Methionine-enkephalin-like immunoreactivity in the nervous ganglion and the ovary of a protochordate, Ciona intestinalis.

When methionine-enkephalin antiserum was applied to paraffin sections of adult Ciona intestinalis it reacted with neurons in the ganglion and along the visceral nerve. The fluorescence was strong before and during spawning season, but partially disappeared at the end of August. With the same antibody a positive immunoreactivity was detected in the ovary during the growth of oocytes. The distribution of positive granules in the cytoplasm did not change significantly with varying lighting conditions (normal photoperiod, permanent light or darkness) in which the animals were maintained. In contrast, treatment with a substance isolated from crude extracts of Ciona ("peroxide 1") induced a dense, crescent-like concentration of positive granules near the nucleus of oocytes. The follicular cells did not show any immunofluorescent reaction.