The sites of origin of projection fibers from the cerebral cortex to the jaw region of the striatum of the rat.

Electrical microstimulation of the jaw region of the rat striatum (SJR) has been reported to provoke clear electromyographic activity in the anterior digastric muscle but not in the masseter muscle (Neurosci. Lett., 252 (1998) 79-82). Thus, in the present study, we examined the sites of origin of cortico-SJR fibers by the retrograde labeling. The SJR, identified by electrical microstimulation, was injected electrophoretically with cholera toxin B subunit. In the cerebral cortex ipsilateral to the injection, there existed two foci of retrograde labeling: One focus was centered on the lateral part of the sensorimotor area, while the other on the insular cortical area around the middle cerebral artery. These foci appeared to correspond to the reported two cortical areas, where two different types of rhythmical jaw movements were induced by repetitive electrical stimulation (Jap. J. Oral Biol., 32 (1990) 57-68).