Glutamatergic afferent projections to the dorsal raphe nucleus of the rat

Based on WGA-apo-HRP-gold (WG) retrograde tracing, the present study revealed that different subdivisions of the dorsal raphe (DR) such as dorsomedial, ventromedial, lateral wing, and caudal regions receive unique, topographically organized afferent inputs, that are more restricted than previously reported. Phaseolus vulgaris leucoagglutinin anterograde tracing studies confirmed that the medial prefrontal cortex provides the major afferent input to each subdivision of the DR. Double-labeling studies combining WG tracing and glutamate immunostaining indicated that the medial prefrontal cortex, various hypothalamic nuclei including perifornical, lateral, and arcuate nuclei, and several medullary regions such as lateral and medial parabrachial nuclei, and laterodorsal tegmental nucleus provide the major glutamatergic input to each subregion of the DR. It should be noted that the degree of glutamatergic input from these afferent sites was specific for each DR subdivision. The present findings indicated that dorsomedial, ventromedial, lateral wing, and caudal subdivisions of the DR receive excitatory inputs from both cortical and subcortical sites which might be involved in regulation or modulation of a broad range of systems, including sensory and motor functions, arousal and sleep–wake cycle, biorhythmic, cognitive, and affective behaviors.