Nerve growth factor (NGF) stimulates 5-HT3 receptor expression although the mechanism(s) responsible for this effect are unknown. We report the nucleotide and deduced amino acid sequences of a nearly complete rat 5-HT3 receptor subunit and use the sequence to develop a reverse transcription-polymerase chain reaction (RT-PCR) assay that measures 5-HT3 mRNA. Exposure of PC12 cells to NGF results in increasing steady-state levels of 5-HT3 mRNA. The four-fold increase in mRNA correlates with and is sufficient to account for increases in receptor measured by agonist induction of whole cell currents.