The Effect of Neonatal Capsaicin Injection on Barrel Cortical Neuron Response Properties after Controlled Mechanical Displacement of Vibrissa in Adult Rats
Introduction: Systemic application of capsaicin to neonatel rodents depletes their primary afferent C-fibers and also results in a wide variety of changes observable in adulthood. The manual methods used for stimulation of vibrissa provide limited information on response properties of barrel cortical Neurons. In this study the effect of C-fiber depletion induced by neonatal capsaicin (Cap) treatment on response properties of barrel cortical neurons, after controlled mechanical displacement, was examined in adult rats. Material and Methods: We destroyed C-fibers of neonatal rats by adminstration of capsaicin (50mg/kg dissolved in 10% ethanol, 10% tween 80, 80% salin, ip) in the first day of birth. Single unit recording was done on barrel cortical cell from both (untreated control and vehicle-treated) and Cap-treated adult rats. The magnitude and latency period of response to the controlled mechanical displacement of principal and peripheral vibrissa were recorded and analyzed. Results: The magnitude of responses evoked by deflection of principal and peripheral vibrissa in Cap-treated rats were significantly (P<0.001) higher than in control rats. There was no difference between control and Cap-treated rats in the response latency to principal vibrissae deflection. (P<0.467) But response latency was significantly decreased redused during peripheral vibrissa deflection (P<0.001). The magnitude of response during principal vibrissae deflection was higher and the response latency was shorter compared to peripheral vibrissae deflection in both groups. Conclusion: These results suggest that C- fibers play an important role in the natural functions of the somatosensory system and are probably required for normal shaping of the functional properties of central somatosensory neurons.