Silence, solitude, and serotonin: how hearing loss and social isolation converge to influence serotonergic regulation of the auditory midbrain
Royal National Institute for Deaf People
Indiana University
The social isolation that often accompanies hearing impairment in older adults co-occurs with other health concerns, including depression, anxiety, and cognitive decline. A contributing factor to these negative outcomes may be dysfunctional communication driven by deficits in auditory processing and perception. We will assess whether noise-induced hearing loss and social isolation additively influence regulation of the auditory system by serotonin.   To test this hypothesis, we will noise-expose CBA/CaJ mice in young adulthood, resulting in exaggerated age-related increases in auditory thresholds. Noise exposure or sham treatment will be factorially combined with a one-month period of individual or social housing in postbreeding mice, to create four treatment groups. Three different outcome measures will be assessed: 1)_x0001_The density of axons labelled with an antibody to the serotonin transporter will assess plasticity in serotonergic projections to the inferior colliculus (IC). 2)_x0001_The numbers of neurons in the dorsal raphe nucleus (DRN) that double-label for antibodies to tryptophan hydroxylase and the immediate early gene product cFos will assess the functional activation of serotonergic neurons during a social encounter. Analysis will focus on DRN subregions that project to the IC. 3)_x0001_Anxiety-like behaviors in the elevated plus, open field, and social encounter tests will be used to assess the engagement of broad mechanisms regulating affective behavior.   The predicted additive effects of hearing loss and isolation on serotonergic axons in the IC, and isolation-only effects on the activity of DRN neurons, could create dysfunctional regulation of auditory processing during social encounters.
2.1 Biological and endogenous factors