Differences in activation of the dorsal raphe nucleus depending on performance of suicide

The serotonergic system has been implicated in the pathogenesis of mood disorders as well as in suicidal behavior. It is unknown, however, whether raphe neurons, which are mostly serotonergic, show altered activity in patients with mood disorders who complete suicide as compared to those without suicidal behavior. In order to measure cellular markers of serotonergic activity in the dorsal raphe nucleus in brains of 12 people with mood disorders and of 12 controls (C), stereological measurements were carried out of nucleolar organizer regions (AgNORs) and of serotonergic neuron numbers. Six patients died from suicide (S) and the other six patients died from natural causes (NS). Results were assessed using ANOVA and post hoc Tukey-HSD tests looking for effects of diagnostic group (S, NS, C). Results show that in the rostral subnuclei of the dorsal raphe there was a significant effect of diagnostic group on the ratios of the nucleolar organizer regions to nuclear area (NOR ratio) and a nearly significant effect on numbers of serotonergic neurons. Post hoc tests revealed larger values for those dependent variables in S compared to NS. Dose equivalents of antidepressants correlated positively with NOR ratios and numbers of serotonergic neurons in the rostral part of the dorsal raphe. In conclusion, the present data suggest that there are functional differences in the dorsal raphe of patients with mood disorders depending on suicidal behavior. Antidepressants appear to contribute to cellular activation in the rostral part of the dorsal raphe.