The commissural transfer of the horizontal optokinetic signalin the rat: a c-Fos study

We applied the Fos method in rats subjected tohorizontal optokinetic stimulation (OKS) to study whetheroptokinetic information is transferred through the commissuralpretectal Wbres from one optic tract nucleus (NOT) tothe opposite. In binocular as well as in monocular nasalwardOKS, the highest Fos immunoreactivity was found inthe NOT contralateral to the nasalward stimulation, asexpression of the activation either of direction-selectivecells and of commissural neurons. Even the opposite NOTshowed many Fos-positive cells activated by the oppositenucleus throughout the commissural pretectal pathway.They might be the GABA positive cells, which are thoughtto allow the activation in one nucleus to be transformed intoinhibition of the opposite side. In monocular temporalwardOKS, the inhibition on direction-selective cells and theconsequent silencing of commissural neurons caused thefaint immunoreactivity in the NOT contralateral to eyestimulated. In the opposite nucleus the few Fos-positivecells emerged as a consequence of the lack of the normaltonic commissurally mediated inhibition.