Differential regulation of synaptic vesicle proteins by antidepressant drugs

Exercise before pregnancy exerts protective effect on prenatal stress-induced impairment of memory, neurogenesis, and mitochondrial function in offspring

Stress during pregnancy has a negative effect on the fetus. However, maternal exercise has a positive effect on the cognitive function of the fetus and alleviates the negative effects of stress. This study aimed to demonstrate whether exercise before pregnancy has a protective effect on prenatal stress-induced impairment of memory, neurogenesis and mitochondrial function in mice offspring. In this experiment, immunohistochemistry, Western blot, measurement of mitochondria oxygen respiration, and behavior tests were performed. Spatial memory and short-term memory of the offspring from the prenatal stress with exercise were increased compared to the offspring from the prenatal stress. The numbers of doublecortin-positive and 5-bromo-2'-deoxyuridine-positive cells in the hippocampal dentate gyrus of the offspring from the prenatal stress with exercise were higher compared to the offspring from the prenatal stress. The expressions of brain-derived neurotrophic factor, postsynaptic density 95 kDa, and synaptophysin in the hippocampus of the offspring from the prenatal stress with exercise were enhanced compared to the offspring from the prenatal stress. Oxygen consumption of the offspring from the prenatal stress with exercise were higher compared to the offspring from the prenatal stress. Exercise before pregnancy alleviated prenatal stress-induced impairment of memory, neurogenesis, and mitochondrial function. Therefore, exercise before pregnancy may have a protective effect against prenatal stress of the offspring.

Rehabilitation Training after Spinal Cord Injury Affects Brain Structure and Function: From Mechanisms to Methods

Spinal cord injury (SCI) is a serious neurological insult that disrupts the ascending and descending neural pathways between the peripheral nerves and the brain, leading to not only functional deficits in the injured area and below the level of the lesion but also morphological, structural, and functional reorganization of the brain. These changes introduce new challenges and uncertainties into the treatment of SCI. Rehabilitation training, a clinical intervention designed to promote functional recovery after spinal cord and brain injuries, has been reported to promote activation and functional reorganization of the cerebral cortex through multiple physiological mechanisms. In this review, we evaluate the potential mechanisms of exercise that affect the brain structure and function, as well as the rehabilitation training process for the brain after SCI. Additionally, we compare and discuss the principles, effects, and future directions of several rehabilitation training methods that facilitate cerebral cortex activation and recovery after SCI. Understanding the regulatory role of rehabilitation training at the supraspinal center is of great significance for clinicians to develop SCI treatment strategies and optimize rehabilitation plans.

Fast antidepressant action of ketamine in mouse models requires normal VGLUT1 levels from prefrontal cortex neurons

The NMDA antagonist ketamine demonstrated a fast antidepressant activity in treatment-resistant depression. Pre-clinical studies suggest that de novo synthesis of the brain-derived neurotrophic factor (BDNF) in the PFC might be involved in the rapid antidepressant action of ketamine. Applying a genetic model of impaired glutamate release, this study aims to further identify the molecular mechanisms that could modulate antidepressant action and resistance to treatment. To that end, mice knocked-down for the vesicular glutamate transporter 1 (VGLUT1+/-) were used. We analyzed anhedonia and helpless behavior as well as the expression of the proteins linked to glutamate transmission in the PFC of mice treated with ketamine or the reference antidepressant reboxetine. Moreover, we analyzed the acute effects of ketamine in VGLUT1+/- mice pretreated with chronic reboxetine or those that received a PFC rescue expression of VGLUT1. Chronic reboxetine rescued the depressive-like phenotype of the VGLUT1+/- mice. In addition, it enhanced the expression of the proteins linked to the AMPA signaling pathway as well as the immature form of BDNF (pro-BDNF). Unlike WT mice, ketamine had no effect on anhedonia or pro-BDNF expression in VGLUT1+/- mice; it also failed to decrease phosphorylated eukaryote elongation factor 2 (p-eEF2). Nevertheless, we found that reboxetine administered as pretreatment or PFC overexpression of VGLUT1 did rescue the antidepressant-like activity of acute ketamine in the mice. Our results strongly suggest that not only do PFC VGLUT1 levels modulate the rapid-antidepressant action of ketamine, but also highlight a possible mechanism for antidepressant resistance in some patients.

The Effect of Sericin on the Cognitive Impairment, Depression, and Anxiety Caused by Learned Helplessness in Male Mice

Learned helplessness (LH) induces cognitive and emotional abnormalities via alteration of synaptic and apoptotic markers in the hippocampus. Given the sericin's neuroprotective effects on different experimental models, this study aimed to address whether sericin is able to reduce LH-induced behavioral and molecular changes in the mouse model. Sixty male mice (3 months old) were randomly divided into control, normal saline (NS), and/or different doses of sericin (Ser [100, 200, and 300 mg/kg]) for 21 days. Accordingly, the animals in NS and sericin-treated groups were subjected to 1 day learned helplessness protocol. Behavioral deficits were evaluated and alterations in both synaptic and apoptotic factors were evaluated in the hippocampus. Induction of LH was associated with behavioral changes (depression and cognitive impairment). On the other hand, the administration of sericin effectively normalized these deficits. At molecular levels, sericin increased the levels of synaptophysin, synapsin-1, and PSD-95, and decreased apoptosis in the hippocampus. Although the exact mechanisms underlying the neuroprotective effects of sericin are not fully understood, our results showed that this effect mediated via modulation of the synaptic and apoptotic proteins in the hippocampus of LH-subjected mice.

The Effect of Early Maternal Separation Combined With Adolescent Chronic Unpredictable Mild Stress on Behavior and Synaptic Plasticity in Adult Female Rats

Our aims were to evaluate the depression model of early maternal separation (MS) combined with adolescent chronic unpredictable mild stress (CUMS) in female adult SD rats to observe the behavior and the expressions of synaptic proteins in rats and to provide a reference for the screening of antidepressant drug activity. In our study, MS and CUMS were conducted to establish a dual stress model on female rats. Behavioral tests, including the sucrose preference test, open field test, and zero maze test, were used to detect depression-like and anxiety-like behavior of animals. Nissl staining was used to detect the number of neuronal cells in the hippocampus CA1 and DG regions of rats from each group. Synaptophysin (SYN), postsynaptic density-95 (PSD-95), and growth-associated protein-43 (GAP-43) expressions in the hippocampus were detected by western blot. Expression of the hippocampus SYN protein was further detected by immunohistochemistry. Rats in the MS+CUMS group presented more serious depression-like and anxiety-like behavior than in the MS group. Also, few Nissl bodies in the hippocampus CA1 and DG regions, less percentage of SYN-positive cells, and downregulated expressions of SYN, PSD-95, and GAP43 were found in the hippocampus of rats in MS+CUMS group. In conclusion, adult female rats that underwent MS and CUMS performed more critical depression-like and anxiety-like behaviors, and this process may be resulted from synaptic plasticity impairment.

