Characterization of the role of corticotropin-releasing hormone and opioid peptides on hippocampal neurodegeneration and functional recovery following global cerebral ischemia in rats

Abstract

The present thesis aimed to further characterize the role of CRH and opioid peptides and receptors in the modulation of neuronal damage induced by an ischemic insult. This thesis also evaluated the possibility that CRH effects may be partly opioid-mediated. Finally, behavioral assessment were performed in order to determine whether neuronal survival was accompanied by an improvement of behavioral deficits. First, we determined whether administration of CRH prior to global cerebral ischemia in rats altered CA1 neuronal degeneration in vivo and open field activity. The impact of the selective blockade of CRH receptors, using the antagonist alpha-helical CRH (9-41), was also investigated. Having shown CRH-induced neuronal protection when administered prior to ischemia, a second objective was to determine whether administration of CRH at specific post-ischemic intervals could also induce protection, further elucidating the time window of its action. CRH was effective to reduce ischemia-induced neuronal damage and significantly improved spatial memory impairments in a radial maze when administered 8h following ischemia in rats. Then, we examined whether the selective blockade of kappa- and delta-opioid receptors (KOR and DOR), using nor-binaltrophimine and naltrindole, respectively, prior CRH administration had an impact on CRH-induced neuronal protection against global ischemic damage, showing interaction between these two peptidergic systems. Our findings revealed neuronal protection conferred by the opioid kappa and delta receptor agonists, and a reduction of CRH-induced neuronal protection when these opioidergic systems were blocked prior CRH administration. We also confirmed the neuroprotective actions of CRH in vitro and determined the impact of pre- and post-CRH administration on cortical neurons injury following a potassium cyanide (KCN)-induced insult in rat primary cortical neurons. We also examined whether CRH neuroprotective effects on KCN-induced injury were altered by prior blockade of either CRH receptors, DOR or KOR. Finally, mRNA expression of enkephalin, dynorphin and DOR and KOR in CRH-treated primary cortical neurons was assessed using reverse transcription polymerase-chain reaction. Together, this series of studies suggest an important role of CRH as a modulator of neuronal survival, and propose this action to be induced via interaction of CRH with opioidergic systems.