Arnold J. Sillman

The photoreceptors and visual pigments of the garter snake (Thamnophis sirtalis): A microspectrophotometric, scanning electron microscopic and immunocytochemical study

Abstract Scanning electron microscopy, immunocytochemistry, and single cell microspectrophotometry were employed to characterize the photoreceptors and visual pigments in the retina of the garter snake, Thamnophis sirtalis. The photoreceptor population was found to be comprised entirely of cones, of which four distinct types were identified. About 45.5% of the photoreceptors are double cones consisting of a large principal member joined near the outer segment with a much smaller accessory member. About 40% of the photoreceptors are large single cones, and about 14.5% are small single cones forming two subtypes. The outer segments of the large single cones and both the principal and accessory members of the doubles contain the same visual pigment, one with peak absorbance near 554 nm. The small single cones contain either a visual pigment with peak absorbance near 482 nm or one with peak absorbance near 360 nm. Two classes of small single cones could be distinguished also by immunocytochemistry and scanning electron microscopy. The small single cones with the 360-nm pigment provide the garter snake with selective sensitivity to light in the near ultraviolet region of the spectrum. This ultraviolet sensitivity might be important in localization of pheromone trails.

Barium suppresses slow PIII in perfused bullfrog retina

Under the appropriate conditions a large, slow, negative-going potential change can be recorded from the vertebrate retina in response to a light stimulus. This slow PHI, as it has come to be called, has been reported in the bullfrog (Sillman et al., 1969), rabbit (Faber, 1969; Hanitzsch, 1973), rat (Ernst and Arden, 1972; Arden, 1977). carp (Witkovsky et al., 1975) and mudpuppy (Karwoski and Proenza, 1977). As a result of their detailed spatial analyses of the response Faber (1969) and Arden (1977) concluded that the slow PI11 has its origin in the Miiller cell. The lengthy time course of the response along with the fact that the potential is not suppressed by treatment of the retina with sodium aspartate, a substance which depolarizes and thereby inactivates retinal neurons proximal to the photoreceptors (Cervetto and MacNichol, 1972; Dowling and Ripps, 1972; Murakami et al., 1972, 1975), led Witkovsky et al., (1975) to the same conclusion. Karwoski and Proenza (1977) who recorded intracellularly from the Miiller cells of the mudpuppy retina, also report a prolonged hyperpolarizing response which they suggest might represent the slow PIII. However, this potential was elicited only by light of very long duration and, therefore, its relationship to the slow PI11 observed in other studies remains unclear. Nevertheless, it is certainly interesting and of importance that the Miiller cell, which is thought to be responsible for the production of the positive going b-wave of the electroretinogram (Miller and Dowling, 1970) can, under appropriate conditions, also produce a negative going slow potential. The Mtlller cell appears to be quite sensitive to alterations in potassium concentration and, therefore, behaves like a potassium electrode (Miller, 1973; Karwoski and Proenza, 1977; Tomita, 1976). It is certainly quite reasonable that the Miiller cells could be responsible for the generation of slow PIII. A decrease in potassium concentration in the vicinity of the photoreceptor, for which there is evidence (Oakley and Green, 1976) could indeed cause the Milller cells to hyperpolarize. Since barium has been shown to decrease potassium conductance (e.g. Sperelakis et al., 1967), it occurred to us that treatment of the retina with barium might provide another test of the suggested relationship between the Mtiller cell and the slow PIII. Accordingly, dark-adapted bullfrog retinae were removed, separated from pigment epithelium and perfused with an aspartate-Ringer solution as described elsewhere (Sillman et al., 1972). In contrast to previous work the perfusate was buffered with Trismaleate (pH 7.8) rather than phosphate to avoid precipitation of the barium. Sodium concentration, however, was maintained at 110 mM. Also as described elsewhere (Sillman et al., 1972), recordings were made extracellularly by means of chlorided silver electrodes embedded in the perfusion chamber, one on each side of the retina. All amplification was direct coupled with the 3 dB roll-off point at 40 Hz. A typical series of records is shown in Fig. 1. Traces (A) and (B) rep resent the response of the retina to a light stimulus (white light, 250 msec, 47 pW/cm*) under normal conditions. One can easily distinguish the very rapid negative going potential, known to originate in the photoreceptors (Silhnan et al., 1969), and the very

Histology and microspectrophotometry of the photoreceptors of a crocodilian, Alligator mississippiensis

