Ontogenesis of neuropeptide degrading enzymes in the mouse brain

The ontogenesis of neuropeptide degrading enzymes was studied in the mouse brain, from the 10th gestational day up to adulthood. Two activities were followed: the pyroglutamate aminopeptidase and the post‐proline cleaving enzyme, using either TRH or specific fluorogenic peptides as substrates. In the hypothalamus as well as in cerebral hemispheres, the specific activities of both enzymes was highest on the 13th fetal day and decline thereafter until the 20–22nd post‐natal day, with a plateau around birth. In contrast, a classical peptidase, the leucyl‐arylamidase increased only in fetal life, and reached the adult level before birth.