dizocilpine-maleate and 9-(2-hydroxy-3-nonyl)adenine

The rodent hippocampus exhibits population activities called sharp waves (SPWs) during slow wave sleep and wake immobility. SPWs are important for hippocampal-cortical communication and memory consolidation, and abnormal sharp wave-ripple complexes are closely related to epileptic seizures. Although the SPWs are known to arise from the CA3 circuit, the local mechanisms underlying their generation are not fully understood. We hypothesize that endogenous adenosine is a local regulator of hippocampal SPWs. We tested this hypothesis in thick mouse hippocampal slices that encompass a relatively large hippocampal circuit and have a high propensity of generating spontaneous in vitro SPWs. We found that application of adenosine A1 receptor antagonists induced in vitro SPWs and that such induction was sensitive to blockade by NMDA receptor antagonists. By contrast, an increase in endogenous adenosine via pharmacological inhibition of adenosine transporters or adenosine degrading enzymes suppressed spontaneous in vitro SPWs. We thus suggest that the initiation and incidence of sharp wave-like population events are under tight control by the activity of endogenously stimulated A1 receptors.

Topics: Adenine; Adenosine; Adenosine A1 Receptor Antagonists; Animals; Dizocilpine Maleate; Electric Stimulation; Excitatory Postsynaptic Potentials; Hippocampus; In Vitro Techniques; Inhibitory Postsynaptic Potentials; Membrane Potentials; Mice; Mice, Inbred C57BL; Microelectrodes; Nucleoside Transport Proteins; Patch-Clamp Techniques; Pyramidal Cells; Quinoxalines; Receptor, Adenosine A1; Receptors, N-Methyl-D-Aspartate; Theophylline; Xanthines

Stimulation of N-methyl-D-aspartate (NMDA) receptors on neurons activates both cAMP and cGMP signaling pathways. Experiments were carried out to determine which phosphodiesterase (PDE) families are involved in the hydrolysis of the cyclic nucleotides formed via this mechanism, using primary neuronal cultures prepared from rat cerebral cortex and hippocampus. The nonselective PDE inhibitor 3-isobutyl-1-methylxanthine (IBMX) potentiated the ability of NMDA to increase cAMP and cGMP. However, among the family-selective inhibitors, only the PDE4 inhibitor rolipram enhanced the ability of NMDA to increase cAMP in the neurons. In contrast, only the PDE2 inhibitor erythro-9-(2-hydroxy-3-nonyl) adenine (EHNA) enhanced the ability of NMDA to increase cGMP. Neither adenosine nor an adenosine deaminase inhibitor mimicked the effect of EHNA; this suggests that EHNA's inhibition of PDE2, not its effects on adenosine metabolism, mediates its effects on NMDA-stimulated cGMP concentrations. The PDE inhibitor-augmented effects of NMDA on cAMP and cGMP formation were antagonized by 5-methyl-10,11-dihydro-5H-dibenzo[a,d] cyclohepten-5,10-imine maleate (MK-801), verifying NMDA receptor mediation. In contrast, only NMDA-mediated cGMP formation was affected by altering either nitric oxide signaling or guanylyl cyclase; this suggests that NMDA-induced changes in cAMP are not secondary to altered cGMP concentrations. Overall, the present findings indicate that cAMP and cGMP formed in neurons as a result of NMDA receptor stimulation are hydrolyzed by PDE4 and PDE2, respectively. Selective inhibitors of the two PDE families will differentially affect the functional consequences of activation of these two signaling pathways by NMDA receptor stimulation.

Topics: 3',5'-Cyclic-AMP Phosphodiesterases; Adenine; Adenosine; Animals; Cells, Cultured; Cerebral Cortex; Cyclic AMP; Cyclic GMP; Cyclic Nucleotide Phosphodiesterases, Type 2; Cyclic Nucleotide Phosphodiesterases, Type 4; Dizocilpine Maleate; Enzyme Inhibitors; Excitatory Amino Acid Agonists; Excitatory Amino Acid Antagonists; Female; Guanylate Cyclase; Hippocampus; N-Methylaspartate; Neurons; Nitric Oxide Donors; Nitric Oxide Synthase; Phosphodiesterase Inhibitors; Phosphoric Diester Hydrolases; Pregnancy; Rats; Rats, Sprague-Dawley; Receptors, N-Methyl-D-Aspartate; Rolipram