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

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          Abstract

          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 references14

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

          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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              Projections of the suprachiasmatic nuclei, subparaventricular zone and retrochiasmatic area in the golden hamster.

              The patterns of projections from the hamster suprachiasmatic nucleus, retrochiasmatic area and subpraventricular hypothalamic zone were examined using anterograde tracing with the plant lectin, Phaseolus vulgaris leucoagglutinin. Suprachiasmatic nucleus efferents comprise four major fiber groups: (i) an anterior projection to the ventral lateral septum, the bed nucleus of the stria terminalis and anterior paraventricular thalmus; (ii) a periventricular hypothalamic projection extending from the preoptic region to the premammillary area; (iii) a lateral thalamic projection to the intergeniculate leaflet and ventral lateral geniculate; and (iv) a posterior projection to the posterior paraventricular thalamus, precommissural nucleus and olivary pretectal nucleus. The retrochiasmatic area showed a similar projection pattern with several major exceptions. There are projections to endopiriform cortex, fundus striati, ventral pallidum, horizontal limb of the nucleus of the diagonal band and three separate routes to the amygdala. There are also projections laterally with fibers of the supraoptic commissures, which enter the superior thalamic radiation and innervate the caudal dorsomedial thalamic nuclei. Other fibers traveling with the commissures terminate in the ventral zona incerta. The subparaventricular zone projects to most targets of the suprachiasmatic nucleus, but not to the intergeniculate leaflet. There is a substantial input to both the subparaventricular zone and retrochiasmatic area from the suprachiasmatic nucleus, but little apparent reciprocity. There is extensive overlap of suprachiasmatic nuclei and retrochiasmatic efferents, and between retrochiasmatic and known medial amygdaloid efferents. The anatomical information is discussed in the context of circadian rhythm regulation, photoperiodism and chemosensory pathways controlling male hamster reproductive behavior.
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                Author and article information

                Journal
                NEN
                Neuroendocrinology
                10.1159/issn.0028-3835
                Neuroendocrinology
                S. Karger AG
                0028-3835
                1423-0194
                1999
                February 1999
                17 February 1999
                : 69
                : 2
                : 97-104
                Affiliations
                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
                Article
                54407 Neuroendocrinology 1999;69:97–104
                10.1159/000054407
                9986922
                f9647d8c-aa04-4748-a581-28a11081b6dd
                © 1999 S. Karger AG, Basel

                Copyright: All rights reserved. No part of this publication may be translated into other languages, reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying, recording, microcopying, or by any information storage and retrieval system, without permission in writing from the publisher. Drug Dosage: The authors and the publisher have exerted every effort to ensure that drug selection and dosage set forth in this text are in accord with current recommendations and practice at the time of publication. However, in view of ongoing research, changes in government regulations, and the constant flow of information relating to drug therapy and drug reactions, the reader is urged to check the package insert for each drug for any changes in indications and dosage and for added warnings and precautions. This is particularly important when the recommended agent is a new and/or infrequently employed drug. Disclaimer: The statements, opinions and data contained in this publication are solely those of the individual authors and contributors and not of the publishers and the editor(s). The appearance of advertisements or/and product references in the publication is not a warranty, endorsement, or approval of the products or services advertised or of their effectiveness, quality or safety. The publisher and the editor(s) disclaim responsibility for any injury to persons or property resulting from any ideas, methods, instructions or products referred to in the content or advertisements.

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

                Endocrinology & Diabetes,Neurology,Nutrition & Dietetics,Sexual medicine,Internal medicine,Pharmacology & Pharmaceutical medicine
                Melatonin,Retrochiasmatic area,Rhythms,N-acetylserotonin,Ibotenic acid,Pineal gland

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