Role of mechanosensitive ion channels in the sensation of pain

Inhibiting Nav1.7 channels in pulpitis: An in vivo study on neuronal hyperexcitability

Pulpitis constitutes a significant challenge in clinical management due to its impact on peripheral nerve tissue and the persistence of chronic pain. Despite its clinical importance, the correlation between neuronal activity and the expression of voltage-gated sodium channel 1.7 (Nav1.7) in the trigeminal ganglion (TG) during pulpitis is less investigated. The aim of this study was to examine the relationship between experimentally induced pulpitis and Nav1.7 expression in the TG and to investigate the potential of selective Nav1.7 modulation to attenuate TG abnormal activity associated with pulpitis. Acute pulpitis was induced at the maxillary molar (M1) using allyl isothiocyanate (AITC). The mice were divided into three groups: control, pulpitis model, and pulpitis model treated with ProTx-II, a selective Nav1.7 channel inhibitor. After three days following the surgery, we conducted a recording and comparative analysis of the neural activity of the TG utilizing in vivo optical imaging. Then immunohistochemistry and Western blot were performed to assess changes in the expression levels of extracellular signal-regulated kinase (ERK), c-Fos, collapsin response mediator protein-2 (CRMP2), and Nav1.7 channels. The optical imaging result showed significant neurological excitation in pulpitis TGs. Nav1.7 expressions exhibited upregulation, accompanied by signaling molecular changes suggestive of inflammation and neuroplasticity. In addition, inhibition of Nav1.7 led to reduced neural activity and subsequent decreases in ERK, c-Fos, and CRMP2 levels. These findings suggest the potential for targeting overexpressed Nav1.7 channels to alleviate pain associated with pulpitis, providing practical pain management strategies.

Gut feelings: mechanosensing in the gastrointestinal tract

The primary function of the gut is to procure nutrients. Synchronized mechanical activities underlie nearly all its endeavours. Coordination of mechanical activities depends on sensing of the mechanical forces, in a process called mechanosensation. The gut has a range of mechanosensory cells. They function either as specialized mechanoreceptors, which convert mechanical stimuli into coordinated physiological responses at the organ level, or as non-specialized mechanosensory cells that adjust their function based on the mechanical state of their environment. All major cell types in the gastrointestinal tract contain subpopulations that act as specialized mechanoreceptors: epithelia, smooth muscle, neurons, immune cells, and others. These cells are tuned to the physical properties of the surrounding tissue, so they can discriminate mechanical stimuli from the baseline mechanical state. The importance of gastrointestinal mechanosensation has long been recognized, but the latest discoveries of molecular identities of mechanosensors and technical advances that resolve the relevant circuitry have poised the field to make important intellectual leaps. This Review describes the mechanical factors relevant for normal function, as well as the molecules, cells and circuits involved in gastrointestinal mechanosensing. It concludes by outlining important unanswered questions in gastrointestinal mechanosensing.

Can placebo and nocebo effects generalize within pain modalities and across somatosensory sensations?

Pain and other somatosensory sensations, such as itch, can be effectively decreased by placebo effects and increased by nocebo effects. There are indications that placebo effects on pain generalize to other sensations and that nocebo effects generalize within itch modalities. However, it has not yet been investigated whether learned effects can generalize within pain stimulus modalities or from pain to itch. Our aims were to test whether placebo and nocebo effects can generalize within pain modalities, ie, from heat pain to pressure pain, and across somatosensory sensations with psychophysiological similarities, ie, from heat pain to cowhage-evoked itch. For this purpose, 65 healthy participants were randomized to either a placebo or nocebo group. All participants first underwent a conditioning and verbal suggestion procedure with heat pain stimuli. Subsequently, responses to heat pain, pressure pain, and cowhage-evoked itch stimuli were tested. Results showed altered levels of heat and pressure pain with the conditioned cue in both placebo and nocebo groups in the expected directions, but no significant difference in itch in both groups. In conclusion, placebo and nocebo effects on pain may generalize within but not across stimulus modalities. This study provides a novel perspective on the role that response generalization plays in physical symptoms.