Neuropeptide Y modulates effects of bradykinin and prostaglandin E ₂ on trigeminal nociceptors via activation of the Y ₁ and Y ₂ receptors

Background and Purpose: Although previous studies have demonstrated that neuropeptide Y (NPY) modulates nociceptors, the relative contributions of the Y ₁ and Y ₂ receptors are unknown. Therefore, we evaluated the effect of Y ₁ and Y ₂ receptor activation on nociceptors stimulated by bradykinin (BK) and prostaglandin E ₂ (PGE ₂). Experimental approach: Combined immunohistochemistry (IHC) with in situ hybridization (ISH) demonstrated that Y _1- and Y _2-receptors are collocated with bradykinin ₂ (B ₂)-receptors in rat trigeminal ganglia (TG). The relative functions of the Y ₁ and Y ₂ receptors in modulating BK/PGE ₂-evoked CGRP release and increased intracellular calcium levels in cultured TG neurons were evaluated. Key results: The Y ₁ and Y ₂ receptors are co-expressed with B ₂ in TG neurons, suggesting the potential for direct NPY modulation of BK responses. Pretreatment with the Y ₁ agonist [Leu31,Pro34]-NPY, inhibited BK/PGE ₂-evoked CGRP release. Conversely, pretreatment with PYY(3-36), a Y ₂ agonist, increased BK/PGE ₂ evoked CGRP release. Treatment with NPY evoked an overall inhibitory effect, although of lesser magnitude. Similarly, [Leu31,Pro34]-NPY inhibited BK/PGE ₂-evoked increases in intracellular calcium levels whereas PYY(3-36) increased responses. NPY inhibition of BK/PGE ₂-evoked release of CGRP was reversed by the Y ₁ receptor antagonist, BIBO3304, and higher concentrations of BIBO3304 significantly facilitated CGRP release. The Y ₂ receptor antagonist, BIIE0246, enhanced the inhibitory NPY effects. Conclusions and implications: These results demonstrate that NPY modulation of peptidergic neurons is due to net activation of inhibitory Y ₁ and excitatory Y ₂ receptor systems. The relative expression or activity of these opposing receptor systems may mediate dynamic responses to injury and pain.