[Ketamine and suicidal behavior: Contribution of animal models of aggression-impulsivity to understanding its mechanism of action]. / Kétamine et suicidalité : modèles animaux pour comprendre son mécanisme d'action.

More than two-thirds of suicides occur during a major depressive episode. Acting out prevention measures and therapeutic options to manage the suicidal crisis are limited. The impulsive-aggressive dimensions are vulnerability factors associated with suicide in patients suffering from a characterized depressive episode: this can be a dimension involved in animals. Impulsive and aggressive rodent models can help analyze, at least in part, the neurobiology of suicide and the beneficial effects of treatments. Ketamine, a glutamatergic antagonist, by rapidly improving the symptoms of depressive episodes, would help reduce suicidal thoughts in the short term. Animal models share with humans impulsive and aggressive endophenotypes modulated by the serotonergic system (5-HTB receptor, MAO-A enzyme), neuroinflammation or the hypothalamic-pituitary-adrenal axis and stress. Significant effects of ketamine on these endophenotypes remain to be demonstrated.

A complex relation between levels of adult hippocampal neurogenesis and expression of the immature neuron marker doublecortin.

We investigated the mechanisms underlying the effects of the antidepressant fluoxetine on behavior and adult hippocampal neurogenesis (AHN). After confirming our earlier report that the signaling molecule ß-arrestin-2 (ß-Arr2) is required for the antidepressant-like effects of fluoxetine, we found that the effects of fluoxetine on proliferation of neural progenitors and survival of adult-born granule cells are absent in the ß-Arr2 knockout (KO) mice. To our surprise, fluoxetine induced a dramatic upregulation of the number of doublecortin (DCX)-expressing cells in the ß-Arr2 KO mice, indicating that this marker can be increased even though AHN is not. We discovered two other conditions where a complex relationship occurs between the number of DCX-expressing cells compared to levels of AHN: a chronic antidepressant model where DCX is upregulated and an inflammation model where DCX is downregulated. We concluded that assessing the number of DCX-expressing cells alone to quantify levels of AHN can be complex and that caution should be applied when label retention techniques are unavailable.

Intrahippocampal injection of a selective blocker of NMDA receptors containing the GluN2B subunit, Ro25-6981, increases glutamate neurotransmission and induces antidepressant-like effects.

Major depressive disorder (MDD) is a serious public health problem, as it is the most common psychiatric disorder worldwide. Antidepressant drugs increase adult hippocampal neurogenesis, which is required to induce some behavioral effects of antidepressants. Adult-born granule cells in the dentate gyrus (DG) and the glutamate receptors subunits 2 (GluN2B) subunit of N-methyl-D-aspartate (NMDA) ionotropic receptors play an important role in these effects. However, the precise neurochemical role of the GluN2B subunit of the NMDA receptor on adult-born GCs for antidepressant-like effects has yet to be elucidated. The present study aims to explore the contribution of the GluN2B-containing NMDA receptors in the ventral dentate gyrus (vDG) to the antidepressant drug treatment using a pharmacological approach. Thus, (αR)-(4-hydroxyphenyl)-(ßS)-methyl-4-(phenylmethyl)-1-piperidinepropanol (Ro25-6981), a selective antagonist of the GluN2B subunit, was acutely administered locally into the ventral DG (vDG, 1 µg each side) following a chronic fluoxetine (18 mg/kg/day) treatment-known to increase adult hippocampal neurogenesis-in a mouse model of anxiety/depression. Responses in a neurogenesis-dependent task, the novelty suppressed feeding (NSF), and neurochemical consequences on extracellular glutamate and gamma-aminobutyric acid (GABA) levels in the vDG were measured. Here, we show a rapid-acting antidepressant-like effect of local Ro25-6981 administration in the NSF independent of fluoxetine treatment. Furthermore, we revealed a fluoxetine-independent increase in the glutamatergic transmission in the vDG. Our results suggest behavioral and neurochemical effects of GluN2B subunit independent of serotonin reuptake inhibition.

Pharmacological Mechanism of Ketamine in Suicidal Behavior Based on Animal Models of Aggressiveness and Impulsivity: A Narrative Review.

