Neurons in the superficial gray layer (SGS) of the superior colliculus receive visual input and excite intermediate layer (SGI) neurons that play a critical role in initiating rapid orienting movements of the eyes, called saccades. In the present study, two types of experiments demonstrate that a population of SGI neurons gives rise to a reciprocal pathway that inhibits neurons in SGS. First, in GAD67-GFP knock-in mice, GABAergic SGI neurons that expressed GFP fluorescence were injected with the tracer biocytin to reveal their axonal projections. Axons arising from GFP-positive neurons in SGI terminated densely in SGS. Next, SGI neurons in rats and mice were stimulated by using the photolysis of caged glutamate, and in vitro whole-cell patch-clamp recordings were used to measure the responses evoked in SGS cells. Large, synaptically mediated outward currents were evoked in SGS neurons. These currents were blocked by gabazine, confirming that they were GABA(A) receptor-mediated inhibitory postsynaptic currents. This inhibitory pathway from SGI transiently suppresses visual activity in SGS, which in turn could have multiple effects. These effects could include reduction of perceptual blurring during saccades as well as prevention of eye movements that might be spuriously triggered by the sweep of the visual field across the retina. This study was conducted by collaboration between Department of Developmental Physiology, National Institute for Physiological Sciences (neuroanatomical analysis), Department of Neurobiology at Duke University, USA (electrophysiological analysis), Department of Physiology, Faculty Pharmaceutical Sciences, Chulalongkorn University, Thailand (neuroanatomical analysis) ad Faculty of Medicine, Gunma University (generation of transgenic mice).
Lee PH*, Sooksawate T*, Yanagawa Y, Isa K, Isa T**, Hall WC**
Identity of s pathway for saccadic suppression.
Proceedings of National Academy of Sciences USA, 104: 6824-6827 (2007)
（online free access）
* = equal contribution, **=co-corresponding authors
