Phorbol ester administration transiently increases aromatic L-amino acid decarboxylase activity of the mouse striatum and midbrain.

Aromatic L-amino acid decarboxylase (AAAD) is required for the synthesis of catecholamines, serotonin, and the trace amines. We found that the protein kinase C activator phorbol 12-myristate 13-acetate administered intracerebroventricularly transiently increased AAAD activity by 30-50% over control values within approximately 30 min in the striatum and midbrain of the mouse. The enzyme increase was manifested as an apparent increase of Vmax with little change of Km for either L-3,4-dihydroxyphenylalanine or pyridoxal phosphate. Chelerythrine, a protein kinase C inhibitor, prevented the phorbol ester-induced increase of AAAD. Moreover, okadaic acid, a serine/threonine-selective protein phosphatase 1 and 2A inhibitor, also increased AAAD activity in the mouse striatum and midbrain. Taken together, these observations suggest that protein kinase C-mediated pathways modulate AAAD activity in vivo.