Glial Cell Expansion Coincides with Neural Circuit Formation in the Developing Auditory Brainstem

Abstract

Neural circuit formation involves maturation of neuronal, glial and vascular cells, as well as cell proliferation and cell death. A fundamental understanding of cellular mechanisms is enhanced by quantification of cell types during key events in synapse formation and pruning and possessing qualified genetic tools for cell type-specific manipulation. Acquiring this information in turn requires validated cell markers and genetic tools. We quantified changing proportions of neurons, astrocytes, oligodendrocytes, and microglia in the medial nucleus of the trapezoid body (MNTB) during neural circuit development. Cell type-specific markers, light microscopy and 3D virtual reality software, the latter developed in our laboratory, were used to count cells within distinct cell populations at postnatal days (P)3 and P6, bracketing the period of nerve terminal growth and pruning in this system. These data revealed a change from roughly equal numbers of neurons and glia at P3 to a 1.5:1 ratio of glia to neurons at P6. PCNA and PH3 labeling revealed that proliferation of oligodendrocytes contributed to the increase in glial cell number during this timeframe. We next evaluated Cre driver lines for selectivity in labeling cell populations. En1-Cre was specific for MNTB neurons. PDGFRα-Cre and Aldh1L1-Cre, thought to be mostly specific for oligodendrocyte lineage cells and astrocytes, respectively, both labeled significant numbers of neurons, oligodendrocytes, and astrocytes and are non-specific genetic tools in this neural system.

Distinct Cellular Profiles of Hif1a and Vegf mRNA Localization in Microglia, Astrocytes and Neurons during a Period of Vascular Maturation in the Auditory Brainstem of Neonate Rats

“…In our previous work, we found evidence that proliferation of MNTB astrocytes occurred during the perinatal period that precedes hearing onset [11]. Other groups have reported proliferation of oligodendrocytes in the mouse MNTB [14]. Future studies could evaluate the localization of proliferating astrocytes and oligodendrocytes with respect to the vasculature.…”

“…The MNTB consists of a population of principal neurons that are innervated by the calyces of Held, specialized glutamatergic synaptic terminals that originate from cochlear nucleus globular bushy neurons (Figure 1A) [8]. Recent studies showed significant changes in the development of MNTB astrocytes, oligodendrocytes and microglia during the postnatal period that precedes hearing onset, which in rats occurs around postnatal day 12 (P12) [10][11][12][13][14][15]. However, to the best of our knowledge, the development of the MNTB vasculature has not been characterized in any species.…”

Microglia Regulate Pruning of Specialized Synapses in the Auditory Brainstem

“…Studies indicate that the intermediate filament GFAP is a marker for mature astrocytes (Eng et al, 1971; Pixley and de Vellis, 1984; Wofchuk and Rodnight, 1995) as well as for reactive astrocytes, as GFAP immunostaining peaks 1 week after bilateral cochlear ablation in the CN of rats (Fuentes-Santamaria et al, 2013, 2017). In the auditory brainstem, glial cell expansion coincides with neural circuit development (Brandebura et al, 2018) and astrocytic markers appear at distinct times during postnatal development. In the MNTB, ALDH1L1-positive cells are present at P0, while S100β expression is sparse and GFAP expression is completely absent.…”

Two types of somatic spines provide sites for intercellular signaling during calyx of Held growth and maturation

“…Type 2 spines, in contrast to type 1 spines, contain organelle structures and can be tortuous and very thin at many locations along their length, so the substrates may exist for multiple modes of communication from electrically and chemically isolated compartments. These signaling modes may mediate synaptic plasticity and local processing within the spine mat that communicates among the intertwined neuronal and glial processes as glial and neuronal elements transform structurally into a mature circuit (Brandebura et al, 2018;Dinh et al, 2014;Holcomb et al, 2013;Rodríguez-Contreras et al, 2008;Saliu et al, 2014).…”