Modulation of Synaptic Plasticity by Exercise Training as a Basis for Ischemic Stroke Rehabilitation

In recent years, rehabilitation of ischemic stroke draws more and more attention in the world, and has been linked to changes of synaptic plasticity. Exercise training improves motor function of ischemia as well as cognition which is associated with formation of learning and memory. The molecular basis of learning and memory might be synaptic plasticity. Research has therefore been conducted in an attempt to relate effects of exercise training to neuroprotection and neurogenesis adjacent to the ischemic injury brain. The present paper reviews the current literature addressing this question and discusses the possible mechanisms involved in modulation of synaptic plasticity by exercise training. This review shows the pathological process of synaptic dysfunction in ischemic roughly and then discusses the effects of exercise training on scaffold proteins and regulatory protein expression. The expression of scaffold proteins generally increased after training, but the effects on regulatory proteins were mixed. Moreover, the compositions of postsynaptic receptors were changed and the strength of synaptic transmission was enhanced after training. Finally, the recovery of cognition is critically associated with synaptic remodeling in an injured brain, and the remodeling occurs through a number of local regulations including mRNA translation, remodeling of cytoskeleton, and receptor trafficking into and out of the synapse. We do provide a comprehensive knowledge of synaptic plasticity enhancement obtained by exercise training in this review.

PKA Inhibitor H89 (N-[2-p-bromocinnamylamino-ethyl]-5-isoquinolinesulfonamide) Attenuates Synaptic Dysfunction and Neuronal Cell Death following Ischemic Injury

The cyclic AMP-dependent protein kinase (PKA), which activates prosurvival signaling proteins, has been implicated in the expression of long-term potentiation and hippocampal long-term memory. It has come to light that H89 commonly known as the PKA inhibitor have diverse roles in the nervous system that are unrelated to its role as a PKA inhibitor. We have investigated the role of H89 in ischemic and reperfusion injury. First, we examined the expression of postsynaptic density protein 95 (PSD95), microtubule-associated protein 2 (MAP2), and synaptophysin in mouse brain after middle cerebral artery occlusion injury. Next, we examined the role of H89 pretreatment on the expression of brain-derived neurotrophic factor (BDNF), PSD95, MAP2, and the apoptosis regulators Bcl2 and cleaved caspase-3 in cultured neuroblastoma cells exposed to hypoxia and reperfusion injury. In addition, we investigated the alteration of AKT activation in H89 pretreated neuroblastoma cells under hypoxia and reperfusion injury. The data suggest that H89 may contribute to brain recovery after ischemic stroke by regulating neuronal death and proteins related to synaptic plasticity.

Orientin improves depression-like behavior and BDNF in chronic stressed mice

SCOPE

Oxidative stress is involved in chronic stress-induced depression and the disruption of neurotransmission and neuroplasticity. Recently, orientin, a phenolic compound abundant in some fruits, millet, and herbs, has been shown to have antioxidant properties. This study investigated the potential antidepressant effects of orientin against chronic stress and its underlying mechanisms.

METHODS AND RESULTS

The chronic unpredictable mild stress (CUMS) model was used to investigate the effects of orientin on behavior and biochemical alterations in mice. After 2 weeks of the CUMS protocol, the mice were treated with orientin (20 mg/kg and 40 mg/kg, oral gavage) for 3 weeks. Administration of orientin significantly alleviated the CUMS-induced depression-like behavior, including sucrose preference reduction, locomotor activity decline, and hypomotility. Orientin treatment attenuated the oxidative stress markers and increased the concentrations of serotonin and norepinephrine in the hippocampus and prefrontal cortex of CUMS mice. Orientin treatment also increased the brain-derived neurotrophic factor and synapse-associated proteins (synaptophysin and postsynaptic density protein 95) of CUMS mice.

CONCLUSION

Orientin exerts antidepressant-like effects on CUMS mice, specifically by improving central oxidative stress, neurotransmission, and neuroplasticity. Therefore, supplementation with orientin-enriched food or fruit could be beneficial as a preventive strategy for chronic stress-induced depression.

Unpredictable chronic mild stress induces anxiety and depression-like behaviors and inactivates AMP-activated protein kinase in mice

The unpredictable chronic mild stress (UCMS) model was developed based upon the stress-diathesis hypothesis of depression. Most effects of UCMS can be reversed by antidepressants, demonstrating a strong predictive validity of this model for depression. However, the mechanisms underlying the effects induced by UCMS remain incompletely understood. Increasing evidence has shown that AMP-activated protein kinase (AMPK) regulates intracellular energy metabolism and is especially important for neurons because neurons are known to have small energy reserves. Abnormalities in the AMPK pathway disturb normal brain functions and synaptic integrity. In the present study, we first investigated the effects of UCMS on a battery of different tests measuring anxiety and depression-like behaviors in female C57BL/6N mice after 4 weeks of UCMS exposure. Stressed mice showed suppressed body weight gain, heightened anxiety, and increased immobility in the forced swim and tail suspension tests. These results are representative of some of the core symptoms of depression. Simultaneously, we observed decrease of synaptic proteins in the cortex of mice subjected to UCMS, which is associated with decreased levels of phosphorylated AMP-activated protein kinase α (AMPKα) and 3-hydroxy-3-methylglutaryl coenzyme A reductase (HMG-CoA reductase). Our findings suggest that AMPKα inactivation might be a mechanism by which UCMS causes anxiety/depression-like behaviors in mice.

Effects of curcumin on chronic, unpredictable, mild, stress-induced depressive-like behaviour and structural plasticity in the lateral amygdala of rats

Depression is a neuropsychiatric disease associated with wide ranging disruptions in neuronal plasticity throughout the brain. Curcumin, a natural polyphenolic compound of curcuma loga, has been demonstrated to be effective in the treatment of depressive-like disorders. The present study aimed to investigate the mechanisms underlying the antidepressant-like effects of curcumin in a rat model of chronic, unpredictable, mild, stress (CUMS) -induced depression. The results showed that CUMS produced depressive-like behaviours in rats, which were associated with ultra-structural changes in neurons within the lateral amygdala (LA). In addition, the expression of synapse-associated proteins such as brain-derived neurotrophic factor (BDNF), PSD-95 and synaptophysin were significantly decreased in the LA of CUMS-treated rats. Chronic administration of curcumin (40 mg/kg, i.p. 6 wk) before stress exposure significantly prevented these neuronal and biochemical alterations induced by CUMS, and suppressed depressive-like behaviours, suggesting that this neuronal dysregulation may be related to the depressive-like behaviours caused by CUMS. Together with our previous results, the current findings demonstrate that curcumin exhibits neuroprotection and antidepressant-like effects in the CUMS-induced depression model. Furthermore, this antidepressant-like action of curcumin appears to be mediated by modulating synapse-associated proteins within the LA. These findings provide new insights into the underlying mechanisms leading to neural dysfunction in depression and reveal the therapeutic potential for curcumin use in clinical trials.

