Biomedical subjects

T A Keil

Publications and source records attributed to T A Keil.

8 recordsLinked to original sources

PubMed1998

Age-related changes in the dendrites of olfactory receptor neurons in the male silkmoth Antheraea peryni (Insecta, Lepidoptera: Saturniidae).

A study was conducted to evaluate the changes that occur with aging at the dendrite level of the olfactory receptor neuron in the male silkmoth Antheraea pernyi. Using calcein AM/ethidium homodimer-1 solutions, we found increased numbers of dendrites with damaged membrane with aging. Correspondingly there was an overall decrease in the electrophysiological activity as evidenced by the decreased number of cells discharging nerve impulse in response to female pheromone. It was also seen that the number of membrane swellings increased with age. In young animals aged 1-4 days, swellings showed intact membrane, and in older animals aged 5-15 days, they showed damaged membranes. With TUNEL assay that detects fragmented DNA in dying cells, an increased number of dendrites showing cytoplasmic labelling with age was found. The presence of fragmented DNA within aged dendrites was also confirmed in polyacrylamide gels after DNA extraction and PCR amplification. When tested for reversal of phosphatidylserine from the inner leaflet to the outer leaflet of plasma membrane no reactivity was seen. It appears that changes that occur during aging of dendrites may reflect some of the recognized symptoms of both apoptosis and necrosis.

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PubMed1997

Functional morphology of insect mechanoreceptors.

This paper reviews the structure and function of insect mechanoreceptors with respect to their cellular, subcellular, and cuticular organization. Four types are described and their function is discussed: 1, the bristles; 2, the trichobothria; 3, the campaniform sensilla; and 4, the scolopidia. Usually, bristles respond to touch, trichobothria to air currents and sound, campaniform sensilla to deformation of the cuticle, and scolopidia to stretch. Mechanoreceptors are composed of four cells: a bipolar sensory neuron, which is enveloped by the thecogen, the trichogen, and the tormogen cells. Apically, the neuron gives off a ciliary dendrite which is attached to the stimulus-transmitting cuticular structures. In types 1-3, the tip of the dendrite contains a highly organized cytoskeletal complex of microtubules, the "tubular body," which is connected to the dendritic membrane via short rods, the "membrane-integrated cones" (MICs). The dendritic membrane is attached to the cuticle via fine attachment fibers. The hair-type sensilla (types 1, 2) are constructed as first-order levers, which transmit deflection of the hair directly to the dendrite tip. In campaniform sensilla (type 3), there is a cuticular dome instead of a hair and the dendrite is stimulated by deformation of the cuticle. In these three types, a slight lateral compression of the dendrite tip is most probably the effective stimulus. In scolopidia, the dendritic membrane is most probably stimulated by stretch. On the subcellular level, connectors between the cytoskeleton, the dendritic membrane, and extracellular (cuticular) structures are present in all four types and are thought to be engaged in membrane depolarization.

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PubMed1996

Identification of cytoskeletal proteins in the antennae of the silkmoths Antheraea polyphemus and A. pernyi.

Although the overall cytoskeletal morphology of the olfactory dendrite in the antennae of the silkmoths Antheraea polyphemus and A. pernyi is known, the cytoskeleton proteins that structurally and functionally support these structures remain to be identified in this paper, we describe the identification of tubulin, actin and intermediate filament-like proteins in the olfactory dendrites, and motor proteins such as kinesin and unconventional myosin in the antennal branches by the use of antibodies. We also show that the tubulins within the olfactory dendrites and in the antennal branches are acetylated. This study provides valuable information concerning the possible role of these proteins in transduction, transport and motility, as is evident in other systems.

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PubMed1992

Fine structure of a developing insect olfactory organ: morphogenesis of the silkmoth antenna.

The olfactory organ of the silkmoth Antheraea polyphemus is the feathered antenna which carries about 70,000 olfactory sensilla in the male. It develops within 3 weeks from a leaf-shaped epidermal sac by means of segmental primary and secondary indentations which proceed from the periphery towards the centerline. During the first day post-apolysis, the antennal epidermis differentiates into segmentally arranged, alternating sensillogenic and non-sensillogenic regions. Within the first 2 days post-apolysis, the anlagen of olfactory sensilla arise from electron-dense mother cells in the sensillogenic epidermis. The axons of the developing sensilla begin to form the primary innervation pattern during the second day. The sensilla develop approximately within the first 10 days to their final shape, while the indentations are completed during the same period of time. The indentations are most probably driven by long basal extensions of epidermal cells, the epidermal feet. Primary indentations follow the course of segmentally arranged tracheal bundles and form the segments of the antenna. The secondary indentations follow the course of the primary segmental nerves which are reconstructed by this process. During the remaining time of development, the cuticle of the antenna and the sensory hairs is secreted by the epidermal and the hair-forming cells.