Around 700,000 people die from suicide each year in the world. Approximately 90% of suicides have a history of mental illness, and more than two-thirds occur during a major depressive episode. Specific therapeutic options to manage the suicidal crisis are limited and measures to prevent acting out also remain limited. Drugs shown to reduce the risk of suicide (antidepressants, lithium, or clozapine) necessitate a long delay of onset. To date, no treatment is indicated for the treatment of suicidality. Ketamine, a glutamate NMDA receptor antagonist, is a fast-acting antidepressant with significant effects on suicidal ideation in the short term, while its effects on suicidal acts still need to be demonstrated. In the present article, we reviewed the literature on preclinical studies in order to identify the potential anti-suicidal pharmacological targets of ketamine. Impulsive-aggressive traits are one of the vulnerability factors common to suicide in patients with unipolar and bipolar depression. Preclinical studies in rodent models with impulsivity, aggressiveness, and anhedonia may help to analyze, at least in part, suicide neurobiology, as well as the beneficial effects of ketamine/esketamine on reducing suicidal ideations and preventing suicidal acts. The present review focuses on disruptions in the serotonergic system (5-HTB receptor, MAO-A enzyme), neuroinflammation, and/or the HPA axis in rodent models with an impulsive/aggressive phenotype, because these traits are critical risk factors for suicide in humans. Ketamine can modulate these endophenotypes of suicide in human as well as in animal models. The main pharmacological properties of ketamine are then summarized. Finally, numerous questions arose regarding the mechanisms by which ketamine may prevent an impulsive-aggressive phenotype in rodents and suicidal ideations in humans. Animal models of anxiety/depression are important tools to better understand the pathophysiology of depressed patients, and in helping develop novel and fast antidepressant drugs with anti-suicidal properties and clinical utility.

Intranasal (R, S)-ketamine delivery induces sustained antidepressant effects associated with changes in cortical balance of excitatory/inhibitory synaptic activity.

In 2019, an intranasal (IN) spray of esketamine SPRAVATO® was approved as a fast-acting antidepressant by drug Agencies US FDA and European EMA. At sub-anesthetic doses, (±)-ketamine, a non-competitive glutamate N-methyl-d-aspartate (NMDA) receptor antagonist, increases the overall excitability of the medial prefrontal cortex (mPFC), an effect being essential for its rapid antidepressant activity. We wondered if this effect of ketamine could come from changes in the balance between neuronal excitation and inhibition (E/I balance) in the mPFC. Here, we performed a preclinical approach to study neurochemical and behavioral responses to a single IN ketamine dose in BALB/cJ mice, a strain more sensitive to stress. By using in vivo microdialysis, we measured cortical E/I balance as the ratio between glutamate to GABA extracellular levels 24 h post-ketamine. We found, for the first time, that E/I balance was shifted in favor of excitation rather than inhibition in the mPFC but more robustly with IN KET than with a single intraperitoneal (IP) dose. Increases in plasma and brain ketamine, norketamine and HNKs levels suggest different metabolic profiles of IP and IN ketamine 30 min post-dose. A significantly larger proportion of ketamine and HNKs in the brain are derived from the IN route 30 min post-dose. It may be linked to the greater magnitude in E/I ratio following IN delivery relative to IP at t24 h. This study suggests that both IP and IN are effective brain delivery methods inducing similar sustained antidepressant efficacy of KET, but the way they induced neurotransmitter changes is slightly different.

Cortical and raphe GABAA, AMPA receptors and glial GLT-1 glutamate transporter contribute to the sustained antidepressant activity of ketamine.

