SST and bipolar disorder: Abnormalities in somatostatin are evident in schizophrenia, major depressive disorder, and bipolar disorder, manifesting as decreased cerebrospinal fluid (CSF) somatostatin levels and reduced somatostatin immunoreactivity across cortical and subcortical regions in both schizophrenia and major depressive disorder (Rubinow, 1986; Lin and Sibille, 2013).