Percentage Of Open Arm Time Research Articles

Leptin/LepRb in the Ventral Tegmental Area Mediates Anxiety-Related Behaviors.

Background:Leptin, an adipose-derived hormone, has been implicated in emotional regulation. We have previously shown that systemic administration of leptin produces anxiolytic-like effects and deletion of the leptin receptor, LepRb, in midbrain dopamine neurons leads to an anxiogenic phenotype. This study investigated whether activation or deletion of LepRb in the ventral tegmental area of adult mice is capable of inducing anxiolytic and anxiogenic effects, respectively.Methods:Mice were cannulated in the ventral tegmental area and received bilateral intra-ventral tegmental area infusions of leptin or the JAK2/STAT3 inhibitor AG490. Anxiety-like behaviors were assessed using the elevated plus-maze, light-dark box, and novelty suppressed feeding tests. Deletion of LepRb in the ventral tegmental area was achieved by bilateral injection of AAV-Cre into the ventral tegmental area of adult Leprflox/flox mice. Anxiety-related behaviors were evaluated 3 weeks after viral injection.Results:Intra-ventral tegmental area infusions of leptin reduced anxiety-like behaviors, as indicated by increased percent open-arm time and open-arm entries in the elevated plus-maze test, increased time spent in the light side and decreased latency to enter the light side of the light-dark box, and decreased latency to feed in the novelty suppressed feeding test. Blockade of JAK2/STAT3 signaling in the ventral tegmental area by AG490 attenuated the anxiolytic effect produced by systemic administration of leptin. Leprflox/flox mice injected with AAV-Cre into the ventral tegmental area showed decreased leptin-induced STAT3 phosphorylation and enhanced anxiety-like behaviors in the elevated plus-maze test and the novelty suppressed feeding test.Conclusions:These findings suggest that leptin-LepRb signaling in the ventral tegmental area plays an important role in the regulation of anxiety-related behaviors.

Central Amygdala PACAP in the Behavioral Stress Response

Anxiety‐related disorders are the most common forms of mental disorders; characterized by feelings of excessive worry in the absence of specific external stimuli, they are accompanied by physical, affective and behavioral symptoms.Pituitary adenylate cyclase‐activating polypeptide (PACAP) is a 38‐amino acid peptide located in the hypothalamus and in various extra‐hypothalamic regions including the central nucleus of the amygdala (CeA). PACAP and PAC1 receptor (PAC1R) have been proposed to play a key role in mediating the behavioral and endocrine responses to stress; however, few studies have examined the involvement of the extrahypothalamic PACAP system in the modulation of stress. Our aim was to elucidate the role of the PACAP/PAC1 system of the CeA in the context of anxiety.We first assessed the effects of PACAP microinfused into the CeA of male rats in the elevated plus maze (EPM) and the acoustic startle response (ASR), behavioral tests sensitive to states of anxiety and fear. PACAP was also given into the basolateral amygdala (BlA) as a control brain region. We then used restraint stress to determine whether the endogenous PACAP‐PAC1 system is recruited by acute stressors.Infusion of PACAP into the CeA significantly reduced percent open arm time in the EPM and increased plasma corticosterone levels, while BlA microinfusion had no effect. Infusion of PACAP into the CeA also increased acoustic startle reactivity. Finally, we observed that an acute, 1h exposure to restraint produced a rapid elevation of PACAP and PAC1R expression in the CeA, but not the BlA.These data prove an anxiogenic role for the PACAP/PAC1 system of the CeA and suggest that hyperactivity of this system may underlie the anxiogenic effects of stress.

Effect of a selective cyclooxygenase type 2 inhibitor celecoxib on depression associated with obesity in mice: an approach using behavioral tests.

