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Background We recently showed that a neurosteroid analogue, (3β,5β,17β)-3-hydroxyandrostane-17-carbonitrile (3β-OH), induced hypnosis in rats. The aim of the present study was to evaluate the hypnotic and anaesthetic potential of 3β-OH further using electroencephalography. Methods We used behavioural assessment and cortical electroencephalogram (EEG) spectral power analysis to examine hypnotic and anaesthetic effects of 3β-OH (30 and 60 mg kg−1) administered intraperitoneally or intravenously to young adult male and female rats. Results We found dose-dependent sex differences in 3β-OH-induced hypnosis and EEG changes. Both male and female rats responded similarly to i.p. 3β-OH 30 mg kg−1. However, at the higher dose (60 mg kg−1, i.p.), female rats had two-fold longer duration of spontaneous immobility than male rats (203.4 [61.6] min vs 101.3 [32.1] min), and their EEG was suppressed in the low-frequency range (2–6 Hz), in contrast to male rats. Although a sex-dependent hypnotic effect was not confirmed after 30 mg kg−1 i.v., female rats appeared more sensitive to 3β-OH with relatively small changes within delta (1–4 Hz) and alpha (8–13 Hz) bands. Finally, 3β-OH had a rapid onset of action and potent hypnotic/anaesthetic effect after 60 mg kg−1 i.v. in rats of both sexes; however, all female rats and only half of the male rats reached burst suppression, an EEG pattern usually associated with profound inhibition of thalamocortical networks. Conclusions Based on its behavioural effects and EEG signature, 3β-OH is a potent hypnotic in rats, with female rats being more sensitive than male rats.

Reduction of natural illumination in fall/winter months causes seasonal affective disorders (SAD) in vulnerable individuals. Neurotransmitter serotonin (5-HT) is involved in the mechanism of SAD. Tryptophan hydroxylase-2 (TPH2) is the key enzyme of 5-HT synthesis in the brain. C1473 G polymorphism in the Tph2 gene is a key factor defining the enzyme activity in the mouse brain. The main aims of the study were to investigate the effects of C1473 G polymorphism on behavior and brain 5-HT system responses to photoperiod alterations. The experiment was carried out on adult mouse males of B6-1473C and B6-1473 G congenic lines with normal and low TPH2 activities, respectively. B6-1473C and B6-1473 G mice were divided into four groups of 8 each and exposed for 28 days to standard-day (14 h light and 10 h darkness) or short-day (4 h light and 20 h darkness) conditions. No effect of photoperiod on locomotor, exploratory activities and anxiety in the open field test was observed. At the same time, photoperiod alterations affected depressive-like immobility in the forced swim test, the 5-HT, 5-hydroxyindoleacetic acid (5-HIAA) levels, 5-HIAA/5-HT ratio and the Htr2a mRNA level in hippocampus and midbrain. The effect of the interaction between C1473 G polymorphism and photoperiod on 5-HT level and 5-HIAA/5-HT ratio in hippocampus was revealed. Short-day conditions reduced the level and increased 5-HIAA/5-HT ratio in this structure only in B6-1473 G mice. At the same time, C1473 G polymorphism does not alter effects of short-day conditions on immobility time in the forced swim test and the Htr2a mRNA level in the brain.

Fear is the emotion that is best understood in terms of brain mechanisms. And the management of fear memories is important when facing mental health disorders such as post-traumatic stress. Adolescence is a transitional stage of physical and psychological human development and the ability to deal with the fear memory in adolescence may be a potent factor for developing mental disorders in adulthood. However, little is known about the direct relationship between the ability to deal with the fear memory and appearance of depressive-like behaviors. To assess this, we used a model of associative learning to induce the fear memories and evaluated the depressive-related behaviors in the fear memory extinction process and its underlying cellular mechanisms from adolescent and adult mice. We found that, compared with adult mice, the adolescent mice exhibited impaired fear memory extinction in contextual fear conditioning extinction process. Meanwhile, impaired fear memory extinction was accompanied by more immobility time in forced swimming test, which was used to assess the depressive-like state. Consistent with this, we observed that long-term potentiation (LTP) induction in the hippocampal CA1 region of adolescent mice persistently larger in extinction process in adolescent mice, which was involved the presynaptic mechanism. Together, our results suggest that adolescent mice exhibited a disability to extinct the fear memory, and that this may lead to the depressive-like behaviors via presynaptic-mediated synaptic plasticity. These findings may give us a new insight in the knowledge of some mental disorders caused by persistent unpleasant memories.

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.

The objective of the present study is to investigate the role of α4, α5, α6 or β2 nAChR subunits in the antidepressant-like effect of bupropion. Adult male mice were treated with subcutaneous acute doses of bupropion (3 and 10 mg/kg) 30 min before the forced swim test (FST) in α4, α5, α6, or β2 nAChR subunit knockout (KO) and wild-type (WT) mice. In addition, the effects of β2* antagonist dihydro-β-erythroidine (DHβE, 3 mg/kg) on antidepressant-like effects of bupropion in C57BL/6 J mice were assessed. Our results showed that baseline immobility and climbing time did not differ between KO and corresponding WT mice except for β2 KO. Bupropion significantly decreased immobility time and increased climbing time in the α4, α6 and β2 nAChR KO mice in comparison to WT littermates, indicating that lack of these nAChR subunits enhanced antidepressant effects of bupropion. On the contrary, the α5 nAChR subunit deletion did not alter the FST behavior in the bupropion-treated mice. Not only in the transgenic mice, bupropion also showed antidepressant-like effects in the WT mice. In addition, DHβE pretreatment before bupropion administration resulted in decreased immobility time and increased climbing time. Taken together, the present study provides evidence on the involvement of α4*, α6*, and β2* (* indicates possible presence of other subunits) nAChRs in the antidepressant-like effects of bupropion in the FST.

Accumulating evidence indicates that the antidepressant effects of ketamine are, in part, mediated by an increase in the AMPA receptor-mediated neurotransmission in depression related areas, such as the prefrontal cortex (PFC). Therefore, activity in PFC-projecting areas related to major depression, such as the dorsal raphe nucleus (DR), may also be modulated by ketamine. We used whole-cell patch-clamp recordings and western blot experiments to determine whether ketamine promotes acute and maintained alterations in glutamatergic transmission and mTOR pathway in the DR. Bath perfusion of ketamine, but not the NMDA receptor antagonist D-AP5, increased the frequency of AMPA receptor-mediated spontaneous EPSCs (sEPSCs) in DR neurons. However, ketamine did not affect evoked EPSCs or spontaneous inhibitory currents (sIPSCs). Pre-incubation of DR slices with the mTOR inhibitor PP242 decreased the frequency of sEPSCs and prevented the effect of ketamine. The results also show that while no electrophysiological effects were detected 24 h after ketamine administration, phosphorylation levels of mTOR were significantly increased in the DR. Nevertheless, expression levels of synaptic proteins were unaffected at that time. Altogether, the present data demonstrate that ketamine transiently increases spontaneous AMPA receptor-mediated neurotransmission in the DR.

