High- and Low-conditioned Behavioral effects of midazolam in Carioca high- and low-conditioned freezing rats in an ethologically based test.

The selective breeding of laboratory rodents with different anxiety-related traits is the subject of growing interest. The present study compared the effects of the benzodiazepine midazolam in the elevated plus maze (EPM) test of anxiety in two lines of Wistar rats that were selectively bred in our laboratory for either high or low anxiety-like traits based on a contextual freezing conditioning paradigm. After phenotyping anxiety-like traits (i.e., conditioned freezing behavior), Carioca High-Freezing [CHF], Carioca Low-Freezing [CLF]) and control rats were intraperitoneally injected (1.0 ml/kg) with .9 % saline or midazolam (.25, .5, .75, and 1.0 mg/kg) and subjected to the EPM 30 min later. After the saline injection, the CHF and CLF groups exhibited lower and higher open-arm exploration in the EPM, respectively, compared with control rats. These results indicate that anxiety-related traits previously selected from an associative learning paradigm can also be phenotypically expressed in an ethologically based animal model of anxiety. All midazolam doses significantly increased open-arm exploration in both CHF and control animals, but this anxiolytic-like effect in CLF rats was only observed at the lowest dose tested (.25 mg/kg). The present findings indicate that these two breeding lines of rats are a useful model for studying anxiety, and the anxiolytic effect of midazolam depends on genetic variability that is associated with basal reactions to threatening situations.

Modulation of tonic immobility by GABAA and GABAB receptors of the medial amygdala.

Tonic immobility (TI) is a temporary state of profound motor inhibition associated with great danger as the attack of a predator. Previous studies carried out in our laboratory evidenced high Fos-IR in the posteroventral region of the medial nucleus of the amygdala (MEA) after induction of the TI response. Here, we investigated the effects of GABAA and GABAB of the MEA on TI duration. Intra-MEA injections of the GABAA agonist muscimol and GABAB agonist baclofen reduced TI response, while intra-MEA injections of the GABAA antagonist bicuculline and GABAB antagonist phaclofen increased the TI response. Moreover, the effects observed with muscimol and baclofen administrations into MEA were blocked by pretreatment with bicuculline and phaclofen (at ineffective doses per se). Finally, the activation of GABAA and GABAB receptors in the MEA did not alter the spontaneous motor activity in the open field test. These data support the role of the GABAergic system of the MEA in the modulation of innate fear.

Failure to detect the action of antidepressants in the forced swim test in Swiss mice.

OBJECTIVE: The aims of this study were to replicate previously published experiments and to modify the protocol to detect the effects of chronic antidepressant treatment in mice. METHODS: Male Swiss mice (n=6-8/group) housed in reversed light/dark cycle were randomly assigned into receive vehicle (10% sucrose), sub-effective doses (1 and 3 mg/kg) or effective doses (10 and 30 mg/kg) of bupropion, desipramine, and fluoxetine and a candidate antidepressant, sodium butyrate (1-30 mg/kg) per gavage (p.o.) 1 h before the forced swim test (FST). Treatments continued daily for 7 and 14 days during retests 1 and 2, respectively. In an additional experiment, mice received fluoxetine (20 mg/kg) or vehicle (10% sucrose or 0.9% saline) p.o. or i.p. before the FST. Mice housed in reversed or standard light/dark cycles received fluoxetine (20 mg/kg) prior FST. Video recordings of behavioural testing were used for blind assessment of the outcomes. RESULTS: According to the expected, doses of antidepressants considered sub-effective failed to affect the immobility time of mice in the FST. Surprisingly, acute and chronic treatment with the high doses of bupropion, desipramine, and fluoxetine or sodium butyrate also failed to reduce the immobility time of mice in the FST. Fluoxetine 20 mg/kg was also ineffective in the FST when injected i.p. or in mice housed in normal light/dark cycle. CONCLUSION: Data suggest the lack of efficacy of orally administered bupropion, desipramine, fluoxetine in the FST in Swiss mice. High variability, due to high and low immobility mice, may explain the limited effects of the treatments.

p,p'-Methoxyl-diphenyl diselenide elicits an antidepressant-like effect in mice without discontinuation anxiety phenotype.