Maternal and postweaning high-fat diets disturb hippocampal gene expression, learning, and memory function

We tested the hypothesis that excess saturated fat consumption during pregnancy, lactation, and/or postweaning alters the expression of genes mediating hippocampal synaptic efficacy and impairs spatial learning and memory in adulthood. Dams were fed control chow or a diet high in saturated fat before mating, during pregnancy, and into lactation. Offspring were weaned to either standard chow or a diet high in saturated fat. The Morris Water Maze was used to evaluate spatial learning and memory. Open field testing was used to evaluate motor activity. Hippocampal gene expression in adult males was measured using RT-PCR and ELISA. Offspring from high fat-fed dams took longer, swam farther, and faster to try and find the hidden platform during the 5-day learning period. Control offspring consuming standard chow spent the most time in memory quadrant during the probe test. Offspring from high fat-fed dams consuming excess saturated fat spent the least. The levels of mRNA and protein for brain-derived neurotrophic factor and activity-regulated cytoskeletal-associated protein were significantly decreased by maternal diet effects. Nerve growth factor mRNA and protein levels were significantly reduced in response to both maternal and postweaning high-fat diets. Expression levels for the N-methyl-d-aspartate receptor (NMDA) receptor subunit NR2B as well as synaptophysin were significantly decreased in response to both maternal and postweaning diets. Synaptotagmin was significantly increased in offspring from high fat-fed dams. These data support the hypothesis that exposure to excess saturated fat during hippocampal development is associated with complex patterns of gene expression and deficits in learning and memory.

Ketamine regulates the presynaptic release machinery in the hippocampus

In the search for new drug targets, that may help point the way to develop fast-acting treatments for mood disorders, we have explored molecular pathways regulated by ketamine, an NMDA receptor antagonist, which has consistently shown antidepressant response within a few hours of administration. Using Sprague-Dawley rats we investigated the effects of ketamine on the presynaptic release machinery responsible for neurotransmitter release at 1, 2 and 4 h as well as 7 days after administration of a single subanesthetic dose of ketamine (15 mg/kg). A large reduction in the accumulation of SNARE complexes was observed in hippocampal synaptic membranes after 1, 2 and 4 h of ketamine administration. In parallel, we found a selective reduction in the expression of the synaptic vesicle protein synaptotagmin I and an increase in the levels of synapsin I in hippocampal synaptosomes suggesting a mechanism by which ketamine reduces SNARE complex formation, in part, by regulating the number of synaptic vesicles in the nerve terminals. Moreover, ketamine reduced Thr(286)-phosphorylated αCaMKII and its interaction with syntaxin 1A, which identifies CaMKII as a potential target for second messenger-mediated actions of ketamine. In addition, despite previous reports of ketamine-induced inhibition of GSK-3, we were unable to detect regulation of its activity after ketamine administration. Our findings demonstrate that ketamine rapidly induces changes in the hippocampal presynaptic machinery similar to those that are obtained only with chronic treatments with traditional antidepressants. This suggests that reduction of neurotransmitter release in the hippocampus has possible relevance for the rapid antidepressant effect of ketamine.

Altered expression of synapse and glutamate related genes in post-mortem hippocampus of depressed subjects

Major depressive disorder (MDD) has been linked to changes in function and activity of the hippocampus, one of the central limbic regions involved in regulation of emotions and mood. The exact cellular and molecular mechanisms underlying hippocampal plasticity in response to stress are yet to be fully characterized. In this study, we examined the genetic profile of micro-dissected subfields of post-mortem hippocampus from subjects diagnosed with MDD and comparison subjects matched for sex, race and age. Gene expression profiles of the dentate gyrus and CA1 were assessed by 48K human HEEBO whole genome microarrays and a subgroup of identified genes was confirmed by real-time polymerase chain reaction (qPCR). Pathway analysis revealed altered expression of several gene families, including cytoskeletal proteins involved in rearrangement of neuronal processes. Based on this and evidence of hippocampal neuronal atrophy in MDD, we focused on the expression of cytoskeletal, synaptic and glutamate receptor genes. Our findings demonstrate significant dysregulation of synaptic function/structure related genes SNAP25, DLG2 (SAP93), and MAP1A, and 2-amino-3-(5-methyl-3-oxo-1,2-oxazol-4-yl)propanoic acid receptor subunit genes GLUR1 and GLUR3. Several of these human target genes were similarly dysregulated in a rat model of chronic unpredictable stress and the effects reversed by antidepressant treatment. Together, these studies provide new evidence that disruption of synaptic and glutamatergic signalling pathways contribute to the pathophysiology underlying MDD and provide interesting targets for novel therapeutic interventions.

Novel insights into depression and antidepressants: a synergy between synaptogenesis and neurogenesis?

Major depressive disorder has been associated with manifold pathophysiological changes. These include metabolic abnormalities in discreet brain areas; modifications in the level of stress hormones, neurotransmitters, and neurotrophic factors; impaired spinogenesis and synaptogenesis in crucial brain areas, such as the prefrontal cortex and the hippocampus; and impaired neurogenesis in the hippocampus. Antidepressant therapy facilitates remission by reversing most of these disturbances, indicating that these dysfunctions may participate causally in depressive symptomatology. However, few attempts have been made to integrate these different pathophysiologies into one model. The present chapter endeavors (1) to review the extant literature in the field, with particular focus on the role of neurogenesis and synaptogenesis in depression; (2) and to suggest a possible interplay between these two processes, as well as, describe the ways by which improving both neurogenesis and synaptogenesis may enable effective recovery by acting on a larger neuronal network.

