Neuropeptide Y inhibits [Ca²⁺]i changes in rat retinal neurons through NPY Y₁, Y₄, and Y₅ receptors

Neuropeptide Y (NPY) and NPY receptors are widely distributed in the CNS, including the retina, but the role of NPY in the retina is largely unknown. The aim of this study was to investigate whether NPY modulates intracellular calcium concentration ([Ca²⁺]i) changes in retinal neurons and identify the NPY receptors involved. As NPY decreased the [Ca²⁺]i amplitudes evoked by 30 mM KCl in only 50% of neurons analyzed, we divided them in two populations: NPY-non-responsive neurons (Δ2/Δ1 greater-than-or-equal 0.80) and NPY-responsive neurons (Δ2/Δ1 < 0.80), being the Δ2/Δ1 the ratio between the amplitude of [Ca²⁺]i increase evoked by the second (Δ2) and the first (Δ1) stimuli of KCl. The NPY Y₁/Y₅, Y₄, and Y₅ receptor agonists (100 nM), but not the Y₂ receptor agonist (300 nM), inhibited the [Ca²⁺]i increase induced by KCl. In addition, the inhibitory effect of NPY on evoked-[Ca²⁺]i changes was reduced in the presence of the Y₁ or the Y₅ receptor antagonists. In conclusion, NPY inhibits KCl-evoked [Ca²⁺]i increase in retinal neurons through the activation of NPY Y₁, Y₄, and Y₅ receptors. This effect may be viewed as a potential neuroprotective mechanism of NPY against retinal neurodegeneration.