Development of dendritic calcium currents in ganglion cells of the rat lower lumbar sympathetic chain.

Post-natal changes in the active membrane properties of ganglion cells of the rat lumbar sympathetic chain have been examined using current-clamp and voltage-clamp techniques. Ganglion cells from the youngest animals studied (3 days post-natal) which received a synaptic input generated action potentials that were abolished by tetrodotoxin (TTX). In neurones from animals aged 7-14 days, a TTX-resistant component of the action potential was revealed which persisted in cells from older animals. Voltage-clamp studies suggested that the TTX-resistant component of the action potential resulted from calcium entry at a point that was electrically close to the somatic voltage clamp at early ages, but became electrically distant in older neurones. The site of the inward calcium current appeared to be restricted to specialized areas on one, or occasionally two, dendrites. Concurrent with these changes, the dendritic trees of the ganglion cells expanded and the nature of the synaptic input changed. Initially preganglionic stimuli initiated only subthreshold excitatory synaptic potentials, whereas in the more mature animals most cells also received at least one suprathreshold ('strong') input. The number of distinct sites of calcium current generation was correlated with the number of strong synaptic inputs that a given neurone received.