The biological mechanisms that link the development of depression to metabolic disorders such as obesity and diabetes remain ambiguous. In the present study the potential of a selective cyclooxygenase inhibitor celecoxib (15mg/kgp.o.) was investigated in depression associated with obesity in mice. Behavioral tests used to assess depressive-like behavior were sucrose preference test, forced swim test (FST), tail suspension test (TST) and elevated plus maze (EPM). The basal locomotor score in obese mice was not altered. Furthermore, estimation of biochemical parameters was performed for plasma glucose, total cholesterol, triglycerides and total proteins. Escitalopram (10mg/kgp.o.) served as reference standard drug. In the results, chronic treatment with celecoxib for 28days significantly attenuated the behavioral alterations as indicated by increased the sucrose consumption, reduced the immobility time in FST and TST, increased the percent open arm time and entries in EPM in obese mice. In the biochemical parameters celecoxib significantly reversed the increased plasma glucose, total cholesterol, triglycerides and total proteins in obese mice. In conclusion, celecoxib exhibited potential antidepressant-like effect in depression associated with obesity, which to some extent is mediated by reversing the altered plasma glucose in obese mice.

Sex differences in diazepam effects and parvalbumin-positive GABA neurons in trait anxiety Long Evans rats

In clinical populations, prevalence rates for a number of anxiety disorders differ between males and females and gonadal hormones are thought to contribute to these differences. While these hormones have been shown to modulate the anxiolytic effects of the benzodiazepine agonist diazepam in some models, findings are inconsistent. Here, we tested for sex differences in response to anxiogenic stimuli following a 30-min diazepam (1.0mg/kg) pre-treatment in male and female rats showing high (HAn) and low (LAn) anxiety-like behavior on the elevated plus maze. Acute diazepam administration resulted in decreased anxiety-like behavior only in HAn males as demonstrated by a significant increase in percent open arm time in the elevated plus maze (EPM). Immunohistochemical analysis for parvalbumin (PV; a calcium-binding protein that selectively stains GABAergic neurons) in central amygdala (CeA), caudate putamen (CPu) and the hippocampus indicated the number of GABAergic interneurons in these areas differed across sex and anxiety trait. In the CPu, females had significantly more PV-immunoreactive (IR) cells than males, and LAn females had greater PV-IR neurons than HAn females. In the CeA, males displayed an increased number of PV-IR neurons compared to females, with no differences found between LAn and HAn. Further, trait differences were evident in the CA2 region of the hippocampus, regardless of sex. Taken together, these data suggest that gonadal hormones and trait anxiety may influence the sensitivity to the anti-anxiety effects of diazepam and these differences may be due in part to the distribution of GABA-containing interneurons.

Periodic maternal deprivation may modulate offspring anxiety-like behavior through mechanisms involving neuroplasticity in the amygdala

Maternal care has been shown to affect the development of behavioral and endocrine systems. In rats, periodic maternal deprivation (PMD) serves as an early life stressor that directly influences maternal care by promoting more pup-directed behaviors in stressed dams. To further assess the qualities of PMD that may ameliorate long-term anxiety effects in trait anxiety animals, we coded behaviors across lactation (postnatal day (PND) 5, 16, 21) in dams phenotyped as high (HAn) and low-anxiety (LAn). We assessed anxiety-like behavior in male offspring using the elevated plus maze (EPM), focusing on percent open arm (%OA) time and latency to enter OA (OA LAT) as measures of anxiety-like behavior. Finally, we examined the brains of representative male pups to determine if the stress-related protein brain-derived neurotrophic factor (BDNF) might show persistent changes in the amygdala. Dams phenotyped as HAn had lower %OA time and longer OA LAT relative to dams designated as LAn. During PMD, HAn dams had higher incidences of licking-grooming (L/G) and more pup-directed behaviors on PND 5 and 16 compared to LAn dams. Further, as adults, HAn male offspring exhibited less anxiety traits than their maternal line with greater %OA time and %OA entries relative to LAn. HAn offspring showed markedly more BDNF immunoreacted cells in the amygdala than LAn. The combination of these findings suggests that the mild stressor, PMD alters anxiety-like behavior in offspring likely by influencing HAn dams' L/G activity and altering stress related proteins in the amygdala.

