Sources of the motor and somatic sensory innervation of the trapezius muscle in the rat

The study was carried out on nine sexually mature male rats of the Wistar breed weighing approximately 250 g each. Animals were anaesthetized with thiopental sodium injected intraperitoneally (30 mg/kg of body weight). The animals were then injected with Fast Blue tracer into the right trapezius muscle. After a survival period of five weeks the rats were transcardially perfused with buffered paraformaldehyde. The following tissue blocks were collected: spinal cord (cervical and thoracic part) with spinal ganglia and whole brain with medulla oblongata. The tissues collected were cut into 12 μm-thick cryostat sections, which were viewed under a fluorescent microscope equipped with a filter block for FB. FB-positive (FB+) neurons were counted in every fourth section to avoid double analysis. After injections of the tracer to the right trapezius muscle FB+ neurons were found in many nuclei and ganglia. The labelled cells of the medulla oblongata nuclei were found in the bilateral vestibular nuclei including superior (SuVe), lateral (LVe), medial (MVe) and spinal (SpVe) vestibular nuclei and also in the dorsal raphe nucleus (DR) which is a single nucleus, but only in the ipsilateral ambiguous nucleus (Amb). FB+ perikarya were also found in the spinal cord, extending between the first cervical segment (C1) and the cranial half of the seventh spinal cervical segment (C7), in an ipsilateral area ventrolateraly with respect to the central canal, within the spinal nucleus of the accessory nerve (SAN). Retrograde labelled sensory neurons were found in the bilateral spinal ganglia (SPG-s), from the second cervical ganglion (C2) to the third thoracic ganglion (Th3).