摘要:

AbstractEvidence is offered that the axons of developing sensory neurons in the wing ofDrosophilaare guided (given both location and polarity information) by the epithelium over which they grow. This guidance is effective in the absence of such potential additional cues as guidepost neurons and physical channels.

ISSN:0022-3034    

DOI:10.1002/neu.480170602

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

年代:1986

数据来源: WILEY

摘要:

AbstractAs this quote and the article it was taken from reflect, it is a commonly held belief that the development of invertebrate nervous systems is so rigidly programmed that it is qualitatively different from that of vertebrates. The facts do not support this assertion, and I will show, using examples from among the arthropods, that appropriate experiments often reveal competition, feedback, and prolonged periods of malleability much as they do for the vertebrates. Indeed, given the well known advantages of studying the invertebrate nervous system, I think it likely that invertebrates can serve as important and useful preparations for studying, at the cellular level, the same biological phenomena that Easter et al. (1985) are trying to understand in vertebrates.

ISSN:0022-3034    

DOI:10.1002/neu.480170603

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

年代:1986

数据来源: WILEY

摘要:

AbstractThe earliest outgrowth of nerve fibers from identified spinal neurons labeled with horseradish peroxidase (HRP) was traced along surgically rearranged pathways in the central nervous system (CNS) ofXenopusembryos. Parts of the CNS were misaligned or inverted rostrocaudally by grafting a segment of labeled spinal cord in place of the same or different spinal cord segment of an unlabeled embryo or by joining two rostral half embryos (head‐to‐head) or two caudal half embryos (tail‐to‐tail), one half of which was derived from a labeled embryo in each combination. Donor embryos were labeled by injection of HRP into a selected blastomere at the 16‐ or 32‐cell stage. Host embryos were unlabeled. Grafts from labeled donors to unlabeled host embryos were made at early neural tube stages before out‐growth of any nerve fibers had started (Jacobson and Huang, 1985). Routes taken by labeled nerve fibers growing into unlabeled CNS were observed at later stages, and the rates of nerve fiber elongation were calculated. Labeled nerve fibers were normal in appearance, and elongated without branching, at normal rates (22–71 μm/h). In head‐to‐head and tail‐to‐tail embryos and in embryos with inverted spinal cord grafts, nerve fibers continued elongating without branching in the direction opposite to normal in the CNS. Many fibers reached lengths that were far greater than normal. No reorientation of such maldirected nerve fibers was seen. These results indicate that nerve fiber elongation is not guided by axially polarized pathway cues or markers and that nerve fibers do not grow to predetermined lengths. However, neurites preferred to grow along streotyped nerve fiber pathways even when forced to grow in the wrong direction or when confront

ISSN:0022-3034    

DOI:10.1002/neu.480170604

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

年代:1986

数据来源: WILEY

摘要:

AbstractGonadal hormones can produce striking behavioral and neural plasticity in adult organisms. For example, systemic administration of testosterone to adult female canaries induces the development of male‐typical song behavior and results in a striking increase in the size of brain nuclei that are known to be involved with song control. The mechanism whereby androgens produce such neural plasticity is not known, although it has seemed likely that growth‐promoting effects of androgens are due to a direct induction of protein synthesis in cells containing hormone receptors (following activation of specific genes by the hormone‐receptor complex). In this experiment we have examined the trophic effect of testosterone in the song‐control nucleus HVc (caudal nucleus of the ventral hyperstriatum), which has been shown to contain androgen‐concentrating cells as well as neurons that are especially responsive to conspecific song. We report here that testosterone administration increases the volume of HVc in hearing adult female canaries only; testosterone‐induced growth of HVc is greatly attenuated in birds that are deprived of auditory stimulation via deafening. Thus, testosterone treatment alone is not a sufficient stimulus for neural growth in HVc. This result suggests that testosterone does not stimulate growth solely via a direct action on hormone receptors in HVc, but rather that testosterone and sensory stimulation can act synergistically to produce structural plasticity in the

