Behavioural alterations in rats induced by single prenatal exposure of haloperidol

Haloperidol (50 mg/kg, i.p.) treatment was given once to two different groups of pregnant Charles Foster rats on gestational day 9 and 14, these being respectively the critical periods of neural morphogenesis and rapid neural cell proliferation in this species. Pregnant control rats were similarly treated with equal volume of vehicle. The pups born were subjected to open-field exploratory behaviour and elevated plus-maze behaviour tests of anxiety and learned helplessness test of depression at 9 weeks of age. The results indicate that prenatal haloperidol treatment on gestational day 14 induces a significant increase in open-field ambulation and faecal droppings whereas haloperidol treatment on gestational day 9 caused significantly decreased rearing and unaltered ambulation in rat offsprings. Rat offsprings treated with haloperidol on gestational day 9 and 14 also displayed significant anxiogenic behaviour pattern on elevated plus-maze. Significantly increased number of escape failures were observed in learned helplessness tests indicating presence of depression in haloperidol treated rat offsprings. These behavioural alterations were found to be more marked in rat offsprings treated with haloperidol on gestational day 14. The results suggest that prenatal single exposure of high dose of haloperidol during critical period of neural cell proliferation leaves a lasting imprint on offsprings resulting in abnormal emotional state.     

Effect of prenatal alprazolam exposure on anxiety patterns in rat offspring

Prenatal alprazolam (APZ) treatment in 0.1 and 0.2 mg/kg/day doses during 13-20 days of gestation induced significant increase in open-field ambulation, rearings, self-grooming and faecal pellets in rat offspring. Prenatal APZ treated rats displayed significantly increased anxiogenic behaviour on elevated plus maze (spent less time on open arms, more time on enclosed arms and made less number of entries on open arms) and increased anxiogenecity on elevated zero maz e(APZ treated rats spent less time on open arms and made less number of head dips and stretched attend postures in comparison to control rat offspring). The results indicate persistent behavioural alterations in the rat offspring after prenatal exposure to APZ.     

Effects of diazepam on the behaviour of weaned pigs in three putative models of anxiety

The present study examined the effects of diazepam (a widely used anxiolytic benzodiazepine) on the behavioural response of pigs to three novel experimental situations used to measure anxiety-related behaviour in rodents. Twelve weaned pigs (two pairs from each of the three litters) were tested in an elevated plus-maze at the age of 6 weeks, a light/dark test at the age of 7 weeks and an open-field test at the age of 8 weeks. Six of the pigs were pre-treated with diazepam (valium) and the other six with saline (control). In the elevated plus-maze, diazepam-treated pigs had a higher number of entries into open arms (P=0.04), spent more time on open arms (P=0.07), and had a higher number of total arm entries (P=0.05) than pigs from the control group. However, diazepam had no significant effects on behaviour in the light/dark test (i.e., latency to enter lit compartment, number of entries into lit compartment and the time spent in lit compartment) or the open-field test (i.e., number of lines crossed, number of entries into centre). In summary, the anxiolytic effects of diazepam on the pigs' behaviour were only demonstrated in the elevated plus-maze, where the time spent on open arms and the number of entries into open arms could be interpreted as measures of anxiety in pigs.     

Peculiarities of exploration behavior of socially deprived rats in stress situation

Male Wistar rats (n = 18) were studied at the age of 120 days after social deprivation in the period from the 22nd to 70th days of postnatal development. They displayed significant lower activity in the open field, elevated plus-maze, and Porsolt test than control animals (n = 19). Decreased exploratory activity was found to be related with higher level of anxiety. This was confirmed by their avoidance of open arms of the elevated plusmaze and reactions to approaching hand. These animals had problems in the maze arm choice. They showed low time variability of choice-related actions (waiting in the center of the open field or elevated plus-maze and change in the movement direction along an open-field wall, including the movement per se, and arm choice and changing, i.e., alternative choice). Shorter time of choice-related actions was observed in situations of unequal alternatives.     

