Predominant synaptic potentiation and activation in the right central amygdala are independent of bilateral parabrachial activation in the hemilateral trigeminal inflammatory pain model of rats

Nociceptive signals originating in the periphery are conveyed to the brain through specific afferent and ascending pathways. The spino-(trigemino-)parabrachio-amygdaloid pathway is one of the principal pathways mediating signals from nociception-specific ascending neurons to the central amygdala (CeA), a limbic structure involved in aversive signal-associated emotional responses, including the emotional aspects of pain. Recent studies suggest that the right and left CeA play distinct roles in the regulation of nociceptive responses. Using a latent formalin inflammatory pain model of the rat, we analyzed the right-left differences in synaptic potentiation at the synapses formed between the fibers from the lateral parabrachial nucleus (LPB) and CeA neurons as well as those in the c-Fos expression in the LPB, CeA, and the basolateral/lateral amygdala (BLA) after formalin injection to either the right or left side of the rat upper lip. Although the single-sided formalin injection caused a significant bilatera...