Childhood absence epilepsy (CAE) is the most common pediatric epilepsy syndrome and is characterized by typical absence seizures (AS). AS are non-convulsive epileptic seizures characterized by a sudden loss of awareness and bilaterally generalized synchronous 2.5–4 Hz spike and slow-wave discharges (SWD). Gamma butyrolactone (GBL) is an acute pharmacological model of AS and induces bilaterally synchronous SWDs and behavioral arrest. Despite the long use of this model, little is known about its strain and sex-dependent features. We compared the dose-response profile of GBL-evoked SWDs in three rat strains (Long Evans, Sprague-Dawley, and Wistar), and examined the modulatory effects of estrous cycle on SWDs in female Wistar rats. We evaluated the number of seizures, the cumulative time seizing, and the average seizure duration as a function of dose, strain, and sex/estrous phase. Long Evans rats displayed the greatest sensitivity to GBL, followed by Wistar rats, and then by Sprague-Dawley rats. GBL-evoked SWDs were modulated by estrous cycle in female rats, with the lowest sensitivity to GBL occurring during metestrus. Wistar rats showed the greatest variability as a function of dose, and the least variability within dose; these features make this strain desirable for interventional studies. Moreover, our finding that the SWD response to GBL differs as a function of estrous cycle underscores the importance of cycle monitoring in studies examining female animals using this model. Together, these strain and sex-dependent findings provide guidance for future studies.

Depression is the most common psychiatric disorder in diabetic patients, showing higher rates in women than in men. This comorbidity has been studied in rodents using the streptozotocin (STZ)-induced diabetes (DM) model, consistently reporting a depressive-like profile in males. Few articles have examined these disturbances in females (ovariectomized or combined with male rats) yielding controversial results. This work was aimed to study whether there are sex differences in the depressive-like profile of STZ-treated male and naturally cycling female Wistar rats. We also analyzed the possible influence of the estrous cycle in females. DM was induced by injecting STZ (50 mg/kg, i.p.) in 2 consecutive days. Ten days later, the depressive-like profile was assessed in the Forced-Swim Test (FST). Locomotion and motor coordination were also evaluated. Body weight and blood glucose levels were registered at the beginning and at the end of the experiment; the estrous cycle, food and water intake were daily monitored. All diabetic subjects showed increased blood glucose levels, polyphagia, polydipsia and decreased body weight as compared to controls, but males were more susceptible to STZ-treatment than females pooled in all phases of the estrous cycle. After treatment with STZ, males and females in proestrus/estrus (P/E) exhibited a depressive-like profile in the FST (increased immobility and reduced swimming); females in metestrus/diestrus were unaffected. The only sex difference observed was a more pronounced reduced swimming in STZ-treated P/E females compared with hyperglycemic males. No changes in locomotion or motor coordination were found. This work emphasizes estrous cycle differences in STZ-treated rats, and in the resultant depressive-like profile. It also supports clinical evidences made in women with DM and stresses the importance of studying STZ-treated naturally cycling females and their estrous cycle phases.

Scopolamine, a muscarinic cholinergic receptor antagonist, exerts fast and prolonged antidepressant effects in the clinic. In contrast, the current treatments for major depressive disorder (MDD) require long-term drug administration. On the other hand, the sole use of scopolamine might be related to the high risk of adverse effects. Therefore, it may be preferable to reduce its therapeutic dose. A new approach might include the co-administration of low-dose scopolamine with selected ligands of metabotropic glutamate (mGlu) receptors, which are known to possess antidepressant-like activity in several rodent tests and models of depression. The aim of the present study was to evaluate the potential antidepressant activity of low-dose scopolamine combined with an allosteric agonist of mGlu7 receptors, AMN082 in C57BL/6 mice. It was found that the combination of scopolamine (0.1 mg/kg) and AMN082 (1 mg/kg) exerted significant antidepressant-like effects in the tail suspension test (TST), but these effects were not observed in the mGlu7−/− mice. Furthermore, low-dose AMN082 co-administered with low-doses scopolamine (0.03 and 0.1 mg/kg) induced antidepressant-like activity in the forced swim test (FST) in mice. The tested compounds did not affect locomotor activity and did not impair spatial memory in the Morris water maze (MWM) test or motor coordination in the rotarod test. The results strongly indicated that there is an enhanced antidepressant-like action of scopolamine by AMN082. Co-administration of scopolamine with AMN082 might be a new strategy with better efficacy and a lower risk of adverse effects compared with the sole use of scopolamine or AMN082.

Tonic immobility (TI) is an innate defensive response exhibited by prey when physical contact with a predator is prolonged and inescapable. This defensive response is able to activate analgesia mechanisms; this activation has adaptive value because, during an attack by a predator, the manifestation of recuperative behaviors can affect the appropriate behavioral defense strategy. Some studies have suggested that similar structures of the central nervous system can regulate the response of both TI and nociception. Thus, this study evaluated the effect of chemical lesion through the administration of ibotenic acid in restricted brain areas of the periaqueductal gray matter (PAG) in guinea pig on the TI response and nociception evaluated in the hot plate test before and after emission of TI. The data showed that an irreversible chemical lesion in the ventrolateral PAG reduced of the TI response as well as defensive antinociception. However, a lesion in the dorsal PAG blocked the defensive antinociception induced by TI but did not alter TI duration. In summary, one could hypothesize that the neural substrates responsible for defensive behavior and antinociception represent similar systems that are distinct in modulation. Thus, the ventrolateral PAG has been associated with the modulation of TI and the defensive antinociception induced by TI. In contrast, the integrity of the dorsal PAG should be necessary for defensive antinociception to occur but not to elicit TI behavior in guinea pigs.

Numerous studies have attributed the psychopathology of anxiety and stress disorders to maladaptive behavioral responses such as an inability to extinguish fear. Therefore, understanding neural substrates of fear extinction is imperative for developing more effective therapies for anxiety and stress disorders. Although several studies indicated a role for cholinergic transmission and nicotinic acetylcholine receptors (nAChRs) in anxiety and stress disorder symptomatology, very little is known about the specific contribution of nAChRs in the fear extinction process. In the present study, we first examined the involvement of several brain regions essential for fear extinction (i.e., dorsal and ventral hippocampus, dHPC and vHPC; infralimbic, IL, and prelimbic, PL of the medial prefrontal cortex, mPFC; basolateral nucleus of the amygdala, BLA) in the impairing effects of a nAChR agonist, nicotine, on contextual fear extinction in mice. Our results showed that systemic administration of nicotine during contextual fear extinction increased c-fos expression in the vHPC and BLA while not affecting dHPC, IL or PL. In line with these results, local nicotine infusions into the vHPC, but not dHPC, resulted in impaired contextual fear extinction. Interestingly, we found that local nicotine infusions into the PL also resulted in impairment of contextual fear extinction. Second, we measured the protein levels of the GABA synthesizing enzymes GAD65 and GAD67 in the dHPC and vHPC during contextual fear extinction. Our results showed that in the group that received acute nicotine, both GAD65 and GAD67 protein levels were downregulated in the vHPC, but not in dHPC. This effect was negatively correlated with the level of freezing response during fear extinction suggesting that the downregulated GAD65/67 levels were associated with disrupted fear extinction. Finally, using c-fos/GAD65/67 double immunofluorescence, we showed that nicotine mainly increased c-fos expression in non-GABAergic ventral hippocampal cells, indicating that acute nicotine increases vHPC excitability. Overall, our results suggest that acute nicotine's impairing effects on fear extinction are associated with ventral hippocampal disinhibition. Therefore, these results further our understanding of the interaction between nicotine addiction and anxiety and stress disorders by describing novel neural mechanisms mediating fear extinction.

