Demonstration of decreased activity of dorsal raphe nucleus neurons in depressed suicidal patients by the AgNOR staining method

BackgroundSuicide and depression are closely related yet distinct phenomena. In both these phenomena, research has focused on central serotonergic system disturbances. The dorsal raphe nucleus (DRN) is the main source of serotonergic innervation of limbic structures crucial for the regulation of emotionally influenced behaviour.MethodsThe study was carried out on paraffin-embedded brains from 23 depressed patients (12 suicides and 11 non-suicides) and 26 matched controls without mental disorders. The karyometric parameters of DRN neurons were evaluated by the AgNOR silver staining method.ResultsThe significant effect of suicide on the nuclear area was found in the cumulative analysis of all DRN subnuclei (ANOVA, P = 0.032). A decreased mean value of this parameter was observed in the suicides group versus controls (t-test, P = 0.032). This effect was especially pronounced in the violent suicide victims (t-test, P = 0.001), who also demonstrated a decreased AgNOR area versus controls (t-test, P = 0.007). No significant effect of depression or polarity on AgNOR parameters was found.LimitationsA major limitation of this study is relatively small case number. A further limitation is given by the lack of data on drug exposure across the whole life span.ConclusionOur findings suggest that hypoactivity of DRN neurons is a distinct phenomenon in depression, specific only for suicidal subgroup of depressed patients.