Behavior In Male Wistar Rats Research Articles

Short photoperiod restores ventral subicular lesion-induced deficits in affective and socio-cognitive behavior in male Wistar rats.

Photoperiod (day-length) has enduring effects on an organism's physiological functions like metabolism and behavioral phenotypes including cognition and affect. Circadian rhythm manipulations are potentially effective non-pharmacological strategies in the management of central nervous system insults. In our previous study, we demonstrated the efficacy of short photoperiod regime (SPR; 06/18hr light-dark cycle) in establishing functional recovery in ventral subicular lesion (VSL) rats. The present study further demonstrates the efficacy of SPR in mitigating anxiety and depression as well as facilitating socio-cognitive behavior in VSL rats. VSL elevated the basal plasma corticosterone levels, increased anxiety, anhedonia, and behavioral despair with decreased self-care. The VSL rats also exhibited a considerable degree of impaired social cognition, in terms of altered social preference and social novelty. Exposure to SPR for 21days mitigated the anxiety- and depressive-like phenotypes as well as improved social cognition significantly. Thus, the study demonstrated the effectiveness of SPR strategy in reversing most of the behavioral deficits caused by VSL. SPR, perhaps, would have regulated the hypothalamo-pituitary-adrenal axis responsiveness as we observed a decrease in plasma corticosterone levels following SPR in VSL rats. The study implies the need for developing a task-dependent SPR strategy to achieve complete behavioral recovery as the functional demands of each behavior is distinct. In summary, the study highlights the efficacy of photoperiod manipulation as a novel, non-pharmacological approach in mitigating the affective and cognitive deficits associated with neuropsychiatric disorders such as bipolar disorder and Alzheimer's disease wherein circadian rhythm alterations are implicated.

Dual exposure to stress in different stages of development affects eating behavior of male Wistar rats

Maternal separation stress is a model of early life stress performed by the separation between dam and pups in the first days of life. The consequences of this early stress have been demonstrated on various behaviors, including feeding behavior. The results, however, are still controversial and it seems that a second exposure to stress later in life exacerbates the adverse outcomes. The present study aimed to determine the effects of maternal separation as a model of stress in early life, with or without a later life stress experience on eating behavior. Lactating Wistar rats were separated from their litters from postnatal day 2 (PND 2) to PND 14 for 3 h in the dark phase of the circadian cycle. The groups control (C) and separated (S) were composed. The assessment of food intake was performed between the ages of 60 and 150 days of life with a group that experienced only the early stress by maternal separation and with a second group that experienced the pre-weaning maternal separation stress and the food stress from 60 days of age. This food stress consisted of allowing visual and olfactory exposure of the animals to palatable food but did not allow the feeding. Maternal separation promoted higher palatable food and lower standard diet intake only after a double exposure to stress. Besides, the double exposure to stress promoted weight loss and an anxiety-like behavior. These outcomes were associated with a resistance to the anorectic effects of fluoxetine suggesting an alteration of the serotonergic system. Together, these findings indicate that maternal separation stress has long-lasting consequences on eating behavior, and that the dual exposure to stress seems more harmful to eating behavior outcomes. In addition, the results suggest that the serotonergic system is one candidate as the system mediating these alterations.

The Role of Amnesia Caused by Cerebral Hypoperfusion on Depression-Like Behavior in Male Wistar Rats

The Role of Amnesia Caused by Cerebral Hypoperfusion on Depression-Like Behavior in Male Wistar Rats

Heparin Modulates the Main Properties of the Central Nervous System in Experimental Post-Traumatic Stress Disorder: A New Concept of the Mechanisms of Pathogenesis and Treatment.

Elevated plus-maze test was used to reveal the role of excitation and inhibition mechanisms in the CNS in the organization of the behavior of male Wistar rats under normal conditions and during modeling experimental post-traumatic stress disorder (with or without administration of low doses of high-molecular-weight heparin). The data about insufficiency in the system of excitation mechanisms and pronounced excess in the system of inhibition mechanisms in post-traumatic stress disorder are prioritized. Heparin seems to be a promising and effective preparation to cope with extreme psychotraumatic abnormalities in CNS.

Combining Quantitative and Qualitative Data in the Study of Feeding Behavior in Male Wistar Rats.

