Mechanical stimulation of the nasopharynx or adjacent regions, particularly in cats, pigs and dogs, induces forceful spasmodic inspiratory efforts, called aspiration reflex (AR) [1,2], closely resembling sniffing or hiccough [3]. Under pentobarbitone anaesthesia (40 mg/kg i.p.) airflow and blood pressure were recorded in 11 cats (6 with induction of 300 AR-es in 30 min and 5 quietly breathing controls). After humane killing, parallel histo-chemical preparation and computer-aided counting, the Fos-like immunoreactive (FLI) dots were compared by Mann-Whitney test, n= 6 and 5. A significant increase in number of FLI dots, indicating strong neuronal activation was observed mostly in the following 12 of 35 selected brainstem nuclei, localised according to Berman’s stereotaxic atlas [4]. Respiratory group neurones indicated a large increase in FLI as follows: commissural nuclei of NTS (10 ×, p<0.01), ambigual, paraambigual and facial nuclei (12 ×, p<0.02). This strong recruitment of active neurones reflects the powerful spasmodic inspiratory activity of the AR. Also the cardiovascular group neurones showed increased FLI: particularly in Nucl. retrofacialis (10 ×, p<0.01) indicating strong cardiovascular effects of the AR with possible implication also in cardio-pulmonary-cerebral resuscitation. The neurones of the Reticular activating system showed also an increased number of FLI dots. Such strong recruitment explains the powerful arousal and revitalisation effects of the AR. Recruitment was observed particularly in the medullary lateral and magnocellular tegmental fields (11 ×, p<0.02), in pontine lateral and magnocellular fields (3 ×, p< 0.02) and in area mesencephalis ventralis -tegmentum tsai (1.6 ×, p< 0.05). The descending reticular tract neurones were strongly activated too, explaining the strong influences on various tonic activities [5]. Particularly the Raphe nuclei (5 ×, p<0.02), and the paragigantocelular lateral nucleus (2.5 ×, p<0.02), were involved. Immunohistochemical c-Fos study indicated very strong neuronal activation of the brainstem respiratory and cardiovascular control mechanisms and both the ascending and descending parts of Reticular formation by AR in cats. The results suggest that the AR can be a very useful tool for studies of various influences, including drugs on 3 main vital functions and particularly their mutual interaction