Major depressive disorder is the most severe and debilitating disease among psychiatric illnesses. The abrupt interruption of antidepressant treatment may lead to a complex physiological and neuropsychiatric syndrome. The organoselenium compound (MeOPhSe)2 has been reported to have neuroprotective properties in animal models. The study aimed to investigate the effects of single or repeated administration of (MeOPhSe)2 on depressive-like behavior and if the compound administration, and its discontinuation, may affect the anxiolytic-like phenotype in Swiss mice. The results showed that repeated intragastric administration of (MeOPhSe)2 (dose range: 0.1-5mg/kg), different from a single administration, reduced the immobility time in the mouse tail suspension test. A single administration of (MeOPhSe)2 at a dose of 5mg/kg decreased the immobility time, increased the swimming time and did not alter the climbing behavior in the modified forced swimming test (mFST). Repeated administration of (MeOPhSe)2 decreased the immobility time, did not alter the swimming time and increased the climbing behavior in the mouse mFST. Repeated administration of (MeOPhSe)2 at a dose of 5mg/kg elicited a mouse anxiolytic-like phenotype in the elevated plus maze and light-dark tests. Markers of hepatic and renal function tests were not altered by repeated administration of (MeOPhSe)2 to mice. The findings indicate that a single or repeated administration of (MeOPhSe)2 elicited an antidepressant-like action in mice. Moreover, repeated treatment with (MeOPhSe)2 produced an anxiolytic-like action in mice and its profile remained stable after discontinuation.

Intracerebroventricular Administration of Streptozotocin as an Experimental Approach to Depression: Evidence for the Involvement of Proinflammatory Cytokines and Indoleamine-2,3-Dioxygenase.

There is a lack of information about the molecular events underlying the depressive-like effect of an intracerebroventricular injection of streptozotocin (ICV-STZ) in mice. Elevated activity of the tryptophan-degrading enzyme indoleamine-2,3-dioxygenase (IDO) has been proposed to mediate depression in inflammatory disorders. In this study, we report that ICV-STZ activates IDO in the hippocampus of mice and culminates in depressive-like behaviors, measured by an increased duration in immobility time in the forced swimming test and decreased total time of grooming in the splash test. Indirect blockade of IDO activation with the cytokine inhibitor minocycline prevents the development of depressive-like behaviors and attenuates STZ-induced upregulation of proinflammatory cytokines in the hippocampus. Minocycline abrogates the increase in tryptophan and kynurenine levels as well as prevents serotonin dysfunction in the hippocampus of STZ-injected mice. These results suggest that hippocampal IDO activation in STZ-associated depressive-like behavior is mediated by proinflammatory cytokine-dependent mechanisms. Our study not only extends the evidence that IDO has a critical role in mediating inflammation-induced depression but also supports the notion that neuroinflammation and the kynurenine pathway are important targets of novel therapeutic drugs for depression. In addition, our study provides new insights into the neurobiological mechanisms underlying ICV-STZ and indicates that this model could be employed in the preclinical research of depression.

Quetiapine treatment reverses depressive-like behavior and reduces DNA methyltransferase activity induced by maternal deprivation.

Stress in early life has been appointed as an important phenomenon in the onset of depression and poor response to treatment with classical antidepressants. Furthermore, childhood trauma triggers epigenetic changes, which are associated with the pathophysiology of major depressive disorder (MDD). Treatment with atypical antipsychotics such as quetiapine, exerts therapeutic effect for MDD patients and induces epigenetic changes. This study aimed to analyze the effect of chronic treatment with quetiapine (20mg/kg) on depressive-like behavior of rats submitted to maternal deprivation (MD), as well as the activity of histone acetylation by the enzymes histone acetyl transferases (HAT) and deacetylases (HDAC) and DNA methylation, through DNA methyltransferase enzyme (DNMT) in the prefrontal cortex (PFC), nucleus accumbens (NAc) and hippocampus. Maternally deprived rats had a depressive-like behavior in the forced swimming test and an increase in the HDAC and DNMT activities in the hippocampus and NAc. Treatment with quetiapine reversed depressive-like behavior and reduced the DNMT activity in the hippocampus. This is the first study to show the antidepressant-like effect of quetiapine in animals subjected to MD and a protective effect by quetiapine in reducing epigenetic changes induced by stress in early life. These results reinforce an important role of quetiapine as therapy for MDD.