The first step in a behavioral study is represented by the organization of a suitable ethogram, that is, a formal description of individual components of the behavior. Then, each component of such a behavioral repertoire can be quantified (e.g., how many times it occurs, its duration, percent distribution, latency, etc.). However, it is our contention that the possibility to describe the behavior of a living being by means of hundreds or even thousands of numbers concerning isolated components, disjointed from the comprehensive behavioral architecture, does not imply the possibility to use those numbers to reconstruct the meaning of behavior. Such a level of comprehension requires a qualitative approach based on the analysis of behavioral structure and its underlying dynamics. By means of synergic utilization of quantitative and qualitative data a more complete description of a given behavior becomes available. In present study we discuss results obtained from observations of feeding behavior in two groups of male Wistar rats: a control group, under standard diet, and a second group, under hyperglycidic one. Results have been presented both in terms of quantitative evaluations and in terms of structural/qualitative ones, the latter obtained by means of T-pattern detection and analysis. As to quantitative results, mean durations showed a significant reduction of Walking and Feeding and an increase of Hind-Paw Licking and Body Grooming; concerning mean occurrences, a significant increase of Front-Paw Licking, Hind-Paw Licking, and Body Grooming was present; percent distributions showed significant reductions for Walking and Feeding and a significant increase for all grooming activities. As to qualitative assessments, T-pattern analysis unveiled a clear-cut behavioral reorganization induced by the hyperglycidic diet. If on the one hand, 50 different T-patterns were detected in subjects under standard diet, on the other hand, 703 different T-patterns were discovered in animals under hyperglycidic treatment, with a highly significant increase of mean lengths and a significant reduction of mean occurrences of T-patterns. Synergic evaluation of results in terms of quantitative and qualitative aspects shows, in rats fed with hyperglycidic diet, an increased anxiety condition, likely dependent on food-related stimuli and suggestive of a pervasive craving-related behavior.

Effects of Nettle on Locomotor Activity and Anxiety Behavior in Male Wistar Rats After Pesticide Intoxication.

The nettle is an herbaceous plant belonging to the family of Urticaceae that has been used for centuries against a variety of diseases. Thanks to its high content of nutriments and bioactive compounds. Therefore, this study was conducted to assess the curative effect of nettle decoction on dimethoate-induced changes in locomotors activity and anxiety reaction in male rats. This experiment was conducted in two stages with 60 healthy male rats that were divided into three groups of 20 rats A, B and C. In the first phase, the treatment groups B and C received dimethoate dissolved in corn oil by gavage at a dose of 100 mg kg-1 b.wt., for 5 weeks. During the same period, the control group A received corn oil. Locomotors activity was controlled by the Open Field (OF), anxiogenic behavior was verified by the Elevated Plus Maze (EPM). For the second phase the group A had kept its control position, the group B was maintained without any treatment to remind the extent of intoxication and was served as second control. Group C received a nettle decoction of 2 mL 100 mg-1 b.wt., for 30 days. The result showed that at the open field level, dimethoate decreased significantly both of the total number of squares crossed by intoxicated rats and the number of elevations. At the EPM level, dimethoate decreased both of the time spent in open arms and the number of entries into the open arms. These results reveal that dimethoate affects the anxiety and mobility of intoxicated rats. On the other hand, the use of nettle decoction as a treatment significantly improved the anxiety level and motor activity of poisoned rats. Dimethoate has an anxiogenic effect on intoxicated rats, as well as a remarkable decrease in their locomotor activity. The use of nettle decoction as a treatment has significantly improved dimethoate induced behavioral and motor disorders.

Expression and Treatment of Pain‐Related Depression of Fixed‐Ratio and Progressive‐Ratio Food‐Maintained Behavior in Rats

