VAGAL SENSORY REINNERVATION AND THE COMPOSITION OF THE STERNOCEPHALICUS MUSCLE IN THE RABBIT

The crossed nerve anastomosis between the peripheral end of the vagus, cut above the nodose ganglion, and the peripheral end of the accessor y nerve has demonstrated the capacity of some vagal afferents to reinn ervate, via the accessory nerve stump, certain sternocephalicus muscle fibers in the rabbit. These results add to our understanding of the c apacity of these afferents to counter the post-denervational atrophyin g process that occurs in the reinnervated muscles and to evaluate the changes induced in these muscles during reinnervation. Our work shows that within 3 months, the vagal sensory reinnervation of previously de nervated sternocephalicus muscles induces their total weight recovery. This recovery is concomitant on the one hand with the hypertrophy of the four muscle fiber types (I, IIBD, IIC and IIA) identified histoche mically in the normal muscles and, on the other, with the appearance o f small newly formed myofibers, which are often underlined by characte ristic central nuclei. The vagal sensory neurones induce important cha nges in the percentages and the muscle cross-sectional distribution of the fibers in reinnervated muscles. In these muscles we see also the disappearance of the fast myosin heavy chains MHCIIB and MHCIID, the u pholding of the fast MHCIIA percentage and an increase in the slow MHC I isoform.