A single base mutation in the Gα(i2) protein (G184S) renders this Gα subunit insensitive to the negative modulatory effects of Regulator of G-protein Signaling (RGS) proteins. Mice expressing this RGS insensitive (RGSi) variant of Gα(i2) (RGSi Gα(i2)) display a spontaneous antidepressant-like phenotype that is reversible by treatment with the 5-HT1A receptor (5-HT1AR) antagonist WAY100635. Here we test the hypothesis that increased activity of 5-HT1ARs in the hippocampus of RGSi Gα(i2) knock-in mice is responsible for the expression of the observed antidepressant-like behavior. We administered the 5-HT1AR antagonist WAY100635 or the agonist 8-OH-DPAT via bilateral intra-hippocampal infusion cannulae and evaluated antidepressant-like behavior using the tail suspension test (TST). WAY100635 reversed the antidepressant-like phenotype of the RGSi Gα(i2) knock-in mice and 8-OH-DPAT produced an antidepressant-like response in wild type mice that was blocked by systemic WAY100635. Furthermore, intra-hippocampal infusion of the RGS4/19 inhibitor CCG-203769 produced an antidepressant-like effect in female mice. Ex-vivo slice recording confirmed the 5-HT1AR-mediated decrease in hippocampal CA1 pyramidal neuron excitability was enhanced in the RGSi Gα(i2) knock-in mice. There was no change in hippocampal 5-HT1AR expression as measured by ligand binding or in the ability of 8-OH-DPAT to activate G-protein as measured in the [(35)S]GTPγS binding assay. The findings demonstrate that RGS protein control of hippocampal 5-HT1AR signaling is necessary and sufficient to account for the antidepressant-like phenotype in the RGSi Gα(i2) knock-in mice and that RGS proteins highly expressed in the hippocampus should be investigated as targets for novel antidepressant therapies.

Rats emit 22 kHz ultrasonic vocalizations (USVs) in association with pain, fear, or distress. Whereas the capacity to produce USVs is innate, reactivity to them appears to require experience. Specifically, 22 kHz USVs fail to elicit freezing behavior in naive laboratory rats. However, these “alarm calls” do elicit freezing in rats that previously experienced foot shocks. These findings led to the hypothesis that acquired reactivity is based on “autoconditioning”—learning in which self-generated 22 kHz USVs serve as Pavlovian cues that become associated with foot shocks. The current study tested the autoconditioning hypothesis by devocalizing rats through a unilateral transection of the recurrent laryngeal nerve (Experimental group). Subsequently, animals in both the Experimental and sham-operated Control groups received five unsignaled foot shocks. One or two days later, both groups were tested for USV-elicited freezing in a novel context. Recurrent laryngeal nerve transection failed to prevent or even diminish USV-elicited freezing. In fact, both groups showed large and comparable increases in freezing to USV presentations. A subset of Control animals failed to vocalize during conditioning, while some Experimental animals did vocalize during conditioning. Animals were therefore re-grouped and reanalyzed based on whether they vocalized during conditioning. Again, both groups showed large and comparable increases in USV-elicited freezing. These results disconfirm the essential tenet or prediction of the autoconditioning hypothesis. Alternative mechanisms for acquired reactivity to 22 kHz USVs are therefore considered.

Stress exposure has been implicated in the development of mood disorders, although little is known about the lasting effects of repeated stress during the adolescent period on sex-specific differences in endocrine and plasticity-signaling responses in adulthood. Using a 10-day combinatory stress paradigm (postnatal day (PND) 26 to 35), we examined sex-specific impact of adolescent stress and inhibition of tyrosine-related kinase B (TrkB) receptor (ANA-12; 0.5 mg/kg, i.p.) on 1) adolescent blood corticosterone levels, 2) adult locomotion and anxiety-like behavior, and 3) region-specific differences in endogenous TrkB full-length (TrkB.FL) and truncated (TrkB.T1) receptor isoforms. Blood collected on days 1, 5 and 10 revealed elevated basal and stress-induced CORT secretion in females compared to males, while ANA-12 attenuated CORT elevations post stress in both sexes. As adults, all females exhibited higher locomotor and exploratory activity than males in the open field test and elevated plus maze, and differences were comparable in the forced swim within stress-naive and stress groups. Biochemically, vehicle-treated males showed elevated TrkB.T1 and TrkB.FL compared to vehicle-treated females in the PFC, hippocampus and NAc, and levels were consistently attenuated by ANA-12 treatment in non-stress males. With regards to stress exposure, expression of both isoforms was strongly down-regulated in the NAc of males only and was associated with increased TrkB.T1 in the PFC. ANA-12 enhanced expression in females, independent of stress exposure, compared to vehicle-treated counterparts, expression being increased for TrkB.T1 versus TrkB.FL and magnitude of the changes being region-specific. In contrast, ANA-12 effects in stressed males were restricted to inhibition of both isoforms in the hippocampus. Together, our findings support that TrkB activation, contingent on stress exposure, differentially affects TrkB isoform regulation during adulthood. Sex-specific biochemical responses at delayed intervals following adolescent stress exposure further support the need to include the sex variable in animal models.

One problem area regarding animal models for affective disorders is unclear reproducibility, including external validity or generalizability. One way to evaluate external validity is with systematic reviews and meta-analyses. The current study presents a meta-analysis of the effects of prototypic antidepressants in the mouse forced swim test (FST). We identified studies that examined effects of antidepressants in the FST in mice and used standard protocol, male mice and acute drug administration. We calculated Effect sizes using Cohen's d, homogeneity using Q statistic and correlations using Pearson's correlation. Results indicate that all drugs reduce immobility in the FST. However, effect sizes for most drugs are heterogeneous and do not show a consistent dose/response relationship across variability factors. Reducing variability by examining only one strain or data from individual laboratories partially increases dose response relationship. These findings suggest that whereas the FST is a valid tool to qualitatively screen antidepressant effects its validity in the context of hierarchical comparison between doses or compounds might be relevant only to single experiments.

Some individuals recover quickly from stressful events, while others do not; this suggests that there are individual differences in stress resilience. Previous studies in rats have shown that an animal’s ability to extinguish conditioned fear can predict their stress resilience. In the present study, we investigated whether rats who are resilient or vulnerable to fear conditioning would consistently show resilient or vulnerable behaviors in other behavioral tests. Male Wistar-Imamichi rats were subjected to a series of behavioral tests, including open field, conditioned place-preference (CPP), forced swim and auditory fear conditioning. The subjects were assigned to one of two different groups: resilient or vulnerable, based on their level of freezing during fear extinction, and their other behavioral phenotypes were then compared. Rats in the resilient group showed faster extinction in the methamphetamine-induced CPP test than rats in the vulnerable group. The results suggest that resilience to stressful events is associated with drug-dependence and that individuals’ abilities to recover from stressful situations and drug-dependence may share a common mechanism.

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.

A high proportion of young methamphetamine (MA) users simultaneously consume alcohol. However, the potential neurological and behavioural alterations induced by such a drug combination have not been systematically examined. We studied in adolescent rats the long-term effects of alcohol, MA, and alcohol and MA combined on anxiety-like behaviour, memory, and neurogenesis in the adult hippocampus. Rats received saline, ethanol (ETOH, 1.5g/kg), MA (MA, 2mg/kg), or ethanol and MA combined (ETHOH-MA, 1.5g/kg ethanol plus 2mg/kg MA) via oral gavage, once daily for 5 consecutive days. Open field (OF), elevated plus maze (EPM) and radial arm maze (RAM) tests were conducted following a 15-day withdrawal period. The results showed alterations in exploratory behaviour in the OF in the MA and ETOH-MA groups, and anxiety-like effects in the EPM in all three drug treatment groups. All three drug groups exhibited reference memory deficits in the RAM, but only the combination treatment group displayed alterations in working memory. Both MA and ETOH-MA treatments increased the length of doublecortin (DCX)-void gaps in the dentate gyrus but only ETOH-MA treatment increased the number of such gaps. An increased number and length of DCX-void gaps correlated with decreased exploratory activity in the OF, and impaired working memory in the RAM was associated with an augmented number of gaps. These findings suggest that alterations in adult hippocampal neurogenesis are linked to the persistent cognitive and behavioural deficits produced by alcohol and MA exposure.

