Study on the involvement of primary afferent neurons in microcirculatory dynamics in oral region

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This study was designed to investigate the involvement of primary afferent neurons in microcirculatory hemodynamics by measuring the blood flow of the rat hind paw and lip with a laser Doppler flowmeter. Moreover the amount of substance P (SP) released into subcutaneous perfusates from hind paw was measured. Electrical stimulation of the sciatic and saphenous nerves containing sensory afferent fibers in the hind paw (10V, 2Hz, 1msec duration) for 30sec inauced an increase of SP release with plasma extravasation and an increase of cutaneous blood flow. Plasma extravasation was determined by pontamine sky blue exudation. Electrical stimulation of the mental nerve, sensory nerve supplying lip, (5v-20V, 2Hz, lmsec duration) for 30 sec also led to an increase of lip blood flow. The cutaneous and lip blood flow increases were significantly inhibited by pretreatment with capsaicin or spantide I.a. injection of phentolamine, propranolol, atropine, methysergide or s.c injection of mepyramine plus cimetidine, on the other handy had no effect. These results suggest that through the peripheral release of SP the small-diameter afferent fibers may play an important role in the regulation of microcirculatory hemodynamics.