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      Expressions of Hippocampal Mineralocorticoid Receptor (MR) and Glucocorticoid Receptor (GR) in the Single-Prolonged Stress-Rats

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          Abstract

          Post-traumatic stress disorder (PTSD) is a stress-related mental disorder caused by traumatic experience. Single-prolonged stress (SPS) is one of the animal models proposed for PTSD. Rats exposed to SPS showed enhanced inhibition of the hypothalamo-pituitary-adrenal (HPA) axis, which has been reliably reproduced in patients with PTSD. Mineralocorticoid receptor (MR) and glucocorticoid receptor (GR) in the hippocampus regulate HPA axis by glucocorticoid negative feedback. Abnormalities in negative feedback are found in PTSD, suggesting that GR and MR might be involved in the pathophysiology of these disorders.

          In the present study, we performed immunohistochemistry and western blotting to examine the changes in hippocampal MR- and GR-expression after SPS. Immunohistochemistry revealed decreased MR- and GR-immunoreactivity (ir) in the CA1 of hippocampus in SPS animals. Change in GR sub-distribution was also observed, where GR-ir was shifted from nucleus to cytoplasm in SPS rats. Western blotting showed that SPS induced significantly decreased MR- and GR-protein in the whole hippocampus, although the degree of decreased expression of both receptors was different. Meanwhile, we also found the MR/GR ratio decreased in SPS rats. In general, SPS induced down-regulation of MR- and GR-expression. These findings suggest that MR and GR play critical roles in affecting hippocampal function. Changes in MR/GR ratio may be relevant for behavioral syndrome in PTSD.

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          Brain corticosteroid receptor balance in health and disease.

          E. de Kloet, E Vreugdenhil, M. Oitzl … (1998)
          In this review, we have described the function of MR and GR in hippocampal neurons. The balance in actions mediated by the two corticosteroid receptor types in these neurons appears critical for neuronal excitability, stress responsiveness, and behavioral adaptation. Dysregulation of this MR/GR balance brings neurons in a vulnerable state with consequences for regulation of the stress response and enhanced vulnerability to disease in genetically predisposed individuals. The following specific inferences can be made on the basis of the currently available facts. 1. Corticosterone binds with high affinity to MRs predominantly localized in limbic brain (hippocampus) and with a 10-fold lower affinity to GRs that are widely distributed in brain. MRs are close to saturated with low basal concentrations of corticosterone, while high corticosterone concentrations during stress occupy both MRs and GRs. 2. The neuronal effects of corticosterone, mediated by MRs and GRs, are long-lasting, site-specific, and conditional. The action depends on cellular context, which is in part determined by other signals that can activate their own transcription factors interacting with MR and GR. These interactions provide an impressive diversity and complexity to corticosteroid modulation of gene expression. 3. Conditions of predominant MR activation, i.e., at the circadian trough at rest, are associated with the maintenance of excitability so that steady excitatory inputs to the hippocampal CA1 area result in considerable excitatory hippocampal output. By contrast, additional GR activation, e.g., after acute stress, generally depresses the CA1 hippocampal output. A similar effect is seen after adrenalectomy, indicating a U-shaped dose-response dependency of these cellular responses after the exposure to corticosterone. 4. Corticosterone through GR blocks the stress-induced HPA activation in hypothalamic CRH neurons and modulates the activity of the excitatory and inhibitory neural inputs to these neurons. Limbic (e.g., hippocampal) MRs mediate the effect of corticosterone on the maintenance of basal HPA activity and are of relevance for the sensitivity or threshold of the central stress response system. How this control occurs is not known, but it probably involves a steady excitatory hippocampal output, which regulates a GABA-ergic inhibitory tone on PVN neurons. Colocalized hippocampal GRs mediate a counteracting (i.e., disinhibitory) influence. Through GRs in ascending aminergic pathways, corticosterone potentiates the effect of stressors and arousal on HPA activation. The functional interaction between these corticosteroid-responsive inputs at the level of the PVN is probably the key to understanding HPA dysregulation associated with stress-related brain disorders. 5. Fine-tuning of HPA regulation occurs through MR- and GR-mediated effects on the processing of information in higher brain structures. Under healthy conditions, hippocampal MRs are involved in processes underlying integration of sensory information, interpretation of environmental information, and execution of appropriate behavioral reactions. Activation of hippocampal GRs facilitates storage of information and promotes elimination of inadequate behavioral responses. These behavioral effects mediated by MR and GR are linked, but how they influence endocrine regulation is not well understood. 6. Dexamethasone preferentially targets the pituitary in the blockade of stress-induced HPA activation. The brain penetration of this synthetic glucocorticoid is hampered by the mdr1a P-glycoprotein in the blood-brain barrier. Administration of moderate amounts of dexamethasone partially depletes the brain of corticosterone, and this has destabilizing consequences for excitability and information processing. 7. The set points of HPA regulation and MR/GR balance are genetically programmed, but can be reset by early life experiences involving mother-infant interaction. 8. (ABSTRACT TRUNCATED)
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            The potential role of hypocortisolism in the pathophysiology of stress-related bodily disorders

