Motor alterations and neuronal damage induced by intracerebral administration of Ruthenium red: effect of NMDA receptor antagonists and other anticonvulsant drugs

The Role of Ruthenium Red as a Partial Agonist in Caffeine-Induced Neurotoxicity in Cerebellar Granular Cell Culture of Rats

Caffeine is widely spread and well known as a mild stimulant of the central nervous system. The present study tested the role of caffeine and Ruthenium red on the intact neuronal cells alone and Ruthenium red in caffeine-induced neurotoxicity. One-day-old newborn rats were used to obtain cerebellar cell cultures. Caffeine at a concentration of 1 mM was found to be most toxic. Dead cell scores were 5.9 +/- 0.8 for control, and 56.2 +/- 3.4 for caffeine (p < .001). Ruthenium red alone has also caused the reduction in neuronal cell number 36.1 +/- 4.5 for 10(-5) and 47 +/- 2.7 for 10(-6) M concentrations (p < .001 for both). Interestingly Ruthenium red used in caffeine-induced neurotoxicity has partly diminished the number of dead cells 28.7 +/- 3.2 for 10(-5) and 23.8 +/- 2.27 for 10(-6) M concentrations (p < .001for both). The results suggest that both Ruthenium red and caffeine are neurotoxic alone but, in combination, the neurotoxicity may be reduced through partial agonistic action.

Ru360, a specific mitochondrial calcium uptake inhibitor, improves cardiac post-ischaemic functional recovery in rats in vivo

BACKGROUND AND PURPOSE

The mitochondrial permeability transition pore (mPTP), an energy-dissipating channel activated by calcium, contributes to reperfusion damage by depolarizing the mitochondrial inner membrane potential. As mitochondrial Ca(2+) overload is a main inductor of mPTP opening, we examined the effect of Ru(360), a selective inhibitor of the mitochondrial calcium uptake system against myocardial damage induced by reperfusion in a rat model.

EXPERIMENTAL APPROACH

Myocardial reperfusion injury was induced by a 5-min occlusion of the left anterior descending coronary artery, followed by a 5-min reperfusion in anaesthetized open-chest rats. We measured reperfusion-induced arrhythmias and functions indicative of unimpaired mitochondrial integrity to evaluate the effect of Ru(360) treatment.

KEY RESULTS

Reperfusion elicited a high incidence of arrhythmias, haemodynamic dysfunction and loss of mitochondrial integrity. A bolus intravenous injection of Ru(360) (15-50 nmol kg(-1)), given 30-min before ischaemia, significantly improved the above mentioned variables in the ischaemic/reperfused myocardium. Calcium uptake in isolated mitochondria from Ru(360)-treated ventricles was partially diminished, suggesting an interaction of this compound with the calcium uniporter.

CONCLUSIONS AND IMPLICATIONS

We showed that Ru(360) treatment abolishes the incidence of arrhythmias and haemodynamic dysfunction elicited by reperfusion in a whole rat model. Ru(360) administration partially inhibits calcium uptake, preventing mitochondria from depolarization by the opening of the mPTP. We conclude that myocardial damage could be a consequence of failure of the mitochondrial network to maintain the membrane potential at reperfusion. Hence, it is plausible that Ru(360) could be used in reperfusion therapy to prevent the occurrence of arrhythmia.

Effect of mitochondrial electron transport chain inhibitors on superoxide radical generation in rat hippocampal and striatal slices

In this study, we have compared the generation of superoxide radical in rat hippocampal and striatal slices in the presence of specific mitochondrial electron transport chain (ETC) inhibitors (complexes I and III) under control and depolarization conditions [incubation in artificial cerebrospinal fluid (ACSF) or depolarizing ACSF (dACSF), respectively]. Superoxide radical generation was increased in both ACSF- and dACSF-incubated hippocampal and striatal slices when rotenone and antimycin A were added to the incubation medium. The increase in superoxide radical was dependent on the concentration of ETC inhibitors under control, but not depolarization conditions. Rotenone was found to be more effective than antimycin A in producing superoxide radical from hippocampal and striatal slices. Our results also showed that hippocampal slices were more sensitive to ETC inhibitors compared with striatal slices. Thus, different regions of the brain seem to differ in their capacity to generate free radicals and vulnerability to oxidative stress conditions. This difference should be considered in developing therapeutic modalities against oxidative stress-related disorders and neurodegeneration.