The photoreceptors in the retina of Alligator mississippiensis were examined by means of in situ, single cell microspectrophotometry and scanning electron microscopy (SEM). The retina is characterized by a system of four cone visual pigments. One type of single cone contains a visual pigment with absorbance maximum (λmax) at 535 nm. A second type contains a visual pigment absorbing maximally at 444 nm. The principal member of the double cone has a visual pigment with λmax at 566 nm whereas the accessory member’s visual pigment absorbs maximally at 503 nm. There is only one rod pigment and it is virtually identical to that within the accessory cone, absorbing maximally at 501 nm. All visual pigments are based on the retinal or vitamin A1 chromophore. SEM confirms that the alligator retina is duplex with rods dominating but cones present in significant numbers. There is a wide range of photoreceptor shapes and sizes throughout the retina

Microspectrophotometry of the photoreceptors of palaeognathous birds — the emu and the tinamou

SummaryWith the aid of a microspectrophotometer the visual pigments and oil globules in the retina of the emu (Dromiceius novae-hollandiae), the brushland tinamou (Nothoprocta c. cinerascens) and the Chilean tinamou (Nothoprocta perdicaria sanborni) were characterized. All three of these palaeognathous birds contain in their rods a typical rhodopsin with λmax near 500 nm. Each of these birds has cones containing iodopsin-like visual pigments with λmax in the 560–570 nm spectral region. No unequivocal evidence was obtained for the presence of cone pigments other than this iodopsin-like pigment, although one cell thought to be a cone, and containing a visual pigment with λmax near 498 nm, was observed in the retina of the brushland tinamou. The oil globule systems of the three palaeognathous species are identical to each other and are much simpler than is typical for neognathous birds in that only two different types of globule are present, one with λT50 at 508 nm and another with λT50 at 568 nm. Comparison of the data with observations made on neognathous species indicates (1) that palaeognathous birds probably have poorer color discrimination capabilities than neognathous birds and (2) that the tinamou is more closely related to the ratites than to the galliform species.

Low levels of cadmium chloride damage the corneal endothelium

The effect of cadmium chloride on the integrity of the endothelium of isolated bullfrog (Rana catesbeiana) corneas was examined by spectrophotometric analysis of corneal uptake of the vital stain Janus green and by scanning electron microscopy (SEM). The uptake of Janus green by the endothelium was dose related between 1.0 and 100.0 μM CdCl2. The effect of cadmium was significantly attenuated by the calcium channel blocker SKF 96365 and was augmented by the calcium ionophore A23187, indicating that cadmium influx through calcium channels is an important determinant of its cellular effect. The effect of cadmium was not altered by changes in the external calcium concentration, indicating that the mechanism does not involve competitive inhibition by calcium. SEM demonstrated significant structural damage to the corneal endothelium exposed to cadmium chloride, including focal disruption and denuding of the apical endothelial membrane.

The photoreceptors and visual pigments of two species of Acipenseriformes, the shovelnose sturgeon (Scaphirhynchus platorynchus ) and the paddlefish (Polyodon spathula )

Abstract Scanning electron microscopy, microspectrophotometry, and spectrophotometry of digitonin extracts were employed to characterize the photoreceptors and visual pigments of two freshwater Acipenseriformes. The retinas of the shovelnose sturgeon, Scaphirhynchus platorynchus (Acipenseridae), and the paddlefish, Polyodon spathula (Polyodontidae) are dominated by large rods with long, broad outer segments. A second rod, rare and much narrower than the dominant rod, is present in Scaphirhynchus but not seen in Polyodon. The absorbance maximum of the visual pigment in the rods of Polyodon is near 540 nm; that of Scaphirhynchus near 534 nm. The retinas of both species contain substantial numbers of large, single cones, about 33% of the photoreceptors in Scaphirhynchus; 37% in Polyodon. Scaphirhynchus cone pigments have absorbance maxima near 610 nm, 521 nm and 470 nm, respectively. Polyodon cone pigments absorb maximally near 607 nm and 535 nm, respectively. All visual pigments are based on vitamin A2. The data are compared to those from other Acipenseriformes and are discussed in terms of lifestyle and behavior.

An action spectrum for the light-dependent inhibition of swimming behavior in newly hatched white sturgeon, Acipenser transmontanus

Newly hatched white sturgeon (Acipenser transmontanus) yolk-sac larvae are negatively phototactic, photokinetic and geotactic--seeking cover in the substrate during daylight hours. If cover is unavailable and the light intensity is low, they move into the water column and alternate periods of rapid, upward swimming with periods of quiescence during which they sink. In the dark they swim almost continuously. A flash of light inhibits swimming activity totally for a period dependent on the light intensity. Using this observation, we obtained an action spectrum for swimming inhibition for 30 newly hatched larvae. This action spectrum is best fit by a single visual pigment with absorbance maximum at 537 nm. The lack of red sensitivity fits well with previous work showing that red-sensitive photoreceptor cells are absent in young sturgeon. The possible significance of red insensitivity is discussed from both ecological and practical standpoints.

