Fig. 4. Possible mechanisms by which spinal nerve ligation alters GABAergic modulations of Aδ- and C-fiber–mediated nociceptive input. (A ) In normal unijured state, there is a profound, most likely presynaptic GABAergic inhibitory tone on the Aδ-fiber–evoked responses and a less pronounced presynaptic inhibition also on the C-fiber–mediated responses. These are not altered in neuropathy. (B ) On the basis of the present findings, we propose enhanced GABAergic control of the polysynaptic C-fiber pathway after nerve injury. (C ) There are also likely to be GABAergic inhibitory interneurons synapsing with the projection neuron. The possible afferent drive on to the GABA neurons is omitted for clarity.