Muscarinic receptor-mediated regulation of OM-853-enhanced dopamine release in striatum of rat

Vinconate, a cognitive enhancer, and PI turnover-phospholipase C systems in the brain

The molecular mechanisms for the stimulation of inositol 1-phosphate (IP1) formation by vinconate were investigated using preparations of rat brain. Vinconate (10(-8)-10(-3) M) dose-dependently inhibited the binding of [3H]quinuclidinyl benzilate ([3H]QNB) to muscarinic acetylcholine receptors and its IC50 value for [3H]QNB binding was 1.7 x 10(-5) M. The rightward shift of carbachol displacement curve of [3H]QNB binding by GTP (10(-4) M) was completely abolished by vinconate (10(-5) M). Carbachol (10(-8)-10(-2) M) increased [3H]IP1 formation in a dose-dependent manner and the carbachol-induced [3H]IP1 formation was significantly accentuated by vinconate (10(-5) M). The enhancement of [3H]IP1 accumulation by vinconate was inhibited by approximately 50% in the presence of atropine (10(-5) M), although phentolamine and ketanserin had no effects on the stimulatory effect of vinconate on [3H]IP1 formation. Vinconate showed no alteration in the binding of [3H]guanosine 5'-(beta, gamma-imino) triphosphate ([3H]Gpp(NH)p) to the crude synaptic membranes. The enhancement of phosphatidylinositol 4,5-biphosphate (PIP2)-specific phospholipase C (PLC) activity by GTP was unaffected in the presence of 10(-3) M vinconate, whereas vinconate alone dose-dependently enhanced the activities of both PIP2-specific and cytosolic PLC. These results suggest that vinconate may induce the facilitation of phosphatidylinositide (PI) turnover via the stimulation of muscarinic acetylcholine receptors, the enhancement of coupling between muscarinic acetylcholine receptors and GTP-binding protein, and the direct activations of PIP2-specific and cytosolic PLC.

Effects of vinconate on neurotransmitter receptor systems in aged rat brain

We investigated the effects of age and (±)-methyl-3-ethyl-2,3,3a,4-tetrahydro-1 H-indolo[3,2,1-de][1,5]naphthyridine-6-carboxylate hydrochloride (vinconate), an indolonaphthyridine derivative, on neurotransmitter receptor systems in the rat brain using quantitative receptor autoradiography. [(3)H]Quinuclidinyl benzilate (QNB), [(3)H]hemicholinium-3 (HC) and [(3)H]muscimol were used to label acetylcholine receptors, high-affinity choline uptake sites and γ-aminobutyric acid(A) (GABA(A)) receptors, respectively. [(3)H]QNB, [(3)H]HC and [(3)H]muscimol binding decreased in any brain areas of 24-month-old (aged) rats in comparison with 6-month-old (adult) animals. Chronic treatment with vinconate (10 and 30 mg/kg, i.p., once a day for 4 weeks) partly ameliorated the reduction in [(3)H]QNB, [(3)H]HC and [(3)H]muscimol biding in aged rat brains. This effect was especially noted in [(3)H]muscimol binding. The results suggest that vinconate may have beneficial effects on age-related changes in neurotransmitter receptor systems.

Positive allosteric action of eburnamonine on cardiac muscarinic acetylcholine receptors

It was discovered recently that alcuronium and strychnine (which is a precursor of alcuronium) allosterically increase the affinity of cardiac muscarinic receptors for the antagonist, N-methylscopolamine. We have now investigated the effects of l-eburnamonine and vincamine, which are both closely related to strychnine. In experiments on rat heart atria, l-eburnamonine was found to increase the binding of [3H]N-methylscopolamine with Ehlert's cooperativity coefficient alpha = 0.35, which indicates that the strength of its allosteric action is close to that of alcuronium and strychnine (alpha = 0.31 and 0.44, respectively). However, the affinity of l-eburnamonine for the cardiac muscarinic receptors is lower than the affinities of alcuronium and strychnine (KAR = 22.6 microM, 0.15 microM, and 3.4 microM, respectively). In spite of its extremely close similarity to l-eburnamonine, vincamine has a negative allosteric effect on the binding of [3H]N-methylscopolamine (alpha = 4.1; KAR = 22.8 microM). It is likely that a systematic investigation of the allosteric effects of the analogues of strychnine will not only yield new allosteric effectors on muscarinic receptors, but also clarify the structural features responsible for the direction (positive or negative) of their allosteric effect.

