Biomedical subjects

E A Seyfarth

Publications and source records attributed to E A Seyfarth.

8 recordsLinked to original sources

PubMed1995

Sodium channel distribution in a spider mechanosensory organ.

A site-directed antibody was used immunocytochemically to measure the distribution of sodium channels in the tissues of a spider mechanoreceptor organ. The VS-3 slit sense organ contains 7-8 pairs of bipolar sensory neurons; these neurons are representative of a wide range of arthropod mechanoreceptors. Sensory transduction is thought to occur at the tips of the dendrites and to cause action potentials that are regeneratively conducted to the cell bodies, although it has not been possible to confirm this by direct intracellular recordings from the dendrites. Wholemount preparations were labelled by immunofluorescence and thin sections were immunogold labelled, using an antibody to the highly conserved SP19 sequence of the voltage-activated sodium channel. Labelling for sodium channels was found in the neurons and in their surrounding glial cells. Both cytoplasm and membranes were labelled, but immunogold particles were clearly aligned along cell membranes, indicating that the majority of labelling represented membrane-bound sodium channels. Channel density in the dendrites was similar to the axons and higher than in the cell bodies, supporting the idea of active conduction in the sensory dendrites. Labelling in glial cell membranes was indistinguishable from the neighboring neurons, suggesting a significant role for sodium channels in the functions of these supporting cells.

Action Potentials↗

PubMed1994

Intracellular characterization of identified sensory cells in a new spider mechanoreceptor preparation.

1. We have developed an isolated mechanoreceptor-organ preparation in which the intact sensory structures are available for mechanical stimulation and electrical recording. The anterior lyriform slit sense organ on the patella of the spider, Cupiennius salei Keys., consists of seven or eight cuticular slits, each innervated by a pair of large bipolar sensory neurons. The neurons are fusiform, and the largest somata are < or = 120 microns long. The innervation of the organ was characterized by light microscopy of neurons backfilled with neuronal tracers. Intracellular recording was used to measure the passive and active electrical properties of the neurons, in several cases followed by identification with Lucifer yellow injection. Both neurons of each pair from one slit responded with action potentials to depolarization by a step current injection. Approximately half of the sensory neurons adapted very rapidly and generated only one or two action potentials in response to a sustained depolarizing step, while a second group produced a burst of action potentials that adapted to silence in approximately 1 s or less. Recordings from identified neuron pairs indicated that each pair consists of one rapidly adapting and one bursting neuron. Measurements of cell membrane impedances and time constants produced estimates of neuronal size that agreed with the morphological measurements. This new preparation offers the possibility of characterizing the mechanisms underlying transduction and adaptation in primary mechanosensory neurons.

Animals↗

PubMed1994

Sodium-dependent receptor current in a new mechanoreceptor preparation.

1. Intracellular microelectrodes recorded the receptor potential and receptor current in the neurons of spider slit sense organs during mechanical stimulation of the slits. 2. Mechanical stimulation produced two patterns of action potential discharge, corresponding to the two groups of neurons described previously by electrical stimulation. 3. Tetrodotoxin eliminated the action potentials and revealed a receptor potential with both static and adapting components. Voltage clamp gave an inward receptor current with a similar time course. 4. Replacement of sodium ions in the bath reversibly eliminated the receptor current, indicating that it is carried by sodium ions. However, this effect was comparatively slow, suggesting that the tips of the sensory dendrites lie in a chemically restricted environment.

Action Potentials↗

PubMed1994

Julia B. Platt (1857-1935): pioneer comparative embryologist and neuroscientist.

Julia Barlow Platt was a comparative embryologist and neurobiologist who was primarily interested in segmentation of the head in vertebrates. She was born on September 14, 1857 in San Francisco, California. Platt grew up in Burlington, Vermont, attended the University of Vermont and began graduate studies at Harvard University. Her nine years as a graduate student were spent on two continents with some of the most influential comparative zoologists of the time. Platt's remarkable scientific accomplishments over a ten year period include a description of axial segmentation currently used in the staging of chick embryos and the first description of a separate anterior head segment in Squalus embryos. Her most controversial study identified ectodermal cells in Necturus embryos that gave rise to head cartilage and dentine, a discovery which was the impetus for the reassessment and modification of the germ layer concept. She was one of the first women to 'matriculate' at a German university and receive a Ph.D. degree. Platt played a pioneer role in opening opportunities for other women who followed her. Platt was one of the first women neuroscientists. Among her contributions, she distinguished dorsolateral placodes, epibranchial placodes, and the first stages of lateral line organs in Necturus, and she described nerve fibers originating in the spinal cord and extending to the notochord in Branchiostoma (= Amphioxus). After receiving a Ph.D. degree in Freiburg, Germany in 1898, Platt was unable to secure a suitable teaching position and, as a result, her scientific career came to an end. She retired to Pacific Grove, California, where she pursued civic duty with the same vigor and energy she had dedicated to scientific research. We provide a sketch of her remarkable life and work as a comparative embryologist, neuroscientist and civic leader.

