Retinal inputs and laminar distributions of the dorsal lateral geniculate nucleus relay cells in the eastern chipmunk (Tamias sibiricus asiaticus).

Retinal inputs and their laminar distributions in the dorsal lateral geniculate nucleus (LGNd) of the eastern chipmunk (Tamias sibiricus asiaticus) were studied using histological and microelectrode recording techniques. A previous anatomical study (Fukuda et al. 1986a) indicated that the chipmunk LGNd had five laminae: contralaterally (contra) innervated lamina 1 and ipsilaterally (ipsi) innervated lamina 2 in its ventromedial part; laminae 3a (contra), 3b (ipsi) and 3c (contra) in its dorsolateral part. We have confirmed this finding in our present anatomical study and have also noted another ipsilaterally innervated thin lamina 0, medial to lamina 1. In our electrophysiological study, however, we were unable to record units from lamina 0 and to investigate it functionally. We recorded 232 units from laminae 1, 2 and the 3 complex, of which 95 were identified as Y-like, 46 as W-like, 15 as X-like, and 8 as mixed Y/W-like cells; the rest were either unclassified or visually unresponsive. In laminae 1 and 2, only Y-like and X-like cells were recorded, whereas in the laminae 3 complex W-like cells were recorded as well. The results suggest that the chipmunk laminae 1, 2 and 3 complex correspond relatively well to the cat laminae A, A1 and C complex, respectively. In the chipmunk LGNd, however, there were more Y-like cells in laminae 1 and 2, and a few X-like cells of which some were color sensitive. Also, lamina 3a had a concentration of mixed-type cells with Y-like receptive field properties and W-like OX latencies. As for retinotopy, the dorsoventral transition of the contralateral visual field (laminae 1, 3a, 3c) is represented along the dorsoventral dimension of the chipmunk LGNd, whereas the temporonasal transition is represented in the rostrocaudal direction. Receptive field positions of the ipsilaterally innervated relay cells are limited to the central overlapping field of the contralateral visual fields of both eyes. Relay cells with visual fields having elevations of below -20 degrees had relatively fast latency range and Y-like properties.