A degeneration study of the somaesthetic afferent systems in the marsupial phalanger, Trichosurus vulpecula.

Abstract

SUMMARYDegenerating fibres in the medial lemniscus and anterolateral columns of the phalanger have been traced using the Marchi technique. The medial lemniscus, arising from a lesion in the dorsal column nuclei, decussates in the lower medulla and fallows a contralateral pathway, except in its most caudal extent where some degeneration on the ipsilateral side at inferior olivary levels is suggestive of a small component of uncrossed fibres. This ipsilateral representation soon fading, the pathway thereafter is completely crossed. It remains in a ventromedial situation throughout the midbrain, and penetrates the subthalamus to terminate in n. ventralis posterolateralis of the thalamus.Anterolateral column lesions in the cervical cord result in ascending degeneration which can be traced into the medulla as an ipsilateral compact anterolateral marginal band (Gower's tract), together with a scatter of degeneration medially into the reticular formation up to the level of the superior olives. At upper pontine levels, fibres of the ventral spinocerebellar tract arch dorsally and turn back to reach the cerebellum through the superior cerebellar peduncle. No myelinated spinotectal fibres are to be found, and there is no direct passage of myelinated fibres to the thalamus.