Zhan, Whenzi

Neuregulin (NRG) is a nerve derived trophic factor that regulates acetylcholine receptor expression during neuromuscular junction development. NRG also has important trophic effects in the adult central nervous system. We hypothesized that NRG is a trophic factor for phrenic motoneurons. In adult male Sprague‐Dawley rats, we examined NRG‐1 immunoreactivity in the vicinity of phrenic motoneurons. Retrogradely‐labeled phrenic motoneurons were imaged and reconstructed in 3D. NRG‐1 boutons were found mainly around the soma and primary dendrites. The co‐localization of NRG boutons and synaptic markers was determined using multicolor confocal microscopy and a custom‐developed application (Metamorph; Universal Imaging). We found that 94 ± 3% of NRG‐containing boutons resided on synapses, as determined by co‐localization with synaptophysin. In addition, 6 ± 3% of synapses on phrenic motoneurons (within 1 micrometer of soma and primary dendrite surface) expressed NRG. Overall, 13 ± 5 NRG boutons were present at the soma vs. 6 ± 3 at each primary dendrite of a motoneuron.Thus, 57% of NRG‐containing boutons were surrounding the motoneuron soma. In summary, NRG‐1 synaptic boutons are present at phrenic motoneurons in the adult, although its role is presently unknown. Supported by NIH grant AR51173.