Phenotypic changes of AADC-only-immunoreactive cells in the alimentary canal of the laboratory shrew, Suncus murinus, induced by systemic administration of monoamine precursors

In order to elucidate the function of anti-aromatic acid decarboxylase (AADC)-only-positive cells in the alimentary canal, 5-hydroxy-L-tryptophan (5-HTP) or L-3,4-dihydroxyphenylalanine (L-DOPA) was intraperitoneally injected into the laboratory shrew, Suncus murinus, and immunohistochemical studies were conducted on continuous sections of the alimentary canal using specific antisera against tyrosine hydroxylase (TH), AADC, dopamine (DA), and serotonin (5-HT). AADC-only-positive cells localized to the epithelial layer of the alimentary canal from the stomach to the large intestine. These AADC-only-positive cells became DA- and AADC-positive cells after L-DOPA injection, and 5-HT- and AADC-positive cells after 5-HTP injection. These results strongly indicate that the AADC-only-positive cells in the alimentary canal of Suncus murinus are capable of synthesizing DA and 5-HT simultaneously upon administration of L-DOPA and 5-HTP.