At sub-anaesthetic doses, ketamine, a non competitive N-methyl-d-aspartate (NMDA) receptor antagonist, has demonstrated remarkable and rapid antidepressant (AD) efficacy in patients with treatment-resistant depression (TRD). However, its mechanism of action of ketamine is not fully understood. Since comorbid depression and anxiety disorders often occur, GABAergic/inhibitory and glutamatergic/excitatory drug treatments may be co-administered in these patients. Information regarding this combination is critical to establish efficacy or treatment restrictions to maximize translation from animal models to TRD patients, effectiveness and safety. To assess the specific role of excitatory/inhibitory neurotransmission in the medial prefrontal cortex-raphe nuclei (mPFC-DRN) circuit in the sustained antidepressant-like activity (AD) of ketamine (at t24h post dose), AMPA-R antagonist (intra-DRN) and GABAA-R agonist (intra-mPFC) were co-administered with ketamine (intra-mPFC). Twenty-four hours later, responses in the forced swim test (FST) and neurochemical consequences on extracellular mPFC glutamate, GABA and 5-HT levels were measured in BALB/cJ mice. Intra-DRN NBQX prevented the sustained AD-like activity of ketamine evidenced by decreases in FST swimming duration and blunted cortical 5-HText and Gluext. Intra-mPFC muscimol blocked ketamine AD-like activity and its effects on cortical 5-HText. Moreover, a selective glutamate transporter GLT-1 inhibitor, dihydrokainic acid (DHK) locally perfused into the mPFC produced an AD-like activity at t24h associated with robust increases in mPFC 5-HText, Gluext and GABAext. Thus, the sustained AD-like activity of ketamine is triggered by AMPA-R activation in the DRN and 5-HT - glutamate release in the mPFC, but limited by GABAA-R activation - GABA release in the mPFC. The local blockade of GLT-1 in the mPFC also mimics the rapid responses of ketamine, thus highlighting the role of neuronal-glial adaptation in these effects. These results also suggests the need to test for the concomitant prescription of ketamine and BZD to see whether its sustained antidepressant activity is maintained in TRD patients.

Role of adult-born granule cells in the hippocampal functions: Focus on the GluN2B-containing NMDA receptors.

Adult-born granule cells constitute a small subpopulation of the dentate gyrus (DG) in the hippocampus. However, they greatly influence several hippocampus-dependent behaviors, suggesting that adult-born granule cells have specific roles that influence behavior. In order to understand how exactly these adult-born granule cells contribute to behavior, it is critical to understand the underlying electrophysiology and neurochemistry of these cells. Here, this review simultaneously focuses on the specific electrophysiological properties of adult-born granule cells, relying on the GluN2B subunit of NMDA glutamate receptors, and how it influences neurochemistry throughout the brain. Especially in a critical age from 4 to 6 weeks post-division during which they modulate hippocampal functions, adult-born granule cells exhibit a higher intrinsic excitability and an enhanced long-term potentiation. Their stimulation decreases the overall excitation/inhibition balance of the DG via recruitment of local interneurons, and in the CA3 region of the hippocampus. However, the link between neurochemical effects of adult-born granule cells and behavior remain to be further examined.

Rapid analysis of glutamate, glutamine and GABA in mice frontal cortex microdialysis samples using HPLC coupled to electrospray tandem mass spectrometry.

In vivo measurement of multiple neurotransmitters is highly interesting but remains challenging in the field of neuroscience. GABA and l-glutamic acid are the major inhibitory and excitatory neurotransmitters, respectively, in the central nervous system, and their changes are related to a variety of diseases such as anxiety and major depressive disorder. This study described a simple method allowing the simultaneous LC-MS/MS quantification of l-glutamic acid, glutamine and GABA. Analytes were acquired from samples of the prefrontal cortex by microdialysis technique in freely moving mice. The chromatographic separation was performed by hydrophilic interaction liquid chromatography (HILIC) with a core-shell ammonium-sulfonic acid modified silica column using a gradient elution with mobile phases consisting of a 25 mM pH 3.5 ammonium formate buffer and acetonitrile. The detection of l-glutamic acid, glutamine and GABA, as well as the internal standards [d6]-GABA and [d5]-glutamate was performed on a triple quadrupole mass spectrometer in positive electrospray ionization and multiple reaction monitoring mode. The limit of quantification was 0.63 ng/ml for GABA, 1.25 ng/ml for l-glutamic acid and 3.15 ng/ml for glutamine, and the intra-day and inter-day accuracy and precision have been assessed for the three analytes. Therefore, the physiological relevance of the method was successfully applied for the determination of basal extracellular levels and potassium-evoked release of these neuroactive substances in the prefrontal cortex in adult awake C57BL/6 mice.

Optogenetic activation of granule cells in the dorsal dentate gyrus enhances dopaminergic neurotransmission in the Nucleus Accumbens.

The dentate gyrus (DG) has distinct roles along its dorso-ventral axis. In the mouse, we recently demonstrated that dorsal DG (dDG) stimulation enhances exploratory behavior (Kheirbek et al., 2013). Dopamine (DA) release in the Nucleus Accumbens (NAcc), which belongs to the reward system, could be a key target of dDG mediating this motivation-related behavior. Here, an optogenetic stimulation of either ventral (vDG) or dDG granule cells was coupled with NAcc DA release monitoring using in vivo microdialysis. Only dDG stimulation enhanced NAcc DA release, indicating differential interconnections between dDG and vDG to the reward system.

