Regional distribution of fast and slow geniculo-cortical relay cells (GCR-cells) within the rat's dorsal lateral geniculate nucleus (LGNd).

Unit activity of 135 GCR-cells in rat's LGNd was recorded extracellularly using micropipettes filled with trypan blue for subsequent marking of recording sites. The latencies of responses to electrical stimulation of the optic chiasma (OX) were mapped, and in accordance with Fukuda (1973) each GCR-cells was classified as fast or slow. Fast cells predominate in the rostroventromedial subregion and slow cells in the caudal part. Both fast and slow subtypes were found in the remaining rostrodorsolateral zone where slow cells made up two thirds of the subsample. The results fit the suggestion that in the LGNd of rats a fast retino-geniculate pathway relays in the ventromedial region, whereas slow pathways exist in the caudal as well as in the dorsolateral zone.