Predator threat stress promotes long lasting anxiety-like behaviors and modulates synaptophysin and CB1 receptors expression in brain areas associated with PTSD symptoms

Several studies have suggested that changes in hippocampal, prefrontal cortex and amygdaloid complex function are associated with the main symptoms of Posttraumatic Stress Disorder (PTSD). Predator exposure can mimic some aspects of PSTD such as hyperarousal and chronic anxiety. However, little is known about the neural substrate involved in this model. Synaptophysin (SYP) expression has been used to evaluate synaptic plastic changes while cannabinoids have emerged as a therapeutic target for the treatment of stress- and anxiety-related disorders. The present work evaluated whether the long lasting behavioral effects evoked by predator exposure are associated to long-term changes in the expression of the Cannabinoid receptor 1 (CB1) and the synaptic protein SYP in brain areas related to the genesis of PTSD symptoms (frontal cortex, hippocampus and amygdaloid complex). Male Wistar rats were exposed to a live or a dummy cat and seven days later submitted to the elevated plus maze test. To explore possible neurobiological mechanisms involved in these effects, CB1 receptor and SYP mRNA expression were measured in the hippocampus, frontal cortex and amygdaloid complex. Single predator exposure promoted long-lasting anxiogenic effects. Seven days after predator threat CB1 mRNA expression was down regulated in the frontal cortex and amygdaloid complex while SYP gene was up regulated in the amygdaloid complex. Our results suggested that predator exposure causes long-lasting anxiogenic effects associated with hyperactivation of amygdaloid complex and modulation of CB1 receptor in brain areas related to PTSD symptoms.

Long-lasting hippocampal synaptic protein loss in a mouse model of posttraumatic stress disorder

Despite intensive research efforts, the molecular pathogenesis of posttraumatic stress disorder (PTSD) and especially of the hippocampal volume loss found in the majority of patients suffering from this anxiety disease still remains elusive. We demonstrated before that trauma-induced hippocampal shrinkage can also be observed in mice exhibiting a PTSD-like syndrome. Aiming to decipher the molecular correlates of these trans-species posttraumatic hippocampal alterations, we compared the expression levels of a set of neurostructural marker proteins between traumatized and control mice at different time points after their subjection to either an electric footshock or mock treatment which was followed by stressful re-exposure in several experimental groups. To our knowledge, this is the first systematic in vivo study analyzing the long-term neuromolecular sequelae of acute traumatic stress combined with re-exposure. We show here that a PTSD-like syndrome in mice is accompanied by a long-lasting reduction of hippocampal synaptic proteins which interestingly correlates with the strength of the generalized and conditioned fear response but not with the intensity of hyperarousal symptoms. Furthermore, we demonstrate that treatment with the serotonin reuptake inhibitor (SSRI) fluoxetine is able to counteract both the PTSD-like syndrome and the posttraumatic synaptic protein loss. Taken together, this study demonstrates for the first time that a loss of hippocampal synaptic proteins is associated with a PTSD-like syndrome in mice. Further studies will have to reveal whether these findings are transferable to PTSD patients.

Fluoxetine affects hippocampal plasticity, apoptosis and depressive-like behavior of chronically isolated rats

Plastic response and successful adaptation to stress are of particular importance in the hippocampus, where chronic stress may cause cell death instead of neural remodeling. Structural modifications that occur both in the brain of depressed patients and animal stress models may be reversed by antidepressants. Since morphological changes induced by stress and/or antidepressants could be mediated by presynaptically located proteins, determining the levels of these proteins may be a useful way to identify molecular changes associated with synaptic plasticity. In this study we analyzed the effects of chronic (six-week) social isolation and long-term (three-week) fluoxetine treatment on molecular markers of plasticity and apoptosis in the hippocampus of Wistar rats. Compartmental redistribution of NFκB transcription factor involved in the regulation of plasticity and apoptosis was also examined. To establish whether social isolation is able to evoke behavioral-like effects, which might be related to the observed molecular changes, we performed the forced swimming test. The results show that synaptosomal polysialic neural cell adhesion molecule (PSA-NCAM), a molecular plasticity marker, was increased in the hippocampus of chronically isolated rats, while subsequent treatment with fluoxetine set it at the control level. In addition, analysis of cytoplasm/mitochondria redistribution of apoptotic proteins Bax and Bcl-2 after exposure to chronic isolation stress, revealed an increase in Bcl-2 protein expression in both compartments, while fluoxetine enhanced the effect of stress only in the mitochondria. The observed alterations at the molecular level were accompanied by normalization of stress-induced behavioral changes by fluoxetine.

Escitalopram affects cytoskeleton and synaptic plasticity pathways in a rat gene-environment interaction model of depression as revealed by proteomics. Part II: environmental challenge

Large-scale investigations aimed at elucidating the molecular mechanism of action of antidepressant treatment are achievable through the application of proteomic technologies. We performed a proteomic study on the Flinders Sensitive Line (FSL), a genetically selected rat model of depression, and the control Flinders Resistant Line (FRL). To evaluate gene-environment interactions, FSL and FRL animals were separated from their mothers for 3 h from postnatal days 2 to 14 (maternal separation; MS), since early-life trauma is considered an important antecedent of depression. All groups received either escitalopram (Esc) admixed to food pellets (25 mg/kg.d) or vehicle for 1 month. Protein extracts from prefrontal/frontal cortex and hippocampus were separated by 2D electrophoresis. Proteins differentially modulated were identified by mass spectrometry. Bioinformatics analyses were performed to discover gene ontology terms associated with the modulated proteins. This paper was focused on the modifications induced by the environmental challenge of MS, both on the predisposed genetic background and on the resistant phenotype. The combination between Esc treatment and MS was investigated by comparing the MS, Esc-treated rats with rats subjected to each single procedure. In MS rats, antidepressant treatment influenced mainly proteins involved in carbohydrate metabolism in FSL rats and in vesicle-mediated transport in FRL rats. When studying the interaction between Esc and MS vs. non-separated rats, proteins playing a role in cytoskeleton organization, neuronal development, vesicle-mediated transport and synaptic plasticity were identified. The results provide further support to the available reports that antidepressant treatment affects intracellular pathways and also suggest new potential targets for future therapeutic intervention.

Chronic stress and antidepressant agomelatine induce region-specific changes in synapsin I expression in the rat brain

The antidepressant agomelatine acts as a melatonergic receptor (MT(1)/MT(2)) agonist and 5-HT(2C) receptor antagonist. Agomelatine has demonstrated efficacy in treating depression, but its neurobiological effects merit further investigation. Preclinical studies reported that agomelatine enhances adult hippocampal neurogenesis and increases expression of several neuroplasticity-associated molecules. Recently, we showed that agomelatine normalizes hippocampal neuronal activity and promotes neurogenesis in the stress-compromised brain. To characterize further the effects of this antidepressant in the stressed brain, here we investigated whether it induces changes in the expression of synapsin I (SynI), a regulator of synaptic transmission and plasticity. Adult male rats were subjected to daily footshock stress and agomelatine treatment for 3 weeks. Their brains were subsequently stained for total and phosphorylated SynI. Chronic footshock and agomelatine induced region-specific changes in SynI expression. Whereas chronic stress increased total SynI expression in all layers of the medial prefrontal cortex, agomelatine treatment abolished some of these effects. Furthermore, chronic agomelatine administration decreased total SynI expression in the hippocampal subregions of both stressed and nonstressed rats. Importantly, chronic stress decreased the fraction of phosphorylated SynI in all layers of the medial prefrontal cortex as well as selectively in the outer and middle molecular layers of the hippocampal dentate gyrus. These stress effects were at least partially abolished by agomelatine. Altogether, our data show that chronic stress and agomelatine treatment induce region-specific changes in SynI expression and its phosphorylation. Moreover, agomelatine partially counteracts the stress effects on SynI, suggesting a modulation of synaptic function by this antidepressant.

