Spatial profiles of store-dependent calcium release in motoneurones of the nucleus hypoglossus from newborn mouse

Abstract

Hypoglossal motoneurones (HMN) are selectively damaged in both human amyotrophic lateral sclerosis (ALS) and corresponding mouse models of this neurodegenerative disease, a process which has been linked to their low endogenous Ca²⁺ buffering capacity and an exceptional vulnerability to Ca²⁺-mediated excitotoxic events. In this report, we investigated local Ca²⁺ profiles in low buffered HMNs by utilizing multiphoton microscopy, CCD imaging and patch clamp recordings in slice preparations. Bath application of caffeine induced highly localized Ca²⁺ release events, which displayed an initial peak followed by a slow ‘shoulder’ lasting several seconds. Peak amplitudes were paralleled by Ca²⁺-activated, apamin-sensitive K⁺ currents (I_KCa), demonstrating a functional link between Ca²⁺ stores and HMN excitability. The potential involvement of mitochondria was investigated by bath application of CCCP, which collapses the electrochemical potential across the inner mitochondrial membrane. CCCP reduced peak amplitudes of caffeine responses and consequently I_KCa, indicating that functionally intact mitochondria were critical for store-dependent modulation of HMN excitability. Taken together, our results indicate localized Ca²⁺ release profiles in HMNs, where low buffering capacities enhance the role of Ca²⁺-regulating organelles as local determinants of [Ca²⁺]_i. This might expose HMN to exceptional risks during pathophysiological organelle disruptions and other ALS-related, cellular disturbances.