Nodose (inferior vagal sensory) ganglia were removed from neonatal rats, enzymatically dispersed using neutral protease, and maintained on previously dispersed rat atriacytes. After 7-10 days in culture, calcitonin gene-related peptide (CGRP) was present in 1-3 times the molar amount of substance P (SP). The content of SP was doubled by the addition of nerve growth factor (NGF) whereas CGRP was significantly less increased by 50% or less. The addition of forskolin increased SP and CGRP levels in cultures with or without NGF by 60-80 percent. Phorbol ester (PMA) did not alter SP content but significantly raised CGRP content by 40% in NGF supplemented cultures (P less than 0.001). Corticosterone, 0.01-0.1 microM, reduced SP content by 30% independently of NGF but had no effect on CGRP. These studies demonstrate that SP in vagal sensory neurons is more sensitive than CGRP to the effects of NGF or corticosterone. Both peptides are up-regulated by presumed increases in intracellular cyclic AMP, while CGRP (or CGRP neurons) may be independently regulated by protein kinase C.