The role of the nigrostriatal dopaminergic pathway in the sequential progress

咀嚼顺序是从摄食到吞咽的一整套动作。根据下颌运动的形式，兔的咀嚼顺序可分为三个公认的阶段（I、IIa、IIb期）。然而，目前尚不清楚哪些神经机制参与了咀嚼阶段的过渡。本研究旨在探讨黑质纹状体多巴胺能神经通路在咀嚼运动过程中的作用。应用微透析技术，观察了清醒家兔连续咀嚼5分钟时壳核细胞外间隙多巴胺（DA）浓度的变化。对微透析液样本的分析表明，与静息期相比，咀嚼期间壳核中DA的浓度显著增加.本实验采用自由活动家兔，通过咀嚼肌视频和肌电图（EMG）观察双侧6-羟基多巴胺（6-OHDA）损毁黑质纹状体多巴胺能通路对摄食行为的影响。我们观察到，摄入行为的持续时间，其中兔子将其嘴插入颗粒盒，似乎拿起颗粒，在损伤后缩短。此外，消耗1g颗粒的摄入行为的数量增加。在进食行为，咬肌肌电活动的变化在对照兔，而这种变化是较小的损伤的主题。这表明，在对照受试者的摄入行为中，捡起颗粒并咀嚼它们的行为是混合的。这种效应仅在黑质到壳核腹侧部的多巴胺能通路被阻断时观察到，而在背侧部被阻断时没有观察到，这些结果表明黑质纹状体多巴胺能通路可能在咀嚼的顺序进展中起作用。

The masticatory sequence is a whole set of movements from ingestion to swallowing. The masticatory sequence could be divided into three recognized stages (stage I, IIa, IIb) in the rabbit based on the form of jaw movements. It is, however, still unclear which neural mechanism is involved in the transition of the masticatory stages. The aim of this project was to clarify the role of the nigrostriatal dopaminergic pathway in the sequential progress during mastication.We obtained the findings in this study as follows ;1. We examined the alteration of dopamine (DA) concentration in the extracellular space of the putamen during 5 consecutive minutes of mastication in the awake rabbit, using the microdialysis. Analysis of the microdialysate samples indicated that the DA concentration in the putamen increased significantly during mastication, compared with resting the period.2. We studied the effect of bilateral 6-hydroxydopamine (6-OHDA) lesions of the nigrostriatal dopaminergic pathway on feeding behavior in freely-moving rabbits by means of video and electromyogram (EMG) of masticatory muscles. We observed that the duration of intake behavior, in which the rabbit inserted its mouth into the pellet-box and seemed to pick up pellets, was shortened after the lesions. Further, the number of intake behaviors for consuming 1 g of pellets was increased. During intake behavior, masseteric EMG activities varied in the control rabbits, whereas this variation was smaller in the lesioned subjects. This suggests that the behaviors of picking up the pellets and chewing them were intermingled during intake behavior in the control subjects. This effect was observed only when the dopaminergic pathway from the substantia nigra to the ventral part of the putamen was interrupted, and not when the dorsal part was disrupted.These results suggested that the nigrostriatal dopaminergic pathway might play a role in the sequential progress during mastication.