Elsevier

Brain Research

Volume 802, Issues 1–2, 17 September 1998, Pages 189-197
Brain Research

Research report
Cyclooxygenase 2 mRNA expression in rat brain after peripheral injection of lipopolysaccharide

https://doi.org/10.1016/S0006-8993(98)00402-8Get rights and content

Abstract

Inducible cyclooxygenase 2 (COX 2) converts arachidonic acid to prostaglandins, which are thought to mediate various peripheral lipopolysaccharide (LPS)-induced central effects, including generation of fever and activation of the hypothalamic–pituitary–adrenal axis. To localize prostaglandin production in the brain following peripheral LPS administration, COX 2 mRNA expression was examined by in situ hybridization histochemistry in rats injected intraperitoneally (i.p.) or intravenously (i.v.) with various doses of LPS or saline. Constitutive expression of COX 2 mRNA was found in neurons of cortex, hippocampus, and amygdala, but not in cells of the blood vessels. COX 2 mRNA levels were not altered in saline-injected animals as compared to non-injected controls. In LPS-injected animals, no consistent changes of neuronal COX 2 mRNA expression were observed. COX 2 mRNA expression appeared ex novo at 0.5-h post-injection in cells closely associated with blood vessels, however, ex novo labeling of the number of labeled cells increased to a peak at 2 h and subsided gradually to basal levels by 24 h. Initially, labeling was observed in cells comprising major surface-lying blood vessels and meninges. Later, vascular and perivascular cells associated with smaller penetrating blood vessels were labeled. This pattern of COX 2 mRNA induction is independent of the route and dose of the LPS injection. The induced COX 2 mRNA producing cells are identified as endothelial and leptomeningeal cells. Changes in COX 2 mRNA expression were not observed in circumventricular organs. These results suggest that peripheral LPS induces a rapid increase in COX 2 production throughout the vasculatures of the brain, which could affect the neuronal activity of widespread brain regions by elevating the levels of prostaglandins.

Introduction

Prostaglandin E2 (PGE2) levels of brain interstitial fluid rise following peripheral injection of LPS [20]. Pharmacological blockade of PGE2 synthesis attenuates many peripheral LPS-induced responses, such as fever [20], brain c-fos expression, hypothalamic–pituitary axis activation [16], increased splenic sympathetic activity [14], activation of serotonergic and noradrenergic neurotransmission in hippocampus [13], and increased blood–brain barrier (BBB) permeability [7]. Increased production of PGE2 in brain, therefore, is critically involved in these central nervous system (CNS)-linked responses to peripheral LPS.

There are three enzymes that are essential for the production of PGE2: phospholipase A2 (PLA2), cyclooxygenase, and PGE2 isomerase. COX is a rate-limiting enzyme in PGE2 synthesis, which catalyzes the conversion of arachidonic acid to prostaglandin H2[11]. Two isoforms of COX exist. COX 1 is a constitutively expressed form, and its levels are relatively insensitive to inflammatory stimulation. COX 2, on the other hand, has low constitutive levels of expression, and it is strongly induced by inflammatory factors such as LPS [8]. The induced expression of COX 2 in the brain is thought to play an important role in the elevation of central PGE2 levels in response to peripheral LPS 4, 5.

Only two studies have investigated the induction of COX 2 mRNA in the brain after peripheral LPS injection. The results of these studies show that COX 2 mRNA expression is induced in cells of the blood–brain barrier (BBB) after peripheral LPS injection 3, 5. Cellular responses in the CNS to peripherally injected LPS, however, depend upon the dose and the route of LPS administration as well as the time after the LPS injection 22, 24. A detailed analysis of COX 2 mRNA expression in response to peripheral LPS injection has not been performed. Furthermore, the phenotypes of the cells producing COX 2 mRNA have not been identified. In this study, we examined the induction of COX 2 mRNA at multiple time points after administration of a wide range of doses of LPS in the rat by either intravenous (i.v.) or intraperitoneal (i.p.) injection. We also identified the phenotypes of COX 2 mRNA expressing cells by combined immunohistochemistry and in situ hybridization histochemistry.

