Afferent and efferent components of the hypoglossal nerve in the grass frog, Rana pipiens

Abstract

In amphibians, the spinomedullary region of the central nervous system is compressed rostrocaudally because of the absence of a neck. In Ranid frogs, the hypoglossal nerve emerges as the ventral ramus of the second spinal nerve. The first spinal nerve, though present in tadpoles, is absent as a separate nerve in adults. To investigate the central nervous system components of the hypoglossal nerve in Rana pipiens, we soaked identified, transected branches of this nerve in horseradish peroxidase, a retrograde and anterograde tracer. We found that the hypoglossal nerve in these frogs originates from two efferent nuclei located in the caudal medulla, a medial and a lateral one. Afferent fibers, primarily from the tongue, are also found in the hypoglossal nerve and travel in the dorsolateral funiculus of the spinal cord, descending to thoracic levels of the cord. Efferents to intrinsic tongue muscles and the genioglossus muscle originate in the medial medullary nucleus. Efferents to the sternohyoid muscle, which travel through the hypoglossal nerve, originate in the lateral medullary nucleus. Since in mammals the sternohyoid muscle is innervated by the first spinal nerve, we have obtained experimental evidence that the hypoglossal nerve in Rana pipiens contains components of this spinal nerve.

Neuromuscular control of prey capture in frogs

“…Thus, we would expect a larger number of motor units in hydrostatic elongators than in inertial elongators. As predicted, approximately 250 motor neurons innervate the M. genioglossus of an inertial elongator, R. pipiens (Stuesse et al 1983), whereas approximately 950 motor neurons innervate the M. genioglossus of a hydrostatic elongator, Hemisus marmoratum (Anderson et al 1998).…”

Sonic Motor Pathways in Teleost Fishes: A Comparative HRP Study

“…Given the origin of in trinsic sonic muscles from head myo tonies, and their innervation by an occipi tal (i.e., hypoglossal) nerve, Tracy's com parison seems unlikely [see also Galeo et al, 1985], As does the SMN, the hypoglossal nu cleus of land vertebrates typically occu pies a position in the caudal medulla [for review see Barnard, 1940]. At least two di visions of a hypoglossal nucleus are recog nized in turtles [Cruce and Nieuwenhuys, 1974], certain lizards [Barbas-Henry and Lohman, 1984], birds [Wild, 1981;Manogue and Nottebohm, 1982;Youngren and Phillips, 1983], frogs [Stuesse et al, 1983] and mammals [Chibuzo and Cum mings, 1982], Each subdivision is usually associated with a distinct pattern of mus cle innervation. A single nucleus is recog nized in snakes [Ulinski, 1974] and some lizards [Kennedy, 1981].…”

Gustatory signal processing in the glossopharyngeo-hypoglossal reflex arc of the frog.

“…10. The area circumscribed by the above three dimensions approximately coincides with that for the HMN in Bufo bufo L. (WEERASURIYA and EWERT, 1981) and in Rana pipiens (STUESSE et al, 1983).…”

“…In an early series of experiments on 18 frogs, the animals were placed in a supine position to expose the IXth nerves on either side and the XIIth nerves on both sides. A length of the IXth nerve from the junction of its medial and lateral branches (IsHiKo et a!.,1979) to a point 2-3 cm proximal to the junction was dissected free from the surrounding tissue and kept intact, while the three main branches of the XIIth nerve, each innervating the hyoglossal, genioglossal and intrinsic muscles (KOZAI, 1974;STUESSE et al, 1983), were isolated and cut peripherally for recordings. Some frogs were further decerebrated by removing the telencephalon above the optic tecta, using a small cotton ball.…”