3.3. Dynorphin/kappa opioid receptors mRNA and protein levels alterations in the mesocorticolimbic system induced by inflammatory pain.
The dynorphinergic system, which comprises the KOR and their ligand DYN, are tightly related to pain induced negative affect. Moreover, the MCLS seems to be involved in the modulation of negative affective states occurring in pain conditions. (Caputi et al., 2019; Jesús David Lorente et al., 2020; Massaly et al., 2019) Thereby, we measured the mRNA levels of pDYN and KOR in the NAc and the Amy by qRT-PCR together with its protein expression in these areas by ELISA and western blot.
On one hand, as observed in Figures 3A to 3D, the presence of inflammatory pain in male rats led to some alterations in the pDYN and KOR mRNA expression in the Amy and NAc at the end point of the behavioural characterisation. However, the protein levels remained unaltered (figure 3E to 3H). Indeed, inflammatory pain in male rats increased pDYN mRNA expression in the Amy (figure 3B, p= 0.05), and interestingly reduced KOR mRNA in the NAc (figure 3C, p= 0.026).
On the other hand, mRNA expression of pDYN and KOR 18 days afterthe inflammatory pain induction, were not significantly altered in the NAc or in the Amy (figure 3I to 3L) of female rats, although some tendencies to increase the mRNA can be perceived. Protein expression also remained unaltered (figure 3N to 3P) regardless of the DYN in the NAc that was significantly reduced in the presence of inflammatory pain (fig 3M, p = 0.003).