Grasse K L, Douglas R M, Mendelson J R
Department of Psychology, York University, Ontario, Canada.
Exp Brain Res. 1993;92(3):453-66. doi: 10.1007/BF00229033.
Visual response properties were examined in the superficial layers of the superior colliculus (SC) of anesthetized, paralyzed cats before and after i.v. administration of d-amphetamine. Receptive fields (RFs) of single SC units were plotted using small spots of light presented to the contralateral eye. Within the first hour following d-amphetamine injections, RF size gradually increased, reaching a maximum 86 min post-injection. On average, the area of the RF increased by 5.6 times and RF expansion was observed in all single units examined in the superficial layers. Over the subsequent 4-8 h following the injection, RF area gradually decreased and returned to control dimensions. Most RFs displayed asymmetrical patterns of expansion, showing relatively more horizontal than vertical growth. As RF expansion developed, responses to stimuli flashed "on" and "off" at various locations both inside and outside the borders of the control RF became progressively more vigorous. In contrast, no significant changes were noted in direction-selective responses at any time after d-amphetamine injections. Using an array of light bar stimuli of different lengths, the strength of surround suppression was found to be significantly diminished by d-amphetamine. The reduction in surround suppression was especially clear for bar lengths which exceeded the diameter of the control RF. No RF expansion was observed in the superficial layers of the SC when d-amphetamine was injected intravitreally. Furthermore, d-amphetamine had no discernable effect on the RF sizes of cells in the visual cortex. These results suggest that the RF changes in the SC were not of either retinal or cortical origin. We conclude that the mean retinal area which can potentially influence the activity of RFs in the superficial layers of the SC may be on average over 5 times greater than the RF area determined using conventional methods and criteria. These findings raise the interesting possibility that the relatively small size and sharp borders characteristic of RFs in the superficial layers arise from local inhibitory networks which delimit a broader field of excitatory activity supplied by retinal and cortical afferent terminals. Thus, in order to generate the RF changes observed here, either these local inhibitory circuits are amphetamine sensitive, or more likely, these inhibitory networks are dynamically modulated by an, as yet unidentified, amphetamine-sensitive input affecting visual RFs in the superficial layers.
在静脉注射d-苯丙胺前后，对麻醉、麻痹猫的上丘（SC）浅层的视觉反应特性进行了研究。使用呈现给对侧眼的小光点绘制单个SC单位的感受野（RFs）。在注射d-苯丙胺后的第一小时内，RF大小逐渐增加，在注射后86分钟达到最大值。平均而言，RF面积增加了5.6倍，并且在浅层检查的所有单个单位中均观察到RF扩大。在注射后的随后4-8小时内，RF面积逐渐减小并恢复到对照尺寸。大多数RF表现出不对称的扩大模式，水平方向的增长相对比垂直方向更多。随着RF扩大的发展，对在对照RF边界内外的不同位置“开”和“关”闪烁的刺激的反应逐渐变得更加活跃。相比之下，在注射d-苯丙胺后的任何时间，方向选择性反应均未观察到明显变化。使用一系列不同长度的光条刺激，发现d-苯丙胺可显著减弱周围抑制的强度。对于超过对照RF直径的光条长度，周围抑制的降低尤为明显。当玻璃体内注射d-苯丙胺时，在SC浅层未观察到RF扩大。此外，d-苯丙胺对视觉皮层中细胞的RF大小没有明显影响。这些结果表明，SC中的RF变化不是视网膜或皮层起源的。我们得出结论，可能影响SC浅层RF活动的平均视网膜面积可能平均比使用传统方法和标准确定的RF面积大5倍以上。这些发现提出了一个有趣的可能性，即浅层RF相对较小的尺寸和清晰的边界是由局部抑制网络产生的，这些网络限定了由视网膜和皮层传入终末提供的更广泛的兴奋活动区域。因此，为了产生此处观察到的RF变化，要么这些局部抑制回路对苯丙胺敏感，要么更有可能的是，这些抑制网络受到一种尚未确定的、影响浅层视觉RF的苯丙胺敏感输入的动态调节。
