The Role of Capsaicin-induced Acute Inactivation of C-fibers on Tactile Learning in Rat

Objective(s): In our previous study, we reported that capsaicin-induced unmyelinated C-fiber depletion can modulate excitatory and integrative circuits in the somatosensory cortex following experience-dependent plasticity. In this study, we investigated the involvement of the capsaicin-induced acute inactivation of c-fibers on tactile learning in rat. Materials and Methods: The delayed novel object recognition test was used to assess tactile learning. This procedure consisted of two phases. The first of these (T1) was a training phase during which the animals explored two similar objects. T2, the test phase, occurred 24 hr later, during which the animals explored one novel and one familiar object. In order to induce acute inactivation of the C-fiber pathway, 25–30 μl of a 10% capsaicin was injected subcutaneously into the rat’s upper lip, 6 h prior to T1. Tactile learning was quantified using a discrimination ratio. Results: In T2, the discrimination ratio in capsaicin-treated animals (37.3±3.8%) was lower than that observed in vehicle-treated animals (54.4±5.1%, P<0.05). Conclusion: These findings indicate that the selective inactivation of a peripheral nociceptor subpopulation affects tactile learning.