Neurotrophins protect neurons against glutamate excitotoxicity, but the signaling mechanisms have not been fully elucidated. We studied the role of the phosphatidylinositol 3-kinase (PI3-K) and Ras/mitogen-activated protein kinase (MAPK) pathways in the protection of cultured hippocampal neurons from glutamate induced apoptotic cell death, characterized by nuclear condensation and activation of caspase-3-like enzymes. Pre-incubation with the neurotrophin brain-derived neurotrophic factor (BDNF), for 24 h, reduced glutamate-evoked apoptotic morphology and caspase-3-like activity, and transiently increased the activity of the PI3-K and of the Ras/MAPK pathways. Inhibition of the PI3-K and of the Ras/MAPK signaling pathways abrogated the protective effect of BDNF against glutamate-induced neuronal death and similar effects were observed upon inhibition of protein synthesis. Moreover, incubation of hippocampal neurons with BDNF, for 24 h, increased Bcl-2 protein levels. The results indicate that the protective effect of BDNF in hippocampal neurons against glutamate toxicity is mediated by the PI3-K and the Ras/MAPK signaling pathways, and involves a longterm change in protein synthesis.

In photodynamic therapy (PDT) a sensitizer, light and oxygen are used to induce death of tumor cells and in the treatment of certain noncancerous conditions. Cell death in PDT may occur by apoptosis or by necrosis, depending on the sensitizer, on the PDT dose and on the cell genotype. Some sensitizers that have been used in PDT are accumulated in the mitochondria, and this may explain their efficiency in inducing apoptotic cell death, both in vitro and in vivo. In this review we will focus on the events that characterize apoptotic death in PDT and on the intracellular signaling events that are set in motion in photosensitized cells. Activation of phospholipases, changes in ceramide metabolism, a rise in the cytosolic free Ca 2 + concentration, stimulation of nitric oxide synthase (NOS), changes in protein phosphorylation and alterations in the activity of transcription factors and on gene expression have all been observed in PDT-treated cells. Although many of these metabolic reactions contribute to the demise process, some of them may antagonize cell death. Understanding the signaling mechanisms in PDT may provide means to modulate the PDT effects at the molecular level and potentiate its antitumor effectiveness. D

No abstract

Glutamate and NPY have been implicated in hippocampal neuropathology in temporal lobe epilepsy. Thus, we investigated the involvement of NPY receptors in mediating neuroprotection against excitotoxic insults in organotypic cultures of rat hippocampal slices. Exposure of hippocampal slice cultures to 2 µM AMPA (α-amino-3-hydroxy-5-methyl-isoxazole-4-propionate) induced neuronal degeneration, monitored by propidium iodide uptake, of granule cells and CA1 pyramidal cells. For AMPA, whereas only the activation of Y2 receptors was effective for CA1 pyramidal cells. When the slice cultures were exposed to 6 µM kainate, the CA3 pyramidal cells displayed significant degeneration, and in this case the activation of Y1, Y2, and Y5 receptors was neuroprotective. For the kainic acid-induced degeneration of CA1 pyramidal cells, it was again found that only the Y2 receptor activation was effective. Based on the present findings, it was concluded that Y1, Y2, and Y5 receptors effectively can modify glutamate receptor-mediated neurodegeneration in the hippocampus.Key words: NPY • AMPA • kainate • neuroprotection • neurodegeneration N europeptide Y (NPY) is a 36-amino-acid peptide abundantly distributed in the brain and associated with a number of physiological and pathological conditions (1). This peptide has been shown to modulate anxiety, pain, memory, eating behavior, and many other functions in the central, as well as in the peripheral, nervous systems (1, 2). Another significant role of NPY that has become evident during the past decade is regulation of seizure activity (3).At least five NPY receptor subtypes have been identified based on different pharmacological profiles: Y1, Y2, Y4, Y5, and y6 (4). A putative Y3 receptor has also been identified (5 In the hippocampus, Y1 and Y2 receptors are highly expressed (11). Receptors of the Y1 subtype are preferentially located in granule cells of the dentate molecular layer, whereas Y2 receptors are expressed at high concentrations in the mossy fiber and Schaffer collateral fields (12). Moreover, Y5 receptor binding sites can also be found in the strata oriens and radiatum of the CA3 and CA1 areas (13,14). Presently, there is evidence for the involvement of these three NPY receptors subtypes in epilepsy. The activation of Y2 receptors suppresses seizure activity in hippocampal slices in vitro (15) and in vivo models (3). In human temporal lobe epilepsy, significant alterations in Y1 and Y2 receptor binding were observed (16). NPY Y5 receptors also seem to be involved in the suppression of seizure activity (17,18). In different animal models of epilepsy, NPY is highly expressed by granule cells and mossy fibers of the hippocampus (19,20), whereas in normal conditions only GABAergic interneurons express this peptide. Furthermore, knockout mice lacking the NPY gene develop spontaneous seizures and are more susceptible to pentylenetetrazol and kainic acid-induced motor seizures, which are inhibited by intracerebral infusion of NPY (21). Thus, these evidences suggest that N...

