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Biomedical subjects

E R Lewis

Publications and source records attributed to E R Lewis.

At least 55 records · Page 3Linked to original sources
PubMed1984

Cellular origin and biosynthesis of rat optic nerve proteins: a two-dimensional gel analysis.

High resolution 2DGE (two-dimensional gel electrophoresis) was used to characterize neuronal and glial proteins of the rat optic nerve, to examine the phases of intraaxonal transport with which the neuronal proteins are associated, and to identify the ribosomal populations on which these proteins are synthesized. Neuronal proteins synthesized in the retinal ganglion cells were identified by injecting the eye with L-[35S]methionine, followed by 2DGE analysis of fast and slow axonally transported proteins in particulate and soluble fractions. Proteins synthesized by the glial cells were labeled by incubating isolated optic nerves in the presence of L-[35S]methionine and then analyzed by 2DGE. A number of differences were seen between filamentous proteins of neurons and glia. Most strikingly, proteins in the alpha- and beta-tubulin region of the 2D gels of glial proteins were distinctly different than was observed for axonal proteins. As expected, neurons but not glia expressed neurofilament proteins, which appeared among the slow axonally transported proteins in the particulate fraction; significant amounts of the glial filamentous protein, GFA, were also labeled under these conditions, which may have been due to transfer of amino acids from the axon to the glial compartment. The fast axonally transported proteins contained relatively large amounts of high-molecular-weight acidic proteins, two of which were shown to comigrate (on 2DGE) with proteins synthesized by rat CNS rough microsomes; this finding suggests that rough endoplasmic reticulum may be a major site of synthesis for fast transported proteins. In contrast, the free polysome population was shown to synthesize the principal components of slow axonal transport, including tubulin subunits, actin, and neurofilament proteins.

Animals↗
PubMed1984

High-frequency rolloff in a cochlear model without critical-layer resonance.

Zwislocki's original cochlear model, incorporating axial fluid inertia and shunt basilar-membrane stiffness and viscous resistance, possesses an operating regime not previously emphasized in the literature. Even in the absence of basilar-membrane mass and the consequent critical-layer resonance, this regime provides extraordinarily steep high-frequency rolloff. That rolloff is not associated with a critical frequency at which energy flow velocity goes to zero, but is attributable instead to a combination of two effects; (1) frequency-dependent energy coupling to the basilar-membrane viscous resistance, leading to local attenuation of the traveling wave at a rate (Np/cycle) that is directly proportional to frequency, and (2) wavelength that decreases with increasing frequency, thus increasing the number of cycles per unit length of basilar membrane. This combination leads to local attenuation of the traveling-wave amplitude (hence energy absorption from the traveling wave) that is strongly dependent on frequency, the rate (Np/cm) being proportional to the square of frequency in the long-wave mode. In Ranke's (two-dimensional, short-wave mode) version of the model, the same operating regime leads to attenuation that is even more intensely dependent on frequency, the rate being proportional to the cube of frequency.

Basilar Membrane↗
PubMed1984

The vertebrate ear as an exquisite seismic sensor.

The neotropical frog Leptodactylus albilabris exhibits the greatest sensitivity to substrate-borne vibrations (seismic stimuli) reported to date for any terrestrial animal. Nerve fibers from the source of this extraordinary sensitivity in the ear show clear stimulus-evoked modulations of their resting discharge rates in response to sinusoidal seismic stimuli with peak accelerations less than 0.001 cm/s2 (10(-6) g). Evidence indicates that its source is the saccule, an organ of hearing in fish and of balance in man. We report that single vibration-sensitive fibers in the white-lipped frog saturate at (whole animal) displacements of 10 A peak to peak [Fig. 1(b)]. Assuming a conservative 20-dB dynamic range for these fibers, the in vivo frog saccule and the mammalian cochlea exhibit roughly equal sensitivities to displacement.

Animals↗
PubMed1984

On the frog amphibian papilla.

