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Biomedical subjects

D Bentley

Publications and source records attributed to D Bentley.

At least 91 records · Page 5Linked to original sources
PubMed1983

Sensory receptor differentiation and axonal pathfinding in the cercus of the grasshopper embryo.

An immunological probe selective for insect neurons (L.Y. Jan and Y.N. Jan, 1982, Proc. Nat. Acad. Sci. USA 79, 2700-2704) was used to characterize the genesis of sensory neurons and the formation of the peripheral nerves in the grasshopper cercus. During embryogenesis the cercal ectoderm produces a characteristic set of sensory neurons in a precise spatiotemporal order. The first neurons migrate from the epidermis into the lumen and send out axons toward the CNS along the epidermal wall. These luminal neurons arise in four distinct groups, each of which establishes a separate branch of the cercal nerve, with the axons of the three distal groups converging onto the cell bodies of the more proximal neurons and thus seeming to use them as an intermediate target on route to the CNS. Epidermal neurons, whose cell bodies remain within the epithelium, begin to appear at a later stage. These cells come to innervate external sensory hairs, and in general their axons grow to the CNS along the preexisting nerves. Each sensory hair possesses two nonneuronal cells--the trichogen (shaft-forming) and tormogen (socket-forming) cells--which also stain with the antibody and begin to display immunoreactivity at the same time as the allied sensory neuron. The trichogen and tormogen cells do not form the hair shaft and socket until much later, with outgrowth occurring in an order quite distinct from that in which the receptors undertook their initial, biochemical differentiation. Thus, these two aspects of trichogen/tormogen differentiation appear to be under separate developmental control.

Animals↗
PubMed1983

Embryogenesis of peripheral nerve pathways in grasshopper legs. I. The initial nerve pathway to the CNS.

The founding of the first nerve path of the grasshopper metathoracic leg was examined at the level of identified neurons, using intracellular dye fills, immunohistochemistry, Nomarski optics, and scanning and transmission electron microscopy. The embryonic nerve is established by the axonal trajectory of a pair of afferent pioneer neurons, the tibial 1 (Ti1) cells. Following a period of profuse filopodial sprouting, the Ti1 axonal growth cones, possessing 75- to 100-microns-long filopodia, navigate a stereotyped path across the limb bud epithelium to the base of the appendage and into the CNS. The Ti1 axons grow from cell to cell along a chain of preaxonogenesis neurons spaced at intervals along the pathway, forming dye-passing junctions with them. The contacted neurons subsequently undergo axonogenesis and follow the pioneer axons into the CNS. Later arising neurons project their axons onto the cell bodies of the chain, thereby establishing the principal branch points of the nerve. Among the later arising afferents are the sensory neurons of the femoral chordotonal and subgenual organs. The morphology of the adult nerve appears to be determined by the stereotyped positioning of neurons in the differentiating limb bud and by the resultant axonal trajectories established during the first 10% of peripheral neurogenesis.

Animals↗
PubMed1983

Embryogenesis of peripheral nerve pathways in grasshopper legs. II. The major nerve routes.

In the preceding paper (H. Keshishian and D. Bentley, 1983a, Dev. Biol. 96, 89-102) the events leading to the morphogenesis of nerve 5B1 in the grasshopper embryonic metathoracic leg were presented. Here the role of later differentiating peripheral neurons in establishing the other major nerves of the leg is examined. In addition to the (tibial 1) (Ti1) pioneer neuron cell pairs that establish nerve 5B1 in the tibia femur, and coxa-trochanter, six later differentiating cells and/or cell pairs were identified and examined with respect to their role in peripheral nerve ontogeny. Nerve path pioneering was observed in two cell pairs of the distal tarsus (Ta1 and Ta2), by neurons of the posterior proximal tibia (Ti2), the posterior midfemur (neurons F3 and F4), and by an additional cell pair in the anterior coxal-trochanteral region of the limb bud (cell pair, CT2). In addition, efferent projections onto limb and epithelia played an important role in establishing nerve branches. In two nerves the axonal trajectory from the periphery to the CNS is established by afferent and efferent pathfinding axons meeting halfway and overgrowing each other's established projections. For each nerve branch examined it was found that axons projected initially to the cell bodies of previously arising neurons along the trajectory. The location along the limb bud ectoderm where neurons arise, and hence their ultimate cell body positions, played an important role in organizing the fasciculation of follower axons and establishing branch points.

Animals↗
PubMed1983

Embryogenesis of peripheral nerve pathways in grasshopper legs. III. Development without pioneer neurons.