Embryology↗

PubMed1993

Octopamine immunoreactive neurons in the fused central nervous system of spiders.

Using antisera directed against octopamine (OA), we identified and mapped octopamine-immunoreactive (OA-ir) neurons and their projections in the fused, central ganglion complex of wandering spiders, Cupiennius salei. Labeled cell bodies are concentrated in the subesophageal ganglion complex (SEG) where they are arranged serially in ventral, midline clusters. OA-ir processes from these cells project dorsally. Some neurites end close to segmental septa; others merge into longitudinal tracts connecting the neuromeres. Labeled collaterals leaving these tracts project into peripheral neuropil. In the brain, OA-ir somata were found only in the two cheliceral hemiganglia, where a cluster of 4-5 relatively large cells (soma diameter 25 microns) lies next to a group of small somata (diameter < 10 microns). Neurites originating from the large somata descend into the SEG and merge into longitudinal tracts. The central body of the brain contains profuse ascending projections. Except for fine varicosities that are confined to the roots of nerves, we found no OA-ir fibers leaving the central nervous system (CNS). Within the CNS, however, OA-ir varicosities are concentrated in neuropil and near hemolymph spaces. This distribution suggests that OA acts as a neurotransmitter and/or local neuromodulator at central synapses, while it is also released into the hemolymph and presumably acts hormonally at peripheral sites. Using high-pressure liquid chromatography measurements, the hemolymph was in fact found to contain 12-40 nM of free octopamine.

Animals↗

PubMed1991

Ludwig Mauthner (1840-1894): neuroanatomist and noted ophthalmologist in Fin-de-Siècle Vienna.

Ludwig Mauthner was only 19 years old when he published his discovery of the colossal fibers in the spinal cord of fishes which now bear his name. Based on Mauthner's works, archival material, and contemporary sources we provide a summary of his life and work as neuroanatomist and ophthalmologist in imperial Austria. In the years 1859-1863 Mauthner published four papers on the structure of the central nervous system in vertebrates. His first report on fishes contains the original description of a 'colossal myelinated nerve fiber' on each side of the central canal, extending through the entire spinal cord. Another, more general, treatise on 'the morphological elements of the nervous system' (published in 1863) summarizes his neurohistological studies of various vertebrates. It includes a classification of nerve cells based on their (histochemical) reaction to carmine. The main findings were soon shown to be artefactual; the paper had a long-range impact, however, because it provoked fruitful controversy among contemporary neuroanatomists. Mauthner published several monographs and numerous articles in ophthalmology, a newly developing branch of medicine that he chose for his later career. After abruptly resigning from a professorship at Innsbruck University, he opened a private practice in Vienna and continued lecturing in his field. He became a noted eye-surgeon, was elected Assistant Director of the Vienna 'Allgemeine Poliklinik', and in 1894 became Professor and Chair of Ophthalmology at the University of Vienna. Mauthner unexpectedly died on the night following the formal announcement of his appointment.

Animals↗

PubMed1984

Proprioceptor distribution and control of a muscle reflex in the tibia of spider legs.

In spiders, retrograde cobalt staining was used to clarify the distribution and detailed innervation of the three types of proprioceptors in the tibio-metatarsal leg joint: internal joint receptors, lyriform slit sense organs, and cuticular spines and hairs. The axons of all these receptors run in just two lateral, ascending nerves, which had previously been associated only with the internal receptors. Each nerve contains several hundred axons ranging in diameter from 0.1 micron to ca. 10 micron. Each slit of the four tibial lyriform organs is innervated by two bipolar sensory neurons. The lateral nerves are entirely sensory and run just beneath the cuticle, a convenient site for electrophysiological recording. We demonstrate simultaneous nerve and muscle recordings from intact spiders; these, in combination with selective sensory ablations, show that a resistance reflex in the flexor metatarsi muscles is elicited by internal joint-receptor units.

Animals↗

PubMed1983

A versatile feedback controller for electro-mechanical stimulation devices.

Neurophysiological and behavioral work often requires that various laboratory stimulators be feedback-stabilized. We describe the design and performance of a versatile electronic controller that can be used to extend and flatten the frequency response of commercially available stimulating devices. The design includes flexible proportional-integral-derivative control action and active second-order, high-pass compensation. As an example application of this controller to 3 different electro-mechanical vibrator/transducer combinations demonstrates that the useful frequency response can be extended by more than a decade as compared with the uncontrolled device.

Animals↗