ANATOMIC RELATIONSHIPS OF THE HUMAN ARCUATE NUCLEUS OF THE MEDULLA - A DII-LABELING STUDY

The arcuate nucleus (ARC) at the ventral surface of the human medulla has been historically considered a precerebellar nucleus. More recentl y, it has been implicated in central chemoreception, cardiopulmonary c oupling and blood pressure responses. A deficiency of the ARC has been reported in a subset of putative human developmental disorders of ven tilatory function. To investigate anatomic relationships of the ARC wi th brainstem regions involved in cardiorespiratory control, we applied crystals of DiI, a lipophilic dye which labels cells and cell process es by lateral diffusion along cell membranes, to 23 paraformaldehyde-f ixed human fetal brainstems at 19 to 22 weeks postconceptional age. Af ter 7 to 15.5 months diffusion, serial frozen sections were examined b y florescence microscopy. DiI diffusion from the ARC labeled fibers an d cell bodies in the medullary raphe labeled the reticular formation, medullary raphe, and the ARC. Diffusion from the pyramid and the basis pontis (negative control) labeled the corticospinal tract, with no la beling of the medullary raphe or ARC. The results suggest the existenc e of cellular connections between the ARC and the caudal raphe, a regi on implicated in cardiorespiratory control.