            Christine Heim, Ulrike Ehlert, Dirk Hellhammer (2000)
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              The potential role of hypocortisolism in the pathophysiology of stress-related bodily disorders.

              C. Heim, U Ehlert, D H Hellhammer (2000)
              Representing a challenge for current concepts of stress research, a number of studies have now provided convincing evidence that the adrenal gland is hypoactive in some stress-related states. The phenomenon of hypocortisolism has mainly been described for patients, who experienced a traumatic event and subsequently developed post-traumatic stress disorder (PTSD). However, as presented in this review, hypocortisolism does not merely represent a specific correlate of PTSD, since similar findings have been reported for healthy individuals living under conditions of chronic stress as well as for patients with several bodily disorders. These include chronic fatigue syndrome, fibromyalgia, other somatoform disorders, rheumatoid arthritis, and asthma, and many of these disorders have been related to stress. Although hypocortisolism appears to be a frequent and widespread phenomenon, the nature of the underlying mechanisms and the homology of these mechanisms within and across clinical groups remain speculative. Potential mechanisms include dysregulations on several levels of the hypothalamic-pituitary adrenal axis. In addition, factors such as genetic vulnerability, previous stress experience, coping and personality styles may determine the manifestation of this neuroendocrine abnormality. Several authors proposed theoretical concepts on the development or physiological meaning of hypocortisolism. Based on the reviewed findings, we propose that a persistent lack of cortisol availability in traumatized or chronically stressed individuals may promote an increased vulnerability for the development of stress-related bodily disorders. This pathophysiological model may have important implications for the prevention, diagnosis and treatment of the classical psychosomatic disorders.
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                Author and article information

                Journal
                Journal ID (nlm-ta): Acta Histochem Cytochem
                Journal ID (publisher-id): AHC
                Title: Acta Histochemica et Cytochemica
                Publisher: Japan Society of Histochemistry and Cytochemistry (Tokyo, Japan )
                ISSN (Print): 0044-5991
                ISSN (Electronic): 1347-5800
                Publication date (Print): 28 August 2008
                Publication date (Electronic): 15 July 2008
                Volume: 41
                Issue: 4
                Pages: 89-95
                Affiliations
                [1 ]Department of Histology and Embryology, Basic Medical College, China Medical University, Shenyang, China
                Author notes
                Correspondence to: Shi Yuxiu, Department of Histology and Embryology, Basic Medical College, China Medical University, Shenyang, 110001, China. E-mail: shiyuxiu@ 123456yahoo.com.cn
                Article
                Publisher ID: AHC08013
                DOI: 10.1267/ahc.08013
                PMC ID: 2532603
                PubMed ID: 18787639
                SO-VID: 8a53537a-9090-47fa-b3c2-e060458afb62
                Copyright © Copyright © 2008 AHC
                License:

                This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

                History
                Date received : 3 April 2008
                Date accepted : 2 June 2008
                Categories
                Subject: Regular Article

                ScienceOpen disciplines: Clinical chemistry
                Keywords: post-traumatic stress disorder,hippocampus,mineralocorticoid receptor,glucocorticoid receptor
                Data availability:
                ScienceOpen disciplines: Clinical chemistry
                Keywords: post-traumatic stress disorder, hippocampus, mineralocorticoid receptor, glucocorticoid receptor

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