c-Fos expression in the optokinetic nuclei of the rat following different visual stimulus conditions

In the present study we characterised by means of the c-Fos method the neuronal populations of the optokinetic nuclei system of the rat activated by different directions of external visual world motion as well as by saccadic exploration of a patterned stationary scene. A major difference was found between the nucleus of the optic tract (NOT) and the nuclei of the accessory optic system (AOS): dorsal terminal (DTN), lateral terminal (LTN) and medial terminal (MTN), c-Fos-positive cells are expressed in the AOS nuclei only after optokinetic stimulation (OKS) according to the direction for which each nucleus is strictly committed: in the DTN after horizontal OKS, in the LTN and MTN after vertical OKS. No segregation of direction-selective cells was observed in the MTN for opposite directions of motion. In the NOT, c-Fos cells became immunoreactive after OKS of any direction, with the greatest expression induced by horizontal OKS in the nucleus contralateral to the eye stimulated nasalward, and even following the presentation of a non-rotating drum. However, the spatial location of the activated neurones is distributed along the nucleus for horizontal OKS and strongly restricted to its rostral region for other stimuli. Given these findings, a larger spectrum of competencies than previously supposed should be attributed to the NOT.