Depression and CSF endorphin fraction I: seasonal variation and higher levels in unipolar than bipolar patients.

Radioreceptor assay of endorphin Fraction I in the cerebrospinal fluid (CSF) of 92 inpatients suffering from major depression revealed the following: (1) clearly elevated levels as compared to normal control subjects, (2) higher level in unipolar than in bipolar patients, and (3) seasonal rhythms showing peaks in early fall for unipolar patients and late fall for bipolar patients. The annual pattern observed bears some resemblance to the known seasonal variations in the incidence of affective disorders and suicide.