Cholinergic boutons are closely associated with excitatory cells and four subtypes of inhibitory cells in the inferior colliculus

Jun 29, 2021Journal of chemical neuroanatomy

Cholinergic nerve endings are closely linked to excitatory cells and four types of inhibitory cells in the sound processing area

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Abstract

Most inferior colliculus (IC) cells exhibit close associations with cholinergic boutons.

Acetylcholine (ACh) is implicated in modulating neuronal excitability and plasticity in the central auditory system.
Four subtypes of GABAergic neurons in the IC were identified, differing in size and distribution.
Cholinergic boutons are closely associated with the somas and proximal dendrites of both excitatory and inhibitory cells.
Similar proportions of each GABAergic subtype are associated with cholinergic boutons.
The differential regulation of GABAergic cells by ACh remains unclear, depending on the types of ACh receptors present.

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Acetylcholine (ACh) is a neuromodulator that has been implicated in multiple roles across the brain, including the central auditory system, where it sets neuronal excitability and gain and affects plasticity. In the cerebral cortex, subtypes of GABAergic interneurons are modulated by ACh in a subtype-specific manner. Subtypes of GABAergic neurons have also begun to be described in the inferior colliculus (IC), a midbrain hub of the auditory system. Here, we used male and female mice (Mus musculus) that express fluorescent protein in cholinergic cells, axons, and boutons to look at the association between ACh and four subtypes of GABAergic IC cells that differ in their associations with extracellular markers, their soma sizes, and their distribution within the IC. We found that most IC cells, including excitatory and inhibitory cells, have cholinergic boutons closely associated with their somas and proximal dendrites. We also found that similar proportions of each of four subtypes of GABAergic cells are closely associated with cholinergic boutons. Whether the different types of GABAergic cells in the IC are differentially regulated remains unclear, as the response of cells to ACh is dependent on which types of ACh receptors are present. Additionally, this study confirms the presence of these four subtypes of GABAergic cells in the mouse IC, as they had previously been identified only in guinea pigs. These results suggest that cholinergic projections to the IC modulate auditory processing via direct effects on a multitude of inhibitory circuits.

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Cholinergic boutons are closely associated with excitatory cells and four subtypes of inhibitory cells in the inferior colliculus

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