Nonvagal tachypnea following alpha(2)-adrenoceptor stimulation in awake goats

To assess the influence of vagal afferent feedback in the development of re spiratory instabilities induced by alpha(2)-adrenoceptor (alpha(2)-AR) stim ulation in the goat, we examined the ventilatory effects of clonidine, an a lpha(2)-AR agonist, in awake tracheostomized goats before and after bilater al mid-cervical vagotomy. Prior to vagal section, systemic administration o f clonidine (0.5-3.0 mu g kg(-1)) induced a highly dysrhythmic pattern of b reathing in all animals that was characterized by alternating episodes of t achypnea and slow irregular breathing patterns including prolonged and vari able expiratory time (TE) intervals. Periods of apnea were commonly observe d. Bilateral vagotomy resulted in a slower deeper breathing pattern and abo lished the tachypnea evoked by intravenous administration of phenylbiguanid e (PBG; 20-50 mu g kg(-1)), a selective serotonin type 3 (5-HT3) receptor a gonist. However, respiratory disturbances associated with alpha(2)-AR stimu lation (including tachypnea) persisted after vagal section and were qualita tively and quantitatively similar to pre-vagotomy data demonstrating that v agal afferent feedback is not necessary for the development of respiratory disturbances induced by clonidine. The results suggest that respiratory dys rhythmias caused by alpha(2)-AR agonists in the goat are mediated by alpha( 2)-ARs in the CNS. (C) 1999 Elsevier Science B.V. All rights reserved.