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PubMed1984

Dendritic membrane from insect olfactory hairs: isolation method and electron microscopic observations.

Sensory hairs from antennae of male saturniid moths (Antheraea polyphemus) were separated while deep-frozen by shaking antennal branches with glass beads. The hairs were collected through their differential adhesion to the surface of a petri dish. The yield, determined by the length of the isolated hair fragments, was about 38% of the estimated total hair length per antenna. The dendritic membrane was separated from the hair fragments by centrifugation through Sephadex and further purified by ultracentrifugation in sucrose buffers. Transmission electron microscopy was used to monitor the steps of the hair and membrane isolation and to investigate the membrane pellet. Some membrane vesicles bound cationized ferritin, thus indicating a negatively charged cell surface coat. Negatively stained membrane vesicles exhibited a pattern of repetitive substructures irregularly distributed over the vesicle surface. The units had a diameter of about 3 nm and a maximal density of 30,000/micron2.

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PubMed1984

Surface coats of pore tubules and olfactory sensory dendrites of a silkmoth revealed by cationic markers.

Negatively charged surface coats have been demonstrated on the pore tubules and dendritic membranes of olfactory hairs of male Antheraea polyphemus silkmoths by application of the cationic markers lanthanum (La3+), ruthenium red (RR), and cationized ferritin (CF). Lanthanum and RR diffused readily into the apically opened hairs, whereas CF penetrated only for a relatively short distance. Deposits of the markers are distributed as follows: the inner surfaces of the hair walls are stained by RR and to a small degree by CF; the surfaces of the pore tubules and the dendritic membranes are stained by all three markers. The pore tubules have the strongest affinity for CF. The number of pore tubule-membrane contacts seems to be increased by the cationic dyes. The dendrites are often penetrated by RR, which forms deposits on the inner membrane leaflets, the cytoplasmic microtubules, and microfilaments, and by La3+, but never by CF. The observations provide support for the assumption that, first, the pore tubule-membrane contacts are formed via surface coats of both structures, possibly influenced by cations and, second, that the dendrites remain intact after pinching off the hair tips.

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PubMed1984

Very tight contact of tormogen cell membrane and sensillum cuticle: ultrastructural basis for high electrical resistance between receptor-lymph and subcuticular spaces in silkmoth olfactory hairs.

A very tight contact is present between the apical membrane of the tormogen cell and the cuticle of the hair base in olfactory sensilla trichodea of Antheraea polyphemus. The contact zone is characterized by numerous hemidesmosome-like structures of the cell membrane, which closely attach the latter to the cuticle. If apically opened hairs are incubated in a LaCl3 solution, the tracer ions do not penetrate the contact zone. It is concluded that the tight contacts are the morphological correlates of the electrical isolation of the receptor-lymph space (cf. de Kramer et al., in press).

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PubMed1982

Contacts of pore tubules and sensory dendrites in antennal chemosensilla of a silkmoth: demonstration of a possible pathway for olfactory molecules.

Antennal olfactory hairs of Antheraea polyphemus were investigated by means of transmission electron microscopy. Adequate preservation of dendrites and extracellular pore tubules is obtained by mechanical opening of the hair lumen and subsequent chemical fixation. The dendritic membrane has a cell coat. The dendrites contain microfilamentous structures in addition to their cytoplasmatic microtubules. The extracellular pore tubules traverse the hair cuticle and reach into the hair lumen for maximally 350 nm. Their diameter varies between 20 and 40 nm, depending on the preparation method. They consist of an electron-dense wall and an electron-lucent core. The wall has a helical substructure and is covered with a fuzzy coat. Contacts of pore tubules and dendritic membranes occur wherever dendrites are near the inner surface of the hair cuticle. Some of the pore tubules terminate approximately at right angles on the dendritic membrane, others lie against the membrane. The contact seems to be made via the surface coats of the tubules and the membrane. The structure of pore tubules which had been negatively stained with uranyl acetate is similar to the conventionally thin-sectioned material. The observations provide support for earlier assumptions that pore tubules are the pathways by which odor molecules reach the dendritic membrane.

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