Establishing a Mouse Model of a Pure Small Fiber Neuropathy with the Ultrapotent Agonist of Transient Receptor Potential Vanilloid Type 1

Abstract

Patients with diabetes mellitus (DM) or those experiencing the neurotoxic effects of chemotherapeutic agents may develop sensation disorders due to degeneration and injury of small-diameter sensory neurons, referred to as small fiber neuropathy. Present animal models of small fiber neuropathy affect both large- and small-diameter sensory fibers and thus create a neuropathology too complex to properly assess the effects of injured small-diameter sensory fibers. Therefore, it is necessary to develop an experimental model of pure small fiber neuropathy to adequately examine these issues. This protocol describes an experimental model of small fiber neuropathy specifically affecting small-diameter sensory nerves with resiniferatoxin (RTX), an ultrapotent agonist of transient receptor potential vanilloid type 1 (TRPV1), through a single dose of intraperitoneal injection, referred to as RTX neuropathy. This RTX neuropathy showed pathological manifestations and behavioral abnormalities that mimic the clinical characteristics of patients with small fiber neuropathy, including intraepidermal nerve fiber (IENF) degeneration, specifically injury in small-diameter neurons, and induction of thermal hypoalgesia and mechanical allodynia. This protocol tested three doses of RTX (200, 50, and 10 µg/kg, respectively) and concluded that a critical dose of RTX (50 µg/kg) is required for the development of typical small fiber neuropathy manifestations, and prepared a modified immunostaining procedure to investigate IENF degeneration and neuronal soma injury. The modified procedure is fast, systematic, and economic. Behavioral evaluation of neuropathic pain is critical to reveal the function of small-diameter sensory nerves. The evaluation of mechanical thresholds in experimental rodents is particularly challenging and this protocol describes a customized metal mesh that is suitable for this type of assessment in rodents. In summary, RTX neuropathy is a new and easily established experimental model to evaluate the molecular significance and intervention underlying neuropathic pain for the development of therapeutic agents.

Central and Peripheral Mechanisms in ApoE4-Driven Diabetic Pathology

“…Diabetic neuropathy impairments in thermal perception are associated with small-fiber-mediated sensation, and pathologies in touch perception and motor coordination are linked to large-fiber neuropathies [36,37,73]. Therefore, we next examined the extent to which the sensorimotor profile of the mice is affected by the APOE genotype and diet effects on small and large fibers utilizing skin IENFD for the first [74] and sciatic electrophysiological measurements [75] for the latter. These experiments revealed no significant effects of either the APOE genotype or diet on these peripheral parameters, suggesting that the observations recorded in the behavioral and sensorimotor paradigms, much like the observed cognitive phenotypes, are driven primarily by the CNS and not by the PNS.…”

Treatment with methyl-β-cyclodextrin prevents mechanical allodynia in resiniferatoxin neuropathy in a mouse model

“…Paradoxically, RTX-induced mechanical allodynia has not been observed with alternative routes of administration (Hockman et al, 2018; Sapio et al, 2018). Accordingly, RTX administered intraperitoneally was systemically but not locally effective in a dose-dependent manner (Lee et al, 2018). Indeed, RTX systemic neurotoxicity has also been demonstrated to induce mechanical allodynia in other species (Pan et al, 2003), and this RTX neuropathy model could mimic distinct neuropathic manifestations, such as those of diabetes patients, in clinics (Hsieh et al, 2018).…”

Remedia Sternutatoria over the Centuries: TRP Mediation

“…It causes severe burning pain in sub-microgram quantities when ingested orally [ 44 ]. Resiniferatoxin has been used in several studies for its ability to activate TRPV1 [ 45 , 46 , 47 ].…”