QCM-4 a novel 5-HT3 antagonist attenuates the behavioral and biochemical alterations on chronic unpredictable mild stress model of depression in Swiss albino mice

The inconsistent therapeutic outcome necessitates identifying novel compounds for the treatment of depression. Therefore, the present study is aimed at evaluating the antidepressant-like effects of a novel 5-HT3 receptor antagonist 3-methoxy-N-p-tolylquinoxalin-2-carboxamide (QCM-4) on chronic unpredictable mild stress (CUMS) induced behavioral and biochemical alterations in mice. Animals were subjected to different stressors for a period of 28 days. Thereafter, battery tests like locomotor score, sucrose preference test, forced swim test (FST), tail suspension test (TST), elevated plus maze (EPM) and open field test (OFT) were performed. Biochemical assays like lipid peroxidation, nitrite levels, reduced glutathione (GSH), catalase and superoxide dismutase (SOD) were assessed in brain homogenate. QCM-4 dose dependently reversed the CUMS induced behavioral and biochemical alterations by increasing the sucrose consumption, reducing the immobility time in FST and TST, increasing the percent time in open arm in EPM and increasing the ambulation along with the rearings and decreased number of fecal pellets in OFT. Further, biochemical alterations were attenuated by QCM-4 as indicated by reduced lipid peroxidation and nitrite levels and elevated antioxidant enzyme levels like GSH, catalase and SOD. QCM-4 attenuated the behavioral and biochemical derangements induced by CUMS in mice, indicating antidepressant behavior of the novel compound.

Evaluation of anxiolytic and sedative effects of 80% ethanolic Carica papaya L. (Caricaceae) pulp extract in mice

Ethnopharmacological relevanceCarica papaya has been used in the Ethiopian traditional medicine to relieve stress and other disease conditions. Aim of the studyThe present study was undertaken to evaluate the anxiolytic and sedative effects of 80% ethanolic Carica papaya (Caricaceae) pulp extract in mice. Materials and methodsCarica papaya pulp extract was screened for anxiolytic effect by using elevated plus maze, staircase and open field tests, and ketamine-induced sleeping time test for sedation at doses of 50, 100, 200, 400mg/kg. Distilled water and Diazepam were employed as negative and positive control groups, respectively. ResultsCarica papaya pulp extract 100mg/kg significantly increased the percentage of open arm time and entry, and reduced the percentage of entry and time spent in closed arm in elevated plus maze test; reduced the number of rearing in the staircase test; and increased the time spent and entries in the central squares while the total number of entries into the open field were not significantly affected, suggesting anxiolytic activity without altering locomotor and sedative effects. A synergistic reduction in the number of rearing and an inverted U-shaped dose response curves were obtained with important parameters of anxiety ConclusionsThe results of this study established a support for the traditional usage of Carica papaya as anxiolytic medicinal plant.

The Essential Oil of <i>Myrtus communis</i> L. Produces a Non-Sedating Anxiolytic Effect in Mice Models of Anxiety

The myrtle shrub (Myrtus communis L., Myrtaceae) is rich in essential oils used in Ethiopian traditional medicine for the treatment of a variety of ailments, including anxiety. Anxiety is a common disorder that attacks many people in society and often accompanied by physiological sensations such as tachycardia, chest pain, shortness of breath, and insensitivity. The present study was undertaken to evaluate the anxiolytic effect of the essential oil of M. communis using different models of anxiety. Swiss Albino mice of either sex were randomly divided into six groups. Tween 80 (5%, v/v) in distilled water was administered to Group I and served as control. Group II was given diazepam (0.5 mg/kg, orally) suspended in Tween 80 and served as standard. Group III-VI were given the essential oil at doses of 50, 100, 200 and 400 mg/kg, respectively. Animals were then subjected to different anxiety tests, including elevated plus maze (EPM), stair case and open field. Parameters, among others, percentage of time spent in each arm and arm entries, number of steps climbed and number of rears, and number of crossings were then measured. Data were presented as mean ± SEM and analyzed by ANOVA followed by Tuckey posthoc test. In EPM studies, the essential oil at both 100 mg/kg (p<0.01) and 200 mg/kg (p<0.05), as well as diazepam (p<0.01) produced a significant increase in percentage of open arm time compared to controls. In the staircase setting, rearing was significantly decreased with 100 mg/kg (p<0.01) and 200 mg/kg (p<0.05) of the oil, and diazepam (p<0.05) relative to controls. However, at doses of 50 mg/kg and 400 mg/kg no detectable changes were noted on the measured parameters in both EPM and stair case models. The total number of entries into open field was comparable in all groups. At a dose of 100 mg/kg, the essential oil of M. communis showed better anxiolytic activity than the standard drug. The possible mechanism by which the oil showed the activity could be through GABA-related mechanisms. The present work, therefore, holds up the traditional use of the plant for the treatment of anxiety.Keywords: Myrtus communis, essential oil, anxiety, elevated plus maze, stair case, open field

