DISTRIBUTION OF THE POSTSYNAPTIC DORSAL COLUMN PROJECTION IN THE CUNEATE NUCLEUS OF MONKEYS

Cells in the spinal cord that are postsynaptic to primary afferent fib ers project to the dorsal column nuclei in the postsynaptic dorsal col umn pathway. The projection of cells in the cervical spinal cord of mo nkeys to the cuneate nucleus has been reported to avoid pars rotunda o f that nucleus, the part that contains the somatotopic representation of the ipsilateral hand. We used the sensitive anterograde tracer Phas eolus vulgaris leucoagglutinin to reexamine this projection. We made m ultiple iontophoretic injections into the cervical enlargements of thr ee monkeys (two Macaca fascicularis and one Macaca mulatta). Control i njections were made in the contralateral dorsal columns of one of thes e and in the dorsal roots of a fourth animal (M. fascicularis) to test for transport by fibers of passage. After 28-39 days, the animals wer e deeply anesthetized and perfused, and the tissue was processed for i mmunohistochemical detection of the label. In all cases (excluding con trol injections), labeled fibers and varicosities were distributed wid ely in the ipsilateral cuneate and external cuneate nuclei, including pars rotunda. The dorsal column nuclei ipsilateral to control injectio ns contained no label or only very few poorly labeled fibers, indicati ng that labeling through fibers of passage did not contribute importan tly to the results. This study indicates that the postsynaptic project ion to the cuneate nucleus is widespread and includes pars rotunda. Su ch projections may contribute to transmission of information originati ng in nociceptors through the dorsal column-medial lemniscal system to the ventrobasal thalamus. (C) 1994 Wileg-Liss, Inc.