The occipitoparietal pathway of the macaque monkey: comparison of pyramidal cell morphology in layer III of functionally related cortical visual areas |
| |
Authors: | Elston GN; Rosa MG |
| |
Institution: | Department of Physiology and Pharmacology, University of Queensland, Australia. |
| |
Abstract: | The dendritic morphology of pyramidal cells located at the base of layer
III in the primary visual area (V1), the second visual area (V2), the
middle temporal area (MT), the ventral portion of the lateral intraparietal
area (LIPv) and in the portion of cytoarchitectonic area 7a within the
anterior bank of the superior temporal sulcus was revealed by injecting
neurons with Lucifer Yellow in fixed, flattened slices of macaque monkey
visual cortex. These areas correspond to different levels of the
occipitoparietal cortical 'stream', which processes information related to
motion and spatial relationships in the visual field. The tissue was
immunocytochemically processed to obtain a light-stable diaminobenzidine
reaction product, revealing the dendritic morphology in fine detail.
Retrogradely labelled MT- projecting neurons in supragranular V1 (layer
IIIc of Hassler's nomenclature, corresponding to Brodmann's layer IVb) were
predominantly pyramidal, although many spiny multipolar (stellate) cells
were also found. The average basal dendritic field area of pyramidal
neurons in sublamina IIIc of V1 was significantly smaller than that in the
homologous layer of V2, within the cytochrome oxidase-rich thick stripes.
Furthermore, the average basal dendritic field areas of V1 and V2 pyramidal
neurons were significantly smaller than those of neurons in MT, LIPv and
area 7a. There was no difference in basal dendritic field area between
layer III pyramidal neurons in areas MT, LIPv and 7a. While the shape of
most basal dendritic fields was circularly symmetrical in the dimension
tangential to the cortical layers, there were significant biases in
complexity, with dendritic branches tending to cluster along particular
axes. Sholl analysis revealed that the dendritic fields of neurons in areas
MT, LIPv and 7a were significantly more complex (i.e. had a larger number
of branches) than those of V1 or V2 neurons. Analysis of basal dendritic
spine densities revealed regional variations along the dendrites, with peak
densities being observed 40-130 microns from the cell body, depending on
the visual area. The peak spine density of layer III pyramidal neurons in
V1 was lower than that observed in V2, MT or LIPv, which were all similar.
Pyramidal neurons in area 7a had the greatest peak spine density, which was
on average 1.7 times that found in V1. Calculations based on the average
spine density and number of dendritic branches at different distances from
the cell body demonstrated a serial increase in the total number of basal
dendritic spines per neuron at successive stations of the occipitoparietal
pathway. Our observations, comparing dendritic fields of neurons in the
homologous cortical layer at different levels of a physiologically defined
'stream', indicate changes in pyramidal cell morphology between
functionally related areas. The relatively large, complex, spine-dense
dendritic fields of layer III pyramidal cells in rostral areas of the
occipitoparietal pathway allow these cells to sample a greater number of
more diverse inputs in comparison with cells in 'lower' areas of the
proposed hierarchy.
|
| |
Keywords: | |
本文献已被 Oxford 等数据库收录! |
|