Histochemical mapping of catecholamine neurons and fiber pathways in the pontine tegmentum of the dog

The distribution of catecholamine-containing neurons and fiber pathways were studied in the dog's pontine tegmentum by the Falck-Hillarp method. There are fundamental similarities between the dog and other mammals. Most catecholamine fluorescent cell bodies in the dog are located within the nucleus locus coeruleus and subcoeruleus in the pontine tegmentum. They are more diffuse and extensive than in the rat, monkey and human, and rather similar to those of the cat. In this study, catecholamine fiber pathways were clearly traced without using the lesion-degeneration technique. The dorsal pathway from the locus coeruleus consists of more compact bundles of non-varicose fibers than the rat, cat and monkey. It runs parallel to the mesencephalic tract of the trigeminal nerve in pons and midbrain. The ventral pathway courses as loosely arranged varicose fibers in the midreticular formation of the pons and sends axon collaterals to the caudal midbrain to form a dense network of varicose fibers. There are fluorescent plexi of fine varicose fibers at the ventromedial and dorsolateral aspect of the superior cerebellar peduncle. Cells of the medial and lateral parabrachial nucleus, in addition to those of locus coeruleus, send fluorescent fibers to this peduncle. No fluorescent fibers are found in other peduncles.