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

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