Enkephalins Found in Ancient Fish Brains — But Not Dynorphin, Suggesting Different Evolutionary Origins
Authentic met-enkephalin and leu-enkephalin were detected in holostean fish and lungfish brains, but dynorphin-related peptides were not — suggesting the enkephalin system is evolutionarily more ancient.
Quick Facts
What This Study Found
Authentic met-enkephalin and leu-enkephalin were detected in holostean fish and lungfish brains. Dynorphin-related peptides were not detected in either species.
Key Numbers
How They Did This
Brain extracts were fractionated by Sephadex G-50 chromatography and analyzed by reverse-phase HPLC with radioimmunoassay for multiple opioid peptides.
Why This Research Matters
These ancient fish sit at key points in vertebrate evolution. Finding enkephalins but not dynorphins suggests the enkephalin system is more evolutionarily ancient.
The Bigger Picture
Tracing opioid peptide evolution helps us understand which aspects of the opioid system are ancient and conserved vs. recently evolved. The enkephalin system appears to be a more fundamental vertebrate feature.
What This Study Doesn't Tell Us
Negative results for dynorphin could reflect low abundance rather than true absence. Detection methods from 1991 were less sensitive than modern techniques. Only two species studied.
Questions This Raises
- ?At what point in vertebrate evolution did the dynorphin system appear?
- ?Are the undetected dynorphins truly absent or just below detection limits?
Trust & Context
- Key Stat:
- Enkephalins present, dynorphins absent Two ancient fish lineages had confirmed enkephalins but no detectable dynorphin-related peptides
- Evidence Grade:
- Preliminary comparative study limited by 1991-era detection sensitivity. Negative results should be interpreted cautiously.
- Study Age:
- Published in 1991. Opioid peptide evolution has been further mapped with genomic approaches.
- Original Title:
- The phylogeny of Met-enkephalin and Leu-enkephalin: studies on the holostean fish Lepisosteus platyrhincus and the Australian lungfish, Neoceratodus forsteri.
- Published In:
- General and comparative endocrinology, 84(2), 228-36 (1991)
- Authors:
- McDonald, L K(2), Joss, J M, Dores, R M(5)
- Database ID:
- RPEP-00201
Evidence Hierarchy
Tests effects in animals (usually mice or rats), not humans.
What do these levels mean? →Frequently Asked Questions
Why study opioid peptides in fish?
Fish evolved hundreds of millions of years before mammals. Finding which opioid peptides they have tells us which parts of the opioid system are ancient and which evolved later.
Could the dynorphins just be at undetectable levels?
Possibly. The detection methods of 1991 were less sensitive than modern techniques. However, the clear presence of enkephalins and absence of dynorphins across two species suggests a real difference in their evolutionary appearance.
Read More on RethinkPeptides
Cite This Study
https://rethinkpeptides.com/research/RPEP-00201APA
McDonald, L K; Joss, J M; Dores, R M. (1991). The phylogeny of Met-enkephalin and Leu-enkephalin: studies on the holostean fish Lepisosteus platyrhincus and the Australian lungfish, Neoceratodus forsteri.. General and comparative endocrinology, 84(2), 228-36.
MLA
McDonald, L K, et al. "The phylogeny of Met-enkephalin and Leu-enkephalin: studies on the holostean fish Lepisosteus platyrhincus and the Australian lungfish, Neoceratodus forsteri.." General and comparative endocrinology, 1991.
RethinkPeptides
RethinkPeptides Research Database. "The phylogeny of Met-enkephalin and Leu-enkephalin: studies ..." RPEP-00201. Retrieved from https://rethinkpeptides.com/research/mcdonald-1991-the-phylogeny-of-metenkephalin
Access the Original Study
Study data sourced from PubMed, a service of the U.S. National Library of Medicine, National Institutes of Health.
This study breakdown was produced by the RethinkPeptides research team. We analyze and report published research findings without making health recommendations. All interpretations are based solely on the published abstract and study data.