Defense Date


Document Type


Degree Name

Doctor of Philosophy


Anatomy & Neurobiology

First Advisor

George Leichnetz


The nucleus raphe magnus (NRM) is known to play an important role in a descending antinociceptive system through its projections to the spinal cord dorsal horn and trigeminal subnucleus caudalis. Identifying those nuclei which project to NRM is essential in determining other CNS cell groups which could influence analgesic mechanisms by virtue of their connections with NRM.

In an attempt to define NRM afferents, 19 adult Sprague-Dawley rats were stereotaxically implanted with a pellet of HRP gel within NRM and in adjacent areas. A transcannula technique was specifically developed for the subcortical placement of HRP in a gel form. Use of a preimplanted stainless steel cannula for delivery of the gel to its target site, prevented contamination along the implantation tract, a factor which has compromised previous studies of this area. Employing tetramethylbenzidine neurohistochemistry, large numbers of retrogradely labelled cells were consistently found in the zona incerta, n. parafascicularis prerubralis (pPfPr), pretectum, dorsal and lateral periaqueductal gray, n. cuneiformis (nC), deep superior colliculus (dSC), and n. of Bechterew. Smaller numbers of cells were seen in the preoptic area, and the dorsomedial n. of the hypothalamus. Confirmational anterograde autoradiographic studies were done by injecting tritiated leucine into the nPfPr and into the area of the dSC and nC. The HRP results are compared and contrasted with control HRP implants in the inferior olive, n. reticularis paragigantocellulais, medial facial n., spinal cord, and the dorsolateral funiculus. Comments are also made concerning the parcellation of the ventromedial medulla and the possible role of both NRM and its afferents in central analgesic mechanisms.


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