Alcohol use disorder and depression are highly comorbid, and both conditions exhibit important sexual dimorphisms. Here, we aimed to investigate voluntary alcohol consumption after 6 weeks of chronic mild stress (CMS) in Wistar rats – employed as an animal model of depression. Male and female rats were investigated, and changes in several molecular markers were analysed in frontal cortex (FCx) and hippocampal formation (HF). CMS induced depressive-like responses in the forced swimming test - increased immobility time - in male and female animals, without affecting anhedonia (sucrose preference test) nor motor activity (holeboard); body weight gain and food intake were diminished only among CMS males. Voluntary alcohol consumption was evaluated in a two-bottle choice paradigm (ethanol 20% versus tap water) for 4 consecutive days; females exhibited a higher preference for alcohol compared to male animals. In particular, alcohol consumption was significantly higher among CMS females compared to CMS male animals. Remarkably, similar changes in both male and female animals exposed to CMS were observed regarding the expression levels of NCAM-140 KDa (decrease), GFAP and CB1R expression (increase) within the FCx as well as for HF PSD-95 levels (increase). However, contrasting effects in males and females were reported in relation to synaptophysin (SYN) protein levels within the FCx, HF CB1R expression (a decrease among male animals but an increase in females); while the opposite pattern was observed for NCAM-140 KDa protein levels in the HF. A decrease in CB2R expression was only observed in the HF of CMS-females. The present study suggests that male and female animals might be differentially affected by CMS regarding later voluntary alcohol consumption. In this initial approach, cortical SYN, and NCAM-140 KDa, CB1R and CB2R expression within the HF have arisen as potential candidates to explain such sex differences in behaviour. However, the depression-alcoholism relationship still deserves further investigation.

Neoechinulin A is an isoprenyl indole alkaloid that exhibits scavenging, neurotrophic factor-like, and anti-apoptotic activities. However, the effectiveness of neoechinulin A in animal models of disease has not yet been explored. In the present study, we investigated the effects of neoechinulin A on memory impairment in lipopolysaccharide (LPS)-treated mice and its antidepressant-like effects in mice. In the Y-maze test, the intracerebroventicular (i.c.v.) administration of LPS (10 μg/mouse) significantly decreased spontaneous alternation behavior, which was prevented by the prior administration of neoechinulin A (300 ng/mouse, i.c.v.). None of the treatments altered the locomotor activity of mice. Moreover, the administration of neoechinulin A decreased the immobility time in the forced-swim test or tail suspension test, which was prevented by the prior administration of WAY100635 (an antagonist of 5-HT1A receptors) and parachlorophenylalanine (an inhibitor of tryptophan hydroxylase). These results suggest that neoechinulin A improves memory functions in LPS-treated mice, and also exerts antidepressant-like effects through changes in the 5-HT system.

Tonic immobility (TI) is an important antipredator response employed by prey in the last stages of a predation sequence. Evolution by natural selection assumes consistent individual variation (repeatability) in this trait. In ectotherms, which experience variable body temperatures, TI should be repeatable over a thermal gradient to be targeted by natural selection; however, information on thermal repeatability of this trait is missing. We examined thermal repeatability of TI in juveniles of two sympatric amphibians, smooth (Lissotriton vulgaris) and alpine (Ichthyosaura alpestris) newts. Both species showed disparate TI responses to body temperature variation (13–28 °C). While the proportion of TI response was repeatable in both taxa, it increased with body temperature in alpine newts but was temperature independent in smooth newts. Duration of TI decreased with body temperature in both taxa but was only repeatable in smooth newts. Our results suggest that a warming climate may affect population dynamics of sympatric ectotherms through asymmetry in thermal reaction norms for antipredator responses.

Experiments were conducted with the aim of determining the influence of melatonin administration on vigilance and tonic immobility (TI) responses of Marshall broiler chickens. The broiler chickens were reared on different lighting regimens and subjected to heat stress during the hot-dry season. Simple random sampling was used to assign 300 broiler chicks into three groups, comprising 100 broiler chicks each. Group I (12D:12L cycle) was raised under natural photoperiod of 12-h light and 12-h darkness, without melatonin supplementation. Group II (CL) was kept under 24-h continuous lighting, without melatonin administration. Group III (CL+MEL) was raised under 24-h continuous lighting; with melatonin supplementation at 0.5mg/kg per os, via drinking water using a syringe. Beginning from day-old, broiler chickens in group III were individually administered with melatonin once daily for 8weeks at 17:00h. TI was induced by manual restraint, and vigilance elicited at self-righting graded for three days, two weeks apart, in 15 labeled broiler chickens from each of the three groups; at 06:00h, 13:00h and 18:00h, starting from week 4-8. Each broiler chicken was laid on its back in a U-shaped cradle, covered with cloth. Thermal microenvironment parameters of dry bulb temperature (DBT) and relative humidity (RH) were recorded at the experimental site, concurrently during the vigilance and TI tests. Inside the broiler chickens' house, the weekly temperature-humidity index (THI) was lowest at week 4 of the study, with the value of 48.60±0.08°C. At week 4, the relationship between the THI and TI induction attempts was stronger in 12D:12L cycle (r=0.589, P0.001) than CL (r=0.264, P0.05) or CL+MEL (r=0.096, P0.05) broiler chickens. This indicated that the broiler chickens on 12D:12L cycle were more active compared to their melatonin-treated counterparts, apparently due to adverse effects of high DBT and high RH on the broiler chickens during the hot-dry season. The highest numbers of TI induction trial attempts were recorded at 13:00h in 12D:12L cycle and CL groups (2.13±0.34 and 2.15±0.22, respectively), when the broiler chickens were at week 8. The overall mean values of induction trial attempts differed significantly (P0.0001) between the groups; with the lowest mean values of 1.22±0.4 recorded in CL+MEL broiler chickens. At day 42, the lowest mean TI duration of 101.87±10.24s in the CL group, recorded at 06:00h rose (P0.001) to 184.07±23.69s at 13:00h. The overall mean duration of TI differed significantly (P0.0001) again between the groups; with the highest mean duration of 167.82±8.35s, recorded in CL+MEL broiler chickens administered with melatonin. The overall mean vigilance behavioural ranking values of 1.85+0.07 and 1.70+0.08, obtained in 12D:12L cycle and CL broiler chickens, respectively were higher (P0.0001) than the value of 1.44+0.05 recorded in melatonin-treated broiler chickens. The results indicated that broiler chickens belonging to both 12D:12L cycle and CL groups were more emotional, fearful or anxious, compared to CL+MEL broiler chickens. It was concluded that melatonin administration elicits boldness and confidence by suppressing freezing behaviour in broiler chickens, and it may improve their welfare and productivity.

In the present study, we investigated the effect of kamishoyosan (KSS) on conditioned fear-induced freezing in ovariectomized (OVX) rats. Socially isolated OVX rats showed the longest freezing time among the following four groups: group-housed sham-operated (Sham), isolated Sham, group-housed OVX, and isolated OVX rats. Repeated oral administration of KSS (30–300 mg/kg) reduced conditioned fear-induced freezing in socially isolated OVX rats. The reduction of freezing by KSS was reversed by flumazenil (3 mg/kg) and bicuculline (3 mg/kg). These findings suggest that the GABA A -benzodiazepine receptor complex is involved in the anxiolytic effect of KSS in socially isolated OVX rats.

