Dorsal medullary pathways subserving oromotor reflexes in the rat: Implications for the central neural control of swallowing

Retrograde and anterograde axonal transport techniques were used to investi gate the organization of inputs from the dorsomedial medulla, a region know n to elicit patterned swallowing reflexes following focal stimulation, to t he fifth (MoV), seventh (VII), tenth (nucleus ambiguus, NA), and twelfth (X II) cranial nerve motor nuclei in the rat, those motor nuclei most directly involved in the control of deglutition. The results may be summarized as f ollows. 1) Dorsal medullary inputs to MoV, VII, and XII arise primarily fro m an extended region of the caudal reticular formation immediately ventral to the nucleus of the solitary tract (NTS), which we term the dorsal medull ary reticular column (DMRC). Projections from the DMRC are largely bilatera l and are distributed preferentially to the ventral subdivision of MoV, to the dorsal and intermediate subdivisions of VII, and to both the dorsal and the ventral subdivisions of XII. In addition, a subpopulation of large mul tipolar neurons embedded within the DMRC gives rise to a primarily crossed input to the dorsal subdivision of MoV. 2) Dorsal medullary inputs to the N A arise from the NTS, are largely uncrossed, and are organized such that th e ventrolateral, intermediate, and interstitial subdivisions of the NTS pro ject to the semicompact formation and to the rostral extension of the compa ct formation (which supplies the pharynx) and to the loose formation (laryn x), whereas the central subdivision of the NTS provides input to the compac t formation (esophagus). 3) Neither the NTS nor the DMRC gives rise to sign ificant projections to the central subnucleus oft;he NTS. Together, these r esults provide evidence for discrete medullary pathways subserving sequenti al activation of swallowing reflexes. (C) 2000 Wiley-Liss, Inc.