LIDOCAINE PREVENTS NOXIOUS EXCITATION OF BLADDER AFFERENTS INDUCED BYINTRAVESICAL CAPSAICIN WITHOUT INTERFERING WITH THE ENSUING SENSORY DESENSITIZATION - AN EXPERIMENTAL-STUDY IN THE RAT

Purpose: The effects of the local anesthetic lidocaine on the noxious excitation and subsequent desensitization of bladder sensory fibers, p roduced by intravesical capsaicin, were evaluated through c-fos activa tion in the spinal cord.Materials and Methods: Noxious excitation was demonstrated by counting Fos-immunoreactive (IR) cells occurring in th e rat spinal cord 2 hours after intravesical administration of 1 mM. c apsaicin, preceded or not by 2% lidocaine. Desensitization was studied by comparing the number of Fos-IR cells induced by 1% acetic acid in rats treated 24 hours before with 1 mM. intravesical capsaicin precede d or not by 2% lidocaine. Results: Lidocaine instilled previously mark edly reduced the number of Fos-IR spinal cells responding to capsaicin -induced bladder afferent excitation. Numbers of Fos-IR cells induced by acetic acid instillation in bladders desensitized by capsaicin admi nistrated 24 hours before were not changed by lidocaine application pr ior to capsaicin. Conclusions: These findings suggest that local anest hetic pretreatment of the bladder with lidocaine reduces the capsaicin -induced noxious excitation of the sensory fibers without decreasing t heir subsequent desensitization.