Immunocytochemical analysis of proenkephalin-derived peptides in the amphibian hypothalamus and optic tectum.

[Met5]-Enkephalin-, [Met5]-enkephalin-Arg6-, [Met5]-enkephalin-Arg6-Phe7-, metorphamide- and BAM 22P-like peptides could be localized in the amphibian brain by immunocytochemistry. However, a [Met5]-enkephalin-Arg6-Gly7-Leu8-like peptide could not be detected in the brain of any anuran species with an antiserum that was capable of detecting this octapeptide in mammalian brain. A synenkephalin-like peptide also could not be detected in the anuran brain with an antiserum that was capable of detecting the antigen in bovine and porcine brain. Although the intensity of proenkephalin-like immunoreactivity depended on the antiserum used, its distribution appeared to be identical with all of the effective antisera. Antisera directed against somatostatin and corticotropin-releasing factor stained perikarya, nerve fibers and terminals in the anuran brain with a distribution that was different from antisera directed against proenkephalin-derived peptides. The distribution of proenkephalin-containing perikarya and nerve fibers in the regions of the anuran brain selected for study showed many similarities to the distribution of proenkephalin-containing perikarya and nerve fibers in the same regions of the amniote brain.