Development of parvalbumin neurons and perineuronal nets in the visual cortex of normal and dark‐exposed cats

• Published in: Journal of comparative neurology (1911) 2021-08, Vol.529 (11), p.2827-2841
• Main Authors: Aronitz, Elise M., Kamermans, Braden A., Duffy, Kevin R.
• Format: Article
• Language: English
• Subjects: Age Factors; Animals; Cats; Cell size; dark exposure; Darkness; development; Firing pattern; Nerve Net - chemistry; Nerve Net - growth & development; Nets; Neural networks; Neurons; Neurons - chemistry; Neurons - physiology; Neuroplasticity; Parvalbumin; Parvalbumins - analysis; Parvalbumins - physiology; perineuronal net; Perineuronal nets; Photovoltaic cells; plasticity; Primary Visual Cortex - chemistry; Primary Visual Cortex - cytology; Primary Visual Cortex - growth & development; Visual cortex; Visual pathways; Visual system
• ISSN: 0021-9967; 1096-9861
• DOI: 10.1002/cne.25127

During development, the visual system maintains a high capacity for modification by expressing characteristics permissive for plasticity, enabling neural circuits to be refined by visual experience to achieve their mature form. This period is followed by the emergence of characteristics that stabilize the brain to consolidate for lifetime connections that were informed by experience. Attenuation of plasticity potential is thought to derive from an accumulation of plasticity‐inhibiting characteristics that appear at ages beyond the peak of plasticity. Perineuronal nets (PNNs) are molecular aggregations that primarily surround fast‐spiking inhibitory neurons called parvalbumin (PV) cells, which exhibit properties congruent with a plasticity inhibitor. In this study, we examined the development of PNNs and PV cells in the primary visual cortex of a highly visual mammal, and assessed the impact that 10 days of darkness had on both characteristics. Here, we show that labeling for PV expression emerges earlier and reaches adult levels sooner than PNNs. We also demonstrate that darkness, a condition known to enhance plasticity, significantly reduces the density of PNNs and the size of PV cell somata but does not alter the number of PV cells in the visual cortex. The darkness‐induced reduction of PV cell size occurred irrespective of whether neurons were surrounded by a PNN, suggesting that PNNs have a restricted capacity to inhibit plasticity. Finally, we show that PV cells surrounded by a PNN were significantly larger than those without one, supporting the view that PNNs may mediate trophic support to the cells they surround. At the peak of the critical period, immersion into complete darkness for 10 days significantly reduces the number of perineuronal nets (PNN) in the primary visual cortex of cats but does not alter the number of parvalbumin (PV) cells that they usually surround. Darkness also reduces the size of PV cells even if they are surrounded by a PNN, indicating that PNNs do not inhibit all forms of neural plasticity.