Pain-related aversion induces astrocytic reaction and proinflammatory cytokine expression in the anterior cingulate cortex in rats

doi:10.1016/j.brainresbull.2010.12.007

Brain Research Bulletin

Volume 84, Issue 2, 1 February 2011, Pages 178-182

https://doi.org/10.1016/j.brainresbull.2010.12.007 Get rights and content

Abstract

Pain involves sensory and affective dimensions. It is well-known that activation of glial cells and a subsequent increase in proinflammatory cytokines contribute to the pathogenesis of pain sensation. However, the role of glial cells and proinflammatory cytokines in pain affect is unclear. Several lines of evidence indicate that the anterior cingulate cortex (ACC) is a key structure for pain affect. Using the formalin-induced conditioned place avoidance (F-CPA) model, which reflects the pain-related negative affective state induced by nociceptive stimuli, we examined the mRNA and protein expression levels of astrocytic markers and proinflammatory cytokines in the ACC. F-CPA produced robust aversion-like behaviors in rats. In parallel, a significant increase of mRNA of astrocytic markers (GFAP and S100B), and proinflammatory cytokines (IL-1β and TNF-α) were observed in the ACC. The protein level of GFAP, IL-1β and TNF-α were also enhanced in the ACC. The results showed for the first time that astrocytes and proinflammatory cytokines are associated with the processing of pain-related aversion and may be crucial players in the affective dimension of pain in rats.

Introduction

Pain is a complex experience, which consists of not only a sensory discriminative dimension (encoding the nature of stimulus, i.e. location, quality and intensity), but also an affective/motivational dimension (unpleasantness or aversion) [20]. The affective dimension of pain is a negative affect that is closely related to painful stimulation or expectation [20]. Although pain-related negative affect has gained more attention in recent years, the mechanism underlying pain affect is still largely unclear.

Several lines of evidence suggest that the anterior cingulate cortex (ACC) is a key structure for pain affect [5], [10], [12], [13], [15]. Animal behavioral studies have demonstrated that the ACC mediated the affect-like responses to tonic pain in formalin-induced conditioned place avoidance (F-CPA) in rats [5], [10], [14]. Microinjection of a glutamate receptor antagonist into the ACC during contextual conditioning blocked formalin-induced place avoidance [9]. Furthermore, intracerebroventricular administration of the N-methyl-d-aspartate (NMDA) receptor antagonist 2-amino-5-phosphovalerate (APV) significantly decreased the place avoidance induced by formalin [15]. It has been recently demonstrated that the NMDA receptor/adenylyl cyclase (AC)-phosphokinase A (PKA)/extracellular signal-regulated kinase (ERK)/cAMP response element binding protein (CREB), signaling pathway in the neurons of the ACC, is required for the induction and expression of pain affect [2]. These data, considered together, suggest that the activation of NMDA receptors in the ACC is important in relation to affective pain.

In recent years, several studies have supported an essential role for spinal glial cells (astrocytes and microglia) in the development and maintenance of pain sensation [7], [23], [27]. Peripheral injury or tissue damage activates astrocytes in the spinal cord with associated increases of the glial fibrillary acidic protein (GFAP), the calcium binding protein S100B, and several proinflammatory cytokines (e.g. IL-1β, TNF-α and IL-6) [7], [21], [31]. The inhibition of astrocyte activation or proinflammatory cytokines have been shown to attenuate nerve injury- or nerve inflammation-induced pain behaviors [6], [18], [32]; however, whether the astrocytes and proinflammatory cytokines are involved in pain affect is completely unknown. In the present study, by using an F-CPA-induced pain-related aversion model, we examined the expression of astrocytic markers GFAP and S100B, as well as proinflammatory cytokines TNF-α and IL-1β in the ACC of rats.

Section snippets

Animals

Experiments were performed on adult male Sprague–Dawley rats weighing 200–220 g. The animals were obtained from the Experimental Animal Center of Nantong University and were maintained on a 12:12 light–dark cycles at a room temperature of 22 ± 1 °C, and received food and water ad libitum. Before experimental manipulations, the animals were habituated to the environment and experimental test. Blinded experiments were performed according to the guidelines of the International Association for the

Behavioral tests

The F-CPA training is a combination of a formalin-induced pain model with the place-conditioning paradigm. Since it was first developed by Johansen et al. [10], it has been widely used in the investigation of the mechanisms of pain-related affect in rats. Here, we use F-CPA to induce the affective pain. The results showed that when formalin injection was paired with a particular compartment in the place-conditioning apparatus, rats spent less time in this compartment on the post-conditioning

Discussion

In this study, we showed for the first time a potential contribution of astrocytes and proinflammatory cytokines in affective pain. Indeed using F-CPA, the affective pain model, we observed that formalin-injected animals undergoing the pain-related aversion test showed increases of S100B mRNA, GFAP mRNA and protein, as well as TNF-α and IL-1β mRNA and protein in the ACC. Interestingly, formalin injection alone (2 d, without CFA training) did not induce GFAP, S100B, TNF-α, or IL-1β upregulation.

Acknowledgements

The authors wish to thank Dr. Temugin Berta for his helpful criticism and linguistic revision of the manuscript. This study was supported by the National Natural Science Foundation of China (NSFC) 30500153, the College and University Natural Science Research Program of Jiangsu Province 05KJB180100 and the Program for New Century Excellent Talents NCET-09-0164.

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Research reportPain-related aversion induces astrocytic reaction and proinflammatory cytokine expression in the anterior cingulate cortex in rats

Abstract

Introduction

Section snippets

Animals

Behavioral tests

Discussion

Acknowledgements

Neurosci. Biobehav. Rev.

Pain

Neurosci. Lett.

Brain Res.

Neuroscience

Exp. Neurol.

Exp. Neurol.

Pain

J. Biol. Chem.

Biochim. Biophys. Acta

Brain Res.

Control of synaptic strength by glial TNFalpha

Science (New York, NY)

Activation of extracellular signal-regulated kinase in the anterior cingulate cortex contributes to the induction and expression of affective pain

J. Neurosci.

Characterization of C6-10A glioma cells highly responsive to beta-adrenergic receptor agonist-induced NGF synthesis/secretion

Glia

Effect of astrocytic energy metabolism depressant on 14C-acetate uptake in intact rat brain

J. Cereb. Blood Flow Metab.

Possible role of spinal astrocytes in maintaining chronic pain sensitization: review of current evidence with focus on bFGF/JNK pathway

Neuron Glia Biol.

Research report
Pain-related aversion induces astrocytic reaction and proinflammatory cytokine expression in the anterior cingulate cortex in rats

Effect of astrocytic energy metabolism depressant on ¹⁴C-acetate uptake in intact rat brain