Anxiety Behavior In Rats Research Articles

Sex differences in prenatally programmed anxiety behaviour in rats: Differential corticotropin-releasing hormone receptor mRNA expression in the amygdaloid complex

We recently reported that male, but not female, offspring born to mothers exposed to social stress during late gestation show heightened anxiety-type behaviour in adulthood. The amygdala organises anxious behaviour, which involves actions of corticotropin-releasing hormone (CRH). CRH gene expression and/or its release are increased in the amygdala in prenatally stressed (PNS) rats. CRH type 1 receptor (CRH-R1) mediates actions of CRH and urocortin I to promote anxiety-like behaviour, whereas the CRH type 2 receptor (CRH-R2) may mediate anxiolytic actions, through actions of urocortins 2 and 3. Here, using quantitative in situ hybridisation, we investigated whether altered CRH receptor mRNA expression in the amygdaloid nuclei may explain the sex differences in anxiety behaviour in adult male and female PNS rats. CRH-R1 mRNA expression was significantly greater in the central amygdala and basolateral amygdala (BLA) in male PNS rats compared with controls, with no change in the basomedial amygdala (BMA) or medial amygdala (MeA). In PNS females, CRH-R1 mRNA expression was greater than controls only in the MeA. Conversely, CRH-R2 mRNA expression was significantly lower in the BMA of male PNS rats compared with controls, but greater in female PNS rats, with no change in the BLA or MeA in either sex. The ratio of CRH-R1:CRH-R2 mRNA in the amygdaloid nuclei was generally increased in PNS males, but not in the PNS females. In conclusion, sex differences in anxiety-type behaviour in PNS rats may be explained by differential mRNA expression for CRH-R1 (pro-anxiogenic) and CRH-R2 (pro-anxiolytic) in the amygdaloid complex.

Dorsal hippocampal N-methyl- d-aspartate glutamatergic and δ-opioidergic systems modulate anxiety behaviors in rats in a noninteractive manner

The present study aimed to investigate the effects of N-methyl- d-aspartate (NMDA)-type glutamate receptor agonist, NMDA, on anxiety-like behavior induced by δ-opioid receptor agents in rats, using the elevated plus maze instrument. The dorsal hippocampus (CA1) is known to play an important role in anxiety formation and modulation. Bilateral administration of different doses of δ-opioid receptor agonist, [ d-pen2,5] enkephalin acetate hydrate (1 μg/rat, 2 μg/rat, 5 μg/rat, and 10 μg/rat; 1 μL/rat; 0.5 μL/rat in each side), into CA1 area induced an anxiolytic-like effect, demonstrated by substantial increases in the percent of open arm time (OAT%) and percent of open arm entries (OAE%). Intra-CA1 injection of different doses of δ-opioid receptor antagonist, naltrindole hydrochloride (0.25 μg/rat, 0.5 μg/rat, 1 μg/rat, and 2 μg/rat), produced significant anxiogenic-like behavior. Furthermore, intra-CA1 administration of NMDA glutamate receptor agonist, NMDA (0.125 μg/rat, 0.25 μg/rat, 0.5 μg/rat, and 0.75 μg/rat), increased the OAT% and OAE%, indicating anxiolytic-like behavior. However, administration of different doses of NMDA glutamatergic antagonist, MK801 (0.125 μg/rat, 0.25 μg/rat, 0.5 μg/rat, and 1 μg/rat), showed no significant effect on the OAT% but decreased the OAE% significantly. The ineffective dose of NMDA (0.125 μg/rat), when coadministered with enkephalin (1 μg/rat, 2 μg/rat, 5 μg/rat, and 10 μg/rat), did not decrease the anxiety behavior significantly. An effective dose of NMDA (0.5 μg/rat), in combination with different doses of naltrindole hydrochloride (0.25 μg/rat, 0.5 μg/rat, 1 μg/rat, and 2 μg/rat), demonstrated no significant interaction with the OAT%, OAE%, and locomotor activity. These results suggest that CA1 δ-opioid and NMDA glutamatergic systems modulate anxiety behaviors in a noninteractive manner.

