Circadian rhythms in the green sunfish retina.

Abstract

We investigated the occurrence of circadian rhythms in retinomotor movements and retinal sensitivity in the green sunfish, Lepomis cyanellus . When green sunfish were kept in constant darkness, cone photoreceptors exhibited circadian retinomotor movements; rod photoreceptors and retinal pigment epithelium (RPE) pigment granules did not. Cones elongated during subjective night and contracted during subjective day. These results corroborate those of Burnside and Ackland (1984. Investigative Ophthalmology and Visual Science. 25 :539-545). Electroretinograms (ERGs) recorded in constant darkness in response to dim flashes (X = 640 nm) exhibited a greater amplitude during subjective night than during subjective day. The nighttime increase in the ERG amplitude corresponded to a 3-10-fold increase in retinal sensitivity . The rhythmic changes in the ERG amplitude continued in constant darkness with a period of -24 h, which indicates that the rhythm is generated by a circadian oscillator . The spectral sensitivity of the ERG recorded in constant darkness suggests that cones contribute to retinal responses during both day and night. Thus, the elongation of cone myoids during the night does not abolish the response of the cones. To examine the role of retinal efferents in generating retinal circadian rhythms, we cut the optic nerve. This procedure did not abolish the rhythms of retinomotor movement or of the ERG amplitude, but it did reduce the magnitude of the nighttime phases of both rhythms. Our results suggest that more than one endogenous oscillator regulates the retinal circadian rhythms in green sunfish. Circadian signals controlling the rhythms may be either generated within the eye or transferred to the eye via a humoral pathway.

Electroretinograms and circadian rhythms in green sunfish.

“…In both instances, the ERG recording consists of a relatively small a-wave followed by a b-wave of approximately equal amplitude. The similarity of these responses is consistent with other results presented in Dearry and Barlow (1987) suggesting that a circadian oscillator acted to induce a photopic condition in the green sunfish eye during subjective day. The change in waveform between subjective day and subjective night may also be a consequence of this oscillator.…”

“…The change in waveform between subjective day and subjective night may also be a consequence of this oscillator. The responses of Dearry and Barlow (1987) possess a time course, waveform, and spectral sensitivity function similar to those observed for ERG responses recorded from a variety of fish (e.g., Witkovsky, 1968;Easter and Hamasaki, 1973;Cohen et al, 1977;Hoffert and Ubels, 1979;Powers et al, 1990). Together, these findings suggest that the potentials recorded by Dearry and Barlow (1987) exhibit the characteristics expected for a vertebrate ERG.…”

“…However, the response to which they refer ( Fig. 3 DAY of Dearry and Barlow, 1987) resembles ERG responses recorded by Witkovsky (1968) from carp exposed to background illumination. In both instances, the ERG recording consists of a relatively small a-wave followed by a b-wave of approximately equal amplitude.…”

“…9 of Dearry and Barlow, 1987) show that optic nerve section significantly altered the waveforms of both the negative (a-wave) and positive (b-wave) components of the ERG. Hence, "constancy of the waveform of negative slow component" is not a valid argument for suggesting that the negative component of the ERG recorded by Dearry and Barlow (1987) is a b-wave. Moreover, it should be noted that sectioning the optic nerve damped subjective night responses proportionally more than subjective day responses (Fig.…”

“…(3) McMahon and Barlow (1992) state that, "The waveform of the negative component [of Dearry and Barlow (1987)] was unchanged by optic nerve section, but the waveform of positive component was altered compared with intact preparations." However, the results to which these authors refer (Fig.…”