Pro-inflammatory cytokines, IL-1ß and TNF-α, produce persistent compromise in tonic immobility defensive behaviour in endotoxemia guinea-pigs.

AIM: Sepsis has been associated with acute behavioural changes in humans and rodents, which consists of a motivational state and an adaptive response that improve survival. However, the involvement of peripheral cytokines synthesized during systemic inflammation as modulators of the tonic immobility (TI) defensive behaviour remains a literature gap. Our purposes were to characterize the TI defensive behaviour in endotoxemia guinea-pigs at acute phase and after recovery from the initial inflammatory challenge. Furthermore, we investigated whether peri-aqueductal grey matter (PAG) exists as a brain structure related to this behaviour and also pro-inflammatory cytokines, tumour necrosis factor (TNF)-α and interleukin (IL)-1ß, act at this mesencephalic nucleus. METHODS: Endotoxemia was induced by lipopolysaccharide (LPS) administration in guinea-pigs. The parameters evaluated included TI defensive behaviour, survival, cytokines production, as well as neuronal activation and apoptosis in the PAG. RESULTS: Endotoxemia guinea-pigs exhibited a reduction in the duration of TI episodes, starting at 2 h after LPS administration and persisting throughout the experimental period evaluated over 7 days. Moreover, endotoxemia increased the c-FOS immunoreactivity of neurones in the ventrolateral PAG (vlPAG), as well as the caspase-3 expression. The LPS microinjection into vlPAG reproduces the same compromise, that is a decrease in the duration of TI defensive behaviour, observed after the peripheral administration. The immunoneutralization against IL-1ß and TNF-α into vlPAG reverts all the effects produced by peripheral LPS administration. CONCLUSION: Our findings confirm that vlPAG is an important brain structure involved in the behavioural alterations induced by endotoxemia, possibly changing the neuronal activity caused by pro-inflammatory cytokines produced peripherally.

Distinct effect of 5-HT1A and 5-HT2A receptors in the medial nucleus of the amygdala on tonic immobility behavior.

The tonic immobility (TI) response is an innate fear behavior associated with intensely dangerous situations, exhibited by many species of invertebrate and vertebrate animals. In humans, it is possible that TI predicts the severity of posttraumatic stress disorder symptoms. This behavioral response is initiated and sustained by the stimulation of various groups of neurons distributed in the telencephalon, diencephalon and brainstem. Previous research has found the highest Fos-IR in the posteroventral part of the medial nucleus of the amygdala (MEA) during TI behavior; however, the neurotransmission of this amygdaloid region involved in the modulation of this innate fear behavior still needs to be clarified. Considering that a major drug class used for the treatment of psychopathology is based on serotonin (5-HT) neurotransmission, we investigated the effects of serotonergic receptor activation in the MEA on the duration of TI. The results indicate that the activation of the 5HT1A receptors or the blocking of the 5HT2 receptors of the MEA can promote a reduction in fear and/or anxiety, consequently decreasing TI duration in guinea pigs. In contrast, blocking the 5HT1A receptors or activating the 5HT2 receptors in this amygdalar region increased the TI duration, suggesting an increase in fear and/or anxiety. These alterations do not appear to be due to a modification of spontaneous motor activity, which might non-specifically affect TI duration. Thus, these results suggest a distinct role of the 5HT receptors in the MEA in innate fear modulation.

Differential involvement of glutamatergic and catecholaminergic activity within the amygdala during taste aversion retrieval on memory expression and updating.

