Concerning the serotonin receptor (5-HT2AR), it was shown that serotonin induced melanogenesis in melanoma cell lines through the 5HT2A-receptor [57], and the melanin concentrating hormone–melanin concentrating hormone receptor (MCHR) system was suggested to be a functional antagonist of the alpha-MSH-MC1R system [58,59]. Here, MCHR1 is linked to melanoma.