Peripheral administration of lipopolysaccharide (LPS) can induce the rodents to a depression-like state accompanied with remarkable changes of neurotransmitter systems. In this study, the effect of an intraperitoneal LPS injection (3 mg/kg) on the concentrations of neurotransmitters was investigated by in vivo microdialysis in rat hippocampus. To further explore dysregulation pattern of the neurotransmitters following continuous inflammatory process, we then analyzed the neurotransmitters in the hippocampus of rats after 2-week LPS exposure (500 μg/kg every other day). Acute treatment of LPS quickly enhanced glutamate release and increased the extracellular levels of dopamine, serotonin and their metabolites. Elevated glutamate status was also found in the chronic inflamed hippocampus, whereas dopamine and serotonin was decreased following prolonged LPS exposure. Interestingly, both acute and chronic treatment of LPS significantly elevated hippocampal kynurenine concentrations and altered the balance between the serotonin and kynurenine branches of tryptophan metabolism—increasing kynurenine/tryptophan ratio, but decreasing serotonin/tryptophan ratio. Additionally, kynurenic acid, the endogenous NMDA receptor antagonist, and the ratio of kynurenic acid/kynurenine were significantly decreased by acute treatment of LPS, which may further strengthen NMDA receptor activation. Since that NMDA activation can exacerbate inflammatory and neurodegenerative process, the enhanced glutamate release and dysregulated kynurenine pathway might constitute a vicious cycle playing a pivotal role in the neuropsychiatric disorders associated with inflammation, such as depression.

Aims Previous studies showed that exposure to certain types of stressors enhance the rewarding effects of many drugs of abuse, including alcohol; however, no systematic study has investigated the role of single prolonged stress (SPS) in acquisition of alcohol conditioned place preference (CPP). The purpose of this study was to examine whether SPS would facilitate the acquisition of alcohol CPP in rats. Main methods Male Sprague-Dawley rats were randomly assigned to either SPS exposure condition or no exposure condition. Freezing behavior and Elevated plus maze (EPM) were employed to evaluate PTSD-like symptoms induced by SPS. Further, using unbiased procedure, CPP conditioning was conducted with alcohol (2 g/kg). Key findings SPS significantly enhanced freezing behavior of rats, decreased percentages (%) of both time spent and number of entry into the open arms, and facilitated the acquisition of alcohol CPP without inhibiting rats' activity. Significance Our findings suggest that SPS plays an important role in alcohol dependence, and CPP paradigm with SPS may be useful for exploring the rewarding mechanism of alcohol with regard to the interaction between alcohol and post-traumatic stress disorder (PTSD).

We investigated whether tipepidine exerts an antidepressant-like effect in the forced swimming test in adrenocorticotropic hormone (ACTH)-treated rats, which is known as a treatment-resistant depression model, and we studied the pharmacological mechanisms of the effects of tipepidine. Male Wistar rats (5–7 weeks old) were used in this study. Tipepidine (20 and 40 mg/kg, i.p.) decreased the immobility time in the forced swimming test in ACTH-treated rats. The anti-immobility effect of tipepidine was blocked by a catecholamine-depleting agent, alpha-methyl- p -tyrosine (300 mg/kg, s.c.), but not by a serotonin-depleting agent, p -chlorophenylalanine. The anti-immobility effect of tipepidine was also blocked by a dopamine D 1 receptor antagonist, SCH23390 (0.02 mg/kg, s.c.) and an adrenaline α 2 receptor antagonist, yohimbine (2 mg/kg, i.p.). In microdialysis technique, tipepidine (40 mg/kg, i.p.) increased the extracellular dopamine level of the nucleus accumbens (NAc) in ACTH-treated rats. These results suggest that tipepidine exerts an antidepressant-like effect in the forced swimming test in ACTH-treated rats, and that the effect of tipepidine is mediated by the stimulation of dopamine D 1 receptors and adrenaline α 2 receptors. The results also suggest that an increase in the extracellular dopamine level in the NAc may be involved in the antidepressant-like effect of tipepidine in ACTH-treated rats.

Previous researches found that apigenin exerted antidepressant-like effects in rodents. However, it is unclear whether the neurotrophic system is involved in the antidepressant-like effects of apigenin. Our present study aimed to explore the neurotrophic related mechanism of apigenin in depressive-like mice induced by chronic corticosterone treatment. Mice were repeatedly injected with corticosterone (40 mg/kg) subcutaneously (s.c) once daily for consecutive 21 days. Apigenin (20 and 40 mg/kg) and fluoxetine (20 mg/kg) were administered 30 min prior to the corticosterone injection. The behavioral tests indicated that apigenin reversed the reduction of sucrose preference and the elevation of immobility time in mice induced by chronic corticosterone treatment. In addition, the increase in serum corticosterone levels and the decrease in hippocampal brain-derived neurotrophic factor (BDNF) levels in corticosterone-treated mice were also ameliorated by apigenin administration. Taken together, our findings intensively confirmed the antidepressant-like effects of apigenin and indicated that the antidepressant-like mechanism of apigenin was mediated, at least partly by up-regulation of BDNF levels in the hippocampus.

Ventrolateral periaqueductal gray (VL-PAG) contains key neuronal circuits related to the analgesic effect involved in integrated defensive behaviors such as immobility response (IR). The latter is characterized by a reversible state of motor inhibition that can be elicited in rats under several conditions including restriction of movements (tonic immobility: TI). It is known that IR-induced analgesia can be elicited by manipulations or drugs acting on the central nervous system (CNS) at different levels. The aim of this study was to assess the role of the opioid and the GABA systems in TI-elicited analgesia. After inducing TI in naïve rats by neck clamping, the analgesic effect was evaluated by the tail-flick (TF) test. Compared to the control group, rats with TI had increased TF latency evidencing an analgesic effect. An opioid receptor agonist and antagonist were injected systemically, as well as microinjected locally in VL-PAG, as well as GABAA receptor agonist and antagonist were microinjected into VL-PAG. Under both injection schemes, morphine increased TF latency and TI duration, while naloxone blocked TI-induced analgesia. Muscimol reduced TF latency and TI duration while bicuculline increased TF latency but not TI duration. This suggests that TI-elicited analgesia was mediated by opioids at different levels of the CNS especially in the VL-PAG by inhibition of intrinsic tonic GABAergic activity. There were no additive analgesic effects of morphine or bicuculline with tonic immobility, which probably means reach a certain upper limit under such conditions.

Tonic immobility (TI) is an innate characteristic of animals related to fear or stress response. Animals can be classified into long TI (LTI) and short TI (STI) phenotypes based on TI test duration. In this study, effect of TI phenotype, chronic corticosterone administration (CORT), and their interaction on cholesterol metabolism in liver was evaluated in broilers. LTI broilers showed higher level of cholesterol in liver compared to STI chickens (p

Evidence suggests that lobeline, a nicotinic acetylcholine receptor ligand, has antidepressant-like properties in mice. The present study investigated the possible additive or synergistic effects of lobeline in combination with commonly used antidepressants, such as reboxetine, fluoxetine, or bupropion, using the tail suspension test (TST) and the forced swim test (FST) in C57BL/6J mice. Reboxetine (5 or 10 mg/kg, i.p.), fluoxetine (5 or 10 mg/kg, i.p.), or bupropion (2 or 4 mg/kg, i.p.) were administered 30 min before TST or FST. A fixed dose of lobeline (1 mg/kg, i.p.) was injected 15 min prior to tests. Co-administration of lobeline and reboxetine, fluoxetine, or bupropion significantly reduced immobility time in the TST and FST in comparison to the antidepressants used alone. The results suggest that lobeline enhanced the effects of reboxetine, fluoxetine, or bupropion in mice. Therefore, lobeline or similar nicotinic receptor ligand may have therapeutic potential as an adjunct for the treatment of major depression.

