Spatiotemporal chloride dynamics in hypothalamic CRHPVNneurons

Chloride (Cl - ) dynamics shape inhibitory neurotransmission in the brain. In the hypothalamus, GABA signalling onto corticotropin-releasing hormone (CRH PVN ) neurons can switch from inhibitory to excitatory during stress. Although Cl - fluctuations mediate this stress-dependent shift in GABA signalling, the underlying Cl - dynamics are poorly understood. Here, using a novel optogenetic strategy to load intracellular Cl - using halorhodopsin, we demonstrate that KCC2 rapidly restores Cl - setpoints in CRH PVN neurons from naïve animals, but that this process is slowed following stress. Further, we report that somatic Cl - homeostasis remains intact after stress. Our results strongly support the idea that KCC2 functions primarily to maintain Cl - setpoints and that inhibitory synapses onto dendritic and somatic compartments of CRH PVN neurons are differentially regulated during stress.