Orexin Changes In Depression And Suicide:Gender Difference

Part I:Orexin-A (hypocretin-1) changes in depression and suicide: gender differencesObjective:Orexin (hypocretin), a neuropeptide produced in the lateral hypothalamic (LH) area, is known to play a key role in the regulation of physiological processes including food intake, sleep-awake cycle, stress response and sexual behavior, all of which show severe disturbance in depression. Significant changes in cerebrospinal fluid (CSF) orexin levels were observed in depressive suicide attempters, while animal studies have shown a bidirectional stimulating relationship between orexin and the hypothalamo-pituitary-adrenal (HPA) axis. HPA-axis is the key regulation system for stress response and hyperactive HPA activity significantly gets involved in the etiology of depression. So far changes in the orexinergic system in depression has not been studied in human brain. Therefore we aimed to elucidate the changes in orexinergic system in postmortem human brain of depression, and their relationships to the characters of depression such as suicide and sex differences. Methods:I) Orexin-A in its production area, i.e. the LH, was quantified by immunocytochemistry with image analysis in mood disorder patients and well-matched control; Ⅱ) orexin-A levels in postmortem ventricular CSF was determined by radioimmunoassay in mood disorder patients and control subjects; and Ⅲ) the alterations in orexin receptors (OXRs)-mRNA expression in orexin projection area, i.e. the anterior cingulate cortex (ACC) and the dorsolateral prefrontal cortex (DLPFC) were measured by quantitative polymerase chain reaction (qPCR).Results:The total amount of orexin-A-immuoreactivity (ir) was significantly positively correlated with the total number of orexin-A neurons in the LH (Rho=0.781, P<0.001). The total amount of LH orexin-A-ir was significantly increased in depression, but only in female patients (P=0.022). There was a trend (Rho=0.640, P=0.065) for a positive correlation between LH orexin-A-ir and corticotropin-releasing hormone (CRH)-ir in the hypothalamic paraventricular nucleus in depressive patients, but not in control subjects, whose CRH-ir had been measured in an earlier study. Such a correlation was highly significant (Rho=0.998, P=0.040) in female depressive patients, although the sample size was small. In addition, in the control subjects LH orexin-ir showed a clear diurnal fluctuation, with higher levels during the nighttime (1900h-0700h, P=0.031), which was absent in depression. There were no significant difference between CSF orexin-A in depression and control, and there was no sex difference and day night difference (all P>0.561). In a group of relatively younger patients (median age:78), both OXR1and OXR2mRNA expression were detectable in the ACC and the DLPFC, while in a group of relatively older patients (median age:40) OXR1-mRNA expression was only detectable in the ACC and OXR2-mRNA only detectable in the DLPFC. In addition, male depressive patients who had committed suicide showed significantly (P=0.015) increased OXR2-mRNA expression in the ACC compared with male controls, while male depressive patients who died of causes other than suicide did not show such a phenomenon, nor did female patients. Conclusion:Our data indicate clear sex-, age-, brain area-, and suicide-dependent changes in the orexinergic system in depression, which are closely related to CRH activity, and thus the HPA activity. 52PART Ⅱ:Orexinergic system changes in the chronic unpredictable stress rats:comparison with human mood disorderObjective:Since we have found in Part I study that the orexinergic system shows significant alterations in depression, which might have a close functional relationship with the activity of the hypothalamo-pituitary-adrenal (HPA) axis, we aimed to find out a suitable animal model for depression for further study on the underlying mechanism. We studied changes in orexinergic system in a often used animal model for depression, i.e. the chronic unpredictable stress (CUS) rats. We compared the animal data with what we have observed in human postmortem brain material, with the purpose of giving evidence if this model is suitable for research on the mechanism of the involvement of orexinergic system in the pathogenesis of depression.Methods:Adult female and male Sprague-Dawley (SD) rats were used to establish CUS model, the paradigm of which lasted for3weeks. Body weights were measured once a week during and after the CUS paradigm. After CUS the sucrose preference and open field tests were performed for evaluate depression-and/or anxiety-like behaviors. Plasma corticosterone (CORT) levels were determined by enzyme-linked immunosorbent assay. mRNA expression levels of corticotropin-releasing hormone (CRH), prepro-orexin (the precursor substance of orexin), orexin receptor1and orexin receptor2(OXR1and OXR2) in the hypothalamus and of OXR1and OXR2in the frontal cortex were measured by qPCR.Results:Both female and male SD rats showed significant decreased bodyweight gains after the second week of the CUS procedure (female CUS:P<0.035; male CUS:P<0.001). Female but not male CUS rats showed significantly decreased sucrose preference (P=0.032). The staying time in the center in the open field test (P=0.040). Plasma CORT levels both increased significantly in female (P=0.006) and male (P=0.002) CUS rats. Only in female CUS rats there was a significant positive correlation (rho=0.775, P=0.007) between the mRNA levels of CRH and prepro-orexin in the hypothalamus and a significantly increased OXR1-mRNA expression (P=0.019) in the frontal cortex.Conclusion:There was a clear sex difference in the alterations of orexinergic system in CUS SD rats. The significant correlation between prepro-orexin-mRNA and CRH-mRNA in the hypothalamus of female CUS rats was similar to what was observed in the postmortem human brain material of depressive patient. The increased OXR1-mRNA expression in the frontal cortex of female CUS rat may be related to their increased vulnerability to CUS, which was, however, not seen in human brain. Therefore the changes of orexinergic system in the CUS rats’ brain show only a part of similarity to those in human brain of depression, special attention should thus be paid to future related studies.