In a recent article in Gut, Hughes et al1 identified distinct patterns of immune dysfunction in IBS patients compared with healthy subjects. In particular, they showed that peripheral blood mononuclear cell (PBMC) supernatants from healthy subjects inhibited colonic afferents in a μ-opioid receptor (MOR)-mediated manner. These findings correlated with β-endorphin from T lymphocytes providing an important MOR-mediated antinociceptive influence in the healthy gut.2 Intriguingly, these inhibitory effects were lost with PBMC supernatants from constipation-predominant IBS patients suggesting a loss of MOR-mediated inhibition, coupled with increased excitatory mediators (TNF-α, IL-1β, IL-6), contributes to abdominal pain.1

We evaluated if this alteration was MOR specific or whether it extended to other members of the opioid receptor family. As clinical studies have shown varying outcomes on visceral pain perception with κ-opioid receptor (KOR) agonists,3^–5 we postulated KOR expression and function are altered during visceral hypersensitivity. Therefore, we determined if the peripherally restricted selective KOR agonist, asimadoline, was able to modify colonic nociceptor function in health and during inflammatory and postinflammatory chronic visceral mechanical hypersensitivity (CVH).6

We performed in vitro afferent recordings from mouse splanchnic high-threshold nociceptors, which respond to focal compression and noxious stretch/distension.1 ,6 …