dizocilpine-maleate and pyridoxal-phosphate-6-azophenyl-2--4--disulfonic-acid

In the present study, the direct drug effects of nicotine and its effects on the cholinergic twitch responses of the electrically stimulated longitudinal muscle-myenteric plexus strip from the ileum of guinea pig were investigated. Nicotine dose-dependently (0.3-10 µmol/l) evoked the well-known contractile responses on its own. Whereas the interposed twitch responses remained present without a change in height at 1 µmol/l nicotine, a nicotine concentration of 3 µmol/l slightly and a concentration of 10 µmol/l markedly diminished the twitch during their presence. After the washout of 1-10 µmol/l nicotine, the height of the twitch response was also temporarily and significantly reduced by 30-77%. The P2X purinoceptor agonist αβ-methylene ATP (1-10 µmol/l) dose-dependently induced contractions on its own and reduced the twitch response during its presence in the organ bath; however, it did not diminish the twitch responses after washout of the drug as nicotine did. The P2X antagonist pyridoxalphosphate-6-azophenyl-2'-4'-disulphonic acid, the NMDA channel blocker MK-801 and the inhibitor of small conductance Ca(2+)-activated K(+) (SK) channels apamin reduced the contractile effect of 1 µmol/l nicotine. Apamin also significantly prevented the 'post-nicotine inhibition of the twitch' following the washout of 1-3 µmol/l nicotine. As a conclusion, we provide evidence for a functional interaction between nicotinic receptors and the P2X receptors in the ileum of the guinea pig. The 'post-nicotine inhibition of the twitch' is not due to nicotinic acetylcholine receptor desensitization or transmitter depletion, but most probably the secondary effects of nicotine on SK channels determine the reduced cholinergic motor neuron excitability.

Topics: Adenosine Triphosphate; Animals; Apamin; Dizocilpine Maleate; Dose-Response Relationship, Drug; Electric Stimulation; Guinea Pigs; Ileum; In Vitro Techniques; Male; Muscle Contraction; Nicotine; Pyridoxal Phosphate

Cell death was assessed by quantitative analysis of propidium iodide uptake in rat hippocampal slice cultures transiently exposed to oxygen and glucose deprivation, an in vitro model of brain ischemia. The hippocampal subfields CA1 and CA3, and fascia dentata were analyzed at different stages from 0 to 48 h after the insult. Cell death appeared at 3 h and increased steeply toward 12 h. Only a slight additional increase in propidium iodide uptake was seen at later intervals. The mitogen-activated protein kinases extracellular signal-regulated kinase 1 and extracellular signal-regulated kinase 2 were activated immediately after oxygen and glucose deprivation both in CA1 and in CA3/fascia dentata. Inhibition of the specific mitogen-activated protein kinase activator mitogen-activated protein kinase kinase by PD98059 or U0126 offered partial protection against oxygen and glucose deprivation-induced cell damage. The non-selective P2X receptor antagonist suramin gave neuroprotection of the same magnitude as the N-methyl-D-aspartate channel blocker MK-801 (approximately 70%). Neuroprotection was also observed with the P2 receptor blocker PPADS. Immunogold data indicated that hippocampal slice cultures (like intact hippocampi) express several isoforms of P2X receptors at the synaptic level, consistent with the idea that the effects of suramin and PPADS are mediated by P2X receptors. Virtually complete neuroprotection was obtained by combined blockade of N-methyl-D-aspartate receptors, P2X receptors, and mitogen-activated protein kinase kinase. Both P2X receptors and N-methyl-D-aspartate receptors mediate influx of calcium. Our results suggest that inhibition of P2X receptors has a neuroprotective potential similar to that of inhibition of N-methyl-D-aspartate receptors. In contrast, our comparative analysis shows that only partial protection can be achieved by inhibiting the extracellular signal-regulated kinase 1/2 mitogen-activated protein kinase cascade, one of the downstream pathways activated by intracellular calcium overload.

Topics: Animals; Animals, Newborn; Blotting, Western; Cell Death; Dizocilpine Maleate; Dose-Response Relationship, Drug; Drug Interactions; Enzyme Activation; Enzyme Inhibitors; Excitatory Amino Acid Antagonists; Glucose; Hippocampus; Hypoxia; Male; Microscopy, Immunoelectron; Mitogen-Activated Protein Kinases; Neurons; Neuroprotective Agents; Organ Culture Techniques; Purinergic P2 Receptor Antagonists; Pyridoxal Phosphate; Rats; Rats, Wistar; Receptors, N-Methyl-D-Aspartate; Receptors, Purinergic P2; Receptors, Purinergic P2X; Time Factors

Effects of agonists and antagonists of P2X-purinoceptors on the regulation of the development of allodynia were examined in mice; the drugs were administered intrathecally to the spinal cord. Suramin (5, 10 microg) and pyridoxalphosphate-6-azophenyl-2', 4'-disulfonic acid (PPADS), antagonists of P2X receptors, inhibited prostaglandin (PG) E(2)-induced allodynia. PPADS did not block glutamate-induced allodynia. alpha,beta-Methylene ATP (alpha, beta-meATP), an agonist of P2X receptor, elicited allodynia. alpha, beta-me ATP-induced allodynia was blocked by co-administration of alpha,beta-meATP with PPADS, MK 801 or N(omega)-nitro-L-arginine methyl ester (L-NAME). Suramin at higher doses (20, 40 microg) induced allodynia, which was inhibited by MK 801 or L-NAME. These results suggest that ATP P2X receptors in the spinal cord are involved in the regulation of tactile allodynia. Glutamate receptor and nitric oxide systems play an important role in the development of allodynia produced by alpha,beta-meATP and suramin.

Topics: Adenosine Triphosphate; Animals; Dinoprostone; Dizocilpine Maleate; Injections, Spinal; Male; Mice; Mice, Inbred ICR; Neuroprotective Agents; Oxytocics; Pain; Platelet Aggregation Inhibitors; Purinergic P2 Receptor Agonists; Purinergic P2 Receptor Antagonists; Pyridoxal Phosphate; Suramin