Interaction between neuropeptide Y (NPY) and brain-derived neurotrophic factor in NPY-mediated neuroprotection against excitotoxicity: a role for microglia

The neuroprotective effect of neuropeptide Y (NPY) receptor activation was investigated in organotypic mouse hippocampal slice cultures exposed to the glutamate receptor agonist alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA). Exposure of 2-week-old slice cultures, derived from 7-day-old C57BL/6 mice, to 8 mu M AMPA, for 24 h, induced degeneration of CA1 and CA3 pyramidal cells, as measured by cellular uptake of propidium iodide (PI). A significant neuroprotection, with a reduction of PI uptake in CA1 and CA3 pyramidal cell layers, was observed after incubation with a Y-2 receptor agonist [NPY(13-36), 300 nM]. This effect was sensitive to the presence of the selective Y-2 receptor antagonist (BIIE0246, 1 mu M), but was not affected by addition of TrkB-Fc or by a neutralizing antibody against brain-derived neurotrophic factor (BDNF). Moreover, addition of a Y-1 receptor antagonist (BIBP3226, 1 mu M) or a NPY-neutralizing antibody helped to disclose a neuroprotective role of endogenous NPY in CA1 region. Cultures exposed to 8 mu M AMPA for 24 h, displayed, as measured by an enzyme-linked immunosorbent assay, a significant increase in BDNF. In such cultures there was an up-regulation of neuronal TrkB immunoreactivity, as well as the presence of BDNF-immunoreactive microglial cells at sites of injury. Thus, an increase of AMPA-receptor mediated neurodegeneration, in the mouse hippocampus, was prevented by neuroprotective pathways activated by NPY receptors (Y-1 and Y-2), which can be affected by BDNF released by microglia and neurons.