Chronic interleukin-6 exposure alters metabotropic glutamate receptor-activated calcium signalling in cerebellar Purkinje neurons

Abstract

Chronic central nervous system expression of the cytokine interleukin-6 (IL-6) is thought to contribute to the histopathological, pathophysiological, and cognitive deficits associated with various neurological disorders. However, the effects of chronic IL-6 expression on neuronal function are largely unknown. Previous studies have shown that chronic IL-6 exposure alters intrinsic electrophysiological properties and intracellular Ca2+ signalling evoked by ionotropic glutamate receptor activation in cerebellar Purkinje neurons. In the current study, using primary cultures of rat cerebellum, we investigated the effects of chronic IL-6 exposure on metabotropic glutamate receptor (mGluR)-activated Ca2+ signalling and release from intracellular Ca2+ stores. Chronic exposure (6-10 days) of Purkinje neurons to 500 units/mL IL-6 resulted in elevated resting Ca2+ levels and increased intracellular Ca2+ signals evoked by the group I mGluR agonist (S)-3,5-dihydroxyphenylglycine (DHPG) compared to untreated control neurons. Chronic IL-6 treatment also augmented Ca2+ signals evoked by brief 100 mM K+ depolarization, although to a lesser degree than responses evoked by DHPG. Depleting intracellular Ca2+ stores with sarcoplasmic-endoplasmic reticulum ATPase inhibitors (thapsigargin or cyclopiazonic acid) or blocking ryanodine receptor-dependent release from intracellular stores (using ryanodine) resulted in a greater reduction of DHPG- and K+-evoked Ca2+ signals in chronic IL-6-treated neurons than in control neurons. The present data show that chronic exposure to elevated levels of IL-6, such as occurs in various neurological diseases, alters Ca2+ signalling involving release from intracellular stores. The results support the hypothesis that chronic IL-6 exposure disrupts neuronal function and thereby may contribute to the pathophysiology associated with many neurological diseases.