CENTRAL AND PERIPHERAL EFFECTS OF THE NONNEURAL SUBSTANCES ON RESPIRATION BEFORE AND AFTER VAGOTOMY

The central effects of capsaicin, veratrine, histamine and bradykinin were studied by injecting them directly into the cerebrospinal fluid a nd their peripheral effects were examined by injecting into femoral ve in. Our experiments were performed in Na-pentobarbital-anaesthetized d ogs. Tidal volume (V-T), respiratory frequency (f/min), systemic arter ial pressure (BP) were recorded. A significant increase in f, and an i nitial apnea or hypoventilation followed by a significant increase in V-T were observed with central and peripheral capsaicin. Vagotomy remo ved the peripheral V-T response, but not the central one. While centra l capsaicin administration increased BP, peripheral administration dec reased. After vagotomy, a significant increase was observed in BP for both administrations. Respiratory responses to central and peripheral administrations of veratrine mere similar to those of capsaicin. Signi ficant increases were observed in f and V-T of the intact group in res ponse to central and peripheral administration of histamine. Response to peripheral administration disappeared after vagotomy. While central and peripheral bradykinin increased V-T significantly, there was no s ignificant change in f. Vagotomy only removed the increase in V-T in r esponse to peripheral administration. In conclusion, respiratory respo nses to central administration of capsaicin and veratrine are due to d irect effects of these substances on respiratory neurons. In periphera l administration, disappearance of the responses after vagotomy indica te that the responses are brought about by stimulation of the lung rec eptors. (C) 1997 Tohoku University Medical Press.