Modality-specific hyperexcitability of dorsal horn neurons to mechanical stimuli in herpetic mice.

Percutaneous inoculation of mice with herpes simplex virus type-1 produces marked dynamic allodynia in the zosteriform dermatome. In this study, we examined the electrophysiological excitability of the wide-dynamic range neuron in the spinal dorsal horn and the tibial nerve in response to mechanical (brush, punctum, and pinch) stimuli in mice with herpetic allodynia. The excitatory response of wide-dynamic range neurons to brush, but neither punctum nor pinch, stimulation of the zosteriform dermatome was increased in herpetic mice. The responses of the tibial nerve to all kinds of mechanical stimuli examined were decreased. These results suggest that dynamic allodynia in the affected dermatome is because of the increased excitability of wide-dynamic range neurons, but not primary afferents, to brush stimulation.