Thiochrome, a natural oxidation product and metabolite of thiamine, is a selective M4 muscarinic receptor of acetylcholine (ACh) affinity enhancer. Thiochrome has neutral cooperativity with ACh at M1 to M3 receptors[1][2].
Thiochrome can increase the intensity of the reproduction process of the representatives of one-cell organisms worms, crustaceans, insects and fishes[1].
[1]. Petrov SA, et al. Administration of Thiamine and Thiochrome Enhanced Reproduction of Chlorella, Drosophila melanogaster, and Danio. J Nutr Sci Vitaminol (Tokyo). 2016;62(1):6-11. [2]. Lazareno S, et al. Thiochrome enhances acetylcholine affinity at muscarinic M4 receptors: receptor subtype selectivity via cooperativity rather than affinity. Mol Pharmacol. 2004 Jan;65(1):257-66.