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. Author manuscript; available in PMC: 2016 Oct 1.
Published in final edited form as: Curr Opin Neurobiol. 2015 Feb 17;34:61–66. doi: 10.1016/j.conb.2015.01.017

Figure 2.

Figure 2

Schematic of the itch spinal cord circuit.

The initial stages of the itch-circuit in the spinal cord are characterized by the expression of neuropeptides and the post-synaptic expression of their cognate receptors. Initially Nppb is released from primary puriceptive neurons (black arrow) and activates Npr1-expressing spinal cord neurons. In turn, Npr1-neurons release GRP which activates tertiary GRPR-expressing cells. The GRPR-neurons then directly or indirectly, (broken white arrow) activate projection neurons which send projections to higher brain centers. Inhibitory Bhlhb5-interneurons (green) express Sst2a receptors and can be hyperpolarized by somatostatin. The Bhlhb5-cells are thought to release the kappa-opioid dynorphin in response to activation by primary afferent DRG stimulation. Dynorphin causes inhibition of the excitatory (red) itch pathway.