Distribution of motoneurons involved in the prey-catching behavior in the Japanese toad, Bufo japonicus.

Coordinated activities of several muscles in the head region underlie the prey-catching behavior of anuran amphibians. As a step in elucidating the neural mechanisms generating these activity patterns in the Japanese toad, we labelled the motoneurons innervating 8 behaviorally relevant muscles using intramuscular (i.m.) injection technique of horseradish peroxidase (HRP), and examined their localization within the motor nuclei whose boundaries were determined by HRP application to the nerve trunk. All the motoneurons innervating the two jaw closer muscles (m. masseter major, m. temporalis) and m. submentalis were localized within the rostral subdivision of the trigeminal motor nucleus. The motoneurons innervating the only mouth opener muscle (m. depressor mandibulae) were scattered throughout the facial motor nucleus. The motoneurons innervating tongue (m. hypoglossus, m. genioglossus) and hyoid muscles (m. sternohyoideus, m. geniohyoideus) appeared within the hypoglossal nucleus with distribution patterns characteristic of the target muscles. Thus, we have revealed the neuroanatomical organization of the motoneurons relevant to the prey-catching behavior.