Neurobiology of the lacertilian parietal eye system

Engbretson, Gustav A.

doi:10.1080/08927014.1992.9525353

Cited by 16 publications

(8 citation statements)

References 33 publications

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“…The structure of the parietal eye, on the other hand, resembles that of the lateral eyes of other vertebrates. It contains a so-called cornea, a lens, a highly structured retina-like sensory epithelium with pigmented cells, highly developed photoreceptor cells capable of transducing photic information, and ganglion cells able to transmit this information to the brain (reviewed in Eakin, 1973 ;Quay, 1979 ;Engbretson, 1992). Axonal projections of the ganglion cells contribute to the parietal nerve, which innervates the pars dorsomedialis of the left medial habenula (Engbretson et al 1981 ;Korf & Wagner, 1981) and other bilateral diencephalic targets ( Fig.…”

Section: Reptiliamentioning

confidence: 99%

Asymmetry in the epithalamus of vertebrates

2001

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The epithalamus is a major subdivision of the diencephalon constituted by the habenular nuclei and pineal complex. Structural asymmetries in this region are widespread amongst vertebrates and involve differences in size. neuronal organisation, neurochemistry and connectivity. In species that possess a photoreceptive parapineal organ, this structure projects asymmetrically to the left habenula, and in teleosts it is also situated on the left side of the brain. Asymmetries in size between the left and right sides of the habenula are often associated with asymmetries in neuronal organisation, although these two types of asymmetry follow different evolutionary courses. While the former is more conspicuous in fishes (with the exception of teleosts), asymmetries in neuronal organisation are more robust in amphibia and reptiles. Connectivity of the parapineal organ with the left habenula is not always coupled with asymmetries in habenular size and/or neuronal organisation suggesting that, at least in some species, assignment of parapineal and habenular asymmetries may be independent events. The evolutionary origins of epithalamic structures are uncertain but asymmetry in this region is likely to have existed at the origin of the vertebrate, perhaps even the chordate, lineage. In at least some extant vertebrate species, epithalamic asymmetries are established early in development, suggesting a genetic regulation of asymmetry. In some cases, epigenetic factors such as hormones also influence the development of sexually dimorphic habenular asymmetries. Although the genetic and developmental mechanisms by which neuroanatomical asymmetries are established remain obscure, some clues regarding the mechanisms underlying laterality decisions have recently come from studies in zebrafish. The Nodal signalling pathway regulates laterality by biasing an otherwise stochastic laterality decision to the left side of the epithalamus. This genetic mechanism ensures a consistency of epithalamic laterality within the population. Between species, the laterality of asymmetry is variable and a clear evolutionary picture is missing. We propose that epithalamic structural asymmetries per se and not the laterality of these asymmetries are important for the behaviour of individuals within a species. A consistency of the laterality within a population may play a role in social behaviours between individuals of the species.

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Section: Reptiliamentioning

confidence: 99%

Asymmetry in the epithalamus of vertebrates

2001

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“…divider. Given that lens cells and glial cells in the parietal eye are analogous to pigment epithelial and Müller cells in the lateral eye (Steinberg et al, 1985;Engbretson & Linser, 1991;Engbretson, 1992;Newman, 1993), it is conceivable that they are similarly endowed primarily with inward rectifying channels. These channels are primarily permeable to potassium, and their conductance varies with the power of the extracellular potassium concentration (Hagiwara & Takahashi, 1974;Newman, 1993).…”

Section: Erg Vs Photoreceptor Responsesmentioning

confidence: 99%

“…1A). It has much in common, both structurally and developmentally, with the more commonly studied lateral eyes but contains a reduced number of cell types (Eakin, 1973;Engbretson, 1992). In addition to photoreceptors, the parietal eye contains ganglion, glial, and lens cells, but lacks interneurons (Engbretson & Anderson, 1990).…”