Pain‐related interference with behavior is a key clinical diagnostic indicator and target in the treatment of pain. Increasingly, preclinical studies on the expression, mechanisms, and treatment of pain have been aimed at improving understanding of pain‐related interference with behavior. Positively reinforced operant behavior is one category of target behaviors that are sensitive to depression by physiologically‐relevant pain stimuli. This pain‐related depression of behavior can be blocked by clinically‐effective analgesics including opioids and nonsteroidal anti‐inflammatory drugs. Most studies using operant conditioning procedures to examine pain‐related depression of behavior have used fixed‐ratio schedules of reinforcement. The primary dependent variable in these studies is the rate of behavior. In contrast, the primary dependent variable in studies using progressive ratio schedules of reinforcement is breakpoint. Breakpoint is often defined as the final ratio completed by the subject or total number of reinforcers earned, and is thought to be related to the efficacy of the reinforcer or the subject's motivation to obtain the reinforcer. The present studies compare the effects of a noxious pain stimulus and a clinically‐relevant analgesic on behavior maintained under fixed‐ratio and progressive‐ratio schedules of behavior in male Wistar rats. The first aim was to determine whether there were differences in the potency of an acute chemical noxious stimulus, intraperitoneal injection of dilute lactic acid, to depress operant behavior maintained by sucrose under fixed‐ and progressive‐ratio schedules of reinforcement. Under the fixed‐ratio schedule, rats were required to perform six lever presses to access 0.1 ml of 10% sucrose, under the progressive‐ratio schedule, the response requirement increased following the delivery of each reinforcer according to a logarithmic function. Lactic acid was more potent at depressing lever pressing under the fixed‐ratio schedule compared to the progressive‐ratio schedule. The second aim of the study was to examine the effects of the NSAID, ketoprofen, on lactic acid‐induced depression of lever pressing. Consistent with previous studies, ketoprofen was effective at blocking pain‐related depression of behavior maintained under both fixed‐ and progressive‐ratio schedules, and ketoprofen was equipotent in both procedures. Together, these findings support the validity of operant procedures as tools to examine candidate analgesics for the treatment of pain‐related depression of behavior. Moreover, the use of diverse schedules of reinforcement may yield important scientific information on the mechanisms underlying pain‐related interference with behavior. Specifically, the finding that, under the current experimental conditions, lactic acid was more potent to depress lever pressing maintained under a fixed‐ratio schedule than a progressive‐ratio schedule may reflect interference with the rats' ability to respond at a high rate at concentrations that did not impact their motivation to do so.Support or Funding InformationSupported by a University of Georgia‐Augusta University (AU) seed grant, the AU Center for Undergraduate Research and Scholarship, and the AU College of Science and Mathematics.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

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The Effects of Hydromethanolic Extracts of Uncoated and Coated Seeds of Garcinia Kola on the Sexual Behaviour of Male Wistar Rats

The Effects of Hydromethanolic Extracts of Uncoated and Coated Seeds of Garcinia Kola on the Sexual Behaviour of Male Wistar Rats

Adolescent binge alcohol exposure increases risk assessment behaviors in male Wistar rats after exposure to an acute psychological stressor in adulthood

Teenage binge drinking is a common practice that has been shown to increase the risk for developing mood disorders in adulthood. The hypothalamo-pituitary-adrenal (HPA) axis is often dysfunctional in mood disorder patients, and animal models of adolescent binge alcohol exposure similarly show disordered HPA axis function, even after long periods of alcohol abstinence. Here, we sought to investigate the anxiety-like behavioral consequences of binge alcohol exposure in a Wistar rat model. Male rats were administered alcohol in a binge pattern during peri-puberty, and one month later, anxiety-like behaviors were measured using the elevated plus maze. A subset of the rats then underwent 30min of restraint stress, and the anxiety-like behaviors were measured again. We observed an increase in risk assessment behaviors due to both adolescent binge alcohol exposure and restraint stress, but no differences in canonical anxiety-like behaviors. We also repeated the observation that adolescent binge alcohol induces long-term changes in HPA axis sensitivity. Therefore, we concluded that a history of peri-pubertal binge alcohol exposure subtly alters the behavioral response to subsequent acute psychological stress during adulthood, which may over time contribute to the development of mood disorders. This relatively pragmatic animal model represents a more clinically relevant tool in understanding the molecular mechanisms underlying the long-term effects of adolescent binge drinking.

Effects of the benzodiazepine inverse agonist FG7142 on the structure of anxiety-related behavior of male Wistar rats tested in hole board.

Little is known about the structural characteristics of the behavior of rats with enhanced anxiety level. To fill this gap, a study was undertaken where effects of an anxiogenic drug were examined on behavioral structure of rats tested in hole board. This study investigates effects of increased anxiety level on the structure of the behavior of rats tested in hole board METHODS: Different doses of FG7142 (1, 4, 8mg/kg IP), a potent anxiety-inducing drug, were administered to three groups of male Wistar rats. A further group was administered saline. Experiments were recorded through a digital camera. Quantitative and multivariate approaches were applied. Percent distributions and durations showed increases of immobile sniffing, rearing, head dip, and edge sniff and a significant reduction of grooming activities and of walking. In addition, a decrease of head dip/edge sniff ratio was detected. Transition matrices evidenced that FG7142 provoked evident modifications of behavioral structure mainly of general exploration of environment and focused exploration of the hole. Finally, adjusted residuals showed a reduced effectiveness of FG7142 on transitions from head dip to edge sniff; on the contrary, transitions from edge sniff to head dip underwent evident dose-dependent changes. Present study provides a useful tool to analyze behavioral responses to different anxiety conditions. Accordingly, it is demonstrated that a condition of increased anxiety deeply modifies the structure of male Wistar rat's behavior in hole board. In addition, our results suggest that evaluation of head dip/edge sniff ratio can be considered a reliable index to appraise effects of pharmacological manipulation of anxiety and related behavioral elements.