During memory retrieval, consolidated memories are expressed and destabilized in order to maintain or update information through a memory reconsolidation process. Despite the key role of the amygdala during memory acquistion and consolidation, the participation of neurotransmitter signals in memory retrieval is poorly understood. Hence, we used conditioned taste aversion and in vivo microdialysis to evaluate changes in glutamate, norepinephrine and dopamine concentrations within the amygdala during memory retrieval. We observed that exposure to an aversive-conditioned stimulus induced an augmentation in glutamate, norepinephrine and dopamine levels within the amygdala, while exposure to a familiar and safe stimulus did not induce changes in these neurotransmitters levels. Also, we evaluated the amygdalar blockade of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA), N-methyl-d-aspartate (NMDA), ß-adrenergic and dopamine D1 receptors in memory retrieval and updating. Results showed that during retrieval, behavioural expression was impaired by intra-amygdalar blockade of AMPA and ß-adrenergic receptors, whereas NMDA, D1 and ß-adrenergic receptors blockade hindered memory updating. In summary, during conditioned taste aversion retrieval there was an increase in the extracellular levels of glutamate, norepinephrine and dopamine within the amygdala, and their receptors activity were differentially involved in the behavioural expression and memory updating during retrieval.

Sub-chronic agmatine treatment modulates hippocampal neuroplasticity and cell survival signaling pathways in mice.

Agmatine is an endogenous neuromodulator which, based on animal and human studies, is a putative novel antidepressant drug. In this study, we investigated the ability of sub-chronic (21 days) p.o. agmatine administration to produce an antidepressant-like effect in the tail suspension test and examined the hippocampal cell signaling pathways implicated in such an effect. Agmatine at doses of 0.01 and 0.1 mg/kg (p.o.) produced a significant antidepressant-like effect in the tail suspension test and no effect in the open-field test. Additionally, agmatine (0.001-0.1 mg/kg, p.o.) increased the phosphorylation of protein kinase A substrates (237-258% of control), protein kinase B/Akt (Ser(473)) (116-127% of control), glycogen synthase kinase-3ß (Ser(9)) (110-113% of control), extracellular signal-regulated kinases 1/2 (119-137% and 121-138% of control, respectively) and cAMP response elements (Ser(133)) (127-152% of control), and brain-derived-neurotrophic factor (137-175% of control) immunocontent in a dose-dependent manner in the hippocampus. Agmatine (0.001-0.1 mg/kg, p.o.) also reduced the c-jun N-terminal kinase 1/2 phosphorylation (77-71% and 65-51% of control, respectively). Neither protein kinase C nor p38(MAPK) phosphorylation was altered under any experimental conditions. Taken together, the present study extends the available data on the mechanisms that underlie the antidepressant action of agmatine by showing an antidepressant-like effect following sub-chronic administration. In addition, our results are the first to demonstrate the ability of agmatine to elicit the activation of cellular signaling pathways associated with neuroplasticity/cell survival and the inhibition of signaling pathways associated with cell death in the hippocampus.

Depressive-like behavior induced by tumor necrosis factor-α is abolished by agmatine administration.

Agmatine, an endogenous cationic amine, has been shown to exert antidepressant-like effects. This study investigated the ability of agmatine administered orally to abolish the depressive-like behavior induced by the administration of the pro-inflammatory cytokine, tumor necrosis factor (TNF-α) in mice. In control animals, agmatine (0.001, 0.01, 0.1, and 1 mg/kg) reduced the immobility time in the tail suspension test (TST). Acute administration of TNF-α (0.001 fg/mouse, i.c.v.) increased immobility time in the TST, indicative of a depressive-like behavior, and agmatine (0.0001, 0.1, and 1 mg/kg) prevented this effect. Additionally, we examined the effects of the combined administration of sub-effective doses of agmatine with antidepressants, the NMDA receptor antagonist MK-801 and the neuronal nitric oxide synthase inhibitor 7-nitroindazole (7-NI) in mice exposed to either TNF-α or saline. In control mice, administration of a sub-effective dose of agmatine (0.0001 mg/kg) combined with sub-effective doses of either fluoxetine (5 mg/kg, p.o.), imipramine (0.1 mg/kg, p.o.), bupropion (1 mg/kg, p.o.), MK-801 (0.001 mg/kg, p.o.) or 7-NI (25 mg/kg, i.p.) produced a synergistic antidepressant-like effect in the TST. All these administrations prevented the increased immobility time induced by TNF-α. The effect of agmatine in the TNF-α model of depression appears to be associated, at least partially, with an activation of the monoaminergic systems and inhibition of NMDA receptors and nitric oxide synthesis, although converging signal transduction pathways that may underlie the effect of agmatine should be further investigated. This set of results indicates that agmatine may constitute a new therapeutic alternative for the treatment of depression associated with inflammation.