Involvement of the dorsal hippocampal dopamine D2 receptors in histamine-induced anxiogenic-like effects in mice

Anxiety-related behaviors increase histamine and dopamine release in the brain. On the other hand, central histamine counteracts reward and reinforcement processes mediated by the mesolimbic dopamine system. We investigated the effects of the histaminergic system and dopamine D2 receptors agents and their interactions on anxiety-related behaviors using the elevated plus-maze (EPM). The intra-hippocampal (Intra-CA1) microinjection of histamine (10μg/mouse) decreased the percentage of open arm time (%OAT) and open arm entries (%OAE) but not the locomotor activity, indicating an anxiogenic-like response. Quinpirole (0.5 and 2μg/mouse) or sulpiride (0.3 and 1μg/mouse) when injected into the dorsal hippocampus also induced anxiety-like behavior, however, the drugs reversed the anxiogenic response induced by the effective dose of histamine (10μg/mouse). Taken together and under the present experimental design, our results indicate that activation of the dorsal hippocampal histaminergic receptors causes anxiety-like behaviors altered by dopamine D2 receptor agonist and antagonist. Histamine can decrease dopaminergic tone in the dorsal hippocampus through decreasing the endogenous dopamine release, whereas quinpirole does the same via the postsynaptic DA receptors’ activation. Sulpiride however renders the same effect through autoreceptors’ blockade and potentiated dopamine transmission. Thus, quinpirole and sulpiride seem to compensate the effects of the intra-CA1 injection of exogenous histamine, and tend to exert anxiolytic effects in the presence of histamine

Evaluation of functional relationship between mouse hippocampal cholinergic and nitrergic systems in anxiogenic-like behavior

Although a body of evidence shows the crucial role of hippocampal nitrergic and cholinergic systems in the modulation of anxiety, little is known about their functional relationship with regard to anxiety. The present study investigated the relationship between intra-CA1 administration of a nicotinic acetylcholine receptor antagonist (mecamylamine) and a nitric oxide synthase inhibitor [Nω-nitro-L-arginine methyl ester (L-NAME)] or its precursor (L-arginine) in anxiety-related behaviors. Mice received bilateral intra-CA1 injections of either L-NAME or L-arginine in the presence of mecamylamine and were subsequently tested in the elevated plus maze. A dose of 0.5 μg/0.5 μl mecamylamine bilaterally administered into CA1 did not change the percentage of open arm time (%OAT) or the percentage of open arm entries (%OAE) in the elevated plus maze task and thus was considered as a subeffective dose. Intra-CA1 administration of either L-arginine (1 and 1.5 μg/0.5 μl, bilaterally) or L-NAME (at 60 ng/0.5 μl, bilaterally) decreased %OAT, which represents an anxiogenic-like effect. Coadministration of the subeffective dose of mecamylamine together with the lower doses of L-NAME (10 and 30 ng/0.5 μl, bilaterally) or L-arginine (0.5 μg/0.5 μl, bilaterally) led to a decrease in %OAT and %OAE. Thus, both L-NAME and L-arginine showed anxiogenic-like effects, but the effects of mecamylamine were too small to support a functional relationship between the hippocampal cholinergic and nitrergic systems.

