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      The Role of the Retrochiasmatic Area in the Control of Pineal Metabolism

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          The aim of the present investigation was to study the effect of neurotoxic ibotenic acid lesion of the retrochiasmatic area on the daily profile of pineal N-acetylserotonin and melatonin synthesis and on the pineal metabolic reactivity to nocturnal short-term retinal photostimulation. Groups of rats were killed 6 h after lights off either in the dark of immediately after being photostimulated for 1 or 15 min. Additionally, groups of rats were sacrificed at six different time points throughout the 24-hour light-dark cycle. The results suggested the presence of two functionally distinct territories in the retrochiasmatic area. The basal retrochiasmatic area, an area situated immediately ventral to the third ventricle, behind the suprachiasmatic nuclei and in front of the arcuate nucleus, is implicated in the nocturnal inhibitory process induced by short-term retinal photostimulation. The lateral retrochiasmatic area, which is situated immediately lateral to the anterior periventricular nucleus, below the anterior hypothalamic nucleus and in front of the ventromedial hypothalamic nucleus, is importantly involved in the control of the peak amplitude of the daily production of N-acetylserotonin and melatonin by the pineal gland.

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          Most cited references 14

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          Pineal N-acetyltransferase and hydroxyindole-O-methyltransferase: control by the retinohypothalamic tract and the suprachiasmatic nucleus.

           D. Klein,  Jamie Moore (1979)
          The visual pathway and central neural structures involved in the photic and endogenous regulation of the activity of pineal N-acetyltransferase and hydroxyindole-O-methyltransferase were investigated. The results indicate that the visual pathway regulating both enzymes is the retinohypothalamic tract, and that the inferior accessory optic tract is clearly not involved in the regulation of hydroxyindole-O-methyltransferase activity, as has been previously thought. In addition, the suprachiasmatic nucleus was found to be necessary for the generation of a rhythm in N-acetyltransferase activity in blinded animals, and to be responsible for the tonic elevation of hydroxyindole-O-methyltransferase activity in blinded animals. Finally, it was concluded that the rapid and large daily changes in N-acetyltransferase activity seen in a normal lighting cycle and the much slower and smaller changes in hydroxyindole-O-methyltransferase activity seen only after weeks in constant lighting conditions are mediated by the same neural tract; the different time courses of the effects of environmental lighting may be explained on the basis of different intracellular regulatory mechanisms.
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            Retinohypothalamic projections in the hamster and rat demonstrated using cholera toxin.

            The organization of retinohypothalamic tract (RHT) projections in the rat and hamster was studied using anterograde transport of cholera toxin conjugated to HRP (CT-HRP). In both species the major RHT projections lead to the suprachiasmatic nuclei (SCN). This projection begins in the rostral SCN as a loose plexus in the hamster and a a dense aggregation of terminals along the chiasmal border in the rat. Through the remainder of the SCN there is a very dense terminal plexus in the ventral and lateral part of the nucleus with fewer terminals present medially. The RHT projection to the SCN is greater contralaterally in the rat whereas in the hamster the contralateral and ipsilateral projections are approximately equal. In addition to projections to the SCN, the RHT projects to the anterior hypothalamic area, the retrochiasmatic area and lateral hypothalamic area in both species. The anterior hypothalamic projections are more extensive in the hamster than in the rat and extend into the perifornical region, the dorsal hypothalamus and zona incerta. The SCN and anterior hypothalamic projections are continuous with a projection to the retrochiasmatic area and, in the hamster, with a projection extending into the subparaventricular zone with some axons and terminals continuing into the paraventricular nucleus. In contrast to these, the lateral hypothalamic projection in the rat is more extensive than in the hamster. Albino and pigmented rats show identical projections. In addition to the hypothalamic projections, there is in the hamster a small projection along the base of the telencephalon to the anterior amygdaloid area and cortical amygdaloid nucleus and a very sparse projection to the anterior thalamic nuclei.(ABSTRACT TRUNCATED AT 250 WORDS)
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              Descending projections from the pontine micturition center.


                Author and article information

                S. Karger AG
                February 1999
                17 February 1999
                : 69
                : 2
                : 97-104
                aDepartment of Physiology and Biophysics, Institute of Biomedical Sciences, University of São Paulo; bLaboratory of Pharmacology, Butantan Institute, São Paulo, Brazil, and cInstitut de Recherche Servier, Courvoisier, France
                54407 Neuroendocrinology 1999;69:97–104
                © 1999 S. Karger AG, Basel

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                Page count
                Figures: 4, References: 53, Pages: 8
                Pineal and Melatonin


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