Comparative morphological studies in living species of frogs and toads (anurans) indicate that the amphibian papilla (a specialized auditory sensory organ of the amphibian inner ear) has undergone considerable elongation over the course of evolution. Physiological studies on the amphibian papilla of one recently-derived species (Rana catesbeiana) provide strong evidence that frequency selectivity (tuning) in that organ is accomplished by one or more traveling wave structures, in many ways analogous to that of the mammalian cochlea. I suggest that the process of elongation inferred from the comparative morphology is a direct reflection of the evolution of a single traveling wave structure (i.e., convergence on an auditory mechanism analogous to that in the mammal). One selective advantage of such a mechanism is the combination of high rejection ratio in frequency filtering and good temporal resolution of acoustical stimuli.

Animals↗
PubMed1983

Transported proteins in the regenerating optic nerve: regulation by interactions with the optic tectum.

The transport of specific proteins in regenerating optic fibers of goldfish depends on the presence or absence of the optic tectum. When optic fibers were allowed to contact the tectum, amounts of rapidly transported proteins having molecular weights between 120,000 and 160,000 increased, and a species of molecular weight 26,000 reverted to normal levels. When nerves were prevented from contacting the tectum, the amount of the 26,000-molecular weight protein remained high for months. Amounts of other transported proteins, in particular a group of acidic components of molecular weight 44,000 to 49,000 that increase greatly at early stages of regeneration, proved to be independent of the tectum.

Animals↗
PubMed1983

Neuronotrophic activity in brain wounds of the developing rat. Correlation with implant survival in the wound cavity.

Neuronotrophic activity accumulates in a wound cavity created in the entorhinal/occipital cortex of developing rats. These trophic factors support the survival of neurons in monolayer cultures of chick embryo spinal cord, ciliary ganglion, sympathetic ganglion and dorsal root ganglion, as well as of mouse dorsal root ganglion. Trophic activity was very low both in non-injured brain tissue and in the wound cavity 1 day post-lesion, but it increased 15- to 300-fold during the subsequent 2-5 days. Together with the trophic activity in the wound fluid were other substances which interfered with the survival of spinal cord neurons. The neuronotrophic factors appeared to be proteins immunologically distinct from mouse submaxillary nerve growth factor. Fragments of rat embryo corpus striatum placed in the cortical wound cavity immediately after its formation showed very poor subsequent survival and no innervation of the host hippocampus. However, if implantation was delayed by 3 or 6 days with respect to the time at which the receiving cavity was made, the survival was greatly improved and innervation of the host took place. The time course for the accumulation of the trophic factors in the cavity paralleled the delay leading to increased survival of brain grafts. It is suggested that the neuronotrophic activity accumulating in the wound cavity during the delay period may be responsible for the increased survival of the implants.

Animals↗
PubMed1983

Neurotransmitter characteristics of brain grafts: striatal and septal tissues form the same laminated input to the hippocampus.

In previous experiments we have studied the development of grafts of embryonic septal tissues implanted alongside the hippocampal formation of neonatal rats. In the present study we examined intracerebral implants of corpus striatum, a brain region that contains acetylcholinesterase-positive cells and does not normally project to the hippocampal formation, in order to evaluate the possibility that neurotransmitter identity may be involved in mechanisms guiding patterns of afferent growth and connectivity. Implant cavities were made in the entorhinal cortices of neonatal rat recipients and 3-6 days later embryonic striatal tissues were grafted to these preformed cavities. Implants were examined with acetylcholinesterase histochemistry one month after implantation. Grafts of embryonic striatal tissues did not survive implantation when the implant was introduced at the same time as the cavity was made. Grafts of corpora striata containing acetylcholinesterase-positive neurons were found in 7 of 11 rats in the delayed implant paradigm and, in all but one of these animals, acetylcholinesterase was present within those terminal laminae in the ipsilateral hippocampus and dentate gyrus that normally receive cholinergic input from the septal area. These findings suggest that cues underlying the development of specific connections between native (and implanted) septal efferents and hippocampal target neurons may be recognized by ingrowing acetylcholinesterase-reactive fibers from striatal implants.