Individual differences in the elevated plus-maze and the forced swim test

The elevated plus-maze is an apparatus composed of enclosed and open (elevated) arms and time spent in the open arms by a rat can be increased/decreased by anxiolytic/anxiogenic agents. In the forced swim test, floating behavior is used as an index of behavioral despair and can be decreased by antidepressant agents. As the comorbidity between anxiety and depression is a remarkable issue in human behavioral disorders, a possible relationship between the behaviors seen in the cited tests is of great relevance. In the present study, fifty-four male rats (Rattus norvegicus) were submitted to a plus-maze session and to a 2-day forced swim protocol. According to their time in the open arms, they were divided into three groups: Low Open, Medium Open and High Open. Some plus-maze measures were found to be coherent with time in the open arms and are suggested to also be reliable anxiety indexes. In the forced swim test, the Low Open group showed decreases in floating duration from forced swim Session 1 to Session 2, an alteration opposite to that observed in the other groups (particularly, the Medium Open group). The Low Open group also showed increases in floating latency, again in sharp contrast with the alteration found in the other groups. Accordingly, positive and negative correlation were found between time in the open arms and floating duration and latency, respectively. Results are compared to previous studies and mediation of the effect by reactivity to aversive stimulation or alterations induced by open arm exposure is discussed.     

Ghrelin increases anxiety-like behavior and memory retention in rats

Ghrelin is a peptide found in the hypothalamus and stomach that stimulates food intake and whose circulating concentrations are affected by nutritional state. Very little is known about other central behavioral effects of ghrelin, and thus, we investigated the effects of ghrelin on anxiety and memory retention. The peptide was injected intracerebroventricularly in rats and we performed open-field, plus-maze, and step-down tests (inhibitory avoidance). The administration of ghrelin increased freezing in the open field and decreased the number of entries into the open spaces and the time spent on the open arms in the plus-maze, indicating an anxiogenic effect. Moreover, the peptide increased in a dose-dependent manner the latency time in the step-down test. A rapid and prolonged increase in food intake was also observed. Our results indicate that ghrelin induces anxiogenesis in rats. Moreover, we show for the first time that ghrelin increases memory retention, suggesting that the peptide may influence processes in the hippocampus.     

Alterations of behavior and spatial learning after unilateral entorhinal ablation of rats

The entorhinal cortex (EC) is the key input and output structure of the hippocampus. It plays a crucial role in sensory processing, memory and learning, as well as in mechanisms of epileptic seizures. Our previous studies on the 4-aminopyridin induced epilepsy model of rats showed that ablation of unilateral EC prompted weakening of limbic seizure manifestation, thus the possibility of therapeutical benefit of this kind of surgery can be risen. Open field, elevated plus-maze and Morris water-maze test were performed to analyze changes of the basal activity level, exploratory behavior, and spatial memory capacity, respectively, of adult Wistar rats having undergone left EC excision. Compared with the sham-operated control group, rats with lesions of the EC showed enhanced locomotor activity in the open-field test. The elevated plus-maze test revealed higher frequency of entries and more time spent in the open arms. Morris water-maze test suggested impairment of the spatial learning capacity following left lateral EC lesion. Therefore, our data showed that EC lesions induced hyperactivity, increased exploratory behavior, and impaired spatial learning. Entorhinal cortex ablation, as a potential method for controlling epileptic seizures has multiple effects on animals' behavior and spatial learning. To determine the cost-benefit ratio of a potential surgical intervention needs further experimental and human investigations.     

Behavioral effects of sinomenine in murine models of anxiety

The present study was designed to investigate the putative anxiolytic-like effect of sinomenine in three experimental models of anxiety in male rats and mice. Use of the elevated plus-maze test revealed that sinomenine (20 and 40 mg/kg, p.o.) increased the percentage of open arm entries and diazepam (2 mg/kg, p.o.) increased the percentage of open arm entries, the percentage of time spent on open arms and total arm entries in mice. In the light/dark transition test, sinomenine (20 and 40 mg/kg, p.o.) increased time spent in the light area and diazepam (2 mg/kg, p.o.) increased time spent in the light area and the overall movements in mice. In the social interaction test, the sinomenine-treated animals significantly increased social interaction time in low light unfamiliar (7 mg/kg, p.o.) and high light unfamiliar conditions (7 and 14 mg/kg, p.o.) as well as diazepam (3 mg/kg, p.o.). Sinomenine (28 mg/kg, p.o.) can also decrease squares entered in rats in social interaction test under low light unfamiliar condition. In the open-field test, sinomenine (160 mg/kg) decreased squares entered in mice. Thus, these findings indicated that sinomenine exhibited anxiolytic-like effect.     

The phenomenon of "one-trial tolerance" to the anxiolytic effect of chlordiazepoxide in the elevated plus-maze is abolished by the introduction of a motivational conflict situation.

