of the work removed basis for this proposal in the squid synapse to a large extent. New models of calcium domains can accommodate a small degree of hysteresis in the voltage-release curves, purely on the basis of the calcium hypothesis. However good the models for the squid giant synapse are, it is not the physiological equivalent of the crustacean or vertebrate synapse. Processes such as long-term facilitation cannot be observed in the squid synapse. Other processes may also exist at the crustacean synapse and not at the squid synapse.
The histological and physiological features of the deep and superficial extensor muscles in the a... more The histological and physiological features of the deep and superficial extensor muscles in the abdomen of the crayfish (Procarabarus) and rock lobster (Panulirus) were investigated. 2. The deep muscles consist entirely of rapidly contracting muscular elements which have the histological features of "phasic" muscle fibres. They have short (24 ft) sarcomeres and a uniform distribution of the myofilaments. In many cases adjacent parts in these muscles show electrotonic interaction. 3. The superficial extensor muscles contract slowly and are histologically of the "tonic" type. The sarcomeres are relatively long (9-11/D and the myofibrils are grouped in clumps. 4. From each segmental ganglion, the deep extensors receive four (rock lobster) or five (crayfish) excitor axons, and one inhibitor. Two of the excitors and the inhibitor send branches to the next posterior segment. 5. The excitor axons typically produce large electrical responses, often spikelike, for each impulse. The responses fatigue readily with repeated stimulation. Post-tetanic potentiation of electrical and mechanical responses is often seen following a train of closely spaced impulses in certain of the axons. 6. The excitor axons of the superficial extensor muscles give small junctional potentials which generally undergo facilitation with repeated stimulation and show little fatigue. 7. The muscle fibres and axons of the deep muscles are adapted for phasic contraction, whereas the corresponding elements of the superficial muscles are adapted for tonic contraction.
An investigation was made of the electrical and mechanical responses of Nephrops closer muscles t... more An investigation was made of the electrical and mechanical responses of Nephrops closer muscles to indirect stimulation via "fast" and "slow" motor axons. 2. Most of the proximal muscle fibres showed large "fast" p.s.p.'s in response to single stimuli, but very small "slow" electrical responses at any frequency of stimulation. Certain distal muscle fibres showed very small "fast" electrical responses, but large "slow" electrical responses when the frequency of stimulation was greater than 30/sec. Indirectly evoked electrically excitable responses occurred in both groups of muscle fibres. 3. Single stimuli applied to the "fast" axon produced a small twitch response of the muscle. Tension was developed when frequencies of stimulation greater than 30/sec were applied to the "slow" axon. 4. Throughout the muscle, directly applied depolarization produced small electrically excitable responses in some muscle fibres, and much larger responses (sometimes with a threshold) in others. 5. It was estimated that the membrane potential threshold for tension development induced by potassium chloride depolarization was 58 mV. 6. "Fast" and "slow" electrical responses exceed the estimated threshold for tension development when tension is produced by indirect stimulation.
An investigation was made of the electrical and mechanical responses to direct and indirect stimu... more An investigation was made of the electrical and mechanical responses to direct and indirect stimulation in Carcinus closer muscles. 2. Three main types of muscle fibre could be distinguished on the basis of electrical responses to indirect stimulation. They were called Types A, B and C. 3. Type A muscle fibres showed large "fast" p.s.p.'s and electrically excitable membrane responses, but usually no response to "slow" axon stimulation. Type B muscle fibres showed large, slowly decaying "slow" p.s.p.'s and small or no "fast" p.s.p.'s. In Type C muscle fibres "fast" and "slow" p.s.p.'s were both present. Both were small at low frequencies of stimulation of the motor axons but increased in size with increasing frequency of stimulation. 4. The electrical properties of the membranes of the three muscle fibre types were found to differ. Type A muscle fibres had low membrane resistances, small time constants and electrically excitable membranes. Type B muscle fibres had high membrane resistances, large time constants and electrically inexcitable membranes. Type C muscle fibres had intermediate properties. The electrical responses to indirect stimulation could be largely explained in terms of the membrane properties of the fibres from which they were recorded. 5. The average membrane potential at which detectable tension was developed by the muscle in response to potassium depolarization was 55 inV. 6. Tension was developed by single directly stimulated Type C muscle fibres when the depolarization at the current-passing microelectrode was 42 mV to 58 mV. 7. During both fast and slow contractions, electrical responses can be observed which exceed the estimated membrane potential threshold for ten~,ion development.
