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| 2. |
- Ekström, Peter, et al.
(författare)
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Electron microscopic analysis of S‐antigen‐ and serotonin‐immuoreactive neural and sensory elements in the photosensory pineal organ of the salmon
- 1990
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Ingår i: Journal of Comparative Neurology. - : Wiley. - 0021-9967. ; 292:1, s. 73-82
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Tidskriftsartikel (refereegranskat)abstract
- Photoreceptor cells in the pineal complex of poikilothermic vertebrates are regarded as homologous with the neuroendocrine pinealocytes in the mammalian pineal organ. They possess an indolamine metabolism, and they contain a number of substances that are immunochemically similar to phototransduction‐related proteins otherwise found in photoreceptors of the lateral eye retina. Using correlative light and electron microscopic pre‐embedding immunocytochemistry, we have identified photosensory and neural elements that are immunoreactive with specific antisera against serotonin (5‐hydroxytryptamine) and the 48 kDa soluble protein S‐antigen (arrestin). One type of serotonin‐immunoreactive (5HTir) photoreceptor cell was identified. This was characterized by a short basal pole, into which an immunoreactive (postsynaptic?) element protruded. Two types of ‐antigen‐immunoreactive (SAir) photoreceptor cells were observed, one characterized by a short basal pole, similar to that of the 5HTir photoreceptors and the other characterized by a long, extensively branching basal pole. In addition, two types of neurons bearing no morphological specializations typical of photoreceptor cells were SAir: bipolar neurons and multipolar neurons. These were often situated dorsally in the pineal organ. The results indicate an emergence of multiple lines of photoreceptor‐derived “pinealocytes” either early in phylogeny, or independently in different taxa. The results are discussed in relation to current theories of pineal evolution.
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| 3. |
- Ekström, Peter, et al.
(författare)
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Evolution of photosensory pineal organs in new light: the fate of neurodocrine photoreceptors
- 2003
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Ingår i: Philosophical Transactions of the Royal Society B: Biological Sciences. - : The Royal Society. - 1471-2970. ; 358:1438, s. 1679-1700
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Forskningsöversikt (refereegranskat)abstract
- Pineal evolution is envisaged as a gradual transformation of pinealocytes (a gradual regression of pinealocyte sensory capacity within a particular cell line), the so-called sensory cell line of the pineal organ. In most non-mammals the pineal organ is a directly photosensory organ, while the pineal organ of mammals (epiphysis cerebri) is a non-sensory neuroendocrine organ under photoperiod control. The phylogenetic transformation of the pineal organ is reflected in the morphology and physiology of the main parenchymal cell type, the pinealocyte. In anamniotes, pinealocytes with retinal cone photoreceptor-like characteristics predominate, whereas in sauropsids so-called rudimentary photoreceptors predominate. These have well-developed secretory characteristics, and have been interpreted as intermediaries between the anamniote pineal photoreceptors and the mammalian non-sensory pinealocytes. We have re-examined the original studies on which the gradual transformation hypothesis of pineal evolution is based, and found that the evidence for this model of pineal evolution is ambiguous. In the light of recent advances in the understanding of neural development mechanisms, we propose a new hypothesis of pineal evolution, in which the old notion 'gradual regression within the sensory cell line' should be replaced with 'changes in fate restriction within the neural lineage of the pineal field'.
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| 4. |
- Ekström, Peter, et al.
(författare)
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Neural elements in the pineal complex of the frog, rana esculenta, i : Centrally projecting neurons
- 1990
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Ingår i: Visual Neuroscience. - 0952-5238. ; 4:5, s. 389-397
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Tidskriftsartikel (refereegranskat)abstract
- The pineal complex of anuran amphibians is a directly photosensory organ, encompassing both an extracranial portion, the frontal organ, and an intracranial portion, the pineal organ proper. The projection neurons of the frontal organ respond differentially according to the wavelengths of the light stimuli. The pineal organ, on the other hand, functions mainly as a luminosity meter. Most of its centrally projecting neurons respond to all increases in ambient illumination with decreases in spontaneous firing of action potentials, although some neural units in the pineal organ may respond according to wavelength. This difference in responses to light stimulation may be reflected in the neural organization of the two parts of the pineal complex. In the present study, we have analyzed the morphology of the projection neurons of the frontal and pineal organs of the frog, Rana esculenta, by backfilling of the neurons with horseradish peroxidase through their cut axons. In the pineal organ, several types of centrally projecting neurons were observed: peripherally situated unipolar and multipolar neurons, the dendrites of which extend into a superficial axon plexus that surrounds the pineal epithelium; smaller unipolar, bipolar, or multipolar neurons situated close to the central pineal tract; and radially oriented bipolar neurons, with short dendritic processes oriented towards the lumen of the pineal organ. This latter type was strongly reminiscent of photoreceptor cells. The centrally projecting neurons of the frontal organ were multipolar, and situated in the ventral part of the organ. One photoreceptor-like bipolar neuron was observed in one frontal organ. The neurons of the frontal organ did not form a superficial plexus of neurites. This difference may relate to the different ratio of chromaticity/luminosity units in the frontal and pineal organs.
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| 5. |
- Meissl, Hilmar, et al.
(författare)
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Action of γ-aminobutyric acid (GABA) in the isolated photosensory pineal organ
- 1991
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Ingår i: Brain Research. - : Elsevier BV. - 0006-8993. ; 562:1, s. 71-78
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Tidskriftsartikel (refereegranskat)abstract
- The effect of GABA (γ-aminobutyric acid), its agonists (muscimol, baclofen) and antagonist (bicuculline) on pineal ganglion cells of the luminosity type were studied in the isolated, superfused pineal organ of the rainbow trout, Oncorhynchus mykiss. Extracellular recordings revealed that GABA added through the superfusion medium caused a clear alteration of the actvity of projecting neurons, which transmit luminosity responses to the brain. Spontaneous discharges of ganglion cells were predominantly suppressed by GABA (33 neurons out of 48), but 10 neurons were clearly excited. Similar effects were observed after addition of muscimol, but not of baclofen. Bicuculline reversed the GABA and muscimol induced inhibition or excitation. In 4 neurons of the luminosity type, GABA caused bidirectional, inhibitory and excitatory responses depending on the state of light- or dark-adaptation. These observations suggest a role of a GABAergic mechanism in the generation and transmission of luminosity responses in the trout pineal organ. It appears that GABA participates in the modulation of light sensitivity during light- and dark-adaptation processes and that this action is mediated by GABAA receptors.
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