Scanning electron microscopy and microspectrophotometry of the photoreceptors of ictalurid catfishes

The retinal photoreceptors from larval channel catfish (Ictalurus punctatus) were studied using single cell, in situ microspectrophotometry. Rods appear at 5 days after hatch; cones are present from day one. The rods contain a visual pigment which absorbs light maximally at 540 nm. The cones contain either a green sensitive visual pigment with peak absorbance at 535 nm or a red sensitive visual pigment with peak absorbance at 608 nm. All pigments are based on vitamin A2. Visual pigment complement does not change with age, as photoreceptors from adultI. punctatus, I. catus andI. melas contain visual pigments virtually identical to those of the larvalI. punctatus. Regardless of age, no visual pigment with peak absorbance in the short wavelength region of the spectrum was ever observed. Scanning electron microscopy of adultI. punctatus retinas showed large rods with long, cylindrical outer segments and smaller cones with short, tapered outer segments. The myoids of both rods and cones are extensable. The rods, embedded in a granular tapetal material, comprise from 50 to 60% of the photoreceptors. Only single cones are present. The data are consistent with the idea that the ictalurid catfishes spend their entire lives in an environment deficient in blue light.

VISUAL PIGMENTS AND PHOTORECEPTORS IN TWO SPECIES OF SHARK, TRIAKIS SEMIFASCIATA AND MUSTELUS HENLEI

The retinal photoreceptors of brown smoothhound sharks (Mustelus henlei) and leopard sharks (Triakis semifasciata) were studied by spectrophotometric analysis of visual pigment extracts, microspectrophotometric examination of single cells, and scanning electron microscopy. Juvenile and adult brown smoothhounds have one, identical visual pigment in their rod photoreceptors. The visual pigment is based on the vitamin A1 chromophore and has a peak absorbance (λmax) (at 496 ± 2 nm. Juvenile and adult leopard sharks also have a single, vitamin A1 based visual pigment, this one with λmax at 502 ± 1 nm. No evidence was found for a shift from a vitamin A2 based visual pigment in the juveniles to a vitamin A1 based pigment in the adults, as is known to occur in the lemon shark, Negaprion brevirostris (Cohen et al. [1990] Vision Res., 30:1949–1953). The retinas of brown smoothhounds and leopard sharks contain both rods and cones, with the rods dominating. The rod outer segments of the brown smoothhound are much longer than are those of the leopard shark. The greater length of brown smoothhound rod outer segments and the shorter wavelength λmax of the brown smoothhounds rod pigment support the idea that brown smoothhounds are either more nocturnal than leopard sharks or are active at greater depths. Cones are very rare in both species with only three identified with the scanning electron microscope and none with the microspectrophotometer. The apparent paucity of cones most likely relates to the bottom dwelling lifestyle of these sharks, although the possibility remains that their retinas contain small, specialized regions of high cone density, which were simply missed.

The Photoreceptors and Visual Pigments of Sharks and Sturgeons

With the exception of the stellate sturgeon, which has only cones, all acipenseriform species studied have a duplex retina. The retina is dominated by rods, but about 20% of the photoreceptors are cones. The rods are structurally similar to those of vertebrates in general. Most rods have outer segments that are broad and long, but at least one species has a very rare, very slender rod as well. Cones are also typical in structure, and they too are rather robust. With one exception, the inner segment of each cone houses a colorless oil droplet, the function of which is unknown. Packing density of both rods and cones is relatively low, indicating that both scotopic and photopic acuity is less than that of other nocturnal creatures. The visual pigment in the rods of all species studied has a peak absorbance near 540 nm. All species studied have multiple cone pigments and, therefore, the photoreceptor basis for wavelength discrimination. However, one cannot yet say whether or not any sturgeon or paddlefish has color vision. All visual pigments are based on the vitamin A2 chromophore, and there is no evidence that there is a shift to the vitamin A 1 chromophore with change of habitat or with age. At least one species does change its cone pigment complement with age. Larval white sturgeon up to 10 weeks of age have only green-sensitive cones; after 10 weeks, blue-sensitive and red-sensitive cones are also present.