Phrenic motoneurons receive monosynaptic inputs from the Kolliker-Fuse nucleus: a light- and electron-microscopic study in the rat

The parabrachial complex, which plays an important role in respiratory regu lation, has been reported to send projection fibers to the phrenic nucleus, but the synaptic organization between the parabrachial fibers and the phre nic motoneurons has not been examined. Using anterograde and retrograde tra cing methods, we found in the rat that the parabrachial fibers originating mainly from the Kolliker-Fuse nucleus (KF) terminated not only within the p honic nucleus but also on the radial dendritic bundles of the phrenic moton eurons. It was further revealed that the KF fibers made asymmetrical synaps es predominantly with dendrites and partly with somata of the phrenic moton eurons. These data suggest that output signals from the KF may exert excita tory influence directly upon the phrenic motoneurons. (C) 2001 Elsevier Sci ence B.V. All rights reserved.