Anxiogenic-like effect induced by TRPV1 receptor activation within the dorsal periaqueductal gray matter in mice

Pharmacological manipulation of TRPV1 (Transient Receptor Potential Vanilloid type-1) receptors has been emerging as a novel target in the investigation of anxiety states. Here, we attempt to show the role played by the TRPV1 receptors within the dorsal periaqueductal gray matter (dPAG), a midbrain structure strongly involved in the modulation of anxiety. Anxiety was assessed by recording spatiotemporal [percent open arm entries (%OE) and percent open arm time (%OT)] and ethological [e.g., head dipping (HD), stretched-attend postures (SAP)] measures in mice exposed to the elevated plus-maze (EPM). Mice received an intra-dPAG injection of the TRPV1 agonist capsaicin (0, 0.01, 0.1 or 1.0nmol/0.2μL; Experiment 1) or antagonist capsazepine (0, 10, 30 or 60nmol/0.2μL; Experiment 2), or combined injections of capsazepine (30nmol) and capsaicin (1.0nmol) (Experiment 3), and were exposed to the EPM to record spatiotemporal and ethological measures. While capsaicin produced an anxiogenic-like effect (it reduced %OE and %OT and frequency of SAP and HD in the open arms), capsazepine did not change any behavior in the EPM. However, when injected before capsaicin (1.0nmol), intra-dPAG capsazepine (30nmol–a dose devoid of intrinsic effects) antagonized completely the anxiogenic-like effect of the TRPV1 agonist. These results suggest that the anxiogenic-like effect produced by capsaicin is primarily due to TRPV1 activation within the dPAG in mice, but that dPAG TRPV1 receptors do not exert a tonic control over defensive behavior in mice exposed to the EPM.

Activation of GABAA receptors in the medial prefrontal cortex produces an anxiolytic-like response.

There has been increasing evidence that the γ-aminobutyric acid (GABA)ergic system is involved in the neurobiology of anxiety. The present study aimed to investigate the role of GABAergic systems in the modulation of anxiety in the medial prefrontal cortex (mPFC) of rats using the elevated plus maze test. Rats were anaesthetised with a mixture of ketamine and xylazine, and then special cannulae were inserted stereotaxically into the mPFC. After 5-7 days of recovery, the effects of intra-mPFC administration of GABAergic agents were studied. Bilateral injection of the GABAA receptor agonist muscimol (0.25, 0.5 and 1 μg/rat) produces an anxiolytic-like effect, shown by significant increases in the percentage of open-arm time (%OAT) and percentage of open-arm entries (%OAE). Intra-mPFC administration of the GABAA receptor antagonist bicuculline (0.25, 0.5 and 1 μg/rat) produces significant anxiogenic-like behaviour. However, intra-mPFC injection of the GABAB receptor agonist baclofen (0.05, 0.1 and 0.2 μg/rat) and the GABAB receptor antagonist CGP35348 (5, 10 and 15 μg/rat) did not alter %OAT and %OAE significantly. The results of the present study demonstrate that the GABAergic system of the mPFC modulates anxiety-related behaviours of rats through GABAA receptors.

Modulation of ventral tegmental area dopamine receptors inhibit nicotine-induced anxiogenic-like behavior in the central amygdala

Nicotine, the major addictive substance in tobacco, increases the activity of the central amygdala (CeA). Amygdala is directly implicated in anxiety modulation and sends projections to the vicinity of the midbrain dopamine neurons, including the ventral tegmental area (VTA) which is a key area that controls nicotine dependence processes. In this study, the role of dopamine D(1) and D(2)/(3) receptors of the VTA on anxiogenic-like behavior induced with intra-CeA injection of nicotine has been investigated. Male Wistar rats with cannula aimed to the left CeA and the left VTA were submitted to the elevated plus-maze (EPM). The nicotine injection (1 μg/rat) into the CeA decreased the percentage of open arm time and open arm entries, but not locomotor activity, indicating an anxiogenic-like response. Intra-VTA injection of a dopamine D1 receptor antagonist, SCH23390 (0.25 μg/rat), and a dopamine D2/3 receptor antagonist, sulpiride (0.7 μg/rat), inhibited the anxiogenic-like response caused by intra-CeA injection of nicotine. These results suggest that the relationship between the VTA and the CeA may be involved in nicotine-induced anxiogenic-like behavior via dopamine D(1) and D(2)/(3) receptors. An understanding of these cellular processes will be crucial for the development of new intervention to combat nicotine effect.

