ABSTRACT
The projections from the nucleus tractus solitarii (NTS) and the nuclei parabrachiales (PB) to the nucleus accumbens (Acc) in the rat have been visulized using anterograde and retrograde HRP tracing techniques. After injecting HRP into the Acc, retrogradely labelled neurons were observed in bilateral PB and NTS with ipsilateral predominance. The labelled neurons were concentrated in the following areas of the PB and NTS: the waist area of the caudal PB, the external subnucleus and other part of the nucleus medialis parabrachialis (PBm), the external, central, and internal subnuclei of the nucleus lateralis parabrachialis (PB1) and the medial subnucleus of the caudal NTS (NTSm). After injecting HRP into the NTSm and commissural nucleus of the NTS, anterogradely labelled terminals were found bilaterally in the PBm and the ventral 3/4 area of the PB1. The densest sites occupied the waist area, the external, central, and internal subnuclei of the PB1. The density of the labelled terminals on the ipsilateral side was little higher than that on the contralateral side. The results indicate that there are two possible pathways from the NTS to the Acc, the one is the direct projection from the medial subnucleus of the caudal NTS to the Ace, the other is an indirect one, i. e. from the medial subnucleus and commissural nucleus of the caudal NTS to the waist area of the caudal PB, the external subnucleus, the dorsal part of the PBm, the external, central, and internal subnuclei of the PB1, where the NTS projection is. presumed to be relayed, and then, project from the PB to the Acc. This connection may be involved in the neural regulation of visceral and locomotor activities.