Studies on rat sympathetic neurons developing in cell culture. II. Synaptic mechanisms.

Sympathetic neurons dissociated from superior cervical ganglia of newborn rats were grown in culture either alone or with non-neuronal cells, as described in the preceding paper. In the presence of the non-neuronal cells, but rarely in their absence, neurons formed functional synapses with each other de novo. The synapses were of two types, both excitatory. One type operated by nonrectifying electrical transmission and comprised only a few percent of the interactions; it was characterized by negligible synaptic delay and the transfer of steady depolarizations or hyperpolarizations from one cell to the other. At the second type of synapse which was chemical, there was a synaptic delay (minimum, 1 msec) and the amplitudes of the chemically mediated postsynaptic potentials (e.p.s.p.'s) were dependent on the concentrations of Ca²⁺ and Mg²⁺ in the extracellular medium. As described in the following paper, the e.p.s.p.'s were sensitive to nicotinic-cholinergic blocking agents. The incidence of chemical transmission increased markedly with age in culture. This increase was associated with the formation of networks in which the neurons were extensively connected to each other. In such cultures an action potential evoked in one neuron often gave rise in other neurons and in the stimulated neuron to a volley of synaptic activity (“complex wave”) which occurred nearly synchronously, though not identically, in each neuron. The complex waves depended on chemical transmission since they, like the simple e.p.s.p.'s, were abolished by nicotinic blocking agents.