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Background Behavioral stress is recognized as a main risk factor for neuropsychiatric diseases. Converging evidence suggested that acute stress is associated with increase of excitatory transmission in certain forebrain areas. Aim of this work was to investigate the mechanism whereby acute stress increases glutamate release, and if therapeutic drugs prevent the effect of stress on glutamate release. Methodology/Findings Rats were chronically treated with vehicle or drugs employed for therapy of mood/anxiety disorders (fluoxetine, desipramine, venlafaxine, agomelatine) and then subjected to unpredictable footshock stress. Acute stress induced marked increase in depolarization-evoked release of glutamate from synaptosomes of prefrontal/frontal cortex in superfusion, and the chronic drug treatments prevented the increase of glutamate release. Stress induced rapid increase in the circulating levels of corticosterone in all rats (both vehicle- and drug-treated), and glutamate release increase was blocked by previous administration of selective antagonist of glucocorticoid receptor (RU 486). On the molecular level, stress induced accumulation of presynaptic SNARE complexes in synaptic membranes (both in vehicle- and drug-treated rats). Patch-clamp recordings of pyramidal neurons in the prefrontal cortex revealed that stress increased glutamatergic transmission through both pre- and postsynaptic mechanisms, and that antidepressants may normalize it by reducing release probability. Conclusions/Significance Acute footshock stress up-regulated depolarization-evoked release of glutamate from synaptosomes of prefrontal/frontal cortex. Stress-induced increase of glutamate release was dependent on stimulation of glucocorticoid receptor by corticosterone. Because all drugs employed did not block either elevation of corticosterone or accumulation of SNARE complexes, the dampening action of the drugs on glutamate release must be downstream of these processes. This novel effect of antidepressants on the response to stress, shown here for the first time, could be related to the therapeutic action of these drugs.

Depression is a severe and life-threatening psychiatric illness whose pathogenesis is still essentially unknown. Proteomic analysis of synaptic terminals (synaptoproteomics) in animal models of depression is a powerful approach to gain insight into the molecular mechanisms underlying vulnerability to mood disorders and the long-term action of drug treatments. Here, we employed two different animal models of depression, the Learned Helplessness rats (a classical behavioral model of depression) and a new model of depression with gene - environment interaction (Flinders Sensitive Line rats subjected to early life stress). Both animal models were treated with the antidepressant escitalopram. Analysis of their synaptoproteomic profile revealed a number of protein spots differently regulated by basic vulnerability and/or early life stress. Using this approach, we obtained information regarding biomarkers that may represent predictors of pathology or response/resistance to drug treatment, as well as potential targets for novel pharmacological and therapeutic strategies.

Purpose and Methods: Genetic studies found no evidence of classic Mendelian inheritance for human depression, while stress factors, such as early-life adverse events, have been shown to interact with a variable background of genetic vulnerability. Indeed, the experience of stressful events in childhood was found to increase the risk for the development of mood disorders in adult life [1]. Moreover, stress can profoundly affect cognitive functions and alter hippocampal synaptic plasticity. Antidepressants have been shown to induce various effects beyond neurotransmitters receptors, such as adaptive changes in gene expression and neuroplasticity. These drugs were also shown to affect long-term potentiation (LTP), a synaptic mechanism underlying learning and memory [2]. We employed an innovative experimental design, attempting at reproducing the combination of environmental adverse events and genetic susceptibility. We used the Flinders Sensitive Line (FSL) rats, a well-validated model of depression carrying genetic vulnerability associated to distinct features of pathology [3]. To reproduce early life stress events the FSL rats and their controls, the Flinders Resistant Line (FRL) rats, were subjected to a standard maternal separation protocol. Moreover, FSL and FRL rats, with or without early-life stress, were treated with escitalopram. LTP was induced in vivo in the hippocampus of FSL/FRL rats by means of high frequency stimulation (HFS) protocol. Furthermore, we purified synaptosomes from the hippocampus of FSL/FRL (not subjected to HFS) and analyzed protein-protein interactions pre- and postsynaptically, as well as changes in synaptic signaling, in order to identify molecular correlates of early-life stress and response to escitalopram treatment. Results and Conclusions: In vivo LTP was significantly lower in basal FSL rats. LTP was reduced in both FRL and FSL escitalopram-treated rats. Maternal separation did not induce significant LTP changes; however, there was a tendency toward increased LTP in FSL after maternal separation. LTP was not further changed by escitalopram in FRL maternally separated, while it was reduced, although not significantly, in FSL maternally separated treated with the antidepressant. Basal expression level of NMDA-NR1 subunit in synaptosomes of FSL was lower and early life stress upregulated NR1 levels. Interaction between CaMKII and NMDA-NR2A/B subunit was reduced in FSL rats compared with FRL, consistent with a lower synaptic NMDA receptor content. Furthermore, we found basal differences between FSL and FRL in phosphorylation levels of CaMKII and of Synapsin-1 (CaMKII site) and in the interaction between CaMKII and syntaxin-1. These results combined suggest a dysfunction of glutamate neurotransmission in FSL. Finally, basal phosphorylation levels of the stress-sensitive kinases ERK1/2 in synaptosomes of FSL were higher and early life stress failed to further increase kinases activation, contrary to the results obtained in FRL. Our experimental design superimposing early environmental adverse events on a genetic background of vulnerability allowed for functional and molecular studies in an animal model more thoroughly reproducing pathology. Our results may contribute to characterize the molecular effectors of plasticity that mediate vulnerability to stress and response to antidepressant action. References [1] Caspi A, Sugden K, Moffitt TE, et al., 2003, Influence of life stress on depression: moderation by a polymorphism in the 5-HTT gene. Science 301, 386– 389. [2] Shakesby AC, Anwyl R, Rowan MJ, 2002, Overcoming the effects of stress on synaptic plasticity in the intact hippocampus: rapid actions of serotonergic and antidepressant agents. J Neurosci 22, 3638–3644. [3] Overstreet DH, Friedman E, Math AA, et al., 2005, The Flinders Sensitive Line rat: a selectively bred putative animal model of depression. Neurosci Biobehav Rev 29, 739–759.

