An NPY Y1 receptor antagonist unmasks latent sensitization and reveals the contribution of protein kinase A and Epac to chronic inflammatory pain

W Fu, TS Nelson, DF Santos, S Doolen, JJP Gutierrez… - Pain, 2019 - journals.lww.com
W Fu, TS Nelson, DF Santos, S Doolen, JJP Gutierrez, N Ye, J Zhou, BK Taylor
Pain, 2019journals.lww.com
Peripheral inflammation produces a long-lasting latent sensitization of spinal nociceptive
neurons, that is, masked by tonic inhibitory controls. We explored mechanisms of latent
sensitization with an established four-step approach:(1) induction of inflammation;(2) allow
pain hypersensitivity to resolve;(3) interrogate latent sensitization with a channel blocker,
mutant mouse, or receptor antagonist; and (4) disrupt compensatory inhibition with a
receptor antagonist so as to reinstate pain hypersensitivity. We found that the neuropeptide …
Abstract
Peripheral inflammation produces a long-lasting latent sensitization of spinal nociceptive neurons, that is, masked by tonic inhibitory controls. We explored mechanisms of latent sensitization with an established four-step approach:(1) induction of inflammation;(2) allow pain hypersensitivity to resolve;(3) interrogate latent sensitization with a channel blocker, mutant mouse, or receptor antagonist; and (4) disrupt compensatory inhibition with a receptor antagonist so as to reinstate pain hypersensitivity. We found that the neuropeptide Y Y1 receptor antagonist BIBO3304 reinstated pain hypersensitivity, indicative of an unmasking of latent sensitization. BIBO3304-evoked reinstatement was not observed in AC1 knockout mice and was prevented with intrathecal co-administration of a pharmacological blocker to the N-methyl-D-aspartate receptor (NMDAR), adenylyl cyclase type 1 (AC1), protein kinase A (PKA), transient receptor potential cation channel A1 (TRPA1), channel V1 (TRPV1), or exchange protein activated by cAMP (Epac1 or Epac2). A PKA activator evoked both pain reinstatement and touch-evoked pERK expression in dorsal horn; the former was prevented with intrathecal co-administration of a TRPA1 or TRPV1 blocker. An Epac activator also evoked pain reinstatement and pERK expression. We conclude that PKA and Epac are sufficient to maintain long-lasting latent sensitization of dorsal horn neurons that is kept in remission by the NPYY1 receptor system. Furthermore, we have identified and characterized 2 novel molecular signaling pathways in the dorsal horn that drive latent sensitization in the setting of chronic inflammatory pain: NMDAR→ AC1→ PKA→ TRPA1/V1 and NMDAR→ AC1→ Epac1/2. New treatments for chronic inflammatory pain might either increase endogenous NPY analgesia or inhibit AC1, PKA, or Epac.
Lippincott Williams & Wilkins