ELSEVIER Neuroscie.nce Letters 182 (1994) 267-270 HEUROSClENCE lETTERS Antidromic vasodilatation in the striated muscle and its sensitivity to resiniferatoxin in the rat R6bert P6rszhsz, J~nos Szolcs~nyi* Department of Pharmacology, Medical University of Pbcs, Szigeti fit 12, PO Box 99, H-7643 P~es, Hungary Received 26 September 1994; Revised version received 19 October 1994; Accepted 19 October 1994 Abstract Antidromic stimulation at the L4-L5 dorsal roots elicited a blood flow increase in ipsilateral muscles of lower extremities in rats measured by laser-Doppler flowmetry. Stimulation with 0.5 Hz; 20 V; 0.5 ms; 50 impulses was much less effective in muscle (18.9 + 6.4 area under the curve (%); mean + S.E.) than in the glabrous skin (80.5 + 8.25; P < 0.001). No significant difference was seen at 10 Hz (51.6 + 10.6 muscle; 60.6 + 17.3 skin). In the muscle the latency period of the response was long (37.4 + 3.1 s; mean + S.E.) at 0.5 Hz stimulation and was much shorter (8.8 + 0.8 s) at the higher frequency of 10 Hz, unlike in the skin where latency values at both frequencies were similar (9.7 + 0.8 s and 8.9 + 0.9 s, respectively). Antidromic vasodilatation in the muscle and the skin was abolished by resiniferatoxin (RTX) in an i.v. dose of 1.0/tg/kg. These results provide a direct evidence for the existence of antidromic vasodilatation in striated muscle and suggest a mediating role for capsaicin/RTX sensitive afferents. Key words: Dorsal root; Antidromic vasodilatation; Striated muscle; Blood flow; Laser-Doppler; Resiniferatoxin; Rat It is well established that antidromic vasodilatation is evoked in the skin by electrical stimulation of the cut dorsal roots. It has been assumed since the classical work of Celander and Folkow [1] that in the striated muscles antidromic vasodilatation cannot be elicited by an- tidromic stimulation of the dorsal roots. The phenome- non has not been analyzed for decades because its func- tional relevance remained unexplained. Recently, it turned out that neuropeptides released from the acti- vated capsaicin-sensitive sensory nerve endings possess significant effector functions suitable for local neuroreg- ulatory responses [4,20]. Calcitonin gene-related peptide (CGRP), which is present in muscle and joint afferents [13] is released from the peripheral sensory nerves and produce vasodilatation [2,4,6,8,22,23]. The major source of CGRP released from skeletal muscle are the A8 and/ or C sensory terminals [14, 16]. Utilization of sensitive laser-Doppler flowmetry was revealed the highly potent effect of dorsal root stimulation in microcirculation of *Corresponding author. Fax: (36) (72) 326244. E-mail: h2292szo@ella.hu. 0304-3940/94/$7.00 © 1994 Elsevier Science B.V. All rights reserved SSDI 0304-3940(94)00815-9 the skin [19]. The present paper provides the first evi- dence for antidromic vasodilatation in the striated mus- cle. The experiments were performed on female Wistar rats (250-350 g) anesthetized with 100 mg/kg i.p. thiobu- tobarbital. The right common carotid artery and the left external jugular vein were cannulated with polyethylene tubing for continuous measurement of arterial blood pressure and for the administration of drugs, respec- tively. Respiratory movements were measured by means of a Y-shaped cannula introduced into the trachea. The body core temperature was maintained around 37°C with a temperature controlled heating pad. The lum- bosacral dorsal roots were exposed after laminectomy and cut near to the spinal cord. The peripheral stump of cut dorsal roots were electrically stimulated by bipolar platinum wire hook electrodes in an oil pool formed from skin flaps [19]. Microcirculatory changes were re- corded with MBF3D dual channel laser-Doppler equip- ment (Moor Instruments Ltd., England). One of the probes was placed onto the glabrous skin of the hind- paw, the other onto the surface of the musculus gluteus maximus. The exposed skeletal muscle was then kept