Morphine-induced anxiolytic-like effect in morphine-sensitized mice: Involvement of ventral hippocampal nicotinic acetylcholine receptors

In the present study, the effects of repeated intra-ventral hippocampal (intra-VH) microinjections of nicotinic acetylcholine receptor agonist or antagonist on morphine-induced anxiolytic-like behavior were investigated in morphine-sensitized mice using elevated plus-maze. Intraperitoneal (i.p.) administration of different doses of morphine (5, 7.5 and 10mg/kg) increased the percentage of open arm time (%OAT), open arm entries (%OAE), but not locomotor activity, indicating an anxiolytic-like response to morphine. The maximum response was obtained by 7.5mg/kg of the opioid. The anxiety-like behavior which was induced by a lower dose of morphine (5mg/kg) was significantly increased in mice that had previously received once daily injections of morphine (10 and 20mg/kg, i.p.) for 3days. It should be considered that this treatment also increased locomotor activity in morphine-sensitized mice. Furthermore, the response to an ineffective dose of morphine (5mg/kg, i.p.) in the EPM was significantly increased in the animals that had previously received nicotine for 3days (0.1, 0.3, 0.5 and 0.7μg/mouse; intra-VH), 5min prior to the injections of morphine (5mg/kg/day×3days; i.p.). On the other hand, the increase of morphine-induced anxiolytic-like effect in animals that had previously received the 3-day morphine (20mg/kg) was dose dependently suppressed by once daily injections of mecamylamine (0.5, 1 and 2μg/mouse/day×3days; intra-VH). It is important to note that repeated intra-VH administrations of the same doses of nicotine or mecamylamine alone caused no significant change in morphine (5mg/kg)-induced anxiety-like parameters in the EPM. In conclusion, it seems that morphine sensitization affects the anxiety-like behavior in the EPM and the cholinergic system in the ventral hippocampus, via nicotinic receptors, may play an important role in this effect.

Inhibition of fatty acid amide hydrolase by URB597 attenuates the anxiolytic-like effect of acetaminophen in the mouse elevated plus-maze test

Acetaminophen is the most widely used analgesic/antipyretic drug. It is metabolized into N-arachidonoylphenolamine (AM404), which inhibits the reuptake of anandamide. In view of the role of endocannabinoids in the effect of acetaminophen, we tested its anxiolytic-like effect by observing the behavior of mice using the elevated plus-maze test. The results indicated that acetaminophen [100 and 200 mg/kg, intraperitoneally (i.p.)] exerted an anxiolytic-like effect that was represented by higher percentage open-arm time, percentage open-arm entries, and total number of head dips compared with the vehicle control (P<0.05). Inhibition of fatty acid amide hydrolase, an enzyme involved in the cerebral metabolism of acetaminophen into AM404, using URB597 (0.07 mg/kg, i.p.), attenuated the anxiolytic-like effect of acetaminophen. Pretreatment with the cannabinoid type-1 receptor antagonist rimonabant (1 mg/kg, i.p.) antagonized the effect of acetaminophen. Remarkably, the selected doses of rimonabant or URB597 did not themselves induce any anxiolytic-like effect. Furthermore, the selected doses of acetaminophen (25, 50, 100, and 200 mg/kg, i.p.) did not significantly alter the locomotor activity of mice in the open-field test. In conclusion, these findings confirmed that acetaminophen shows an anxiolytic-like effect in mice that involves, at least in part, AM404-mediated accumulation of anandamide in the brain and consequent activation of cannabinoid type-1 receptors.

