Corticotropin-releasing hormone and pro-opiomelanocortin gene expression in female monkeys with differences in sensitivity to stress

Background/aims: The expressions of corticotropin-releasing hormone (CRH) and pro-opiomelanocortin (POMC) were assessed in brain tissue collected from nonstressed female cynomolgus monkeys previously categorized as highly stress resilient (HSR), medium stress resilient (MSR), or stress sensitive (SS) with respect to stress-induced anovulation.

Methods: In situ hybridization and quantitative image analysis was used to measure mRNAs coding for CRH in the hypothalamic paraventricular nucleus (PVN) and thalamic center median-subfascicular complex (CM-Sf). Then, CRH neurons in the PVN were immunostained and the area of immunostaining was measured. Also, CRH fibers were immunostained in the central nucleus of the amygdala and the area of immunostaining was obtained. Finally, POMC mRNA expression was characterized in the hypothalamic infundibular nucleus. The groups were compared with ANOVA and Student-Newman-Keul's (SNK) post hoc comparison.

Results: CRH mRNA was significantly elevated in the caudal PVN in the MSR and SS animals compared to HSR animals (p < 0.05, SNK). There was a significant increase in average and total CRH-positive area in the MSR and SS groups compared to the HSR group (p < 0.05, SNK). There was also a significant increase in CRH volume in the MSR and SS groups compared to the HSR group (p < 0.05, SNK). In the CM-Sf, the average CRH optical density was significantly higher in the MSR and SS groups than in the HSR group (p < 0.05, SNK). In the central nucleus of the amygdala, the area of CRH fiber staining was significantly higher in the SS group than in the MSR or HSR groups (p < 0.05, SNK). There was no difference between the groups in POMC mRNA expression in the mediobasal hypothalamus.

Conclusion: Macaques that exhibit immediate suppression of reproductive function upon stress are considered stress sensitive. These animals have elevated CRH in the hypothalamus and limbic structures, which may play a role in suppressing the hypothalamic-gonadal axis upon stress initiation.