Origin of ascending intratrigeminal pathways in the cat

The retrograde horseradish peroxidase technique was used to locate neurons projecting to rostral trigeminal areas via ascending intranuclear pathways. After rostral trigeminal injections, labeled neurons were found in the subnucleus interpolaris and in all laminae of the medullary dorsal horn. Most neurons were labeled ipsilaterally in laminae III and IV, but some small neurons were labeled in lamina II in the medullary dorsal horn. The distribution of labeled cells suggested that these projections are topographically arranged. Labeled neurons were found in lamina I and lamina V, bilaterally; this was especially true if the parabrachial complex was included in the injection.