A single exposure to the elevated plus-maze test of anxiety reduces or abolishes the anxiolytic efficacy of benzodiazepines. The present study was designed to examine whether this phenomenon of "one-trial tolerance" resulted from a motivational deficit on trial 2. We hypothesized that whereas there is a motivational conflict on trial 1 in relation to the open arms (exploration drive X natural fear of open spaces), there is no "reason" for an animal to explore it on trial 2. A motivational conflict was introduced on trial 2 by rendering the enclosed arms of the apparatus aversive on trial 1. Thus, every time rats entered the enclosed arms, an aversive situation (light and hot air blow) was produced until they left the arm. On trial 2, rats did not receive this aversive stimulation. Chlordiazepoxide significantly enhanced the percent open arm time as well as the percent open arm entries on trial 2 in rats that had been submitted to the aversive stimulation in the enclosed arms on trial 1, but was not effective in rats which had been exposed to the apparatus in the absence of the aversive stimulation on trial 1. In addition, there was no difference in the percent open arm time and entries on trial 2 between saline-treated rats submitted to the aversive or non-aversive condition on trial 1. The aversive condition on trial 1 did not modify the number of total arm entries on trial 2, either. The results suggest that the anxiolytic effect of chlordiazepoxide in the elevated plus-maze depends on the presence of a motivational conflict situation.     

Effects of under- and overcrowding on exploratory behavior in the elevated plus-maze

The present work investigated whether the number of rats housed in a cage affects exploration of an elevated plus-maze. Male Wistar-derived rats were kept 1, 2, 3, 4, 6, 8, 12, 16, or 24 to same size cages either for 1 or 14 days and tested in the elevated plus-maze. Rats kept 6 to a cage were arbitrarily considered controls because this is the housing condition adopted in many laboratories, ours included. In comparison to controls, 1-day housed rats kept 1, 2, 16, and 24 to a cage decreased the percentage of entries into the open arms. Similar decreases were also found in the time spent in the open arms, the only exception being the group with rats kept 16 to a cage which failed to show significant differences from the control group. Fourteen-day housed rats kept 1, 2, 16, or 24 to a cage decreased the percentage of entries and time spent in the open arms. We found plus-maze exploration to be similar in groups in which rats were kept from 4 to 12 to a cage. The present data indicate that anxiogenic effects resulting from under- and overcrowding should be taken into consideration in behavioral studies.     

Prenatal stress increases anxiety related behavior and alters cerebral lateralization of dopamine activity

Effects of unpredictable (random) prenatal stress on the level of anxiety and cerebral lateralization of dopamine turnover rates were studied in rats. The observation of a decrease in the amount of time spent in the open arms of a "plus-maze" supported earlier findings of an increased fearfulness to stressful situations in the offspring in adulthood. We also observed elevated rates of dopamine turnover in the right prefrontal cortex and reduced dopamine activity in the right nucleus accumbens and left corpus striatum of the prenatally stressed animals. This resulted in directional shifts of left-right differences in dopamine activity in all 3 areas. These findings indicate that prenatal stress induces permanent alterations in dopaminergic activity and in cerebral asymmetry. We suggest that the changes in cerebral lateralization of dopamine function may underly the increase in reactivity to anxiety-provoking situations in prenatally stressed offspring.     

Repeated oral administration of capsaicin increases anxiety-like behaviours with prolonged stress-response in rats

This study was conducted to examine the psycho-emotional effects of repeated oral exposure to capsaicin, the principal active component of chili peppers. Each rat received 1 mL of 0.02% capsaicin into its oral cavity daily, and was subjected to behavioural tests following 10 daily administrations of capsaicin. Stereotypy counts and rostral grooming were significantly increased, and caudal grooming decreased, in capsaicin-treated rats during the ambulatory activity test. In elevated plus maze test, not only the time spent in open arms but also the percent arm entry into open arms was reduced in capsaicin-treated rats compared with control rats. In forced swim test, although swimming duration was decreased, struggling increased in the capsaicin group, immobility duration did not differ between the groups. Repeated oral capsaicin did not affect the basal levels of plasma corticosterone; however, the stress-induced elevation of plasma corticosterone was prolonged in capsaicin treated rats. Oral capsaicin exposure significantly increased c-Fos expression not only in the nucleus tractus of solitarius but also in the paraventricular nucleus. Results suggest that repeated oral exposure to capsaicin increases anxiety-like behaviours in rats, and dysfunction of the hypothalamic-pituitary-adrenal axis may play a role in its pathophysiology.     

