SP-like immunoreactivity in the primary trigeminal neurons projecting to the nucleus tractus solitarii

Using the double-labeling method of retrograde transport of HRP combined with PAP immunocytochemistry, the neurons containing SP-like immunoreactivity (SPLI) of the trigeminal nerve projecting to the nucleus tractus solitarii (NTS) were examined. HRP-SP double-labeled neurons in the trigeminal ganglion, mainly small or middle-sized, were found after the NTS or the lingual nerve was injected with HRP followed by SP-immunoreaction. These findings demonstrate that the projection of the trigeminal nerve to the NTS contains SPLI.