Regulators of Adult Visual Cortex Plasticity in Mice

Article: Learning and protecting itself: how the brain adapts
Source: University of Göttingen (Germany)
Published: December 10, 2021 

Neurons in the mouse visual cortex enwrapped by ECM molecules (red)

Learning and recovery from injuries depend on the brain's plasticity. This plasticity between neuronal connections relies heavily on the network of macromolecules in between and surrounding the nerve cells, known as the extracellular matrix (ECM). As the brain becomes more mature, the stability of the ECM increases, providing a scaffold for the existing arrangements and synaptic circuits of nerve cells. New experiences require that this extracellular matrix be loosened in order for new connections to form. Similarly, when the brain experiences an injury such as a stroke, it needs to reorganize itself and form new connections. This balance between stability and plasticity is regulated by the proteolytic activity of enzymes such as matrix metalloproteinases (MMPs), which "digest" the ECM in order to "loosen" it. Researchers in Germany studying the visual cortex of mice showed that blocking the matrix metalloproteinases MMP2 and MMP9 can have opposing effects depending on whether the brain is sick, such as after stroke, or healthy. In the primary visual cortex of healthy mice, blocking MMP2 and MMP9 led to decreased ocular dominance plasticity. In mice studied immediately after a stroke, inhibition of MMP2 and MMP9 (which spike for a short time after a stroke) rescued neuronal plasticity that had been compromised by the stroke, that is, the MMPs had a therapeutic effect. The researchers point out that the intentional inhibition of the metaloproteinases immediately after inducing an experimental stroke was in order to simulate treatment. The authors argue that these findings show that levels of MMPs must be precise and optimal in the brain, as both too low or too high an amount can prevent neuronal plasticity.

My rating of this study: ⭐⭐

Akol I, Kalogeraki E, Pielecka-Fortuna J, et al. "MMP2 and MMP9 Activity Is Crucial for Adult Visual Cortex Plasticity in Healthy and Stroke-Affected Mice." Journal of Neuroscience.  JN-RM-0902-21. 11 November 2021. https://doi.org/10.1523/JNEUROSCI.0902-21.2021