Identification of different size motoneurons labeled by the retrograde axonal transport of horseradish peroxidase.

Three main groups of motoneurons of different size have been labeled in adult cats by using the method for retrograde axonal transport following injection of horseradish peroxidase in the medial gastrocnemius and soleus muscles. In particular small, medium-size and large neurons which probably correspond respectively to gamma, small alpha and large alpha motoneurons innervating the calf muscles, have been identified and the corresponding area measured.