Excitatory and Depressant Properties of Certain Brain Fractions

Abstract

ALTHOUGH it is generally believed that at most synapses in the brain ‘transmitter’ substances are released from nerve endings to excite or inhibit the post-synaptic cells, the identity of the transmitters involved is still very much in doubt. Gray and Whittaker¹ have shown that a fraction of brain homogenates can be prepared containing mainly pinched-off nerve endings. More recently it has been possible to release apparently intact synaptic vesicles from such a nerve-ending fraction and to separate them from other membrane structures by density-gradient centrifugation². The purified vesicle fraction contains acetylcholine but not the other components of the acetylcholine system. Since nerve endings can be expected to contain substantial amounts of various transmitter substances, we have examined the excitatory and depressant effects produced by various subtractions of guinea-pig brain, when applied from micropipettes to single units in the guinea-pig's cerebral cortex.