Phenylephrine suppresses the pain modulation of diffuse noxious inhibitory control in rats.

Background: 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).

Effects of alpha-adrenergic agonists on pain modulation in diffuse noxious inhibitory control.

Background: Diffuse noxious inhibitory control (DNIC) is thought to be mediated by neural networks in supraspinal brain structures. The descending antinociceptive system (DAS) is an important component of the DNIC neural network, but the precise structure of the neural network and the related neurotransmitters have not been examined.

Methods: The study was designed to examine whether systemic administration of the adrenergic agonists dexmedetomidine (DEX) and phenylephrine (PE) influences DNIC in the rat.