Parvalbumin immunoreactivity in the auditory cortex of a mouse model of presbycusis

Age-related hearing loss (presbycusis) affects w35% of humans older than sixty-five years. Symptoms of presbycusis include impaired discrimination of sounds with fast temporal features, such as those present in speech. Such symptoms likely arise because of central auditory system plasticity, but the underlying components are incompletely characterized. The rapid spiking inhibitory interneurons that co-express the calcium binding protein Parvalbumin (PV) are involved in shaping neural responses to fast spectrotemporal modulations. Here, we examined cortical PV expression in the C57bl/6 (C57) mouse, a strain commonly studied as a presbycusis model. We examined if PV expression showed auditory cortical fieldand layer-specific susceptibilities with age. The percentage of PV-expressing cells relative to Nissl-stained cells was counted in the anterior auditory field (AAF) and primary auditory cortex (A1) in three age groups: young (1e2 months), middle-aged (6e8 months) and old (14e20 months). There were significant declines in the percentage of cells expressing PV at a detectable level in layers IeIV of both A1 and AAF in the old mice compared to young mice. In layers VeVI, there was an increase in the percentage of PV-expressing cells in the AAF of the old group. There were no changes in percentage of PV-expressing cells in layers VeVI of A1. These data suggest cortical layer(s)- and field-specific susceptibility of PV+ cells with presbycusis. The results are consistent with the hypothesis that a decline in inhibitory neurotransmission, particularly in the superficial cortical layers, occurs with presbycusis.