Exposure of neonatal rats to alcohol has differential effects on neuroinflammation and neuronal survival in the cerebellum and hippocampus

Abstract

BackgroundFetal alcohol exposure is a leading cause of preventable birth defects, yet drinking during pregnancy remains prevalent worldwide. Studies suggest that activation of the neuroimmune system plays a role in the effects of alcohol exposure during the rodent equivalent to the third trimester of human pregnancy (i.e., first week of neonatal life), particularly by contributing to neuronal loss. Here, we performed a comprehensive study investigating differences in the neuroimmune response in the cerebellum and hippocampus, which are important targets of third trimester-equivalent alcohol exposure.MethodsTo model heavy, binge-like alcohol exposure during this period, we exposed rats to alcohol vapor inhalation during postnatal days (P)3–5 (blood alcohol concentration = 0.5 g/dL). The cerebellar vermis and hippocampus of rat pups were analyzed for signs of glial cell activation and neuronal loss by immunohistochemistry at different developmental stages. Cytokine production was measured by reverse transcriptase polymerase chain reaction during peak blood alcohol concentration and withdrawal periods. Additionally, adolescent offspring were assessed for alterations in gait and spatial memory.ResultsWe found that this paradigm causes Purkinje cell degeneration in the cerebellar vermis at P6 and P45; however, no signs of neuronal loss were found in the hippocampus. Significant increases in pro-inflammatory cytokines were observed in both brain regions during alcohol withdrawal periods. Although astrocyte activation occurred in both the hippocampus and cerebellar vermis, microglial activation was observed primarily in the latter.ConclusionsThese findings suggest that heavy, binge-like third trimester-equivalent alcohol exposure has time- and brain region-dependent effects on cytokine levels, morphological activation of microglia and astrocytes, and neuronal survival.Electronic supplementary materialThe online version of this article (doi:10.1186/s12974-015-0382-9) contains supplementary material, which is available to authorized users.

Sex Differences in Early Postnatal Microglial Colonization of the Developing Rat Hippocampus Following a Single-Day Alcohol Exposure

“…Interestingly, TGF-β was not affected by AE at either time point, in contrast to our previous report of increased levels following PD4–9 AE. Recent work by Topper et al (2015) also reported no changes in TGF-β expression in the male rat hippocampus following a PD3–5 alcohol exposure. It is possible that a more prolonged exposure to alcohol is needed to elicit a TGF-β response.…”

“…In the healthy developing brain, microglia are involved in many necessary, normal development processes including the culling of apoptotic cells, synaptic pruning, and masculinization of the brain and behavior (Dalmau et al 1998; Bessis et al 2007; Paolicelli et al 2011; Lenz et al 2013). Following identification of a pathogen, microglia respond by changing their phenotypic activation state to increase production of pro-inflammatory cytokines (Kreutzberg 1996; Hanisch 2002; Town et al 2005; Neumann et al 2008; Kane et al 2011; McClain et al 2011; Topper et al 2015; Boschen et al 2016). …”

“…Subregion-specific microglial counts and expression of five genes that code for pro-inflammatory (interleukin-1β [IL-1β], C-C motif chemokine ligand 4 [CCL4], tumor necrosis factor-α [TNF-α], and cluster of differentiation molecule 11B [CD11b]) or anti-inflammatory (TGF-β) markers (cytokines, chemokines, or cell surface receptors) were measured to assess both the number of microglial cells throughout development and level of activation of microglia in the hippocampus either 24 or 96 h post-alcohol exposure. The above classical markers of inflammatory response were chosen for this study as they have all been shown to be affected by immune insults in similar lines of research (McClain et al 2011; Marshall et al 2013; Topper et al 2015; Boschen et al 2016). Developmental and neuroimmune sex differences were analyzed both at baseline (in controls without alcohol exposure) and in response to alcohol.…”

Salt-Inducible Kinase 1 (SIK1) is Induced by Alcohol and Suppresses Microglia Inflammation via NF-κB Signaling

“…Changes in microglia activity and increases in pro-inflammatory cytokines are thought to both result from and contribute to alcohol pathologies [3,4]. The effects of alcohol exposure on the immune system are complex, and adding to this complexity is the fact that microglia can function in different contexts as either neuroprotective or cytotoxic agents [5].…”

“…Alcohol induces a number of changes in the immune system, generally resulting in a proinflammatory state in the CNS [4,[15][16][17][18]. For example, alcohol has been shown to stimulate toll-like receptor 4 (TLR4) and toll-like receptor 2 (TLR2) expression in microglia, thereby increasing pro-inflammatory mediators, reactive oxygen species, and neuronal apoptosis [8,9,19].…”