CCG-4986 KCNQ4 activator Medicine TrkB adenosine A1 receptor adjunctive therapy age-related hearing loss aging astrocytes auditory brainstem brain-derived neurotrophic factor chronic oral treatment circadian dysregulation clock genes cochlear nucleus cochlear rescue d-galactose deafness development gap junctions hearing loss hearing protection high-fat diet hyperbaric oxygenation hypoxic inferior colliculus inner ear intratympanic drug delivery lateral superior olive microRNAs