Role of endogenous PACAP38 in olfactory neuron survival. A, PACAP38 antagonist decreases olfactory neuron number. Incubation of primary cultures with the PACAP38 antagonist PACAP(6–38) [PAC(6–38)] for 2 d caused a 15–20% loss of neurons, without altering glial cell number (*p < 0.05). B, Neutralizing antibody against PACAP38 induces neuronal loss. Incubation of primary cultures with anti-PACAP38 antibody (αPAC) at 1:250 dilution for 1 d caused a 35% decrease in NST-positive cells relative to control (**p < 0.001). This loss can be prevented by coaddition of PACAP38 (αPAC + PAC). Nonimmune control rabbit serum (IgG) had no effect on neuronal number.