Organization of Projections from the Gracile, Medial Cuneate and Lateral Cuneate Nuclei in the North American Opossum

Abstract

Using the horseradish peroxidase technique on the North American opossum, we were able to locate the neurons within the dorsal column and lateral cuneate nuclei which innervate the cerebellum and thalamus as well as those within the dorsal column nuclei which project spinalward. The medial and lateral cuneate nuclei supply axons to the anterior lobe, the paramedian lobule and the pyramis of the cerebellum and the lateral cuneate nucleus provides an additional projection to the uvula. The cerebellar projections from these nuclei arise from neurons located rostral to the obex. The thalamic projections from the gracile and medial cuneate nuclei originate from neurons throughout their rostral to caudal extent, although most of them are located just rostral to the obex. Neurons within the lateral cuneate nucleus which innervate the thalamus are found at intermediate rostrocaudal levels where most of them approximate the medial cuneate nucleus. The medial cuneate also projects to at least lumbar levels of the spinal cord in the opossum and neurons giving rise to such connections are found at the level of the obex and caudal to it. Neurons within the dorsal part of the dorsal column nuclei were labelled only after thalamic injections. Our results in the opossum are compared with those obtained in several placental mammals.

Contralateral as Well as Ipsilateral Projections to Raccoon Cerebellum from External Cuneate Nuclei and Cell Groups f and x

“…The lateral reticular nuclei showed la belling on both ipsilateral and contralater al sides as has been reported for cats [3] and opossums [5].…”

“…No contralater al projections were reported in other stud ies of cats [8] and opossums [5]. Two recent studies report the contralateral as well as ipsilateral projections in cats: Gould [4, p. 8] does not report the relative extents and frequencies of the projecting cells; Somana and Walberg [9] report a few relative frequencies from certain small injection sites, but do not report the nuclear loca tions of projecting cells.…”

Dorsal Column Nuclei Projection to the Cerebellar Caudal Vermis in the Rabbit Revealed by the Fluorescent Double-Labeling Method

“…The involvement of the CuL is the largest; that of the Gr+CuM is considerably smaller, and that of the Gr and CuM is minor. With regard to the CuL, a similar projection exists in the opossum [Gray et al, 1981] and the rat [Massopust et al, 1985]. However, in the latter, the projection is ipsilateral and arises to a greater extent from the lateral region of the nucleus.…”

“…The DCN cerebellar connections were revealed in the cat with the use of degenerative [Voogd, 1964;Cheek et al, 1975] and electrophysiological [Gordon and Seed, 1961] methods as well as in the cat [Rinvik and Walberg, 1975;Somana and Walberg, 1980], opossum [Gray et al, 1981] and rat [Päällysaho et al, 1991;Tolbert and Gutting, 1997] with the use of the axonal transport method.…”

“…the paramedian lobule, crus I and II of the ansiform lobule. The less numerous CuM cerebellar fibers terminate in the vermis of the anterior and posterior lobes [Cheek et al, 1975;Rinvik and Walberg, 1975;Somana and Walberg, 1980;Gray et al, 1981;Matsushita and Okado, 1981;Haring and Rowiński, 1982;Gerrits et al, 1985;Massopust et al, 1985]. The Gr is a source of relatively weak cerebellar afferents which end in the anterior lobe and paravermal zone as well as the uvula (Uv; caudal vermis) and the flocculus and paraflocculus (parts of the vestibulocerebellum) [Matsushita and Okado, 1981;Massopust et al, 1985;Bermejo et al, 2003].…”