Early and delayed glutamate effects in rat primary cortical neurons

Decursinol and decursin protect primary cultured rat cortical cells from glutamate-induced neurotoxicity

We previously reported six neuroprotective decursinol derivatives, coumarins from Angelica gigas (Umbelliferae) roots. To elucidate the action patterns of decursinol derivatives, we investigated the neuroprotective effects of decursinol and decursin, which showed highly significant activity and were major constituents of A. gigas, using primary cultures of rat cortical cells in-vitro. At concentrations of 0.1–10.0 μM, both decursinol and decursin exerted a significant neuroprotective activity pretreatment and throughout treatment. In addition, decursin had a neuroprotective impact in the post-treatment paradigm implying that decursin might possess different action mechanisms from that of decursinol in the protection of neurons against glutamate injury. Both decursinol and decursin effectively reduced the glutamate-induced increased intracellular calcium ([Ca2+]i) in cortical cells, suggesting that these two coumarins may exert neuroprotection by reducing calcium influx by overactivation of glutamate receptors. This suggestion was supported by the result that decursinol and decursin protected neurons against kainic acid (KA)-induced neurotoxicity better than against that induced by N-methyl-D-aspartate (NMDA). Moreover, both decursinol and decursin significantly prevented glutamate-induced decreases in glutathione, a cellular antioxidant, and glutathione peroxidase activity. In addition, both compounds efficiently reduced the overproduction of cellular peroxide in glutamate-injured cortical cells. These results suggested that both decursinol and decursin protected primary cultured rat cortical cells against glutamate-induced oxidative stress by both reducing calcium influx and acting on the cellular antioxidative defence system. Moreover, decursin is considered to probably have a different action mechanism from that of decursinol in protecting cortical cells against glutamate injury.

Protective effects of Chlorpromazine and Verapamil against cadmium-induced kidney damage in vivo

Overexposure to cadmium (Cd) can induce kidney damage, which was related to the oxidative damage and disturb intracellular Ca2+ homeostasis. Chlorpromazine (CPZ), targeting calmodulin (CaM), and the Ca2+ channel blocker Verapamil (Ver) are involved in intracellular Ca2+ homeostasis processes. The aim of the study was to investigate the kidney damage caused by Cd administrated for 6 weeks and to evaluate the effects of pre-treatment with either chlorpromazine or verapamil on Cd-induced kidney damage. Thirty-two Wistar rats were divided randomly into 4 groups by weight, i.e., control group, Cd-treated group, and CPZ or Ver pre-treated group. The Cd-treated group rats were subcutaneously (s.c.) injected with 7micromol CdCl2/kg body weight/day. The CPZ and Ver pre-treated group rats were intraperitoneally (i.p.) injected with 5mg CPZ/kg body weight/day, 4mg Ver/kg body weight/day, respectively, 1h before the s.c. administration of 7micromol CdCl2/kg body weight/day. The control group rats were injected s.c. with saline at the same time. The volume of injection was 2ml/kg body weight, 5 times per week, for up to 6 weeks. After 6 weeks, Cd concentrations in the renal cortex and urine were significantly higher in Cd-treated group than that in controls. Cd concentrations of the urine in CPZ and Ver pre-treated groups were significantly lower than that in Cd-treated group, but there were no significant changes in the renal cortex. Compared with the controls, urinary NAG, ALP activities, and the levels of GSH, MDA, and the activities of PKC, Na(+)-K(+)-ATPase, and Ca(2+)-ATPase in rats from the Cd-treated group were significantly increased. SOD activity was suppressed by Cd. Urinary NAG activity and the level of GSH and the activities of PKC and Ca(2+)-ATPase in both CPZ and Ver pre-treated groups were significantly lower than that in Cd-treated rats. The present results showed that Cd-induced kidney damage was related to the oxidative damage and disturb intracellular Ca2+ homeostasis. Both CPZ and Ver possess some ability to prevent cadmium-induced kidney damage via antioxidative action and by maintaining calcium homeostasis.

Mechanisms of sodium azide-induced changes in intracellular calcium concentration in rat primary cortical neurons

