Endocannabinoid-mediated synaptically evoked suppression of GABAergic transmission in the cerebellar cortex.

Presynaptic CB(1) cannabinoid receptors are frequently targets of endogenous cannabinoids (endocannabinoids) released from postsynaptic neurons. It is known that the glutamatergic afferent input to a neuron can trigger endocannabinoid production and that the released endocannabinoid can suppress the glutamatergic input. We tested the hypothesis that activation of the glutamatergic input to a neuron leads to an endocannabinoid-mediated suppression of the GABAergic afferent input to the same neuron. Spontaneous postsynaptic currents (sPSCs) were recorded with patch-clamp techniques in Purkinje cells in mouse cerebellar brain slices. Activation of the climbing fiber-mediated glutamatergic input to Purkinje cells led to a suppression of the sPSCs by 34+/-3%. This suppression was mostly due to suppression of GABAergic spontaneous inhibitory postsynaptic current (sIPSCs), because 93% of the sPSCs recorded in Purkinje cells were GABAergic sIPSCs. Blockade of ionotropic, but not metabotropic glutamate receptors, prevented the suppression. The climbing fiber activation led to an increase in calcium concentration in the Purkinje cells, and this increase was necessary for the suppression of sPSCs, because the suppression did not occur when the calcium increase was prevented by BAPTA. No sPSC suppression was observed in the presence of the CB(1) antagonist rimonabant or the diacylglycerol lipase inhibitor orlistat. In a further series of experiments GABAergic sIPSCs were recorded: these sIPSCs were also suppressed after climbing fiber activation, and the suppression was sensitive to the CB(1) antagonist SLV319. Finally, the GABAergic synaptic transmission between molecular layer interneurons and Purkinje cells was directly studied on simultaneously patch-clamped neuron pairs. Climbing fiber activation led to suppression of the interneuron --> Purkinje cell synaptic transmission. The results point to a novel form of endocannabinoid-mediated heterosynaptic plasticity. The endocannabinoid production in a neuron is triggered by its glutamatergic synaptic input and is dependent on an increase in intracellular calcium concentration. The produced endocannabinoid, in turn, suppresses the GABAergic synaptic input to the neuron by activating CB(1) cannabinoid receptors.

Regulation of the extracellular signal-regulated kinases following acute and chronic opioid treatment.

The adaptations in extracellular signal-regulated kinase (ERK) pathway activity result in alterations in transcription of several genes that can be essential for development of both opioid tolerance and dependence. In this study, we investigated the effect of acute and prolonged opioid treatment on ERK pathway activity in SH-SY5Y cells. Acute administration of morphine and DAMGO stimulated ERK activity and this stimulation required activation of Ca(2+)/calmodulindependent kinase II (CaMKII) and protein kinase C (PKC). In contrast, prolonged morphine treatment decreased the level of phosphorylated ERK. The pr ecipitation of withdrawal further decreased the ERK1/2 activity. The principal finding of these studies is demonstration that the activation of CaMKII and PKC is required for ERK stimulation following acute opioid treatment while in a chronic morphine treatment and withdrawal, the up-regulation of PKC and CaMKII pathways seems to be engaged in the ERK inhibition. These results provide evidence that both opioid administration and opioid withdrawal, affecting similar intracellular pathways, can exert different effects on ERK activity.

Novel thiazole-based heterocycles as selective inhibitors of fibrinogen-mediated platelet aggregation.

The synthesis and biological activity of novel thiazole-based heterocycles as inhibitors of thrombin-induced human platelet aggregation are described. Further evaluation of selected compounds show they inhibit platelet aggregation as stimulated by a variety of agonists. The more active compounds also were found to inhibit fibrinogen binding to platelets. To further delineate the mechanism of action of these compounds, direct binding studies with the purified glycoprotein (GP) IIb/IIIa receptor were performed. Flow cytometry analyses of 24 and 32 indicate that these compounds block the activation process of the GPIIb/IIIa receptor without denaturing the integrin receptor. On the basis of these studies, 32 exhibited the best profile as a novel nonpeptide inhibitor of fibrinogen-mediated platelet aggregation.

Thiophene systems. 14. Synthesis and antihypertensive activity of novel 7-(cyclic amido)-6-hydroxythieno[3,2-b]pyrans and related compounds as new potassium channel activators.

The synthesis and antihypertensive activity of novel 7-(cyclic amido)-6-hydroxy-5,5-dimethylthieno[3,2-b]pyrans and related compounds are described. The compounds were tested for oral antihypertensive activity in spontaneously hypertensive rats (SHR) and selected compounds were evaluated in vitro for increases in 86Rb efflux in rabbit isolated mesenteric arteries. The effects on activity in SHR of lactam ring size, the presence of heteroatoms in the lactam ring, the relative stereochemistry at C-6 and C-7, and the substituents on the thiophene ring are examined. The best racemic compound in this series is 32, trans-5,6-dihydro-6-hydroxy-5,5-dimethyl-2-nitro-7-(2-oxopiperidin -1-yl)-5H- thieno[3,2-b]pyran, which is 10-fold more potent than cromakalim with an ED30 = 0.015 mg/kg in SHR. Compound 32 could be resolved and the antihypertensive activity determined to reside primarily in the (6S,7S)-(-)-enantiomer 41. Surprisingly, the elimination of water to give the enamides 50-52, thiophene isosteres of bimakalim, diminishes activity significantly.