LAUSR

As the first point where sensory information enters the central nervous system, the cell types and connections in the dorsal horn are of great interest. Correct processing of sensory information within the dorsal horn relies on the balance of excitation and inhibition, although the cell types and circuitry underlying normal transmission of sensory information are still poorly understood. Despite this, there is significant evidence that changes occur in the dorsal horn in pain states, making it an attractive target for novel analgesics to stop aberrant sensory information before it reaches the brain. Progress in this area has been hindered, however, because we do not have a clear picture of how information is modulated within the dorsal horn in naive conditions, let alone in the context of injury. A number of recent studies have used genetic tools to target subpopulations of spinal neurons with the goal of understanding their function within the context of somatosensory integration. These discoveries provide important new insights, yet force us to grapple with a new of level complexity. We also need to remember that most studies to date use mouse models, and future experiments will be required to address whether these organization principles hold true in other species. In this review, we highlight some major themes that are emerging, as well as the issues that need to be addressed for a clearer understanding of the spinal processing of itch and pain, and the logic through which this information is conveyed to the brain.