Dobbins E G, Feldman J L
Department of Physiological Science, University of California Los Angeles 90015-1527, USA.
J Comp Neurol. 1995 Jul 3;357(3):376-94. doi: 10.1002/cne.903570305.
Protrusion and retraction of the tongue are essential components of such orofacial behaviors as mastication, respiration, and swallowing. Stimulation of the medial branch of the hypoglossal nerve yields tongue protrusion, while stimulation of the lateral branch yields tongue retraction in rat. We exploited the transsynaptic transport capabilities of pseudorabies virus to determine specific circuits that innervate protruder and retractor muscles of the rat tongue. Each group of muscles is innervated by distinct populations of hypoglossal motoneurons: caudal ventral and ventrolateral motoneurons form the largest proportion of those innervating protruders, whereas rostral dorsal motoneurons innervate retractors. Our primary finding was differential innervation of protruder and retractor motoneurons by premotoneurons in the lateral tegmental field: premotoneurons innervating protruder motoneurons were more ventral and ventromedial than those innervating retractor motoneurons. In addition, protruder motoneurons received projections from the ipsilateral lateral parabrachial nucleus but not spinal trigeminal nucleus or medial and ventral subnuclei of the solitary tract; the converse was true for retractor motoneurons. These results suggest segregation of functional networks that control hypoglossal motoneurons. The dorsal medulla, in or around the solitary tract, contains neurons specific to retractor motoneurons, and the region ventrolateral to the hypoglossal nucleus contains circuitry specific to protruder motoneurons. Common innervation of medial and lateral branch motoneurons is provided by premotoneurons in the raphe and gigantocellular reticular formation of the medial medulla. The midline medullary nuclei with diverse projections may coordinate complex behavior or modulate general motoneuron excitability, whereas the lateral reticular formation, with anatomically discrete projections, may control motoneurons that contribute to distinct orofacial behaviors.
舌头的伸出和缩回是咀嚼、呼吸及吞咽等口面部行为的重要组成部分。刺激大鼠舌下神经的内侧支会引起舌头伸出，而刺激外侧支则会导致舌头缩回。我们利用伪狂犬病病毒的跨突触运输能力来确定支配大鼠舌头伸出肌和缩回肌的特定神经回路。每组肌肉由不同的舌下运动神经元群支配：尾侧腹侧和腹外侧运动神经元构成支配伸出肌的运动神经元的最大比例，而头侧背侧运动神经元支配缩回肌。我们的主要发现是，外侧被盖区的运动前神经元对伸出肌和缩回肌运动神经元的支配存在差异：支配伸出肌运动神经元的运动前神经元比支配缩回肌运动神经元的运动前神经元更靠腹侧和腹内侧。此外，伸出肌运动神经元接受来自同侧外侧臂旁核的投射，但不接受三叉神经脊束核或孤束核内侧和腹侧亚核的投射；缩回肌运动神经元则相反。这些结果表明控制舌下运动神经元的功能网络是分离的。孤束内或其周围的延髓背侧包含特定于缩回肌运动神经元的神经元，舌下神经核腹外侧区域包含特定于伸出肌运动神经元的神经回路。内侧和外侧支运动神经元的共同支配由延髓内侧中缝和巨细胞网状结构中的运动前神经元提供。具有多样投射的中线髓质核可能协调复杂行为或调节一般运动神经元的兴奋性，而具有解剖学上离散投射的外侧网状结构可能控制参与不同口面部行为的运动神经元。