Altered expression of 5-HT1A receptors in adult rats induced by neonatal treatment with clomipramine.

Chronic administration of clomipramine (CMI) to neonatal rats produces behaviors that resemble a depressive state in adulthood. Dysfunctions in the activity of the central nervous system's serotonergic function are important in understanding the pathophysiology of depression. The serotonin system is implicated in major depression and suicide and is negatively regulated by somatodendritic 5-HT1A autoreceptors. Desensitization of 5-HT1A autoreceptors is implicated in the long latency of some antidepressant treatments. Alterations in 5-HT1A receptor levels are reported in depression and suicide. In this study, we analyzed the effect of neonatal administration of CMI on the activity of 5-HT1A receptors, both pre- and post-synaptically, by administering an agonist of 5-HT1A receptors, 8-OH-DPAT, and then subjecting the rats to the forced swimming test (FST) a common procedure used to detect signs of depression in rats. Also measured were levels of the mRNA expression of 5-HT1A receptors in the dorsal raphe (DR), the hypothalamus and the hippocampus. Wistar rats were injected twice daily with CMI at doses of 15mgkg(-1) or saline as vehicle (CON) via s.c. from postnatal day 8 for 14days. At 3-4months of age, one set of rats from each group (CON, CMI) was evaluated for the effect of a selective agonist to the 5-HT1A receptor subtype, 8-OH-DPAT, by testing in the FST. Also determined was the participation of the pre- or post-synaptic 5-HT1A receptor in the antidepressant-like action of 8-OH-DPAT. This involved administering an inhibitor of tryptophan hydroxylase, parachlorophenylalanine (PCPA), and pretreatment with 8-OH-DPAT before the FST test and to evaluate the rectal temperature and locomotor activity. The expression of the mRNA of the 5-HT1A receptors was examined in the dorsal raphe nucleus, the hypothalamus and the hippocampus using the semi-quantitative RT-PCR method. The results from this study corroborate that neonatal treatment with clomipramine induces a pronounced immobility in the FST when animals reach adulthood, manifested by a significant decrease in swimming behavior, though counts of climbing behavior were not modified. This effect was similar in magnitude when 8-OH-DPAT was administered to CON group. Furthermore, the administration of 8-OH-DPAT induces a significant and similar increase in rectal temperature and locomotor activity in both the CON as in the CMI group. Neonatal treatment with CMI resulted in a significant decrease in the expression of the mRNA of the 5-HT1A receptors in the DR (% more than vehicle) in adulthood. In the case of the postsynaptic receptors located in the hypothalamus and hippocampus, neonatal treatment with CMI induced a significant increase in the mRNA expression of the 5-HT1A receptors. These data suggest that neonatal treatment with CMI induces a downregulation of the mRNA of the 5-HT1A autoreceptors in the DR, and an increment in the expression of the postsynaptic 5-HT1A receptors. The results after the administration of PCPA and 8-OH-DPAT on FST, rectal temperature and locomotor activity for both groups suggest that the function of postsynaptic receptors remains unchanged. All together these data show that the depressive behavior observed in adulthood in this animal model may be associated with long-term alterations in the expression of the mRNA of the 5-HT1A receptors.

Diphenyl diselenide supplemented diet reduces depressive-like behavior in hypothyroid female rats.

