Auditory function and dysfunction in Müller’s organ of Schistocerca gregaria

Auditory system function declines with age, which is exacerbated in humans due to noisy environments. Age-related and noise-induced auditory decline are also found in insects, which provide an ideal resource for studying fundamental and widely conserved mechanisms of hearing loss. In this thesis we use the locust’s auditory Müller’s organ to understand fundamental physiological and genetic bases of auditory function dysfunction. Müller’s organ is especially accessible for electrophysiological analysis, can be swiftly extracted to quantify changes in gene expression and the tympanum can be measured non-invasively. Using a range of approaches, we demonstrate age-related changes in the locusts auditory system function such as robustness (amount of deviation from the baseline) and resilience (the ability to recover). Robustness of the auditory nerve slightly decreases with age, but remains equally resilient throughout its life, as does resilience of the tympanum. We reveal a plastic mechanism that compensates for the age-related decline in the ability of the transduction current to recover from noise (resilience). Next, we test a long-standing hypothesis: a decrease in ear metabolism is causative for age-related auditory decline. Here, we demonstrate for the first time that auditory organ metabolism decreases with age, but we fail to establish a direct causative link. Throughout this thesis we also examine sex differences in the properties of the locust auditory organ, revealing a faster age-related decrease in tympanal displacement in females. The metabolic rate of the female auditory organ also remains higher than that of males throughout adulthood. Finally, we seek to examine the molecular properties of the insect auditory system at the level of the mechanotransduction channel.