The critical period is a postnatal window characterized by a high level of experience-dependent neuronal plasticity in the central nervous system and sensory deprivation during this period significantly impacts neurological function. Perineuronal nets (PNNs) are specialized aggregates of the extracellular matrix which ensheath neuronal cell bodies, primary dendrites and axon hillocks and function in neuronal protection and stabilize synapses. PNNs are generally not present at birth, but reach adult-like patterns by the end of the third or fourth postnatal week. Their appearance is believed to mark the close of the critical period and sensory deprivation during this epoch disrupts development of PNNs. Here we investigate the postnatal development of two PNN markers (Wisteria floribunda agglutinin [WFA] and Cat-315) and the effect of neonatal conductive hearing loss (CHL) on their development. Our data indicates that these PNN markers are not present in the superior olivary complex (SOC) at birth, but develop over the first four postnatal weeks in different temporal patterns and also that neonatal CHL results in a significant decrease in the number of SOC neurons associated with Cat-315 reactive PNNs.
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