Perineuronal nets (PNNs) are specialised extracellular matrix structures on the neuronal surface that control neuronal plasticity. The key components of PNNs are flexible carbohydrate polymers including the glycosaminoglycans chondroitin sulphate (CS) and hyaluronan. In the adult brain, PNNs have a reticular structure, effectively defining holes through which neighbouring neurons can establish synaptic connections (somewhat akin to a microscale ‘print board’). Current imaging technologies provide a rather crude visualisation of the PNN morphology. In order to understand how PNNs regulate neuronal plasticity, a better knowledge of the topography, permeability and mechanical properties of PNNs is required. 

We will employ a scanning probe technique based on nanopipettes, called Scanning ion conductance microscopy (SICM) to investigate, for the first time, the dynamics of PNNs. We will simultaneously map the topography and biophysical properties (e.g. permeability and elasticity) of PNNs with a spatial resolution down to 100 nm and less, and explore how external stimuli such as additional PNN crosslinking proteins affect those properties. 

Nanopipettes are also attractive tools for the analysis of macromolecules, as they can detect single molecules travelling through the nanopore tip. The SICM analysis of PNNs on neurons will be complemented with the nanopipette analysis of the key molecular components of PNNs: glycosaminoglycans (GAGs) and their covalent complexes with proteins.

This project will explore a new application area for nanopipettes and SICM for the analysis of glycan-rich cell coats and their molecular components. In the long term, the results of this multidisciplinary project may also provide invaluable insights to facilitate the design of PNN modulators to improve the retention of long-term memory, and to repair neuronal connections after injury.