TFF2 and Pain: Considering that opioids had better analgesic effects in CFA and control rats than in DNP and neuropathic pain rats (Przewlocka et al., 1999; Mousa et al., 2013; Shaqura et al., 2013; Zhang et al., 2016), the loss of inhibition of SP release may contribute to opioid resistance in chronic neuropathic pain.