Influence of nitric oxide agents in the dorsal hippocampus of mice on anxiogenic-like effect induced by histamine

Histaminergic receptors and neuronal nitric oxide synthase (nNOS) are co-expressed at high levels in the hippocampal neurons and alter anxiety-like behaviors in rodents. Since the dorsal hippocampus may be involved in modulation of anxiety-like behaviors, the aim of the present study was to assess whether the nitric oxide (NO) system in the dorsal hippocampus affects anxiety-like behaviors induced by histaminergic agents in mice. The effects of the NO precursor, L-arginine and NOS inhibitor, L-nitro-amino-methyl-ester (L-NAME) on histamine, pyrilamine and ranitidine responses in elevated plus maze (E.P.M.) in mice were investigated. Intra-CA1 microinjection of histamine (9μg/mouse) or H1 receptor antagonist, pyrilamine (3, 6 and 9μg/mouse), but not H2 receptor antagonist, ranitidine decreased the percentage of open arm time (%OAT) and open arm entries (%OAE), without affecting locomotor activity, suggesting an anxiogenic-like response. Both L-arginine (0.4 and 0.8μg/mouse) and L-NAME (40ng/mouse) when injected into the dorsal hippocampus induced anxiety-like behaviors, but the drugs reversed the anxiogenic response induced by the effective dose of histamine (9μg/mouse) or pyrilamine (9μg/mouse). Our results also indicated that intra-CA1 administration of L-arginine and L-NAME, in the presence or absence of ranitidine, exerted an anxiogenic effect. The results may indicate a modulatory role for NO in the dorsal hippocampus in the anxiogenic-like response induced by histamine or pyrilamine.

The effect of intermittent alcohol vapor or pulsatile heroin on somatic and negative affective indices during spontaneous withdrawal in Wistar rats

Once dependent on alcohol or opioids, negative affect may accompany withdrawal. Dependent individuals are hypothesized to "self-medicate" in order to cope with withdrawal, which promotes escalated alcohol and drug use. The current study aimed to develop a reliable animal model to assess symptoms that occur during spontaneous alcohol and opioid withdrawal. Dependence was induced using intermittent alcohol exposure or pulsatile heroin delivery and assessed for the presence of withdrawal symptoms during acute withdrawal by measuring somatic signs, behavior in the forced swim test (FST), and air-puff-induced 22-kHz ultrasonic vocalizations (USVs). Additional animals subjected to 8 weeks of alcohol vapor exposure were evaluated for altered somatic signs, operant alcohol self-administration, and 22-kHz USV production, as well as performance in the elevated plus maze (EPM). During spontaneous withdrawal from pulsatile heroin or intermittent alcohol vapor, animals displayed increased somatic withdrawal signs, FST immobility, and 22-kHz USV production but did not show any behavioral change in the EPM unless the duration of alcohol exposure was extended to 4 weeks. Following 8 weeks of alcohol vapor exposure, animals displayed somatic withdrawal signs, escalated alcohol self-administration, and increased 22-kHz USVs. These paradigms provide consistent methods to evaluate the behavioral ramifications, and neurobiological substrates, of alcohol and opioid dependence during spontaneous withdrawal. As immobility in the FST and percent open-arm time in the EPM were dissociable, with 22-kHz USVs paralleling immobility in the FST, assessment of air-puff-induced 22-kHz USVs could provide an ethologically valid alternative to the FST.

P.2.018 Antidepressants specifically inhibiting noradrenaline reuptake enhance recognition memory in rats

Despite being potent anxiolytic agents, benzodiazepines (BDZ) sometimes show reduced therapeutic efficacy in stressed rodents. However, the effectiveness of norepinephrine reuptake inhibitors (NRI) and serotonin–norepinephrine reuptake inhibitors (SNRI) or other anxiolytic interventions, e.g., exercise, remained elusive. Here, we demonstrated that male rats subjected to restraint stress for 4 weeks showed decreases in percent open arm time and open arm entry, as determined by elevated plus-maze test (EPM). Increases in inhibitory avoidance trial 2 and outer zone time were also observed in elevated T-maze (ETM) and open field test (OFT), respectively. To evaluate the anxiolytic-like actions of exercise and anxiolytic drugs, stressed rats were subjected for 4 weeks to swimming or daily gavage with 2 mg/kg diazepam (BDZ), or 10 mg/kg fluoxetine (selective serotonin reuptake inhibitor), reboxetine (NRI), or venlafaxine (SNRI). In EPM, the open arm activity was higher in the swimming, reboxetine-treated and venlafaxine-treated groups as compared to age-matched controls, while diazepam and fluoxetine were without effect. In ETM, a reduction in avoidance latency was observed only in swimming and venlafaxine-treated groups. However, the combined swimming and pharmacological treatment showed no additive anxiolytic-like effect. It could be concluded that restraint stress induced anxiety-like behaviors, which were not responsive to diazepam or fluoxetine, whereas reboxetine, venlafaxine and swimming showed anxiolytic-like actions in stressed rats.

