Serotoninergic projections from periaqueductal gray and dorsal raphe nucleus to parabrachial nucleus in rats

    JI Wei, PEI Liª²Yu, Shi Juan, LI Yunª²Qing, LI Jiª²Shuo

    Department of Anatomy and K. K. Leung Brain Research Centre, School of Basic Medicine, Fourth Military Medical University, Xi¬ðan 710033, China

    ¡¾Abstract¡¿ AIM: To observe the serotoninergic projections from the periaqueductal gray (PAG) and dorsal raphe nucleus (DR) to the parabrachial nucleus (PBN) in rats. METHODS: Fluoroª²Gold (FG) retrograde tracing combined with serotonin (5ª²HT) immunofluorescence histochemical staining method was used. RESULTS: In the rats injected with FG into the PBN, many neurons retrogradely labeled with FG were observed in the ventrolateral subdivision at the caudal level of the PAG and in the DR. 5ª²HTª²like immunoreactive neurons were densely localized in the DR. Some 5ª²HTª²like immunoreactive neurons were also found in the ventrolateral subdivision at the caudal level of the PAG. A few FG retrogradely labeled neurons also showed 5ª²HTª²like immunoreactivities. The majority of the FG/5ª²HT double labeled neurons distributed in the ventrolateral subdivision at the caudal level of the PAG and in the DR. CONCLUSION: 5ª²HT released from the PAG and DR neurons which send projection fibers to the PBN may modulate ascending somatic and/or visceral nociceptive information as it is relayed through the PBN to the forebrain sites. ......