Fontanesi G, Siciliano R, Porciatti V, Bagnoli P
Department of Physiology and Biochemistry, University of Pisa, Italy.
Vis Neurosci. 1996 Mar-Apr;13(2):327-34. doi: 10.1017/s0952523800007574.
This study was performed in order to establish whether selective depletion of somatostatin (SS) in the rat primary visual cortex obtained by cysteamine (CSH) administration results in changes of visual evoked potentials (VEPs). VEPs in response to a contrast reversal (0.5 Hz) of an optimal sinusoidal grating (0.1 cycle/deg, contrast 90%, mean luminance 15 cd/m2) were recorded from different layers of the binocular portion of the primary visual cortex of anesthetized rats with saline injection as well as before and after CSH treatment (90 mg/kg, s.c.). VEPs of CSH treated rats, as compared to those obtained either in saline-injected animals or before drug administration, are reduced in amplitude at intermediate cortical layers whereas they are increased at deeper layers. VEP changes depend on CSH treatment and not on the extended anesthesia since no alterations in the VEP profile can be observed in saline-injected animals maintained in the same experimental condition. Forty-eight hours following CSH treatment, the VEP profile is comparable to that of saline-injected animals. Immunocytochemical analysis of the visual cortex of rats recorded 7 h after CSH treatment shows a 20-30% reduction in the number of SS-containing cortical cells. The highest reduction can be observed in cortical layer 5 although a significant decrease is also found in layers 2-3. In contrast, the pattern of SS immunoreactivity of the visual cortex of rats recorded 48 h after CSH administration is similar to that obtained in control conditions. These results indicate that a selective toxin for somatostatinergic systems induces a transient decrease of SS-containing cell number in selected cortical layers. Accordingly, CSH can serve as a useful pharmacological tool for the study of somatostatinergic function in the rat visual cortex since changes in VEPs can be related to a reduction of somatostatinergic neurons associated to CSH treatment. In particular, the present results suggest that one of the possible actions of somatostatinergic neurons in the rat visual cortex is to modulate the excitatory-inhibitory balance.
本研究旨在确定通过给予半胱胺（CSH）使大鼠初级视觉皮层中的生长抑素（SS）选择性耗竭是否会导致视觉诱发电位（VEP）的变化。在麻醉大鼠初级视觉皮层双眼部分的不同层记录对最佳正弦光栅（0.1周/度，对比度90%，平均亮度15 cd/m²）的对比度反转（0.5 Hz）的VEP，记录时间包括注射生理盐水时以及CSH处理（90 mg/kg，皮下注射）前后。与注射生理盐水的动物或给药前相比，CSH处理大鼠的VEP在中间皮层层的幅度降低，而在较深层则增加。VEP变化取决于CSH处理，而非延长的麻醉时间，因为在相同实验条件下维持的注射生理盐水的动物中未观察到VEP波形的改变。CSH处理后48小时，VEP波形与注射生理盐水的动物相当。对CSH处理7小时后记录的大鼠视觉皮层进行免疫细胞化学分析显示，含SS的皮层细胞数量减少了20 - 30%。尽管在2 - 3层也发现有显著减少，但在皮层第5层减少最为明显。相反，CSH给药后48小时记录的大鼠视觉皮层的SS免疫反应模式与对照条件下相似。这些结果表明，一种针对生长抑素能系统的选择性毒素会导致选定皮层层中含SS细胞数量的短暂减少。因此，CSH可作为研究大鼠视觉皮层中生长抑素能功能的有用药理学工具，因为VEP的变化可能与CSH处理导致的生长抑素能神经元减少有关。特别是，目前的结果表明，大鼠视觉皮层中生长抑素能神经元的可能作用之一是调节兴奋 - 抑制平衡。
