Modular-extramodular organization in developing multisensory shell regions of the mouse inferior colliculus

Area of Science:

• Neuroscience
• Neuroanatomy
• Auditory System Development

Background:

• The inferior colliculus (IC) integrates auditory information, with its lateral cortex (LCIC) exhibiting complex, less-understood functional organization.
• LCIC's proposed multimodal mosaic structure includes patchy modular networks and surrounding extramodular domains, distinct from the central nucleus's tonotopic organization.

Purpose of the Study:

• To investigate the emerging microarchitecture of the lateral cortex of the inferior colliculus (LCIC) using neurochemical markers.
• To characterize the developmental timeline and spatial distribution of modular and extramodular compartments within the LCIC.

Main Methods:

• Histochemical and immunocytochemical staining for markers including acetylcholinesterase (AChE), NADPH-diaphorase (NADPH-d), glutamic acid decarboxylase (GAD), cytochrome oxidase (CO), and calretinin (CR) in developing mice.
• Analysis of marker expression in serial sections and double-labeling experiments to identify distinct cellular compartments.

Main Results:

• Discontinuous layer 2 modules within the LCIC showed positive staining for AChE, NADPH-d, GAD, and CO, forming a patchy network.
• These modular features emerged during the first postnatal week, becoming more distinct with age, while extramodular fields remained largely negative.
• Calretinin (CR) staining was complementary, highlighting extramodular zones, and NADPH-d and CR labeled non-overlapping compartments.

Conclusions:

• The LCIC develops a distinct modular-extramodular microarchitecture characterized by specific neurochemical profiles.
• This emerging organization, evident before hearing onset, suggests a complex functional compartmentalization within the developing auditory midbrain.