Topographic organization of the projections from the interstitial system of the spinal trigeminal tract to the parabrachial nucleus in the rat.

Neurons in the paratrigeminal nucleus are known to project to the parabrachial region, but both these areas are heterogeneous, and the subnuclei that account for these connections are not known. To characterize better these projections, we injected small amounts of fluorogold or latex beads labeled with rhodamine or fluorescein into the parabrachial area in the rat and evaluated the retrograde transport of tracer to the paratrigeminal nucleus and neighboring regions. The results show that the rostral part of the paratrigeminal nucleus projects to the medial subnucleus of the parabrachial nucleus.