Differential expression of synaptic proteins after chronic restraint stress in rat prefrontal cortex and hippocampus

Prolonged stress has been associated with altered synaptic plasticity but little is known about the molecular components and mechanisms involved in the stress response. In this study, we examined the effect of chronic restraint stress (CRS) on the expression of genes associated with synaptic vesicle exocytosis in rat prefrontal cortex and hippocampus. Rats were stressed daily using a 21day restraint stress paradigm, with durations of half an hour or 6h. RNA and protein were extracted from the same tissue sample and used for real-time quantitative polymerase chain reaction (real-time qPCR) and immunoblotting, respectively. Focusing on the SNARE complex, we investigated the expression of the SNARE core components syntaxin 1A, SNAP-25, and VAMP2 at both transcriptional and protein levels. In addition, the expression of 10 SNARE regulatory proteins was investigated at the transcriptional level. Overall, the prefrontal cortex was more sensitive to CRS compared to the hippocampus. In prefrontal cortex, CRS induced increased mRNA levels of VAMP2, VAMP1, syntaxin 1A, snapin, synaptotagmins I and III, and synapsins I and II, whereas SNAP-25 was down-regulated after CRS. Immunoblotting demonstrated equivalent changes in protein levels of VAMP2, syntaxin 1A, and SNAP-25. In hippocampus, we found increased mRNA levels of VAMP2 and SNAP-29 and a decrease in VAMP1 levels. Immunoblotting revealed decreased VAMP2 protein levels despite increased mRNA levels. Changes in the expression of synaptic proteins may accompany or contribute to the morphological, functional, and behavioral changes observed in experimental models of stress and may have relevance to the pathophysiology of stress-related disorders.

Sex differences in synaptic plasticity in stress-responsive brain regions following chronic variable stress

Increased stress responsiveness is implicated in the etiology of mood and anxiety disorders, including depression and post-traumatic stress disorder. Additionally, stress-related affective disorders have a higher incidence in women than men. Chronic stress in rodents produces numerous neuromorphological changes in a variety of limbic brain regions. Here, we examined the sex-dependent differences in presynaptic innervation of the paraventricular nucleus of the hypothalamus (PVN), prefrontal cortex (PFC), bed nucleus of the stria terminalis (BST), and amygdala in response to chronic variable stress (CVS). Following 14 days of CVS, the presynaptic protein synaptophysin was assessed in male and female rats. Our results demonstrate that synaptophysin staining density was higher in females than males in all brain areas evaluated, indicating sex differences in the organization of presynaptic innervation. After CVS, the PVN, principal nucleus of the BST (BSTpr), and basolateral nucleus of the amygdala (BLA) displayed significantly reduced synaptophysin density in females but not males. Furthermore, males showed an increase in synaptophysin in the PVN after CVS, suggesting a sex difference in the modulation of presynaptic inputs to the PVN following chronic stress. Overall, these data suggest marked sex differences in PVN, BSTpr, and BLA presynaptic innervation as a consequence of chronic stress, which may be associated with differential stress responsivity and perhaps susceptibility to pathologies in males and females.

Fluoxetine treatment induces EAAT2 expression in rat brain

Synaptic pathology and disturbed glutamatergic neurotransmission contribute to the neurobiology of depression. Reduced expression of glutamate transporters, most importantly excitatory amino acid transporter (EAAT2), was reported in human studies and animal models. We therefore assessed the effects of antidepressant treatment upon EAAT2 expression. Male Sprague-Dawley rats received daily intraperitoneal injections of the antidepressants desipramine (DES, N = 7), fluoxetine (FLU, N = 7), tranylcypromine (TRAN, N = 5) or a saline control (CON, N = 5) for a period of 14 days. The expression of the major glial glutamate transporter EAAT2 was evaluated by semi-quantitative in situ hybridizations using a (35)S-labeled cRNA probe. Treatment with FLU significantly induced EAAT2 expression in hippocampal and cortical regions in comparison with saline injections, while DES and TRAN-applications did not exert significant effects. It can be postulated that increased expression of EAAT2 may counterbalance the tonus of glutamatergic neurotransmission. Our findings are in concert with human post-mortem findings, valid animal models of depression, antidepressive effects of NMDA-antagonists, and the glutamatergic theory of depression. Further studies should examine the effects of antidepressant treatments upon EAAT2 expression in rodent models of depression to further elucidate the underlying molecular mechanisms.

Fluoxetine administration modulates the cytoskeletal microtubular system in the rat hippocampus

A number of studies suggest that stressful conditions can induce structural alterations in the hippocampus and that antidepressant drugs may prevent such deficits. In particular, the selective serotonin reuptake inhibitor (SSRI) fluoxetine was more effective in modulating different neuronal plasticity phenomena and related molecules in rat hippocampus. Cytoskeletal microtubule dynamics are fundamental to dendrites and axons remodeling, leading to the hypothesis that fluoxetine may affect the microtubular system. However, despite reports of stress-induced alterations in microtubule dynamics by different stressors, only few studies investigated the in vivo effects of antidepressants on microtubules in specific rat brain regions. The present study investigated the dose-related (1, 5, or 10 mg/kg i.p.) effects of acute and chronic (21 days) treatments with fluoxetine on the ratio of hippocampal alpha-tubulin isoforms which is thought to reflect microtubule dynamics. Western Blot analysis was used to quantify alpha-tubulin isoforms, high-performance liquid chromatography and fluorescence detection was used to measure ex vivo monoamine metabolism. The results showed that acute fluoxetine increased the stable forms acetylated and detyrosinated alpha-tubulin. Conversely, chronic fluoxetine decreased acetylated alpha-tubulin, indicative of increased microtubule dynamics. The neuron-specific Delta2-Tubulin was increased by chronic fluoxetine indicating neuronal involvement in the observed cytoskeletal changes. Although acute and chronic fluoxetine similarly altered serotonin metabolism by inhibition of serotonin reuptake, this showed no apparent correlation to the cytoskeletal perturbations. Our findings demonstrate that fluoxetine administration modulates microtubule dynamics in rat hippocampus. The cytoskeletal effect exerted by fluoxetine may eventually culminate in promoting events of structural neuronal remodeling.