S 47445 Produces Antidepressant- and Anxiolytic-Like Effects through Neurogenesis Dependent and Independent Mechanisms.

Glutamatergic dysfunctions are observed in the pathophysiology of depression. The glutamatergic synapse as well as the AMPA receptor's (AMPAR) activation may represent new potential targets for therapeutic intervention in the context of major depressive disorders. S 47445 is a novel AMPARs positive allosteric modulator (AMPA-PAM) possessing procognitive, neurotrophic properties and enhancing synaptic plasticity. Here, we investigated the antidepressant/anxiolytic-like effects of S 47445 in a mouse model of anxiety/depression based on chronic corticosterone administration (CORT) and in the Chronic Mild Stress (CMS) model in rats. Four doses of S 47445 (0.3 to 10 mg/kg, oral route, 4 and 5 weeks, respectively) were assessed in both models. In mouse, behavioral effects were tested in various anxiety-and depression-related behaviors : the elevated plus maze (EPM), open field (OF), splash test (ST), forced swim test (FST), tail suspension test (TST), fur coat state and novelty suppressed feeding (NSF) as well as on hippocampal neurogenesis and dendritic arborization in comparison to chronic fluoxetine treatment (18 mg/kg, p.o.). In rats, behavioral effects of S 47445 were monitored using sucrose consumption and compared to those of imipramine or venlafaxine (10 mg/kg, i.p.) during the whole treatment period and after withdrawal of treatments. In a mouse model of genetic ablation of hippocampal neurogenesis (GFAP-Tk model), neurogenesis dependent/independent effects of chronic S 47445 treatment were tested, as well as BDNF hippocampal expression. S 47445 reversed CORT-induced depressive-like state by increasing grooming duration and reversing coat state's deterioration. S 47445 also decreased the immobility duration in TST and FST. The highest doses (3 and 10 mg/kg) seem the most effective for antidepressant-like activity in CORT mice. Furthermore, S 47445 significantly reversed the anxiety phenotype observed in OF (at 1 mg/kg) and EPM (from 1 mg/kg). In the CMS rat model, S 47445 (from 1 mg/kg) demonstrated a rapid onset of effect on anhedonia compared to venlafaxine and imipramine. In the CORT model, S 47445 demonstrated significant neurogenic effects on proliferation, survival and maturation of hippocampal newborn neurons at doses inducing an antidepressant-like effect. It also corrected CORT-induced deficits of growth and arborization of dendrites. Finally, the antidepressant/anxiolytic-like activities of S 47445 required adult hippocampal neurogenesis in the novelty suppressed feeding test contrary to OF, EPM and ST. The observed increase in hippocampal BDNF levels could be one of the mechanisms of S 47445 responsible for the adult hippocampal neurogenesis increase. Altogether, S 47445 displays robust antidepressant-anxiolytic-like properties after chronic administration through neurogenesis dependent/independent mechanisms and neuroplastic activities. The AMPA-PAM S 47445 could have promising therapeutic potential for the treatment of major depressive disorders or generalized anxiety disorders.

Investigating potentially salvageable penumbra tissue in an in vivo model of transient ischemic stroke using sodium, diffusion, and perfusion magnetic resonance imaging.

BACKGROUND: Diffusion magnetic resonance imaging (MRI) is the current-state-of-the-art technique to clinically investigate acute (0-24 h) ischemic stroke tissue. However, reduced apparent diffusion coefficient (ADC)-considered a marker of tissue damage-was observed to reverse spontaneously during the subacute stroke phase (24-72 h) which means that low ADC cannot be used to reflect the damaged tissue after 24 h in experimental and clinical studies. One reason for the change in ADC is that ADC values drop with cytotoxic edema (acute phase) and rise when vasogenic edema begins (subacute phase). Recently, combined 1H- and 23Na-MRI was proposed as a more accurate approach to improve delineation between reversible (penumbra) and irreversible ischemic injury (core). The aim of this study was to investigate the effects of reperfusion on the ADC and the sodium MRI signal after experimental ischemic stroke in rats in well-defined areas of different viability levels of the cerebral lesion, i.e. core and penumbra as defined via perfusion and histology. Transient middle cerebral artery occlusion was induced in male rats by using the intraluminal filament technique. MRI sodium, perfusion and diffusion measurement was recorded before reperfusion, shortly after reperfusion and 24 h after reperfusion. The animals were reperfused after 90 min of ischemia. RESULTS: Sodium signal in core did not change before reperfusion, increased after reperfusion while sodium signal in penumbra was significantly reduced before reperfusion, but showed no changes after reperfusion compared to control. The ADC was significantly decreased in core tissue at all three time points compared to contralateral side. This decrease recovered above commonly applied viability thresholds in the core after 24 h. CONCLUSIONS: Reduced sodium-MRI signal in conjunction with reduced ADC can serve as a viability marker for penumbra detection and complement hydrogen diffusion- and perfusion-MRI in order to facilitate time-independent assessment of tissue fate and cellular bioenergetics failure in stroke patients.