Elucidating the multi-faceted relationship between cognitive competence and affective states is a major pursuit in behavioral sciences. Mood disorders constitute a good research model for this question, as cognitive impairment may accompany clinical depression and persist after full remission. This suggests cognitive dysfunction as an etiological factor of depression, rather than an epiphenomenon. Complementing clinical studies, animal models utilizing well-controlled, systematic paradigms are essential to elucidate the complex relationship between cognitive competence and affective states. In current set of experiments, we investigated the extent to which cognitive competence determines the stress response in Wistar rats by utilizing two well-established spatial memory paradigms with different degrees of complexity together with the forced swim test. We revealed that rats with low cognitive competence as assessed by learning performance in the Y-Maze, but not in the radial arm maze, were significantly more vulnerable to behavioral despair. In contrast, rats with high cognitive competence were resilient to the negative effects of the forced swim test, irrespective of the spatial memory task used. These results point to a nonlinear relationship between spatial memory performance and behavioral despair, suggesting that different types of cognitive functioning may have differential effects on affective processes.

The aims of this study were to identify behavioral strategies to cope with social defeat, evaluate their impact on tumor development and analyze the contributions of both to changes in physiology and behavior produced by chronic defeat stress. For this purpose, OF1 mice were inoculated with B16F10 melanoma cells and subjected to 18 days of repeated defeat stress in the presence of a resident selected for consistent levels of aggression. Combined cluster and discriminant analyses of behavior that manifested during the first social interaction identified three types of behavioral profiles: active/aggressive (AA), passive/reactive (PR) and an intermediate active/non-aggressive (ANA) profile. Animals that showed a PR coping strategy developed more pulmonary metastases at the end of the social stress period than animals in other groups. The ANA but not AA group also showed higher tumor metastases than non-stressed subjects. In addition, the ANA group differed from the other groups because it displayed the highest corticosterone levels after the first interaction. Chronic stress reduced sucrose consumption, which indicates anhedonia, in all the stressed groups. However, the PR subjects exhibited a longer immobility time and swam for less time than other subjects in the forced swim test (FST), and they travelled a shorter distance in the open field test (OFT). In this test, the ANA group also travelled smaller distances than the non-stressed group, but the difference was more moderate. In contrast, tumor development but not stress increased behaviors associated with anxiety in the OFT (e.g., time in the center) in all tumor-bearing subjects. In summary, although the effects of social stress and tumor development on behavior were rather moderate, the results indicate the importance of behavioral coping strategies in modulating the effects of chronic stress on health.

Chronic stress during critical periods of human fetal brain development is associated with cognitive, behavioral, and mood disorders in later life. Altered glutamate receptor (GluR) expression has been implicated in the pathogenesis of stress-dependent disorders. To test whether prenatal chronic mild stress (PCMS) enhances offspring's vulnerability to stress-induced behavioral and neurobiological abnormalities and if this enhanced vulnerability is sex-dependent, we measured depression-like behavior in the forced swimming test (FST) and regional changes in GluR subunit expression in PCMS-exposed adult male and female rats. Both male and female PCMS-exposed rats exhibited stronger depression-like behavior than controls. Males and females exhibited unique regional changes in GluR expression in response to PCMS alone, FST alone (CON-FST), and PCMS with FST (PCMS-FST). In females, PCMS alone did not alter N-methyl-d-aspartate receptor (NMDAR) or metabotropic glutamate receptor (mGluR) expression, while in PCMS males, higher mGluR2/3, mGluR5, and NR1 expression levels were observed in the prefrontal cortex. In addition, PCMS altered the change in GluR expression induced by acute stress (the FST test), and this too was sex-specific. Male PCMS-FST rats expressed significantly lower mGluR5 levels in the hippocampus, lower mGluR5, NR1, postsynaptic density protein (PSD)95, and higher mGluR2/3 in the prefrontal cortex, and higher mGluR5 and PSD95 in the amygdala than male CON-FST rats. Female PCMS-FST rats expressed lower NR1 in the hippocampus, lower NR2B and PSD95 in the prefrontal cortex, lower mGluR2/3 in the amygdala, and higher PSD95 in the amygdala than female CON-FST rats. PCMS may increase the offspring's vulnerability to depression by altering sex-specific stress-induced changes in glutamatergic signaling.

We have hypothesized that a downregulation of reelin and deficient maturation of adult-born hippocampal neurons are important factors in the pathogenesis of depression. This hypothesis is based on previous work showing that depression-like behavior in rats treated with protracted corticosterone develops in concert with decreased dendritic complexity in newborn hippocampal granule neurons and decreased reelin expression in the proliferative subgranular zone of the dentate gyrus. In addition, heterozygous reeler mice with approximately 50% of normal brain levels of reelin are more vulnerable to the depressogenic effects of corticosterone than wild-type mice. The purpose of this experiment was to provide pharmacological validation for the link between reelin, neuronal maturation, and depression by examining whether the deleterious effects of corticosterone on these measures could be prevented by co-administration of the antidepressant imipramine. Rats received corticosterone injections, corticosterone injections plus either 10 or 15mg/kg imipramine injections, or vehicle injections for 21 consecutive days. They were then subjected to the forced swim test to assess depression-like behavior and sacrificed for immunohistochemical examination of immature neuron number and dendritic complexity and the presence of reelin+cells. We found that corticosterone increases depression-like behavior, decreases the number of reelin+cells in the subgranular zone, and decreases the number and complexity of immature neurons in the granule cell layer. All of these behavioral and cellular phenotypes were prevented by imipramine, providing further support for the idea that reelin is involved in the pathogenesis of depression.

Poly (ADP-ribose) polymerase-1 (PARP-1) functions at the center of cellular stress and sways the immune system at several key points, thus modulates inflammatory diseases. The antiinflammatory properties of PARP-1 inhibitors have been demonstrated ameliorating effect in various neuroinflammatory disorders. It has been reported that there is a close relationship between the inflammatory processes and major depressive disorder. In the present study, we have elucidated the role of oxidative-nitrosative stress-PARP-1 pathway in lipopolysaccharide (LPS)-induced neurobehavioral and neurochemical alterations in mice. 3-Aminobenzamide (10 and 30mg/kg) and imipramine (10 and 30mg/kg) were administered once daily for 14days. Mice were challenged with LPS (1mg/kg, i.p.) 30min after drug administration on the 14th day. The mRNA expression level of PARP-1 (12h after LPS injection) in the hippocampus was measured through quantitative real-time PCR. All the behavioral and biochemical parameters were assessed at 24h after LPS injection. The expression level of PARP-1mRNA was found significantly up-regulated in the hippocampus at 12h after LPS administration. Results showed that the LPS-challenged mice exhibited an increase in immobility time seen in forced swimming test and tail suspension test. LPS increased the levels of proinflammatory cytokines and oxido-nitrosative stress parameters in the hippocampus. However, pretreatment with 3-aminobenzamide (30mg/kg) significantly reversed the LPS-induced alterations in behavioral parameters, proinflammatory cytokines, oxidative-nitrosative stress and PARP-1 mRNA levels. Imipramine failed to prevent the up-regulation of PARP-1 induced by LPS administration. Our results emphasized that oxidative-nitrosative stress-PARP-1 cascade can play a key role in LPS-induced neurobehavioral and neurochemical anomalies.

