Labeled trigeminal mesencephalic neurons following tracer injections into the vibrissal pad (Dil) and masseter muscle (True Blue). 1-3: Schematic drawings of brainstem sections at the caudal level of the mesencephalic trigeminal nucleus (Me5) showing the locations on the cell bodies of axons joining the whisker pad (1: red dots), the masseter muscle spindles (2: blue dots), and both structures (3: green dots). LC: locus ceruleus; MPB: medial parabrachial nucleus. A: Labeled neurons (asterisks) within the Me5 following Dil injection into the ipsilateral mystacial pad. Scale bar: 50 μm. B: Greater magnification of a trigeminal mesencephalic neuron (TMne) labeled by Dil. Scale bar: 10 μm. C: Labeled neurons in the Me5 following True Blue injection into the ipsilateral masseter muscle. Scale bar: 100 μm. D: Greater magnification of two TMne labeled by True Blue. Scale bar: 20 μm. E-F: Greater magnification of a TMne double labeled by Dil (E) and True Blue (F). Scale bar: 20 μm.