抄録
The ascending pathway from the dorsal horn to the laterocapsular part (CeLC) of the central amygdala via the nucleus parabrachialis (PB) plays an important role in the pain-related negative emotion. We have already demonstrated that excitatory PB-CeLC transmission is potentiated in a manner independent of NMDA receptor components in rats with chronic neuropathic pain persisting for a week (Ikeda et al., Pain, 2007). Here we analyzed the course of the PB-CeLC transmission during the first post-operational week to reveal the establishment process of this potentiation. The L5 spinal nerve of young Wistar rats was ligated unilaterally and the paw withdraw threshold was assessed with von Frey filaments. We recorded excitatory postsynaptic currents evoked by PB afferent stimulation in the CeLC at various post-operational days (D) in the brain slices. The tactile allodynia of the hindpaw ipsilateral to the ligation appeared at D0.25 and lasted to D7. In contrast, the PB-CeLC transmission was potentiated in two steps: early (D0.25-1) and late (D2-7) phases. The former was observed in the bilateral CeLC whereas the latter was observed only in the contralateral CeLC. The potentiation at both phases remained even in the presence of NMDA receptor blockers. These results indicate that the side-specific synaptic potentiation in the CeLC resulting from enhanced nociceptive inputs via the spinal cord-PB-CeLC pathway, which is essentially contralaterally projecting, takes place at 1.5-2 days after the onset of persistent pain. [J Physiol Sci. 2008;58 Suppl:S134]
