Functional significance of nociceptive amygdala in pain-induced negative emotion

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The majority of nociception-specific projecting neurons in the spinal dorsal horn project to the lateral parabrachial nucleus(LPB) that in turn project to the capsular part of the central amygdala(CeC), forming an anatomical basis for direct link between nociception and emotion. The aim of this study was to identify the mechanism and physiological significance of the potentiated LPB-CeC transmission in chronic pain models. We analyzed the LPB-CeC transmission as well as those within other amygdaloid subnuclei in acutely prepared brain slices prepared from neuropathic pain models by spinal nerve ligation and streptozocin-induced diabetics. Estimation of mono-vesicular content, single fiber release and amplitude fluctuation at different release probabilities unequivocally demonstrated an increased number of release sites allowing multiple vesicles to be released in synchrony from single fiber terminals in potentiated synapses. These results point to a specific structural plasticity and its consolidation in the amygdala synapses in the chronic neuropathic pain, which would provide basis for the enhanced link between nociception and negative emotion.