A Lack of Serotonin 1B Autoreceptors Results in Decreased Anxiety and Depression-Related Behaviors.

The effects of serotonin (5-HT) on anxiety and depression are mediated by a number of 5-HT receptors, including autoreceptors that act to inhibit 5-HT release. While the majority of anxiety and depression-related research has focused on the 5-HT1A receptor, the 5-HT1B receptor has a lesser known role in modulating emotional behavior. 5-HT1B receptors are inhibitory GPCRs located on the presynaptic terminal of both serotonin and non-serotonin neurons, where they act to inhibit neurotransmitter release. The autoreceptor population located on the axon terminals of 5-HT neurons is a difficult population to study due to their diffuse localization throughout the brain that overlaps with 5-HT1B heteroreceptors (receptors located on non-serotonergic neurons). In order to study the contribution of 5-HT1B autoreceptors to anxiety and depression-related behaviors, we developed a genetic mouse model that allows for selective ablation of 5-HT1B autoreceptors. Mice lacking 5-HT1B autoreceptors displayed the expected increases in extracellular serotonin levels in the ventral hippocampus following administration of a selective serotonin reuptake inhibitor. In behavioral studies, they displayed decreased anxiety-like behavior in the open field and antidepressant-like effects in the forced swim and sucrose preference tests. These results suggest that strategies aimed at blocking 5-HT1B autoreceptors may be useful for the treatment of anxiety and depression.

Nrf2-signaling and BDNF: A new target for the antidepressant-like activity of chronic fluoxetine treatment in a mouse model of anxiety/depression.

Several studies have shown that Nrf2, a major redox-sensitive transcription factor involved in the cellular defense against oxidative stress, increases susceptibility to depressive-like behavior. However, little is known about the influence of antidepressant drugs on Nrf2 signaling and expression of its target genes (GCLC, NQO1, HO-1) in the brain. We found that chronic treatment of a mouse model of anxiety/depression (CORT model) with a selective serotonin reuptake inhibitor (SSRI, fluoxetine, 18mg/kg/day) reversed CORT-induced anxiety/depression-like behavior in mice. Chronic fluoxetine treatment restored CORT-induced decreases in Nrf2 protein levels and its target genes in the cortex and hippocampus. Furthermore, we found that chronic fluoxetine also increased brain derived neurotrophic factor (BDNF) protein levels in cortex and hippocampus of CORT-treated Nrf2 knockout mice (KO, Nrf2(-/-)). Taken together, these data suggest that Nrf2 signaling contributes to fluoxetine-induced neuroprotection via an unexpected mechanism involving 5-HT transporter SERT blockade, and not through enhancement of BDNF expression.

Distinct Circuits Underlie the Effects of 5-HT1B Receptors on Aggression and Impulsivity.

Impulsive and aggressive behaviors are both modulated by serotonergic signaling, specifically through the serotonin 1B receptor (5-HT1BR). 5-HT1BR knockout mice show increased aggression and impulsivity, and 5-HT1BR polymorphisms are associated with aggression and drug addiction in humans. To dissect the mechanisms by which the 5-HT1BR affects these phenotypes, we developed a mouse model to spatially and temporally regulate 5-HT1BR expression. Our results demonstrate that forebrain 5-HT1B heteroreceptors expressed during an early postnatal period contribute to the development of the neural systems underlying adult aggression. However, distinct heteroreceptors acting during adulthood are involved in mediating impulsivity. Correlating with the impulsivity, dopamine in the nucleus accumbens is elevated in the absence of 5-HT1BRs and normalized following adult rescue of the receptor. Overall, these data show that while adolescent expression of 5-HT1BRs influences aggressive behavior, a distinct set of 5-HT1B receptors modulates impulsive behavior during adulthood.

