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Biomedical subjects

R D Fernald

Publications and source records attributed to R D Fernald.

70 records · Page 4Linked to original sources
PubMed1985

Growth of the visual system in the African cichlid fish, Haplochromis burtoni. Optics.

We have measured the chromatic aberration and optical resolution of the lens of the African cichlid fish, Haplochromis burtoni as a function of growth. We found that in H. burtoni, lenses of all sizes have a longitudinal chromatic aberration of ca 1.9% of the focal length. The resolution of the lens increases as the lens grows larger, presumably because diffraction effects decrease and any imperfections in the lens become relatively less significant. We found the lens in H. burtoni is very nearly diffraction limited so that a small lens (0.59 mm) has a resolution of 289 sec of arc and a large lens (2.90 mm) has a resolution of 66 sec of arc in red light (604 nm). This resolution is nearly ten times greater than can be resolved by the cone matrix.

Animals↗
PubMed1985

Growth of the visual system in the African cichlid fish, Haplochromis burtoni. Accommodation.

We have both measured directly and computed the amplitude of accommodation as a function of fish size to discover how the accommodative process changes during growth in the African cichlid fish, Haplochromis burtoni. We found that accommodation is achieved by lens movement in the pupillary plane along the naso-temporal axis. Accommodative lens movement is thereby directed toward a region of retinal specialization characterized by higher density of all cell types (except rods) in H. burtoni. When relaxed, the temporal retina is focused for near vision and active accommodation through lens movement adjusts the focus in the temporal retina for far vision. As the animal grows, the near and far focus points change appropriately for the fish size.

Accommodation, Ocular↗
PubMed1982

Retinal projections in the African cichlid fish, Haplochromis burtoni.

The retinal projections of the African cichlid fish, Haplochromis burtoni, have been traced by two different methods. Following unilateral enucleation, a modified Nauta technique was used to demonstrate degenerating axons and terminals. Some degeneration was found after 5 days but optimal survival time was 20-25 days. Orthograde transport of horseradish peroxidase (HRP) into the cut optic nerve also was used to examine retinal fiber distribution in the brain. The optic nerve is completely crossed and gives rise to two major tracts, the tractus opticus dorsomedialis and the tractus opticus ventrolateralis, as well as minor fascicles. Projections were found in the suprachiasmatic nucleus, ventral thalamus, dorsal thalamus, the pretectal complex, and the tectum opticum. The optic tectum is large and laminated and the great majority of the optic fibers terminate there. Degeneration methods revealed projections in the tectum to the stratum opticum, stratum griseum et fibrosum superficiale, and stratum album centrale. HRP staining confirmed these projections and revealed another projection to the stratum griseum centrale.

Animals↗
PubMed1976

The effect of testosterone on the behavior and coloration of adult male cichlid fish (Haplochromis burtoni, Günther).

The African cichlid fish Haplochromis burtoni shows specific behavioral responses to the intramuscular injection of testosterone. Approaching and attacking were significantly increased by injections, while six other observed behaviors remained unchanged. The results suggest that the injected testosterone affected the control of both sexual and agonistic behaviors.

Animals↗
PubMed1971

A neuron model with spatially distributed synaptic input.

I have assembled a neuron model simulating contiguous patches of nerve cell membrane. With this model I have examined the functional significance of different spatial and temporal distributions of synaptic inputs. The model consists of two terminal electronic analogue circuits with inputs controlled by a LINC computer. One terminal represents the inside of a membrane patch, the other represents the outside. Two circuit designs are used: one simulates spike-generating regions of the neuron, the other simulates subthreshold activity in inexcitable regions. To simulate a neuron, patches are assembled in various spatial arrangements by suitable connection to the "intracellular" nodes. Thus the relation of neuron geometry to aspects of spatiotemporal summation of synaptic inputs can be investigated readily. Performance of the model is assessed by comparison with results from microelectrode studies in the cochlear nucleus of the cat. In particular, the peristimulus time (PST) histogram and averaged membrane potential are used for quantitative comparison. The model suggests that the geometry of the neuron's receptive surface can account for a wide variety of physiologically observed behavior, particularly in response to dynamic stimuli.

Action Potentials↗
PubMedDate not supplied

Localization and expression of insulin-like growth factor in the teleost retina.

