![]() This involved imaging LOC neurons stained with a marker for dopamine and measuring the activity of nerve fibers in the inner ear. studied the hearing system of mice that had been exposed to different levels of sound. But it is unclear what role dopamine plays in this auditory feedback loop. LOC neurons use a diverse range of molecules to modify the activity of auditory nerve fibers, including the ‘feel-good’ neurotransmitter dopamine. When these neurons receive information on external sounds, they signal back to the hearing organs and adjust the activity of auditory nerve fibers that communicate this information to the brain. This is thought to reduce the damage loud sounds can cause to the sensory organ inside the ear.Ī set of nerve cells located at the base of the brain called the lateral olivocochlear (LOC) neurons coordinate this adjustment to different volumes and sounds. For example, if a noise is too loud, the volume can be turned down by dampening the signals nerve fibers in the ear send to the brain. Our hearing system responds to these acoustic changes by fine-tuning sounds before they enter the brain. eLife digestĮvery day, we hear sounds that might be alarming, distracting, intriguing or calming – or simply just too loud. Collectively, our results suggest that LOC intrinsic neurons can undergo on-demand neurotransmitter re-specification to re-calibrate ANF activity, adjust the gain at hair cell/ANF synapses, and possibly to protect these synapses from noise damage. We further demonstrate that dopamine down-regulates ANF firing rates by reducing both the hair cell release rate and the size of synaptic events. Sound exposure upregulates tyrosine hydroxylase, an enzyme responsible for dopamine synthesis, in cholinergic LOC intrinsic neurons, suggesting that individual LOC neurons might at times co-release ACh and DA. Here we present quantitative evidence in rodents that the dopaminergic LOC input to ANFs is dynamically regulated according to the animal’s recent acoustic experience. Little is known about how individual neurotransmitter systems are differentially utilized in response to the ever-changing acoustic environment. Lateral olivocochlear (LOC) efferent neurons modulate auditory nerve fiber (ANF) activity using a large repertoire of neurotransmitters, including dopamine (DA) and acetylcholine (ACh). ![]()
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