Electrical synapses by guided growth of cultured neurons from the snail Lymnaea stagnalis.

The ability to assemble neuronal networks with designed topology would allow uniquely defined experiments on neurocomputing. We describe a fundamental step, the controlled formation of synapses by guided outgrowth, in vitro for the first time combining simple neuritic geometry with predefined connectivity. We used neurons from the A-clusters in the pedal ganglia of the snail Lymnaea stagnalis. They were cultured on a substrate with linear patterns made by adsorption of brain-derived conditioning factors and photolithography. We induced and observed the frontal collision of two growth cones on narrow lanes. Following such encounters. individual electrical synapses formed that were sometimes strong enough for prolonged presynaptic stimulation to reach the threshold of postsynaptic firing.