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-3β (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.

Electroconvulsive therapy is the most effective therapy for major depressive disorder (MDD). The remission rate is above 50% in previously pharmacoresistant patients but the mechanisms of action are not fully understood. Electroconvulsive stimulation (ECS) in rodents mimics antidepressant electroconvulsive therapy (ECT) in humans and is widely used to investigate the underlying mechanisms of ECT. For the translational value of findings in animal models it is essential to establish models with the highest construct, face and predictive validity possible. The commonly used model for ECT in rodents does not meet the demand for high construct validity. For ECT, cortical surface electrodes are used to induce therapeutic seizures whereas ECS in rodents is exclusively performed by auricular or corneal electrodes. However, the stimulation site has a major impact on the type and spread of the induced seizure activity and its antidepressant effect. We propose a method in which ECS is performed by screw electrodes placed above the motor cortex of rats to closely simulate the clinical situation and thereby increase the construct validity of the model. Cortical ECS in rats induced reliably seizures comparable to human ECT. Cortical ECS was more effective than auricular ECS to reduce immobility in the forced swim test. Importantly, auricular stimulation had a negative influence on the general health condition of the rats with signs of fear during the stimulation sessions. These results suggest that auricular ECS in rats is not a suitable ECT model. Cortical ECS in rats promises to be a valid method to mimic ECT.

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.

Broilers of the same genetic origin were classified as short or long tonic immobility duration (STI and LTI, respectively) phenotypes and treated chronically with vehicle (control) or corticosterone (CORT) dissolved in drinking water between 27 and 42 d of age. Differential expression of proteins and mRNA was examined using 2-dimensional gel electrophoresis and real-time PCR to elucidate the mechanism behind the severe retardation of broiler breast muscle growth caused by LTI and CORT. The majority of the 13 proteins found to be differentially expressed in breast muscle of STI and LTI broilers are involved in either glycolysis (5 proteins) or myofilament formation (5 proteins). Of the 16 proteins differentially expressed in breast muscle following CORT treatment, 6 are structural proteins, 5 are categorized as cellular defense and stress proteins, and 3 (pyruvate kinase, l-lactate dehydrogenase, and creatine kinase) are involved in responses to stress and muscle damage. Real-time PCR results indicated that expression of these proteins is transcriptionally and posttranscriptionally regulated. Protein synthesis capacity, estimated by the RNA-to-protein ratio, was significantly lower in the breast muscle of CORT-treated broilers than in untreated control broilers. The level of Leu, Gly, and Ser in serum was significantly higher in CORT-treated broilers than in the control birds. Therefore, we conclude that CORT treatment retards the growth of skeletal muscle by suppressing protein synthesis and augmenting protein catabolism, paralleling the response to severe stress and muscle damage, and the negative effect of LTI on muscle growth is likely mediated through glucose metabolism. No interaction was observed between CORT and tonic immobility affecting growth performance or any parameter examined in the current study.

Fragmentation of rapid eye movement sleep (REMS) is well described in individuals with posttraumatic stress disorder (PTSD) and likely has significant functional consequences. Fear-conditioned rodents may offer an attractive model of the changes in sleep that characterize PTSD. Following fear conditioning (FC), Wistar-Kyoto (WKY) rats, a strain known to be particularly stress-sensitive, have increased REMS fragmentation that can be quantified as a shift in the distribution of REMS episodes towards the more frequent occurrence of sequential REMS (inter-REMS episode interval ≤ 3 min) vs. single REMS (interval > 3 min). The α1 adrenoceptor antagonist prazosin has demonstrated efficacy in normalizing sleep in PTSD. To determine the utility of fear-conditioned WKY rats as a model of sleep disturbances typical of PTSD and as a platform for the development of new treatments, we tested the hypothesis that prazosin would reduce REMS fragmentation in fear-conditioned WKY rats. Sleep parameters and freezing (a standard measure of anxiety in rodents) were quantified at baseline and on days 1, 7, and 14 following FC, with either prazosin (0.01 mg/kg, i.p.) or vehicle injections administered prior to testing in a between-group design. Fear conditioning was achieved by pairing tones with a mild electric foot shock (1.0 mA, 0.5 s). One, 7, and 14 days following FC, prazosin or vehicle was injected, the tone was presented, freezing was measured, and then sleep was recorded from 11 AM to 3 PM. WKY rats given prazosin, compared to those given vehicle, had a lower amount of seq-REMS relative to total REMS time 14 days after FC. They also had a shorter non-REMS latency and fewer non-REMS arousals at baseline and on days 1 and 7 after FC. Thus, in FC rats, prazosin reduced both REMS fragmentation and non-REMS discontinuity.

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.

Tonic immobility (TI), which can be divided into short (STI) or long (LTI) duration, is a character related to fear. Our previous study has demonstrated LTI phenotype and chronic corticosterone (CORT) administration retarded growth of breast muscle in broiler chickens. In order to investigate the mechanism behind the negative effects of LTI and CORT on growth, the level of mRNA transcription of several key genes linked to energy and protein metabolism was measured in muscle. LTI broilers showed lower levels of ATP, energy charge (EC) (p0.01), and lower muscle glycogen content (p0.05) but higher level of ADP (p = 0.08) than STI birds. CORT treatment elevated EC level (p0.05) and reduced liver glycogen content (p0.05). Real-time PCR results showed that STI chickens had higher mRNA expression of PPAR α (p = 0.06) and AMPK α (p = 0.09) than LTI. CORT significantly down-regulated α-enolase mRNA expression in breast muscle compared to control (p0.05). Neither TI nor CORT altered gene expression in Akt/mTOR/p70s6k cascade pathway in muscle (p0.05). However, western blot results showed that LTI chickens exhibited higher protein content of total Akt (p = 0.05) and phosphorylated Akt (p = 0.06) than STI. CORT treatment decreased the total protein content of Akt (p = 0.09) and p70s6k (p = 0.08). These results suggest that the retardation of muscle growth by LTI and chronic CORT administration parallels a strong alternation in energy status but slight changes of Akt/mTOR/p70s6k cascade, indicating that a decrease in muscle growth induced by LTI and CORT might not be mediated through mTOR-dependent signaling pathways.

Attention deficit/hyperactivity disorder (ADHD) is encountered among patients with epilepsy at a significantly higher rate than in the general population. Mechanisms of epilepsy-ADHD comorbidity remain largely unknown. We investigated whether a model of chronic epilepsy in rats produces signs of ADHD, and thus, whether it can be used for studying mechanisms of this comorbidity. Epilepsy was induced in male Wistar rats via pilocarpine status epilepticus. Half of the animals exhibited chronic ADHD-like abnormalities, particularly increased impulsivity and diminished attention in the lateralized reaction-time task. These impairments correlated with the suppressed noradrenergic transmission in locus coeruleus outputs. The other half of animals exhibited depressive behavior in the forced swimming test congruently with the diminished serotonergic transmission in raphe nucleus outputs. Attention deficit/hyperactivity disorder and depressive behavior appeared mutually exclusive. Therefore, the pilocarpine model of epilepsy affords a system for reproducing and studying mechanisms of comorbidity between epilepsy and both ADHD and/or depression.

