Biochemical markers associated with the prognosis of depression in humans are being described in the literature, whereas experimental studies in animal models in search for antidepressant strategies are lacking. The aim of this study was to evaluate platelet morphology, platelet activity and nitric oxide (NO) synthesis as possible biomarkers of depressive-like behavior by using FST alone and in the presence of fluoxetine. Naïve rats were compared to those receiving vehicle or fluoxetine at 10mg/kg i.p. in acute, subchronic and chronic administration in the FST. After behavioral assessment, platelets were isolated from blood samples and analyzed by flow cytometry to determine the platelet mitochondrial membrane potential and NO synthesis. In addition, HPLC and electron microscopy were used to examine 5-HT and tryptophan levels and morphology of platelets, respectively. Rats receiving vehicle and exposed to FST showed depressive-like behavior at all the times tested; after chronic FST rats showed a similar pattern of alteration in platelet morphology and in the studied as possible biochemical markers as those previously recognized in depressive humans. Depressive-like behavior in rats exposed to FST was prevented in the presence of fluoxetine administration at all the times tested and associated with the prevention of alterations in platelet morphology, platelet activity and NO synthesis, and/or in 5-HT concentrations. The results of the present study suggest that platelet function and morphology might be relevant markers for the prognosis of depression and the search for functional treatments. Besides, the relevance of FST as model to study this psychiatric illness is reinforced.
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