Biomedical subjects

Jack B Calderone

Publications and source records attributed to Jack B Calderone.

5 recordsLinked to original sources

PubMed2004

Photoreceptors and photopigments in a subterranean rodent, the pocket gopher (Thomomys bottae).

Pocket gophers (Thomomys bottae) are rodents that spend much of their lives in near-lightless subterranean burrows. The visual adaptations associated with this extreme environment were investigated by making anatomical observations of retinal organization and by recording retinal responses to photic stimulation. The size of the eye is within the normal range for rodents, the lens transmits light well down into the ultraviolet, and the retina conforms to the normal mammalian plan. Electroretinogram recording revealed the presence of three types of photopigments, a rod pigment with a spectral peak of about 495 nm and two types of cone pigment with respective peak values of about 367 nm (UV) and 505 nm (medium-wavelength sensitive). Both in terms of responsivity to lights varying in temporal frequency and in response recovery following intense light adaptation, the cone responses of the pocket gopher are similar to those of other rodents. Labeling experiments indicate an abundance of cones that reach densities in excess of 30,000 mm-2. Cones containing UV opsin are found throughout the retina, but those containing medium-wavelength sensitive opsin are mostly restricted to the dorsal retina where coexpression of the two photopigments is apparently the rule. Rod densities are lower than those typical for nocturnal mammals.

Adaptation, Ocular↗

PubMed2003

Topography of photoreceptors and retinal ganglion cells in the spotted hyena (Crocuta crocuta).

The spatial distributions of photoreceptors and retinal ganglion cells were examined in the spotted hyena (Crocuta crocuta). Two populations of cones were identified by immunocytochemical labeling. The hyena retina contains approximately 2.3 million middle- to long-wavelength sensitive (M/L) cones that reach peak densities of about 7,500/mm(2) in the vicinity of the optic nerve head. A sparser population of short-wavelength sensitive (S) cones, totaling about 0.3 million, was also detected. There is a striking disparity in the spatial distributions of the two cone types with S cones achieving peak density in a region located well below the optic nerve head. The differences in the spatial distributions of the two cone types have implications both for visual sensitivity and for color vision. Hyena rods outnumber cones by about 100:1 with rod density falling off modestly along a central-peripheral gradient. Ganglion cells were identified in retinal wholemounts by Nissl staining patterns. Their distribution defines a prominent visual streak with highest spatial packing (approx. 4,200/mm(2)) in an area centralis that is located in the temporal retina. The total number of ganglion cells is estimated at about 260,000. Using standard assumptions the maximum spatial resolution of the spotted hyena is calculated to be about 8.4 cycles/degree, a value similar to estimates obtained for other terrestrial carnivores.

Animals↗

PubMed2003

Cone photoreceptor recovery after experimental detachment and reattachment: an immunocytochemical, morphological, and electrophysiological study.

PURPOSE: To compare the morphologic and functional recovery of the retina after detachment and reattachment in an animal with a cone-dominant retina, the ground squirrel. METHODS: Ground squirrel (Spermophilus beecheyi) retinas were detached for 1 day and reattached for 7, 35, or 96 days (n = 2, each time point). Flicker ERGs were recorded 1 day after the detachment and at various times after reattachment. Contrast-response functions were measured for isochromatic modulation and for selective modulation of short-wavelength-sensitive (S) and middle-wavelength-sensitive (M) cones. At the end of the experiment, retinas were prepared for light microscopy or immunocytochemical staining with antibodies to rod opsin, S and M cone opsins, cytochrome oxidase, synaptophysin, glial fibrillary acidic protein (GFAP), cellular retinaldehyde-binding protein (CRALBP), interphotoreceptor-binding protein (IRBP), and peanut agglutinin lectin (PNA). Photoreceptor density maps were created from wholemount preparations labeled with biotinylated PNA and anti-S cone opsin. Cell counts of photoreceptor nuclei and cone outer segments (OS) were compared with flicker ERG data. Cell death was examined by the TUNEL method. RESULTS: Reattachment stopped photoreceptor cell death and reversed the disruption of interphotoreceptor matrix as well as the redistribution of Müller cell proteins. It also activated some astrocytes based on anti-GFAP staining. S- and M-cone OS showed a gradual recovery in length after reattachment, and this recovery continued to the longest time points examined. ERG contrast gains also recovered after reattachment, but these reached asymptotic levels by approximately a week after reattachment. There were significant correlations between outer nuclear layer (ONL) cell counts and ERG contrast gains. No differences were noted in the indices of recovery of M and S cones. CONCLUSIONS: The ERG can be used to follow specifically the changes in the retina that occur after retinal detachment and reattachment.

Animals↗

PubMed2002

An animal model for studying cone function in retinal detachment.

In people, retinal detachment often leads to a significant loss in cone-based vision. Most of the animal models commonly used for studying the consequences of retinal detachment have rod-dominated retinas. The purpose of this investigation was to evaluate the possibility that the ground squirrel, a rodent with a heavily cone-dominated retina, might provide a useful model for studying cone function in retinal detachment. Corneal ERGs were recorded from ground squirrels for large-field temporal modulations presented on a computer-controlled color monitor. Modulations were chosen to selectively stimulate either of the two classes of cone found in the ground squirrel retina. Under these test conditions, large and reliable cone ERGs could be readily recorded. In animals in which the retina had been surgically detached, the loss of cone signal was directly related to the number of cones in the detachment zone relative to the total cone population and that relationship did not differ for short-wavelength sensitive (S) and middle-wavelength sensitive (M) cones. Surgical reattachment produced a progressive recovery of cone-based signals. The ground squirrel seems likely to provide a useful animal model for studying the dynamics of cone function in retinal detachment and subsequent events.

Animals↗

PubMedDate not supplied

Spectral properties and retinal distribution of ferret cones.

The spectral mechanisms of the ferret (Mustela putorious furo) were studied with electroretinogram (ERG) flicker photometry. Variations in adaptation state and flicker rate were used to define corneally based spectral sensitivities for the three classes of receptor present in the retina of this mustelid-rods (lambdamax = 505 nm), S cones (430 nm), and L cones (558 nm). The retinal distributions of the two classes of cone were determined using opsin antibody labeling. Ferret retinas contain a total of about 1.3 million cones with L cones outnumbering S cones in a ratio of approximately 14:1. ERGs were also recorded using 18.75-Hz flickering stimuli that were designed to isolate signals from individual cone classes. The contrast/response functions for signals originating from both S and L cones were linear over low-to-moderate levels of contrast, but with greatly different slopes for the two cone types. The L:S contrast gain ratio derived from a comparison of these slopes, as well as inferences drawn from another experiment in which responses to various combinations of L- and S-cone activation were analyzed, suggest that contributions of these two cone types to the flicker ERG have a relative weighting of about 4:1 to 5:1 (L/S).

Animals↗