Synaptic pathways and inhibitory gates in the spinal cord dorsal horn

Disinhibition in the dorsal horn accompanies peripheral nerve injury and causes the development of hypersensitivity to mild stimuli. This demonstrates the critical importance of inhibition in the dorsal horn for maintaining normal sensory signaling. Here we show that disinhibition induces a novel polysynaptic low-threshold input onto lamina I output neurons, suggesting that inhibition normally suppresses a preexisting pathway that probably contributes to abnormal pain sensations such as allodynia. In addition, we show that a significant proportion of superficial dorsal horn inhibitory neurons are activated by low-threshold input. These neurons are well situated to contribute to suppressing low-threshold activation of pain output neurons in lamina I. We further discuss several aspects of inhibition in the dorsal horn that might contribute to suppressing pathological signaling.