Dessem D, Donga R, Luo P
Department of Physiology, University of Maryland Dental School, Baltimore 21201-1586, USA.
J Neurophysiol. 1997 Jun;77(6):2925-44. doi: 10.1152/jn.1997.77.6.2925.
Single jaw-muscle spindle afferent axons were characterized physiologically and intracellularly stained to determine whether particular physiological types of spindle afferent show distinctive morphologies. Microelectrodes filled with either horseradish peroxidase (HRP) or biotinamide (Neurobiotin) were advanced into the mesencephalic trigeminal nucleus (Vme) in anesthetized rats. Intracellular recordings then were characterized by their response: to palpation of the jaw muscles; when pressure was applied to the teeth and during passive ramp and hold and sinusoidal jaw movement. Seventy-one afferents were characterized physiologically and injected with HRP; an additional 61 afferents were typed and injected with biotinamide. The response of 43 stained neurons was recorded in the presence of suxamethonium. The major projection areas of these afferents were the: trigeminal motor nucleus (Vmo); region dorsal to Vmo; reticular formation, spinal trigeminal nucleus, superior cerebellar peduncle and Vme. One afferent type was modulated strongly during stretching of the jaw-elevator muscles. Based on their high sensitivity during stretching of the jaw muscles and/or their silencing during the release phase of muscle stretch, these afferents were classified as primary-like spindle afferents. These afferents projected most strongly to Vmo. A second type of afferent was modulated only modestly during stretching of the jaw-elevator muscles. These tonic afferents were classified as secondary-like spindle afferents because of their low dynamic sensitivity during ramp muscle stretch and their continued discharge during the release phase of muscle stretch. Secondary-like afferents projected most strongly to the region dorsal to Vmo. Boutons (n = 3,834) from 11 afferents were studied in detail. Secondary-like afferents had statistically larger boutons within Vmo. In both secondary- and primary-like spindle afferents, only a small number of boutons were associated closely with the somata and proximal dendrites of trigeminal motoneurons. In these cases, however, two to five boutons appeared to contact individual motoneurons, implying multiple monosynaptic inputs to a selective subset of jaw-elevator motoneurons. Some "giant" boutons were present dorsal to Vmo and in Vme. These results demonstrate that dynamically sensitive and nondynamically sensitive jaw-elevator muscle spindle afferents project preferentially to different regions. Primary-like spindle afferents are capable of providing feedback related to the dynamic phases of muscle stretch and project most heavily to Vmo. Secondary-like spindle afferents can transmit a feedback signal associated with muscle length and project most strongly to the supratrigeminal region. Both types of afferent have projections caudal to Vmo that may serve longer latency jaw-muscle stretch reflexes and/or the projection of proprioceptive information to the thalamus and cerebellum.
对单根颌肌梭传入轴突进行生理特性鉴定并进行细胞内染色，以确定特定生理类型的梭传入纤维是否具有独特的形态。将充满辣根过氧化物酶（HRP）或生物素酰胺（神经生物素）的微电极推进到麻醉大鼠的中脑三叉神经核（Vme）。然后通过细胞内记录对其反应进行特性鉴定：对颌肌触诊的反应；对牙齿施加压力时的反应；以及在被动斜坡和保持以及正弦颌运动期间的反应。对71根传入纤维进行了生理特性鉴定并注射了HRP；另外61根传入纤维进行了类型鉴定并注射了生物素酰胺。在琥珀胆碱存在的情况下记录了43个染色神经元的反应。这些传入纤维的主要投射区域包括：三叉神经运动核（Vmo）；Vmo背侧区域；网状结构、三叉神经脊束核、上小脑脚和Vme。一种传入纤维类型在颌上提肌伸展时受到强烈调制。基于它们在颌肌伸展时的高敏感性和/或在肌肉伸展释放阶段的沉默，这些传入纤维被归类为初级样梭传入纤维。这些传入纤维向Vmo投射最强。第二种传入纤维类型在颌上提肌伸展时仅受到适度调制。这些紧张性传入纤维被归类为次级样梭传入纤维，因为它们在肌肉斜坡伸展时动态敏感性低，并且在肌肉伸展释放阶段持续放电。次级样传入纤维向Vmo背侧区域投射最强。对11根传入纤维的3834个终扣进行了详细研究。次级样传入纤维在Vmo内的终扣在统计学上更大。在次级样和初级样梭传入纤维中，只有少数终扣与三叉神经运动神经元的胞体和近端树突紧密相关。然而，在这些情况下，两到五个终扣似乎与单个运动神经元接触，这意味着对颌上提运动神经元的一个选择性亚群有多个单突触输入。在Vmo背侧和Vme中有一些“巨型”终扣。这些结果表明，动态敏感和非动态敏感的颌上提肌梭传入纤维优先投射到不同区域。初级样梭传入纤维能够提供与肌肉伸展动态阶段相关的反馈，并向Vmo投射最重。次级样梭传入纤维可以传递与肌肉长度相关的反馈信号，并向三叉上区投射最强。两种类型的传入纤维都有向Vmo尾侧的投射，这可能用于更长潜伏期的颌肌伸展反射和/或将本体感觉信息投射到丘脑和小脑。
