a serotonin antibody is the best; there are several types of tryptophan hydroxylases TPH1 and TPH2 depending which type of cells make the serotonin. If it is in neurons that you aim at localizing serotonin, then TPH2 would be the appropriate enzyme. Some serotonin antibodies label the soma/cell body of neurons better than the processes and other do the reverse. So search wisely. Godd luck!