Distribution of innervating neurons of masticatory muscle spindles in the rat: an HRP study.

Neurons innervating representatives of supramandibular and suprahyoidal muscles of the rat were identified in the mesencephalic and motor nuclei of the trigeminal nerve and in the accessory nuclei of the trigeminal and facial nerves after intramuscular injections of horseradish peroxidase. Labeling was always ipsilateral with respect to the injection site. The supramandibular motoneurons showed a bimodal size distribution, whereas suprahyoidal motoneurons were unimodally distributed. Mesencephalic neurons were labeled only after supramandibular injections. These results indicate a strict ipsilateral organization of muscle spindles supplying sensory and motoneurons.