strychnine and Pruritus

Scratching relieves itch, but the underlying neural mechanisms are poorly understood. We presently investigated a role for the inhibitory neurotransmitters GABA and glycine in scratch-evoked inhibition of spinal itch-signaling neurons in a mouse model of chronic dry skin itch. Superficial dorsal horn neurons ipsilateral to hindpaw dry skin treatment exhibited a high level of spontaneous firing that was significantly attenuated by cutaneous scratching, pinch and noxious heat. Scratch-evoked inhibition was nearly abolished by spinal delivery of the glycine antagonist, strychnine, and was markedly attenuated by respective GABA(A) and GABA(B) antagonists bicuculline and saclofen. Scratch-evoked inhibition was also significantly attenuated (but not abolished) by interruption of the upper cervical spinal cord, indicating the involvement of both segmental and suprasegmental circuits that engage glycine- and GABA-mediated inhibition of spinal itch-signaling neurons by noxious counterstimuli.

Topics: Action Potentials; Animals; Cervical Vertebrae; GABA Antagonists; Glycine; Mice; Mice, Inbred ICR; Models, Neurological; Nerve Block; Neural Inhibition; Neural Pathways; Neurons; Neurotransmitter Agents; Physical Stimulation; Pruritus; Signal Transduction; Spinal Nerves; Strychnine; Temperature