A role of p38 mitogen-activated protein kinase in adenosine A(1 )receptor-mediated synaptic depotentiation in area CA1 of the rat hippocampus

BACKGROUND: Although long-term potentiation (LTP) of synaptic strength is very persistent, current studies have provided evidence that various manipulations or pharmacological treatment when applied shortly after LTP induction can reverse it. This kind of reversal of synaptic strength is termed as depotentiation and may have a function to increase the flexibility and storage capacity of neuronal networks. Our previous studies have demonstrated that an increase in extracellular levels of adenosine and subsequent activation of adenosine A(1 )receptors are important for the induction of depotentiation; however, the signaling downstream of adenosine A(1 )receptors to mediate depotentiation induction remains elusive. RESULTS: We confirm that depotentiation induced by low-frequency stimulation (LFS) (2 Hz, 10 min, 1200 pulses) was dependent on adenosine A(1 )receptor activation, because it was mimicked by bath-applied adenosine A(1 )receptor agonist N(6)-cyclopentyladenosine (CPA) and was inhibited by the selective adenosine A(1 )receptor antagonist 8-cyclopentyl-1,3-dipropylxanthine (DPCPX). Pretreatment of the hippocampal slices with the selective p38 mitogen-activated protein kinase (MAPK) inhibitors, 4-(4-fluorophenyl)-2-(4-methylsulfinylphenyl]-5-(4-pyrudyl)-1H-imidazole (SB203580) or trans-1-(4-hydroxycyclohexyl)-4-(fluorophenyl)-5-(2-methoxypyrimidin-4-yl)imidazole (SB239063), prevented the induction of depotentiation by LFS and CPA. In agreement with electrophysiological observation, both LFS- and CPA-induced depotentiation are associated with an increase in p38 MAPK activation, which are blocked by DPCPX or SB203580 application. CONCLUSION: These results suggest that activation of adenosine A(1 )receptor and in turn triggering p38 MAPK signaling may contribute to the LFS-induced depotentiation at hippocampal CA1 synapses.