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  • The pineal eye in Xenopus laevis embryos and larvae: A photoreceptor with a direct excitatory effect on behaviour

    27 November 2018

    Behavioural experiments demonstrate that embryos and young larval stages of Xenopus laevis when exposed to a sudden drop in light intensity may show locomotor activity. Recordings from motoneurone axons demonstrate that the integrity of the pineal eye photoreceptors are essential for this response to occur. Thus the pineal has a direct excitatory effect on behaviour. The pineal eye arises embryologically as a single dorsal vesicular evagination of the diencephalon and anatomically it is very similar to that of other developing amphibians. Recording from the pineal eye using a suction electrode demonstrates that suddenly lowering the light intensity evokes a burst of impulses followed by a raised firing frequency. Conversely, increasing the light intensity leads to a lowered firing frequency. With prolonged exposure to white light at a range of intensities, the frequency of spike discharge is dependent upon the light intensity. The pineal eye can therefore act as a luminance detector. The pineal photoreceptors are most sensitive to light of a wavelength near 520 nm, this probably enables maximum sensitivity to the wavelengths of light that penetrate the freshwater environment. The possible role of the pineal eye in controlling locomotor activity is discussed. © 1982 Springer-Verlag.

  • A comparison of some photoreceptor characteristics in the pineal and retina - I. The Japanese quail (Coturnix coturnix)

    27 November 2018

    Immunocytochemistry with a rod-specific antiserum was used to study the post-hatch development (2 days-300 days) of photoreceptor elements within the pineal of the Japanese quail. At all ages staining was restricted to limited numbers of pinealocytes scattered throughout the gland. An enzyme-linked immunosorbent assay (ELISA), with the same rod-specific antibody, was then used to obtain a quantitative measure of rod opsin in total eye and pineal extracts in both the developing retina and pineal. The opsin content of both tissues shows a marked increase during the first 30 days after hatch and then plateaued to 0.84±0.02 nmoles opsin in the eye and 2.20±0.11 pmoles opsin equivalents in the pineal. The increase in opsin in the retina may be associated with continued post-hatch development of the photoreceptors. We then attempted to demonstrate the presence of the rhodopsin chromophore within pineal and retinal extracts using HPLC analysis. In both retinal and pineal extracts, 11-cis retinaldehyde was identified and a light-induced shift from the 11-cis to the all-trans isomer was clearly shown. This analysis also allowed us to calculate the total content of 11-cis and all-trans retinaldehyde (derived from both rod and non-rod photoreceptors) of the eye and pineal (eye: 1.7±0.2 nmoles; pineal: 4.6±0.5 pmoles). In the quail eye, the total amount of retinaldehyde is more than twice the amount of rod-like opsin. This probably reflects the large contribution of cones in the quail retina; the cone pigments will contribute to the retinaldehyde content but are not recognized by the rodspecific antibodies. In the pineal, we also found more than double the concentration of retinaldehyde than we would have predicted from the amount of rod-like opsin. These results, coupled with our immunocytochemical findings, suggest that the quail pineal contains at least two classes of photoreceptor, some 'rod-like', others 'non rod-like'. © 1989 Springer-Verlag.

  • The involvement of a rhodopsin-like photopigment in the photoperiodic response of the Japanese quail

    27 November 2018

    A technique has been developed for the investigation of the photopigment involved in the photoperiodic control of reproduction in Japanese quail, Coturnix coturnix. When these photoreceptors were exposed to white or monochromatic light a clear relationship was found between light intensity and the extent of photo-induced luteinizing hormone (LH) secretion. A spectroradiometric investigation of the passage of light through the skull and brain enabled us to illuminate the hypothalamic region with equal numbers of photons at a range of wavelengths. Action spectra were then conducted and showed a photopigment with a peak sensitivity at wavelengths near 500 nm. An excellent match was obtained when the standard absorption spectrum for a rhodopsin was fitted to the action spectrum, suggesting a rhodopsin maximally sensitive at 492 nm. The absolute sensitivity of the photoreceptors was calculated at a range of wavelengths: with light at 500 nm, 2.85×10-12 μE·cm-2·s-1 triggered the photoperiodic response. This level of sensitivity is matched only by the rhodopsin visual pigments. © 1985 Springer-Verlag.

  • Immunocytochemical identification of photoreceptor proteins in hypothalamic cerebrospinal fluid-contacting neurons of the larval lamprey (Petromyzon marinus)

    27 November 2018

    Antibodies directed against different visual pigment opsins, and an antibody raised against the C terminal of the α-subunit of retinal G protein (transducin) labelled cerebrospinal fluid-contacting cells located within the hypothalamus (postoptic commissural nucleus and ventral hypothalamic nucleus) of ammocoete lampreys (Petromyzon marinus). These antibodies also labelled photoreceptor cells within the retina and the pineal and parapineal organs, but no other areas of the brain. Despite considerable behavioural and physiological evidence for the existence of deep brain photoreceptors, numerous studies have failed to identify photoreceptor proteins within the basal brain. The results presented in this paper support our recent results in the lizard Anolis carolinensis, suggesting that a group of cerebrospinal fluid-contacting neurons within the vertebrate brain have a photosensory capacity. We speculate that these cells mediate extraocular and extrapineal photoreception in nonmammalian vertebrates. © 1994 Springer-Verlag.

  • Opsin localization and chromophore retinoids identified within the basal brain of the lizard Anolis carolinensis

    27 November 2018

    Since the beginning of this century evidence has accumulated which demonstrates that non-mammalian vertebrates possess photoreceptors situated deep within the brain. While many attempts have been made to localize these sensory cells, studies have either failed or been inconclusive. In this report we have used several experimental approaches to localize the deep brain photoreceptors of the lizard Anolis carolinensis. Using 3 antibodies that bind vertebrate cone opsins, we have immunolabelled cerebrospinal fluid (CSF)-contacting neurons located at the ventricular border within the nucleus ventromedialis of the septum. Western blot analysis indicates that these antibodies recognized a single 40 kD protein in ocular, anterior brain, and pineal extracts. Immunoblots of rodent brain did not show a similar protein band. We have also identified specific retinoids associated with phototransduction (11-cis and all-trans-3,4-didehydroretinaldehyde) within anterior brain extracts. This combined data provides the most detailed analysis of deep brain photoreceptors in any vertebrate. Consequently, we feel Anolis provides an excellent model to study this unexplored sensory system of the vertebrates. © 1993 Springer-Verlag.

  • Visual pigment in fish iridocytes

    27 November 2018

    The iridophores of some fishes including the neon tetra, Paracheirodon innesi, contain regular alternating layers of guanine and cytoplasm whose spacing changes in response to light, even in decapitated animals. As a result, the wavelength of light that is most strongly reflected also changes and the iridophore changes colour. These iridophores give the colour to the bright iridescent lateral stripe that includes the iris and runs laterally along the body. The iridophores themselves are located between the dermal collagen and the underlying muscle. The photosensitive site appears to be located within the cell itself, or very close to it. Using an immunofluorescence technique, we describe here the identification of an opsin-based visual pigment within the neon tetra iridophore.