Descending hypothalamic medullary pathways in the cat

Posterior hypothalamic electrocoagulative lesions were stereotaxically placed in 20 cats. The resulting degenerating pathways to the medullary centers were studied using the Nauta technique. The size of the lesions was less than 1 mm in diameter. The resulting degeneration did not conform to a discrete pathway but passed in a diffuse manner into the brainstem reticular formation. In the lower medulla the degenerating axons appeared to become more concentrated in the dorso‐lateral visceral gray in close association with the dorsal motor nuclei of X. Pre‐terminal axons were noted adjacent to large and medium sized neurons in this area. A progressive decrease in degenerating fibers was apparent below this level. A small number of degenerating axons could be identified in the lateral reticular process of the central gray matter at the level of C2.