"Dress" makes the neuron - different forms of the extracellular matrix in the vertebrate central nervous system

Introduction: Extracellular matrix is a key component of most connective tissues. For decades, the presence of this chemically heterogeneous interface has been largely unaddressed or even denied in the central nervous system. It was not until the end of the last century that scientists turned their attention to this enigmatic substance and unravelled its versatile roles in the developing as well as the adult nervous system. Aim: The aim of the authors was to characterize different parts of the human central nervous system: the hippocampus, the lateral geniculate nucleus and the spinal cord. In addition they looked for connections between brain plasticity and extracellular matrix indifferent animal models. Method: The authors used two perfusion fixed human brain and spinal cord samples, 23 further human brain samples for disease-related investigations, 16 adult rat brains and 18 chicken brains of hatchlings, 13 days or three months of age. They visualized the extracellular matrix via lectin-and immunohistochemistry. Results: It was demonstrated that the human central nervous system shows a bewildering phenotypic versatility in its various parts. The human spinal cord harbours perineuronal nets around long-range projection neurons whilst perisynaptic coats are enriched in the dorsal horn. Periaxonal coats protect functional synapses in neurodegeneration. In the rat thalamus, perineuronal matrix is enriched in less plastic territories and develops in accordance with its linked cortical region. In the chicken, perineuronal matrix is well established already at birth and its further development is not functionally dependent. Conclusions: In human, the perineuronal matrix shows a large diversity depending on regional distribution and function. The authors argue that the development and differentiation of extracellular matrix is strongly linked to those of neurons. This observation was based on findings in the domestic chick which exhibits an immediate maturity after hatching as well as on observations in rat thalamic nuclei which reflect the plasticity of their corresponding cortical fields.