We investigated the functional interaction between neuropeptide Y (NPY) receptors using nerve terminals and cultured rat hippocampal neurons, and we evaluated the involvement of voltage-gated Ca(2+) channels (VGCCs) in NPY receptors-induced inhibition of Ca(2+) influx and glutamate release. The KCl-evoked release of glutamate from hippocampal synaptosomes was inhibited by 1 microM NPY and this effect was insensitive to either BIBP3226 (Y1 receptor antagonist) or L-152,804 (Y5 receptor antagonist), but was sensitive to BIIE0246 (Y2 receptor antagonist). We could also pharmacologically dissect the NPY receptors activity by using Y1, Y2 and Y5 receptor agonists ([Leu(31),Pro(34)]NPY, NPY13-36, NPY (19-23)-(Gly(1),Ser(3),Gln(4),Thr(6),Ala(31),Aib(32),Gln(34))-pancreatic polypeptide (PP), respectively), and in all the cases we observed that these agonists could inhibited the KCl-induced release of glutamate. However, the selective and specific co-activation of both Y1 and Y2 or Y2 and Y5 receptors resulted in non-additive inhibition, and this effect was prevented in the presence of the Y2 antagonist, but was insensitive to the Y1 or Y5 receptor antagonist. Moreover, as we previously showed for Y1 receptors, we also observed that the activation of Y5 receptors inhibited the glutamate release in the dentate gyrus and CA3 subregion, without significant effect in the CA1 subregion of the hippocampus. The same qualitative results were obtained when we investigated the role of NPY Y1 and Y2 receptors in modulating the changes in [Ca(2+)](i) due to KCl depolarisation in cultured hippocampal neurons. The inhibitory effect of nitrendipine (L-type VGCC blocker) or omega-conotoxin GVIA (omega-CgTx; N-type VGCC blocker) was not potentiated by the simultaneous activation of Y1 or Y2 receptors. Moreover, the exocytotic release of glutamate was inhibited by omega-agatoxin IVA (omega-Aga; P-/Q-type VGCC blocker), and this VGCC blocker did not potentiate Y1, Y2 or Y5 receptor-mediated inhibition of glutamate release. Also, the effect of ionomycin in inducing the exocytotic release of glutamate from hippocampal synaptosomes was insensitive to the activation of NPY receptors. In the present paper, we identified a role for NPY Y1, Y2 and Y5 receptors in modulating the exocytotic release of glutamate and the [Ca(2+)](i) changes in the rat hippocampus. In conditions of co-activation, there appears to exist a physiological cross-talk between Y1 and Y2 and also between Y2 and Y5 receptors, in which Y2 receptors play a predominant role. Moreover, we also show that Y1 and Y2 receptors exert their inhibitory action by directly modulating L-, N-, and P-/Q-type VGCCs, whereas the inhibition of glutamate release mediated by the Y5 receptors seems to involve P-/Q-type VGCCs.

