Effect of catecholamine depletion and denervation on neuropeptide Y(NPY) and tyrosine-hydroxylase (TH) mRNA levels in rat sympathetic ganglia.

Neuropeptide Y (NPY) and noradrenaline (NA) are synthesized and stored in sympathetic nerves and concomitantly released in response to appropriate stimuli. The two substances have been reported to interact on various levels: postjunctionally, by mutually potentiating their vasoconstrictor effects, prejunctionally, by inhibiting each other's release. The possibility of an interaction on the levels of their synthesis was investigated in this study. Specific cDNA probes were used for the measurement of the steady state levels of the mRNAs encoding prepro-NPY and tyrosine hydroxylase (TH) in the superior sympathetic cervical and stellate ganglia of rats. Reserpine (5 mg/kg) was administered for inducing catecholamine depletion. This caused a large decrease in the NA content of the heart associated with an about 50% reduction in cardiac NPY levels. Ganglionic NPY and TH mRNA levels increased 3-6 fold as compared to vehicle treated animals. To determine whether this effect was due to transynaptic induction, superior cervical ganglia were decentralized in a subgroup of rats. Decentralized ganglia displayed significantly lower NPY and TH mRNA levels than intact ones. The response to reserpine was almost completely prevented by decentralization. These Observations indicate that the activation of gene expression of NPY and TH by reserpine depends on intact ganglionic innervation and is therefore reflexly mediated. Trans-synaptic induction may regulate NPY and TH mRNA levels also under basal conditions.