Acetylcholinesterase↗
PubMed1983

Morphological basis for tonotopy in the anuran amphibian papilla.

The amphibian papilla of the more-recently derived frogs and toads is similar to the mammalian cochlea in at least three ways: 1. Its sensory surface is a slender, curved structure. 2. It exhibits tonotopy, with the highest-frequency sensitivity located at the end apparently closest to the source of acoustical excitation. 3. Its single-axon tuning curves exhibit extremely steep high-frequency slopes and gentle low-frequency slopes, consistent with selection by a distributed-parameter, low-pass filter with cutoff frequency that decreases as one moves farther from the source of acoustical excitation. The filter operation in the cochlea is centered around the basilar membrane, a structure whose profound taper is largely responsible for the decreasing cutoff frequency. Although the amphibian papilla lacks a basilar membrane, it does possess a conspicuously tapered tectorial membrane, which might serve a similar function. In this paper, after reviewing briefly an old and simple model of the cochlear filter and the morphology of the amphibian papilla and its tectorial membrane, we are unable to reconcile the structure of the latter with the topological requirements for realization of a filter analogous to the former. In fact, we are unable to deduce the principles of frequency selectivity in the frog auditory endorgan.

Acoustic Stimulation↗
PubMed1983

Increased transport of 44,000- to 49,000-dalton acidic proteins during regeneration of the goldfish optic nerve: a two-dimensional gel analysis.

Proteins synthesized in goldfish retinal ganglion cells and rapidly transported to the terminals of regenerating optic nerves were analyzed by two-dimensional (2-D) gel electrophoresis. Among the rapidly transported components, the most dramatic change observed during regeneration was for a family of polypeptides having molecular weights between 44,000 and 49,000 (44-49K) and isoelectric points of 4.6 to 4.9. Studies using [35S]methionine as a metabolic precursor in the eye showed that these proteins are present in both membranous and soluble fractions of the optic tectum, particularly during early stages of regeneration. Contralateral visual pathways, left intact to serve as controls, showed only very low levels of the proteins. These labeling changes were quantified in double-isotope studies, in which proteins from intact and regenerating sides were differentially labeled with [3H]proline and [14C]proline, comigrated on 2-D gels, and then counted for 3H/14C ratios. The labeling change for the 44-49K acidic proteins relative to the intact state was found to be over 100-fold in some day 19 regeneration samples and about 30-fold on day 40. Silver-stained gels of a tectal membrane fraction also revealed increased levels of the 44-49K acidic proteins during regeneration, indicating that the observed synthetic changes are accompanied by a net accumulation of the proteins.

Animals↗
PubMed1982

Acute seismic sensitivity in the bullfrog ear.

Single axons in the auditory/vestibular nerve of the American bullfrog exhibit by far the most exquisite sensitivity to substrate-borne vibration yet reported for a quadruped vertebrate. Earlier dye-injection studies revealed that these axons, which are relatively insensitive to airborne sound, originate at the saccular and lagenar maculae of the bullfrog inner ear. The more sensitive axons exhibited clear responses to vibratory sinusoids with peak accelerations as low as 0.005 cm/s2.

Acoustic Stimulation↗
PubMed1982

Brain injury causes a time-dependent increase in neuronotrophic activity at the lesion site.

A cavity was made in the brain (entorhinal cortex) of developing or adult rats, and a small piece of Gelfoam was emplaced to collect fluid secreted into the wound. The neuronotrophic activity of the fluid was assayed with sympathetic and parasympathetic neurons in culture. The results show that wounds in the brain of developing or adult rats stimulate the accumulation of neuronotrophic factors and that the activity of these factors increases over the first few days after infliction of the damage.

Adrenergic Fibers↗
PubMed1982

Mechanisms of septal lamination in the developing hippocampus revealed by outgrowth of fibers from septal implants. III. Competitive interactions.

