HTR5A and Anxiety: Indeed, some of the earliest hypotheses on the function of 5-HT in the brain proposed that it serves to suppress behavioural response to pain (Harvey et al., 1975), anxiety (Wise et al., 1970) and aversive stimuli more generally (Deakin and Graeff, 1991; Soubrie, 1986) and these ideas continue to have traction (Deakin, 2013; Yanowitch and Coccaro, 2011).