Differences in the effects of membrane depolarization on levels of preprosomatostatin mRNA and tyrosine hydroxylase mRNA in rat sympathetic neurons in vivo and in culture.

Regulation of preprosomatostatin mRNA and tyrosine hydroxylase mRNA were examined in sympathetic neurons of the rat superior cervical ganglion (SCG). Surgical denervation of the adult SCG increased ganglion levels of preprosomatostatin (SS) mRNA more than 11-fold, and levels of the mRNA remained elevated 14 days after surgery. By contrast, denervation decreased levels of tyrosine hydroxylase (TH) mRNA. Potassium- or veratridine-induced membrane depolarization of cultured neonatal sympathetic neurons decreased levels of SS mRNA but elevated levels of TH mRNA. Sodium channel blockade with tetrodotoxin prevented the effects of veratridine on SS and TH mRNAs. In toto these observations suggest that transsynaptic nerve impulse activity and sympathetic neuron membrane depolarization decrease SS synthesis but increase TH synthesis at the mRNA level. Thus nerve impulse activity may alter the relative levels of different transmitters co-expressed in the same neuronal population by inhibiting levels of some species of mRNA while simultaneously stimulating levels of others.