The nuclei of origin of brainstem serotonergic projections to the rodent spinal trigeminal nucleus.

The origins of the serotonergic projections to the spinal trigeminal nucleus in the rat were determined utilizing the combined HRP retrograde transport-immunohistochemical technique. The areas providing the greatest number of serotonergic afferent projections to the spinal trigeminal nucleus are the raphe magnus, raphe obscurus, nucleus reticularis gigantocellularis pars alpha, and the nucleus reticularis paragigantocellularis. A smaller serotonergic input to the spinal trigeminal nucleus was found to arise from the raphe pallidus, periaqueductal gray, raphe dorsalis, raphe pontis and mesencephalic reticular formation. These results indicate that the spinal trigeminal nucleus receives serotonergic input from all levels of the brainstem including the midbrain cell group B7.