Fig. 4

Forest plots of within-group meta-analyses measuring peripheral brain-derived neurotrophic factor (BDNF) levels in subjects with bipolar disorder before and after treatment for an index acute manic or depressive mood episode. (a) Mania studies grouped according the source of the blood sample. All studies presented response to the manic episode after pharmacological treatment, as defined as a decrease of at least 50 % on the Young Mania Rating Scale scores. Plasma BDNF levels increased after successful treatment of an index manic episode. Serum BDNF levels remained unchanged. (b) Depression studies grouped according the source of the blood sample. Serum and plasma BDNF levels remained unchanged after treatment of an index depressive episode. (c) Depression studies grouped according response or non-response to pharmacological treatment of the acute depressive episode, defined as a decrease of at least 50 % on the Hamilton Depression Rating Scale scores. Serum and plasma BDNF levels remained unchanged after treatment of an index depressive episode regardless of response or non-response to treatment. The sizes of the circles are proportional to the sample size. Circles depict individual studies and diamonds depict the pooled effect sizes