Tonic immobility (death-feigning) behavior of the red flour beetle, Tribolium castaneum, is a predator defense mechanism; it is a reflex elicited when a beetle is jarred with the substrate, often a result of the activities of a predator. We previously demonstrated that the frequency of predation by a jumping spider, Hasarius adansoni, was significantly lower among beetles with higher frequencies and longer durations of tonic immobility (L-type) than those with lower frequencies and shorter durations of tonic immobility (S-type). However, we found that the population of L-type beetles is much smaller than that of S-type beetles in their natural habitat. Here we demonstrated that L-type beetles are significantly more sensitive to environmental stressors such as mechanical vibration and high or low temperatures. We measured expression levels of stress-responsive genes such as heat shock proteins (Hsps) and antioxidant enzymes in both types of beetles. Among the genes we investigated, only catalase gene expression levels were significantly higher in S-type than in L-type beetles. Furthermore, a similar difference in the gene expression was observed in the T. castaneum ortholog of the insect cytokine growth-blocking peptide (GBP) gene. These results indicate the possibility that high expression of catalase and GBP in S-type beetles contributes to augmentation of their anti-stress capacity and expansion of their population in their natural habitat.

The present study investigated the involvement of the PI3K, GSK-3β, heme oxygenase-1 (HO-1) and mTOR in the antidepressant-like effect of ascorbic acid in the tail suspension test (TST). Male Swiss mice were pretreated with ascorbic acid (1 mg/kg, p.o.) or vehicle and 45 min after, LY294002 (10 μg/site, i.c.v., reversible PI3K inhibitor), rapamycin (0.2 nmol/site, i.c.v., selective mTOR inhibitor), zinc protoporphyrin (ZnPP – 10 ng/site, i.c.v., HO-1 inhibitor) or vehicle was administered. We also investigated the synergistic effect of ascorbic acid (0.1 mg/kg, p.o., sub-effective dose in the TST) with lithium chloride (10 mg/kg, p.o., non-selective GSK-3β inhibitor), AR-A014418 (0.01 μg/site, i.c.v., selective GSK-3β inhibitor) or cobalt protoporphyrin (CoPP – 0.01 μg/site, i.c.v., HO-1 inducer) in the TST. The antidepressant-like effect of ascorbic acid (1 mg/kg, p.o.) was prevented by the treatment of mice with LY294002, rapamycin or ZnPP. In addition, sub-effective doses of lithium chloride, AR-A014418 or CoPP, combined with a sub-effective dose of ascorbic acid produced a synergistic antidepressant-like effect. We also demonstrated that 1 h after its administration, ascorbic acid increased the phosphorylation of p70S6K and the immunocontent of PSD-95 in the hippocampus of mice. These results indicate that the antidepressant-like effect of ascorbic acid in the TST might be dependent on the activation of PI3K and mTOR, inhibition of GSK-3β as well as induction of HO-1, reinforcing the notion that these are important targets for antidepressant activity and contributing to better elucidate the mechanisms underlying the antidepressant-like effect of ascorbic acid.

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.

PTSD is a debilitating neuropsychiatric disorder and many patients do not respond sufficiently to current treatments. Neuropeptide Y (NPY) is suggested to provide resilience to the development of PTSD and co-morbid depression. Injections of NPY to the rodent brain are anxiolytic. Recently we showed that intranasal delivery of NPY to rats before or immediately after exposure to single prolonged stress (SPS) animal model of PTSD prevented development of many biochemical and behavioral symptoms of PTSD, indicating its prophylactic potential. Here, we investigated whether intranasal NPY might provide benefits once symptoms have already developed. One week after exposure to SPS stressors, animals were given intranasal NPY or vehicle and tested on elevated plus maze 2h or 2 days later. The NPY treated rats had lower anxiety-like behavior than vehicle treated rats as indicated by more entries into open arms and fewer into closed arms, lower anxiety index, higher risk assessment and unprotected head dips and reduced grooming time. Their anxiety index was similar to that of unstressed controls. On most of these variables there was no effect of time interval and rats displayed similar overall changes 2h or 2 days after the infusion. Moreover, intranasal NPY led to reduced depressive-like behavior, assessed by forced swim test. Thus, intranasal NPY reversed several behavioral impairments triggered by the traumatic stress of SPS and has potential for non-invasive PTSD therapeutic intervention.

Thanatosis is a common phenomenon in which prey appear to feign death when attacked by predators. It was once widely believed that thanatosis exploited predators' tendencies to avoid dead prey. However, this hypothesis has never been tested, and its feasibility has been questioned to the point that it has been largely abandoned [1,2]. Here, I show that naive birds quickly learned that dead Indian stick insects Carausius morosus were unpalatable, and subsequently rejected live insects that displayed thanatosis, but not those that failed to show thanatosis. Thanatosis had no effect on the behavior of birds that had never experienced dead insects, or those that had experienced dead insects whose resemblance to thanatosic insects had been destroyed. Therefore, thanatosis clearly caused predators to avoid prey that they mistakenly perceived to be dead.

Despite a wealth of clinical and preclinical data implicating the serotonin (5-HT) system in fear-related affective disorders, a precise definition of this neuromodulator's role in fear remains elusive. Using convergent anatomical and functional approaches, we interrogate the contribution to fear of basal amygdala (BA) 5-HT inputs from the dorsal raphe nucleus (DRN). We show the DRN→BA 5-HT pathway is engaged during fear memory formation and retrieval, and activity of these projections facilitates fear and impairs extinction. The DRN→BA 5-HT pathway amplifies fear-associated BA neuronal firing and theta power and phase-locking. Although fear recruits 5-HT and VGluT3 co-expressing DRN neurons, the fear-potentiating influence of the DRN→BA 5-HT pathway requires signaling at BA 5-HT1A/2A receptors. Input-output mapping illustrates how the DRN→BA 5-HT pathway is anatomically distinct and connected with other brain regions that mediate fear. These findings reveal how a discrete 5-HT circuit orchestrates a broader neural network to calibrate aversive memory.

Prior adverse experience alters behavioral responses to subsequent stressors. For example, exposure to a brief swim increases immobility in a subsequent swim test 24 h later. In order to determine if qualitative differences (e.g. 19 °C versus 25 °C) in an initial stressor (15 min swim) impact behavioral, physiological, and associated neural responses in a 5 min, 25 °C swim test 24 h later, rats were surgically implanted with biotelemetry devices one week prior to experimentation then randomly assigned to one of 6 conditions (Day 1 (15 min)/Day 2 (5 min)): 1) home cage (HC)/HC, 2) HC/25 °C swim, 3) 19 °C swim/HC, 4) 19 °C swim/25 °C swim, 5) 25 °C swim/HC, 6) 25 °C swim/25 °C swim. Core body temperature (Tb) was measured on Days 1 and 2 using biotelemetry; behavior was measured on Day 2. Rats were transcardially perfused with fixative 2 h following the onset of the swim on Day 2 for analysis of c-Fos expression in midbrain serotonergic neurons. Cold water (19 °C) swim on Day 1 reduced Tb, compared to both 25 °C swim and HC groups on Day 1, and, relative to rats exposed to HC conditions on Day 1, reduced the hypothermic response to the 25 °C swim on Day 2. The 19 °C swim on Day 1, relative to HC exposure on Day 1, increased immobility during the 5 min swim on Day 2. Also, 19 °C swim, relative to HC conditions, on Day 1 reduced swim (25 °C)-induced increases in c-Fos expression in serotonergic neurons within the dorsal (DRD) and interfascicular (DRI) parts of the dorsal raphe nucleus (DR). These results suggest that exposure to a 5 min 19 °C cold water swim, but not exposure to a 5 min 25 °C swim alters physiological, behavioral and serotonergic responses to a subsequent stressor.