Afferent projections to the oral motor nuclei in the rat

TLDR

Afferent input to the trigeminal, facial, ambiguus, and hypoglossal motor nuclei is largely supplied by the brain‑stem reticular formation, with projections organized along a rostro‑caudal axis and differing in rostral origins among nuclei. The study mapped these projections by applying horseradish peroxidase histochemistry to trace afferent pathways to the oral motor nuclei. The identified interneuron pools linking these nuclei offer new insight into the brain‑stem circuitry underlying oral and ingestive behaviors.

Abstract

Abstract Projections to the trigeminal, facial, ambiguus, and hypoglossal motor nuclei were determined by using horseradish peroxidase histochemistry. Most of the afferent projections to these motor nuclei were from the brain‐stem reticular formation, frequently in areas adjacent to other synergetic motor nuclei. The reticular formation lateral to the hypoglossal nucleus and reticular structures surrounding the trigeminal motor nucleus projected to each of these other brainstem motor nuclei involved in oral‐facial function. Afferent projections to these motor nuclei also were organized along the ros‐trocaudal axis. Within the reticular formation most of the afferent projections to the trigeminal motor nucleus originated rostral to the majority of neurons projecting to the hypoglossal and ambiguus nuclei, which in turn were rostral to the primary source of reticular afferents to the facial nucleus. In comparison, projections from the sensory trigeminal nuclei and nucleus of the solitary tract were sparse. The interneuron pools that project to the orofacial motoneurons provide one further link in understanding the brain‐stem substrates for integrating oral and ingestive behaviors.