Lesions of the Hippocampal Efferent Pathway (Fimbria-Fornix) Do Not Alter Sensitivity of Adrenocorticotropin to Feedback Inhibition by Corticosterone in Rats
| Autor: | Mary F. Dallman, Alison M. Strack, M J Bradbury |
|---|---|
| Rok vydání: | 1993 |
| Předmět: |
Male
Hypothalamo-Hypophyseal System endocrine system medicine.medical_specialty Endocrinology Diabetes and Metabolism medicine.medical_treatment Pituitary-Adrenal System Adrenocorticotropic hormone Biology Hippocampal formation Efferent Pathways Hippocampus Feedback Rats Sprague-Dawley Cellular and Molecular Neuroscience chemistry.chemical_compound Endocrinology Adrenocorticotropic Hormone Anterior pituitary Stress Physiological Corticosterone Internal medicine medicine Animals Receptor Endocrine and Autonomic Systems Adrenalectomy Osmolar Concentration Fornix Rats medicine.anatomical_structure chemistry hormones hormone substitutes and hormone antagonists Glucocorticoid medicine.drug |
| Zdroj: | Neuroendocrinology. 58:396-407 |
| ISSN: | 1423-0194 0028-3835 |
| DOI: | 10.1159/000126569 |
| Popis: | The hypothalamic-pituitary-adrenal (HPA) axis controls the diurnal and stress-induced release of adrenal corticosteroids into the general blood circulation. In turn, corticosteroids inhibit the HPA axis under basal conditions and during stress through occupation of their receptors (types I and II) in the brain by closing a negative feedback loop. The primary site in the brain at which corticosteroids act to inhibit the HPA axis has not been identified. High concentrations of both types of receptors are found in neurons of the hippocampal formation, a structure which has been reported by some, but not others, to control activity within the HPA axis by serving as a major negative feedback site. In many of these past studies, blood was collected after extensive handling or exposure to ether, conditions which do not favor the detection of basal hormone concentrations. To address these controversies, we tested the feedback sensitivity of the anterior pituitary hormone responsible for corticosteroid production, adrenocorticotropin (ACTH), to corticosterone (B), the main corticosteroid in rats, in total fornix- and, as controls, cortex-lesioned rats. All rats were given vascular catheters to avoid any handling-induced differences in plasma B or ACTH when sampling blood. In some experiments, fornix- and cortex-lesioned rats were adrenalectomized and given 1 of 3 doses of exogenous B provided in a subcutaneous pellet to ensure that plasma B was equal in different lesion groups. We hypothesized that if the hippocampal formation were an important site of B-mediated inhibition of the HPA axis, fornix-lesioned rats would have higher plasma B as a result of increased endogenous secretion in the morning or the evening compared to cortex-lesioned rats in rats with adrenal glands. In addition, we hypothesized that adrenalectomized fornix-lesioned rats given the same low to moderate levels of exogenous constant B would have higher basal and stress-induced ACTH than cortex-lesioned rats. Diurnal plasma B was not affected by fornix lesions in intact rats. Moreover, basal ACTH measured in the morning and the evening and stress-induced ACTH was the same in adrenalectomized fornix- and cortex-lesioned rats with constant exogenous B. We conclude, therefore, that information about occupancy of B receptors in the hippocampus carried by the fornix primarily subserves functions which do not directly regulate activity in the HPA axis. |
| Databáze: | OpenAIRE |
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