Corticotropin-Releasing Factor Facilitates Epileptiform Activity in the Entorhinal Cortex: Roles of CRF2 Receptors and PKA Pathway

Lalitha Kurada,Chuanxiu Yang,Saobo Lei,Jean-Luc Gaiarsa

doi:10.1371/journal.pone.0088109

Lalitha Kurada, Chuanxiu Yang + Show 2 more

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https://doi.org/10.1371/journal.pone.0088109

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Journal: PloS one	Publication Date: Feb 4, 2014
Citations: 7	License type: CC BY 4.0

Affiliation: University of North Dakota

Abstract

Whereas corticotropin-releasing factor (CRF) has been considered as the most potent epileptogenic neuropeptide in the brain, its action site and underlying mechanisms in epilepsy have not been determined. Here, we found that the entorhinal cortex (EC) expresses high level of CRF and CRF2 receptors without expression of CRF1 receptors. Bath application of CRF concentration-dependently increased the frequency of picrotoxin (PTX)-induced epileptiform activity recorded from layer III of the EC in entorhinal slices although CRF alone did not elicit epileptiform activity. CRF facilitated the induction of epileptiform activity in the presence of subthreshold concentration of PTX which normally would not elicit epileptiform activity. Bath application of the inhibitor for CRF-binding proteins, CRF6-33, also increased the frequency of PTX-induced epileptiform activity suggesting that endogenously released CRF is involved in epileptogenesis. CRF-induced facilitation of epileptiform activity was mediated via CRF2 receptors because pharmacological antagonism and knockout of CRF2 receptors blocked the facilitatory effects of CRF on epileptiform activity. Application of the adenylyl cyclase (AC) inhibitors blocked CRF-induced facilitation of epileptiform activity and elevation of intracellular cyclic AMP (cAMP) level by application of the AC activators or phosphodiesterase inhibitor increased the frequency of PTX-induced epileptiform activity, demonstrating that CRF-induced increases in epileptiform activity are mediated by an increase in intracellular cAMP. However, application of selective protein kinase A (PKA) inhibitors reduced, not completely blocked CRF-induced enhancement of epileptiform activity suggesting that PKA is only partially required. Our results provide a novel cellular and molecular mechanism whereby CRF modulates epilepsy.

Highlights

Epilepsy is a common neurological disorder characterized by excessive excitation of brain regions including the entorhinal cortex (EC), hippocampus and amygdala
Both CRF1 and CRF2 receptors are primarily coupled to Gs proteins resulting in activation of adenylyl cyclase (AC) and an increase in the level of intracellular cyclic AMP that activates protein kinase A (PKA) [15,16] CorticotropinReleasing Factor (CRF) receptors have the ability to interact with other G-protein systems including Gq, Gi, Go, Gi1/2, and Gz [17] to modulate protein kinase B, protein kinase C, mitogenactivated protein kinases and intracellular Ca2+ concentrations in a tissue-specific manner [15,16]
What is the action site in the brain for the effects of CRF on epilepsy because intracerebroventricular application of CRF can influence almost all the brain regions? Which type of CRF receptors is involved in CRF-mediated facilitation of epilepsy? What are signaling molecules required for CRF-induced facilitation of epilepsy? Since the EC is an important structure involved in epilepsy and mRNA of CRF receptors has been detected in the EC by in situ hybridization [14], we examined the effects of CRF on picrotoxin (PTX)-induced epileptiform activity recorded from entorhinal slices

Summary

Introduction

Epilepsy is a common neurological disorder characterized by excessive excitation of brain regions including the entorhinal cortex (EC), hippocampus and amygdala. CRF1 receptors are expressed in pituitary, cerebellar cortex, neocortex, median eminence, and sensory relay nuclei [9,10,11] whereas CRF2 receptors are localized mostly to subcortical regions including the septum, amygdala, hippocampus and EC [12,13,14] Both CRF1 and CRF2 receptors are primarily coupled to Gs proteins resulting in activation of adenylyl cyclase (AC) and an increase in the level of intracellular cyclic AMP (cAMP) that activates protein kinase A (PKA) [15,16] CRF receptors have the ability to interact with other G-protein systems including Gq, Gi, Go, Gi1/2, and Gz [17] to modulate protein kinase B, protein kinase C, mitogenactivated protein kinases and intracellular Ca2+ concentrations in a tissue-specific manner [15,16]. The biological actions of CRF are likely to be mediated by these CRF receptors and their intracellular signals

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