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      Projections of the Estrogen Receptor-Immunoreactive Ventrolateral Hypothalamus to Other EstrogenReceptor-Immunoreactive Sites in Female Guinea Pig Brain

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          Abstract

          The ventrolateral hypothalamus in female guinea pigs includes an estrogen receptor dense region adjacent to the ventromedial hypothalamus. This region is reciprocally connected with other estrogen receptor-containing areas suggesting that steroid hormone receptor-containing cells may be directly linked. Phaseolus vulgaris leucoagglutinin, an anterograde tract tracer, was specifically placed in this region with the aim of labeling some projections from estrogen receptor-containing neurons. These projections were colocalized immunocytochemically with the distribution of estrogen receptor-containing cells. Dense ventrolateral hypothalamic innervation was observed in some regions also containing a high concentration of estrogen receptor-containing cells. These regions included the medial preoptic area, the bed nucleus of the stria terminalis, the ventrolateral hypothalamus anterior and posterior to the injection site, and the midbrain central gray. A low density of ventrolateral hypothalamic fibers and terminals was observed in two regions rich in estrogen receptors, the amygdala and the arcuate nucleus. In general, ventrolateral hypothalamic fibers and terminals were present in all regions where estrogen receptors were found except the medial thalamus and habenular region. Labeled terminal boutons and perineuronal baskets were found around estrogen receptor-containing cells in most regions which contained estrogen receptor-containing cells. These close appositions were suggestive of synaptic contacts, suggesting that the ventrolateral hypothalamus may influence steroid-dependent behaviors via the modulation of estrogen receptor-containing cells. Furthermore, ventrolateral hypothalamic projections may include direct connections with estrogen receptor-containing cells, suggesting the presence of a network of interconnected estradiol-sensitive neurons involved in the regulation of estradiol-dependent functions.

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          Most cited references 20

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          An anterograde neuroanatomical tracing method that shows the detailed morphology of neurons, their axons and terminals: immunohistochemical localization of an axonally transported plant lectin, Phaseolus vulgaris leucoagglutinin (PHA-L).

          A new neuroanatomical method for tracing connections in the central nervous system based on the anterograde axonal transport of the kidney bean lectin, Phaseolus vulgaris-leucoagglutinin (PHA-L) is described. The method, for which a detailed protocol is presented, offers several advantages over present techniques. First, when the lectin is delivered iontophoretically, PHA-L injection sites as small as 50-200 micron in diameter can be produced, and are clearly demarcated since the neurons within the labeled zone are completely filled. Second, many morphological features of such filled neurons are clearly demonstrated including their cell bodies, axons, dendritic arbors and even dendritic spines. Third, there is some evidence to suggest that only the neurons at the injection site that are filled transport demonstrable amounts of the tracer, raising the possibility that the effective injection site can be defined quite precisely. Fourth, even with the most restricted injections, the morphology of the labeled axons and axon terminals is clearly demonstrated; this includes boutons en passant, fine collateral branches, and various terminal specializations, all of which can be visualized as well as in the best rapid Golgi preparations. Fifth, when introduced iontophoretically, PHA-L appears to be transported preferentially in the anterograde direction; only rarely is it transported retrogradely. Sixth, PHA-L does not appear to be taken up and transported effectively by fibers of passage. Seventh, there is no discernible degradation of the transported PHA-L with survival times of up to 17 days. Finally, since the transported marker can be demonstrated with either peroxidase or fluorescent antibody techniques, it may be used in conjunction with other neuroanatomical methods. For example, double anterograde labeling experiments can be done using the autoradiographic method along with immunoperoxidase localization of PHA-L, and the retrogradely transported fluorescent dyes can be visualized in the same tissue sections as PHA-L localized with immunofluorescence techniques.
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            Phaseolus vulgaris leuco-agglutinin tracing of intrahypothalamic connections of the lateral, ventromedial, dorsomedial and paraventricular hypothalamic nuclei in the rat.

            Intrahypothalamic connections of the lateral (LHA), ventromedial (VMH), dorsomedial (DMH) and paraventricular (PVN) hypothalamic nuclei were studied with anterograde transport of iontophoretically injected Phaseolus vulgaris leuco-agglutinin and the immunocytochemical detection of labeled structures. The LHA was found to give rise to a minor projection in the VMH, whereas the VMH in reverse maintains few connections with the ventromedial part of the tuberal LHA. Tracer deposits in both the LHA and VMH resulted in anterograde terminal labeling in the DMH. The DMH, in turn, donates a small number of projections to the LHA and VMH. The main projection of the DMH is aimed at the parvocellular paraventricular nucleus. Direct outflow pathways from the VMH to the PVN were not found, but lectin injections in the LHA on the other hand gave rise to terminal labeling in both the parvocellular and magnocellular divisions of the PVN. The PVN in turn was found to give only minor reciprocal projections to the LHA, DMH and VMH. These findings indicate that the main stream of connections in the hypothalamus runs from the LHA and VMH to the DMH, and from the DMH to the PVN. The identified circuitry patterns were discussed with respect to the role of the hypothalamus in the control of homeostasis and metabolic regulation, and more specifically in relation to the modulation of the hormone release from the pancreas and adrenal glands.
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              Axon-sparing lesion of the preoptic area enhances receptivity and diminishes proceptivity among components of female rat sexual behavior.

              Stereotaxic infusion of ibotenic acid deleted neurons in the medial preoptic area (POA) in the ovariectomized female rats. A well-circumscribed lesion was infiltrated by astrocytes; local axons of passage were spared. Following estrogen priming and progesterone supplement, the females with the lesion had higher lordosis quotients than the vehicle-infused controls, when males successfully mounted them. On the other hand, the treatment did not induce solicitation in females with the lesion nor reduced their rejection of male partners. Meanwhile, gradual and persistent suppression of the lordosis reflex followed electrical stimulation through electrodes placed in the POA lesion. Except that the females with the POA lesion needed less estrogen to obtain comparable prestimulation quotients with the controls, the lesioned and control animals responded similarly to the stimulation. Because an adjunct neural transection dorsal to the POA lesion abolished the stimulus-bound suppression of lordosis, the effect was due to the activation of axons of passage that presumably descend from the septum. It is concluded that the POA is the major target for estrogen in eliciting proceptive behavior; local POA neurons as well as septal efferents appear to inhibit the lordosis reflex, the principal receptive component in female rat sexual 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
                January 1999
                27 January 1999
                : 69
                : 1
                : 63-76
                Affiliations
                Neuroscience and Behavior Program, University of Massachusetts, Amherst, Mass., USA
                Article
                54404 Neuroendocrinology 1999;69:63–76
                10.1159/000054404
                9892852
                © 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.

                Page count
                Figures: 8, Tables: 1, References: 69, Pages: 14
                Categories
                Differentiating Effects and Localization ofEstrogen Receptors

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