Screening of Drugs for Peripheral Neuropathy

Introduction & screening strategy

• Definition — Screening for peripheral-neuropathy drugs is the set of experimental assays that reproduce, in rodents, the cardinal sensory signs of human peripheral neuropathy — spontaneous burning pain, hyperalgesia and allodynia — so candidate analgesic/neuroprotective agents can be tested against a validated behavioural (and where possible electrophysiological) readout.
• Neuropathy vs neuropathic pain — Neuropathy is the broad disorder of peripheral nerves (sensory, motor and autonomic derangement — not all painful); neuropathic pain is the state in which the injured/dysfunctional nerve itself is the pain source. Allodynia (pain from a normally innocuous stimulus) is the most reproducibly modelled and most troublesome sign; causalgia (spontaneous burning pain + hyperalgesia + allodynia after incomplete nerve injury) is the human phenotype the surgical models mimic.
• Aetiological spectrum modelled — Models are chosen to represent the human aetiologies — metabolic (diabetic; glycosylation end-products inhibit axonal transport and Na⁺/K⁺-ATPase), toxic (chemotherapy/radiation, thallium, isoniazid, lead, arsenic), traumatic (phantom-limb pain, CRPS-I/II), infectious (post-herpetic neuralgia, HIV, leprosy), autoimmune (CIDP, vasculitic) and hereditary (Charcot–Marie–Tooth, amyloidosis).
• How a screen is assembled — A complete screen pairs (a) an induction method (surgical nerve injury, metabolic/diabetic, or toxic/chemotherapeutic) with (b) one or more quantitative sensory endpoints over a defined time-course, against (c) a reference/standard drug for validation.
• Species & laterality — The workhorse is the male Sprague–Dawley or Wistar rat (~130–250 g); mouse variants (e.g. PKCγ-null) allow genetic dissection. Most surgical models are unilateral — the operated (ipsilateral) hind limb is the test side and the contralateral sham/mobilised-only limb is the within-animal control ("difference-score" analysis).
• Time-window — In the constriction model maximum hyperaesthesia develops between day 7 and day 14 after surgery; drug testing is scheduled inside this window against pre-drug baselines.