Mitochondrial Ca uptake by the MCU facilitates pyramidal neuron excitability and metabolism during action potential firing.

Neuronal activation is fundamental to information processing by the brain and requires mitochondrial energy metabolism. Mitochondrial Ca uptake by the mitochondrial Ca uniporter (MCU) has long been implicated in the control of energy metabolism and intracellular Ca signalling, but its importance to neuronal function in the brain remains unclear. Here, we used in situ electrophysiology and two-photon imaging of mitochondrial Ca, cytosolic Ca, and NAD(P)H to test the relevance of MCU activation to pyramidal neuron Ca signalling and energy metabolism during action potential firing. We demonstrate that mitochondrial Ca uptake by the MCU is tuned to enhanced firing rate and the strength of this relationship varied between neurons of discrete brain regions. MCU activation promoted electron transport chain activity and chemical reduction of NAD to NADH. Moreover, Ca buffering by mitochondria attenuated cytosolic Ca signals and thereby reduced the coupling between activity and the slow afterhyperpolarization, a ubiquitous regulator of excitability. Collectively, we demonstrate that the MCU is engaged by accelerated spike frequency to facilitate neuronal activity through simultaneous control of energy metabolism and excitability. As such, the MCU is situated to promote brain functions associated with high frequency signalling and may represent a target for controlling excessive neuronal activity.