Anxiolytic-like actions of reboxetine, venlafaxine and endurance swimming in stressed male rats

Despite being potent anxiolytic agents, benzodiazepines (BDZ) sometimes show reduced therapeutic efficacy in stressed rodents. However, the effectiveness of norepinephrine reuptake inhibitors (NRI) and serotonin–norepinephrine reuptake inhibitors (SNRI) or other anxiolytic interventions, e.g., exercise, remained elusive. Here, we demonstrated that male rats subjected to restraint stress for 4 weeks showed decreases in percent open arm time and open arm entry, as determined by elevated plus-maze test (EPM). Increases in inhibitory avoidance trial 2 and outer zone time were also observed in elevated T-maze (ETM) and open field test (OFT), respectively. To evaluate the anxiolytic-like actions of exercise and anxiolytic drugs, stressed rats were subjected for 4 weeks to swimming or daily gavage with 2mg/kg diazepam (BDZ), or 10mg/kg fluoxetine (selective serotonin reuptake inhibitor), reboxetine (NRI), or venlafaxine (SNRI). In EPM, the open arm activity was higher in the swimming, reboxetine-treated and venlafaxine-treated groups as compared to age-matched controls, while diazepam and fluoxetine were without effect. In ETM, a reduction in avoidance latency was observed only in swimming and venlafaxine-treated groups. However, the combined swimming and pharmacological treatment showed no additive anxiolytic-like effect. It could be concluded that restraint stress induced anxiety-like behaviors, which were not responsive to diazepam or fluoxetine, whereas reboxetine, venlafaxine and swimming showed anxiolytic-like actions in stressed rats.

Anxiogenic effect of CCK8s in the ventral hippocampus of rats: possible involvement of GABAA receptors

AbstractCholecystokinin (CCK) as an important neuropeptide in the brain has been implicated in the modulation of anxiety. The effects of this neurotransmitter on anxiety-like behavior in the ventral hippocampus have not been evaluated yet. Moreover, some evidences show a functional interaction between GABA and CCK in the nervous system. Bilateral injections of three doses of CCK8s (0.01, 0.05 and 0.1μg/rat) into the ventral hippocampus decreased percentage of open arm time (%OAT) and open arm entries (%OAE) that are representative of anxiogenic-like behavior in the elevated plus-maze test of anxiety. Bilateral injections of LY225910, a selective CCK2 receptor antagonist, at the doses of 0.01, 0.1 and 0.5μg/rat did not change anxiety-related parameters. Administration of muscimol, a selective GABAA receptor agonist, at the doses of 0.001, 0.005 and 0.01μg/rat produced dose dependent increase in %OAT and %OAE indicating an anxiolytic-like effect, while administration of bicuculline, a selective GABAA receptor antagonist, at the doses of 0.1, 0.2 and 0.5μg/rat decreased %OAT and %OAE showing that this drug promoted anxious behavior of the rats. Co-administration of bicuculline (0.2μg/rat) with CCK8s decreased the anxiogenic effects of CCK8s. Furthermore, co-administration of LY225910 (0.5μg/rat) with muscimol increased the anxiolytic effect of muscimol at the dose of 0.001μg/rat. The results of this study suggest that both CCK and GABAergic system have important and opposite roles in the modulation of anxiety-like behavior in the ventral hippocampus of rats and they may have a complex interaction in the ventral hippocampus to modulate anxiety-related behavior.