UNIT ACTIVITY IN THE MEDULLA OBLONGATA OF FISHES

Adrian & Buytendijk (1931) have recorded potential waves in respiratory rhythm from the isolated brainstem of the gold-fish. The waves could continue for 1 hr. or more. During an investigation of the electrical activity of single cells in the central nervous system these results prompted us to explore with microelectrodes the medulla oblongata of fishes for unit activity in the respiratory centre. Carp, varying in size from 15 to 30 cm. (nose to tail) have been used in all experiments. The actual size of the animal is, however, of little importance as the brain volume does not differ appreciably in bigger and smaller carps, the surplus space in the skull of the bigger specimen being occupied by a jelly-like substance. The animals were anaesthetized by keeping them in a 1 % urethane solution till the reflexes disappeared. They were then fixed to a splint by means of a bandage; a cannula was tied into the mouth to lead a current of tap-water through the gills. When required, 10 % urethane solution was added. In later experiments the anaesthetized fish was placed in a basin with only the top of the skull above water