Distribution of cells projecting to thalamus vs. Those projecting to cerebellum in subdivisions of the dorsal column nuclei in raccoons

Abstract

To learn the distribution of cells projecting to the thalamus, as opposed to the cerebellum, in the mechanosensory nuclei of the dorsal medulla of raccoons, we analyzed the retrograde transport of horseradish peroxidase from the ventrobasal complex of the thalamus and from the cerebellum. We found six nuclear regions projecting heavily to the thalamus with very small projections to the cerebellum: Bischoff's, central cuneate, central gracile, rostral cuneate, rostral gracile nuclei, and cell group z. Two regions showed heavy projections to the cerebellum with no projections to the thalamus: the lateral portion of the external cuneate nucleus and the compact portion of cell group x. Four regions showed more equivalent projections to both target regions: basal cuneate, medial portion of the external cuneate nucleus, medial tongue extension of the external cuneate nucleus, and reticular portion of cell group x. Three more ventral regions were labeled: lateral cervical nucleus from thalamic injections but not from cerebellar injections; central cervical nucleus from cerebellar injections, which crossed the midline, but not from thalamic injections; and lateral reticular nucleus from both target regions. In most medullary regions, most cells project to one target and very few project to the other; we suggest that the cells projecting to the minor target convey samples of the information going to the major target.

Somatosensory brainstem, thalamus, and cortex of the California sea lion (Zalophus californianus)

“…We also report a distinct dorsal‐medial cell group at the caudal extent of the gracile nucleus that may be an example of Bischoff's nucleus. Bischoff's nucleus is a DCN found in some animals and is often associated with the representation of the tail (Johnson et al, ; Ostapoff and Johnson, ; Sarko et al, ). However, sea lions have diminutive tails, so it is surprising to find such a distinct cell group.…”

Somatosensory Nuclei of the Manatee Brainstem and Thalamus

“…The principal somatosensory brainstem nuclei for the manatee include the trigeminal, cuneate, gracile, and Bischoff's nuclei. Bischoff's nucleus, a distinct group of cells in the midline of the caudal medulla (Johnson et al, 1968), has not been identified previously in the manatee but has been shown, along with the cuneate and gracile nuclei, to project heavily to the ventroposterior thalamus (VP) in the raccoon (Ostapoff and Johnson, 1988). In the raccoon, the tail representation occupies the dorsal portion of VP, whereas the hindlimb representation occupies the ventral portion (Johnson et al, 1968).…”

“…The somatosensory brainstem nuclei of interest for the manatee include Bischoff's nucleus, the cuneate–gracile complex, and the trigeminal nucleus (in particular, the principal sensory component). Bischoff's nucleus is a distinct group of cells in the midline of the caudal medulla that projects heavily to the ventrobasal thalamus in the raccoon (Johnson et al, 1968; Ostapoff and Johnson, 1988) and constitutes the tail representation in most mammals with a well‐developed tail (Kappers and Ubbo, 1960). By analogy, Bischoff's nucleus would represent the fluke in the manatee and might occupy a disproportionately large area compared with other species due to the tactile hairs present on the fluke.…”

Organization of primary afferent projections to the gracile nucleus of the dorsal column system of primates

“…1). In this study we included the cell clusters devoted to the tail in the gracile nucleus, although others have distinguished this cell group as Bischoff's nucleus (Kappers et al, 1936;Johnson et al, 1968;Ostapoff and Johnson, 1988). By injecting compounds that were transported from the skin to the terminations of cutaneous afferents in the gracile nucleus, we were able to determine where in the gracile nucleus afferents from different body parts terminate in the four primates studied.…”