Lipopolysaccharide acutely inhibits proliferation of neural precursor cells in the dentate gyrus in adult rats

doi:10.1016/j.brainres.2010.07.032

Brain Research

Volume 1352, 17 September 2010, Pages 35-42

https://doi.org/10.1016/j.brainres.2010.07.032 Get rights and content

Abstract

Lipopolysaccharide (LPS), a bacterial endotoxin released during infection, is known to suppress neurogenesis in the dentate gyrus (DG) in mature rats. The present study aimed to elucidate acute effect of LPS, as well as possible mechanisms involved in the effect, on the neurogenesis in the DG of adult rats. In the first experiment, proliferating cells in the DG were labeled with bromodeoxyuridine (BrdU). Double-labeled immunohistochemistry performed 28 days after the BrdU incorporation revealed co-expression of NeuN, a marker of mature neurons, in most of the BrdU-positive cells in the DG. The rat was injected intraperitoneally with LPS or saline at various intervals after the BrdU incorporation, and BrdU-positive cells were examined 24 h thereafter. The endotoxin reduced the number of BrdU-positive cells that were labeled 24 h before, but not 7 or 28 days before sacrifice, suggesting rapid LPS actions on precursor cells during proliferation, but not after mitosis. In the second experiment, cells in the DG positively stained with BrdU or serine10 phosphorylated histone H3 (pHH3) were examined 5 h after the injection of LPS or saline. BrdU was incorporated 2 h before sacrifice. In these rats, LPS reduced the number of BrdU- or pHH3-positive cells. LPS did not affect the number of terminal deoxynucleotidyl transferase mediated dUTP nick end labeling (TUNEL)-positive cells within 5, 8 or 24 h. These results indicate that the endotoxin acutely suppresses neurogenesis in the DG in adult rats, presumably by inhibiting proliferation of neural precursor cells, but not by increasing cell death.

Research Highlights

►LPS injection reduced the number of proliferating cells in the SGZ within 5 h. ►LPS did not affect the number of post mitotic newborn neurons within 24 h. ►LPS did not increase cell death in the SGZ within 5, 8 or 24 h. ►LPS acutely inhibits neurogenesis in the DG presumably by inhibiting proliferation.

Introduction

The dentate gyrus (DG) in the hippocampus is one of the regions in which neurogenesis is maintained throughout life. Several studies have indicated that neurogenesis in this area contributes to the hippocampal function including the spatial learning (Jessberger et al., 2009, Zhang et al., 2008). It is known that neurogenesis in the DG changes under some physiological and pathophysiological conditions. For example, it is promoted by running or environmental enrichment, while suppressed by psychological stress (Dranovsky and Hen, 2006, van Praag et al., 1999, Kempermann et al., 1997).

Recent studies have reported that neurogenesis in the DG was suppressed within several days after the peripheral injection of lipopolysaccharide (LPS), the endotoxin released from Gram-negative bacteria, possibly by increasing cell death (Wu et al., 2007, Bastos et al., 2008, Monje et al., 2003). On the other hand, Koo and Duman have shown that restraint stress inhibits neurogenesis in the DG within a few hours, indicating that at least a certain kind of stress affects neurogenesis very rapidly (Koo and Duman, 2008). The same authors also suggested that the restraint-induced inhibition of neurogenesis occurs independently of apoptosis.

The present study was aimed to clarify whether LPS may acutely affect neurogenesis in the DG, and if so, whether the effect may be due to facilitation of cell death, suppression of proliferation, or both. In the first experiment, proliferating cells in the DG of adult rats were labeled in vivo with bromodeoxyuridine (BrdU), that is incorporated into newly synthesized DNA during cell division. Acute effects of LPS on BrdU-positive cells in the DG were immunohistochemically examined during proliferative and post mitotic periods by injecting the endotoxin at various intervals after the BrdU labeling. In the second experiment, acute effects of LPS on cell proliferation in the DG were studied by immunohistochemistry of BrdU labeled shortly before, as well as that of serine10 phosphorylated histone H3 (pHH3), an intrinsic marker of proliferating cells. The effect of LPS on cell death was also studied by means of terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) staining which visualizes nuclear DNA fragmentation that occurs during apoptosis and some types of necrotic cell death (Gavrieli et al., 1992, Nishiyama et al., 1996).

Section snippets

LPS decreased BrdU-labeled cells in the DG of rats 24 h but not 7 or 28 days after the BrdU incorporation

Confocal microscopic examination performed 28 days after the BrdU injection revealed that 109 of 115 (94.7%) BrdU-immunoreactive (ir) cells in the subgranular zone (SGZ) and granule cell layer (GCL) also expressed NeuN, a marker of mature neurons, indicating differentiation of the majority of proliferating cells in the DG into neurons (Fig. 1).

In order to assess the effect of acute LPS injection on proliferating cells in the DG, rats were administered with LPS (0.1 or 1 mg/kg) or saline

Discussion

BrdU is an analogue of thymidine, which is incorporated into newly synthesized DNA at the S-phase of cell division. The distribution of BrdU-ir cells in the DG 24 h, 7 days and 28 days after the BrdU injection in the present study was similar to that reported previously (Kuhn et al., 1996), confirming the proliferation of cells in this region.

Although neural stem cells isolated from the adult rat brain could generate both neurons and glial cells in vitro (Palmer et al., 1999), the majority of

Animals

Male Wistar–Imamichi rats (Imamichi Institute for Animal Reproduction, Ibaraki, Japan) were purchased at the age of 6 weeks. The rats were group-housed (3 rats/cage) and given one week to acclimate to vivarium conditions before the start of the experiment. They were kept under controlled illumination (light on 0630 h–1830 h) and temperature (22–24 °C), and given food and water ad libitum. All experiments were performed according to the Guiding Principles for the Care and Use of Experimental Animals

Acknowledgments

We thank Drs Miyako Furuta and Yuji Ogura for valuable discussion and technical advice, Ms. C. Kakehashi for technical assistance and Ms. Y. Ohnuma for secretarial help. This work was supported by Research Grant of St. Marianna University School of Medicine.

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Research ReportLipopolysaccharide acutely inhibits proliferation of neural precursor cells in the dentate gyrus in adult rats

Abstract

Research Highlights

Introduction

Section snippets

LPS decreased BrdU-labeled cells in the DG of rats 24 h but not 7 or 28 days after the BrdU incorporation

Discussion

Animals

Acknowledgments

Physiol. Behav.

Neurosci. Lett.

Neuroscience

Neuroscience

Biol. Psychiatry

Brain Res. Mol. Brain Res.

Neuroscience

Neurosci. Lett.

Neurosci. Lett.

J. Chem. Neuroanat.

Hepatology

Brain Res.

Citron kinase is required for postnatal neurogenesis in the hippocampus

Dev. Neurosci.

Leukemia inhibitory factor is a key signal for injury-induced neurogenesis in the adult mouse olfactory epithelium

J. Neurosci.

Transient expression of doublecortin during adult neurogenesis

J. Comp. Neurol.

Adult neurogenesis produces a large pool of new granule cells in the dentate gyrus

J. Comp. Neurol.

Identification of programmed cell death in situ via specific labeling of nuclear DNA fragmentation

J. Cell Biol.

Proliferation of granule cell precursors in the dentate gyrus of adult monkeys is diminished by stress

Proc. Natl Acad. Sci. USA

Research Report
Lipopolysaccharide acutely inhibits proliferation of neural precursor cells in the dentate gyrus in adult rats