Regulation of corticotropin-releasing hormone neuronal network activity by noradrenergic stress signals.

Noradrenaline is a neurotransmitter released in response to homeostatic challenge and activates the hypothalamic-pituitary-adrenal axis via stimulation of corticotropin-releasing hormone (CRH) neurons. Here we investigated the mechanism through which noradrenaline regulates activity within the CRH neuronal network. Using a combination of in vitro GCaMP6f Ca 2+ imaging and electrophysiology, we show that noradrenaline induces a robust increase in excitability in a proportion of CRH neurons with many neurons displaying a bursting mode of activity. Noradrenaline-induced activation required α 1 -adrenoceptors and L-type voltage-gated Ca 2+ channels, but not GABA/glutamate synaptic transmission or sodium action potentials. Exposure of mice to elevated corticosterone levels was able to suppress noradrenaline-induced activation. These results provide further insight into the mechanisms by which noradrenaline regulates CRH neural network activity and hence stress responses. KEY POINTS: GCaMP6f Ca 2+ imaging and on-cell patch-clamp recordings reveal that corticotropin-releasing hormone neurons are activated by noradrenaline with many neurons displaying a bursting mode of activity. Noradrenaline-induced activation requires α 1 -adrenoceptors. Noradrenaline-induced Ca 2+ elevations persist after blocking GABA A , AMPA, NMDA receptors and voltage-gated Na + channels. Noradrenaline-induced Ca 2+ elevations require L-type voltage-gated Ca 2+ channels. Corticosterone suppresses noradrenaline-induced excitation.