Post-natal development of ganglia in the lower lumbar sympathetic chain of the rat.

The initial stages in the development of functional synapses have been examined in ganglia of the lower lumbar sympathetic chain of the rat using intracellular recording techniques. In animals of age up to 7 days post-natal, many impaled cells were inexcitable and possessed no synaptic input. The proportion of excitable cells impaled increased with the age of the animal. Two types of action potential could be identified. Initially the synaptic input consisted of one or a few subthreshold synaptic potentials. The number of preganglionic inputs to each cell increased over the first 1-2 weeks after birth. The quantal content of each input was initially very low. At least some inputs showed an increase in quantal content during development; eventually one or occasionally two inputs became suprathreshold. Voltage-clamp studies indicated that the time course of excitatory synaptic currents did not change during development. The amplitudes of miniature excitatory synaptic currents in animals aged less than 10 days were some three to five times the size of those recorded from mature animals.