Abstract: To assess nervous mechanism responsibility for cardiovascular response induced by ammonia stimulation of nasal mucous membrane(CVRA),especially the effect of the cardio-sympathetic nervous system.Changes in heart rate and blood pressure were observed on 38 rabbits.Inhalation of ammonia resulted in bradycardia and increased in blood pressure.The bradycardia was not abolished by bilateral vagotomy but was done by injection of propranolol.The response of blood pressure was reduced by iujection of phentolamine.After severed the buffer nerve,the CVRA was the same but bradycardia and a decrease in blood pressure was induced by electric stimulation of the central end of depressor nerve.The CVRA was not changed by olfactory bulb section but was depressed by midbrain section.These results suggest that integration of trigeminal input occurs at pons medulla;the excitation of cardio-vagal centre and sympathetic constrictor centre and inhibition of cardio-sympathetic centre activity occurs during CVRA.The CVRA may be facilitated by higher central nervous system.The central mechanism of the CVRA differs from that of the depressor reflex.It may be concluded that in intact animal the cardiovascular response iuduced by various environmetal stimuli appears in characteristic and regular integrative patterns.

Key words: trigeminal nerve, heart rate, blood pressure, ammonia, rabbit