Evidence for separate pathways within the tecto-geniculate projection in the tree shrew.

Two layers (3 and 6) in the dorsal lateral geniculate nucleus (GLd) of the tree shrew (Tupaia belangeri) receive projections from the superficial layers of the superior colliculus. The goal of this study was to determine whether the same or different cells in the superior colliculus give rise to the projections to layers 3 and 6 by following individual axons labeled with biocytin from the superior colliculus to the GLd. The results show that the terminal fields differ in the two layers--those in layer 3 are restricted to a line of projection, whereas those in layer 6 are elongated along the dimension orthogonal to a line of projection.

Terminal arbors of individual, physiologically identified geniculocortical axons in the tree shrew's striate cortex.

We studied the terminal patterns of single, physiologically identified geniculocortical axons in the striate cortex of the tree shrew by using intracellular recording and labeling methods. Axons were classified by their response to the onset (ON-center) or offset (OFF-center) of a light stimulus presented to the ipsilateral or contralateral eye. Then, we attempted to penetrate each axon for labeling with horseradish peroxidase.

Sublaminar organization within layer VI of the striate cortex in Galago.

In this study we examined the organization of projections from the striate cortex to the dorsal lateral geniculate (GL) and pulvinar (PUL) nuclei in the prosimian Galago by using retrograde transport methods. Injections of wheat germ agglutinin-conjugated horseradish peroxidase (WGA-HRP) into the PUL labeled two bands of cells in the striate cortex: the first consisted of large pyramidal cells in the upper half of layer V; the second consisted of small and medium-size pyramidal cells located in the deepest part of layer VI. The location of cells within layer VI coincided with a clear cytoarchitectonic sublayer, VIb, which contains fewer and paler staining cells than VIa.

Innervation patterns of single physiologically identified geniculocortical axons in the striate cortex of the tree shrew.

We examined the termination patterns of single geniculocortical axons in the striate cortex of the tree shrew by using intracellular recording and horseradish peroxidase staining methods. Axons were classified by whether they responded to light onset (ON center) or light offset (OFF center) and whether they were driven by the ipsi- or contralateral eye. Afferents with ON-center responses end in the upper part of layer IV (IVa) whereas afferents with OFF-center responses end in the lower part of layer IV (IVb).