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Efferent and Afferent Connections of the Supratrigeminal Neurons Conveying Orofacial Muscle Proprioception in Rats

Yoshida, A;Inoue, M;Sato, F;Morita, Y;Tsutsumi, Y;Furuta, T;Uchino, K;Akhter, F;Bae, Y;Tachibana, Y;Inoue, T;

The supratrigeminal nucleus (Su5) is a key structure for controlling jaw-movements since it receives proprioceptive sensation from jaw-closing muscle spindles (JCMSs) and sends projection to the trigeminal motor nucleus (Mo5). However, the central projection and regulation of JCMS proprioceptive sensation have not been fully understood. Therefore, we aimed to reveal the efferents and afferents of the Su5 by means of neuronal tract tracings. Anterograde tracer injections into the Su5 revealed that the Su5 sent contralateral projections (or bilateral projections with a contralateral predominance) to the Su5, basilar pontine nuclei, pontine reticular nucleus, deep mesencephalic nucleus, superior colliculus, caudo-ventromedial edge of ventral posteromedial thalamic nucleus, parafascicular thalamic nucleus, zona incerta, and lateral hypothalamus, and ipsilateral projections (or bilateral projections with an ipsilateral predominance) to the intertrigeminal region, trigeminal oral subnucleus, dorsal medullary reticular formation, and hypoglossal nucleus as well as the Mo5. Retrograde tracer injections into the Su5 demonstrated that the Su5 received bilateral projections with a contralateral predominance (or contralateral projections) from the primary and secondary somatosensory cortices, granular insular cortex and Su5, and ipsilateral projections (or bilateral projections with an ipsilateral predominance) from the dorsal peduncular cortex, bed nuclei of stria terminalis, central amygdaloid nucleus, lateral hypothalamus, parasubthalamic nucleus, trigeminal mesencephalic nucleus, parabrachial nucleus, juxtatrigeminal region, trigeminal oral and caudal subnuclei, and dorsal medullary reticular formation. These findings suggest that the Su5 receiving JCMS proprioceptive sensation has efferent and afferent connections with multiple brain regions, which are involved in emotional and autonomic functions as well as orofacial motor functions.