Tolerance to Morphine-Induced Inhibition of TTX-R Sodium Channels in Dorsal Root Ganglia Neurons Is Modulated by Gut-Derived Mediators

Abstract

SUMMARYIn the clinical setting, analgesic tolerance is a primary driver of diminished pain control and opioid dose escalations. Integral to this process are primary afferent sensory neurons, the first-order components of nociceptive sensation. Here, we characterize the factors modulating morphine action and tolerance in mouse small diameter dorsal root ganglia (DRG) neurons. We demonstrate that acute morphine inactivates tetrodotoxin-resistant (TTX-R) Na+ channels in these cells. Chronic exposure resulted in tolerance to this effect, which was prevented by treatment with oral vancomycin. Using colonic supernatants, we further show that mediators in the gut microenvironment of mice with chronic morphine exposure can induce tolerance and hyperexcitability in naive DRG neurons. Tolerance (but not hyperexcitability) in this paradigm was mitigated by oral vancomycin treatment. These findings collectively suggest that gastrointestinal microbiota modulate the development of morphine tolerance (but not hyperexcitability) in nociceptive primary afferent neurons, through a mechanism involving TTX-R Na+ channels.

The “Culture” of Pain Control: A Review of Opioid-Induced Dysbiosis (OID) in Antinociceptive Tolerance

“…A recent study observed that colon tissue supernatants from mice with chronic morphine exposure induced tolerance and hyperexcitability in naive mouse DRG neurons. 77 Oral vancomycin treatment in this paradigm was sufficient to block tolerance development, but not hyperexcitability. This evidence suggests that tolerance development in vivo involves a peripheral, gut-mediated component in addition to the central mechanisms that have been extensively described.…”

“…At present, data are insufficient to determine whether OID impacts the mechanisms of OIH, but studies using vancomycin to eliminate Gram-positive organisms have not observed any influence in the setting of chronic morphine exposure. 77 Regarding the opioid epidemic, the need for novel opioid-sparing strategies is self-evident. New therapeutic methods that reduce the dose and duration of opioid use are essential, as each is predictive of physical dependence, addiction, and overdose.…”

“…This theme persisted in a further study examining the inactivation kinetics of tetrodotoxin-resistant (TTX-R) Na + channels (Na v 1.8/1.9). 77 Of note, these observations in peripheral afferents do not dispute central mechanisms of opioid tolerance, but rather imply that additional mechanisms are contributing.…”

“…Colon tissue supernatants: The use of supernatants from colon tissue samples has arisen as an innovative and powerful paradigm for investigating the mechanisms of peripheral nociception in both mice and human patients. 1,10,20,77,124 Full-circumference colon tissue segments are resected and incubated in culture medium such that biochemical mediators in the gut wall (eg, bacterial products and proinflammatory cytokines) leach out into the culture medium. The liquid supernatant may then be transferred to a target cell population (eg, naive DRG cultures) to assess the impact of gutlocalized mediators on neuronal excitability.…”

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

“…Voltage-gated sodium channels are critical to the action potential upstroke and altered sodiumchannel kinetics in acute and chronic morphine-treated DRG and myenteric neurons have been demonstrated previously (Chen et al, 2012;Smith et al, 2012Smith et al, , 2014Mischel et al, 2018). Analysis of single-cell RNA sequencing data from Zeisel at al.…”