Pathway-Specific Alterations of Cortico-Amygdala Transmission in an Arthritis Pain Model.

Medial prefrontal cortex (mPFC) and amygdala are closely interconnected brain areas that play a key role in cognitive-affective aspects of pain through their reciprocal interactions. Clinical and preclinical evidence suggests that dysfunctions in the mPFC-amygdala circuitry underlie pain-related cognitive-affective deficits. However, synaptic mechanisms of pain-related changes in these long-range pathways are largely unknown. Here we used optogenetics and brain slice physiology to analyze synaptic transmission in different types of amygdala neurons driven by inputs from infralimbic (IL) and prelimbic (PL) subdivisions of the mPFC. We found that IL inputs evoked stronger synaptic inhibition of neurons in the latero-capsular division of the central nucleus (CeLC) of the amygdala than PL inputs, and this inhibition was impaired in an arthritis pain model. Furthermore, inhibition-excitation ratio in basolateral amygdala neurons was increased in the pain model in the IL pathway but not in the PL pathway. These results suggest that IL rather than PL controls CeLC activity, and that changes in this acute pain model occur predominantly in the IL-amygdala pathway.