Impaired executive functions in experimental model of temporal lobe epilepsy.

The present study aimed to investigate cognitive and behavioural changes consistent with attention deficit hyperactivity disorder (ADHD -like behavior in male Wistar rats with temporal lobe epilepsy (TLE). Male Wistar rats at 25 day of age were submitted to animal model of TLE by pilocarpine injection (350 mg/kg, ip) and a control group received saline 0.9%. The animals were continuously video monitored up to the end of experiments. The behavioural tests (open field, elevated plus maze and operant conditioning box) started from 60 days postnatal. Animals with TLE exhibited elevated locomotor activity, reduced level of anxiety-related behavior, impulsivity and impaired visuospatial working memory. Taken as a whole, we concluded that animals with TLE exhibited some cognitive and behavioural changes consistent with ADHD-like behavior.

Effects of gonadectomy and serotonin depletion on inter-individual differences in anxiety-like behaviour in male Wistar rats

Previous studies in Wistar rats suggest inter-individual differences in anxiety-like behaviour as assessed using the elevated plus maze (EPM), both between sexes and among males, to be abolished by serotonin depletion. To shed further light on the influence of sex steroids and serotonin – and on the interplay between the two – on proneness for EPM-assessed anxiety in males, outbred Wistar rats were divided into those with high and low anxiety, respectively, and exposed to gonadectomy or sham operation followed by administration of a serotonin synthesis inhibitor, para-chlorophenylalanine, or saline. Whereas gonadectomy enhanced anxiety-like behaviour in low anxiety rats so that these no longer differed in this regard from the high anxiety group, serotonin depletion reversed this effect, and also reduced anxiety in the low anxiety group regardless of gonadal state. A previously observed association between high anxiety-like behaviour and high expression of the serotonin-synthesizing enzyme tryptophan hydroxylase 2 (Tph2) in the raphe was confirmed in sham-operated animals but absent in gonadectomised rats, an ANCOVA revealing a significant interactive effect of baseline anxiety and gonadal state on Tph2 expression. It is suggested that androgens may contribute to upholding inter-individual differences in anxiety-like behaviour in male rats by interacting with serotonergic neurotransmission.

Effect of the aqueous extract of the aerial parts of Monsonia angustifolia E. Mey. Ex A. Rich., on the sexual behaviour of male Wistar rats.

BackgroundMonsonia angustifolia (Geraniaceae) is a medicinal plant traditionally used in South Africa to increase libido and to treat erectile dysfunction.MethodsIn-vivo aphrodisiac activities of the crude extracts of the plant prepared in water at 3, 30 and 300 mg/kg body weight were evaluated for 7 days using sildenafil citrate (Viagra) and 1 % ethanol in distilled water as positive and negative controls respectively. Male rats were selected and monitored in each group for sexual behaviour by exposing them to sexually receptive females on days 1, 3 and 7 for 60 minutes each between 7:00 pm and 3:00 am. The following male sexual parameters were observed: Mount Frequency (MF), Intromission Frequency (IF), Mount Latency (ML), Intromission Latency (IL), Ejaculation Frequency (EF), Ejaculatory Latency (EL) and Post-Ejaculatory Interval (PEI).ResultsThe administration of the extract resulted in significant increase (p < 0.05) in mount frequency, intromission frequency, ejaculation frequency, ejaculation latency and serum hormone concentrations. The computed indices of sexual behaviour such as erection, quick flips, long flips and total penile reflexes were also increased. However, the mount latency, intromission latency and post ejaculation interval were significantly decreased throughout the experimental period. The administration of 300 mg/kg body weight of the aqueous extract produced the best effects in all the parameters.ConclusionGenerally, the extract of Monsonia angustifolia produced pro-sexual stimulatory effects in the male rats especially when administered at 300 mg/kg body weight. The results validate the use of the plant by the indigenous people to increase libido and treat premature ejaculation and erectile dysfunction in males.