ISSN:0022-3034    

DOI:10.1002/neu.480170605

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

年代:1986

数据来源: WILEY

摘要:

AbstractThe segmental ganglia of adults of the moth,Manduca sexta, are constructed both from remodeled larval neurons and from adult‐specific cells. The latter are produced by identified stem cells (neuroblasts) during larval life and then differentiate to form functional neurons during metamorphosis. The mitotic activity of the larval neuroblasts could be irreversibly blocked by the DNA‐synthesis inhibitor hydroxyurea (HU). Treatment on day 1 of the third larval stage resulted in 80–90% of the neuroblasts being blocked before they produced any progeny while leaving the functional larval neurons unaffected. Treated larvae finished growth, underwent metamorphosis, and produced an adult CNS that contained the normal set of remodeled larval neurons but lacked most of the new adult‐specific cells. When HU treatment was delayed until the start of the fourth or fifth larval stage, the neuroblasts produced the early portions of their respective lineages before they were blocked. The immature neurons that were generated prior to treatment survived to contribute adult‐specific neurons to the moth CNS, but the remainder of each lineage was missing. This technique therefore enables one to produce adult nervous systems containing the basic set of remodeled larval cells plus defined sets of adult‐speci

ISSN:0022-3034    

DOI:10.1002/neu.480170606

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

年代:1986

数据来源: WILEY

摘要:

AbstractWe have studied the development of a neuromuscular system for which mature function has been lost through evolution in the grasshopper,Barytettix psolus(Cohn and Cantrall, 1974).Barytettixis flightless throughout life and has only vestigial wings that are incapable of active movement. AdultBarytettixlack muscles homologous to the indirect flight muscles of locusts and grasshoppers that fly, while other thoracic muscles are similar. We have found, using light and electron microscopic examination of tissues from various developmental stages, that the metathoracic dorsal longitudinal muscle is present and is innervated during nymphal life but is absent in adults. Yet its nerve persists and, in the adult, contains axonal presynaptic specializations opposite inappropriate targets such as glial processes and basal lamina. Our findings indicate that selective muscle death during development is one mechanism underlying the reduction of the flight system ofBarytettixthrough evolution. The finding that presynaptic terminals persist in the absence of the muscle indicates that the muscle and its innervation follow programs of development that are at least partially independent and reinforces the concept that in insects motorneurons, and perhaps neurons in general, are not dependent upon trophic influences from their targets for survival and maintenance of their differentiated phenotype.

ISSN:0022-3034    

DOI:10.1002/neu.480170607

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

年代:1986

数据来源: WILEY

摘要:

AbstractRapid axonal transport of a pulse of35S‐methionine‐labelled material was studiedin vitroin the sensory neurons of amphibian sciatic nerve using a position‐sensitive detector. For 10 nerves studied at 23.0 ± 0.2°C it was found that a pulse moved in the anterograde direction characterized by front edge, peak, and trailing edge transport rates of (mm/d) 180.8 ± 2.2 (±SEM), 176.6 ± 2.3, and 153.7 ± 3.0, respectively. Following its arrival at a distal ligature, a smaller pulse was observed to move in the retrograde direction characterized by front edge and peak transport rates of 158.0 ± 7.3 and 110.3 ± 3.5, respectively, indicating that retrograde transport proceeds at a rate of 0.88 ± 0.04 that of anterograde. The retrograde pulse was observed to disperse at a rate greater than the anterograde. Reversal of radiolabel at the distal ligature began 1.49 ± 0.15 h following arrival of the first radiolabel. Considerable variation was seen between preparations in the way radiolabel accumulated in the end (ligature) regions of the nerve. Although a retrograde pulse was seen in all preparations, in 7 of 10 preparations there was no evidence of this pulse accumulating within less than 2–3 mm of a proximal ligature; however, accumulation was observed within less than 5 mm in

ISSN:0022-3034    

DOI:10.1002/neu.480170608

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

年代:1986

数据来源: WILEY

摘要:

