However, studies on 5-HT1A receptor expression in the raphe nuclei of patients with depression measured in vivo using positron emission tomography (PET) or in post-mortem brains have yielded contradictory findings: some investigators reported decreased expression (Drevets et al., 1999; Sargent et al., 2000; Arango et al., 2001; Meltzer et al., 2004), while others found enhanced expression (Stockmeier et al., 1998) or no difference compared to controls (Parsey et al., 2006). Here, HTR1A is linked to major depressive disorder.