Responses from two firing patterns in inferior colliculus neurons to stimulation of the lateral lemniscus dorsal nucleus

Research progress of the inferior colliculus: from Neuron, neural circuit to auditory disease

The auditory midbrain, also known as the inferior colliculus (IC), serves as a crucial hub in the auditory pathway. Comprising diverse cell types, the IC plays a pivotal role in various auditory functions, including sound localization, auditory plasticity, sound detection, and sound-induced behaviors. Notably, the IC is implicated in several auditory central disorders, such as tinnitus, age-related hearing loss, autism and Fragile X syndrome. Accurate classification of IC neurons is vital for comprehending both normal and dysfunctional aspects of IC function. Various parameters, including dendritic morphology, neurotransmitter synthesis, potassium currents, biomarkers, and axonal targets, have been employed to identify distinct neuron types within the IC. However, the challenge persists in effectively classifying IC neurons into functional categories due to the limited clustering capabilities of most parameters. Recent studies utilizing advanced neuroscience technologies have begun to shed light on biomarker-based approaches in the IC, providing insights into specific cellular properties and offering a potential avenue for understanding IC functions. This review focuses on recent advancements in IC research, spanning from neurons and neural circuits to aspects related to auditory diseases.

Focal electrical stimulation of dorsal nucleus of the lateral lemniscus modulates auditory response properties of inferior collicular neurons in the albino mouse

The inferior colliculus (IC) receives and integrates excitatory and inhibitory inputs from many bilateral lower auditory nuclei, intrinsic projections within IC, contralateral IC through the commissure of IC and from the auditory cortex (AC). These excitatory and inhibitory inputs from both ascending and descending auditory pathways contribute significantly to auditory response properties and temporal signal processing in IC. The present study examines the contribution of gamma-aminobutyric acid-ergic (GABAergic) inhibition of dorsal nucleus of the lateral lemniscus (DNLL) in influencing the response properties and amplitude sensitivity of contralateral IC neurons using focal electrical stimulation of contralateral DNLL and by the application of bicuculline to the recording site of modulated IC neurons. Focal electrical stimulation of contralateral DNLL produces inhibition (78.1%), facilitation (7.1%) or no effect (14.8%) in the number of spikes, firing duration and the first-spike latency of modulated IC neurons. The degree of modulation is inversely correlated to the difference in best frequency (BF) between electrically stimulated DNLL neurons and modulated IC neurons (p < 0.01). The application of bicuculline to the recording site of modulated IC neurons abolishes the inhibitory effect of focal electrical stimulation of DNLL neurons. DNLL inhibition also modulates the amplitude sensitivity of IC neurons by changing the dynamic range (DR) and the slope of rate-amplitude function (RAF) of modulated IC neurons. Possible biological significance of these findings in relation to auditory signal processing is discussed.