Acute neurosteroid treatment with allopregnanolone enhances dorsal vagal motor neuron inhibition

Abstract

Neurons in the dorsal motor nucleus of the vagus (DMV) comprise the preganglionic parasympathetic motor output to much of the viscera and critically contribute to autonomic regulation of energy homeostasis. DMV neuron function is tightly regulated by gamma‐aminobutyric (GABA) input to GABAA receptors, which inhibits neuronal excitability. Extrasypnatically localized GABAA receptors, primarily containing δ‐subunits, respond to ambient GABA, setting the tonic inhibitory tone in DMV neurons. Allopregnanolone is a centrally and peripherally produced neuroactive steroid metabolite which readily crosses the blood brain barrier and is a potent allosteric activator of GABAA receptors. Outside of the DMV, allopregnanolone has been shown to increase inhibitory tonic current in a GABAA‐δ dependent manner. DMV neurons have significant tonic inhibition. These currents are largely mediated by the GABAA receptors containing the δ‐subunit. However, no studies to date have investigated the potential for allopregnanolone to induce changes in GABAergic signaling to DMV neurons. Therefore, we hypothesized that acute allopregnanolone exposure increases GABAA receptor mediated inhibition in DMV neurons through a GABAAR δ‐subunit dependent manner. To test this hypothesis, we incubated brainstem slices in allopregnanolone (100nM) or vehicle containing artificial cerebral spinal fluid (ACSF) for 30 minutes. We then analyzed GABAA receptor mediated inhibition in DMV neurons at 30, 60, and 120 minutes following the completion of this incubation. We examined both modalities of GABAA receptor inhibition, phasic and tonic using the specific GABAA antagonist bicuculline (BIC) and wholecell patch‐clamp electrophysiology. Allopregnanolone treatment increased most measures of inhibition in DMV neuron at 30 minutes, including spontaneous inhibitory postsynaptic current (sIPSC) decay time and BIC‐sensitive tonic current. DMV neurons from slices incubated in either allopregnanolone or control ACSF were probed for choline acetyltransferase and GABAA‐δ subunit expression using immunohistochemistry. Brief exposure to allopregnanolone transiently potentiates GABAA receptor response to ambient GABA. Allopregnanolone may play an important role in dynamically modulating vagal inhibition in models of disease.Support or Funding InformationAmerican Heart Association Grant# 16SDG26590000 and NIH Grant# 5T32HL007446‐37This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.