PLASMA EXTRAVASATION IN THE SKIN AND PELVIC ORGANS EVOKED BY ANTIDROMIC STIMULATION OF THE LUMBOSACRAL DORSAL ROOTS OF THE RAT

Electrical stimulation of the distal stump of cut peripheral nerves is a commonly accepted way to evoke neurogenic inflammation. Nevertheless, the modulatory effect of biogenic amines and vasoactive peptides released from efferent fibres can be excluded only if the dorsal roots are stimulated. The present study was focussed to investigate plasma extravasation in the appropriate skin and mucosal areas as well as in the genito-urinary organs in response to antidromic stimulation of the lumbar and sacral dorsal roots of the rat. Plasma extravasation was detected by quantitative measurement of the accumulated Evans Blue tracer in tissue pieces. Two unilateral posterior roots were stimulated simultaneously (20 V, 0.5 ms, 5 Hz, 5 min) in each anaesthetized rat. Intensive blueing response occurred in the following tissues: plantar glabrous skin, L(4)-L(5) (L(6)); dorsum of the hindpaw and ankle joint, L(2)-L(4); ventral surface of the thigh, L(2)-L(4) (L(1)); abdominal skin, L(1)-L(4); caudal nipples, L(1)-L(2); root of the tail, S-1 (L(6)); clitoris, L(5)-S-1; orifice of the vagina, S-1 (L(6)); vagina, L(2)-L(3), L(5)-S-1; cervix and corpus uteri, L(2)-L(3), L(5)-S-1; lower two-thirds of the uterine horns, L(1)-L(3); urinary bladder, L(1)-L(3), L(6)-S-1; rectum, L(5)-S-1; scrotum (dorsal surface and lower pole), L(6)-S-1; scrotum (ventral surface), L(3)-L(5). No significant dye accumulation was observed in the muscles, testicles, vas deferens and prostate. Plasma extravasation caused by antidromic activation of the dorsal roots was absent or highly reduced after systemic capsaicin pretreatment of the rats. Neurogenic inflammation evoked by antidromic stimulation of the dorsal roots makes this method suitable for mapping the organs where capsaicin-sensitive sensory nerve endings exert their ''efferent functions''. This first functional description of segmental innervation of capsaicin-sensitive afferent fibres is in agreement with retrograde tracing studies and immunohistochemical localization of substance P in the dorsal root ganglia and peripheral tissues.