Spinothalamic lamina I neurons selectively sensitive to histamine: a central neural pathway for itch

We found a class of lamina I spinothalamic tract (STT) neurons selectively excited by iontophoretic histamine. The responses of this class of neurons parallel the pure itching sensation this stimulus elicits in humans, and ma tch the responses of peripheral C-fibers that have similar selectivity. The se neurons have distinct central conduction velocities and thalamic project ions, indicating that they constitute a unique subset of STT neurons. These findings can explain why a lesion of the lateral STT disrupts itch along w ith pain and temperature sensations. Our findings provide strong evidence t hat itch is subserved by specific neural elements both peripherally and cen trally.