Immunohistochemical studies have demonstrated the co-existence of neuronal NOS (nNOS) and serotonin in the rat hippocampus, medial septum and amygdala, which are brain areas rich of 5-HT1A receptors and critically involved in anxiety (Bredt et al. 1991; Dawson et al. 1991). This evidence concerns the gene HTR1A and Anxiety.