Anesthesia and analgesia
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Anesthesia and analgesia · Apr 2010
Phenylephrine suppresses the pain modulation of diffuse noxious inhibitory control in rats.
Diffuse noxious inhibitory control (DNIC) is a phenomenon whereby wide dynamic range neurons are selectively and powerfully inhibited through the central nervous system by noxious stimuli heterotopically applied to a body area distant from their excitatory receptive fields. Previous work has shown that systemic administration of an alpha1-adrenoceptor agonist, phenylephrine (PE), blocked the DNIC. We hypothesized that descending inhibitory pathways mediate the DNIC mechanism and that the neural network of the DNIC loop exists in the middle brainstem, likely in a more rostral part than formerly assumed, possibly the nucleus raphe magnus (RMg). The aim of this study was to determine whether DNIC is directly modulated by PE when administered close to the RMg. ⋯ Direct administration of PE close to the RMg inhibited DNIC, thereby affecting and modulating the intrinsic pain inhibition system. These findings suggest that the RMg may be involved in the regulation of DNIC.