OBSERVATION AND QUANTITATION OF EXOCYTOSIS FROM THE CELL BODY OF A FULLY-DEVELOPED NEURON IN PLANORBIS-CORNEUS

We have discovered a neuronal system that releases neurotransmitter vi a exocytosis from the cell body, In the large dopamine cell of the pon d snail Planorbis corneus, depolarization induces rhythmic release of dopamine from the cell body. When a stimulant is applied extracellular ly or intracellularly in situ to the cell body, transient dopamine con centration packets that appear in a bursting pattern are observed. Dop amine release is calcium dependent and release is on the time scale ex pected for exocytosis (2 to 4 msec rise times). Quantitation of indivi dual events reveals an average of 818,000 molecules per exocytotic eve nt. As many as 89,000 individual exocytotic events have been observed following a single stimulation of one cell. Neurotransmitter exocytosi s from the neuronal cell body appears to represent an alternative form of neurocommunication to synaptic transmission.