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E R Lewis

Publications and source records attributed to E R Lewis.

At least 73 records · Page 4Linked to original sources
PubMed1980

Mechanisms of septal lamination in the developing hippocampus revealed by outgrowth of fibers from septal implants. I. Positional and temporal factors.

Pieces of embryonic septal tissue were implanted into a cavity within the entorhinal or occipital cortices of neonatal rat hosts (2-3 days old). The initial outgrowth of fibers originating from the grafts and their pattern of termination within the host hippocampal formation was examined using a histochemical stain for acetylcholinesterase (AChjE). Fimbrial transections were performed in conjunction with the implant surgery to eliminate native septohippocampal fibers. When placed in the occipital cortex, septal implants innervate specific laminar zones within the host hippocampus and dentate gyrus; these are the same laminar zones that receive septal efferents in the normal animal. Septal implants placed in the entorhinal cortex also produce a pattern of AChE staining in the host hippocampus which is similar to that seen in the normal hippocampus. In the dentate gyrus ipsilateral to the implant, however, the unstained commissural/association (C/A) zone is expanded. Temporal characteristics of the outgrowth of fibers from the implant were studied in animals sacrificed 6, 8, 10 and 12 days after the implant surgery. AChE activity indicative of innervation from the implant is present in 50% of the animals sacrificed 10 days post-implant; by 12 days post-implant all but one animal displayed AChE reaction product in the dentate molecular layer. AChE-positive processes emanating from cells in the implant were oriented toward the hippocampus throughout the developmental period. The position of the afferent source and the time of arrival of the afferent fibers in the target area do not seem to be critical to the mechanisms underlying the development of specific connection patterns in the septohippocampal system. We have proposed that contact between a 'critical afferent' (C/A system in this case) and the target cell might initiate the events underlying the development of appropriate patterns of connectivity.

Acetylcholinesterase↗
PubMed1980

Factors specifying the development of synapse number in the rat dentate gyrus: effects of partial target loss.

The development of the dentate gyrus has been studied under conditions of partial reduction of granule cell number. Neonatal rats were subjected to X-irradiation, a procedure which reduces the number of granule cells to 20% of control values. In X-irradiated rats, quantitative analyses were performed on cells in the entorhinal cortex which give rise to the perforant path projection to the dentate granule cells, and on the remaining, undamaged dentate granule cells. These residual cells were examined morphologically for possible hyperdevelopment in comparison to granule cells from control animals. Granule cells in X-irradiated animals were similar to granule cells in control animals with respect to dendritic structure and synaptic density. The number of neurons in both the medial and lateral entorhinal cortices in X-irradiated animals appeared normal until day 12, at which time a selective reduction in cell numbers became apparent. By day 30, 25-55% of the cells of origin of the perforant path were absent in X-irradiated animals. It is hypothesized that these cells are subject to retrograde transynaptic degeneration as a result of target removal. Further, it appears that granule cells play an important role in determining the density of their innervation.

Animals↗
PubMed1977

Prediction of schistosome cercarial shedding with a physiological - time model.

While making longitudinal observations on schistosome cercarial shedding, Pitchford and Visser found that there is an annual fluctuation in the minimum time for cercarial development, which is apparently related to temperature (1). Schistosome control strategy could be designed to take advantage of this fluctuation if it were predictable. Inspired by the successes of physiological time models ('heat-unit models') in predicting life-stage durations of various agricultural pests (2,3), we have developed a model of this type for the schistosomes. This model fits the data of Pitchford and Visser quite well. Coupled with recent temperature history and short term temperature forecast, it could be a useful tool for predicting the onset of cercarial shedding.

Biomphalaria↗
PubMed1976

Surface morphology of the bullfrog amphibian papilla.

The bullfrog amphibian papilla, which has been identified as the peripheral source of two of the three types of auditory axon in that animal, is shown to have a continual distribution of receptor types based on surface topography, but a dichotomy of types based on the adjacent tectorium and its apparent mechanical linkage to the receptors and their supporting cells and a second dichotomy based on receptor polarization patterns. Each dichotomy divides the receptors into two approximately equal populations and thus might correspond to the previously observed division of primary axons into two frequency-response types.

Animals↗
PubMed1971

Morphological basis for a mechanical linkage in otolithic receptor transduction in the frog.

Observations made with a scanning electron microscope confirm the binding of the stereocilia to a matchhead-like bulbous terminal at the apex of the kinocilium in frog saccular receptor cells. Since the kinocilium is shown to rest on a portion of the receptor cell that lacks the rigid cuticular base of the stereocilia, movenment of the ciliary ensemble results in a "plunging-like" effect of the kinocilium which produces a distension of the membranc at its base. This membrane distension is envisaged as bringing about the ionic conductance changes necessary for the production of a generator potential and, thus, for the transduction of movement into vestibular nerve activity.

Animals↗
PubMed1969

Studying neural organization in Aplysia with the scanning electron microscope.

Preliminary attempts have been made to employ the scanning electron microscope in the mapping of a simple nervous system, the abdominal ganglion of Aplysia californica. Early results are encouraging: neuronal fibers have been identified and traced over relatively long distances from their cell bodies to structures tentatively identified as synapses and to structures tentatively identified as electrotonic connections.

Abdomen↗
PubMed1968

Neural modeling.

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Animals↗