Methionine-enkephalin immunoreactivity in the gonads and nervous system of two insect species: Locusta migratoria and Sarcophaga bullata.

Methionine(met)-enkephalin immunoreactivity as visualized by the peroxidase-antiperoxidase procedure, is present in spermatogonia, spermatocytes, spermatids, and young ovarian follicles of Locusta (panoistic type) and Sarcophaga (polytrophic type). Follicle cells and mature spermatozoa are always immunonegative as are locust vitellogenic follicles. In oocytes and in trophocytes, the met-enkephalin-like material first appears around the nucleus and is then dispersed throughout the cytoplasm. Later, it is present only in the periphery. In the ovary of both insects, no immunoreactivity is found with antisera against adrenocorticotrophic hormone, melanophore stimulating hormone, beta-endorphin, corticotropin releasing factor, or leucine-enkephalin. All these antisera yield a positive reaction when applied to the central nervous system as does the met-enkephalin antiserum. This study indicates that the met-enkephalin-like peptide may play a role in reproductive physiology.