Modulator effects of interleukin-1beta and tumor necrosis factor-alpha on AMPA-induced excitotoxicity in mouse organotypic hippocampal slice cultures.

The inflammatory cytokines interleukin-1beta and tumor necrosis factor-alpha (TNF-alpha) have been identified as mediators of several forms of neurodegeneration in the brain. However, they can produce either deleterious or beneficial effects on neuronal function. We investigated the effects of these cytokines on neuronal death caused by exposure of mouse organotypic hippocampal slice cultures to toxic concentrations of AMPA. Either potentiation of excitotoxicity or neuroprotection was observed, depending on the concentration of the cytokines and the timing of exposure. A relatively high concentration of mouse recombinant TNF-alpha (10 ng/ml) enhanced excitotoxicity when the cultures were simultaneously exposed to AMPA and to this cytokine. Decreasing the concentration of TNF-alpha to 1 ng/ml resulted in neuroprotection against AMPA-induced neuronal death independently on the application protocol. By using TNF-alpha receptor (TNFR) knock-out mice, we demonstrated that the potentiation of AMPA-induced toxicity by TNF-alpha involves TNF receptor-1, whereas the neuroprotective effect is mediated by TNF receptor-2. AMPA exposure was associated with activation and proliferation of microglia as assessed by macrophage antigen-1 and bromodeoxyuridine immunohistochemistry, suggesting a functional recruitment of cytokine-producing cells at sites of neurodegeneration. Together, these findings are relevant for understanding the role of proinflammatory cytokines and microglia activation in acute and chronic excitotoxic conditions.

Activation of neuropeptide Y receptors is neuroprotective against excitotoxicity in organotypic hippocampal slice cultures.

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 microM AMPA (alpha-amino-3-hydroxy-5-methyl-isoxazole-4-propionate) induced neuronal degeneration, monitored by propidium iodide uptake, of granule cells and CA1 pyramidal cells. For dentate granule cells, selective activation of Y1, Y2, or Y5 receptors with 1 microM [Leu31,Pro34]NPY, 300 nM NPY13-36 or 1 microM 500 nM NPY(19-23)-(Gly1,Ser3,Gln4,Thr6,Ala31,Aib32,Gln34)-PP, respectively, had a neuroprotective effect against AMPA, whereas only the activation of Y2 receptors was effective for CA1 pyramidal cells. When the slice cultures were exposed to 6 microM 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.