Introduction: Agomelatine is a potent melatonergic receptor (MT1/MT2) agonist and 5HT2C receptor antagonist with proven antidepressant efficacy in both animal models of depression and in depressed patients. In previous studies we had found that following a 2 week-chronic treatment with different antidepressants [1] depolarization-evoked release of glutamate in the hippocampus but not GABA was markedly reduced, suggesting that antidepressants may change the balance between excitatory and inhibitory neurotransmission. The functional changes in glutamatergic neurotransmission were accounted for by alterations of neurotransmitter release regulating protein-protein interactions: in particular, we found a reduction of syntaxin-1/aCalcium-CaM dependent Kinase II (aCaMKII) interaction, suggested to promote the formation of exocytotic SNARE complex, and an increase of syntaxin-1/Munc-18 interaction, that reduces formation of SNARE complex and neurotransmitter release [1,2]. Purpose: In order to determine whether also a chronic treatment with agomelatine would induce similar synaptic functional and molecular changes, we measured depolarization-evoked release of glutamate and selected presynaptic molecular mechanisms involved in the regulation of glutamatergic transmission in the hippocampus of chronically treated rats. Methods: Rats were intraperitoneally treated with agomelatine (40 mg/kg), the reference antidepressant venlafaxine (10 mg/kg) or vehicle at 5 pm (2 h before the start of the 12 h-dark-phase), for 21 days. 17 hrs after the final administrations, rat hippocampi were dissected and synaptosomes and synaptic membranes were prepared by centrifugation on Percoll gradients followed by differential centrifugation and ultracentrifugation. Glutamate release was measured in freshly purified synaptosomes by using superfusion technique [1]. aCaMKII and Munc-18 were independently immunoprecipitated with specific antibodies and coimmunoprecipitated syntaxin-1 was measured by SDS-PAGE and Western blot. SDS-resistant SNARE complex was measured by SDS-PAGE and Western blot. Results: Chronic treatment with agomelatine significantly (p

Recent findings suggested a role for soluble amyloid-beta (Abeta) peptides in Alzheimer's disease associated cognitive decline. We investigated the action of soluble, monomeric Abeta(1-40) on CaM kinase II, a kinase involved in neuroplasticity and cognition. We treated organotypic hippocampal cultures short-term (up to 4h) and long-term (5 days) with Abeta(1-40) (1nM-5microM). Abeta did not induce cell damage, apoptosis or synaptic loss. Short-term treatment down-regulated enzymatic activity of the kinase, by reducing its Thr(286) phosphorylation. In contrast, long-term treatment (1nM-microM) markedly and significantly up-regulated enzymatic activity, with peak stimulation at 10nM (three-fold). Up-regulation of activity was associated with increased expression of the alpha-isoform of CaM kinase II, increased phosphorylation at Thr(286) (activator residue) and decreased phosphorylation at Thr(305-306) (inhibitory residues). We investigated the effect of glutamate on CaM kinase II following exposure to 1 or 10nM Abeta(1-40). As previously reported, glutamate increased CaM kinase II activity. However, the glutamate effect was not altered by pretreatment of slices with Abeta. Short- and long-term Abeta treatment showed opposite effects on CaM kinase II, suggesting that long-term changes are an adaptation to the kinase early down-regulation. The marked effect of Abeta(1-40) on the kinase suggests that semi-physiological and slowly raising peptide concentrations may have a significant impact on synaptic plasticity in the absence of synaptic loss or neuronal cell death.