The distributions of photoreceptors and ganglion cells in the California ground squirrel, Spermophilus beecheyi.

The topographical distributions of photoreceptors and ganglion cells of the California ground squirrel (Spermophilus beecheyi) were quantified in a light microscopic study. The central retina contains broad, horizontal streaks of high photoreceptor density (40-44,000/mm2) and high ganglion cell density (20-24,000/mm2). The isodensity contours of both cell types are elliptical and oriented along the nasal-temporal axis. There are roughly five-fold decreases in both photoreceptor and ganglion cell densities with increasing eccentricity, the lowest densities being found in the superior retina. Large transitions in cell density and retinal thickness occur across the linear optic nerve head. Rod frequency increases with increasing eccentricity, from 5 to 7% in the central retina to 15 to 20% in the periphery. Roughly 10% of the cones possess wide, dark-staining ellipsoids. These cones are uniformly distributed across the retina which suggests that they may belong to a separate cone class, possibly blue-sensitive cones. The ganglion cell soma size distribution is unimodal, with the majority of somata being 25-50 micron2. Large ganglion cells (somata greater than 100 micron2) are rare in the central retina, but their frequency increases with increasing eccentricity. No evidence for separate size classes of ganglion cells was found. The gradual decrement of photoreceptor density across the ground squirrel retina suggests that there are only relatively small changes in acuity across much of the animal's visual space compared with species possessing either a narrow visual streak or fovea or area centralis.

Beachside preparation of jellyfish nematocyst tentacles.

A comparison of methods for preparing a jellyfish nematocyst suspension from sea nettle (Chrysaora quinquecirrha) fishing tentacles at the beachside was conducted. Autolysis of the tentacle followed by straining and sedimentation on ice was found to be a satisfactory technique. This procedure utilized a tea strainer, plastic cup and conical centrifuge tube, all of which could be made available at a minimally equipped laboratory.

The cone matrix sheath in the normal and diseased retina: cytochemical and biochemical studies of peanut agglutinin-binding proteins in cone and rod-cone degeneration.

The fate of the cone-associated extracellular domain, or cone matrix sheath (CMS), was examined in two canine models of hereditary retinal degeneration. The diseases, which affect cones selectively (cd = cone degeneration), or rods and cones temporally (prcd = progressive rod-cone degeneration), were examined biochemically (SDS-PAGE/lectin blots) and cytochemically (light microscopy) using peanut agglutinin lectin (PNA) to selectively label this domain and associated structures. Most of the cones had disappeared in the adult cd retina. In the remaining cones, PNA labeled the ectopically located somata and the CMSs that were present around severely diseased ones. Loss of cones resulted in background label in the IPM and the loss of the pedicle-associated label in the OPL. SDS-PAGE of retinal extracts showed that all the major classes of the lower molecular weight PNA-binding proteins were present, but only the 40- and 60-kD bands remained prominent. Because of the selectivity of the cd mutation, this suggests considerable heterogeneity within the various size classifications of the retinal PNA-binding glycoproteins. In prcd, CMSs were normal at a time when cones were structurally normal and disease was limited to the rod outer segments. The CMSs remained intact during the degenerative phase of the disease, and only became compressed in association with the collapse and narrowing of the photoreceptor layer; CMS labeling was lost with disappearance of the cone inner segment. The lectin biochemical results were normal until 1.7 years of age; thereafter, there was a decreased prominence of all major bands. Because of spatial heterogeneity in disease severity, it was not possible to correlate the lectin biochemical and cytochemical results in prcd.

Disc shedding and autophagy in the cone-dominant ground squirrel retina.

The temporal pattern of cone outer-segment disc shedding was examined in the retina of the California ground squirrel, Spermophilus beecheyi, under two different lighting conditions. Squirrels were entrained to either 10-180 lx (room lighting) or 1,400 lx. Cone shedding during the dark period was biphasic in both conditions, with increases occurring at 2-3 hr and 5-6 hr after light offset. Entrainment to 1400 lx resulted in an increase in shedding at 2 hr after light offset and a slight advance in the timing of both peaks. Dense granules were often found in photoreceptors, retinal neurons, Müller cells, microglia and vascular cells. These granules, which were found primarily during the dark period and early light period, were lipofuscin-like in their lipophilia, size and autofluorescence. Many of the granules were probably autophagic in origin, but some within Müller cells may have originated via endocytosis of extracellular material which was exocytosed by photoreceptors.

Interphotoreceptor retinoid-binding protein (IRBP) in progressive rod-cone degeneration (prcd)--biochemical, immunocytochemical and immunologic studies.

Interphotoreceptor retinoid-binding protein (IRBP) is synthesized and secreted by photoreceptor cells and is thought to facilitate the transport of retinoids during the visual cycle as well as fatty acids essential to the maintenance of normal outer segment membranes. Proteins such as IRBP, which are unique to the photoreceptor cells in the retina, are prime candidates in the consideration of biochemical defects which could contribute to photoreceptor cell degeneration in man and animals. In this study, the association between IRBP and retinal degeneration was examined using the progressive rod-cone degeneration (prcd) mutant retina in dogs as an animal model. This study shows that loss of IRBP is not an early occurrence in prcd. IRBP is present in relatively normal amounts and distribution even at 1.7 years of age, a time when there is extensive visual cell disease and degeneration. By 2.7-3.0 years of age, IRBP loss correlates with the severity of the disease and concomitant loss of photoreceptor cells. IRBP immunoreactivity was present in the interphotoreceptor matrix (IPM) as long as inner segments were present to a significant degree. The late loss of IRBP immunoreactivity seems to be, therefore, the result of advanced degeneration and end-stage atrophy of the retina. In addition, immunological studies were carried out in order to examine the possible role of an autoimmune response against IRBP in the disease cascade. Normal, heterozygote and prcd-affected dogs had measurable antibody titers to IRBP, but there was no correlation between disease state and antibody levels.