Abstract
Burst firings of intermediate gray layer (SGI) neurons in the superior colliculus (SC) are important for generation of saccadic eye movements. Although GABAB receptors (GABABRs) are abundantly expressed in the SC, the role of these receptors for the burst generation has been unclear. In the present study, we examined this issue using whole-cell recordings in brain slice preparations obtained from GAD67-GFP knock-in mice in which GABAergic neurons express GFP fluorescence. In the presence of a GABAAR antagonist gabazine, single electrical stimulation of the superficial gray layer (SGS) evoked burst EPSCs in non-GABAergic SGI neurons. Addition of a GABABR antagonist CGP52432 (CGP) significantly increased the duration but not amplitude of the burst EPSCs, indicating that synaptically released GABA activates GABABRs. When CGP was locally puff-applied to the SGS, but not to the SGI, the burst EPSCs duration was also prolonged, suggesting that the site of CGP action was SGS. Consistent with these results, CGP also prolonged the duration of burst firings in non-GABAergic SGS neurons. Moreover, in the presence of antagonists for ionotropic glutamate receptors and GABAAR, local repetitive stimulation which mimicked GABAergic burst firings induced CGP-sensitive slow outward currents in some non-GABAergic SGS neurons. These results suggest that GABABRs localized in the SGS function as a negative-feedback mechanism for the burst responses in the SC. [J Physiol Sci. 2007;57 Suppl:S149]
