Different determinants on growth and synapse formation in cultured neurons

The influence of substrate and target on growth and synapse formation was investigated in identified leech neurons in culture. Nociceptive neurons and annulus erector motoneurons were cultured on ganglion capsules, a substrate they encounter in the leech. Within a few hours, single nociceptive cells sprouted profusely, whereas annulus erector cells failed to grow. When annulus erector neurons were plated near a nociceptive cell on the same capsule both neurons grew, made contact and formed an electrical synapse, different from the chemical synapse they form in the ganglion, but identical to that formed when plated on Concanavalin A. These results suggest that substrate and target have complementary effects regulating growth, but fail to define the type of synapse formed.