Evaluation of the Anxiolytic Activity of NR‐ANX‐C (a Polyherbal Formulation) in Ethanol Withdrawal‐Induced Anxiety Behavior in Rats

The present study investigates the anxiolytic activity of NR-ANX-C, a standardized polyherbal formulation containing the extracts of Withania somnifera, Ocimum sanctum, Camellia sinensis, Triphala, and Shilajit in ethanol withdrawal- (EW-) induced anxiety behavior in rats. Ethanol dependence in rats was produced by substitution of drinking water with 7.5% v/v alcohol for 10 days. Then, ethanol withdrawal was induced by replacing alcohol with drinking water, 12 hours prior to experimentation. After confirming induction of withdrawal symptoms in the alcohol deprived animals, the anxiolytic activity of the test compound in graded doses (10, 20, and 40 mg/kg) was compared to the standard drug alprazolam (0.08 mg/kg) in the elevated plus maze and bright and dark arena paradigms. In our study, single and repeated dose administration of NR-ANX-C reduced EW-induced anxiety in a dose-dependent manner. Even though the anxiolytic activity was not significant at lower doses, NR-ANX-C at the highest dose tested (40 mg/kg) produced significant anxiolytic activity that was comparable to the standard drug alprazolam. Based on our findings we believe that NR-ANX-C has the potential to be used as an alternative to benzodiazepines in the treatment of EW-induced anxiety.

The Effect of Phencyclidine New Derivatives on Anxiety Behaviors in Rats

Objective(s) Anxiety is a common disorder which afflicts many people in any society and is often accompanied by physiological sensations such as tachycardia, chest pain, shortness of breath, insensitivity, etc. The purpose of present study was to evaluate the putative anxiolytic-like effects of phencyclidine (1-(1-phenylcyclohexyl) piperidine, CAS 956-90-1, PCP, I) and its methyl and methoxy hydroxyl derivatives (II, III) using elevated plus maze test of anxiety. Materials and Methods Phencyclidine as well as its methyl and methoxy hydroxyl derivatives (I, II, III) (hydrochloride, 1, 2, 5 mg/kg) were synthesized and administrated intraperitoneally (IP) on adult male Wistar rats. Results The results of this study demonstrated that, intraperitoneal (IP) administration of PCP analogues (I, II, III) hydrochloride (1, 2, 5 mg/kg) increases the percentage of open arm time (OAT%) and percentage of open arm entries (OAE%). Conclusion This study revealed that both derivatives of phencyclidine (II, III) were more effective than PCP (I) itself in modulation of anxiety behavior in rats.

Sexual experience of male rats influences anxiety-like behavior and androgen levels

There is a wide body of literature to suggest that sexual experience may influence androgen secretion in various species, in turn, androgens may also influence anxiety. We hypothesized that sexual experience may alter anxiety behavior and secretion of endogenous androgens. Experiment 1: anxiety behavior of rats with a history of sexual experience was compared to that of sexually-inexperienced, naïve male rats. Sexually-experienced rats showed less anxiety-like behavior in the open field and elevated plus maze, and exhibited increased plasma and hippocampal testosterone (T) levels. Experiment 2: the effects of recent sexual experience on anxiety behavior of sexually-experienced male rats, sexually-responsive but inexperienced male rats, and sexually-unresponsive, inexperienced male rats exposed to a receptive female immediately prior to testing was examined. Recent sexual experience significantly decreased anxiety-like behavior in the open field, elevated plus maze, and the elevated zero maze tasks, and tended to decrease anxiety-like behavior in the light-dark task. Rats with recent sexual experience exhibited increased plasma and hippocampal T levels. Experiment 3: to examine the effect of recent sexual experience, anxiety behavior of rats with a history of sexual experience that received sexual experience with a stimulus female immediately prior to testing was compared to that of rats with a history of sexual experience that did not receive sexual experience immediately prior to behavioral testing. Experienced rats that were exposed to a female prior to testing showed decreased anxiety-like behavior in the open field, elevated plus maze, and light-dark transition tasks, and showed increased plasma and hypothalamic, T and 3α-diol, and increased hippocampal T. Thus, sexual experience is associated with lower levels of anxiety-like behavior and higher levels of androgen secretion.

Cellular Mechanisms Underlying the Anxiolytic Effect of Low Doses of Peripheral Δ9-Tetrahydrocannabinol in Rats

