Axon arbors of functionally distinct whisker afferents are similar in medullary dorsal horn

Using the intra-axonal horseradish peroxidase (HRP) technique, we have found that the central axon arbors of functionally distinct mystacial whisker primary afferents in rat medullary dorsal horn were all similar with respect to their shape and density of terminal boutons. Arbors from slowly adapting, rapidly adapting, velocity or nociceptive biased whisker afferents all appeared to form a series of highly localized terminal aggregates within a specific rostrocaudal segment of the superficial or deep half of the lamina III-IV magnocellular region. Other trigeminal afferents adhered to previously described somatosensory structure-function relationships in the cat lumbosacral spinal cord. These findings suggest that topographic constraints, as well as functional considerations, are important in determining primary afferent terminal arbor patterns in the medullary dorsal horn.