Zhang Hong-Qi, Al-Chaer Elie D, Willis William D
School of Chinese Medicine, Hong Kong Baptist University, Kowloon Tong, Hong Kong.
J Neurophysiol. 2002 Sep;88(3):1185-96. doi: 10.1152/jn.2002.88.3.1185.
Recent discoveries of visceral nociceptive inputs sharing the classical tactile pathway in the dorsal-column medial lemniscus system have opened a new venue for the investigation of somatovisceral interactions. The current study was designed to determine whether somatic innocuous inputs modulate visceral nociceptive transmission at the thalamic level. The investigation was carried out by means of extracellular single-unit recordings in the ventroposterior lateral nucleus of the thalamus in rats anesthetized with pentobarbital. Noxious visceral stimulation was achieved by reproducible colorectal distension (CRD, 20-80 mmHg) with a balloon catheter. Tactile stimulation was delivered by means of a feedback-controlled mechanical stimulator. The response of the neurons to CRD was compared before and after the conditioning procedure by giving tactile stimulation either immediately before CRD or overlapping it. Twenty-five ventroposterior lateral (VPL) thalamic neurons were found among numerous tactile-only neurons to have convergent inputs from both tactile and visceral sources. Their responses to CRD were excitatory (19), inhibitory (4), or bimodal. When cutaneous tactile stimuli were delivered before CRD, the responses were reduced in 18 cases. The reduction, however, was usually short-lasting, immediately following tactile stimulation and could not be enhanced by a prolonged conditioning procedure. It was unlikely to be attributable to neuronal habituation as the inverted procedure, CRD stimulation before tactile, often produced the opposite effect, that is, an enhanced response to skin stimulation. Repeated CRD could bring about sensitization of the responses of thalamic neurons as manifested by increased spontaneous discharge, lowered response threshold, and increased response level. Under such circumstances, the original effect of tactile stimulation on CRD responses could be weakened. In conclusion, tactile stimulation may in most circumstances inhibit thalamic neuronal responses to visceral nociceptive input produced by CRD. However, the effect appears to be mild and short-lasting at the individual neuronal level in the VPL thalamus.
最近在内脏伤害性传入在背柱内侧丘系系统中共享经典触觉通路方面的发现，为研究躯体-内脏相互作用开辟了新途径。本研究旨在确定躯体无害性传入是否在丘脑水平调节内脏伤害性传递。研究通过在戊巴比妥麻醉的大鼠丘脑腹后外侧核进行细胞外单单位记录来开展。通过用球囊导管进行可重复的结肠扩张（CRD，20 - 80 mmHg）实现有害内脏刺激。触觉刺激通过反馈控制的机械刺激器施加。通过在CRD之前立即给予触觉刺激或使其与CRD重叠，比较神经元在条件刺激程序前后对CRD的反应。在众多仅对触觉有反应的神经元中，发现25个丘脑腹后外侧（VPL）神经元具有来自触觉和内脏源的汇聚输入。它们对CRD的反应是兴奋性的（19个）、抑制性的（4个）或双峰的。当在CRD之前给予皮肤触觉刺激时，18例反应减弱。然而，这种减弱通常是短暂的，紧接在触觉刺激之后，并且不能通过延长的条件刺激程序增强。这不太可能归因于神经元习惯化，因为反向程序，即在触觉之前进行CRD刺激，通常会产生相反的效果，即对皮肤刺激的反应增强。重复的CRD可导致丘脑神经元反应的敏化，表现为自发放电增加、反应阈值降低和反应水平增加。在这种情况下，触觉刺激对CRD反应的原始作用可能会减弱。总之，在大多数情况下，触觉刺激可能会抑制丘脑神经元对CRD产生的内脏伤害性输入的反应。然而，在VPL丘脑的单个神经元水平上，这种作用似乎是轻微且短暂的。
