Objective To observe the relationship between 5-Hydroxytryptamine (5-HT)like immunoreactive terminals and the vestibuloparabrachial nucleus projection neurons which may express 5-HTSUB>1A/SUB> receptor in the vestibular nuclear complex (VNC). Methods Retrogradedtract tracing technique combined with double labeling of immunofluorescence histochemical was used, and the stained sections were observed under a confocal laserscanning microscope. Results Following injection of tetramethylrhodamine (TMR) into the parabrachial nucleus, many retrogradely labeled neurons were observed bilaterally within VNC, but with an ipsilateral predominance. Immunofluorescence histochemical staining showed that many neurons expressed 5-HTSUB>1A/SUB> receptorlike immunoreactivity and a large number of 5-HT immunostained fibers or terminals were found in the medial, spinal, superior, lateral vestibular nucleus (MVe, SpVe, SuVe, LVe), X nucleus and Y nucleus. Confocal laserscanning microscopy revealed that some TMRlabeled neurons were 5-HTSUB>1A/SUB>R immunopositive, and some of the cell bodies or dendrites of TMR/5-HTSUB>1A/SUB>R doublelabeled neurons were closely apposed by 5-HTlike immunoreactive termina