摘要:

AbstractAxoplasm extruded from the giant axon of the squid contains Ca2+‐activated proteases. The protease in the 100,000X g of supernatant of axoplasm is very specific and degrades only the 200,000 MW, neurofilament protein (NF200), whereas the protease(s) in the pellet has a much wider range of substrate specificity. The activation of the supernatant protease is restricted to the Ca2+ion, and no other divalent cation will substitute. The protease requires Ca2+at a higher concentration than 0.5 mMfor activation, and has a pH optimum of about 7.5. Degradation of the NF200appears to proceed through a 100,000 MW and possibly a 47,000–50,000‐MW intermediate form before degradation to TCA‐soluble peptides. Activity of the protease is inhibited by divalent cation chelators, Cu2+and Fe2+, sulphydryl inhibitors, and leupeptin. This specific Ca2+‐activated protease in squid axoplasm has identical properties to Ca2+‐activated proteases found in various non‐neural tissues. Despite its narrow protein substrate specificity, Ca2+‐activated protease purified from human platelets effectively degrades squid NF200, suggesting a possible structural relationship between platelet and muscle actin‐binding proteins and neuro

ISSN:0022-3034    

DOI:10.1002/neu.480110102

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

年代:1980

数据来源: WILEY

摘要:

AbstractA compressed network of “giant” neurons, lying within the inner nerve‐ring of the hydrozoan jellyfishPolyorchis, functions as the overall pattern generator and the motor neuron system for the subumbrellar swimming musculature. The neurons that form the network are all electrically coupled. The coupling is tight, so that action potentials and slow membrane‐potential oscillations are synchronous throughout the network. The fluorescent dye Lucifer Yellow CH passes throughout the network following iontophoretic injection into a single neuron. The sites of both current and dye passage are presumably the numerous gap junctions which are found where the giants run together. Based on the morphological identification of the giant network from the dye injections and ultrastructural studies, the electrophysiological data on the firing pattern and input–output relations of the network, and its position relative to other neurons in the inner nerve‐ring, the giant network can be considered an identified neu

ISSN:0022-3034    

DOI:10.1002/neu.480110103

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

年代:1980

数据来源: WILEY

摘要:

AbstractInnervation patterns, synaptic properties, and fiber ultrastructure were studied in three muscles of the second maxilla ofProcambarus clarkiiandOrconectes virilus. All three muscles, ASDM (anterior scaphognathite depressor muscle), CFM (coxopodite flexor muscle), and SFM (scaphognathite flexor muscle), were polyneuronally innervated, receiving two, three, and four excitors, respectively. Two of the four excitors innervating SFM were branches of the two excitors supplying ASDM. No muscle received inhibitor axons. Synapses tended to be low output and show a high degree of facilitation as measured by the facilitation index of Atwood and Bittner. Ranges of EPSP amplitudes and facilitation indices were common to all excitors. Muscle fibers uniformly showed short sarcomere lengths and low thin‐to‐thick filament ratios. These physiological and ultrastructural peripheral features are consistent with the nature of the motor score from the central rhythm genera

ISSN:0022-3034    

DOI:10.1002/neu.480110104

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

年代:1980

数据来源: WILEY

摘要:

AbstractAxonal transport of the 16S molecular form of acetylcholinesterase (16S‐AChE) in doubly ligated rat sciatic nerves was studied by means of velocity sedimentation analysis on sucrose gradients. This form of AChE was selectively confined to motor, and not to sensory, fibers in the sciatic nerve, where it represented 3–4% of total AChE. Its activity increased linearly with time (4–20 hr) in nerve segments (7 mm) proximal to the central ligature (4.5 mU/24 hr) and distal to the peripheral ligature (2.0 mU/24 hr). From the linear rates of accumulation of 16S‐AChE, we conclude that the enzyme is conveyed by anterograde and retrograde axonal transport at velocities close to those previously defined for the movement of total AChE (410 mm/day, anterograde; 220 mm/day, retrograde). The transport of AChE molecular forms, other than the 16S form, could not be resolved presumably due to their presence in blood as well as at extraaxonal sites. The present findings are consistent with the view that in rat sciatic nerve most, if not all, of the small portion of total AChE (approximately 3%) which is transported may be accounted for by 1

ISSN:0022-3034    

DOI:10.1002/neu.480110105

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

年代:1980

数据来源: WILEY

摘要:

AbstractIntracellular recordings from Purkinje cells (PC) in the cerebellum of adult staggerer mutant mice revealed that the orthodromic response of PCs to juxtafastigial (JF) stimulation closely resembled a climbing fiber response (CFR). However, for most of the PCs studied, these responses were graded in a stepwise manner when the stimulus strength was increased. The underlying excitatory synaptic potentials (EPSPs) had the typical shape of EPSPs mediated through climbing fibers (CFs), but their size fluctuated in discrete steps, the highest one reaching the firing level. In the same PCs, the size of the spontaneous EPSPs fluctuated in a similar fashion and the frequency of each step was in the range of CF‐mediated EPSPs. These results strongly suggest that in staggerer mice several CFs synapse with each PC instead of a single CF as in normal adults. Furthermore, the activation through some of these CFs does not reach the firing level of the corresponding P