Section snippets

Animals and LPS injection

Male Sprague–Dawley rats (175–200 g; Taconic Farms, Germantown, NY) were group housed and handled daily prior to experimentation. Initially, they were injected i.p. with 2.5 mg/kg of LPS dissolved in 0.9% saline or 0.9% sterile saline alone. Animals were then killed by decapitation at 0.5, 1, 2, 4, 8, 12 or 24 h after the injection (n=3–5 per time point). To control for the effects due to saline injection alone, control animals which received no injection were also sacrificed (n=3). Injections

Results

Representative film autoradiographs of COX 2 mRNA hybridization in coronally cut sections at the level of pituitary are shown in Fig. 1. Constitutively expressed COX 2 mRNA was labeled in cortical regions, hippocampus, and dentate gyrus (Fig. 1A), and the labeling appeared to be neuronal. The same pattern and intensity of COX 2 mRNA hybridization were found in all the saline-injected and non-injected animals (data not shown).

After LPS injection (2.5 mg/kg, i.p.), induction of COX 2 mRNA was

Discussion

The present study confirms the previous results showing that COX 2 mRNA is induced by peripheral LPS primarily in the vascular and leptomeningeal cells of the brain 4, 5whereas no consistent changes in neuronal expression of COX 2 mRNA were detected. Unique to the present study, we made the following observations: (1) The COX 2 mRNA induction always occurs in the close vicinity of blood vessels regardless of the dose and route of the peripheral LPS administration. (2) The COX 2 mRNA induction

Conclusion

Peripheral LPS injections induces rapid COX 2 mRNA expression in endothelial cells of the blood vessels of the brain, which may elevate prostaglandin levels globally to modulate the function of CNS.

References (27)

  • D.N. Angelov et al.

    ED2-positive perivascular cells act as neuronophages during delayed neuronal loss in the facial nucleus of the rat

    Glia

    (1996)
  • M. Anthonisen et al.

    Histamine and prostaglandin interaction in the central regulation of ACTH secretion

    Neuroendocrinology

    (1997)
  • C.D. Breder et al.

    Characterization of inducible cyclooxygenase in rat brain

    J. Comp. Neurol.

    (1995)
  • Cited by (147)

    • Contributions of cytokines to febrile seizures

      2022, Febrile Seizures: New Concepts and Consequences
    • Neuroinflammation and oxidative injury in developmental neurotoxicity

      2022, Reproductive and Developmental Toxicology
    • Involvement and relationship of bacterial lipopolysaccharides and cyclooxygenases levels in Alzheimer's Disease and Mild Cognitive Impairment patients

      2021, Journal of Neuroimmunology
      Citation Excerpt :

      LPSs can in vitro trigger the induction of COX-2 in macrophages, astroglia and microglia (Eliopoulos, 2002; Font-Nieves et al., 2012; Wang et al., 2005). COX-2 upregulation in vasculature cells of the BBB is also documented after peripheral shots of LPSs (Cao et al., 1995; Quan et al., 1998), and in the brain microglia and astroglia after cerebroventricular shot (Font-Nieves et al., 2012). As an additional note, multilinear regression analysis run for COX-1/2 proved that COX-2 levels in serum are mainly attributed to LPSs, while COX-2 levels in CSF are strongly linked with COX-1 levels.

    • Cyclooxygenase-2 inhibition reduces anxiety-like behavior and normalizes enhanced amygdala glutamatergic transmission following chronic oral corticosterone treatment

      2019, Neurobiology of Stress
      Citation Excerpt :

      Importantly, LMX completely normalized this increase without affecting glutamatergic transmission in naïve mice, paralleling our behavioral findings. COX-2 is expressed at low levels in the BLA where it localizes to dendritic spines (Breder et al., 1995; Sang et al., 2005; Kaufmann et al., 1996), but, as noted above, is rapidly up-regulated by CORT, stress, and high-frequency stimulation associated with the induction of long-term potentiation (Madrigal et al., 2003a; Cao et al., 1995; Chen et al., 2017; Quan et al., 1998; Bliss and Collingridge, 1993). Furthermore, increased COX-2 expression and activity has previously been shown to enhance glutamatergic transmission via prostaglandin receptor activation, and potentially via generation of PG-Gs (Sang et al., 2005; Yang et al., 2008).

    View all citing articles on Scopus
    View full text