Core Concept: Perineuronal nets gain prominence for their role in learning, memory, and plasticity.

Abstract

In the field of brain research, neurons have long held the center of attention. But in recent years, some researchers are starting to expand their focus beyond neurons to a long-overlooked structure called the perineuronal net. Lattice-like elements called perineuronal nets wrap around certain neurons, sharing components with cartilage. Researchers constructed this image of perineuronal nets in the mouse visual cortex using a super-resolution microscope and a fluorescent marker that labels certain sugar-rich molecules. Image courtesy of Yaron Sigal, Xiaowei Zhuang, and Takao Hensch (Harvard University, Cambridge, MA). Discovered in the late 1800s, this lattice-like element wraps around certain neurons and shares some components with cartilage. But far from providing mere structural support, growing evidence suggests that perineuronal nets, which are highly organized aggregates of proteins and sugar chains, help regulate the brain’s ability to make new connections and tweak existing ones. Researchers are now eager to understand how these nets may contribute to healthy brain function, as well as disease. This modern revival stems from a chance meeting between two neuroscientists about 2 decades ago. While studying spinal cord injury in rats, James Fawcett at the University of Cambridge in the United Kingdom tested an enzyme that he hoped would help regrow severed nerves. It did, to a limited extent, but more notably, it appeared to encourage rapid rewiring and compensatory activity by spared nerves. Tommaso Pizzorusso, then at the Scuola Normale Superiore di Pisa in Italy, was intrigued by the finding. The two scientists decided to combine the treatment with studies of the developing rat visual system conducted by Pizzorusso’s group (1). The enzyme, it turns out, was degrading perineuronal nets. When the researchers applied it to the visual cortex of adult rats, they found that neural circuits returned to a younger, more malleable or “plastic” state. …