Hypothyroidism has been associated to psychiatric disorder development and tissue oxidative damage. In this study, we evaluated the effect of diphenyl diselenide supplementation on depressive-like behavior triggered by methimazole exposure in female rats. Additionally, thiobarbituric acid reactive substances (TBARS), reactive oxygen species (ROS) and non-protein thiol (NP-SH) levels were analyzed in cerebral cortex, hippocampus and striatum structures of rats. Monoamine oxidase (MAO) activity was evaluated in total brain. Firstly, female rats received methimazole (MTZ) 20mg/100ml in the drinking water for 30days and were evaluated in open-field and forced swimming tests (FST). In this set of experiments, the rats exposed to MTZ presented a depressive-like behavior, which was evidenced by a significant increase in the immobility time when compared to control group. Thereafter, MTZ-induced hypothyroid rats received either a standard or a diet containing 5ppm of diphenyl diselenide, and then they were evaluated monthly in open-field and FST tests during 3months. No alteration on the locomotor performance was observed among the groups. The depressive-like behavior of hypothyroid rats was blunted by diphenyl diselenide supplementation during all experimental periods. The levels of thyroid hormones remained low in MTZ exposed groups until the end of experimental period. The MTZ group had an increase in TBARS and ROS levels that were restored by diphenyl diselenide supplementation. NP-SH content of cerebral structures was not modified by MTZ exposure and/or diphenyl diselenide supplementation. Diphenyl diselenide supplementation restored the MAO B activity that was decreased in MTZ group. In summary, our results show that hypothyroidism induced by MTZ methimazole triggers a depressive-like behavior in female rats and that dietary diphenyl diselenide was able to reduce this effect.

Agmatine abolishes restraint stress-induced depressive-like behavior and hippocampal antioxidant imbalance in mice.

Agmatine has been recently emerged as a novel candidate to assist the conventional pharmacotherapy of depression. The acute restraint stress (ARS) is an unavoidable stress situation that may cause depressive-like behavior in rodents. In this study, we investigated the potential antidepressant-like effect of agmatine (10mg/kg, administered acutely by oral route) in the forced swimming test (FST) in non-stressed mice, as well as its ability to abolish the depressive-like behavior and hippocampal antioxidant imbalance induced by ARS. Agmatine reduced the immobility time in the mouse FST (1-100mg/kg) in non-stressed mice. ARS caused an increase in the immobility time in the FST, indicative of a depressive-like behavior, as well as hippocampal lipid peroxidation, and an increase in the activity of hippocampal superoxide dismutase (SOD), glutathione peroxidase (GPx) and glutathione reductase (GR) activities, reduced catalase (CAT) activity and increased SOD/CAT ratio, an index of pro-oxidative conditions. Agmatine was effective to abolish the depressive-like behavior induced by ARS and to prevent the ARS-induced lipid peroxidation and changes in SOD, GR and CAT activities and in SOD/CAT activity ratio. Hippocampal levels of reduced glutathione (GSH) were not altered by any experimental condition. In conclusion, the present study shows that agmatine was able to abrogate the ARS-induced depressive-like behavior and the associated redox hippocampal imbalance observed in stressed restraint mice, suggesting that its antidepressant-like effect may be dependent on its ability to maintain the pro-/anti-oxidative homeostasis in the hippocampus.

A proposal for refining the forced swim test in Swiss mice.

The forced swim test (FST) is a preclinical test to the screening of antidepressants based on rats or mice behaviours, which is also sensitive to stimulants of motor activity. This work standardised and validated a method to register the active and passive behaviours of Swiss mice during the FST in order to strength the specificity of the test. Adult male Swiss mice were subjected to the FST for 6 min without any treatment or after intraperitoneal injection of saline (0.1 ml/10 g), antidepressants (imipramine, desipramine, or fluoxetine, 30 mg/kg) or stimulants (caffeine, 30 mg/kg or apomorphine, 10mg/kg). The latency, frequency and duration of behaviours (immobility, swimming, and climbing) were scored and summarised in bins of 6, 4, 2 or 1 min. Parameters were first analysed using Principal Components Analysis generating components putatively related to antidepressant (first and second) or to stimulant effects (third). Antidepressants and stimulants affected similarly the parameters grouped into all components. Effects of stimulants on climbing were better distinguished of antidepressants when analysed during the last 4 min of the FST. Surprisingly, the effects of antidepressants on immobility were better distinguished from saline when parameters were scored in the first 2 min. The method proposed here is able to distinguish antidepressants from stimulants of motor activity using Swiss mice in the FST. This refinement should reduce the number of mice used in preclinical evaluation of antidepressants.

