Persistent pain has a strong emotional component. As part of the limbic system the amygdala plays a key role in the affective and autonomic aspects of behavior, the evaluation of the emotional significance of sensory stimuli, emotional learning and memory, and stress responses. A novel pathway from the pontine parabrachial region to the amygdala has been described and may provide an important link between spinal and brainstem regions that receive pain input with higher brain centers including the central nucleus of the amygdala (CeA). The role of the amygdala and CeA neurons, in particular, in persistent pain is not clear and is the subject of this proposal. The effects of persistent pain on the activity of CeA neurons will be studied using the kaolin/carrageenan inflamed knee joint model in the rat. Extracellular single unit recording in vivo and whole cell voltage- and current-clamp recordings from brain slices in vitro are used to examine functional properties of CeA neurons and to assess the influence of glutamate receptor subtypes on cellular responses.
Specific Aim 1 compares the nociceptive and non-nociceptive responses of CeA neurons before and during persistent inflammatory pain in vivo. In parallel experiments in vitro, synaptic transmission and membrane properties at two sources of input to the CeA, the pontine parabrachial complex-CeA (pPB-CeA) input and the basolateral amygdala-CeA (BLA-CeA) are analyzed.
Specific Aim 2 determines the involvement of glutamate receptors (ionotropic and metabotropic) in the inflammation-enhanced nociceptive processing in vivo. In parallel experiments in vitro, the influence of glutamate receptor subtypes is analyzed for effects on synaptic transmission including pre- versus postsynaptic influences and membrane properties after inflammation.
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