Increasing evidence suggests that tachykinins are involved in the control of different pathological conditions, including psychiatric disorders. In this study we evaluated the expression of NK(1) and NK(2) receptors (NK-1R and NK-2R), as well as the effects of substance P (SP) and neurokinin A (NKA), in monocytes isolated from 15 healthy subjects and 15 patients with recurrent major depressive disorder (RMDD), under stable antidepressant therapy. NK-1R expression in monocytes from RMDD patients was significantly decreased as compared to healthy subjects, whereas NK-2R expression was markedly increased. Both NK-1R and NK-2R expression correlated with HAM-D, but not HAM-A, score. SP, NKA and selective NK-1R and NK-2R agonists stimulated TNF-α release in monocytes of both groups, with a significant higher effect observed in RMDD. Moreover they induced NF-κB activation, which was reversed by selective NK-1R and NK-2R antagonists, so demonstrating that it was receptor-mediated. The occurrence of a profound alteration in NK receptor expression in RMDD is a novel finding that suggests NK-1R and NK-2R pathways as possible relevant players in major depressive disorder, so improving our understanding of the complex pathogenesis of the disease.
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