PHOTOPIGMENTS AND PHOTOENTRAINMENT IN THE SYRIAN GOLDEN-HAMSTER

The Syrian golden hamster (Mesocricetus auratus) is an important model in the study of circadian rhythms. However, as in other mammals, litt le is known about the photoreceptors that mediate circadian entrainmen t. Using immunocytochemistry and RNA blot hybridization, we found no e vidence for the presence of blue-/UV-sensitive opsin. In contrast, gre en-sensitive cone opsin was demonstrated in the retina both by immunoc ytochemistry and reverse-transcription PCR. When used as a probe in RN A blot hybridization, this PCR fragment labelled one transcript (5.8 k b) in hamster retinal RNA. These findings are in accordance with preli minary data from other investigators using electroretinography, which showed one cone-mediated photoreceptive mechanism with a maximum sensi tivity of 501 nm, but none at shorter wavelengths. However, we found t hat non-saturating pulses of ultraviolet radiation (357 nm) caused pha se shifts in locomotor behaviour. These results corroborate earlier re ports that UV radiation can regulate the photoperiodic response in thi s animal. Having confirmed these apparently contradictory earlier repo rts, we discuss the mechanisms that might create a UV-triggered non-vi sual response in a green cone monochromat. Finally, we propose the use of the Syrian golden hamster as a model for photoreceptor development and function in the absence of S/UV cones. (C) 1997 Elsevier Science B.V.