Chronic fluoxetine treatment increases expression of synaptic proteins in the hippocampus of the ovariectomized rat: role of BDNF signalling

Antidepressant drugs have been suggested to regulate synaptic transmission and structure. We hypothesised that antidepressant-induced changes in synapses and their associated proteins might become more apparent if they were measured under conditions of reduced synapse density. Therefore, in the present study, we examined whether chronic treatment with the antidepressant, fluoxetine alters expression of synaptic proteins in the hippocampus of rodents that underwent ovariectomy, a procedure which reportedly decreases synapse density in the CA1 region of the rat hippocampus. Using Western blotting, we measured changes in hippocampal expression of proteins associated with synapse structure, strength and activity namely, postsynaptic density protein 95 (PSD-95), the alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPA-R) subunit GluR1 and phosphosynapsin (Ser9), respectively. We found that fluoxetine treatment increased expression of phosphosynapsin, PSD-95 and synaptic GluR1 (but not total GluR1) in the hippocampus of ovariectomized but not sham rats. Since BDNF and signalling at its receptor, TrkB, can mediate behavioural responses to antidepressants and induce neuronal plasticity, we investigated the contribution of TrkB signalling to fluoxetine-induced changes in synaptic protein expression by using a transgenic mouse model overexpressing a truncated form of the TrkB receptor (TrkB.T1). Fluoxetine produced a small but significant increase in hippocampal PSD-95 in ovariectomized wildtype mice but not in ovariectomized TrkB.T1 mice or sham mice. In contrast to rats, fluoxetine did not alter expression of synaptic GluR1 and did not reverse ovariectomy-induced decreases in hippocampal phosphosynapsin in either genotype. Taken together, these results suggest that chronic fluoxetine treatment can increase synaptic protein expression in the hippocampus and at least some of these effects require TrkB signalling. Moreover, these effects were only observed in ovariectomized animals, thus suggesting that fluoxetine-induced increases in synaptic protein levels might only occur or become detectable when hippocampal synaptic connectivity is perturbed.

Remodeling of hippocampal spine synapses in the rat learned helplessness model of depression

BACKGROUND

Although it has been postulated for many years that depression is associated with loss of synapses, primarily in the hippocampus, and that antidepressants facilitate synapse growth, we still lack ultrastructural evidence that changes in depressive behavior are indeed correlated with structural synaptic modifications.

METHODS

We analyzed hippocampal spine synapses of male rats (n=127) with electron microscopic stereology in association with performance in the learned helplessness paradigm.

RESULTS

Inescapable footshock (IES) caused an acute and persistent loss of spine synapses in each of CA1, CA3, and dentate gyrus, which was associated with a severe escape deficit in learned helplessness. On the other hand, IES elicited no significant synaptic alterations in motor cortex. A single injection of corticosterone reproduced both the hippocampal synaptic changes and the behavioral responses induced by IES. Treatment of IES-exposed animals for 6 days with desipramine reversed both the hippocampal spine synapse loss and the escape deficit in learned helplessness. We noted, however, that desipramine failed to restore the number of CA1 spine synapses to nonstressed levels, which was associated with a minor escape deficit compared with nonstressed control rats. Shorter, 1-day or 3-day desipramine treatments, however, had neither synaptic nor behavioral effects.

CONCLUSIONS

These results indicate that changes in depressive behavior are associated with remarkable remodeling of hippocampal spine synapses at the ultrastructural level. Because spine synapse loss contributes to hippocampal dysfunction, this cellular mechanism may be an important component in the neurobiology of stress-related disorders such as depression.

PUFA induce antidepressant-like effects in parallel to structural and molecular changes in the hippocampus

Epidemiological data suggest that omega-3 polyunsaturated fatty acids (PUFA) consumption may be inversely correlated to the prevalence and severity of depression but little is known about the underlying mechanisms. In this study, we experimentally investigated whether a chronic supplementation with PUFA may induce antidepressant-like effects in mice in parallel to brain structural and molecular changes. Six weeks feeding with a PUFA-enriched diet induced behavioral changes in the Forced Swim Test (FST), the Tail Suspension Test and the Novelty-Suppressed Feeding Test. Moreover, more than 5 weeks supplementation with a PUFA blend containing 70% alpha-linolenic acid induced antidepressant-like effects in the FST with an increase in both swimming and climbing behaviors. The combination of a shorter duration of PUFA supplementation with a low dose of imipramine also induced an additive effect in the FST. Finally, PUFA supplementation was associated with an increase in the hippocampal volume, an over-expression of both synaptophysin and BDNF, and a raise in the number of newborn cells. Besides the possible modulation of brain plasticity, present results highlight the effectiveness of PUFA given alone or in combination with antidepressant drug as potential treatment of depressive disorders.

Mifepristone repairs region-dependent alteration of synapsin I in hippocampus in rat model of depression

Clinical investigations present much evidence that the glucocorticoid receptor (GR) antagonist mifepristone leads to a rapid amelioration of depression. The molecular mechanisms of mifepristone involved in the treatment of depression are not fully understood. Depression is associated with hippocampal plasticity, for which increased excitatory amino acid (EAA) release in CA3 induced by chronic stress is responsible, and glucocorticoids have a permissive role and act synergistically with EAAs in producing neuronal damage. Moreover, glucocorticoids increase synapsin I, which has a key role in the release of neurotransmitter, including EAAs. Hereby, we hypothesize that major depression involves synapsin I alteration and that mifepristone blocks this alteration. In the present study, we observed both the expression of hippocampal synapsin I and depression-associated behavior in a rat model of depression induced by chronic unpredictable mild stress (CUMS). The result showed that a region-dependent synapsin I alteration occurs in the rat hippocampus after 21 days of CUMS, that is, it increases in dentate gyrus (DG)/CA3 and decreases in the CA1 region. Correlation analysis indicated that the decrease of synapsin I in CA1 is highly correlated with the increase in the DG/CA3 subfield. Simultaneously, the region-dependent alteration of synapsin I is correlated with depression-associated behaviors. Both the alteration of synapsin I and the depression-associated behavior were rapidly restored after treatment with mifepristone for 1 week. The result suggests that the molecular mechanism underlying the treatment of depression with mifepristone is associated with the rapid repair of the synaptic alteration.

