ANDERSON, C.W.: Anatomical evidence for brainstem circuits mediating hypoglossal motor output in the leopard frog, Rana pipiens
Using injections of fluorescein dextran amine (FDA) combined with activity-dependent uptake of sulforhodamine 101 (SR101), brainstem circuits presumed to be involved in hypoglossal motor output were investigated. Injections into the cerebellar cortex combined with retrograde labeling of the peripheral hypoglossal nerve demonstrate convergence at the level of the medial reticular formation. This convergence suggests an integrative region for afferent feedback from the hypoglossal nerve and information through the Purkinje cell layer of the cerebellar cortex. Injections of FDA into the cerebellar nuclei also demonstrate a bilateral efferent projection to the hypoglossal motor neurons. The SR101 data suggest a reciprocal pathway between the medulla and the trigeminal nuclei. This pathway was identified through peripheral hypoglossal stimulation while SR101 was bath applied to a semi-intact brainstem preparation. Additionally, the SR101 uptake clearly labeled the ventrolateral hypoglossal nuclei, the medial reticular formation and the Purkinje cell layer of the cerebellar cortex. The trigeminal nuclei coordinate the motor output of the levator mandibulae complex, the mouth closing muscles, and this pathway may provide a mechanism for coordinating tongue movements (through hypoglossal nuclei) with jaw movements during feeding. Taken together, these data provide additional insight for understanding the neurophysiological pathways used to coordinate the proper timing of feeding motor output in anurans.