Melanotan II and social behavior in a mouse model of autism
A week of Melanotan II restored social behavior in a maternal immune activation mouse model. What the study shows, and the caveats that matter.
Published . Updated
Summaries of published research for educational discussion. Not medical advice.
Melanotan II is best known as a tanning peptide. Its effects come from activating melanocortin receptors, a family of receptors involved in skin pigment, appetite, and sexual function. One of those receptors, MC4R, also influences oxytocin, a hormone tied to social bonding. That connection led researchers to test whether Melanotan II could change social behavior in a mouse model of autism.
The study
The 2019 study, published in PLOS ONE by researchers at UCLA and collaborators, used a maternal immune activation model. Pregnant mice receive an immune challenge that mimics a serious infection, and their offspring grow up with behaviors resembling some autism traits. Human population studies have linked serious infections during pregnancy with somewhat higher autism risk, which is the rationale for the model.
The adult male offspring showed what the model is designed to produce:
- Reduced interest in other mice
- Fewer ultrasonic vocalizations, which mice use to communicate
- More repetitive behaviors
The researchers then gave these mice Melanotan II continuously over seven days.
What they found
- Social behavior improved. Melanotan II restored the social measures that were impaired in the model mice.
- Normal mice didn’t become more social. In typical mice, the peptide didn’t meaningfully change social behavior, suggesting it corrected a deficit rather than generally boosting sociability.
- It caused significant weight loss in normal mice over the week, consistent with MC4R’s known role in suppressing appetite.
The authors propose that activating MC4R stimulates the brain’s oxytocin system, which has its own research history in social behavior.
Important caveats
- Mice aren’t people, and this is one model. Autism in humans is highly varied and largely genetic. A model built on prenatal immune activation captures one possible contributing pathway, not autism as a whole.
- Only males were treated, and only briefly. Long-term effects weren’t studied.
- “Reverses autistic features”, the paper’s title, refers to behavioral measures in mice. It shouldn’t be read as reversing autism.
- Melanotan II has real side effects. Nausea, flushing, appetite loss, and spontaneous erections are common. There are also case reports of new or changing moles, which is why dermatologists warn against its use for tanning. It isn’t approved as a drug anywhere. A related, more selective compound, bremelanotide (Vyleesi), is FDA-approved for low sexual desire in premenopausal women.
- Oxytocin itself has had mixed results in human autism trials, which tempers expectations for approaches that work through it.
Bottom line
The study is a neat demonstration that the melanocortin system can influence social behavior in a mouse model. It’s an interesting lead for researchers, not evidence that Melanotan II helps autistic people.
Sources
- Minakova E, Lang J, Medel-Matus JS, Gould GG, Reynolds A, Shin D, Mazarati A, Sankar R. Melanotan-II reverses autistic features in a maternal immune activation mouse model of autism. PLOS ONE. 2019;14(1):e0210389. doi:10.1371/journal.pone.0210389