Chronic antidepressant treatment induces contrasting patterns of synaptophysin and PSA-NCAM expression in different regions of the adult rat telencephalon

Structural modifications occur in the brain of severely depressed patients and they can be reversed by antidepressant treatment. Some of these changes do not occur in the same direction in different regions, such as the medial prefrontal cortex, the hippocampus or the amygdala. Differential structural plasticity also occurs in animal models of depression and it is also prevented by antidepressants. In order to know whether chronic fluoxetine treatment induces differential neuronal structural plasticity in rats, we have analyzed the expression of synaptophysin, a protein considered a marker of synaptic density, and the expression of the polysialylated form of the neural cell adhesion molecule (PSA-NCAM), a molecule involved in neurite and synaptic remodeling. Chronic fluoxetine treatment increases synaptophysin and PSA-NCAM expression in the medial prefrontal cortex and decreases them in the amygdala. The expression of these molecules is also affected in the entorhinal, the visual and the somatosensory cortices.

Inhibition of nitric oxide synthase increases synaptophysin mRNA expression in the hippocampal formation of rats

Synaptophysin is a protein involved in the biogenesis of synaptic vesicles and budding. It has been used as an important tool to investigate plastic effects on synaptic transmission. Nitric oxide (NO) can influence plastic changes in specific brain regions related to cognition and emotion. Experimental evidence suggests that NO and synaptophysin are co-localized in several brain regions and that NO may change synaptophysin expression. Therefore, the aim of the present work was to investigate if inhibition of NO formation would change synaptophysin mRNA expression in the hippocampal formation. Male Wistar rats received single or repeated (once a day for 4 days) i.p. injections of saline or l-nitro-arginine (l-NOARG, 40mg/kg), a non-selective inhibitor of nitric oxide synthase (NOS). Twenty-four hours after the last injection the animals were sacrificed and their brains removed for 'in situ' hybridization study using (35)S-labeled oligonucleotide probe complementary to synaptophysin mRNA. The results were analyzed by computerized densitometry. Acute administration of l-NOARG induced a significant (p<0.05, ANOVA) increase in synaptophysin mRNA expression in the dentate gyrus, CA1 and CA3. The effect disappeared after repeated drug administration. No change was found in the striatum, cingulated cortex, substantia nigra or nucleus accumbens. These results reinforce the proposal that nitric oxide is involved in plastic events in the hippocampus.

Chronic fluoxetine treatment increases the expression of PSA-NCAM in the medial prefrontal cortex

Recent hypotheses suggest that changes in neuronal structure and connectivity may underlie the etiology of depression. The medial prefrontal cortex (mPFC) is affected by depression and shows neuronal remodeling during adulthood. This plasticity may be mediated by the polysialylated form of the neural cell adhesion molecule (PSA-NCAM), which is intensely expressed in the adult mPFC. As the expression of PSA-NCAM is increased by serotonin in other cerebral regions, antidepressants acting on serotonin reuptake may influence PSA-NCAM expression and thus counteract the effects of depression by modulating neuronal structural plasticity. Using immunohistochemistry, we have studied the relationship between serotoninergic fibers and PSA-NCAM expressing neurons in the adult rat mPFC and the expression of serotonin receptors in these cells. The effects of fluoxetine treatment for 14 days on mPFC PSA-NCAM expression have also been analyzed. Although serotoninergic fibers usually do not contact PSA-NCAM immunoreactive neurons, most of these cells express 5-HT3 receptors. In general, chronic fluoxetine treatment induces significant increases in the number of PSA-NCAM immunoreactive neurons and in neuropil immunostaining and coadministration of the 5-HT3 antagonist ondansetron blocks the effects of fluoxetine on PSA-NCAM expression. These results indicate that fluoxetine, acting through 5-HT3 receptors, can modulate PSA-NCAM expression in the mPFC. This modulation may mediate the structural plasticity of this cortical region and opens new perspectives on the study of the molecular bases of depression.

Expression of brain derived neurotrophic factor, activity-regulated cytoskeleton protein mRNA, and enhancement of adult hippocampal neurogenesis in rats after sub-chronic and chronic treatment with the triple monoamine re-uptake inhibitor tesofensine

The changes of gene expression resulting from long-term exposure to monoamine antidepressant drugs in experimental animals are key to understanding the mechanisms of action of this class of drugs in man. Many of these genes and their products are either relevant biomarkers or directly involved in structural changes that are perhaps necessary for the antidepressant effect. Tesofensine is a novel triple monoamine reuptake inhibitor that acts to increase noradrenaline, serotonin, and dopamine neurotransmission. This study was undertaken to examine the effect of sub-chronic (5 days) and chronic (14 days) administration of Tesofensine on the expression of brain derived neurotrophic factor (BDNF) and activity-regulated cytoskeleton protein (Arc) in the rat hippocampus. Furthermore, hippocampi from the same animals were used to investigate the effect on cell proliferation by means of Ki-67- and NeuroD-immunoreactivity. We find that chronic, but not sub-chronic treatment with Tesofensine increases BDNF mRNA in the CA3 region of the hippocampus (35%), and Arc mRNA in the CA1 of the hippocampus (65%). Furthermore, the number of Ki-67- and neuroD-positive cells increased after chronic, but not sub-chronic treatment. This study shows that Tesofensine enhances hippocampal gene expression and new cell formation indicative for an antidepressant potential of this novel drug substance.

Increased levels of SNAP-25 and synaptophysin in the dorsolateral prefrontal cortex in bipolar I disorder

OBJECTIVE

In order to identify whether the mechanisms associated with neurotransmitter release are involved in the pathologies of bipolar disorder and schizophrenia, levels of presynaptic [synaptosomal-associated protein-25 (SNAP-25), syntaxin, synaptophysin, vesicle-associated membrane protein, dynamin I] and structural (neuronal cell adhesion molecule and alpha-synuclein) neuronal markers were measured in Brodmann's area 9 obtained postmortem from eight subjects with bipolar I disorder (BPDI), 20 with schizophrenia and 20 controls.

METHODS

Determinations of protein levels were carried out using Western blot techniques with specific antibodies. Levels of mRNA were measured using real-time polymerase chain reaction.

RESULTS

In BPDI, levels of SNAP-25 (p < 0.01) and synaptophysin (p < 0.05) increased. There were no changes in schizophrenia or any other changes in BPDI. Levels of mRNA for SNAP-25 were decreased in BPDI (p < 0.05).

CONCLUSION

Changes in SNAP-25 and synaptophysin in BPDI suggest that changes in specific neuronal functions could be linked to the pathology of the disorder.