Noradrenergic neurotransmission within the bed nucleus of the stria terminalis modulates the retention of immobility in the rat forced swimming test.

The bed nucleus of the stria terminalis (BNST) is a limbic structure that has a direct influence on the autonomic, neuroendocrine, and behavioral responses to stress. It was recently reported that reversible inactivation of synaptic transmission within this structure causes antidepressant-like effects, indicating that activation of the BNST during stressful situations would facilitate the development of behavioral changes related to the neurobiology of depression. Moreover, noradrenergic neurotransmission is abundant in the BNST and has an important role in the regulation of emotional processes related to the stress response. Thus, this study aimed to test the hypothesis that activation of adrenoceptors within the BNST facilitates the development of behavioral consequences of stress. To investigate this hypothesis, male Wistar rats were stressed (forced swimming, 15 min) and 24 h later received intra-BNST injections of vehicle, WB4101, RX821002, CGP20712, or ICI118,551, which are selective α(1), α(2), ß(1), and ß(2) adrenoceptor antagonists, respectively, 10 min before a 5-min forced swimming test. It was observed that administration of WB4101 (10 and 15 nmol), CGP20712 (5 and 10 nmol), or ICI118,551 (5 nmol) into the BNST reduced the immobility time of rats subjected to forced swimming test, indicating an antidepressant-like effect. These findings suggest that activation of α(1), ß(1), and ß(2) adrenoceptors in the BNST could be involved in the development of the behavioral consequences of stress.

Entopeduncular nucleus endocannabinoid system modulates sleep-waking cycle and mood in rats.

Since the pioneering work of Gadea-Ciria (Gadea-Ciria M, Stadler H, Lloyd KG, Bartholini G. Acetylcholine release within the cat striatum during the sleep-wakefulness cycle. Nature 1973; 243:518-519) indicating pointing to the involvement of acetylcholine and basal ganglia in sleep regulation; extensive literature has suggested that this brain complex participates in the control of the sleep-waking cycle (SWC). On the other hand, it has been demonstrated that the endocannabinoid system (eCBS) is prominently involved in the regulation of the SWC, mood and its related disorders. Since cannabinoid receptor 1 (CB1R) is highly expressed in basal ganglia, in particular in the entopeduncular nucleus (EP), we believe that it is important to know what the role of the EP CB1R is on SWC, depression, and anxiety. To provide insight into the role of the EP CB1R in the regulation of wakefulness (W), non-rapid eye movement sleep (NREMs) and rapid eye movement sleep (REMs), rats were recorded for 24h immediately after a single intra-EP administration of N-arachidonoylethanolamine (AEA) or 1-(2,4-dichlorophenyl)-5-(4-iodophenyl)-4-methyl-N-(1-piperidyl)pyrazole-3-carboxamide (AM251; CB1 inverse agonist). Likewise, the effect of these drugs on anxiety and depression was tested by means of the elevated plus maze (EPM) and forced swim test (FST), respectively. Results demonstrate that AEA increases NREMs expression, while AM251 increases W and decreases both NREMs and REMs. In addition, administration of AM251 decreases the time rats spent in the open arms and increases immobility time in the FST. It seems that activation of the CB1R in the EP is important to induce sleep, while its blockade promotes W, as well as anxiety and depression, somewhat resembling insomnia in humans. These results suggest that the EP CB1R is modulating sleep and mood.

