TPH1 and hyperinsulinism: To investigate the effect of insulin on mRNA expression of SERT, TPH1 and MAOA, ACH-3P cells were cultured in the absence (control) or presence of 10 nM insulin (hyperinsulinemia) in conditions of 6.5% O2 or 2.5% O2, for 24 or 48 h (Figure 2).