ISSN:0022-3034    

DOI:10.1002/neu.480110106

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

年代:1980

数据来源: WILEY

摘要:

AbstractThin section and freeze‐fracture electron microscopy have been used to characterize the changes in membrane morphology of reaggregating cultures of chick optic tectum. The cells are rounded and freely dispersed at 0 hr after dissociation. Between 2 and 6 hr the cells become closely apposed on all sides by other cells and form small aggregates. At this timepunta adhaerentiajunctions and focal densities are seen along the membranes of neighboring cells. Between 1 and 5 daysin vitro(DIV) neurites containing growth cone regions are present. At 5 DIV the first synaptic contacts are observed. Between 7 and 14 DIV, the number of synaptic contacts increase and fewer growth cone regions are observed. As early as 7 DIV profiles are observed which strongly resemble both astrocytic and oligodendroglial cell somata and processes. Freeze‐fracture analysis of aggregates at 0–4 hr reveals a sparse particle distribution on the P and E faces of apposed cells. By 1 DIV small clusters of loosely packed, large sized particles are seen on the P face of apposed cell membranes which may represent junctional contacts. Apparent coated vesicle fusion sites are common on the P face at 1–2 DIV. By 7 DIV, E face particle arrays are seen on cell bodies and neurites which correspond to specializations characteristic of excitatory synaptic junctions. By 8–10 DIV particle arrays are seen on the P face of post‐synaptic membrane which may represent inhibitory synaptic contacts. Other types of particle specializations seen in freeze‐fracture replicas include: specializations characteristic of gap junctions between cells and orthogonal assemblies of particles thought to be characteristic

ISSN:0022-3034    

DOI:10.1002/neu.480110107

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

年代:1980

数据来源: WILEY

摘要:

AbstractThis paper describes the results of investigating burst generation by the cyberchron network in the snailHelisoma. The cyberchron network is composed of approximately 20 electrically coupled neurons and controls the feeding behavior of the snail. The electrical coupling between network members has made it particularly difficult to distinguish between the importance and involvement of single‐cell and network properties in burst generation by this system. The present investigations utilized the new single‐electrode voltage clamp to examine the membrane properties and network interactions of the cyberchron neurons: (1) A slow outward current is activated by moderately large depolarizing commands (−40 to 0 mV) and does not undergo inactivation decay (i.e., decline in magnitude) during a command potential step maintained for 10 sec or more. The lack of inactivation of the outward current in cyberchron neurons appears to be due to the dominating role of a Ca‐dependent K current. (2) There are two functionally distinct classes of cyberchrons—current generator cyberchrons and follower cyberchrons. (3) Primary current generator cyberchrons have membrane properties similar to endogenous bursting neurons (e.g., persistent inward Ca current and negative resistance region inI–Vplot) and appear to provide the main driving and timing current for the rest of the network. (4) The vast majority of cyberchrons are secondary current generator cyberchrons with membrane properties which exhibit inward‐going rectification and appear to burst as a result of regenerative excitation with one another and the primary current generator cyberchrons. (5) The second class of cyberchrons are driven by the electrical synaptic input from the current generator cyberchrons, do not exhibit inward‐going rectification, and are called follower cyberchrons. (6) Burst termination is due to activation of a slow outward tail current in most cyberchrons during the burst (probably Ca‐activated K current) which causes a hyperpolarization in individual cyberchrons, terminating the burst. (7) Decay of the outward tail current causes the cyberchrons to depolarize, which activates the persistent inward Ca current in the primary current generator cyberchrons, starting the

ISSN:0022-3034    

DOI:10.1002/neu.480110108

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

年代:1980

数据来源: WILEY

摘要:

AbstractThe large octopaminergic dorsal unpaired median neuron of the locust that innervates the extensor tibiae muscle, DUMETi, was examined electronmicroscopically. Its soma contains many Golgi complexes apparently making dense‐core vesicles similar to those found in peripheral branches and terminals. There are also larger stores of the dense material in the soma, especially near the exit of the principal neurite, that are not in vesicular form. Since the neurons can readily be penetrated and stimulated by microelectrodes, they form favorable subjects for direct studies of the control of neurosecretion. Preterminal fine branches of the neuron were located in proximal outer bundles of muscle fibers into which they had been traced electrophysiologically. They contain numerous large dense‐core vesicles arrayed in rows near microtubules. These fine branches have a thick layer of collagenous connective tissue between the axon and the muscle fiber. Final terminals have varicosities containing many vesicles, lying inside the outer layers of the sarcolemmal complex of muscle fibers. They do not form synaptic structures. Terminals of another DUM neuron, one that innervates the dorsal longitudinal flight muscles (DUMDL), were similar in detail to those of DUMETi. DUMETi swelled about 20‐fold in cross‐sectional area above a ligature, in a 12‐hr period, indicating that there is an extensive centrifugal flow of material in it, and sprouted

ISSN:0022-3034    

DOI:10.1002/neu.480110109

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

年代:1980

数据来源: WILEY

ISSN:0022-3034    

DOI:10.1002/neu.480110110

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

年代:1980

数据来源: WILEY

ISSN:0022-3034    

DOI:10.1002/neu.480110111

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

年代:1980

数据来源: WILEY