Juvenile Hippocampal CA2 Region Expresses Aggrecan

Area of Science:

• Neuroscience
• Cell Biology
• Developmental Biology

Background:

• Perineuronal nets (PNNs) primarily ensheath inhibitory interneurons in the hippocampus.
• PNNs are also found around excitatory neurons, regulating plasticity and excitability.
• Recent work identified PNNs around hippocampal CA2 pyramidal cells, but their developmental trajectory in this region remains unclear.

Purpose of the Study:

• To investigate the developmental timeline of PNNs in the mouse hippocampal CA2 subregion during postnatal maturation.
• To characterize the presence and distribution of PNN components in the developing CA2 region.

Main Methods:

• Immunohistochemistry was used to detect aggrecan, a key PNN component.
• The CA2 region was identified using the marker protein regulator of G protein signaling 14 (RGS14).
• Comparisons were made between anterior and posterior sections of the CA2 area.

Main Results:

• Aggrecan, a major PNN component, was detected in the pyramidal cell layer of the presumptive CA2 subarea before the definitive appearance of the CA2 region (marked by RGS14).
• Aggrecan immunoreactivity showed a gradient, being more pronounced in anterior CA2 sections compared to posterior sections.
• This suggests a developmental emergence of PNNs in CA2 preceding the full regional definition.

Conclusions:

• PNNs in the hippocampal CA2 region begin to form during early postnatal development, even before the region is fully established.
• The anterior-posterior gradient of aggrecan suggests regional functional specialization of CA2 PNNs.
• These findings provide insights into the developmental regulation and potential functional heterogeneity of PNNs in hippocampal excitatory circuits.