Human adult dental pulp stem cells (DPSCs) reside within the perivascular niche of dental pulp and are thought to originate from migrating cranial neural crest (CNC) cells. During embryonic development, CNC cells differentiate into a wide variety of cell types, including neurons of the peripheral nervous system. Previously, we have demonstrated that DPSCs derived from adult human third molar teeth differentiate into cell types reminiscent of CNC embryonic ontology. We hypothesized that DPSCs exposed to the appropriate environmental cues would differentiate into functionally active neurons. The data demonstrated that ex vivo-expanded human adult DPSCs responded to neuronal inductive conditions both in vitro and in vivo. Human adult DPSCs, but not human foreskin fibroblasts (HFFs), acquired a neuronal morphology, and expressed neuronal-specific markers at both the gene and protein levels. Culture-expanded DPSCs also exhibited the capacity to produce a sodium current consistent with functional neuronal cells when exposed to neuronal inductive media. Furthermore, the response of human DPSCs and HFFs to endogenous neuronal environmental cues was determined in vivo using an avian xenotransplantation assay. DPSCs expressed neuronal markers and acquired a neuronal morphology following transplantation into the mesencephalon of embryonic day-2 chicken embryo, whereas HFFs maintained a thin spindle fibroblastic morphology. We propose that adult human DPSCs provide a readily accessible source of exogenous stem/precursor cells that have the potential for use in cell-therapeutic paradigms to treat neurological disease. Disclosure of potential conflicts of interest is found at the end of this article.

Voltage-gated sodium (Na_v) channels initiate action potentials in most neurons, including primary afferent nerve fibres of the pain pathway. Local anaesthetics block pain through non-specific actions at all Na_v channels, but the discovery of selective modulators would facilitate the analysis of individual subtypes of these channels and their contributions to chemical, mechanical, or thermal pain. Here we identify and characterize spider (Heteroscodra maculata) toxins that selectively activate the Na_v1.1 subtype, the role of which in nociception and pain has not been elucidated. We use these probes to show that Na_v1.1-expressing fibres are modality-specific nociceptors: their activation elicits robust pain behaviours without neurogenic inflammation and produces profound hypersensitivity to mechanical, but not thermal, stimuli. In the gut, high-threshold mechanosensitive fibres also express Na_v1.1 and show enhanced toxin sensitivity in a mouse model of irritable bowel syndrome. Together, these findings establish an unexpected role for Na_v1.1 channels in regulating the excitability of sensory nerve fibres that mediate mechanical pain.

Background & Aims The transient receptor potential (TRP) channel family includes transducers of mechanical and chemical stimuli for visceral sensory neurons. TRP ankyrin 1 (TRPA1) is implicated in inflammatory pain; it interacts with G-protein-coupled receptors, but little is known about its role in the gastrointestinal (GI) tract. Sensory information from the GI tract is conducted via 5 afferent subtypes along 3 pathways. Methods Nodose and dorsal root ganglia whose neurons innnervate 3 different regions of the GI tract were analyzed from wild-type and TRPA1^−/− mice using quantitative reverse-transcription polymerase chain reaction, retrograde labeling, and in situ hybridization. Distal colon sections were analyzed by immunohistochemistry. In vitro electrophysiology and pharmacology studies were performed, and colorectal distension and visceromotor responses were measured. Colitis was induced by administration of trinitrobenzene sulphonic acid. Results TRPA1 is required for normal mechano- and chemosensory function in specific subsets of vagal, splanchnic, and pelvic afferents. The behavioral responses to noxious colonic distension were substantially reduced in TRPA1^−/− mice. TRPA1 agonists caused mechanical hypersensitivity, which increased in mice with colitis. Colonic afferents were activated by bradykinin and capsaicin, which mimic effects of tissue damage; wild-type and TRPA1^−/− mice had similar direct responses to these 2 stimuli. After activation by bradykinin, wild-type afferents had increased mechanosensitivity, whereas, after capsaicin exposure, mechanosensitivity was reduced: these changes were absent in TRPA1^−/− mice. No interaction between protease-activated receptor-2 and TRPA1 was evident. Conclusions These findings demonstrate a previously unrecognized role for TRPA1 in normal and inflamed mechanosensory function and nociception within the viscera.

A distinctive feature of the voltage-dependent chloride channels ClC-0 (the Torpedo electroplaque chloride channel) and ClC-1 (the major skeletal muscle chloride channel) is that chloride acts as a ligand to its own channel, regulating channel opening and so controlling the permeation of its own species. We have now studied the permeation of a number of foreign anions through ClC-1 using voltage-clamp techniques on Xenopus oocytes and Sf9 cells expressing human (hClC-1) or rat (rClC-1) isoforms, respectively. From their effect on channel gating, the anions presented in this paper can be divided into three groups: impermeant or poorly permeant anions that can not replace Cl⁻ as a channel opener and do not block the channel appreciably (glutamate, gluconate, HCO₃⁻, BrO₃⁻); impermeant anions that can open the channel and show significant block (methanesulfonate, cyclamate); and permeant anions that replace Cl⁻ at the regulatory binding site but impair Cl⁻ passage through the channel pore (Br⁻, NO₃⁻, ClO₃⁻, I⁻, ClO₄⁻, SCN⁻). The permeability sequence for rClC-1, SCN⁻ ∼ ClO₄⁻ > Cl⁻ > Br⁻ > NO₃⁻ ∼ ClO₃⁻ > I⁻ >> BrO₃⁻ > HCO₃⁻ >> methanesulfonate ∼ cyclamate ∼ glutamate, was different from the sequence determined for blocking potency and ability to shift the P_open curve, SCN⁻ ∼ ClO₄⁻ > I⁻ > NO₃⁻ ∼ ClO₃⁻ ∼ methanesulfonate > Br⁻ > cyclamate > BrO₃⁻ > HCO₃⁻ > glutamate, implying that the regulatory binding site that opens the channel is different from the selectivity center and situated closer to the external side. Channel block by foreign anions is voltage dependent and can be entirely accounted for by reduction in single channel conductance. Minimum pore diameter was estimated to be ∼4.5 Å. Anomalous mole-fraction effects found for permeability ratios and conductance in mixtures of Cl⁻ and SCN⁻ or ClO₄⁻ suggest a multi-ion pore. Hydrophobic interactions with the wall of the channel pore may explain discrepancies between the measured permeabilities of some anions and their size.