Based on the results of the present study and previous literature, we propose the following model for KP dysregulation in schizophrenia: inflammatory mechanisms induce an increased conversion of TRP to KYN in the periphery (which can cross the BBB) leading to elevated brain KYN that is converted to KYNA by the proinflammatory-driven increase in KAT enzyme activity via increased mRNA in astroglia. This evidence concerns the gene NPPA and schizophrenia.