Homeostatic plasticity and synaptic scaling in the adult mouse auditory cortex.

It has been demonstrated that sensory deprivation results in homeostatic adjustments recovering neuronal activity of the deprived cortex. For example, deprived vision multiplicatively scales up mEPSC amplitudes in the primary visual cortex, commonly referred to as synaptic scaling. However, whether synaptic scaling also occurs in auditory cortex after auditory deprivation remains elusive. Using periodic intrinsic optical imaging in adult mice, we show that conductive hearing loss (CHL), initially led to a reduction of primary auditory cortex (A1) responsiveness to sounds. However, this was followed by a complete recovery of A1 activity evoked sounds above the threshold for bone conduction, 3 days after CHL. Over the same time course patch-clamp experiments in slices revealed that mEPSC amplitudes in A1 layers 2/3 pyramids scaled up multiplicatively in CHL mice. No recovery of sensory evoked A1 activation was evident in TNFα KO animals, which lack synaptic scaling. Additionally, we could show that the suppressive effect of sounds on visually evoked visual cortex activity completely recovered along with TNFα dependent A1 homeostasis in WT animals. This is the first demonstration of homeostatic multiplicative synaptic scaling in the adult A1. These findings suggest that mild hearing loss massively affects auditory processing in adult A1.