Effects of developmental noise exposure on inhibitory cell densities and perineuronal nets in A1 and AAF of mice

Within the auditory cortex, there are two primary-like regions considered to be 'core' cortical fields, the primary auditory cortex (A1) and the anterior auditory field (AAF). Both fields have sharp frequency tuning, tonotopic organization, and inputs from the ventral division of the medial geniculate body of the thalamus. AAF seems to be more specialized for faster spectrotemporal processing than A1, but the underlying mechanisms are unclear. A1 has been studied extensively in developmental plasticity, but how AAF changes with developmental experience is less clear. To address potential cellular correlates of processing differences between the two fields, we used immunohistochemistry to quantify the density of GABA, parvalbumin (PV), and somatostatin (SOM) cells in A1 and AAF of mice. We also compared the density of perineuronal nets (PNN) between A1 and AAF. PNNs are a specialized assembly of extracellular matrix involved in network maturation and plasticity. Finally, we compared the effects of developmental noise exposure on inhibitory and PNN cell density in these two core regions. In adult mice, there were more PV cells and PNNs surrounding cell bodies in AAF than in A1. Moderate level noise exposure during early development leads to 1) increased GABA and SOM cell density in both A1 and AAF, and 2) decreased PNN cell density in A1, but not AAF. Inhibitory cells without PNN appear to be more susceptible to changes following developmental noise exposure in both fields. Deep layers (5/6) are more susceptible to change in PNN density compared to superficial layers (1-4) of A1. Results are consistent with altered cortical gain control models and impaired maturation of cortex in response to noisy environments, and suggest that PNNs may be more prone to modification in A1 than AAF. (C) 2019 Elsevier B.V. All rights reserved.