Alterations of intracellular calcium homeostasis and mitochondrial function are involved in ruthenium red neurotoxicity in primary cortical cultures

Ruthenium red (RR) is a polycationic dye that induces neuronal death in vivo and in primary cultures. To characterize this neurotoxic action and to determine the mechanisms involved, we have analyzed the ultrastructural alterations induced by RR in rat cortical neuronal cultures and measured its effect on cytoplasmic Ca(2+) concentration ([Ca(2+)](i)) and on mitochondrial function. RR produced a dose-dependent, progressive disruption of neurites and plasma membrane of neuronal somata after 8-24 hr of incubation. RR caused also an elevation of both the basal [Ca(2+)](i) and its maximal levels after K(+) depolarization. Mitochondrial oxidative function, assessed by reduction of 3-(4,5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide and by changes in dihydrorhodamine-123 fluorescence, was significantly diminished after treatment with RR, both in cultured neurons and in isolated brain mitochondria. La(3+) did not prevent but rather potentiated RR-induced cell death. Glutamate receptor antagonists also failed to prevent RR neurotoxicity. Apoptotic electron microscope images were not observed, and protein synthesis inhibitors did not show any protective effect. It is concluded that RR penetrates neurons and that its neurotoxic damage probably is due to intracellular Ca(2+) dishomeostasis and disruption of mitochondrial oxidative function. These results enhance our understanding of the intracellular mechanisms underlying neuronal death.

Synaptogenesis of mossy fibers induced by spatial water maze overtraining

Synaptic plasticity has been proposed as a mechanism underlying learning and memory. Synaptic reorganization of hippocampal mossy fibers has been observed after experimentally induced epilepsy, and after brief high-frequency activation inducing long-term potentiation. Furthermore, it has been suggested that synaptic changes in the hippocampus may occur after spatial learning. In this study, by using a zinc-detecting histologic technique (Timm), we demonstrate a significant increase of mossy fiber terminals in the CA3 stratum oriens region induced by training rats during 3 days in a spatial Morris water maze. In contrast, animals trained for only 1 day and animals that were just allowed to swim or were overtrained in a stress-motivated inhibitory avoidance task did not show increments of mossy fiber terminals in the stratum oriens. Electron microscopy confirmed that synaptic density of mossy fiber terminals in the stratum oriens increases significantly in water maze overtrained animals compared with the swimming control animals. Taken together, these results suggest that overtraining in a spatial learning task induces mossy fiber synaptogenesis that could be involved in the mechanisms underlying long-term memory storage. Hippocampus 1999;9:631-636.

Injection of Xenopus oocytes with mRNA from cultured neurons induces new currents and susceptibility to the damaging action of ruthenium red

The hexacationic dye ruthenium red produce neuronal death in primary cultures. We injected messenger RNA (mRNA) from cultured neurons into Xenopus laevis oocytes to test whether this treatment can make oocytes sensitive to the damaging action of ruthenium red. Two-microelectrode voltage clamp and resting membrane potential were used to evaluate mRNA expression and to assess the effect of the dye on oocyte survival, when added to the medium or when injected into the cells, at 20, 50, or 100 microM concentrations. Injection of mRNA from cultured cortical or cerebellar granule neurons produced both new outward currents and membrane hyperpolarization. Exposure of mRNA-injected oocytes to extracellular ruthenium red for 24 h induced a remarkable depolarization, but no significant damage was observed. Injection of the dye into buffer-injected oocytes did not cause any change in membrane potential or cell survival, whereas in mRNA-injected oocytes an important depolarization was observed at 24 h after ruthenium red introduction, and 29% of the cells showed serious damage. The results suggest that oocytes become sensitive to intracellular ruthenium red toxicity because they express neuronal-specific proteins involved in cell death.

