Microglia and astrocytes show limited, acute alterations in morphology and protein expression following a single developmental alcohol exposure

Fetal alcohol spectrum disorders (FASD) are the most common cause of nonheritable, preventable mental disability and are characterized by cognitive, behavioral, and physical impairments. FASD occurs in almost 5% of births in the United States, but despite this prevalence there is no known cure, largely because the biological mechanisms that translate alcohol exposure to neuropathology are not well understood. While the effects of early ethanol exposure on neuronal survival and circuitry have received more attention, glia, the cells most closely tied to initiating and propagating inflammatory events, could be an important target for alcohol in the developing brain. Inflammation is known to alter developmental trajectories, but it has recently been shown that even small changes in both astrocytes and microglia in the absence of full-blown inflammatory signaling can alter brain function long-term. Here, we studied the acute response of astrocytes and microglia to a single exposure to ethanol in development across sexes in a mouse model of human third trimester exposure, in order to understand how these cells may transition from their normal developmental path to a different program that leads to FASD neuropathology. We found that although a single ethanol exposure delivered subcutaneously on postnatal day 4 did not cause large changes in microglial morphology or the expression of AldH1L1 and GFAP in the cortex and hippocampus, subtle effects were observed. These findings suggest that even a single, early ethanol exposure can induce mild acute alterations in glia that could contribute to developmental deficits.

Cortical interlaminar astrocytes across the therian mammal radiation

Interlaminar astrocytes (ILA) in the cerebral cortex possess a soma in layer I and extend an interlaminar process that runs perpendicular to the pia into deeper cortical layers. We examined cerebral cortex from 46 species that encompassed most orders of therian mammalians, including 22 primate species. We described two distinct cell types with interlaminar processes that have been referred to as ILA, that we termed pial ILA and supial ILA. ILA subtypes differ in somatic morphology, position in layer I, and presence across species. We further described rudimentary ILA that have short GFAP⁺ processes that do not exit layer I, and "typical" ILA with longer GFAP⁺ processes that exit layer I. Pial ILA were present in all mammalian species analyzed, with typical ILA observed in Primates, Scandentia, Chiroptera, Carnivora, Artiodactyla, Hyracoidea, and Proboscidea. Subpial ILA were absent in Marsupialia, and typical subpial ILA were only found in Primate. We focused on the properties of pial ILA by investigating the molecular properties of pial ILA and confirming their astrocytic nature. We found that while the density of pial ILA somata only varied slightly, the complexity of ILA processes varied greatly across species. Primates, specifically bonobo, chimpanzee, orangutan, and human, exhibited pial ILA with the highest complexity. We showed that interlaminar processes contact neurons, pia, and capillaries, suggesting a potential role for ILA in the blood-brain barrier and facilitating communication among cortical neurons, astrocytes, capillaries, meninges, and cerebrospinal fluid.

Characterization of the Filum terminale as a neural progenitor cell niche in both rats and humans

Neural stem cells (NSCs) reside in a unique microenvironment within the central nervous system (CNS) called the NSC niche. Although they are relatively rare, niches have been previously characterized in both the brain and spinal cord of adult animals. Recently, another potential NSC niche has been identified in the filum terminale (FT), which is a thin band of tissue at the caudal end of the spinal cord. While previous studies have demonstrated that NSCs can be isolated from the FT, the in vivo architecture of this tissue and its relation to other NSC niches in the CNS has not yet been established. In this article we report a histological analysis of the FT NSC niche in postnatal rats and humans. Immunohistochemical characterization reveals that the FT is mitotically active and its cells express similar markers to those in other CNS niches. In addition, the organization of the FT most closely resembles that of the adult spinal cord niche. J. Comp. Neurol. 525:661–675, 2017. © 2016 Wiley Periodicals, Inc.