We have examined the consequence of deleting the first pathfinding neurons to differentiate in the metathoracic leg, cell pair tibial 1 (Ti1) (C. M. Bate, 1976, Nature (London) 260, 54-56; H. Keshishian, 1980, Dev. Biol. 80, 388-397) on the development of two uniquely identifiable follower sensory neurons, and upon the subsequent development of nerve 5B1 in the leg. Following the equivalent of 10-15% of embryonic development in culture the follower sensory neurons were found to have formed topologically normal axonal trajectories in the leg, and to have established contacts with later differentiating sensory and motor axons in an essentially normal fashion. The results show that followers can navigate the route normally taken by the pioneers, and suggest that the pioneers do not have unusual pathfinding capabilities.

Animals↗
PubMed1981

Embryonic and postembryonic morphogenesis of a grasshopper interneuron.

The object of this study was to describe the embryonic and postembryonic morphogenesis of a grasshopper interneuron in order to determine how, and when, this cell comes to assume its mature form. DCMD is an intensively investigated interneuron whose morphology, input and output physiology, and role in behavior are relatively well-known in the adult. We examined the morphology of DCMD in the brain at each stage of its development with silver-intensified cobalt-fills. It arises at 40 +/- 4% of embryogenesis and is probably one of the early progeny from its stem cell. In the ensuing 40% of development, its brain arborization grows quite directly into its mature form. Branches appear first and are always longest and densest in the brain region where the adult arborization is found. Thus, the adult form arises by initially directed growth and not by secondary selection of branches from a diffuse or overgrown arborization. Restricted secondary branch loss of lateral filopodia and probably of a few early branches does occur. Embryonic and postembryonic development of the cell are distinctly different. Embryogenesis is the period of morphological differentiation as indicated by the growth and shaping of the brain and also thoracic (axonal) arborizations, the appearance of cytological specializations, and the logarithmic growth of the neurite and soma. The brain arborization has its mature form, although not size, by the completion of embryogenesis. Postembryonic development is a period of substantial, but primarily allometric, growth. The soma and neurite grow linearly (with time), and the arborization grows in proportion to brain size.

Animals↗
PubMed1980

Direct fractionation of genes by preparative electrophoresis of Bacillus subtilis DNA.

Discontinuous electrophoresis through agarose has been shown to be a satisfactory method for preparation of biologically active restriction fragments from milligram quantities of DNA. The DNA is obtained in sufficient quantity for: (1) direct use in genetic transformation, (2) the production of multiple-dimensional restriction analyses, or (3) use as a high-resolution hybridization probe.

Bacillus subtilis↗
PubMed1979

Quantitative staging of embryonic development of the grasshopper, Schistocerca nitens.

During development of the grasshopper embryo, it is feasible to examine the structure, pharmacology, and physiology of uniquely identified cells. These experiments require a fast, accurate staging system suitable for live embryos. We present a system comprising (1) subdivision of embryogenesis into equal periods, (2) expression of stage in percent of complete embryogenesis time, (3) characterization of stages by light micrographs (and descriptive test), and (4) illustration of stages at the egg, embryo, and limb levels of resolution. Advantages of a percent-system include communicability, flexibility in temporal resolution, accurate assignment of elapsed time in developmental processes, and uniform coverage of the period of embryogenesis. The stages described are at 5% intervals with an estimated error of +/- 1%.

Animals↗
PubMed1977

Ecdysis: neural orchestration of a complex behavioral performance.

Cricket ecdysis (molting) requires continuously changing output in hundreds of motoneurons over a period of several hours, and exhibits considerable plasticity. Despite this complexity, analysis of identified motor units reveals a highly organized three-layered infrastructure, and indicates that the "small system" paradigm currently applied to simple invertebrate motor programs can be extended to much more sophisticated behavioral performances.

Animals↗
PubMed1976

Finger Clubbing: A quantitative survey by analysis of the shadowgraph.

Finger-clubbing has been measured from the magnified silhouette of the right index finger (shadowgram) in 125 subjects, comprising children and young adults. The profile and hyponychial angles were both found to be good discriminators of clubbing and to be independent of age and sex. The normal profile angle was 168.3 degrees +/- 3.6 and the mean normal hyponychial angle was 180.1 degrees +/- 4.2. Patients with cystic fibrosis and cyanotic congenital heart-disease were found to have grossly elevated values of these angles. Some asthmatics were found to have a moderate degree of clubbing with significantly elevated values of these angles. The shadowgram proved a convenient objective method for recording the degree and progress of fingerclubbing in clinical practice.

Adolescent↗
PubMed1975

Single gene cricket mutations: effects on behavior, sensilla, sensory neurons, and identified interneurons.

Crickets are suitable for studying the effects of single gene mutations on single nerve cells. In one mutant, three classes of sensilla are lost sequentially. The absence of one class of mechanoreceptors throughout postembryonic development deprives certain sensory neurons of normal stimulation and results in abnormal physiological and structural development of an identified interneuron.

Animals↗