Conflict as a determinant of rat behavior in three types of elevated plus-maze

Three groups of rats were tested in different types of elevated plus-mazes, a normal one (two closed and two open arms), a totally closed one (four closed arms) and a totally open (four open arms). Closed arms were surrounded by 40-cm high wooden walls and open arms were surrounded by 0.5-cm high transparent Plexiglas ledges. As expected, in the closed maze rats explored equally all the arms, both in terms of time and frequency of entries, as well as in exploration of the extremities. Rats in the totally open maze also presented a similar pattern of exploration, that is, no significant differences were found between the results obtained with the closed and the open mazes in terms of central and extremities exploration. It is suggested that the typical behavior of rats in the conventional elevated plus-maze is caused by the contrasting characteristics of open and closed arms rather than by the physical aversive characteristics of the open arms per se. Results also confirm a prediction made by a computer model simulating rat exploratory behavior in virtual mazes, normal, totally open and totally closed.     

Effects of pair-housing after social defeat experience on elevated plus-maze behavior in rats

Social defeat experience in male rats causes an increase in anxiety-like behavior in the elevated plus-maze. Some researchers have suggested that housing rats socially following social defeat attenuates and/or prevents an increase in anxiety-like behavior. However, many other studies have shown that individual housing per se enhances anxiety-like behavior even in the absence of social defeat. In the present study, we assessed the relative contributions of the experience of social defeat and housing conditions on animals’ performance in the elevated plus-maze. Rats were assigned to one of the following four groups: defeat/individual housing, defeat/pair-housing, non-defeat/individual housing, and non-defeat/pair-housing. The elevated plus-maze test was conducted 2 weeks after the defeat experience. Our results demonstrated that the defeat/individual housing group spent less time than the other groups in the open arms: moreover, there were no differences between the other three groups. These results confirm the claim that the group-housing of rats prevents an increase in anxiety-like behavior caused by defeat.     

Anxiogenesis induced by nitric oxide synthase inhibition and anxiolytic effect of melanin-concentrating hormone (MCH) in rat brain.

In this study, the involvement of nitric oxide (NO) in the mechanism of anxiety was investigated. The rats received an intraamygdaline or intrahippocampal injection of the nitric oxide synthase inhibitor, N(G)-nitro-l-arginine (L-NOARG), and were then tested in the plus-maze test. L-NOARG induced a decrease in the time spent by rats in the open arms. Conversely, the administration of the melanin-concentrating hormone (MCH) into these structures increased the number of entries into the open arms as well as the time spent on them. MCH injected in rats pretreated with L-NOARG also was able to revert the anxiogenic effects of L-NOARG in amygdala.     

Effects of (−)-Sesamin on Chronic Stress-Induced Anxiety Disorders in Mice

This study investigated the effects of (?)-sesamin on chronic electric footshock (EF) stress-induced anxiety disorders in mice. Mice were treated with (?)-sesamin (25 and 50 mg/kg) orally once a day for 21 days prior to exposure to EF stress (0.6 mA, 1 s every 5 s, 3 min). Mice treated with (?)-sesamin (25 and 50 mg/kg) exhibited less severe decreases in the number of open arm entries and time spent on open arms in the elevated plus-maze test and the distance traveled in the open field test following exposure to chronic EF stress. Similarly, mice treated with (?)-sesamin exhibited significantly less severe decreases in brain levels of dopamine, norepinephrine, and serotonin following exposure to chronic EF stress. Increases in serum levels of corticosterone and expression of c-Fos were also less pronounced in mice treated with (?)-sesamin (25 and 50 mg/kg). These results suggest that (?)-sesamin may protect against the effects of chronic EF stress-induced anxiety disorders by modulating dopamine, norepinephrine, and serotonin levels, c-Fos expression, and corticosterone levels.     

Anxiolytic-like effect of succinic acid in mice

The putative anxiolytic activity of succinic acid was examined in male mice by using a number of experimental paradigms of anxiety and compared with that of the known anxiolytic compound diazepam. Use of the elevated plus-maze test revealed that diazepam (1.0, 2.0 and 4.0 mg/kg, PO) or succinic acid (3.0 or 6.0 mg/kg, PO) increased the percentage of entries into open arms and of time spent on open arms. In novel food consumption test, succinic acid (3.0, 6.0, and 12.0 mg/kg, IP) caused significant increases in food intake during 5 min when compared with the vehicle. In the stress-induced hyperthermia test, 40 min after drug administration rectal temperature was measured, succinic acid at dose of 1.5 mg/kg, inhibited stress-induced hyperthermia. Thus, these findings indicated that, in contrast with diazepam, succinic acid exhibits anxiolytic-like effect.     

