Ethanol Reversal of Oxycodone Tolerance in Dorsal Root Ganglia Neurons

Abstract

Oxycodone is a semisynthetic opioid compound that is widely prescribed, used, and abused today, and has a well-established role in shaping the current opioid epidemic. Previously, we have shown that tolerance develops to the antinociceptive and respiratory depressive effects of oxycodone in mice, and that a moderate dose of acute ethanol or a protein kinase C (PKC) inhibitor reversed that tolerance. To investigate further if tolerance was occurring through neuronal mechanisms, our aims for this study were to assess the effects of acute and prolonged oxycodone in isolated dorsal root ganglia (DRG) neurons and to determine if this tolerance was reversed by either ethanol or a PKC inhibitor. We found that an acute exposure to 3 M oxycodone reduced neuronal excitability, as measured by increased threshold potentials and reduced action potential amplitude, without eliciting measurable changes in resting membrane potential. Exposure to 10M oxycodone for 18-24 hours prevented oxycodone's effect on neuronal excitability, indicative of tolerance development. The development of opioid tolerance was mitigated in DRG neurons from -arrestin 2 knockout mice. Oxycodone tolerance was reversed in isolated DRG neurons by the acute application of either ethanol (20 mM) or the PKC inhibitor, bisindolylmaleimide XI hydrochloride (Bis XI), when a challenge of 3M oxycodone significantly reduced neuronal excitability following prolonged exposure. Through these studies, we concluded that oxycodone acutely reduced neuronal excitability, tolerance developed to this effect, and reversal of that tolerance occurred at the level of a single neuron, suggesting that reversal of oxycodone tolerance by either ethanol or Bis XI involves cellular mechanisms.

Rapid tolerance to morphine in the myenteric neurons of the small intestine is independent of β-arrestin-2 and mediated by PKC

“…Morphine, in particular, is known to preferentially induce PKC-mediated MOR phosphorylation, which has been implicated in the mechanism of in vivo tolerance to antinociception (Smith et al, 1999(Smith et al, , 2006Inoue and Ueda, 2000;Hua et al, 2002;Kliewer et al, 2019) and cellular tolerance in DRG (Jacob et al, 2018) and locus coeruleus neurons (Levitt and Williams, 2012;Arttamangkul et al, 2018). The present study showed that PKC mediates morphine tolerance to small intestinal transit in vivo and in myenteric plexus neurons.…”

Role of Acetaldehyde in Ethanol Reversal of Tolerance to Morphine-Induced Respiratory Depression in Mice

“…All data are presented as mean ± s.e.m. Statistical comparison made by One-way ANOVA (C) with Bonferroni’s comparison (F (DFn, DFd—F ( 3 , 20 ) = 0.570). * indicates p < 0.05 as shown.…”

“…We have previously reported that in mice a low dose of ethanol, which by itself did not depress respiration, rapidly reversed tolerance to both morphine-and oxycodone-induced respiratory depression as well as tolerance to their antinociceptive effects (16)(17)(18)(19)(20) but did not reverse tolerance induced by methadone (17). We also observed that a low concentration of ethanol (20 mM) could reverse μ opioid receptor (MOR) desensitization and cellular tolerance to morphine in locus coeruleus (LC) neurons as well as tolerance to oxycodone in dorsal root ganglion neurons (20,21). Ethanol also reduced the phosphorylation of MOR induced by morphine (21).…”

Prolonged ethanol administration prevents the development of tolerance to morphine-induced respiratory depression

“…We have previously reported that in mice acute, low doses of ethanol rapidly reverse tolerance to the respiratory depressant and analgesic effects of morphine and oxycodone (Hull et al, 2013, Hill et al, 2016, Jacob et al, 2017, Hill et al, 2018 but do not reverse tolerance induced by methadone (Hill et al, 2016). Reversal of morphine tolerance by a low concentration of ethanol (20 mM) can also be observed at the single neuron level in vitro (Llorente et al, 2013, Jacob et al, 2018 indicating that the effect is at the level of cells -opioid receptors to reverse receptor desensitization, rather than an action to alter drug disposition in the brain.…”