Chronic antidepressants reduce depolarization-evoked glutamate release and protein interactions favoring formation of SNARE complex in hippocampus

Glutamate neurotransmission was recently implicated in the action of stress and in antidepressant mechanisms. We report that chronic (not acute) treatment with three antidepressants with different primary mechanisms (fluoxetine, reboxetine, and desipramine) markedly reduced depolarization-evoked release of glutamate, stimulated by 15 or 25 mm KCl, but not release of GABA. Endogenous glutamate and GABA release was measured in superfused synaptosomes, freshly prepared from hippocampus of drug-treated rats. Interestingly, treatment with the three drugs only barely changed the release of glutamate (and of GABA) induced by ionomycin. In synaptic membranes of chronically treated rats we found a marked reduction in the protein-protein interaction between syntaxin 1 and Thr286-phosphorylated alphaCaM kinase II (alpha-calcium/calmodulin-dependent protein kinase II) (an interaction previously proposed to promote neurotransmitter release) and a marked increase in the interaction between syntaxin 1 and Munc-18 (an interaction proposed to reduce neurotransmitter release). Furthermore, we found a selective reduction in the expression level of the three proteins forming the core SNARE (soluble N-ethylmaleimide-sensitive factor attachment protein receptor) complex. These findings suggest that antidepressants work by stabilizing glutamate neurotransmission in the hippocampus and that they may represent a useful tool for the study of relationship between functional and molecular processes in nerve terminals.

Hippocampal synapsin I, growth-associated protein-43, and microtubule-associated protein-2 immunoreactivity in learned helplessness rats and antidepressant-treated rats

Learned helplessness rats are thought to be an animal model of depression. To study the role of synapse plasticity in depression, we examined the effects of learned helplessness and antidepressant treatments on synapsin I (a marker of presynaptic terminals), growth-associated protein-43 (GAP-43; a marker of growth cones), and microtubule-associated protein-2 (MAP-2; a marker of dendrites) in the hippocampus by immunolabeling. (1) Learned helplessness rats showed significant increases in the expression of synapsin I two days after the attainment of learned helplessness, and significant decreases in the protein expression eight days after the achievement of learned helplessness. Subchronic treatment of naïve rats with imipramine or fluvoxamine significantly decreased the expression of synapsin I. (2) Learned helplessness increased the expression of GAP-43 two days and eight days after learned helplessness training. Subchronic treatment of naïve rats with fluvoxamine but not imipramine showed a tendency to decrease the expression of synapsin I. (3) Learned helplessness rats showed increased expression of MAP-2 eight days after the attainment of learned helplessness. Naïve rats subchronically treated with imipramine showed a tendency toward increased expression of MAP-2, but those treated with fluvoxamine did not. These results indicate that the neuroplasticity-related proteins synapsin I, GAP-43, and MAP-2 may play a role in the pathophysiology of depression and the mechanisms of antidepressants.

Antidepressants differentially affect expression of complexin I and II RNA in rat hippocampus

Disturbance of synaptic transmission is currently viewed as an important pathophysiological mechanism and therapeutic target of mood disorders. Amongst other lines of evidence this theory is based on human post-mortem investigations showing differential expression of complexins. In order to discriminate between molecular correlates of the disease itself and effects of psychotropic drugs given to patients, we performed an animal trial using subchronic antidepressant treatment. Cohorts of adult male Sprague-Dawley rats were treated over a period of 14 days with intraperitoneal injections of either saline (0.9%, n=8), desipramine (15 mg/kg, n=7), fluoxetine (10 mg/kg, n=8), or tranylcypromine (10 mg/kg, n=5). Brain slices were used for in situ hybridizations with 35S labelled RNA probes of the genes complexin I, complexin II and syntaxin 1 A, the SNARE complex protein interacting with the complexins, and assessed semi-quantitatively for region-specific expression levels. Expression of complexin I was induced only in habenular nuclei after treatment with fluoxetine. In contrast, complexin II was significantly induced by desipramine and tranylcypromine, but not fluoxetine, in several brain regions. All treatment groups, but most significantly fluoxetine-treated animals, showed higher expression levels of syntaxin 1A. Antidepressants differentially affect expression levels of complexin I and more prominently complexin II and syntaxin 1A. The induction of complexin II and syntaxin 1A might strengthen the synaptic transmission at axo-dendritic or axo-axonal synapses. Previous post-mortem findings reporting on downregulation of complexins cannot be explained as mere effects of psychotropic drug treatment.

Evidence for increased expression of the vesicular glutamate transporter, VGLUT1, by a course of antidepressant treatment

The therapeutic effect of a course of antidepressant treatment is believed to involve a cascade of neuroadaptive changes in gene expression leading to increased neural plasticity. Because glutamate is linked to mechanisms of neural plasticity, this transmitter may play a role in these changes. This study investigated the effect of antidepressant treatment on expression of the vesicular glutamate transporters, VGLUT1-3 in brain regions of the rat. Repeated treatment with fluoxetine, paroxetine or desipramine increased VGLUT1 mRNA abundance in frontal, orbital, cingulate and parietal cortices, and regions of the hippocampus. Immunoautoradiography analysis showed that repeated antidepressant drug treatment increased VGLUT1 protein expression. Repeated electroconvulsive shock (ECS) also increased VGLUT1 mRNA abundance in regions of the cortex and hippocampus compared to sham controls. The antidepressant drugs and ECS did not alter VGLUT1 mRNA abundance after acute administration, and no change was detected after repeated treatment with the antipsychotic agents, haloperidol and chlorpromazine. In contrast to VGLUT1, the different antidepressant treatments did not commonly increase the expression of VGLUT2 or VGLUT3 mRNA. These data suggest that a course of antidepressant drug or ECS treatment increases expression of VGLUT1, a key gene involved in the regulation of glutamate secretion.

Chronic stress, depression and antidepressants: effects on gene transcription in the hippocampus

Depressive disorders are among the most frequent forms of mental illness. Both genetic and environmental factors, such as stress, are involved in the etiology of depression. Therefore, chronic stress paradigms in laboratory animals constitute an important tool for research in this field. The molecular bases of chronic stress/depression are largely unknown, although a large amount of information has been accumulated during recent years. Dysregulation of the hypothalamic-pituitary-adrenal (HPA) axis as well as structural and physiological alterations in the hippocampus and neocortex are known to occur. Modifications in the expression level of some genes, such as brain-derived neurotrophic factor, cAMP-response-element binding protein, serotonin receptors and HPA axis components were consistently associated in a number of experimental models. However, recent results suggest that several synaptic proteins, transcription factors and proteins involved in neuronal growth/differentiation, are also modified in their expression in experimental models of chronic stress. In general, these alterations can be reversed by treatment with antidepressants. Thus, a complex pattern of gene expression leading to stress/depression is starting to emerge. We summarize here recent findings on the alterations of gene expression in the hippocampus of chronically stressed and antidepressant treated animals.