Microglial peri‐somatic abutments classify two novel types of GABAergic neuron in the inferior colliculus. (28th January 2021)

• Record Type: Journal Article
• Authors: Webb, Samuel David; Orton, Llwyd David
• Other Names: Majewska Ania guestEditor.; Verkhratsky Alexej guestEditor.; Hughes Ethan guestEditor.
• Is Part Of: European journal of neuroscience. Volume 54:Number 5(2021)
• Page Start: 5815
• Page End: 5833
• Publication Date: 2021-01-28
• Subjects: anatomy -- auditory -- colliculi -- confocal microscopy -- glia -- immunohistochemistry; Nervous system -- Periodicals; 612.8
• DOI: 10.1111/ejn.15075
• Languages: English
• ISSNs: 0953-816X

Abstract

Abstract: Emerging evidence suggests functional roles for microglia in the healthy, mature nervous system. However, we know little of the cellular density and ramified morphology of microglia in sensory systems, and even less of their inter‐relationship with inhibitory neurons. We therefore conducted fluorescent multi‐channel immunohistochemistry and confocal microscopy in guinea pigs of both sexes for Iba1, GAD67, GFAP, calbindin, and calretinin. We explored these markers in the inferior colliculi (IC), which contain sub‐regions specialized for different aspects of auditory processing. First, we found that while the density of Iba1+ somata is similar throughout the IC parenchyma, Iba1+ microglia in dorsal cortex are significantly more ramified than those in the central nucleus or lateral cortex. Conversely, Iba1+ ramifications in ventral central nucleus, a region with the highest density of GAD67+ (putative GABAergic) neurons in IC, are longer with fewer ramifications. Second, we observed extensive abutments of ramified Iba1+ processes onto GAD67+ somata throughout the whole IC and developed novel measures to quantify these. Cluster analyses revealed two novel sub‐types of GAD67+ neuron that differ in the quantity of Iba1+ somatic abutments they receive. Unlike previous classification schemes for GAD67+ neurons in IC, these clusters are not related to GAD67+ soma size. Taken together, these data demonstrate that microglial ramifications vary between IC sub‐regions in the healthy, adult IC, possibly related to the ongoing demands of their niche. Furthermore, Iba1+ abutments onto neuronal somata are a novel means by which GAD67+ neurons can be classified. Abstract : Ramified microglial process in the inferior colliculi vary in opposition to the number of GABAergic cells – i.e. more ramified in dorsal cortex and least ramified in central nucleus. Microglial peri‐somatic abutments onto GAD67 + somata classified two new sub‐types of GABAergic cells – those with extensive peri‐somatic contacts, and those without. Microglia have morphological specializations in auditory sub‐regions and interactions between microglia and GAD67 + somata are a novel way to classify neuronal sub‐types.