Cocaine Directly Inhibits α6-Containing Nicotinic Acetylcholine Receptors in Human SH-EP1 Cells and Mouse VTA DA Neurons.

Dejie Chen,Zegang Ma,Taleen Der-Ghazarian,Paul Whiteaker,Jason Brek Eaton,Yuanbing Huang,Yongchang Chang,Janet Neisewander,Jie Wu,Quanxi Su,Xiaokuang Ma,Ming Gao,Fenfei Gao

doi:10.3389/fphar.2019.00072

Abstract

Alpha6-containing nicotinic acetylcholine receptors are primarily found in neurons of the midbrain dopaminergic (DA) system, suggesting these receptors are potentially involved in drug reward and dependence. Here, we report a novel effect that cocaine directly inhibits α6N/α3Cβ2β3-nAChR (α6*-nAChRs) function. Human α6*-nAChRs were heterologously expressed within cells of the SH-EP1 cell line for functional characterization. Mechanically dissociated DA neurons from mouse ventral tegmental area (VTA) were used as a model of presynaptic α6*-nAChR activation since this method preserves terminal boutons. Patch-clamp recordings in whole-cell configuration were used to measure α6*-nAChR function as well as evaluate the effects of cocaine. In SH-EP1 cells containing heterologously expressed human α6*-nAChRs, cocaine inhibits nicotine-induced inward currents in a concentration-dependent manner with an IC50 value of 30 μM. Interestingly, in the presence of 30 μM cocaine, the maximal current response of the nicotine concentration-response curve is reduced without changing nicotine’s EC50 value, suggesting a noncompetitive mechanism. Furthermore, analysis of whole-cell current kinetics demonstrated that cocaine slows nAChR channel activation but accelerates whole-cell current decay time. Our findings demonstrate that cocaine-induced inhibition occurs solely with bath application, but not during intracellular administration, and this inhibition is not use-dependent. Additionally, in Xenopus oocytes, cocaine inhibits both α6N/α3Cβ2β3-nAChRs and α6M211L/α3ICβ2β3-nCAhRs similarly, suggesting that cocaine may not act on the α3 transmembrane domain of chimeric α6N/α3Cβ2β3-nAChR. In mechanically isolated VTA DA neurons, cocaine abolishes α6*-nAChR-mediated enhancement of spontaneous inhibitory postsynaptic currents (sIPSCs). Collectively, these studies provide the first evidence that cocaine directly inhibits the function of both heterologously and naturally expressed α6*-nAChRs. These findings suggest that α6*-nAChRs may provide a novel pharmacological target mediating the effects of cocaine and may underlie a novel mechanism of cocaine reward and dependence.

Highlights

Cocaine is a widely used psychostimulant drug, and its abuse is associated with multiple physical and psychiatric sequelae
The difference between pretreatment and without pretreatment was statistically significant. These results suggest that acute cocaine reversibly inhibits α6*-nicotinic acetylcholine receptor (nAChR)-mediated currents
This study suggests that cocaine directly inhibits α6*-nAChR function, which is a novel finding

Summary

Introduction

Cocaine is a widely used psychostimulant drug, and its abuse is associated with multiple physical and psychiatric sequelae. Cocaine use disorder leads to a series of neurological disorders such as seizures, optic neuropathy, cerebral infarction, subarachnoid and intracerebral hemorrhage, multifocal cerebral ischemia, and cerebral atrophy, as well as cardiac dysfunction including myocardial infarction triggering global brain ischemia and edema (Moorman et al, 2013; Bodmer et al, 2014; Cagienard et al, 2014; Sharma et al, 2014; Sordo et al, 2014). Despite this broad foundation of clinical knowledge, the detailed mechanisms underlying cocaine-induced effects in the brain remain largely unknown

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