Search PubMed⌕ Search

Biomedical subjects

N A Schellart

Publications and source records attributed to N A Schellart.

27 records · Page 2Linked to original sources
PubMed1983

Octavolateral projections to the torus semicircularis of the trout, Salmo gairdneri.

Microiontophoretic delivery of horseradish peroxidase in the torus semicircularis of the trout resulted in heavy labeling of somata in the rhombencephalic nucleus intermedius octavolateralis and nucleus octavus magnocellularis. In addition some labeled somata were found closely to the fasciculus longitudinalis lateralis and in the diencephalon. Efferents leave the torus to the diencephalon, the tegmentum and the tectum and, via the fasciculus longitudinalis lateralis, to the rhombencephalon and the spinal cord. It is concluded that in the trout the torus receives octaval and lateral line input mainly directly from the octavolateral area in the hindbrain, without involvement of a superior olive.

Animals↗
PubMed1980

O2 consumption and CO2 influence on the pH and electroretinogram of isolated retina of goldfish.

From micropolarographic O2 measurements, it can be concluded that the isolated goldfish retina is sufficiently supplied with oxygen when 100% O2 is blown over the retina. The retinal O2 consumption amounts to about 60 microliters of O2 per milligram dry weight per hour. Small amounts (0.25% to 2.0%) of CO2 added to the O2 gas diminish the retinal pH, which is 7.0 to 7.1 in situ and after isolation. Moreover, CO2 strongly reduces the ERG amplitude.

Animals↗
PubMed1978

A Golgi study of goldfish optic tectum.

A study of goldfish optic tectum was performed with rapid-Golgi, Golgi-Kopsch and a modified Golgi-Cox impregnation which proved quite suitable to impregnate cells in the middle tectal layers and to study more closely axonal properties. Fifteen cell types are distinguished, based upon the position of dendritic trees and axonal properties. Two cell types are found with dendrites in the marginal layer: type I with an axon terminating in the central gray layer and type II without an impregnated axon. Three cell types (III, IV and V) have dendrites in a single, specific tectal layer and an axon terminating within the tectum. Five cell types (VI-X) have dendrites in two horizontal planes. Two of them have myelinated axons leaving the tectum, whereas the axons of the remaining three types project to different tectal layers. While these first ten cell types have dendrites almost exclusively in the superficial half of the tectum, the remaining five types have dendrites in deeper layers too. This especially holds for the most conspicuous tectal cells (types XII and XIII), which have dendritic trees branching at three or more horizontal levels and a myelinated axon leaving the tectum, with sometimes a very peculiar course (XIII1). Also type XI has three or more dendritic trees, but its axon was not found. The numerous cells with cell bodies in the deepest tectal layer (type XIV) have dendrites and axonal terminations anywhere in the tectum, except in the most superficial and the deepest layer. However, most dendrites occur in the optic layers, whereas the axons, always originating from the dendritic shaft in the superficial tectal half, generally terminate in the middle tectal layers. Type XV cells have their soma in the deepest tectal layer as well, but their dendrites do not reach the optic layers. Per tectal lobe the following numbers are estimated: type I : 5,000-20,000 neurons; Type III : 2,500-10,000; types IV--XIII : each 500-2,000 and type XIV : 1,000,000-2,000,000. The total number of myelinated tectal efferents is estimated at 2,000-8,000. Comparison with other Golgi studies in teleosts leads to the conclusion that the tecta of these species of fish are basically similar.

Animals↗
PubMed1976

Visual acuity at hyperbaric air pressure.

The visual acuity of five divers in a dry pressure chamber was measured with a Landolt C test. Only one of them showed a significant reduction at 7.0 atm. These results contrast sharply with open sea experiments, which show a considerable reduction at much lower pressures (Baddeley, 1968). It is suggested that besides stresses, luminance differences, also turbidity, as a function of depth may account for the discrepancy.

Air Pressure↗
PubMed1974

Influence of temperature on retinal ganglion cell response and E.R.G. of goldfish.

1. Extracellular recordings were made from the colour and spatial coded ganglion cells in the isolated goldfish retina.2. Electroretinograms (e.r.g.s) were obtained from unanaesthetized goldfish.3. For both types of responses the amplitude and phase characteristics were determined at various temperatures by means of Gaussian noise modulated light.4. The shape of these characteristics, depicted as Bode plots, is invariant with temperature. For the ganglion cell responses this holds from 7 to 19 degrees C, whereas for the e.r.g.s invariance is found over the entire range of temperatures used (6-30 degrees C).5. To obtain overlapping Bode plots shifts along the frequency axis are needed that are in accordance with the Arrhenius relation. The Q(10) of the e.r.g. is about 1.9 and of the spike response about 2.7.6. These relatively low values of Q(10) indicate that the dynamics of retinal signal transformations are dominated by diffusion controlled reactions. This implies that real transport delays can be neglected in retinal input-output relations.7. To verify whether a relationship exists between temperature and spectral coding, as has been suggested on the basis of behavioural studies, photopic e.r.g. action spectra were recorded and the spectral coding of ganglion cells were determined as a function of temperature.8. The results point to a temperature invariance of both the photopic e.r.g. action spectra and the colour coding of ganglion cell responses.9. The general conclusion of this study is that ;rules' found in the poikilothermic goldfish are not bound by temperature.

Action Potentials↗
PubMed1972

Dynamic characteristics of retinal ganglion cell responses in goldfish.

A cross-correlation technique has been applied to quantify the dependence of the dynamic characteristics of retinal ganglion cell responses in goldfish on intensity, wavelength, spatial configuration, and spot size. Both theoretical and experimental evidence justify the use of the cross-correlation procedure which allows the completion of rather extensive measurements in a relatively short time. The findings indicate the following. (a) The shape of the amplitude characteristics depends on the energy per unit of time (power) falling within the center of a receptive field rather than on the intensity of the stimulus spot. For spot diameters of up to 1 mm, identical amplitude characteristics can be obtained by interchanging area and intensity. Therefore the receptor processes do not contribute to the change in the amplitude characteristics as a function of the power of the stimulus light. (b) For high frequencies the amplitude characteristics obtained as a function of power join together in a common envelope if plotted on an absolute sensitivity scale. For spontaneous ganglion cells this envelope holds over a range of three log units and the shape is identical for central and peripheral processes. (c) The amplitude characteristics of the central and peripheral processes converging to a ganglion cell are identical, irrespective of the sign (on or off) and the spectral coding of the response. Therefore we have no evidence for interneurons in the goldfish retina unique to the periphery of the receptive field.

Animals↗