PhD Scientific Days 2021

NE_I_L: Neurosciences I. Lectures

Modular Organization of Signal Transmission in the Primate Somatosensory Cortex

Text of the abstract

Introduction: Axonal connections of column size cortical regions exhibit patchy distribution all over the primate cerebral cortex. The axonal patches represent specific target sites as e.g. columns of similar orientation preference in the visual cortex. However, axonal connections also densely distribute outside of the patches without any apparent grouping. Instead, the out-patch axons exhibit a radial spreading from the origin towards probably distant target sites including the patches. Interestingly both patch and out-patch axons form axon terminal-like structures suggesting their role in synaptic transmission.
Aim: The aim of our study is to know whether axons play a similar role in the propagation of activity and dissemination of information within and outside of the patches.
Methods: Distal finger pad representations of six squirrel monkeys that were injected with BDA via iontophoresis in area 3b (3 cases) and area 1 (3 case). Aldehyde fixation was made by transcardial perfusion after 10-20 days survival. Series of 50 μm thick horizontal, vibratome sections were collected at regular intervals from flattened cortex. Standard ABC protocol was used to visualize BDA labeling with nickel intensified DAB as the chromogen. Sections were then osmicated and flat embedded in Durcupan. Intra and Inter areal axons of areas 3b and 1 were studied. Axonal patches were mapped and outlined by using Neurolucida. Reconstruction of the BDA labelled axonal fibers was also made with Neurolucida at high magnification within and outside of the axonal patches. Tortuosity, Inter-varicosity distance, Thickness, Bouton convergence, and Density of varicosity thickness of the individual axonal segments within and out of the patches were compared.
Conclusion: The increased bouton density accompanied by extensive axonal convergence (cris-cross) could result in a highly efficient way of signal transmission in terminal arborization patches of the cerebral cortex. In contrast, the long range thick axons outside the patches could provide input to extra classical receptive field and form the structural correlate of cortical plasticity.
Supported by NIH NS093998 and OTKA NN118902.

University and Doctoral School

Semmelweis University, János Szentágothai Doctoral School of Neurosciences