Bout R G, Tellegen A J, Dubbeldam J L
Neurobehavioral Morphology, Institute of Evolutionary and Ecological Sciences, Leiden University, The Netherlands.
Anat Rec. 1997 Aug;248(4):554-65. doi: 10.1002/(SICI)1097-0185(199708)248:4<554::AID-AR7>3.0.CO;2-L.
In the mallard duck, functionally distinct groups of jaw muscles are each innervated by a different subnucleus of the main trigeminal (mV) or facial (mVII) motor nucleus. The other subnuclei of mV and mVII innervate several head muscles, including lingual muscles. The reticular premotor cells of the trigeminal and facial jaw motor subnuclei occupy different areas in the parvocellular reticular formation (RPc). The cell bodies of jaw muscle spindle afferents are situated in the mesencephalic nucleus (MesV). In the present study, the central connections of MesV with jaw motor subnuclei and their premotor areas are investigated.
In a first series of experiments, horseradish peroxidase (HRP) injections were made in electrophysiologically identified trigeminal and facial subnuclei. In a second series of experiments, HRP was delivered iontophoretically at different parts of RPc. Anterograde tracing with tritiated leucine was used to confirm the central connections of MesV. Double labeling with fluorescent tracers was used to investigate whether MesV collaterals reach both the rostral and caudal parts of RPc.
MesV projects to only two of the five different subnuclei of the trigeminal motor nucleus. The subnuclei that receive spindle afferents innervate jaw adductor muscles (mV2) or pro- and retractors of the mandible (pterygoid muscles; mV1). The three other subnuclei innervate jaw-opener muscles or other head muscles. MesV fibers also project to the rostral part of the dorsolateral RPc (RPcdl), which serves as a premotor area for the motor subnuclei of adductor and pterygoid muscles. The intermediate part of RPcdl does not contain premotor cells of mV or mVII, and a clear projection of MesV to this area is absent. The caudal part of RPcdl projects to the mV and mVII subnuclei that innervate jaw-opener muscles. This part of RPc receives a projection from the same MesV cells as the rostral RPcdl. The MesV projection to RPc does not include premotor cells of mV and mVII in the ventromedial part of RPc (RPcvm).
Spindle afferents from jaw-closer muscles project only to mV subnuclei innervating jaw-closer muscles (mV1, mV2) and to a population of premotor cells in the rostral RPcdl that innervates these subnuclei. The mixed population of premotor cells in RPcvm, which innervates both jaw-opener and jaw-closer subnuclei, does not receive a MesV projection. However, a premotor area for jaw-opener subnuclei in the caudal part of RPcdl does receive MesV input and may serve as a relay through which proprioceptive information from jaw closer spindles can reach jaw opener muscles.
在绿头鸭中，功能不同的颌肌群分别由三叉神经（V）主核或面神经（VII）运动核的不同亚核支配。V和VII的其他亚核支配包括舌肌在内的几块头部肌肉。三叉神经和面神经颌运动亚核的网状前运动细胞在小细胞网状结构（RPc）中占据不同区域。颌肌梭传入纤维的细胞体位于中脑核（MesV）。在本研究中，对MesV与颌运动亚核及其前运动区的中枢连接进行了研究。
在第一系列实验中，将辣根过氧化物酶（HRP）注射到经电生理鉴定的三叉神经和面神经亚核中。在第二系列实验中，通过离子电泳将HRP输送到RPc的不同部位。用氚标记的亮氨酸进行顺行追踪以确认MesV的中枢连接。用荧光示踪剂进行双重标记以研究MesV的侧支是否到达RPc的头端和尾端部分。
MesV仅投射到三叉神经运动核的五个不同亚核中的两个。接受梭传入纤维的亚核支配颌内收肌（V2）或下颌骨的前伸肌和后缩肌（翼状肌；V1）。其他三个亚核支配颌张开肌或其他头部肌肉。MesV纤维也投射到背外侧RPc（RPcdl）的头端部分，它作为内收肌和翼状肌运动亚核的前运动区。RPcdl的中间部分不包含V或VII的前运动细胞，并且MesV没有向该区域的明显投射。RPcdl的尾端部分投射到支配颌张开肌的V和VII亚核。RPc的这一部分与头端RPcdl接受来自相同MesV细胞的投射。MesV向RPc的投射不包括RPc腹内侧部分（RPcvm）中的V和VII前运动细胞。
来自颌闭合肌的梭传入纤维仅投射到支配颌闭合肌的V亚核（V1、V2）以及RPcdl头端的一群支配这些亚核的前运动细胞。RPcvm中支配颌张开肌和颌闭合肌亚核的混合前运动细胞群不接受MesV投射。然而，RPcdl尾端部分中颌张开肌亚核的前运动区确实接受MesV输入，并且可以作为一个中继站，通过它来自颌闭合肌梭的本体感觉信息可以到达颌张开肌。
