Trafficking of neurokinin-1 receptors in serotonin neurons is controlled by substance P within the rat dorsal raphe nucleus.

Substance P (SP) modulates serotonin neurotransmission via neurokinin-1 receptors (NK1rs), and exerts regulatory effects on mood through habenular afferents to the dorsal raphe nucleus (DRN). We have previously demonstrated that, in the caudal DRN of rat, some serotonin neurons are endowed with NK1rs that are mostly cytoplasmic, whereas these receptors are mostly membrane bound in non-serotonin neurons. Here, we first examined by double-labeling immunocytochemistry the relationships between SP axon terminals and these two categories of DRN neurons.