The trigeminal sensory nuclei consist of the principal sensory nucleus and the spinal trigeminal nuclei, which are subdivided into the oralis, interpolalis and caudalis (Sp5C) on the basis of the cytoarchitecture. Sp5C is especially important in the processing of nociceptive information from the orofatial region. A number of previous studies have shown that Sp5C is mainly innervated by trigeminal nerve fibers which mediate nociceptive information. Furthermore, Sp5C has been suggested to relay nociceptive information to a number of brain structures involved in pain processing, such as the thalamus, periaqueductal gray (PAG), parabrachial nuclei (PB) and hypothalamus, and play a role in discrimination of nociceptive stimulation, modulation of sensitivity, emotion, and autonomic responses, respectively. However, it is unknown to which these areas a single Sp5C neurons sends axon fibers. In the present study, we labeled axonal arborization of a few Sp5C neurons in rat brain by a neuron labeling method with Sindbis viral vectors expressing palmitoylation site-attached green fluorescent protein (palGFP) or monomeric red fluorescent protein (pal-mRFP). The location of neurons infected with the Sindbis viral vectors was examined by Nissl-like staining. The palGFP- or pal-mRFP-labeled Sp5C neurons were completely visualized by immunoperoxidase staining for fluorescent proteins, and their axonal arborization was reconstructed. When the viral vectors were injected into the rostral part of the Sp5C, anterogradely labeled axon fibers were observed mainly in the PB. After injection of the viral vectors into the caudal part of the Sp5C, labeled axon fibers were distributed in the thalamus as well as PAG, PB. The present results suggest that the rostral part of the Sp5C is related to emotions, whereas the caudal part contributes to discrimination and modulation of nociceptive information.