Delayed Effects of Brain Irradiation – Part 1: Adrenocortical Axis Dysfunction and Hippocampal Damage in an Adult Rat Model

There is no author summary for this article yet. Authors can add summaries to their articles on ScienceOpen to make them more accessible to a non-specialist audience.

Abstract

Background: Brain irradiation (BI) in humans may cause behavioral changes, cognitive impairment and neuroendocrine dysfunction. The effect of BI on the hypothalamic-pituitary-adrenal (HPA) axis is not fully understood. Objectives: To evaluate the effect of BI on HPA axis responses under basal and stressful conditions as well as following pretreatment with dexamethasone (Dex). Methods: Adult male rats were exposed to whole BI. HPA axis responses were examined at 2, 4, 9 and 20 weeks after BI. Histological evaluations of the irradiated rats and matched controls were conducted at 4 and 20 weeks after BI. Results: In contrast to the control group, the basal and stress-induced corticosterone levels were enhanced at 9 and 20 weeks after BI and the inhibitory effect of Dex was reduced. BI also caused hyposuppression of the adrenocortical response to stress. Histological assessment of the irradiated brains revealed hippocampal atrophy at 20 weeks after BI. The neuronal counts were lower only in the CA1 region of the irradiated brains. BI caused a decrease in the binding capacity of Dex to the hippocampal cytosolic fraction. Conclusions: Enhanced stress-induced HPA axis responses and the reduced effect of Dex suggest that BI has delayed effects on HPA axis responses as manifested by impairment of the negative feedback exerted by glucocorticoids (GCs). The mechanisms underlying these effects of BI are unknown. It is possible that the marked BI-induced damage in the hippocampus, which plays an important role in the regulation of the feedback effect of GCs, may cause abnormal HPA axis responses following BI.

Related collections

Most cited references 33

Record: found
Abstract: found
Article: not found

Adult hippocampal neurogenesis buffers stress responses and depressive behavior

Jason Snyder, Amélie Soumier, Michelle Brewer … (2011)

Summary Glucocorticoids are released in response to stressful experiences and serve many beneficial homeostatic functions. However, dysregulation of glucocorticoids is associated with cognitive impairments and depressive illness 1, 2 . In the hippocampus, a brain region densely populated with receptors for stress hormones, stress and glucocorticoids strongly inhibit adult neurogenesis 3 . Decreased neurogenesis has been implicated in the pathogenesis of anxiety and depression, but direct evidence for this role is lacking 4, 5 . Here we show that adult-born hippocampal neurons are required for normal expression of the endocrine and behavioral components of the stress response. Using transgenic and radiation methods to specifically inhibit adult neurogenesis, we find that glucocorticoid levels are slower to recover after moderate stress and are less suppressed by dexamethasone in neurogenesis-deficient mice compared with intact mice, consistent with a role for the hippocampus in regulation of the hypothalamic-pituitary-adrenal (HPA) axis 6, 7 . Relative to controls, neurogenesis-deficient mice showed increased food avoidance in a novel environment after acute stress, increased behavioral despair in the forced swim test, and decreased sucrose preference, a measure of anhedonia. These findings identify a small subset of neurons within the dentate gyrus that are critical for hippocampal negative control of the HPA axis and support a direct role for adult neurogenesis in depressive illness.

0 comments Cited 490 times – based on 0 reviews      Review now

Bookmark

Record: found
Abstract: found
Article: not found

Central mechanisms of stress integration: hierarchical circuitry controlling hypothalamo–pituitary–adrenocortical responsiveness

James P Herman, Helmer Figueiredo, Nancy K. Mueller … (2003)

Appropriate regulatory control of the hypothalamo-pituitary-adrenocortical stress axis is essential to health and survival. The following review documents the principle extrinsic and intrinsic mechanisms responsible for regulating stress-responsive CRH neurons of the hypothalamic paraventricular nucleus, which summate excitatory and inhibitory inputs into a net secretory signal at the pituitary gland. Regions that directly innervate these neurons are primed to relay sensory information, including visceral afferents, nociceptors and circumventricular organs, thereby promoting 'reactive' corticosteroid responses to emergent homeostatic challenges. Indirect inputs from the limbic-associated structures are capable of activating these same cells in the absence of frank physiological challenges; such 'anticipatory' signals regulate glucocorticoid release under conditions in which physical challenges may be predicted, either by innate programs or conditioned stimuli. Importantly, 'anticipatory' circuits are integrated with neural pathways subserving 'reactive' responses at multiple levels. The resultant hierarchical organization of stress-responsive neurocircuitries is capable of comparing information from multiple limbic sources with internally generated and peripherally sensed information, thereby tuning the relative activity of the adrenal cortex. Imbalances among these limbic pathways and homeostatic sensors are likely to underlie hypothalamo-pituitary-adrenocortical dysfunction associated with numerous disease processes.