AbstractDuring embryonic development skin sensory neurons in lumbosacral dorsal root ganglia (DRGs) establish their dermatomes and axonal projections in a precise, orderly fashion in the chick. To investigate mechanisms responsible for this specific outgrowth, the rostrocaudal order of DRGs T7‐LS3 was reversed by rotating the corresponding segments of neural crest, either alone or together with the underlying neural tube in St.15–16 embryos. The resulting skin sensory innervation patterns, mapped physiologically or an‐atomically at St.29–40, differed between the two experimental groups. Following neural tube rotations DRGs tended to establish innervation patterns that were consonant with their original position in the embryo. Axons from these rotated DRGs generally projected into the appropriate pathways and innervated the appopriate region of skin. Neural crest rotations left the ventral neural tube (including the motor neuron precursors) largely intact. In this case rotated DRGs tended to establish innervation patterns in accordance with their new position in the embryo, almost as if no rotation had been made. These results cannot be explained solely by the inherent specificity of sensory neurons. Instead, the results are largely consistent with the suggestion (Honig et al., 1986; Landmesser and Honig, 1986) that motor axons can direct the outgrowth of sensory axons and thereby influence the establishment of sensory innervation patterns. Other mechanisms that may also affect the development of sensory innervation patterns are di

ISSN:0022-3034    

DOI:10.1002/neu.480170609

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

年代:1986

数据来源: WILEY

摘要:

AbstractEvidence is presented indicating that the mesocerebrum of the terrestrial snail,Helix aspersa, has a major role in the control of sexual behavior. Morphological and physiological results demonstrate a right‐sided bias in the mesocerebrum that is consistent with the fact that sexual behavior is executed almost entirely on the animal's right side. Thus, the right lobe has 23% more neurons than the left lobe, and they are 24% larger. Excitatory synaptic inputs derive predominately from neurons on the right side. The axons of right‐side mesocerebral neurons go to the right pedal ganglion almost without exception, and even the axons of left‐side neurons travel mostly in right‐side connective nerves. Direct evidence for a role of the mesocerebrum in commanding sexual behavior comes from experiments with electrical stimulation.Extracellular stimulation of the right mesocerebrum, but not the left mesocerebrum, resulted in movements of the “love dart” sac and the penis. Intracellular stimulation of neurons in the right mesocerebrum evoked measurable movements of either the dart sac or the penis, or both, in 17% of the cells tested. The latencies ranged between 5 and 50 s. In an intact animal, these movements would cause a release of the dart and an eversion of the penis. The motor effects were mediated through the right cerebropedal connective and the pedal nerve NCPD, with the motorneurons probably situated in the right ped

ISSN:0022-3034    

DOI:10.1002/neu.480170610

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

年代:1986

数据来源: WILEY

摘要:

AbstractThe effects of the calmodulin inhibitors amitriptyline, desipramine, imipramine, and clomipramine on fast axonal transport, oxidative metabolism, and density of axonal microtubules were measured in bullfrog spinal nerves in vitro. The four drugs tested inhibited the fast orthograde transport of [3H]leucine‐labelled proteins and the fast retrograde transport of acetylcholinesterase at a concentration of 0.2 mM. Amitriptylin, desipramine, and imipramine were equipotent inhibitors of transport, and clomipramine was a more potent inhibitor than imipramine. The adenosine triphosphate content of the nerves was reduced by at most 19% by the compounds under study; such a reduction cannot account for the inhibition of fast axonal transport. Desipramine and imipramine had no significant effect on the density of microtubules in unmyelinated axons, whereas amitriptyline only reduced it by 18%; the inhibition of axonal transport by these three drugs can therefore not be explained by microtubule disruption. Clomipramine reduced microtubular density by 40%, and this effect may have contributed to the inhibition of fast axonal transport. The inhibition of fast axonal transport by desipramine, imipramine, and amitriptyline may be related to the inhibition of calmodulin function by these drugs. The similar potency of these three durgs as inhibitors of fast axonal transport goes in parallel with their known similar potency as calmodulin antagonist

ISSN:0022-3034    

DOI:10.1002/neu.480170611

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

年代:1986

数据来源: WILEY