MODALITY-SPECIFIC HYPERSENSITIVITY OF DORSAL HORN CONVERGENT NEURONS DURING REPERFUSION OF THEIR RECEPTIVE-FIELDS ON THE RATS TAIL

In rats anaesthetised with enflurane, we examined the responses of convergent neurones in the dorsal horn of the spinal cord to noxious thermal and mechanical stimulation and to innocuous brushing, during reperfusion of their receptive fields on the tail, following transient ischaemia. Neurones were included if they responded, before induction of ischaemia, to both pinching and brushing of receptive fields restricted to the tail. Ischaemia was induced by occluding the blood supply to the tail for 30 min using a tourniquet. Compared to their own responses before ischaemia, during reperfusion almost all the neurones (17 of 20) exhibited significantly increased activity to noxious pinching and innocuous brushing of their receptive fields, following 30 and 60 min of reperfusion. Receptive field size increased markedly in 16 of 20 of the neurones tested. Only 13 of 35 of the neurones responded to noxious thermal stimulation of the tail before induction of ischaemia, and of these only two exhibited enhanced sensitivity to thermal stimulation during reperfusion. Our results indicate that there is a population of convergent neurones that demonstrates hypersensitivity to mechanical stimulation of the rat's tail, but not to noxious thermal stimulation, during reperfusion of their receptive fields following transient ischaemia.