Protein Kinase C-Dependent Effects of Neurosteroids on Synaptic GABAA Receptor Inhibition Require the δ-Subunit

Abstract

The dorsal motor nucleus of the vagus (DMV) contains preganglionic motor neurons important for interpreting sensory input from the periphery, integrating that information, and coding the appropriate parasympathetic (vagal) output to target organs. Despite the critical role of hormonal regulation of vagal motor output, few studies examine the role of neurosteroids in the regulation of the DMV. Of the few examinations, no studies have investigated the potential impact of allopregnanolone (Allo), a neuroactive progesterone-derivative, in the regulation of neurotransmission on the DMV. Since DMV neuronal function is tightly regulated by GABAA receptor activity and Allo is an endogenous GABAA receptor ligand, the present study used in vitro whole cell patch clamp to investigate whether Allo alters GABAergic neurotransmission to DMV neurons. Although Allo did not influence GABAergic neurotransmission during initial application (5–20 min), a TTX-insensitive prolongment of decay time and increase in frequency of GABAergic currents was established after Allo was removed from the bath for at least 30 min (LtAllo). Inhibition of protein kinase C (PKC) abolished these effects, suggesting that PKC is largely required to mediate Allo-induced inhibition of the DMV. Using mice that lack the δ-subunit of the GABAA receptor, we further confirmed that PKC-dependent activity of LtAllo required this subunit. Allo also potentiated GABAA receptor activity after a repeated application of δ-subunit agonist, suggesting that the presence of Allo encodes stronger δ-subunit-mediated inhibition over time. Using current clamp recording, we demonstrated that LtAllo-induced inhibition is sufficient to decrease action potential firing and excitability within DMV neurons. We conclude that the effects of LtAllo on GABAergic inhibition are dependent on δ-subunit and PKC activation. Taken together, DMV neurons can undergo long lasting Allo-dependent GABAA receptor plasticity.

Zolpidem Profoundly Augments Spared Tonic GABAAR Signaling in Dentate Granule Cells Ipsilateral to Controlled Cortical Impact Brain Injury in Mice

“…Male mice were tested in this study because cycling female hormones, e.g., estrogen and progesterone, robustly alter GABA A R signaling and require dedicated examination of ovariectomized (OVX) females and OVX-treated females given select hormone replacement and/or pharmacological modification of key biochemical steps in ovarian hormone pathways. This biology has been studied by our labs ( Littlejohn and Boychuk, 2021 ) and others ( Twyman and Macdonald, 1992 ; Fáncsik et al, 2000 ; Wohlfarth et al, 2002 ; Griffiths and Lovick, 2005 ; Maguire and Mody, 2007 ; Abramian et al, 2014 ; Carver et al, 2014 ). All procedures were approved by the University of Kentucky Animal Care and Use Committee (Assurance #A3336-01) and adhered to NIH guidelines for the care and use of laboratory animals.…”

Gabrb2 knock-out mice exhibit double-directed PMDD-like symptoms: GABAAR subunits, neurotransmitter metabolism disruption, and allopregnanolone binding

“…Previous research indicates that corticotropin-releasing hormone (CRH) neurons are modulated by neurosteroid tetrahydrodeoxycorticosterone (THDOC) and act on GABAARcontaining δ subunits which share close associations with anxiety-like behaviors [32]. The δ-Subunit is necessary for Protein Kinase C-dependent effects of neurosteroids on synaptic GABA A receptor inhibition [33]. Besides, GABAA(δ)R may promote fear extinction via a route relying on non-synaptic plasticity [34].…”

The roles of RACK1 in the pathogenesis of Alzheimer's disease

“…Targeting the activated PKC to GABA A Rs by RACK1 is critical for regulating GABA A currents through the 5HT2-PKC signaling pathway. A large number of compounds that interact with GABA receptors, such as neurosteroids [ 74 ] , alcohol [ 75 ] and sodium valproate [ 76 ] , work through the RACK1/PKC-βⅡ-dependent pathway. In the prefrontal cortex, Aβ impairs GABAergic transmission mediated by muscarinic receptors; however, overexpression of RACK1 rescues this damage [ 45 ] .…”