Projection patterns of individual X‐ and Y‐cell axons from the lateral geniculate nucleus to cortical area 17 in the cat

Abstract

Horseradish peroxidase was injected intracellularly into single, physiologically-identified X- and Y-cell geniculocortical axons projecting to area 17 of the cat. This injection anterogradely labeled the axon terminal fields in cortex and retrogradely labeled the somata of these same axons in laminae A and A1 of the lateral geniculate nucleus (LGN). The laminar projections of 21 X- and 15 Y-cell axons were analyzed. For these, the laminar terminations of ten X- and seven Y-cell axons were also related to their cells' positions in the A-laminae. The terminal fields of X- and Y-cell axons overlapped substantially in layers IV and VI of area 17. Some X-cells terminated mainly in IVb, others mainly in IVa, and still others throughout IVa and IVb. The latter two groups also projected up to 100 micron into lower layer III. Y-cells terminated primarily in layer IVa and projected up to 200 microns into lower layer III. Some also arborized throughout the depth of layer IVb. Both X- and Y-cell axons terminated throughout the depth of layer VI, although more so in the upper half. We found no relationship between the diameter of the parent axon and its sublaminar projection within layer IV. Within layer IV, X-cell axons generally terminated within a single, continuous clump and had surface areas of 0.6 to 0.9 mm2. Axons of Y-cells often terminated in two to three separate clumps, separated by terminal free gaps 400 to 600 micron wide. Their total surface areas, including gaps, were 1.0 to 1.8 mm2, roughly 1.6 times the surface areas of X-cell axons. Despite considerable overlap, Y-cell arbors contained significantly more boutons than did X-cell arbors. The sublaminar projections of the X- and Y-cell axons within layer IV reflected the locations of the cells' somata within the depth of the A-laminae. X-cells located in the dorsal or ventral thirds of the depths of the laminae projected mainly to layer IVa or throughout layer IV in cortex. Those located in the central thirds projected mainly to layer IVb. Y-cells showed a similar positional relationship, but they appeared to follow different rules. Y-cells in the outer thirds of the A-laminae projected mainly to layer IVa; those in the central thirds, in addition, expanded their projections to include layer IVb. In general, larger sized somata in the LGN gave rise to more widely spreading terminal arbors and greater numbers of boutons in cortex than did smaller somata.(ABSTRACT TRUNCATED AT 400 WORDS)

How Thalamus Connects to Spiny Stellate Cells in the Cat's Visual Cortex

“…In our study of thalamic connectivity with corticothalamic neurons (da Costa and Martin, 2009b), multiple synapses from the same axon were formed with the same dendritic segment. Here we never detected multiple synapses on a dendrite from a single axon despite the fact that SSs are surrounded by a much higher density (ϳ10ϫ) (Humphrey et al, 1985) of thalamic boutons than are the layer 6 corticothalamic neurons. We did, however, observe in both the SS and the corticothalamic cells one example in which a bouton formed two synapses with a dendrite.…”

“…Unfortunately, we could not rely on the reconstruction of the axonal arbors of the SS to disprove this, since the axons were incompletely filled and overlap with several branches of thalamic axons. However, previous reconstructions of SS axonal arbors have shown that in the cat the local axon of SS forms few boutons in the volume of neuropil that surrounds its own dendrite (Gilbert and Wiesel, 1979;Martin and Whitteridge, 1984;Binzegger et al, 2004) and so it is unlikely that SS synapses are a significant contamination of the several thousand boutons (Humphrey et al, 1985) formed by all the labeled thalamic axons.…”

“…1). Part of the ipsilateral label is attributable to thalamic boutons formed between ocular dominance clusters (Freund et al, 1985a;Humphrey et al, 1985), and in some cases also to spillover of the injection site to lamina A1.…”

Directional asymmetries in the length‐response profiles of cells in the feline dorsal lateral geniculate nucleus.

“…In the light of the strategy used, we do believe that our approach has isolated cells exhibiting significant directional influences within the length-tuning profile. The implication is that geniculate cells distinguished by these criteria may, in a similar way to the X and Y (Bullier & Henry, 1979a, b, c) and on-and off-centre classifications (Humphrey, Sur, Uhlrich & Sherman, 1985;Bowling & Wieniawa-Narkiewicz, 1986), contact functionally distinct groups of cells in the visual cortex.…”

Emergence of orientation selective simple cells simulated in deterministic and stochastic neural networks

“…Further, only bilobed or trilobed profiles are found and the widths of the lobes vary with receptive field diameter. Finally, if one assumes C0 >~ 0.5 mm for immature systems (which is reasonable, since mature afferents mostly project to two or more ocular dominance stripes which are separated by about 0.8-1mm (Lund 1988; see also Humphrey et al 1985 for kittens)) the emerging receptive fields of layer IVc cells are smaller than these values of ~ would predict. For instance, at one degree of visual angle from the fovea, the magnification factor rn is found to be 4 mm/degree, so that Q0 = 0.5 mm would lead to a receptive field size of (1/4) ~ • (1/4) ~ which is just the projection area 2Q/m • 2Q/m .…”