Morphological evidence for recurrent jaw-muscle spindle afferent feedback within the mesencephalic trigeminal nucleus.

Horseradish peroxidase was injected into the jaw-elevator muscles of rats. Jaw-muscle spindle afferent axons were then intracellularly stained with biotinamide. Eleven intracellularly stained somata were closely apposed by intracellularly labeled spindle afferent boutons. Spindle afferent boutons closely apposed another 10 mesencephalic trigeminal nucleus (Vme) perikarya labeled from the jaw muscles. These results indicate that an anatomical substrate exists for recurrent feedback between jaw-muscle spindle afferents within Vme.