dizocilpine-maleate and zaprinast

Adenosine is an important regulator of neuronal excitability. Zaprinast is a cyclic nucleotide phosphodiesterase inhibitor, and has been shown in the hippocampal slice to suppress excitation. This action can be blocked by an adenosine receptor antagonist, and therefore is presumably due to adenosine release stimulated by exposure to zaprinast. To explore the mechanism of this phenomenon further, we examined the effect of zaprinast on adenosine release itself in cultured rat forebrain neurons. Zaprinast significantly stimulated extracellular adenosine accumulation. The effect of zaprinast on adenosine appeared to be mediated by increasing intracellular cyclic adenosine monophosphate (cAMP) and activation of protein kinase A (PKA): (i) zaprinast stimulated intracellular cAMP accumulation; (ii) a cAMP antagonist (Rp-8-Br-cAMP) significantly reduced the zaprinast effect on adenosine; (iii) an inhibitor of phosphodiesterase (PDE)1 (vinpocetine) and an activator of adenylate cyclase (forskolin) mimicked the effect of zaprinast on adenosine. We also found that zaprinast had no effect on adenosine in astrocyte cultures, and tetrodotoxin completely blocked zaprinast-evoked adenosine accumulation in neuronal cultures, suggesting that neuronal activity was likely to be involved. Consistent with a dependence on neuronal activity, NMDA receptor antagonists (MK-801 and D-APV) and removal of extracellular glutamate by glutamate-pyruvate transaminase blocked the effect of zaprinast. In addition, zaprinast was shown to stimulate glutamate release. Thus, our data suggest that zaprinast-evoked adenosine accumulation is likely to be mediated by stimulation of glutamate release by a cAMP- and PKA-dependent mechanism, most likely by inhibition of PDE1 in neurons. Furthermore, regulation of cAMP, either by inhibiting cAMP-PDE activity or by stimulating adenylate cyclase activity, may play an important role in modulating neuronal excitability. These data suggest the existence of a homeostatic negative feedback loop in which increases in neuronal activity are damped by release of adenosine following activation of glutamate receptors.

Topics: Adenosine; Animals; Animals, Newborn; Astrocytes; Cells, Cultured; Cyclic AMP; Cyclic GMP; Dizocilpine Maleate; Dose-Response Relationship, Drug; Drug Interactions; Embryo, Mammalian; Enzyme Activation; Excitatory Amino Acid Agonists; Excitatory Amino Acid Antagonists; Extracellular Space; Female; Glutamic Acid; Intracellular Space; Male; Membrane Potentials; Models, Neurological; N-Methylaspartate; Neurons; Patch-Clamp Techniques; Phosphodiesterase Inhibitors; Pregnancy; Prosencephalon; Purinones; Rats; Rats, Sprague-Dawley; Thionucleotides

1. The mechanism of stimulation of noradrenaline (NA) release by nicotine (NIC) was investigated in human cerebral cortex slices preloaded with 3H-noradrenaline. 2 NIC (10-1000 micro M) increased 3H-NA release in a concentration-dependent manner. 3. NIC (100 micro M)-evoked 3H-NA release was largely dependent on external Ca2+, and was attenuated by omega-conotoxin GVIA (0.1 micro M) but not by nitrendipine (1 micro M). 4. Tetrodotoxin (1 micro M) and nisoxetine (0.1 micro M) attenuated the NIC (100 micro M)-evoked release of 3H-NA. 5. Mecamylamine (10 micro M), dihydro-beta-erythroidine (10 micro M) and d-tubocurarine (30 micro M), but not alpha-bungarotoxin (alpha-BTX, 0.1 micro M), attenuated the NIC (100 micro M)-evoked release of 3H-NA. 6. NIC (100 micro M)-evoked release of 3H-NA was not affected by 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX, 30 micro M) and D(-)-2-amino-5-phosphonopentanoic acid (D-AP5, 100 micro M), but attenuated by MK-801 (10 micro M). MK-801 (0.1-1000 micro M) displaced the specific binding of 3H-nisoxetine with K(i) values of 91.2 micro M. NIC (100, 300 and 1000 micro M) did not induce 3H-D-aspartate release in human cerebral cortex slices. 7. NIC (100 micro M)-evoked release of 3H-NA was attenuated by 7-nitroindazole (10 micro M), N(G)-nitro-L-arginine methyl ester HCl (L-NAME, 30 micro M), N(G)-monomethyl-L-arginine acetate (L-NMMA, 300 micro M). [(3)H]-NA release induced by NIC (100 micro M) was attenuated by methylene blue (3 micro M) and 1H-[1,2,4]oxadiazole[4,3-alpha]quinoxalin-1-one (ODQ, 10 micro M), and enhanced by zaprinast (30 micro M). 8. In conclusion, NIC stimulates the release of 3H-NA through activation of alpha-BTX-insensitive nicotinic acetylcholine receptors in the human cerebral cortex slices and this action of NIC is associated with modulation of the NO/cGMP pathway.

Topics: Adolescent; Adult; Arginine; Calcium; Calcium Channel Blockers; Cerebral Cortex; Dihydro-beta-Erythroidine; Dizocilpine Maleate; Dose-Response Relationship, Drug; Enzyme Inhibitors; Fluoxetine; Ganglionic Stimulants; Guanylate Cyclase; Humans; In Vitro Techniques; Indazoles; Male; Mecamylamine; Methylene Blue; Neuroprotective Agents; NG-Nitroarginine Methyl Ester; Nicotine; Nicotinic Antagonists; Nitrendipine; Nitric Oxide Synthase; Norepinephrine; omega-Conotoxin GVIA; Oxadiazoles; Purinones; Quinoxalines; Tetrodotoxin; Tritium; Tubocurarine

The stimulation of NMDA receptor increased [3H]GABA release from preloaded cultured retina cells. This effect appears to be mediated by NO production, since addition of L-NA reduces NMDA-evoked [3H]GABA release. Spermine/NO complex, an NO donor, mimics the effect produced by NMDA. The addition of zaprinast, a phosphodiesterase inhibitor, as well as 8-Br-cGMP enhances the NMDA-evoked [3H]GABA release. These results agree with the existence in chick retina cells of NO/cGMP pathways and support a role for NO in NMDA-evoked events. The activation of this receptor complex through maturative stages of the retina together with the NO-mediated increase in GABA release may account for NMDA differentiative effect in culturing retina cells.

Topics: 1-Methyl-3-isobutylxanthine; Animals; Cell Differentiation; Cells, Cultured; Chick Embryo; Cyclic GMP; Dizocilpine Maleate; gamma-Aminobutyric Acid; Isoquinolines; N-Methylaspartate; Nitric Oxide; Nitroarginine; Nitrogen Oxides; Purinones; Receptors, N-Methyl-D-Aspartate; Retina; Spermine; Tritium