Vortioxetine for the treatment of major depressive disorder.

Vortioxetine (Brintellix(®), 1-[2-(2,4-dimethylphenyl-sulfanyl)-phenyl]-piperazine) is a multimodal antidepressant targeting the 5-HT1A, 5-HT1B, 5-HT1D, 5-HT3, 5-HT7 receptors and the serotonin (5-HT) transporter (5-HTT). Vortioxetine administration induces antidepressant- and anxiolytic-like effects, and can enhance cognitive performance in rodents. Several clinical trials have reported the efficiency and a satisfactory tolerability of vortioxetine treatment in depressed patients. Remarkably, vortioxetine has a specific positive impact on cognitive symptoms in depressed patients. Overall, vortioxetine is an efficacious antidepressant drug for the treatment of patients with a major depressive episode and has a unique mechanism of action offering a new therapeutic option.

Learning and memory impairments in a neuroendocrine mouse model of anxiety/depression.

Cognitive disturbances are often reported as serious incapacitating symptoms by patients suffering from major depressive disorders (MDDs). Such deficits have been observed in various animal models based on environmental stress. Here, we performed a complete characterization of cognitive functions in a neuroendocrine mouse model of depression based on a chronic (4 weeks) corticosterone administration (CORT). Cognitive performances were assessed using behavioral tests measuring episodic (novel object recognition test, NORT), associative (one-trial contextual fear conditioning, CFC), and visuo-spatial (Morris water maze, MWM; Barnes maze, BM) learning/memory. Altered emotional phenotype after chronic corticosterone treatment was confirmed in mice using tests predictive of anxiety or depression-related behaviors. In the NORT, CORT-treated mice showed a decrease in time exploring the novel object during the test session and a lower discrimination index compared to control mice, characteristic of recognition memory impairment. Associative memory was also impaired, as observed with a decrease in freezing duration in CORT-treated mice in the CFC, thus pointing out the cognitive alterations in this model. In the MWM and in the BM, spatial learning performance but also short-term spatial memory were altered in CORT-treated mice. In the MWM, unlike control animals, CORT-treated animals failed to learn a new location during the reversal phase, suggesting a loss of cognitive flexibility. Finally, in the BM, the lack of preference for the target quadrant during the recall probe trial in animals receiving corticosterone regimen demonstrates that long-term retention was also affected in this paradigm. Taken together, our results highlight that CORT-induced anxio-depressive-like phenotype is associated with a cognitive deficit affecting all aspects of memory tested.

Pro-inflammatory mediators and apoptosis correlate to rt-PA response in a novel mouse model of thromboembolic stroke.

BACKGROUND: A recent study suggests that patients with persistent occlusion of the middle cerebral artery (MCA) following treatment with recombinant tissue plasminogen activator (rt-PA) have better outcomes than patients with MCA occlusion not receiving rt-PA. We performed a study to elucidate possible mechanisms of this finding in a new model of thromboembolic stroke closely mimicking human pathophysiology. METHODS: Thromboembolic stroke was induced by local injection of thrombin directly into the right MCA of C57 black/6J mice. Rt-PA was administered 20 and 40 min after clot formation. The efficiency of rt-PA to induce thrombolysis was measured by laser Doppler. After 24 h, all animals were euthanized and interleukin (IL)-6, tumor necrosis factor-alpha (TNF-α), matrix metalloproteinase (MMP)-9, Caspase-3, hsp 32 and hsp 70 protein levels were investigated by immunofluorescence. Presence of hemorrhage was verified and infarct volume was measured using histology. RESULTS: Thrombin injection resulted in clot formation giving rise to cortical brain infarction. Early rt-PA treatment starting at 20 min after the clot formation resulted in 100% recanalization. However, rt-PA-induced thrombolysis dissolved the clot in only 38% of the animals when administered 40 min after clot formation. Protein levels of IL-6, TNF-α, MMP-9, Caspase-3, hsp 32 and hsp 70 were increased after MCAO, whereas treatment with rt-PA attenuated the expressions of inflammatory markers in those animals where the thrombolysis was successful. In addition, the infarct size was significantly reduced with rt-PA treatment compared to non-treated MCAO, regardless of whether MCA thrombolysis was successful. CONCLUSIONS: The present study demonstrates a clear correlation of the protein expression of inflammatory mediators, apoptosis and stress genes with the recanalization data after rt-PA treatment. In this model rt-PA treatment decreases the infarct size regardless of whether vessel recanalization is successful.

