TRPV1 Sensitization in Primary Sensory Neurons

Pain is a major personal and community burden throughout the world with currently limited treatment options for persistent pain due to unacceptable side effects, dependence or frank inefficacy. It is necessary to understand the anatomical and molecular pathways leading to pain to better cope with the current challenge of treating it

Activity-dependent silencing reveals functionally distinct itch-generating sensory neurons

The peripheral terminals of primary sensory neurons detect histamine and non-histamine itch-provoking ligands through molecularly distinct transduction mechanisms. It remains unclear, however, whether these distinct pruritogens activate the same or different afferent fibers. We utilized a strategy of reversibly silencing specific subsets of murine pruritogen-sensitive sensory axons by targeted delivery of a charged sodium-channel blocker and found that functional blockade of histamine itch did not affect the itch evoked by chloroquine or SLIGRL-NH2, and vice versa. Notably, blocking itch-generating fibers did not reduce pain-associated behavior. However, silencing TRPV1+ or TRPA1+ neurons allowed AITC or capsaicin respectively to evoke itch, implying that certain peripheral afferents may normally indirectly inhibit algogens from eliciting itch. These findings support the presence of functionally distinct sets of itch-generating neurons and suggest that targeted silencing of activated sensory fibers may represent a clinically useful anti-pruritic therapeutic approach for histaminergic and non-histaminergic pruritus

Photochemical activation of TRPA1 channels in neurons and animals

Optogenetics is a powerful research tool because it enables high-resolution optical control of neuronal activity. However, current optogenetic approaches are limited to transgenic systems expressing microbial opsins and other exogenous photoreceptors. Here, we identify optovin, a small molecule that enables repeated photoactivation of motor behaviors in wild type animals. Surprisingly, optovin's behavioral effects are not visually mediated. Rather, photodetection is performed by sensory neurons expressing the cation channel TRPA1. TRPA1 is both necessary and sufficient for the optovin response. Optovin activates human TRPA1 via structure-dependent photochemical reactions with redox-sensitive cysteine residues. In animals with severed spinal cords, optovin treatment enables control of motor activity in the paralyzed extremities by localized illumination. These studies identify a light-based strategy for controlling endogenous TRPA1 receptors in vivo, with potential clinical and research applications in non-transgenic animals, including humans

Why do animal eyes have pupils of different shapes?

There is a striking correlation between terrestrial species' pupil shape and ecological niche (that is, foraging mode and time of day they are active). Species with vertically elongated pupils are very likely to be ambush predators and active day and night. Species with horizontally elongated pupils are very likely to be prey and to have laterally placed eyes. Vertically elongated pupils create astigmatic depth of field such that images of vertical contours nearer or farther than the distance to which the eye is focused are sharp, whereas images of horizontal contours at different distances are blurred. This is advantageous for ambush predators to use stereopsis to estimate distances of vertical contours and defocus blur to estimate distances of horizontal contours. Horizontally elongated pupils create sharp images of horizontal contours ahead and behind, creating a horizontally panoramic view that facilitates detection of predators from various directions and forward locomotion across uneven terrain

Why do animal eyes have pupils of different shapes?

There is a striking correlation between terrestrial species’ pupil shape and ecological niche (that is, foraging mode and time of day they are active). Species with vertically elongated pupils are very likely to be ambush predators and active day and night. Species with horizontally elongated pupils are very likely to be prey and to have laterally placed eyes. Vertically elongated pupils create astigmatic depth of field such that images of vertical contours nearer or farther than the distance to which the eye is focused are sharp, whereas images of horizontal contours at different distances are blurred. This is advantageous for ambush predators to use stereopsis to estimate distances of vertical contours and defocus blur to estimate distances of horizontal contours. Horizontally elongated pupils create sharp images of horizontal contours ahead and behind, creating a horizontally panoramic view that facilitates detection of predators from various directions and forward locomotion across uneven terrain

