Indeed, the findings that progenitor cells of some form exist both in the regenerative zebrafish heart, and in the hearts of less-regenerative mammals supports this idea. Zebrafish have ostensibly found some method to optimize the activity of progenitor cells, perhaps either by maintaining more cells, or by harboring a more cultivating environment for regeneration. Also, both mammalian and nonmammalian hearts contain an epicardial cell layer, yet zebrafish have found some way to activate the epicardium after injury, a process linked with essential neovascularization of regenerating muscle (Lepilina et al., 2006. This result points to the adult mammalian epicardium as a potential cellular source to assist myocardial regeneration or survival. Indeed, mammalian myocardial infarcts typically show poor or insufficient neovascularization, a response that many are trying to improve experimentally. Recent findings have indicated that the G-actin sequestering protein, Thymosin-ß4, may influence the mammalian epicardium. Treatment of adult cardiac explants with Thymosin-ß4 induced the migration of fibroblasts, endothelial and smooth muscle cells as assessed by gene expression and cellular morphology (Smart et al., 2007). In addition, in vivo Thymosin-ß4 treatment could partially restore cardiac survival and function following coronary ligation (Bock-Marquette et al., 2004). Notably, Thymosin-ß4 expression is induced in the injured zebrafish heart, suggesting that fish naturally release this epicardial stimulant on injury (Lien et al., 2006).

Jump up ^ Venkatesh B, Si-Hoe SL, Murphy D, Brenner S (November 1997). "Transgenic rats reveal functional conservation of regulatory controls between the Fugu isotocin and rat oxytocin genes". Proceedings of the National Academy of Sciences of the United States of America. 94 (23): 12462–6. Bibcode:1997PNAS...9412462V. doi:10.1073/pnas.94.23.12462. PMC 25001. PMID 9356472.

In mammals, many mysteries remain. Oxytocin is difficult to measure reliably in the brain, making it hard to know exactly where, when and how much is normally released; nor do scientists understand precisely how it works to alter behaviour. “What we need to start thinking about is the more fundamental role that oxytocin plays in the brain,” Young says. The determination to find out has been strengthened by a growing move in neuroscience to characterize circuits that are important in brain operations. “That's the level that's critical for understanding how the brain is regulating behaviour,” says Thomas Insel, director of the US National Institute of Mental Health in Bethesda, Maryland, who has studied oxytocin in voles.
Both the production of oxytocin and response to oxytocin are modulated by circulating levels of sex steroids. The burst of oxytocin released at birth seems to be triggered in part by cervical and vaginal stimulation by the fetus, but also because of abruptly declining concentrations of progesterone. Another well-studied effect of steroid hormones is the marked increase in synthesis of uterine (myometrial) oxytocin receptors late in gestation, resulting from increasing concentrations of circulating estrogen.
The first bit of evidence that points to oxytocin as nature’s love glue comes from researchers who measured the hormone in couples. Psychology professor Ruth Feldman at Bar-Ilan University in Israel, spent years studying oxytocin’s role in the mother–child bond and recently decided to dive into the uncharted waters of romantic bonds by comparing oxytocin levels in new lovers and singles. “The increase in oxytocin during the period of falling in love was the highest that we ever found,” she says of a study she and her colleagues published in Psychoneuroendocrinology. New lovers had double the amount Feldman usually sees in pregnant women.
Research shows that co-administration with carbidopa greatly increases plasma 5-HTP levels.[46] However, several studies have reported that 5-HTP is effective even without a peripheral decarboxylase inhibitor (e.g. carbidopa).[47][unreliable medical source?] Other studies have indicated the risk of a scleroderma-like condition resulting from the combination of 5-HTP and carbidopa.[48]
When combined with antidepressants of the MAOI or SSRI class, very high parenteral doses of 5-HTP can cause acute serotonin syndrome in rats.[23][24] It is unclear if such findings have clinical relevance, as most drugs will cause serious adverse events or death in rodents at very high doses. In humans 5-HTP has never been clinically associated with serotonin syndrome, although 5-HTP can precipitate mania when added to an MAOI.[25]