摘要:

AbstractThe nerves and nerve terminals to tonic larval muscle fibers in third and fifth instar caterpillars were studied to compare them with those formed by the same motor neurons on phasic flight muscles in adult moths.Scanning micrographs showed a primary nerve branch running the length of each fiber, with secondary nerve branches extending from it at intervals. There was a great deal of variability in both the length of the branches and the distance from the nerve at which the neuromuscular junctions were formed. The rapid increase in muscle fiber size during larval development may be responsible for this variability. The nerves and junctions were often found to be obscure by overlying fibroblasts and tracheoblasts or entering the deep muscle clefts. Those examined were similar in appearance to the adult junctions formed by the same neurons, although some may have formed single branches instead of y‐shapes.The membrane specializations of the synapse seen infreeze‐fracturedspecimens were similar to those of the adult junction. However, the overall shape of the nerve terminal within the junction differed. The larval nerve terminals appeared varicose instead of having a uniform diameter. The spacing of the nerve plaques varied, in contrast with the relatively straight alignment and even spacing of plaques found in adult junctions. Such differences could result from an interaction between the motor neuron and the two different types of muscle fiber that it innervates, an intrinsic change in the motor neurons themselves that occurs with metamorphosis, or a plastic functional response that occurs as a result of the different types of motor patterns that are used in the two sta

ISSN:0022-3034    

DOI:10.1002/neu.480160202

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1985

数据来源: WILEY

摘要:

Abstract(1)Stimulation of the phasic (fast) motor axon of the isolated crayfish claw preparation at relatively low frequency (0.1 Hz) leads to depression of the excitatory junction potential (EJP) recorded from single muscle fibers.(2)When the same stimulation is delivered following depression of the EJP at a higher frequency (5 Hz), a potentiated EJP appears, which is more resistant to low frequency depression. The potentiation appears to be analogous to “long‐term facilitation” observed after stimulation of a tonic motor axon in crayfish and crabs.(3)Long‐term facilitation can be detected in preparations made from claws of animals in which the phasic motoneuron was stimulated at 5 Hz for 2 hin situ. This effect lasts for at least one day after one conditioning trial. Long‐term facilitation is observed after stimulation of decentralized axonsin situ, indicating that the change is attributable to local changes in terminal regions of the axon, and does not require the cell body.(4)When electrodes are implantedin situand the phasic motoneuron stimulated at 5 Hz for 2 h each day, synaptic depression becomes less pronounced and initial EJP amplitude becomes smaller over a period of several days.(5)The latter changes, which adapt the neuron to a more tonic activity pattern, usually require several days for completion. Adaptation of fatigability occurs more rapidly than adaptation of initial EJP amplitude, and once established, remains for many days without further superimposed activity.(6)Long‐term adaptation does not occur in decentralized axons.(7)Long‐term facilitation and long‐term adaptation are different responses of the neuron to enhanced activity. The former can occur in isolated or decentralized axons and leads to enhancement of EJP amplitude for a period of several hours to at least one day after a single episode of conditioning. The latter requires more time to be established, and leads to reduction of initial EJP amplitude and to lessened fatigability which persist

ISSN:0022-3034    

DOI:10.1002/neu.480160203

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1985

数据来源: WILEY

ISSN:0022-3034    

DOI:10.1002/neu.480160204

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1985

数据来源: WILEY

摘要:

AbstractThere are two pairs of muscles in each abdominal segment of the crab; one pair of flexors and one pair of extensors. In the early larval stages the muscles have short sarcomeres—a property of fast fibers—and high thin to thick filament ratios—a property of slow fibers. In the adult the abdominal muscles are intermediate and slow, since they have fibers with intermediate and long sarcomeres, high thin to thick filament ratios, low myofibrillar ATPase activity, and high NADH diaphorase activity. The different fiber types are regionally distributed within the flexor muscle.Microelectrode recordings from single flexor muscle fibers in the adult showed that most fibers are supplied by three excitatory motor axons, although some are supplied by as many as five efferents. One axon supplies all of the flexor muscle fibers in its own hemisegment, and the evoked junctional potentials exhibit depression. This feature together with the innervation patterns of the fibers are similar to those reported for the deep flexor muscles of crayfish and lobsters. Therefore, in the adult crab, the abdominal flexor muscles have some features in common with the slow superficial flexors of crayfish and other features in common with the fast deep flexor mu

ISSN:0022-3034    

DOI:10.1002/neu.480160205

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1985

数据来源: WILEY

摘要:

AbstractAn identified serotonergic neuron (C1) in the cerebral ganglion ofHelisoma trivolvissprouts following axotomy and rapidly (seven to eight days) regenerates to recover its regulation of feeding motor output from neurons of the buccal ganglia. The morphologies of normal and regenerated neurons C1 were compared. Intracellular injection of the fluorescent dye, Lucifer Yellow, into neuron C1 was compared with serotonin immunofluorescent staining of the cerebral and buccal ganglia. The two techniques revealed different and complimentary representations of the morphology of neuron C1. Lucifer Yellow provided optimal staining of the soma, major axon branches, and dendritic arborization. Immunocytochemical staining revealed terminal axon branches on distant targets and showed an extensive plexus of fine fibers in the sheaths of ganglia and nerve trunks. In addition to C1, serotonin‐like immunoreactivity was localized in approximately 30 other neurons in each of the paired cerebral ganglia. Only cerebral neurons C1 had axons projecting to the buccal ganglia. No neuronal somata in the buccal ganglia displayed serotonin‐like immunoreactivity.Observations of regenerating neurons C1 demonstrated: (1) Actively growing neurites, bothin situand in cell culture, displayed serotonin‐like immunoreactivity; (2) severed distal axons of C1 retained serotonin‐like immunoreactivity for up to 28 days; (3) axotomized neurons C1 regenerated to restore functional control over the feeding motor

ISSN:0022-3034    

DOI:10.1002/neu.480160206

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1985

数据来源: WILEY

ISSN:0022-3034    

DOI:10.1002/neu.480160207

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1985

数据来源: WILEY

ISSN:0022-3034    

DOI:10.1002/neu.480160201

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1985

数据来源: WILEY