Unaltered histaminergic system in depression: a postmortem study

Background Rodent experiments suggested that the neuronal histaminergic system may be involved in symptoms of depression. Methods We determined, therefore, in postmortem tissue of 12 mood disorder patients (8 major depression disorder (MDD) and 4 bipolar disorder (BD)) and 12 well matched controls the expression of the rate-limiting enzyme for histamine production and histidine decarboxylase in the tuberomamillary nucleus (TMN) by quantitative in situ hybridization. In addition we used qPCR to determine the expression of the 4 histamine receptors and of the enzyme breaking down histamine, histamine N-methyltransferase (HMT), in the dorsolateral prefrontal cortex (DLPFC) and anterior cingulated cortex (ACC). Results No changes were observed in the expression of these molecules, except for a significant lower HMT mRNA expression in the ACC of MDD subjects. Limitations Several inherent and potentially confounding factors of a postmortem study, such as medication and cause of death, did not seem to affect the conclusions. The group size was relatively small but well documented, both clinically and neuropathologically. Conclusion Except for a lower HMT mRNA expression in the ACC of MDD subjects, the neuronal histaminergic system did not show significant changes, either in the rate limiting enzyme involved in its production or in its receptors in 2 main projection sites, the ACC/DLPFC.