A B S T R A C T Fragmented sarcoplasmic reticulum isolated from skeletal muscle of the rabbit has a cation-binding capacity of about 350 #eq/g of protein at neutral pH. The same binding sites bind Ca, Mg, K, and H ions and, consequently, the selective binding of Ca induced by ATP releases an amount of the other cations equivalent to the Ca taken up. At pH values below 6.2, an increasing number of binding sites are associated with H + and ATP induces exchange of Ca mostly for H +. At pH values above 6.2, the binding sites exist in the form of Mg and K, and Ca is bound in exchange for these cations. The total bound Ca + Mg + K, expressed in microequivalents of cations bound per gram of protein, is approximately constant at various pCa values, which indicates a stoichiometric exchange of Ca for the other cations. To accomplish the same degree of exchange of Ca for other cations bound, in the absence of ATP, concentrations of free Ca ++ of about 1000-fold higher than those needed in the presence of ATP are required in the medium. We cannot distinguish between a mechanism whereby Ca actively transported into a compartment of the microsomal vesicles containing also the binding sites is bound passively to these sites in exchange for Mg, K, and H and another in which ATP selectively increases the affinity of surface-binding sites for Ca. Irrespective of the mechanism of accumulation, the Ca retained does not contribute to the activity of the cation in the membrane fraction. Caffeine (10 mu) has no effect on the binding of Ca, but releases a more labile fraction of Ca, which presumably accumulates in excess of the bound Ca. Procaine (5 m~t) antagonizes the effect of caffeine. Acetylcholine and epinephrine have no effect on the binding of Ca.T h e contraction-relaxation cycle evoked in a muscle cell by depolarizing the plasma m e m b r a n e is probably regulated by a transient increase in the concentration of free calcium ions in equilibrium with the myofibrils (1-4). Ebashi (5, 6), Hasselbach (7,8), Weber (9-11) and their coworkers have shown that x3~7

The decrease in Na+ and K+ gradients resulting from the energy depletion of the synaptosomes under ischemic conditions or resulting from the inhibition of Na+, K+-ATPase by ouabain promotes the reversal of the neurotransmitter transporters. The decrease in uptake of neurotransmitters may also contribute to the rise in the extracellular concentration of different transmitters observed during brain ischemia.

We investigated the role of desensitization of alpha-amino-3-hydroxy-5-methyl-isoxazole-4-propionate (AMPA) receptors on the neurotoxicity and on the [Ca2+]i changes induced by kainate or by AMPA in cultured rat hippocampal neurons. The neuronal viability was evaluated either by the 3-(4,5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide (MTT) assay, or by analysis of cell morphology. Short-term exposure of the neurons to kainate or AMPA (30 min) was not toxic, but the exposure for 24 h to the excitotoxic drugs caused a concentration-dependent neurotoxic effect which was prevented by LY 303070, a noncompetitive AMPA receptor antagonist. In the presence of cyclothiazide (CTZ), kainate or AMPA was toxic (30 min exposure), or the toxic effect was significantly enhanced (24 h exposure), but in this case LY 303070 did not completely protect the cells against kainate-induced toxicity. The alterations in the [Ca2+]i caused by kainate or AMPA showed a great cell-to-cell variability. LY 303070 completely or partially inhibited the responses stimulated by kainate. CTZ differentially affected the responses evoked by kainate or AMPA. In the majority of hippocampal neurons, CTZ did not potentiate, or only slightly potentiated, the kainate-stimulated responses but in 11% of neurons there was a great potentiation. In AMPA-stimulated neurons, the responses were slightly or greatly potentiated in the majority of neurons, but not in all of them. The results show that AMPA and kainate may be toxic, depending on the time of exposure and on the blockade of the desensitization of the AMPA receptors. Overall, our results clearly show that there exist different populations of hippocampal neurons with different sensitivities to kainate, AMPA, CTZ and LY 303070. Moreover, the effects of CTZ on both [Ca2+]i alterations and neurotoxicity are not fully correlated.