ADCYAP1 and Keratoconjunctivitis sicca: Development of dry eye-like symptoms such as reduced tear secretion and corneal keratinization has been reported in PACAP-null mice, which could be improved by PACAP eye drops via the PAC1R/adenylyl cyclase/cAMP/protein kinase A (PKA)/aquaporin 5 (AQP5) cascade [224].