Teleost fish retinas continue to add neurons throughout life, and evidence from in vitro experiments have implicated insulin-like growth factors (IGFs) in this process. To discover whether these factors are expressed in vivo, we have examined their expression in the cichlid fish, Haplochromis burtoni. Three lines of evidence show that IGFs are present in the fish retina. An IGF-I specific antibody, sm 1.2, binds preferentially to the retinal outer plexiform layer, in areas of cone photoreceptor synaptic endings. Northern blots of mRNA hybridized with riboprobes from trout IGF-I and IGF-II genes revealed transcripts of approximately 6.5 and 4.9 kb, respectively. The IGF-I probe detected an additional transcript of 1.2 kb in liver but not in retinal mRNA. In situ hybridization with digoxigenin-labeled riboprobes revealed that the IGF gene product is localized in the cone photoreceptors. These results show that cone photoreceptors are the source of IGFs in the fish retina, consistent with the hypothesis that IGFs play a role in regulating production of new neurons in the teleost retina.

Animals↗
PubMedDate not supplied

Retinal transformation at metamorphosis in the winter flounder (Pseudopleuronectes americanus).

Winter flounder (Pseudopleuronectes americanus) are hatched as bilaterally symmetric larvae which live near the ocean surface. At metamorphosis, they become laterally compressed, one eye migrates to the opposite side of the head, and they live the remainder of their lives lying on their blind side on the ocean floor. The present study characterizes and quantifies retinal cell distribution throughout the larval period and contrasts it with the adult retina. Based on light- and electron-microscopic analyses, retinas of larval flounder contain only a single cone-like photoreceptor type, arranged in a hexagonal array. In contrast, after metamorphosis, the adult retina has three types of photoreceptors: rods, single cones, and double cones. Rod photoreceptors are numerous in the ventral retina and decrease in density dorsad. The cone photoreceptor density, in contrast to rods, is higher in the dorsal retina decreasing ventrad. Adult cone photoreceptors are arranged in a square mosaic with four double cones surrounding one single cone. The differences in larval and adult retinal morphology reflect the distinctly different habitat each occupies.

Animals↗
PubMedDate not supplied

Photoreceptor spectral absorbance in larval and adult winter flounder (Pseudopleuronectes americanus).

The habitat occupied by larval winter flounder (Pseudopleuronectes americanus) differs considerably in light regime from that of the adult. To understand how the visual system has adapted to such changes, photoreceptor spectral absorbance was measured microspectrophotometrically in premetamorphic and postmetamorphic specimens of winter flounder. Before metamorphosis, larval flounder retinas contain only one kind of photoreceptor which is morphologically cone-like with peak absorbance at 519 nm. After metamorphosis, the adult retina has three types of photoreceptors: single cones, double cones, and rods. The visual pigment in single cones has a peak absorbance at lambda max = 457 nm, the double cones at lambda max = 531 and 547 nm, and the rod photoreceptors at lambda max = 506 nm. Double cones were morphologically identical, but the two members contained either different (531/547 nm) or identical pigments (531/531 nm). The latter type were found only in the dorsal retina. The measured spectral half-bandwidths (HBW) were typical of visual pigments with chromophores derived from vitamin A1 with the possible exception of the long-wavelength absorbing pigment in double cones which appeared slightly broader. Because the premetamorphic pigment absorbance has a different lambda max than those of the postmetamorphic pigments, different opsin genes must be expressed before and after metamorphosis.

Animals↗
PubMedDate not supplied

Maintenance of optical quality during crystalline lens growth.

Vertebrate lenses grow throughout life by the division of cells at the lens surface. The fibre cells thus produced are gradually covered by newer tissue, giving a layered structure. During growth, the lens must remain transparent and retain its refractile properties. The severity of these constraints is perhaps most evident in teleost fish which have a spherical lens that may increase in volume by a thousandfold during the first year of life. The dioptric power of the teleost fish eye is vested entirely in this spherical lens, as water, the cornea and the intraocular vitreous humour have almost identical refractive indices. Spherical lenses of uniform refractive index produce poor images because rays entering at different distances from the optic axis are focused at different distances from the lens. Teleost fish do not suffer from this imperfection and it has long been presumed that this is because there exists a refractive index gradient having a high value in the centre and decreasing continuously and symmetrically with radius in all directions. Here we demonstrate in the African cichlid fish, Haplochromis burtoni, that a refractive index gradient does exist, although its form is significantly different from that previously postulated.

Animals↗