Visualization of NMDA receptor-induced mitochondrial calcium accumulation in striatal neurons

Ca2+ influx through NMDA receptor-gated channels and the subsequent rise in intracellular Ca2+ concentration ([Ca2+]i) have been implicated in cytotoxic processes that lead to irreversible neuronal injury. While many studies have focused on cytosolic Ca2+ homeostasis, much less is known about Ca2+ fluxes in subcellular organelles, such as mitochondria. The mitochondria play an important role in Ca2+ homeostasis by sequestering cytosolic Ca2+ loads. However, mitochondrial Ca2+ overload can impair ATP synthesis, induce free radical formation, and lead to lipid peroxidation. Thus, it is also important to understand the mitochondrial Ca2+ fluxes induced by NMDA. In this study, changes in mitochondrial Ca2+ concentration ([Ca2+]m) in cultured striatal neurons were monitored with a Ca(2+)-binding fluorescent probe, rhod-2, and laser scanning confocal microscopy. The rhod-2 fluorescence signal was highly localized in mitochondrial areas of confocal images. A rapid increase of [Ca2+]m was observed when neurons were treated with 100 microM NMDA. The increased [Ca2+]m induced by NMDA could not be observed in the presence of ruthenium red, an inhibitor of the mitochondrial Ca2+ uniporter, or CCCP, a protonophore that breaks down the mitochondrial membrane potential necessary for Ca2+ uptake. The magnitude and reversibility of changes in [Ca2+]m induced by NMDA were variable. In neurons receiving multiple pulses of NMDA, [Ca2+]m did not return to baseline. The elevated [Ca2+]m may persist indefinitely and may rise further after successive NMDA exposures. These data demonstrate that Ca2+ accumulates in mitochondria in response to NMDA receptor activation. This Ca2+ accumulation may play a role in the excitotoxic mitochondrial dysfunction induced by NMDA.

Protection by NMDA receptor antagonists against seizures induced by intracerebral administration of 4-aminopyridine

The effects of NMDA receptor antagonists on the convulsant action of the administration of 4-aminopyridine in the rat lateral cerebral ventricle (i.c.v. injection) and motor cerebral cortex (i.cx. injection) were studied. 4-Aminopyridine administration in both regions induced various preconvulsive symptoms, such as salivation, tremors, chewing and rearing, followed by continuous clonic convulsions and, only after i.c.v. injection, running fits and generalized tonic convulsions. This behavioral pattern appeared 5-9 min after administration of 4-aminopyridine and persisted for 100-150 min. 4-Aminopyridine also generated epileptiform electroencephalographic (EEG) discharges characterized by isolated spikes, poly-spikes and spike-wave complexes, which began some seconds after administration of the drug and were present for more than 2 h. The NMDA receptor antagonists (+/-)-3-(2-carboxy-piperazin-4-yl)-propyl-1-phosphonic acid (CPP), (+/-)-2-amino-7-phosphono-heptanoic acid (AP7) and (+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine hydrogen maleate (MK-801) clearly protected against some of the behavioral alterations induced by i.c.v. 4-aminopyridine, particularly the tonic convulsions, but were less effective against those produced by i.cx. 4-aminopyridine. These antagonists also delayed the appearance of EEG epileptiform discharges, reduced its amplitude, frequency and duration, and blocked their propagation to other cortical regions after i.cx. 4-aminopyridine. These results, together with previous data showing that 4-aminopyridine stimulates the release of glutamate in vivo, suggest that an excessive glutamatergic neurotransmission involving NMDA receptors is implicated in 4-amino-pyridine-induced seizures.