Abstract
Perineuronal nets (PNNs), proteoglycan-rich extracellular matrix structures, are thought to be expressed around inhibitory neurons and contribute to critical periods of brain function and synaptic plasticity. However, in some specific brain regions such as the amygdala, PNNs were predominantly expressed around excitatory neurons. These neurons were recruited during auditory fear conditioning and memory retrieval. Indeed, the activation of PNN-expressing excitatory neurons predicted cognitive performance.
Highlights
Perineuronal nets (PNNs), proteoglycan-rich extracellular matrix structures, are thought to be expressed around inhibitory neurons and contribute to critical periods of brain function and synaptic plasticity
We investigated the overall distribution of PNN using Wisteria floribunda agglutinin (WFA), a ubiquitous marker for PNNs11, in GAD67-GFP knock-in adult mice in which GABAergic neurons are labeled by GFP12
WFA-positive PNNs were widely observed around GFPpositive inhibitory neurons throughout the adult brain, a finding consistent with those reported previously[3,13] (Fig. 1A); we found it surprising that WFA-labeling and GFP fluorescence were mutually exclusive in some regions, including the dorsal tenia tecta, the piriform cortex, the lateral amygdala, the basolateral amygdala, the basomedial amygdala, the hippocampal CA2 region, the ventromedial hypothalamus, the entorhinal cortex, the temporal association cortex, and the ectorhinal cortex, even though these regions contained many GFP-positive GABAergic neurons (Fig. 1B)
Summary
Perineuronal nets (PNNs), proteoglycan-rich extracellular matrix structures, are thought to be expressed around inhibitory neurons and contribute to critical periods of brain function and synaptic plasticity. In some specific brain regions such as the amygdala, PNNs were predominantly expressed around excitatory neurons These neurons were recruited during auditory fear conditioning and memory retrieval. Recent studies using enzymes that degrade PNNs demonstrate that PNNs regulate synaptic plasticity, critical period closure, and fear memory[6,7,8]. Despite these important functions, it is unclear what differentiates neurons with PNNs from those without. We compared the expression of c-Fos, a marker of neuronal activity[9], between neurons with and without PNNs after fear conditioning, which is a form of associative learning[10]
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