0 comments Cited 284 times – based on 0 reviews      Review now

Bookmark

Record: found
Abstract: found
Article: not found

The role of the hippocampus in feedback regulation of the hypothalamic-pituitary-adrenocortical axis.

L. Jacobson, R Sapolsky (1991)

There is considerable, although not entirely consistent, evidence that the hippocampus inhibits most aspects of HPA activity, including basal (circadian nadir) and circadian peak secretion as well as the onset and termination of responses to stress. Although much of the evidence for these effects rests only on the measurement of corticosteroids, recent lesion and implant studies indicate that the hippocampus regulates adrenocortical activity at the hypothalamic level, via the expression and secretion of ACTH secretagogues. Such inhibition results largely from the mediation of corticosteroid feedback, although more work is required to determine whether the hippocampus supplies a tonic inhibitory input in the absence of corticosteroids. It must be noted that the hippocampus is not the only feedback site in the adrenocortical system, since removal of its input only reduces, but does not abolish, the efficacy of corticosteroid inhibition, and since other elements of the axis appear eventually to compensate for deficits in feedback regulation. The importance of other feedback sites is further suggested not only by the presence of corticosteroid receptors in other parts of the brain and pituitary, but also by the improved prediction of CRF levels by combined hypothalamic and hippocampal receptor occupancy. The likelihood of feedback mediated by nonhippocampal sites underscores the need for future work to characterize hippocampal influence on HPA activity in the absence of changes in corticosteroid secretion. However, despite the fact that the hippocampus is not the only feedback site, it is distinguished from most potential feedback sites, including the hypothalamus and pituitary, by its high content of both type I and II corticosteroid receptors. The hippocampus is therefore capable of mediating inhibition over a wide range of steroid levels. The low end of this range is represented by corticosteroid inhibition of basal (circadian nadir) HPA activity. The apparent type I receptor specificity of this inhibition and the elevation of trough corticosteroid levels after hippocampal damage support a role for hippocampal type I receptors in regulating basal HPA activity. It is possible that basal activity is controlled in part through hippocampal inhibition of vasopressin, since the inhibition of portal blood vasopressin correlates with lower levels of hippocampal receptor occupancy, and the expression of vasopressin by some CRF neurons is sensitive to very low corticosteroid levels. At the high end of the physiological range, stress-induced or circadian peak corticosteroid secretion correlates strongly with occupancy of the lower affinity hippocampal type II receptors.(ABSTRACT TRUNCATED AT 400 WORDS)

0 comments Cited 243 times – based on 0 reviews      Review now

Bookmark

All references

Author and article information

Journal

Journal ID (publisher-id): NIM

Journal ID (nlm-ta): Neuroimmunomodulation

Journal ID (doi): 10.1159/issn.1021-7401

Title: Neuroimmunomodulation

Publisher: S. Karger AG

ISSN (Print): 1021-7401

ISSN (Electronic): 1423-0216

Publication date Subscription-year: 2013

Publication date (Print): December 2012

Publication date (Electronic): 23 November 2012

Volume: 20

Issue: 1

Pages: 57-64

Affiliations

^aDepartment of Neurology, The Agnes Ginges Center for Human Neurogenetics, and ^bDepartment of Hematology, Leslie and Michael Gaffin Center for Neuro-Oncology, Hadassah-Hebrew University Medical Center, Jerusalem, Israel

Author notes

*Haim Ovadia, PhD, Department of Neurology, Hadassah University Hospital, POB 12000, Jerusalem 91120 (Israel), E-Mail ovadia@hadassah.org.il

Article

Publisher ID: 342522 Other ID: Neuroimmunomodulation 2013;20:57–64

DOI: 10.1159/000342522

PubMed ID: 23183099

SO-VID: d977b65f-cc26-4d5f-8355-9028a459aa96

License:

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

Date received : 06 June 2012

Date accepted : 09 August 2012

Page count

Figures: 5, Tables: 1, Pages: 8

Comments

Comment on this article

scite_

Cited by 1

The Extent of Irradiation-Induced Long-Term Visceral Organ Damage Depends on Cranial/Brain Exposure
Authors: François-Xavier Boittin, Josiane Denis, Jean-François Mayol …

See all cited by

Most referenced authors 248

See all reference authors

- Version 1

Delayed Effects of Brain Irradiation – Part 1: Adrenocortical Axis Dysfunction and Hippocampal Damage in an Adult Rat Model

Read this article at

Abstract

Related collections

Karger: Endocrinology

Most cited references 33

Adult hippocampal neurogenesis buffers stress responses and depressive behavior

Central mechanisms of stress integration: hierarchical circuitry controlling hypothalamo–pituitary–adrenocortical responsiveness

The role of the hippocampus in feedback regulation of the hypothalamic-pituitary-adrenocortical axis.

Author and article information

Journal

Affiliations

Author notes

Article

History

Page count

Categories

Comments

Comment on this article

Similar content 68

Cited by 1

Most referenced authors 248