Year of Publication

2001

Document Type

Dissertation

College

Medicine

Department

Anatomy and Neurobiology

First Advisor

James P. Herman

Abstract

Glucocorticoid activation of two types of adrenocorticosteroid receptors (ACRs), themineralocorticoid receptor (MR) and the glucocorticoid receptor (GR), influences hippocampalneuron vulnerability to injury. Excessive activation of GR may compromise hippocampalneuron survival after several types of challenge including ischemic, metabolic, and excitotoxicinsults. In contrast, MR prevents adrenalectomy-induced loss of granule neurons in the dentategyrus. The present thesis addresses the respective roles of MR and GR in modulating neuronalsurvival following two forms of neuronal injury, excitotoxicity and traumatic brain injury. MaleSprague-Dawley rats were pretreated with MR antagonist spironolactone or GR antagonistmifepristone (RU486) and subsequently injected with kainic acid, an excitotoxic glutamateanalog, or injured with a controlled cortical impact. Twenty-four hours following injury,hippocampal neuron survival was measured to test the hypotheses that MR blockade wouldendanger and GR blockade would protect hippocampal neurons following injury. MessengerRNA levels of viability-related genes including bcl-2, bax, p53, BDNF, and NT-3 were alsomeasured to test the hypothesis that ACR regulation of these genes wouldcorrelate with neuronal survival. In addition, ACR mRNA levels were measured followingreceptor blockade and injury to test the hypothesis that glucocorticoid signaling is alteredfollowing neuronal injury via regulation of ACR expression.Mineralocorticoid receptor blockade with spironolactone increased neuronal vulnerability toexcitotoxic insult in hippocampal field CA3, and GR blockade with RU486 prevented neuronalloss after traumatic brain injury in field CA1. These results are consistent with the hypothesesthat MR protects and GR endangers hippocampal neurons. Adrenocorticosteroid receptorblockade decreased mRNA levels of the anti-apoptotic gene bcl-2 in select regions of uninjuredhippocampus, yet ACR regulation of bcl-2 did not consistently correspond with measures ofneuronal survival after injury. Kainic acid decreased MR mRNA levels in CA1 and CA3, whileboth kainic acid and controlled cortical impact dramatically decreased GR mRNA levels indentate gyrus. These data suggest that injury modulation of glucocorticoid signaling throughregulation of ACR expression may influence hippocampal neuron viability following injury.

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