Form, function and intracortical projections of spiny neurones in the striate visual cortex of the cat.

Abstract

SUMMARY1. We have studied the neuronal circuitry and structure-function relationships of single neurones in the striate visual cortex of the cat using a combination of electrophysiological and anatomical techniques.2. Glass micropipettes filled with horseradish peroxidase were used to record extracellularly from single neurones. After studying the receptive field properties, the afferent inputs of the neurones were studied by determining their latency of response to electrical stimulation at different positions along the optic pathway. Some cells were thus classified as receiving a mono-or polysynaptic input from afferents of the lateral geniculate nucleus (l.g.n.), via X-or Y-like retinal ganglion cells.3. Two striking correlations were found between dendritic morphology and receptive field type. All spiny stellate cells, and all star pyramidal cells in layer 4A, had receptive fields with spatially separate on and off subfields (S-type receptive fields). All the identified afferent input to these, the major cell types in layer 4, was monosynaptic from X-or Y-like afferents.4. Neurones receiving monosynaptic X-or Y-like input were not strictly segregated in layer 4 and the lower portion of layer 3. Nevertheless the X-and Y-like l.g.n. fibres did not converge on any of the single neurones so far studied.5. Monosynaptic input from the l.g.n. afferents was not restricted to cells lying within layers 4 and 6, the main termination zones of the l.g.n. afferents, but was also received by cells lying in layers 3 and 5.6. The projection pattern of cells receiving monosynaptic input differed widely, depending on the laminar location of the cell soma. This suggests the presence of a number of divergent paths within the striate cortex.7. Cells receiving indirect input from the l.g.n. afferents were located mainly within layers 2, 3 and 5. Most pyramidal cells in layer 3 had axons projecting out ofthe striate cortex, while many axons of the layer 5 pyramids did not.8. The layer 5 cells showed the most morphological variation of any layer, were the most difficult to activate by electrical stimulation, and contained some cells which responded with the longest latencies of any cells in the striate cortex. This suggests that they were several synapses distant from the J.g.n. input.9. The majority of cells in layers 2, 3, 4 and 6 had the same basic S-type receptive field structure.

Studies of stimulus parameters for seizure disruption using neural network simulations

“…This was in keeping with current studies on epilepsy spread which seem to indicate the predominance of the Layer II/ III and Layer V lateral connections (DeFazio andHablitz 2005, Telfeian andConnors 1998). It is clear from histological studies that lateral projections from stellate cells as well as Layer VI play a functional role in the activity of primate visual cortex (Martin and Whitteridge 1984;Gilbert and Wiesel 1983;Lund et al 1988;Schwark et al 1992). Similar connections need to be added to this current neuronal model to investigate their effects on seizure evolution, especially as we plan on adding in thalamic interactions.…”

Columnar Organization of Dendrites and Axons of Single and Synaptically Coupled Excitatory Spiny Neurons in Layer 4 of the Rat Barrel Cortex

“…The axonal projections of spiny layer 4 neurons in the visual cortex are well documented, in contrast to the barrel cortex (Martin and Whitteridge, 1984;Lund, 1988;Burkhalter, 1989;Ahmed et al, 1994). Spiny stellate and star pyramidal cells show a multitude of axonal projection patterns.…”

“…2 B, 3A, 4, 5), in contrast to spiny stellate cells in layer 4 of the visual cortex that generally display a multipolar, almost radially symmetric dendritic field (LeVay, 1973;Lund, 1984;Martin and Whitteridge, 1984;1988; but see Katz et al, 1989;Kossel et al, 1995). Three to six thick primary dendrites emerged from the spherical to ovoid somata that gave rise to several secondary, tertiary, and higher-order dendrites.…”

“…Most of these neurons resemble spiny stellate cells, whereas a smaller fraction has been described as star pyramidal cells (Lund, 1984;Ahmed et al, 1994;Hirsch, 1995). Thus, these neurons are the first elements involved in intracortical signal processing (Mountcastle and Powell, 1959;Hubel and Wiesel, 1962;LeVay, 1973;Martin and Whitteridge, 1984;McGuire et al, 1984;Douglas and Martin, 1991;ArmstrongJames et al, 1992;for review, see McCormick, 1992). …”

“…In analogy to the visual cortex, spiny layer 4 neurons may also establish synaptic contacts with layer 6 pyramidal neurons and in turn may receive synapses from these neurons (Gilbert and Wiesel, 1979;Martin and Whitteridge, 1984;McGuire et al, 1984;Benshalom and White, 1986;Ahmed et al, 1994;Stratford et al, 1996;Tarczy-Hornoch et al, 1999). The axonal projection of spiny layer 4 neurons toward layer 6 makes it likely that such a feed-forward A functional cortical column is superimposed in light gray.…”