Bortezomib-induced neuropathy is in part mediated by the sensitization of TRPV1 channels

Abstract TRPV1 is an ion channel that transduces noxious heat and chemical stimuli and is expressed in small fiber primary sensory neurons that represent almost half of skin nerve terminals. Tissue injury and inflammation result in the sensitization of TRPV1 and sustained activation of TRPV1 can lead to cellular toxicity though calcium influx. To identify signals that trigger TRPV1 sensitization after a 24-h exposure, we developed a phenotypic assay in mouse primary sensory neurons and performed an unbiased screen with a compound library of 480 diverse bioactive compounds. Chemotherapeutic agents, calcium ion deregulators and protein synthesis inhibitors were long-acting TRPV1 sensitizers. Amongst the strongest TRPV1 sensitizers were proteasome inhibitors, a class that includes bortezomib, a chemotherapeutic agent that causes small fiber neuropathy in 30–50% of patients. Prolonged exposure of bortezomib produced a TRPV1 sensitization that lasted several days and neurite retraction in vitro and histological and behavioral changes in male mice in vivo. TRPV1 knockout mice were protected from epidermal nerve fiber loss and a loss of sensory discrimination after bortezomib treatment. We conclude that long-term TRPV1 sensitization contributes to the development of bortezomib-induced neuropathy and the consequent loss of sensation, major deficits experienced by patients under this chemotherapeutic agent

Prophylaxis Against Cytomegalovirus Infections with Oral Maribavir in Allogeneic Stem Cell Transplant Recipients: Results of a Randomized, Double-Blind, Placebo-Controlled Trial.

Abstract Cytomegalovirus (CMV) remains a major threat to recipients of allogeneic stem cell transplants (SCT). Potential toxicities of currently available anti-CMV agents complicate their use in this population. Maribavir (MBV) is an oral antiviral drug with a unique mechanism of action against CMV and a promising safety profile in early clinical studies. This randomized, double-blind, multicenter, dose-ranging study enrolled adult CMV-seropositive recipients of allogeneic SCT. After engraftment, patients were randomized to receive CMV prophylaxis with placebo or MBV at one of three doses for up to 12 weeks. CMV surveillance was performed weekly with both CMV pp65 antigenemia and plasma CMV DNA PCR assays. If CMV was detected, study drug was stopped and preemptive anti-CMV therapy started as per standard practice at each center. A total of 111 patients were enrolled (median age 47 years; 70% myeloablative SCT; 53% related donor). Incidence of CMV infection or disease in the first 100 days post-SCT are shown in the table. The safety profile of maribavir was favorable in this patient population; most adverse events occurred at similar rates in placebo and MBV groups. There was no adverse impact of MBV on neutrophil counts or other laboratory or ECG parameters. Consistent with prior clinical studies, the most notable events that appeared to be associated with MBV were mild-moderate taste disturbance, nausea, and diarrhea. In conclusion, maribavir prophylaxis reduced the rate of CMV infection compared to placebo, with a favorable safety profile in this complex patient population. Phase 3 studies of maribavir in stem cell and solid organ transplant recipients are being planned. Placebo MBV 100 mg BID MBV 400 mg QD MBV 400 mg BID N evaluable 28 27 27 26 p values represent comparison to placebo (stratified by myeloablative or nonmyeloablative SCT) CMV infection or disease based on:     pp65 antigenemia 11 (39%) 4 (15%) 5 (19%) 4 (15%) p=0.046 p=0.116 p=0.053     plasma CMV DNA PCR 13 (46%) 2 (7%) 3 (11%) 5 (19%) p=0.001 p=0.007 p=0.038 Use of preemptive anti-CMV Rx 16 (57%) 4 (15%) 8 (30%) 4 (15%) p=0.001 p=0.051 p=0.002 CMV disease only 3 (11%) 0 0 0 p=0.089 p=0.084 p=0.091</jats:p