Early animal studies have demonstrated that injections of allopregnanolone result in dose-dependent marked scratching behaviour in atopic dermatitis mice, whilst administration of 2-methyl-5-HT (a tryptamine derivative closely related to serotonin that acts as a moderate 5HT3 agonist) almost completely suppressed the allopregnanolone-induced scratching [55]. Here, HTR3A is linked to atopic eczema.