Section: Introductionmentioning

confidence: 99%

Electroretinogram of the parietal eye of lizards: Photoreceptor, glial, and lens cell contributions

Solessio

Engbretson²

1999

Vis Neurosci

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Local electroretinograms (ERGs) were recorded in the parietal eye of Xantusia vigilis. The responses to monochromatic light under dark- and light-adapted conditions were studied. We found that two antagonistic chromatic mechanisms dominate the overall response. With the electrode tip in the lumen of the eye, light stimulation under dark-adapted conditions evoked responses of negative polarity with maximum sensitivity to green light. Intense green background illumination saturated the green-sensitive mechanism, and superposition of a blue stimulus then elicited responses of opposite polarity, driving the potentials back toward the dark resting level. The spectral sensitivities of the two chromatic mechanisms were determined using chromatic adaptation. The lower threshold, green-sensitive mechanism has a maximum sensitivity at 495 nm while the antagonistic mechanism, with its maximal spectral sensitivity at 430 nm, is at least 2 log units less sensitive. The polarity of the ERG recording inverts as the electrode traverses the photoreceptor layer, suggesting that the photoreceptors are the major source of the ERG. This result was confirmed with intracellular recordings from photoreceptors, glial, and lens cells. The glial and lens cells of the parietal eye respond to local changes in [K+]o. Intracellular recordings of the responses of these cells to light stimuli follow time courses similar to changes in extracellular potassium concentrations measured with K+ -specific electrodes. These results suggest that the glial and lens cell membranes are highly permeable to potassium and, therefore, the electrical responses of these cells are evoked by changes in [K+]o elicited by light stimulation of the photoreceptors. Nevertheless, the major component of the parietal eye ERG is the photoreceptor signal. A circuit model of the ERG sources is presented.

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“…Electrophysiological studies (review in Engbretson 1992) show that the parietal eye not only has an on-off response to light but responds differentially to light of different wavelengths. Furthermore, the parietal eye is linked to the brain by the parietal nerve, which carries afferent fibres to the habenular complex (Kappers 1967;Engbretson et al 1981).…”

Section: Discussionmentioning

confidence: 99%

The pineal complex and melatonin affect the expression of the daily rhythm of behavioral thermoregulation in the green iguana

Tosini

Menaker

1996

J Comp Physiol A

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Daily variation in the body temperature of the green iguana (Iguana iguana) was studied by telemetry in laboratory photo-thermal enclosures under a 12Light:12Dark (L:D) photoperiod. The lizards showed robust daily rhythms of thermoregulation maintaining their body temperatures (Tb) at higher levels during the day than during the night. Some animals maintained rhythmicity when kept in constant darkness. On light:dark cycles parietalectomy produced only a transient increase of median Tb in the first or second night following the operation. Pinealectomized lizards on the other hand maintained their body temperatures as significantly lower levels during the day and at significantly higher levels during the night than did sham-operated or intact lizards. This effect was apparently permanent, since one month after pinealectomy lizards still displayed the altered pattern. Plasma melatonin levels in intact animals were high during the night and low during the day and were unaffected by parietalectomy. Pinealectomized lizards showed low levels of plasma melatonin during both the day and the night. A daily intraperitoneal injection of melatonin in pinealectomized animals given a few minutes after the light to dark transition decreased the body temperatures selected by the lizards during the night and increased the body temperatures selected during the following day. Control injections of saline solution had no effect. The significance of these results is discussed in relation to the role of the pineal complex and melatonin in the mediation of thermoregulatory behavior.

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Neurobiology of the lacertilian parietal eye system

Cited by 16 publications

References 33 publications

Asymmetry in the epithalamus of vertebrates

Asymmetry in the epithalamus of vertebrates

Electroretinogram of the parietal eye of lizards: Photoreceptor, glial, and lens cell contributions

The pineal complex and melatonin affect the expression of the daily rhythm of behavioral thermoregulation in the green iguana

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