Embryonic septal tissues grafted alongside the hippocampal formation in neonatal rat hosts were used to test for the presence of competitive interactions between developing native axons and those from the septal grafts. When native septal afferents to the target hippocampal formation are removed at the time of implantation, axons from septal grafts visualized with acetylcholinesterase (AChE) histochemistry enter the appropriate laminar zones in the host hippocampus. The pattern of septal implant growth differs markedly when native septohippocampal fibers are left intact. Under these conditions, implant-associated AChE staining is intense in the cortical area surrounding the graft but little or no reaction product is present in the host dentate gyrus and hippocampus proper. A similar result is obtained when implant viability is enhanced by introducing it 3 days after the cavity is made. These data illustrate an apparent hierarchy in competitive interactions for developing septal fibers. Septal afferents can inhibit the growth of other septal fibers and commissural/associational (c/a) axons can exclude septal fibers from their terminal field. Septal fibers and entorhinal afferents will develop concurrently.

Animals↗
PubMed1982

Mechanisms of septal lamination in the developing hippocampus analyzed by outgrowth of fibers from septal implants. II. Absence of guidance by degenerative debris.

In previous study (Lewis, E.R., and C. W. Cotman (1980) Brain Res. 96: 307--330; E. R. Lewis and C. W. Cotman, submitted for publication), we have shown that septal tissues grafted to the brain of a neonatal rat will extend fibers into special terminal laminae within the hippocampal formation of the recipient. As a consequence of the implantation surgery, neurons in the developing entorhinal cortex are ablated and it is possible that processes of implanted cells may be guided by degenerating afferent fibers in the host. In order to test this hypothesis, we have characterized the distribution of degeneration argyrophilia that results from the implant surgery and the time course of its removal and examined the growth of septal implants in a host brain devoid of observable degenerative debris. The pattern of degeneration argyrophilia shortly after the implantation surgery did not correspond to the pattern of implant-associated AChE staining in the host hippocampal formation. By 72 hr after surgery, the great majority of argyrophilic debris had been removed. Implants placed in a cavity created 72 hr after surgery demonstrated excellent viability and produced the typical pattern of AChE staining in the hippocampal formation of the host. This suggests that the presence of degenerating host axons is not necessary to guide the ingrowth of axons and establish septohippocampal laminated fields.

Acetylcholinesterase↗
PubMed1981

Evolution of inner-ear auditory apparatus in the frog.

The morphology of typical anuran amphibian papillae is thoroughly distinct from that of urodeles. However, the morphological discontinuity lies not between the frogs and the salamanders, but between the most primitive living frog, Ascaphus truei, and the more derived anurans. Three features distinguishing the papillae of more derived anurans from that of Ascaphus apparently provide peripheral tonotopy in the former. The adaptive significance of a fourth feature, kinociliary bulbs, is not clear.

Animals↗
PubMed1981

Suggested evolution of tonotopic organization in the frog amphibian papilla.

As one progresses from the most primitive to the most derived frogs, one observes remarkable changes in that peculiarly amphibian auditory organ, the amphibian papilla. In all but the most primitive frog, the papilla comprises two patches with separate innervation and apparently corresponding to a spatial separation of frequency sensitivity (i.e. tonotopic organization). The caudal patch is quite variable and in the more derived frogs exhibits an elongation that apparently corresponds to extension of auditory sensitivity to higher frequencies.

Animals↗
PubMed1981

Dissecting aortic aneurysm in childhood and adolescence. Case report and literature review.

A 15-year-old adolescent male with dissecting aortic aneurysm is presented. His young age, lack of predisposing factors, and fulminant course with rapid progression to death precluded a correct antemortem diagnosis. Review of the literature reveals that most instances of dissecting aortic aneurysm in childhood and adolescence are associated with predisposing conditions, especially congenital cardiovascular anomalies. The clinical picture is generally characteristic. Prompt evaluation and therapy may be lifesaving.

Adolescent↗