Augmentation of the NO-cGMP cascade induces anxiogenic-like effect in mice.

Several studies have reported the anxiolytic-like effects of various nitric oxide synthase inhibitors in distinct animal models. However, in the context of anxiety, the possible involvement of cyclic GMP, believed to be one of the main targets of NO, remains obscure. Cyclic GMP is degraded by the specific phosphodiesterases in the brain. Therefore, we studied the effect of the selective phosphodiesterase type 5 inhibitor sildenafil in the mouse elevated plus-maze test of anxiety and in the open field test of locomotion. We found that sildenafil (0.05-10 mg/kg i.p.) alone did not affect the behavior of animals in the plus-maze or open field tests, but the anxiogenic beta-carboline DMCM given in a subconvulsive dose (2 mg/kg i.p.) decreased the time spent on open arms in the elevated plus-maze. Treatment with the NO precursor L-arginine (200 mg/kg i.p.) did not modify the behavior of animals in the plus-maze, however, when sildenafil (1 mg/kg i.p.) was administered in combination with L-arginine (200 mg/kg i.p.), both the time spent on the open arms and the percentage of open arm visits were significantly decreased. We conclude that augmentation of the NO-cGMP cascade induces anxiogenic-like effect in mice.     

One-trial tolerance to the effects of chlordiazepoxide in the elevated plus-maze is not due to acquisition of a phobic avoidance of open arms during initial exposure

A single exposure to the elevated plus-maze (EPM) test of anxiety reduces or abolishes the anxiolytic-like efficacy of benzodiazepines. This phenomenon called one-trial tolerance has been suggested to represent the acquisition of a phobic-like response to the open arms during trial 1. The present study was designed to examine the effects of chlordiazepoxide (5 mg/kg, ip) on the behaviour of rats in a conventional EPM apparatus after previous exposure to a four-open-arm EPM, a four-enclosed arm EPM or a conventional EPM, as well as in naive rats. Chlordiazepoxide had clear-cut anxiolytic-like effects (increased percentage of time spent on the open arms) in a traditional EPM in naive rats and in animals previously exposed to a four-open-arm EPM. However, it was ineffective in rats previously exposed to a traditional or a four-closed-arm EPM. Thus, the phenomenon of one-trial tolerance does not depend upon initial open-arm experience.     

Behavioural evaluation of methods for assessing fear responses in weaned pigs

Models of anxiety and fear of novelty were evaluated using correlations and principal component analysis. A total of 84 pigs (LandracexYorkshire) from nine different litters were subjected to a tonic immobility (TI) test at the age of 2.5 weeks, an elevated plus-maze (EPM) at the age of 6 weeks, a light/dark (L/D) exploration test at the age of 7 weeks and an open-field (OF) test at the age of 8 weeks.The first component from the principal component analysis had the highest correlation with number of entries into open arms in the EPM but was also highly correlated to variables from the other three tests confirming a common aversion-related element in the four experimental tests. The second component was negatively correlated with percent entries into and time spent on open arms in the EPM, but positively correlated with the number of entries into closed arms in the same test, number of lines crossed in the OF and time spent in the lit compartment of the L/D test. The last point illustrates a negative relationship between "anxiety" and "activity" in the EPM and OF. To achieve purer measures of fear of novelty and activity in the tests, the components were rotated using the Varimax criterion. The rotated factor pattern demonstrated a simple structure where variables related to "anxiety" or "fear of novelty" (i.e., percent entries into open arms and time spent on open arms of the EPM) had the highest loading on factor 1, whereas variables related to activity (i.e., number of entries into the closed arms in the EPM, number of lines crossed in the OF and time spent in the lit compartment of the L/D test) had the highest loading on factor 2. TI duration loaded more strongly on factor 1 ("fear of novelty") than on factor 2 ("activity"), but did not represent any pure measure of either fear of novelty or activity.In conclusion, all of the test variables were related to one another. Open-arm avoidance represented the purest measure of fear of novelty, whereas entries into closed arms and number of lines crossed in the OF were the purest measures of activity. The EPM appeared to provide the best way to separate the fear of novelty and activity-related elements, indicating that the EPM may be a useful behavioural model of fear of novelty or avoidance in pigs.