Cholecystokinin (CCK)/gastrin-like immunoreactive neurones in the cerebral ganglion of the protochordate ascidians Styela clava and Ascidiella aspersa.

Antisera raised against the COOH-terminal sequence of mammalian CCK/gastrin were used to ascertain the distribution of CCK/gastrin-like immunoreactive cells in the cerebral ganglion of two ascidian protochordates. Styela clava and Ascidiella aspersa. the cell bodies were found to have a specific regional distribution in Ascidiella, but not in Styela. In addition to central immunoreactive nerve fibres, a number of peripherally located immunoreactive fibres was found. These observations support the idea that some centrally originating protochordate neuronal peptides may have a peripheral role and give weight to the hypothesis that many vertebrate brain-gut peptides had their origin in the neuronal elements of more primitive species.