摘要:

AbstractThe nucleus isthmi (NI) is the primary relay for the frog's ipsilateral visuotectal projection. Using electrophysiological methods, ipsilateral visuotectal activity has been recorded in thyroxine‐treated, postmetamorphic axolotls but not in larval axolotls. In order to determine whether changes in isthmotectal projections are responsible for this change in electrophysiological responsiveness, we have investigated the connections between the tectum and the NI using horseradish peroxidase. Our results indicate that the axolotl's isthmotectal pathways are strikingly similar to those of the frog NI, and that the NI sends bilateral projections to the tecta in both larval and thyroxine‐treated, postmetamorphic axolotls. Thus, the anatomical connections underlying the ipsilateral visuotectal projection are present during larval stages, despite the lack of electrophysiological evidence for the larval ipsilateral visuotectal projection. We hypothesize that thyroxine‐induced metamorphosis produces changes in the terminal arborizations of the crossed isthmotectal projection which allow them to be detected by presynaptic electrophysiological techn

ISSN:0022-3034    

DOI:10.1002/neu.480190202

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

年代:1988

数据来源: WILEY

摘要:

AbstractThe superficial flexor muscles of the crayfish are a neuromuscular system of a few muscle cells innervated by six neurons in a precise position‐dependent pattern. The neurons are capable of regenerating their normal connectivity patterns within a short span of time when conditions are favorable. The superficial flexor muscles of the second and third segments, despite their similarities in neuronal and muscle cell size and number, have distinctive connectivity patterns; some homologous neurons form similar patterns but other homologous neurons form patterns that are reversed between segments. We transplanted each segment's nerve into each other's muscle in order to observe regeneration of the nerves into a target area that differed in connectivity patterns from their original muscle. During the first weeks of regeneration all neurons formed a connectivity pattern with more connections medially and declining connections laterally, a pattern determined bythe medial location of the nerve transplant. This pattern is maintained for most of the neurons, but for some there is an eventual reduction in medial connections as maximum synapse formation shifts to the lateral muscle fibers. Three of the eight neurons studied were able to regenerate connectivity patterns that corresponded to their segment of origin and not to their host muscle. This suggests that intersegmental muscle differences are not influencing the formation of these connectivity patterns, so the neurons will follow their inherent synaptogenesis progra

ISSN:0022-3034    

DOI:10.1002/neu.480190203

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

年代:1988

数据来源: WILEY

摘要:

AbstractThe superficial flexor muscle of the crayfish is a neuromuscular system in which the neurons form position‐dependent connectivity patterns with the muscle fibers. This system could be formed with the help of a single medial‐to‐lateral gradient during development that embodies positional information. To test this gradient hypothesis we changed the nerve's normal medial entrypoint into the muscle by transplanting it to the middle ofthe muscle sheet. When all the muscle fibers were present in the target area, most of the neurons studied passed through a stage during regeneration in which they showed preference for either medial or lateral synapse formation. Those neurons that in normal animals innervated preferentially the medial fibers showed a medial preference for new contacts; the neuron that normally innervated the lateral fibers showed a lateral preference for new contacts; the neuron that normally innervated everywhere regenerated equallywell into both medial and lateral fibers. Therefore, theseneurons are able to detect information regarding their position within the muscle mass and respond to it by preferential synapse formation. The effect of a positional gradient could not be detected when half of the target field was removed prior to regeneration. In this instance, the neuron that innervated the missing target area now regenerated to almost all the available fibers. It is suggested that the interplay of positional cues with other factors at different points in time could determine the final connectivity patterns formed by these

ISSN:0022-3034    

DOI:10.1002/neu.480190204

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

年代:1988

数据来源: WILEY

摘要:

AbstractInvestigations of the cues by which axonal growth cones navigate long distances to their targets have revealed the use of a rich and complex diversity of cellular and extracellular information. In the present study we describe one of the most conceptually simple pathfinding cues: a single identified cell in the leech,Hirudo medicinalis, that may guide axons several hundred micrometers to innervate a particular target. One of the stereotyped nerves ofH. medicinalisis a “sex nerve” thatprojects from the anterior root of ganglion 6 [SNA (6)] tothe male reproductive structures in the adjacent anterior segment. The pathway for SNA (6) is completely underlainbya single peripheral cell, here called the axonal runway cell (ARC), before axons enter the pathway. The ARC is apparently a nonneuronal cell that stains with a monoclonalantibody that recognizes leech muscle cells. The importance ofthe ARC for establishing SNA (6) was tested by ablating itbefore axons entered the pathway. When the ARC was killed either by physical disruption with a microelectrode, or byphotoablation after filling it with the fluorescent dye Lucifer yellow, SNA(6) always failed to form, whereas all other nerves formed normally. Killing other peripheral cellsin proximity to the ARC did not interfere with SNA(6) formation. Ablation of possible “pioneer neurons” for SNA(6) also did not prevent its formation. These results show that formation of a particular nerve requires onlya single cell to serve as a guide for outgrowingpr

ISSN:0022-3034    

DOI:10.1002/neu.480190205

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

年代:1988

数据来源: WILEY

摘要:

AbstractPrevious studies by Prives et al. (1980, 1982a and b) have shown that acetylcholine receptors (AchRs) are extracted from muscle cells in vitro by Triton X‐100 at different rates, and that clustered receptors extract most slowly. The present study was aimed at comparing the relative extractability of receptors in clusters with those in intercluster regions and the role of neural factors in regulating this extractability. Using primary rat muscle cells in vitro we confirmed that receptor extraction with Triton X‐100 does not fit a single exponential but has more than one rate, and that in control cells clustered receptors extract more slowly than do receptors in intercluster regions. The major new observation in this study was that neural extract lowered the overall Triton extraction rate of intercluster receptors to that of clustered receptors. Additional new observations include the findings that (1) both clustered and intercluster receptors show multiphasic extraction rates; (2) stabilization of AchRs against Triton extraction increases with time in the surface membrane; (3) the effect of neural extract on Triton extractability of AChR is dependent on factors that control RNA synthesis, cytoskeletal elements, and collagen; (4) fixation and/or buffer washes accelerate receptor extraction only incells that are treated with Triton, but not in control cells; (5) in control cells (not exposed to neural factors) Triton X‐100 causes new clusters to form. From experiments using Con A we suggest that the Tritoninduced new clusters may not be formed by a redistribution of receptorsbut are, most likely, due to the presence of groups of intercluster receptors with extraction rates lower than thoseof surrounding rece

ISSN:0022-3034    

DOI:10.1002/neu.480190206

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

年代:1988

数据来源: WILEY

ISSN:0022-3034    

DOI:10.1002/neu.480190201

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

年代:1988

数据来源: WILEY