C3 and constipation disorder: To achieve this, alterations in the key parameters for the cyclic adenosine monophosphate (cAMP) downstream signaling pathway were analyzed in the mid-colons of the C3 KO and Lop-induced constipation models because it is commonly involved in the downstream signaling pathway of the C3 receptor and Lop binding opioid receptor [24,25] (Figure 8A and Table S1).