Postsurgical tactile-evoked pain: a role for brain-derived neurotrophic factor-tropomyosin receptor kinase B-dependent novel tactile corpuscles.

Introduction: Millions of people undergo surgical procedures each year with many developing postsurgical pain. Dynamic allodynia can arise when, for example, clothing brushing close to the surgical site elicits pain. The allodynia circuits that enable crosstalk between afferent tactile inputs and central pain circuits have been studied, but the peripheral tactile drive has not been explored. Objective: Investigate the innervation of the skin in the rat plantar hindpaw skin-muscle incision model. Results: Incision increased epidermal thickness and cell layers and reduced intraepidermal nerve fibre density, identified with PGP9.5 immunostaining. Strikingly, Collagen IV immunostaining revealed the development of dermal protrusions, oriented towards the incision site, that were reminiscent of the dermal papillae that exist in glabrous footpads. S100 immunostaining for lamellar Schwann cells revealed the presence of novel tactile corpuscles (S100-positive bulb) within incision-induced putative dermal papillae. The occurrence of these novel tactile corpuscles coincided with behavioural observations of dynamic allodynia. Tactile corpuscles require brain-derived neurotrophic factor- tropomyosin receptor kinase B (BDNF-TrkB) signalling to form during development, and an increase in BDNF-immunostaining intensity was observed close to the incision site. Local acute administration of TrkB-Fc, to block BDNF-TrkB signalling, reduced, by approximately 50%, both tactile corpuscle size (S100+ bulb area) and dynamic allodynia. Conclusion: Surgery induces the development of novel tactile corpuscles in the incision surround, in a BDNF-TrKB-dependent manner, that contributes to postsurgical tactile-evoked pain.