We investigated the effect of low doses of intraperitoneal Delta(9)-tetrahydrocannabinol (THC) on anxiety behavior in rats using the elevated plus maze (EPM). An anxiolytic effect was obtained in a range of doses between 0.075 and 1.5 mg/kg, the 0.75 dose being the most effective. Pretreatment with the CB1 receptor antagonist AM251 fully reversed THC's effect, suggesting CB1 receptors were involved. In order to elucidate the neuroanatomical substrates underlying the effect of the maximal effective dose of THC, we investigated cFos expression in anxiety-related brain regions (prefrontal cortex, nucleus accumbens, amygdala, and hippocampus) of rats exposed to the EPM. THC significantly lowered the amount of cFos in prefrontal cortex and amygdala without affecting the other cerebral areas. As there is increasing evidence that CREB function regulates anxiety-like behavior in rats, the second biochemical parameter we measured was phosphorylated CREB in the same brain areas. Rats treated with THC showed a significant increase in CREB activation in the prefrontal cortex and hippocampus. In the prefrontal cortex this increased activation was linked to an increase in ERK activation, whereas in the hippocampus there was a drop in the activity of CAMKII, a kinase with inhibitory effect on CREB activation. All these effects were reversed by AM251 pretreatment, suggesting that stimulation of CB1 receptors is fundamental for triggering the biochemical events. Our results suggest that the stimulation of these receptors in the prefrontal cortex, amygdala, and hippocampus with the subsequent activation of different signaling pathways is the first event underlying the effects of cannabinoids on anxious states.

Age-dependent effects of gestational and lactational iron deficiency on anxiety behavior in rats

Gestational iron deficiency (ID) has been linked to alterations in GABA neurotransmission, but whether these neuronal changes are mirrored in altered anxiety behavior in rats is not known. In this experiment, two tests of GABA-related affective behaviors in rats, ultrasonic vocalizations (USVs) and elevated plus maze (EPM) were used to investigate the consequences of maternal ID. Female rats were randomly assigned to one of three diet groups: low iron (10–20 ppm Fe), recommended (standard) iron control (60 ppm Fe) or lab chow (250 ppm Fe) control. Diets started 7 days prior to mating and continued until 10 days after birth (PN10). Maternal behavior and offspring growth and activity were also assessed. Blood samples taken on PN10 revealed a significant decrement in serum iron and an increase in total iron binding capacity in the low iron groups compared to the two control groups. Relative to the two control groups, the low iron group weighed less on PN1, and this weight difference persisted in adulthood. In neonates, the rate of USVs in the low iron group was significantly higher than the two control groups, and their general activity was significantly less than the controls. Maternal behavior was not significantly different across groups. By adulthood, anxiety behavior and motor activity in the low iron group were comparable to controls, although the iron deficient subjects habituated more slowly. This study shows that prenatal iron deficiency results in increased anxiety behavior in neonates that appears to be reversed with iron repletion but that some aspects of altered exploratory behavior and growth persist into adulthood.

Effects of clonidine injections into the bed nucleus of the stria terminalis on fear and anxiety behavior in rats

Emotions such as fear and anxiety are mediated by a neural network containing nuclei like the amygdala, the bed nucleus of the stria terminalis and the periaqueductal gray. Noradrenaline is a neurotransmitter closely connected with the processing of stimuli eliciting these emotions. The bed nucleus of the stria terminalis contains the highest density of noradrenaline within the brain. In the present study, we investigated effects of injections of the noradrenergic α 2-adrenoceptor agonist clonidine into the bed nucleus of the stria terminalis on learned and unlearned fear (anxiety) in rats on different animal models of fear and anxiety: acquisition and expression of fear-potentiated startle, sensitization of the acoustic startle response by foot shocks and light-enhanced startle. Clonidine injections disrupted acquisition and expression of fear-potentiated startle, as well as light-enhanced startle, whereas sensitization was not affected. These results indicate that noradrenaline within the bed nucleus of the stria terminalis mediates both fear and anxiety. We suggest that there is rather a neurochemical than a neuroanatomical dissociation between learned fear and anxiety as hypothesized by Walker and Davis (Walker, D.L. and M. Davis, 1997b, Double dissociation between the involvement of the bed nucleus of the stria terminalis and the central nucleus of the amygdala in startle increases produced by conditioned versus unconditioned fear, J. Neurosci. 17, 9375–9383.).