We have identified EMS-induced mutations in Drosophila Miro (dMiro), an atypical mitochondrial GT... more We have identified EMS-induced mutations in Drosophila Miro (dMiro), an atypical mitochondrial GTPase that is orthologous to human Miro (hMiro). Mutant dmiro animals exhibit defects in locomotion and die prematurely. Mitochondria in dmiro mutant muscles and neurons are abnormally distributed. Instead of being transported into axons and dendrites, mitochondria accumulate in parallel rows in neuronal somata. Mutant neuromuscular junctions (NMJs) lack presynaptic mitochondria, but neurotransmitter release and acute Ca2+ buffering is only impaired during prolonged stimulation. Neuronal, but not muscular, expression of dMiro in dmiro mutants restored viability, transport of mitochondria to NMJs, the structure of synaptic boutons, the organization of presynaptic microtubules, and the size of postsynaptic muscles. In addition, gain of dMiro function causes an abnormal accumulation of mitochondria in distal synaptic boutons of NMJs. Together, our findings suggest that dMiro is required for controlling anterograde transport of mitochondria and their proper distribution within nerve terminals.
International Review of Neurobiology - INT REV NEUROBIOL, 1986
Publisher Summary This chapter focuses on some of the recent physiological and morphological work... more Publisher Summary This chapter focuses on some of the recent physiological and morphological work and modeling that is of most immediate relevance to an overview of synaptic properties and plasticity in crustacean neuromuscular junctions. The data on the acute control of synaptic transmission comes from the squid giant synapse. All important features of transmission and short-term facilitation can reasonably be accounted for on the basis of calcium entry and subsequent distribution within the terminal; there seems to be no need to propose a voltage-dependent second step for that synapse. Most of the work removed basis for this proposal in the squid synapse to a large extent. New models of calcium domains can accommodate a small degree of hysteresis in the voltage-release curves, purely on the basis of the calcium hypothesis. However good the models for the squid giant synapse are, it is not the physiological equivalent of the crustacean or vertebrate synapse. Processes such as long-term facilitation cannot be observed in the squid synapse. Other processes may also exist at the crustacean synapse and not at the squid synapse.
The opener and closer muscles of the spider crab, Chionecetes tanneri, contain thick and thin mus... more The opener and closer muscles of the spider crab, Chionecetes tanneri, contain thick and thin muscle fibres. The former have short sarcomeres and a uniformly fibrillar appearance in cross section, whereas the latter have much longer sarcomeres and are often deeply invaded by sarcolemmal elements. 2. The thick fibres often gave large spikes and fast, phasic mechanical responses to direct stimulation. 3. The thin fibres did not produce spikes, and their mechanical responses were very slow. 4. In the opener muscle, the thick fibres produced repetitive spikes when the single motor axon was stimulated at high frequencies. The thin fibres gave large, slowly decaying post-synaptic poten~als at low frequencies of stimulation. The slow mechanical response of the muscle as a whole at these frequencies was attributable to contraction of the latter fibres. 5. In the closer muscle, the thin fibres responded to stimulation of the "slow" motor axon and the "common" inhibitor axon. Membrane conductance in these fibres was markedly increased by v-aminobutyric acid. The thick fibres of the closer responded mainly to the "fast" motor axon and were relatively insensitive to stimulation of the inhibitor axon and to 7-aminobutyric acid.
Crustacean tonic and phasic motoneurons have neuromuscular synaptic properties corresponding with... more Crustacean tonic and phasic motoneurons have neuromuscular synaptic properties corresponding with their functional requirements. Phasic axon synapses produce large excitatory postsynaptic potentials (EPSPs) which depress rapidly during repetitive activation. Tonic axon synapses generally produce smaller EPSPs which are more resistant to fatigue. To test whether nerve impulse activity of the motoneuron plays a role in the establishment of these synaptic properties, a phasic axon was tonically stimulated in vivo. The "fast" closer excitor of the crayfish claw, which normally fires few impulses, was stimulated for 2 hr/ day at 5 Hz, through implanted electrodes. In young crayfish, this stimulation produced an 11-fold decrease in synaptic fatigue at the fast axon's neuromuscular synapses, as determined from measurements of EPSPs during 5 Hz stimulation of the fast axon for 30 min. In comparison with EPSPs of the contralateral control claw, the initial EPSP amplitude was 4...
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