hide
Free keywords:
-
Abstract:
Introduction: The primary visual cortex of the primate shows distinct regions of increased cytochrome oxidase activity, the so called “blobs”. When visualized in tangential sections the blobs form a pattern of regularly distributed patches which are most prominent in the third cortical layer. Since cytochrome oxidase is an enzyme of the oxidative chain, increased local enzyme activity indicates an increased metabolic activity of a given region. It has been shown in the squirrel monkey cortex that this metabolic difference is reflected in the density of the cortical vascularization. The aim of this study was to replicate and extend this finding with a quantitative and layer specific assessment of the vascular density in blob and interblob regions.
Methods: Formalin-fixed frozen sections of 2 animals (M. mulatta) were first stained with the classical cytochrome oxidase staining method that uses the enzyme activity to precipitate DAB. The sections were then further processed for fluorescence immunohistochemistry. They were incubated with anti-collagen type IV and a Cy3-conjugated secondary antibody to stain for blood vessels. Epifluorescence micrographs were taken and the vessels were manually and automatically delineated. The length density (mm/mm³) and volume fraction (mm³/mm³) of vessels was taken as a measure for the vascular density. The blobs were determined in the corresponding brightfield micrograph of the same section on the basis of the cytochrome oxidase stain.
Results: The vascular length density and volume fraction was significantly higher inside the blobs as compared to the interblob regions (paired t-test, p<0.001). The absolute values were 535.2 +/-57.8 mm/mm³ (mean +/- SD of 2 animals) for the blobs and 485.5 +/- 51.2 mm/mm³ for interblob areas, which is 108.7 for blobs and 98.1 for interblobs of the overall mean vascular length density in V1. The blob-interblob difference was most prominent in cortical layer IV.
Conclusion: In summary, the blobs’ vascular density is significantly higher as compared to the surrounding cortex in V1. This reflects an adaptation of blood supply in these metabolically and most likely also functionally different regions of V1. However, the measured difference is considerably smaller when compared to the previously published data. This discrepancy could be due inter-species or methodological differences between the studies.
