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

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 IC 50 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 EC 50 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.

Distinct sub-second dopamine signaling in dorsolateral striatum measured by a genetically-encoded fluorescent sensor

“…This is consistent with previous findings using FSCV and is due to off target cocaine inhibition of nAChRs, which contribute significantly to striatal dopamine release. This off target cocaine inhibition of nAChRs was first shown electrophysiologically 16,17 and then with striatal FSCV 18,19 .…”

Nicotine Modifies Responding for Cocaine in a Concurrent Rodent Self-administration Model

“…Nicotine increases mesolimbic dopamine release via nicotinic acetylcholine receptors (nAChRs), and there is evidence that suggests cocaine acts as a nAChR antagonist (Acevedo-Rodriguez, Zhang, Zhou et al, 2014; Chen, Gao, Ma et al, 2019). Therefore nAChRs may represent a target of interest for future studies of combined cocaine and nicotine self-adminsitration.…”

Cocaine potently blocks neuronal α3β4 nicotinic acetylcholine receptors in SH-SY5Y cells

“…Behavioral experiments showed that local injection of a selective α 4 β 2 nAChR antagonist (dihydro-β-erythroidine, DHβE) into the ventral tegmental area (VTA) prevents cocaine-induced locomotor activity [ 14 ], while the α 7 -selective antagonist methyllycaconitine (MLA) did not alter cocaine-induced behavioral sensitization [ 15 ]. Recently, nAChRs containing the α 6 subunit (α 6 * nAChRs), but not those containing the α 4 subunit, were shown to play a role in the induction of cocaine-conditioned reward [ 16 ], and we have recently reported that cocaine blocks human α 6 * nAChRs expressed in human SH-EP1 cells [ 17 ]. The α 3 β 4 nAChR may also be an important target that mediates the effects of cocaine.…”