Antidepressant- and anticompulsive-like effects of purinergic receptor blockade: involvement of nitric oxide.

Activation of purinergic receptors by ATP (P2R) modulates glutamate release and the activation of post-synaptic P2R is speculated to induce nitric oxide (NO) synthesis. Increased glutamatergic and nitrergic signaling have been involved in the neurobiology of stress-related psychiatric disorders such as anxiety and depression. Therefore, the aim of this study was to test the effects of two P2R antagonists (PPADS and iso-PPADS) in animals submitted to models predictive of antidepressant-, anxiolytic- and anticompulsive-like effects. Swiss mice receiving PPADS at 12.5mg/kg showed reduced immobility time in the forced swimming test (FST) similarly to the prototype antidepressant imipramine (30mg/kg). This dose was also able to decrease the number of buried marbles in the marble-burying test (MBT), an anticompulsive-like effect. However, no effect was observed in animals submitted to the elevated plus maze (EPM) and to the open field test. The systemic administration of iso-PPADS, a preferential P2XR antagonist, also reduced the immobility time in FST, which was associated to a decrease in NOx levels in the prefrontal cortex. In addition, P2X7 receptor was found co-immunoprecipitated with neuronal nitric oxide synthase (NOS1) in the prefrontal cortex. These results suggest that P2X7, possibly coupled to NOS1, could modulate behavioral responses associated to stress-related disorders and it could be a new target for the development of more effective treatments for affective disorders.

Interactive effects of N-acetylcysteine and antidepressants.

N-acetylcysteine (NAC), a glutathione precursor and glutamate modulator, has been shown to possess various clinically relevant psychopharmacological properties. Considering the role of glutamate and oxidative stress in depressive states, the poor effectiveness of antidepressant drugs (ADs) and the benefits of drug combination for treating depression, the aim of this study was to explore the possible benefit of NAC as an add on drug to treat major depression. For that matter we investigated the combination of subeffective and effective doses of NAC with subeffective and effective doses of several ADs in the mice tail suspension test. The key finding of this study is that a subeffective dose of NAC reduced the minimum effective doses of imipramine and escitalopram, but not those of desipramine and bupropion. Moreover, the same subeffective dose of NAC increased the minimum effective dose of fluoxetine in the same model. In view of the advantages associated with using the lowest effective dose of antidepressant, the results of this study suggest the potential of a clinically useful interaction of NAC with imipramine and escitalopram. Further studies are necessary to better characterize the molecular basis of such interactions, as well as to typify the particular drug combinations that would optimize NAC as an alternative for treating depression.

Antidepressant-like effect of riparin II from Aniba riparia in mice: evidence for the involvement of the monoaminergic system.

In a previous study conducted by our group, riparin II (ripII) isolated from the green fruit of Aniba riparia presented antianxiety effects in mice. This study investigates a possible antidepressant activity of rip II using two predictive tests for antidepressant activity in rodents: the forced swimming test (FST) and tail suspension test (TST). Additionally, the mechanisms involved in the antidepressant-like effect in mice were also assessed. Rip II was acute administered by intraperitoneal (i.p.) and oral (p.o) routes to male mice at doses of 25 and 50 mg/kg. Results showed that ripII at both tested doses and administration routes produced a significant decrease of immobility time in FST and TST. The pretreatment of mice with prazosin (1 mg/kg, i.p., an α1-adrenoceptor antagonist), SCH23390 (15 µg/kg, i.p., a dopamine D1 receptor antagonist), sulpiride (50 mg/kg, i.p., a dopamine D2 receptor antagonist), p-chlorophenylalanine (100 mg/kg, an inhibitor of serotonin synthesis), or NAN-190 (0.5 mg/kg, a serotonin 5-HT1A receptor antagonist) completely blocked the anti-immobility effects elicited by riparin II (50 mg/kg, p.o.) in the FST. This study indicates that riparin II produces significant antidepressant-like activity in the forced swimming and TSTs, and this effect seems to be dependent on its interaction with noradrenergic, dopaminergic, and serotonergic systems.