Redgrave P, Simkins M, McHaffie J G, Stein B E
Department of Psychology, University of Sheffield, UK.
Exp Brain Res. 1996 May;109(2):197-208. doi: 10.1007/BF00231781.
A wealth of evidence implicates the crossed descending projection from the superior colliculus (SC) in orientation and approach behaviours directed towards novel, non-noxious stimuli. In our preceding paper, we identified a population of nociceptive neurones in the rat SC that have axons that project to the contralateral brainstem via this output pathway. The purpose of the present study was, therefore, to evaluate the prediction that the crossed descending projection of the SC is also involved in the control of orientation and approach movements of the head and mouth made during the localisation of persistent noxious stimuli. An independent-groups design was used to test the effects of interrupting the contralateral descending projection from the SC on the behavioural reactions elicited by noxious mechanical stimuli presented to the tail and hindpaws. In different groups of animals, a microwire knife was used to cut the contralateral descending fibres at two different locations: (1) a sagittal cut at the level of the dorsal tegmental decussation; (2) a bilateral coronal cut of the predorsal bundle at the level of the medial pontine reticular formation. Retrograde anatomical tracing techniques were then used to evaluate the effectiveness of the cuts and to assess possible involvement of non-collicular fibre systems in both lesioned and control animals. Additional behavioural procedures were performed to test for general neurological status and responsiveness of animals to non-noxious stimuli. Anatomical tracing data indicated that the largest population of neurones with fibres severed by both cuts were the cells-of-origin of the contralateral descending projection in the intermediate white layer of the SC. Behavioural results showed that significantly more animals in both lesion groups failed to locate and bite a mechanical clip placed on the tail. Instead of switching to motor behaviours to localise and remove noxious stimuli, they persisted with defensive reactions, which included freezing, vocalisation or forward and backward escape. In contrast, when the clip was placed on the hindpaws, it was successfully localised by most lesioned and control animals; however, lesioned animals had reliably longer latencies and spent less time in close contact with the clip. Consistent with the established role of the contralateral descending projection in non-noxious orientation, lesioned animals also showed orienting deficits to a range of non-noxious sensory stimuli. These data suggest that, under certain behavioural circumstances, nociceptive information from the SC is integral to the elaboration of orienting and approach movements of the head and mouth elicited by persistent noxious stimuli.
大量证据表明，上丘（SC）的交叉下行投射参与了针对新的、无害刺激的定向和趋近行为。在我们之前的论文中，我们在大鼠的上丘中鉴定出一群伤害性神经元，它们的轴突通过这条输出通路投射到对侧脑干。因此，本研究的目的是评估以下预测：上丘的交叉下行投射也参与控制在定位持续性有害刺激过程中头部和口部的定向和趋近运动。采用独立组设计来测试中断上丘对侧下行投射对呈现于尾巴和后爪的有害机械刺激所引发的行为反应的影响。在不同组的动物中，使用微丝刀在两个不同位置切断对侧下行纤维：（1）在背侧被盖交叉水平进行矢状切割；（2）在脑桥内侧网状结构水平对背侧前束进行双侧冠状切割。然后使用逆行解剖追踪技术来评估切割的有效性，并评估病变动物和对照动物中非上丘纤维系统可能的参与情况。还进行了额外的行为程序来测试动物的一般神经状态和对无害刺激的反应性。解剖追踪数据表明，被两种切割切断纤维的神经元中，数量最多的是上丘中间白层中对侧下行投射的起源细胞。行为结果显示，两个病变组中明显更多的动物未能定位并咬住放置在尾巴上的机械夹子。它们没有转向运动行为来定位和去除有害刺激，而是持续出现防御反应，包括僵住、发声或前后逃窜。相反，当夹子放置在后爪上时，大多数病变动物和对照动物都能成功定位；然而，病变动物的潜伏期明显更长，与夹子密切接触的时间更短。与对侧下行投射在无害定向中的既定作用一致，病变动物对一系列无害感觉刺激也表现出定向缺陷。这些数据表明，在某些行为情况下，来自上丘的伤害性信息对于由持续性有害刺激引发的头部和口部定向及趋近运动的精细调节至关重要。
