Crosstalk Between ATP-P2X7 and Adenosine A2A Receptors Controlling Neuroinflammation in Rats Subject to Repeated Restraint Stress

Abstract

Depressive conditions precipitated by repeated stress are a major socio-economical burden in Western countries. Previous studies showed that ATP-P-2X7 receptors (P2X7R) and adenosine A(2A) receptors (A(2A)R) antagonists attenuate behavioral modifications upon exposure to repeated stress. Since it is unknown if these two purinergic modulation systems work independently, we now investigated a putative interplay between P2X7R and A(2A)R. Adult rats exposed to restraint stress for 14 days displayed an anxious (thigmotaxis, elevated plus maze), depressive (anhedonia, increased immobility), and amnesic (modified Y maze, object displacement) profile, together with increased expression of Iba-1 (a marker of microglia "activation") and interleukin-1 beta (IL1 beta) and tumor necrosis factor alpha (TNF alpha; proinflammatory cytokines) and an up-regulation of P2X7R (mRNA) and A(2A)R (receptor binding) in the hippocampus and prefrontal cortex. All these features were attenuated by the P2X7R-preferring antagonist brilliant blue G (BBG, 45 mg/kg, i.p.) or by caffeine (0.3 g/L, p.o.), which affords neuroprotection through A(2A)R blockade. Notably, BBG attenuated A(2A)R upregulation and caffeine attenuated P2X7R upregulation. In microglial N9 cells, the P2X7R agonist BzATP (100 mu M) or the A(2A)R agonist CGS26180 (100 nM) increased calcium levels, which was abrogated by the P2X7R antagonist JNJ47965567 (1 mu M) and by the A(2A)R antagonist SCH58261 (50 nM), respectively; notably JNJ47965567 prevented the effect of CGS21680 and the effect of BzATP was attenuated by SCH58261 and increased by CGS21680. These results provide the first demonstration of a functional interaction between P2X7R and A(2A)R controlling microglia reactivity likely involved in behavioral adaptive responses to stress and are illustrative of a cooperation between the two arms of the purinergic system in the control of brain function.