Research in this laboratory is concerned with the study of transmitter release at a CNS synapse in the lamprey spinal cord. The advantages of this preparation are two fold. First, the spinal cord can be removed from the animal and the cells remain viable for several hours; thus, the preparation is ideal for in vitro studies. Second, many of the cells as well as presynaptic elements can be seen with the aid of a dissecting microscope and placement of microelectrodes can be made under visual control. The model used for study is the giant interneuron, which receives three main afferent inputs from: 1) other giant interneurons; 2) primary afferent fibers; 3) a giant axon whose cell body is located in the brain. Experiments so far have been concerned with the calculation of the mean quantum release at the synapse made between giant axon and interneuron; the determination of the reversal potential of iontophoretically applied 1-glutamate to the interneuron; the origin of spontaneously occurring post synaptic potentials at the giant interneuron. Experiments are now underway which will correlate the post synaptic responses on the interneuron produced by the three afferent inputs described above with an electron microscopic examination of the synapse in question.