The postischemic environment differentially impacts teratoma or tumor formation after transplantation of human embryonic stem cell-derived neural progenitors.

BACKGROUND AND PURPOSE: Risk of tumorigenesis is a major obstacle to human embryonic and induced pluripotent stem cell therapy. Likely linked to the stage of differentiation of the cells at the time of implantation, formation of teratoma/tumors can also be influenced by factors released by the host tissue. We have analyzed the relative effects of the stage of differentiation and the postischemic environment on the formation of adverse structures by transplanted human embryonic stem cell-derived neural progenitors. METHODS: Four differentiation stages were identified on the basis of quantitative polymerase chain reaction expression of pluripotency, proliferation, and differentiation markers. Neural progenitors were transplanted at these 4 stages into rats with no, small, or large middle cerebral artery occlusion lesions. The fate of each transplant was compared with their pretransplantation status 1 to 4 months posttransplantation. RESULTS: The influence of the postischemic environment was limited to graft survival and occurrence of nonneuroectodermal structures after transplantation of very immature neural progenitors. Both effects were lost with differentiation. We identified a particular stage of differentiation characterized in vitro by a rebound of proliferative activity that produced highly proliferative grafts susceptible to threaten surrounding host tissues. CONCLUSIONS: The effects of the ischemic environment on the formation of teratoma by transplanted human embryonic stem cell-derived neural progenitors are limited to early differentiation stages that will likely not be used for stem cell therapy. In contrast, hyperproliferation observed at later stages of differentiation corresponds to an intrinsic activity that should be monitored to avoid tumorigenesis.

A functional subdivision of the circadian clock is revealed by differential effects of melatonin administration.

The biological clock of the suprachiasmatic nuclei drives numerous physiological and behavioural circadian rhythms. In this study, we addressed the question as to whether different components of the clock may control separately various circadian functions. Using the rat transpineal microdialysis tool, we analysed the effect of clock perturbation by exogenous melatonin injection on two hormonal clock outputs: pineal melatonin and adrenal corticosterone secretions. As already reported, a single melatonin injection at the light/dark transition induces a marked increase in the endogenous pineal melatonin peak for the two following days. In the same animals, by contrast, the amplitude of the corticosterone rhythm was not altered following melatonin injection. These data show that the melatonin injection does not display an overall effect on the circadian clock, but rather influences a subpopulation of melatonin-sensitive neurons involved, among other functions, in the circadian control of the pineal pathway.

Combined 192 IgG-saporin and 5,7-dihydroxytryptamine lesions in the male rat brain: a neurochemical and behavioral study.

In a previous experiment [Eur J Neurosci 12 (2000) 79], combined intracerebroventricular injections of 5,7-dihydroxytryptamine (5,7-DHT; 150 microg) and 192 IgG-saporin (2 microg) in female rats produced working memory impairments, which neither single lesion induced. In the present experiment, we report on an identical approach in male rats. Behavioral variables were locomotor activity, T-maze alternation, beam-walking, Morris water-maze (working and reference memory) and radial-maze performances. 192 IgG-saporin reduced cholinergic markers in the frontoparietal cortex and the hippocampus. 5,7-DHT lesions reduced serotonergic markers in the cortex, hippocampus and striatum. Cholinergic lesions induced motor deficits, hyperactivity and reduced T-maze alternation, but had no other effect. Serotonergic lesions only produced hyperactivity and reduced T-maze alternation. Beside the deficits due to cholinergic lesions, rats with combined lesions also showed impaired radial-maze performances. We confirm that 192 IgG-saporin and 5,7-DHT injections can be combined to produce concomitant damage to cholinergic and serotonergic neurons in the brain. In female rats, this technique enabled to show that interactions between serotonergic and basal forebrain cholinergic mechanisms play an important role in cognitive functions. The results of the present experiment in male rats are not as clear-cut, although they are not in obvious contradiction with our previous results in females.