Inhibitory interneurons of the spinal dorsal horn play critical roles in the processing of noxious and innocuous sensory information. They form a family of morphologically and functionally diverse neurons that likely fall into distinct subtypes. Traditional classifications rely mainly on differences in dendritic tree morphology and firing patterns. Although useful, these markers are not comprehensive and cannot be used to drive specific genetic manipulations targeted at defined subsets of neurons. Here, we have used genome-wide expression profiling of spinal dorsal horns of wild-type mice and of two strains of transcription factor-deficient mice (Ptf1a^−/−andAscl1/Mash1^−/−mice) to identify new genetic markers for specific subsets of dorsal horn inhibitory interneurons.Ptf1a^−/−mice lack all inhibitory interneurons in the dorsal horn, whereas only the late-born inhibitory interneurons are missing inAscl1^−/−mice. We found 30 genes that were significantly downregulated in the dorsal horn ofPtf1a^−/−mice. Twenty-one of those also showed reduced expression inAscl1^−/−mice.In situhybridization analyses of all 30 genes identified four genes with primarily non-overlapping expression patterns in the dorsal horn. Three genes,pDyncoding the neuropeptide dynorphin,Kcnip2encoding a potassium channel associated protein, and the nuclear receptor encoding geneRorb, were expressed inAscl1-dependent subpopulations of the superficial dorsal horn. The fourth gene,Tfap2b, encoding a transcription factor, is expressed mainly in aAscl1-independent subpopulation of the deep dorsal horn. Functional experiments in isolated spinal cords showed that theAscl1-dependent inhibitory interneurons are key players of nociceptive reflex plasticity.