The effect of thermal stimulation on primary afferent neurons and its modulation by Ruthenium Red (RR) has been investigated in the isolated perfused rabbit ear with intact neuronal connection to the animal. Capsaicin, K(+)-depolarization as well as increasing the temperature of the perfusate to 50 degrees C, increased the amount of substance P-like immunoreactivity (SP-IR) in the outflow in a calcium-dependent manner. High performance liquid chromatography (HPLC) revealed that SP-IR which was released by thermal stimulation consisted of two components, one of which co-eluted with synthetic substance P. The same two components of SP-IR were also present in extracts of the auricular nerve and were released by capsaicin. RR attenuated the effect of capsaicin and thermal stimulation but did not reduce potassium-evoked release of SP-IR. To evaluate an inhibitory action of RR on the excitation of primary afferents, the isolated perfused ear with intact neuronal connection to the anaesthetized rabbit was used. Intraarterial injection of capsaicin or bradykinin as well as superfusion of a skin area of approximately 2 cm2 with water at 53 degrees C for 1 min, produced a depressor reflex. RR attenuated the response to thermal stimulation and to capsaicin, but did not block the bradykinin-induced depressor reflex. These results demonstrate that, in the rabbit ear, thermal stimuli excite primary afferent neurons and evoke the calcium-dependent release of neuropeptides from their peripheral terminals by a mechanism which is sensitive to RR.

Animals↗

PubMedDate not supplied

Effects of PGE2 and colchicine on the intestinal fluid volume.

a) Colchicine, prostaglandin E2 (PGE2) and carbachol increase the intestinal fluid volume in the rat. b) The effect of carbachol and prostaglandin E2 is augmented whereas that of colchicine is diminished in the pithed rat. c) The effect of colchicine is diminished in anaesthesia whereas that of PGE2 remains unchanged. d) The effect of PGE2 and of colchicine are both inhibited by atropine. e) The effects of PGE2 and of colchicine are both enhanced by phentolamine. f) Pretreatment with indomethacin decreased the effect of colchicine whereas that of PGE2 remained unchanged. g) The PGE2-induced increase in intestinal fluid volume may partly be mediated by a peripheral mechanism involving acetylcholine receptors. h) The increase in intestinal fluid volume by colchicine can mainly be explained by a central action of the drug which is mediated by cholinergic neurones.

Animals↗