The role of the nigrostriatal dopaminergic pathway in the sequential progress

咀嚼序列是从吞咽到吞咽的一整套动作。根据下颌运动的形式，兔的咀嚼序列可分为三个公认的阶段(I期、IIa期、IIb期)。然而，目前还不清楚是哪种神经机制参与了咀嚼阶段的转变。本研究的目的是为了阐明黑质纹状体多巴胺能通路在咀嚼过程中的作用。本研究获得的结果如下：1.用微透析法检测清醒兔咀嚼连续5分钟内壳核细胞外间隙中多巴胺(DA)浓度的变化。对微透析液样品的分析表明，与静止期相比，咀嚼过程中壳核中的DA浓度显著增加。用视频和咀嚼肌肌电信号的方法研究了黑质纹状体多巴胺能通路损毁双侧6-羟基多巴胺(6-OHDA)对自由活动兔摄食行为的影响。我们观察到，在损伤后，兔子将嘴插入弹丸盒并似乎捡起弹丸的摄取行为的持续时间缩短了。此外，每摄入1g颗粒的摄取行为次数增加。在摄食行为中，对照兔的咀嚼肌肌电活动发生变化，而受损受试者的这种变化较小。这表明，对照组受试者在进食行为中，捡起颗粒并咀嚼它们的行为是混合的。只有当黑质至壳核腹侧的多巴胺能通路中断时才能观察到这种效应，而背侧部分被破坏时则不能观察到这种效应。这些结果表明黑质纹状体的多巴胺能通路可能在咀嚼过程中起着作用。

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.