3.2. Inflammatory pain influence on corticotropin releasing
factor (CRF), CRF receptor 1 (CRFR1) and blood cortisol levels.
CRF signalling is increased as a result of the presence of stress
activating the hypothalamus-pituitary-adrenal axis (HPA) to produce a
neurohormonal response. Chronic stress and negative affect derived from
this stress affects the HPA and the functioning of some brain areas such
as amygdala or nucleus accumbens. Activation of the HPA system leads to
increased corticosteroids blood levels to respond to a threat or
stressful event, but finally this increase exerts negative feedback to
the HPA system to limit this response (Herman et al., 2016; Koob et al.,
2014). Thereby, we measured mRNA and protein levels of CRF and CRFR1 in
the NAc and the Amy by qRT-PCR and western blot. In addition, we also
measured blood cortisol levels by ELISA (fig. 2).
mRNA levels of CRF in NAc and Amy where significantly increased in
CFA-treated male rats (fig 2A, p= 0.045; 2B, p=0.038) together with an
increase in the mRNA of CRFR1 only in Amy and not in NAc (fig 2C, p=
0.075; fig 2D, p= 0.046) at the endpoint of the experimental protocol.
However, further analysis of the CRFR1 protein expression showed that
this altered expression in the mRNA had no effect on the local receptor
expression (Figure 2E, p= 0.999 and figure 2F, p= 0.093). Finally, blood
cortisol levels, at this time point, were not altered in CFA-treated
male rats (fig 1G, p= 0.589).
Very interestingly, we did not observe any changes in the levels of the
CRF or CRFR1 mRNAs or proteins in the NAc or in the Amy of CFA-female
rats (figure 2H, p= 0.445; figure 2I, p= 0.177; figure 2J, p= 0.394;
figure 2K, p= 0.42; figure 2L, p= 0.818; figure 2M, p= 0.590). However,
as shown in figure 2N, females with inflammatory pain presented a
significant lower blood cortisol level than saline-treated females (p =
0.033).