Determination Of Plasma Neuroactive Substances And The Chronical Unpredictable Stress Rat Model For The Study Of Major Depressive Disorder

Part Ⅰ:Changes in plasma neuroactive amino acids and nitric oxide levels in melancholic major depressive disorderBackground:Amino acid neurotransmitters including glutamic acid (Glu), aspartic acid (Asp), glycine (Gly), and gammaaminobutyric acid (GABA), and nitric oxide (NO) are crucially involved in the pathogenesis of major depressive disorder (MDD). Here we want to establish whether changes in their plasma levels may serve as biomarker for the melancholic subtype of MDD.Methods:Plasma levels of Glu, Asp, Gly, GABA, as well as NO levels(deterined as the ratio of citrulline/L-arginine(Cit/Arg)) were measured in27medicine-naive melancholic MDD patients and30healthy control subjects matched for age and sex. The24-item Hamilton Depression Scale (HAMD) was used to rate the severity of depression, and the relationship between the clinical symptoms and the levels of these compounds was analyzed. In addition, seven out of the27MDD patients participated in a follow-up study after2months’ antidepressant treatment of Fluoxetine, whose mood and HAMD scores came back within normal range. Moreover, the correlation between plasma and cerebral-spinal fluid (CSF) levels of these compounds was analyzed in an additional group of10non-depressed subjects whose CSF and plasma samples were both available.Results:The plasma levels of Asp (P=0.003), Gly (P<0.001) and GABA (P=0.021) were significantly lower whereas the NO levels (P=0.005) were significantly higher in these melancholic MDD patients. There were no significant correlations between the plasma levels of these compounds and the HAMD scores. In addition, no significant changes in these compounds were observed after the2months treatment of fluoxetine (P>0.128). Moreover, in the additional10non-depressed subjects, no significant correlation was found between the plasma and the CSF levels of these compounds (P≥0.511), although there was a trend towards a positive correlation between plasma and CSF levels of Glu (rho=0.588, P=0.074).Conclusion:The decreased plasma levels of Asp, Gly and GABA and the increased NO levels may serve as trait-markers for the melancholic MDD, the specificity and the sensitivity of which need to be confirmed by studies in larger patient samples and in other subtypes of depessions. PART Ⅱ:Nitric oxide synthase and nitric oxide alterations in chronical stressed rats:a model for nitric oxide in major depressive disorderObjective:Previous studies have observed that the gaseous neurotransmitter nitric oxide (NO) and the neuronal NO synthase (NOS1) are involved in the pathogenesis of depression. The chronic unpredictable stress (CUS) rats model is one of the important model to study the pathogenesis of depression, however, it remained unclear whether the CUS model may express similar molecular changes, such as in the NOS1-NO system, to those in the depressive patients. In the present study, we compared the alterations in the plasma levels of NO and the NOS in the brain in rats exposed to CUS with those in medicine-naive major depressive disorder (MDD) patients, with the purpose of making clear whether the CUS rat model could be used for studying the NOS-NO system in MDD patients.Methods:In male CUS rats, we measured plasma levels of NO and corticosterone (CORT), hypothalamic NOS activity, and NOS1-immunoreactive (ir) cell densities and co-localization of NOS1with stress-related neuropeptides corticotropin-releasing hormone (CRH), vasopressin (AVP) or oxytocin (OXT) in the paraventricular nucleus (PVN). In addition, we measured plasma NO and cortisol levels in male medicine-naive MDD patients during their acute episodes. Results:In the male CUS rats the total NOS activity in the hypothalamus (P=0.018) and NOS1-ir cell density (P=0.018) in the PVN were both significantly decreased, in addition, NOS1-ir was found to be mainly co-localized in OXT-ir neurons. Interestingly, plasma NO levels were significantly increased both in male MDD patients (P<0.001) and in male CUS rats (P=0.001). Plasma CORT levels were increased in male CUS rats (P=0.001), while male MDD patients did not show a significant change in cortisol levels (P=0.427).Conclusion:Changes in plasma and hypothalamic NOS-NO systems of CUS rats and of the MDD patients are highly similar. The CUS rat model may thus be helpful to be applied for the investigation on the NO system alterations in MDD.