GABA A but not GABA B receptor stimulation induces antianxiety profile in rats

The effect of GABA receptor agonists and antagonists on anxiety behavior in rats in the elevated-plus-maze has been investigated. The increase in two parameters of %open arm entries (%OAE) and %time spent in the open arms (%OAT) and decrease in the %time spent in closed arm (%CAT) was considered as antianxiety effects. Intracerebroventricular (icv) injection of different doses of the GABA A receptor agonist muscimol (0.25, 0.5, and 1 μg/rat) increased %OAE and %OAT and decreased %CAT in rats dose-dependently. The higher response was obtained with 1 μg/rat of the drug. Neither icv (0.05, 0.1, and 0.2 μg/rat) nor intraperitoneal (ip) (1, 2, and 4 mg/kg) injection of the GABA B receptor agonist baclofen altered %OAE, %OAT, and %CAT. However, the GABA B receptor antagonist CGP35348 (5, 10, and 30 μg/rat icv) increased %OAE and %OAT and decreased %CAT in the animals. The response induced by injection of muscimol (0.5 μg/rat icv) or administration of CGP35348 (10 μg/rat icv) was reduced by icv (1, 2, and 4 μg/rat) or ip (0.25, 0.5, and 0.75 mg/kg) injection of the GABA A receptor antagonist bicuculline, except the effect of CGP35348 on %CAT which was not significantly altered by ip administration of bicuculline. Ip but not icv administration of bicuculline by itself reduced both %OAE and %OAT but did not alter %CAT. None of the drugs altered the locomotor activity of the animals. The current findings support our hypothesis that the anxiolytic effects of GABA B antagonist are mediated by autoreceptor blockade-induced release of endogenous GABA, which in turn activates postsynaptic GABA A receptors.

Inhibition of anxiety in rats by antisense to cholecystokinin precursor protein

Background: Cholecystokinin (CCK) and its analogs generates anxiety in humans and measurable anxiety-like behaviors in rats. CCK receptor blockers have had mixed results as a treatment approach for anxiety disorders. Since CCK is a peptide, we explored another strategy to reduce CCK levels in brain by antisense oligodeoxynucleotide inhibition of DNA transcription or messenger RNA (mRNA) translation for CCK precursor protein. Methods: Antisense oligodeoxynucleotide complementary to the start coding region of rat CCK-precursor was intracerebroventricularly (icv) infused into rats three times at 24-hour intervals. Control groups received infusions of either a scramble sequence oligodeoxynucleotide or vehicle. On the fourth day, rats were assessed in the elevated plus maze paradigm. Results: Compared to vehicle and scramble sequence oligodeoxynucleotide control, icv CCK-antisense exogenous administration for 3 days significantly diminished anxiety behavior in rats. Conclusions: Antisense inhibition of CCK-mediated anxiety could have therapeutic potential in human anxiety disorders.

Central oxytocin administration reduces stress-induced corticosterone release and anxiety behavior in rats.

Endocrine responses to noise stress and anxiety-related behaviors were measured in groups of ovariectomized, estradiol-treated female rats given central infusions of oxytocin. Control animals receiving isotonic saline showed a large increase in plasma corticosterone concentrations in response to 10 min of white noise. This response to noise stress was significantly and dose dependently decreased by oxytocin administered intracerebroventricularly at 10 or 100 ng/h for 5 days. Oxytocin also significantly decreased rearing behavior during this stress. When a second noise stress was given 3 days after cessation of oxytocin infusion, corticosterone responses did not differ between the control and previously oxytocin-infused animals. Administration of vasopressin had no significant effect on either the corticosterone or behavioral responses to noise stress. Anxiety-related behaviors were measured on the elevated plus-maze. No significant differences were seen in maze exploration between saline- and oxytocin-treated animals when housed and tested in the same environment. However, when animals were mildly stressed by testing in an unfamiliar environment, oxytocin-treated animals showed a higher proportion of open arm entries and spent significantly more time in the open arms of the maze. Thus, oxytocin exerts a central anxiolytic-like effect on both endocrine and behavioral systems and could play a role in moderating behavioral and physiological responses to stress.

Central Oxytocin Administration Reduces Stress-Induced Corticosterone Release and Anxiety Behavior in Rats

Central Oxytocin Administration Reduces Stress-Induced Corticosterone Release and Anxiety Behavior in Rats

Sex differences in anxiety behavior in rats: Role of gonadal hormones

These experiments examined the role of gonadal hormones at both the organizational and activational time periods on sex differences in plus-maze behavior. In the first experiment, adult female Long-Evans rats were found to spend more time on the open arms of the plus maze than adult males, indicating less anxious behavior. In the second experiment, male and female subjects received a neonatal treatment (chemical castration with flutamide or tamoxifen, vehicle injection, or no injection) and a prepubertal treatment (gonadectomy, sham surgery, or no surgery). Adult females receiving either neonatal tamoxifen or prepubertal ovariectomy spent less time on the open arms than control females, but females who received both treatments were the most defeminized subjects. Males were not affected by the absence of gonadal hormones at either time period. These experiment indicate that female gonadal hormones play an important role both organizationally and activationally in plus-maze behavior. The role of the GABA receptor complex in mediating this effect is discussed. Knowledge of sex differences in plus-maze behavior may help to make this maze a more useful tool in investigating anxiety behavior in rats.