Winter 1996 Volume 5, Number 1
By studying the synapses in the hippocampus, Karin Sorra and Kristen Harris at Children's Hospital are probing the relationship between the actual shape of the synapse and its function in this key memory structure of the brain. Using various techniques, the researchers make the synapses visible and analyze computer-aided reconstructions to uncover the complex 3-dimensional organization of the connections. They document the number, geometry and subcellular compositon of the synapses
Of particular importance to the researchers are "dendritic spines," the finger-like protrusions on neurons (called "postsynaptic" neurons) that receive excitatory input from signal-sending neurons. The researchers want to know if dendritic spines change their shape or if new spines form when hippocampal circuits "learn." To answer this question, they use a slice of hippocampal tissue containing many thousands of synapses kept alive over many hours in a dish. They record the electrical signals of the synapses and stimulate them with a high-frequency signal (as a new piece of information would do in a living brain). Then, in effect, they "freeze" the synapses with a chemical fixative to see if the stimulation has changed them and how. In this manner, Sorra and Harris will determine whether an anatomical basis underlies hippocampal learning and memory in these neurons.
