Sex-specific age-related changes in excitatory and inhibitory intra-cortical circuits in mouse primary auditory cortex

Abstract

A common impairment in aging is age-related hearing loss (presbycusis), which manifests as impaired spectrotemporal processing. Aging is accompanied by alteration in normal inhibitory (GABA) neurotransmission and changes in excitatory (NMDA and AMPA) synapses in the auditory cortex (ACtx). However, the circuit mechanisms responsible for age-related auditory dysfunction remain unknown. Here we investigated how auditory cortical microcircuits change with age. We performed laser-scanning photostimulation (LSPS) combined with whole-cell patch clamp recordings from Layer (L) 2/3 cells in primary auditory cortex (A1) in young adult (postnatal day (P) 47-P72) and aged (P543 to P626) male and female CBA/CaJ mice. We found that L2/3 cells in aged male animals display functional hypoconnectivity of both excitatory and inhibitory circuits originating from L4. Compared to cells from young adult mice, cells from aged male mice have fewer inhibitory connections from L4 while female mice show weaker connection strength. These results suggest a sex-specific reduction in excitatory and inhibitory intralaminar cortical circuits in aged mice compared with young adult animals. We speculate that these unbalanced changes in cortical circuits contribute to the functional manifestations of age-related hearing loss in both males and females.