Early life stress (ELS) increases 5-HT1A expression in the Edinger–Westphal nuclei (EWcp). ELS and serotonin transporter (5-HTT) genotypes affect DNA methylation of the urocortin 1 gene in the EWcp. 5-HTT deficiency is associated with decreased 5-HT innervation of EWcp-urocortin 1 neurons. ELS is associated with an increased number of 5-HT neurons in the lateral wings of the dorsal raphe nucleus.