Effect of vinconate on the extracellular levels of dopamine and its metabolites in the rat striatum: microdialysis studies

The effects of (+/-)-methyl-3-ethyl-2,3,3 alpha, 4-tetrahydro-1H- indolo[3,2,1-de][1,5]naphthyridine-6-carboxylate hydrochloride (vinconate), an indolonaphthyridine derivative, on the extracellular levels of dopamine and its metabolites in the rat striatum were examined using brain microdialysis. Single administration of vinconate (10, 100 mg/kg i.p.) increased the extracellular level of dopamine and its metabolites. This enhancing effect of vinconate was antagonized by scopolamine (10 microM), a muscarinic receptor antagonist, which was added to the perfusate from 30 min before vinconate treatment. These findings suggest that vinconate, even when systemically administered, enhances the endogenous release of dopamine in the striatum, probably via the stimulation of presynaptic muscarinic receptors.

Non-competitive antagonism by hirsuteine of nicotinic receptor-mediated dopamine release from rat pheochromocytoma cells

Effects of hirsuteine, an indole alkaloid extracted from Uncaria genus, on nicotine- and high K-induced responses were investigated in rat pheochromocytoma PC12 cells. Hirsuteine (300 nM-10 microM) inhibited dopamine release evoked by 100 microM nicotine in a concentration-dependent manner. Hirsuteine did not produce a parallel shift of the concentration-response relationship curve for nicotine, but reduced maximal dopamine release. Dopamine release evoked by 60 and 155 mM KCl was also inhibited by hirsuteine, but the concentration necessary for significant inhibition was higher (more than 10 microM). Under whole cell voltage-clamp, hirsuteine reversibly inhibited inward currents activated by 100 microM nicotine. The current inhibition was slightly accelerated by hyperpolarization. The results suggest that hirsuteine non-competitively antagonizes nicotine-evoked dopamine release by blocking ion permeation through nicotinic receptor channel complexes. The blockade of Ca channels, which are activated during nicotine-evoked depolarization, may not play a major role in the antagonism.

Protective effect of vinconate on ischemia-induced neuronal damage in the rat hippocampus

The protective effect of vinconate, a vinca alkaloid derivative, on ischemia-induced neuronal damage was investigated using a model of rat forebrain ischemia caused by occlusion of four vessels. Hippocampal cell loss was observed histologically and neurochemically 5 days after 10 min of ischemia. Treatment with vinconate (50 and 200 mg/kg i.p.) before cerebral ischemia significantly suppressed neuronal cell loss in the hippocampal CA1 region and the decrease in the content of neuroactive amino acids in the hippocampus. The release of neuroactive amino acids in the hippocampus was significantly increased by cerebral ischemia. Pretreatment with vinconate (50 and 200 mg/kg i.p.) significantly attenuated the increased release of glutamic acid and aspartic acid, but not the release of gamma-aminobutyric acid (GABA), taurine and glycine. This suppressive effect of vinconate was antagonized by scopolamine (10(-5) M). The addition of vinconate (10(-11)-10(-4) M) had no effect on the binding of [3H]MK-801. These results indicate that pretreatment with vinconate attenuates the ischemia-induced release of excitatory amino acids into the extracellular space of the hippocampus via the stimulation of presynaptic muscarinic acetylcholine receptors. The present results also suggest that this suppressive effect of vinconate on the release of excitatory amino acids (glutamic acid and aspartic acid) may play a crucial role in the protective action of this agent against ischemia-induced neuronal damage in the hippocampus.

Effects of vinconate, a novel vinca alkaloid, on spatial learning deficits induced by the basal forebrain lesion in rats

We investigated the effects of vinconate, a novel vinca alkaloid, on spatial learning deficits induced by the basal forebrain (BF) lesion in rats. Bilateral BF lesions were produced by injecting ibotenic acid (6 micrograms/0.5 microliter/side). In BF-lesioned rats, impairment of spatial learning in escaping onto the platform during training and decrease in spatial bias during the spatial probe trial in Morris's water maze task were both observed. Vinconate (5 and 10 mg/kg) treatment shortened the increase of escape latency to the platform in BF-lesioned rats and significantly reversed the decrease in spatial bias induced by the BF lesion. Vinconate (10 mg/kg) attenuated the decrease in choline acetyltransferase activity in the frontoparietal cortex caused by the BF lesion. The present study suggests that vinconate has an antiamnesic effect on the BF-lesion-induced amnesia by ameliorating the dysfunction in cholinergic neurons.

Effects of vinconate on spatial learning impairments induced by medial septal lesion in rats

We investigated the effects of vinconate, a novel vinca alkaloid, on spatial learning deficits induced by medial septal (MS) lesion in rats. MS lesion was produced by passing an anodal DC current. In vehicle-treated MS-lesioned rats impairment of spatial learning was observed, shown by a decrease in correct choices and an increase in total errors during training in a radial arm maze task. Vinconate (10 mg/kg) treatment alleviated the decrease in correct choices and the increase in total errors induced by MS lesion. Vinconate (5 and 10 mg/kg) treatment showed a tendency to reverse the decrease in choline acetyltransferase activity in the hippocampus caused by MS lesion. The present study suggests that vinconate has an anti-amnesic effect on MS lesion-induced amnesia by ameliorating the dysfunction in cholinergic (ACh) neurons.