An intracellular calcium ([Ca(2+)](i)) increase is involved in sodium azide (NaN(3))-induced neurotoxicity, an in vitro model of brain ischemia. In this study the questions of possible additional sources of calcium influx, besides glutamate receptor activation, and of the time-course of NaN(3) effects have been addressed by measuring [Ca(2+)](i) in rat primary cortical cultures with the FURA-2 method. Basal [Ca(2+)](i) of neuronal populations was concentration-dependently increased 30 min, but not 24h, after a 10-min NaN(3) (3-30 mM) treatment; conversely, the net increase induced by electrical stimulation (10Hz, 10s) was consistently reduced. All the above effects depended on glutamate release and consequent NMDA receptor activation, since the NMDA antagonist MK-801 (1 microM) prevented them, and the spontaneous efflux of [(3)H]-d-aspartate from superfused neurons was concentration-dependently increased by NaN(3). In single neuronal cells, NaN(3) application progressively and concentration-dependently increased [Ca(2+)](i) (to 177+/-5% and 249+/-7% of the controls, 4 and 12 min after a 10mM-treatment, respectively). EGTA (5mM) pretreatment reduced the effect of 10mM NaN(3) (to 118+/-5% at 4 min, and to 148+/-10% at 12 min, respectively), while 1 microM cyclosporin A did not. Both MK-801 and CNQX (a non-NMDA glutamate antagonist, 10 microM) prevented NaN(3) effect at 4 min (to 147+/-8% and 153+/-5%, respectively), but not at 12 min after NaN(3) treatment. Conversely, 10 microM verapamil and 0.1 microM omega-conotoxin (L- and N-type calcium channel blockers, respectively) significantly attenuated NaN(3) effects at 12 min (to 198+/-8% and 164+/-5%, respectively), but not at 4 min; the P/Q-type calcium channel blocker, agatoxin, 0.3 microM, was ineffective. These findings show that the predominant source of calcium increase induced by NaN(3) is extracellular, involving glutamate receptor activation in a first step and calcium channel (mainly of the N-type) opening in a second step.

Differential activation of protein kinase C isoforms following chemical ischemia in rat cerebral cortex slices

The aim of the current study was to characterize the effects of chemical ischemia and reperfusion at the transductional level in the brain. Protein kinase C isoforms (alpha, beta(1), beta(2), gamma, delta and epsilon) total levels and their distribution in the particulate and cytosolic compartments were investigated in superfused rat cerebral cortex slices: (i) under control conditions; (ii) immediately after a 5-min treatment with 10mM NaN(3), combined with 2mM 2-deoxyglucose (chemical ischemia); (iii) 1h after chemical ischemia (reperfusion). In control samples, all the PKC isoforms were detected; immediately after chemical ischemia, PKC beta(1), delta and epsilon isoforms total levels (cytosol+particulate) were increased by 2.9, 2.7 and 9.9 times, respectively, while alpha isoform was slightly reduced and gamma isoform was no longer detectable. After reperfusion, the changes displayed by alpha, beta(1), gamma, delta and epsilon were maintained and even potentiated, moreover, an increase in beta(2) (by 41+/-12%) total levels became significant. Chemical ischemia-induced a significant translocation to the particulate compartment of PKC alpha isoform, which following reperfusion was found only in the cytosol. PKC beta(1) and delta isoforms particulate levels were significantly higher both in ischemic and in reperfused samples than in the controls. Conversely, following reperfusion, PKC beta(2) and epsilon isoforms displayed a reduction in their particulate to total level ratios. The intracellular calcium chelator, 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid, 1mM, but not the N-methyl-d-asparate receptor antagonist, MK-801, 1muM, prevented the translocation of beta(1) isoform observed during ischemia. Both drugs were effective in counteracting reperfusion-induced changes in beta(2) and epsilon isoforms, suggesting the involvement of glutamate-induced calcium overload. These findings demonstrate that: (i) PKC isoforms participate differently in neurotoxicity/neuroprotection events; (ii) the changes observed following chemical ischemia are pharmacologically modulable; (iii) the protocol of in vitro chemical ischemia is suitable for drug screening.

Pharmacologically induced calcium oscillations protect neurons from increases in cytosolic calcium after trauma

Increases in cytosolic calcium ([Ca(2+)](i)) following mechanical injury are often considered a major contributing factor to the cellular sequelae in traumatic brain injury (TBI). However, very little is known on how developmental changes may affect the calcium signaling in mechanically injured neurons. One key feature in the developing brain that may directly impact its sensitivity to stretch is the reduced inhibition which results in spontaneous [Ca(2+)](i) oscillations. In this study, we examined the mechanism of stretch-induced [Ca(2+)](i) transients in 18-days in vitro (DIV) neurons exhibiting bicuculline-induced [Ca(2+)](i) oscillations. We used an in vitro model of mechanical trauma to apply a defined uniaxial strain to cultured cortical neurons and used increases in [Ca(2+)](i) as a measure of the neuronal response to the stretch insult. We found that stretch-induced increases in [Ca(2+)](i) in 18-DIV neurons were inhibited by pretreatment with either the NMDA receptor antagonist, APV [D(-)-2-Amino-5-phosphonopentanoic acid], or by depolymerizing the actin cytoskeleton prior to stretch. Blocking synaptic NMDA receptors prior to stretch significantly attenuated most of the [Ca(2+)](i) transient. In comparison, cultures with pharmacologically induced [Ca(2+)](i) oscillations showed a substantially reduced [Ca(2+)](i) peak after stretch. We provide evidence showing that a contributing factor to this mechanical desensitization from induced [Ca(2+)](i) oscillations is the PKC-mediated uncoupling of NMDA receptors (NMDARs) from spectrin, an actin-associated protein, thereby rendering neurons insensitive to stretch. These results provide novel insights into how the [Ca(2+)](i) response to stretch is initiated, and how reduced inhibition - a feature of the developing brain - may affect the sensitivity of the immature brain to trauma.