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Altered chloride homeostasis removes synaptic inhibitory constraint of the stress axis

Abstract

In mammals, stress elicits a stereotyped endocrine response that requires an increase in the activity of hypothalamic parvocellular neuroendocrine neurons. The output of these cells is normally constrained by powerful GABA-mediated synaptic inhibition. We found that acute restraint stress in rats released the system from inhibitory synaptic drive in vivo by down-regulating the transmembrane anion transporter KCC2. This manifested as a depolarizing shift in the reversal potential of GABAA-mediated synaptic currents that rendered GABA inputs largely ineffective. Notably, repetitive activation of GABA synapses after stress resulted in a more rapid collapse of the anion gradient and was sufficient to increase the activity of neuroendocrine cells. Our data indicate that hypothalamic neurons integrate psychological cues to mount the endocrine response to stress by regulating anion gradients.

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Figure 1: Acute stress reduces the strength of synaptic GABAA-mediated inhibition.
Figure 2: KCC2 regulates Cl homeostasis.
Figure 3: Stress-induced shift in EGABA is not associated with a change in protein expression and can be mimicked by α1 adrenoceptor activation.
Figure 4: Effects of repetitive synaptic stimulation on GABA IPSCs and postsynaptic activity.

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Acknowledgements

We thank members of the Bains laboratory, Q.J. Pittman and W.H. Mehaffey for comments and thoughtful discussion regarding the manuscript. We also thank C. Sank for assistance with microinjections and corticosterone assays. S.A.H. was supported by a studentship from the Alberta Heritage Foundation for Medical Research. J.I.W. is supported by a T. Chen Fong Scholarship from the Hotchkiss Brain Institute and scholarships from the Faculty of Graduate Studies, University of Calgary and the Government of Alberta. J.S.B. is an Alberta Heritage Foundation for Medical Research Senior Scholar. This work is funded by an Operating Grant from the Canadian Institutes for Health Research.

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S.A.H. conducted the in vivo stress and corticosteroids measurements, the EGABA, PPR and repetitive synaptic activation experiments, analyzed the data and wrote the manuscript. J.I.W. conducted the cell-attached experiments in Figure 1, as well as performing some gramicidin recordings. E.U.K. designed and performed immunoblot experiments and analyses. J.S.B. designed the experiments, analyzed the data, prepared the manuscript and supervised the project.

Corresponding author

Correspondence to Jaideep S Bains.

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Hewitt, S., Wamsteeker, J., Kurz, E. et al. Altered chloride homeostasis removes synaptic inhibitory constraint of the stress axis. Nat Neurosci 12, 438–443 (2009). https://doi.org/10.1038/nn.2274

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