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bioRxiv · 10.1101/606509

Iba1+ Microglia Colocalize with Synaptophysin+ and Homer1+ Puncta and Reveal Two Novel Sub-types of GABAergic Neuron in Guinea Pig Inferior Colliculus

Webb, S. D.·Orton, L. D.
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Abstract

Microglia have classically been viewed as the endogenous phagocytes of the brain, however, emerging evidence suggests roles for microglia in the healthy, mature nervous system. We know little of the contribution microglia make to ongoing processing in sensory systems. To explore Iba1+ microglial diversity, we employed the inferior colliculi (IC) as model nuclei, as they are characterized by sub-regions specialized for differing aspects of auditory processing. We conducted fluorescent multi-channel immunohistochemistry and confocal microscopy in guinea pigs of both sexes and discovered that the density and morphology of Iba1+ labelling varied between parenchymal sub-regions of IC, while GFAP+ labelling of astrocytes was confined to the glia limitans externa and peri-vascular regions. The density of Iba1+ microglia somata was similar across sub-regions, however a greater amount of labelling was found in dorsal cortex than ventral central nucleus or lateral cortex. To further understand these differences between sub-regions in IC, Sholl and skeleton analyses of individual microglia revealed a greater number of branching ramifications in dorsal cortex. We also quantified abutments of Iba1+ microglial processes onto GAD67+ (putative GABAergic) somata. Cluster analyses revealed two novel sub-types of GAD67+ neuron, which can be distinguished solely based on the quantity of axo-somatic Iba1+ abutments they receive. These data demonstrate Iba1+ microglia exhibit different morphologies and interactions with GAD67+ neurons in distinct sub-regions of the mature, healthy IC. Taken together, these findings suggest significant heterogeneity amongst microglia in the auditory system, possibly related to the ongoing functional demands of their niche.

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Webb, S. D., Orton, L. D.. 2019-04-12. Iba1+ Microglia Colocalize with Synaptophysin+ and Homer1+ Puncta and Reveal Two Novel Sub-types of GABAergic Neuron in Guinea Pig Inferior Colliculus. https://doi.org/10.1101/606509

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