I. POLIACEK 1 , J. JAKUS 1 , J. KNOCIKOVA 1 , H. BARANI 1 , E. HALASOVA 2 , N. VISNOVCOVA 1 MEDULLARY RAPHE MIDLINE IS INVOLVED IN PRODUCTION OF EXPULSIVE EXPIRATIONS IN ANESTHETIZED RABBITS 1 Institute of Medical Biophysics and 2 Institute of Medical Biology, Jessenius Faculty of Medicine, Comenius University, Martin, Slovakia Effects of kainic acid lesions in the medullary raphe midline on reflex expirations induced mechanically from the trachea were examined. Spontaneously breathing rabbits were anesthetized by ketamine and xylazine i.m., followed by pentobarbitone i.v. Excitatory neurotoxin kainic acid (2 mg/ml in artificial CSF, total volume of 55- 100 nl) was pressure microinjected into the medullary midline, rostral to the obex (2 microinjections at 2 different depths). The lesion (mostly affected the obscurus and magnus raphe nuclei) reduced the number of reflex expirations by 80% and expiratory amplitudes of esophageal pressure, abdominal EMG moving averages, and abdominal EMG powers by 71%, 62%, and 57%, respectively (in all cases P<0.05). The duration of abdominal activity in post-lesion responses was not altered. Control microinjections of artificial CSF had no effect on the reflex responses. We conclude that in rabbits, the medullary raphe nuclei participate in the control of expiratory expulsions originating from the trachea. Key words: expiration, cough, kainic acid, rabbit, raphe midline INTRODUCTION Expiratory expulsions of the cough, sneeze, and expiration reflexes play a crucial role in the airway defense. They enable to expel penetrating particles and irritants from relevant parts of the airways (1). The motor pattern of the cough and expiration reflex (ER) seems to be produced by a common respiratory/cough generating neuronal network located in the rostral ventrolateral medulla (VLM; 2, 3). Our studies support a view that expiratory (E) neurons of the rostral VLM JOURNAL OF PHYSIOLOGY AND PHARMACOLOGY 2008, 59, Suppl 6, 597-605 www.jpp.krakow.pl