MEDULLARY LOCI CRITICAL FOR EXPRESSION OF GASPING IN ADULT-RATS

1. Our purpose was to define whether a region of medulla could be iden tified that is critical for the expression of gasping. 2. Decerebrate, vagotomized, paralysed and ventilated adult rats were used. The patte rn of phrenic activity was reversibly altered from eupnoea to gasping by exposure to hypoxia or anoxia. 3. Gasping was irreversibly eliminat ed following unilateral electrolytic lesions of the lateral tegmental field of the medulla. The eupnoeic rhythm continued after these lesion s. 4. Injections of kainic acid into the lateral tegmental field also eliminated gasping. Phrenic activity in eupnoea was not altered. 5. Le sions outside the lateral tegmental field caused marked changes in the eupnoeic rhythm, including expiratory apnoea. Upon exposure to hypoxi a or anoxia, gasping was still induced. 6. This region for the neuroge nesis of gasping in rats is identical to the region that serves a comp arable function in cats. Moreover, it overlaps with the 'pre-Botzinger ' complex which has been described for the in vitro brainstem preparat ion of the neonatal rat. Our results raise doubts that this complex pl ays a role in the neurogenesis of eupnoea.