The role of sodium influx mediated by nicotinic receptors as an initial event in trans-synaptic induction of tyrosine hydroxylase in adrenergic neurons

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Abstract
1. Isolated superior cervical ganglia of the rat were incubated for 2–30 min (37°C) in Krebs' solution or tissue culture medium (BGJb) containing 22Na and then washed for 30 min in ice-cold 22Na-free Krebs' solution (to clear the extracellular space). The radioactivity remaining in the ganglia was taken as a measure of 22Na influx into the intracellular compartment of the ganglion. 2. Addition of cholinomimetics (100 μM nicotine or 100 μM carbachol) to the incubation medium led to an increase in 22Na influx. This increase reached maximal values after 10 min of incubation; it was more pronounced after incubation in Krebs' solution than in BGJb medium. 3. While chlorisondamine (3 μM) or dopamine (100 μM) greatly reduced the carbachol-induced 22Na influx, tetrodotoxin (2 μM) did not have any effect. 4. In ganglia obtained from animals treated with 6-hydroxydopamine in the early postnatal phase (resulting in an extensive destruction of peripheral sympathetic neurons) neither carbachol (100 μM) nor nicotine (100 μM) produced an increase in 22Na influx demonstrating that the intraneuronal compartment is responsible for this enhanced influx. 5. The effects of dopamine, chlorisondamine and tetrodotoxin on the carbachol-induced 22Na uptake into superior cervical ganglia are similar to their effects on carbachol-mediated induction of tyrosine hydroxylase in superior cervical ganglia kept in tissue culture (Thoenen and Otten 1977b). It is concluded that the induction of tyrosine hydroxylase via nicotinic receptors is closely linked to the enhanced sodium influx into the adrenergic neurons mediated by the same receptors.