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C W Hawryshyn

Publications and source records attributed to C W Hawryshyn.

26 records · Page 2Linked to original sources
PubMed1992

Thyroxine induces a precocial loss of ultraviolet photosensitivity in rainbow trout (Oncorhynchus mykiss, Teleostei).

Small (< 30 g) juvenile rainbow trout (Oncorhynchus mykiss) possess retinal photoreceptor mechanisms sensitive to ultraviolet (UV), short (S), middle (M) and long (L) wavelengths. During normal development, the sensitivity peak of the UV cone mechanism (360 nm) shifts towards the S-wavelengths (to an intermediate lambda max of 390 nm) until, at approx. 60 g, individuals are no longer sensitive in the UV (only a S-wavelength peak at 430 nm remains). This shift in spectral sensitivity is associated with the loss of small accessory corner cones from the retinal photoreceptor cell mosaic. Treating small (< 30 g) rainbow trout with thyroid hormone induced a precocial loss of UV photosensitivity and an associated change in the retinal photoreceptor cell mosaic, identical to the events that occur during normal development.

Aging↗
PubMed1991

Spatial summation of cone mechanisms in goldfish.

Experiments were performed to evaluate the spatial summation areas of the u.v.-, blue-, green- and red-sensitive cone mechanisms of goldfish. All the cone mechanisms were in compliance of Ricco's law, summing target radiance linearly over a certain range of target diameters with an average slope of 2.4. The critical diameters of the blue-, green- and red-sensitive cone mechanisms were all close to 6 deg. However, the critical diameter for the u.v.-sensitive cone mechanism was 8.0 deg, clearly different form than other cone mechanisms. The observation that the u.v.-sensitive cone mechanism has a larger spatial summation area suggests that u.v.-sensitive ganglion cells may have larger receptive field centers.

Animals↗
PubMed1991

Ultraviolet photoreception in carp: microspectrophotometry and behaviorally determined action spectra.

This study demonstrates correlations between u.v. sensitivity and microspectrophotometric absorption spectra determined sequentially for the same group of individuals. We used the heart-rate conditioning technique to measure spectral sensitivity of carp, a species known to have u.v.-sensitive photoreceptors. Mean spectral sensitivity (n = 3) determined with a spectrally-broad background (450 nm long pass filter) revealed a small but consistent u.v. peak (lambda max of 380 nm) in addition to the other long wavelength peaks. An intense blue-green background (490 nm) produced a more prominent u.v. peak (lambda max of 400 nm) when a 450 nm longpass filter was added to the background. Microspectrophotometric measurements of u.v.-sensitive photoreceptors from one individual, which belonged to the group used in the spectral sensitivity experiments, revealed an average lambda max of 377.5 nm (SD +/- 4.5 nm, n = 5 cells). Bleaching and dichroic measurements of these receptors ensured that we were examining typical vertebrate visual pigments and not stable photoproducts. The mean spectral sensitivity points were compared with the u.v. and blue-sensitive visual pigment absorption spectra. A linear subtractive model and ocular media absorption were used in this comparison for the various photic conditions used in the heart-rate conditioning experiments. The model successfully described the sensitivity of the test fish in two cases but in a third case there was some discrepancy. The model generated curve was broader than the spectral sensitivity of the u.v.-sensitive cone mechanism on the shortwave side even though the ocular media corrections had been accounted for.

Animals↗
PubMed1991

Light-adaptation properties of the ultraviolet-sensitive cone mechanism in comparison to the other receptor mechanisms of goldfish.

The light-adaptation properties of goldfish photoreceptor mechanisms were examined using Stiles' two-color threshold technique. Threshold vs. background intensity (TVI) curves were determined for isolated cone and rod mechanisms using the heart-rate conditioning technique. The principal aim of this study was to compare the light-adaptation properties of the ultraviolet (UV)-sensitive cone mechanism to the other receptor mechanisms of goldfish. This examination revealed several striking functional differences: (1) The UV-sensitive cone mechanism threshold vs. background intensity (TVI) exhibited a slope of 0.65 (compared to the approximate 1.0 for the other cone mechanisms on a log/log plot) and thus was not in accordance with Weber's law. This may in part be related to the intrusion of the blue-sensitive mechanism at the upper radiance range. (2) The operation of the UV-sensitive cone mechanism was limited to intermediate intensities (i.e. not very dim or bright). (3) The UV-sensitive cone mechanism exhibited a Weber fraction or luminance contrast threshold of 0.316 that was approximately six times larger than the other cone mechanisms but comparable to the rod mechanism. This indicates that the UV-sensitive cone mechanism performs relatively poorly in terms of brightness contrast detection.

Adaptation, Ocular↗
PubMed1989

The ontogeny of ultraviolet photosensitivity in rainbow trout (Salmo gairdneri).

The present study examines the changes in ultraviolet (UV) photosensitivity that occur during the growth of rainbow trout (Salmo gairdneri). A comparison of the ocular media transmission of small (n = 3) and large (n = 3) trout eyes did not reveal large changes in the transmission of UV radiation through the eye. We used the heart-rate conditioning technique to measure spectral sensitivity in immobilized trout. Four trout, each weighing less than 30 g, exhibited a UV-sensitivity peak at 360 nm while four additional trout weighing more than 60 g each exhibited no evidence of UV sensitivity. Spectral-sensitivity measurements of two trout weighing 44 g and 60 g revealed UV sensitivity, but when measured one month later (after a 25% increase in body weight) both fish exhibited no UV-sensitivity peak. At this time their sensitivity appeared to conform to the known blue-sensitive cone mechanism.

Aging↗
PubMed1989

Sideband transmission in interference filters and its implications for measurements of spectral sensitivity.

Commercial interference filters used in much of comparative vision science are constructed to suppress the transmission of light outside the primary passband. However, despite attempts to suppress sideband transmission, it does occur. This sideband transmission can lead to serious problems when working in the ultraviolet (UV) spectrum. The use of UV interference filters with a tungsten source which is calibrated with a silicon photodiode, produce large reproducible errors.

Calibration↗
PubMed1985

Ultraviolet photosensitivity in goldfish: an independent u.v. retinal mechanism.

Heart rate conditioned goldfish were sensitive to u.v. stimuli at wavelengths down to 340 nm. A u.v. peak had maximum sensitivity at about 380 nm and was depressed selectively by a u.v. adapting background. An opaque cone restricted light to the eye, reducing the probability of a dermal or pineal gland source of the response. Three experiments demonstrated a retinal origin for the u.v. peak. The conditioned response to u.v. stimuli was abolished following injection of Lidocaine into the eye. U.V. sensitivity remained when the cornea, iris and lens were extirpated. Finally, the u.v. peak showed an orderly change in sensitivity with alteration in adapting u.v. illumination.

Animals↗