The nonsteroidal antiinflammatory drug piroxicam reverses the onset of depressive-like behavior in 6-OHDA animal model of Parkinson’s disease

Depression is one of the most common psychiatric symptoms in patients with Parkinson’s disease (PD). Some authors have reported that depression is characterized by activation of the inflammatory response. Animal models of PD also present with depressive-like behavior, such as increased immobility time in the modified forced swim test and anhedonia-like behavior in the sucrose preference test. Considering the potential neuroprotective effect of nonsteroidal antiinflammatory drugs in neurodegenerative diseases, the objective of the present study was to investigate the effects of piroxicam on depressive-like behavior in male Wistar rats lesioned with 6-hydroxydopamine (6-OHDA) in the substantia nigra (SN). Antidepressant-like effects were observed after prolonged administration of piroxicam for 21days. In the forced swim test, the 6-OHDA+saline group exhibited significant reductions in swimming time and increased immobility time compared with the sham+saline. In the sucrose preference test, the 6-OHDA+piroxicam group exhibited no reduction of sucrose preference compared with the sham+saline, with significant effects of treatment and time and a significant treatment×time interaction. 5-Hydroxytryptamine (5-HT) levels significantly decreased in the hippocampus in the 6-OHDA+saline group and not changed in the 6-OHDA+piroxicam group when compared with the sham+saline on day 21. In conclusion, 21-day treatment with piroxicam reversed the onset of depressive-like behavior and prevented the reduction of hippocampal 5-HT levels.

Enduring effects of post-weaning rearing condition on depressive- and anxiety-like behaviors and motor activity in male rats

Environmental manipulation at early critical periods could have long-lasting effects. In spite of the great interest in the biological effects of the environmental condition so far, its long-lasting effects are less documented. This study looks at the enduring effects of rearing condition on tasks that measure affective responses and exploratory behavior in male Wistar rats. The animals were reared from weaning to adulthood in an enriched environment, standard laboratory condition, or isolated condition. Then, all rats were housed in standard laboratory cages to provide a common environment, and successively exposed to different tests between 0 and 11weeks post-manipulation. The open field test indicated a more efficient exploratory behavior in the enriched group, and an enhanced spontaneous motor activity in both standard and isolated groups. In addition, rats reared in standard condition showed heightened motor activity in forced swimming test and elevated plus maze. Forced swimming test showed an antidepressive-like effect in the enriched environment group by increased climbing behavior. In respect to the anxiety behavior, environmental enrichment improved threat detection ability. It is concluded that rearing condition from weaning to adulthood has important and long-lasting effects on depressive- and anxiety-like and exploratory behaviors as well as motor activity.

Risk-assessment and risk-taking behavior predict potassium- and amphetamine-induced dopamine response in the dorsal striatum of rats.

Certain personality types and behavioral traits display high correlations to drug use and an increased level of dopamine in the reward system is a common denominator of all drugs of abuse. Dopamine response to drugs has been suggested to correlate with some of these personality types and to be a key factor influencing the predisposition to addiction. This study investigated if behavioral traits can be related to potassium- and amphetamine-induced dopamine response in the dorsal striatum, an area hypothesized to be involved in the shift from drug use to addiction. The open field and multivariate concentric square field™ tests were used to assess individual behavior in male Wistar rats. Chronoamperometric recordings were then made to study the potassium- and amphetamine-induced dopamine response in vivo. A classification based on risk-taking behavior in the open field was used for further comparisons. Risk-taking behavior was correlated between the behavioral tests and high risk takers displayed a more pronounced response to the dopamine uptake blocking effects of amphetamine. Behavioral parameters from both tests could also predict potassium- and amphetamine-induced dopamine responses showing a correlation between neurochemistry and behavior in risk-assessment and risk-taking parameters. In conclusion, the high risk-taking rats showed a more pronounced reduction of dopamine uptake in the dorsal striatum after amphetamine indicating that this area may contribute to the sensitivity of these animals to psychostimulants and proneness to addiction. Further, inherent dopamine activity was related to risk-assessment behavior, which may be of importance for decision-making and inhibitory control, key components in addiction.

Chronic administration of thiamine pyrophosphate decreases age-related histological atrophic testicular changes and improves sexual behavior in male Wistar rats.

Aging is a multifactorial universal process and constitutes the most important risk factor for chronic-degenerative diseases. Although it is a natural process, pathological aging arises when these changes occur quickly and the body is not able to adapt. This is often associated with the generation of reactive oxygen species (ROS), inflammation, and a decrease in the endogenous antioxidant systems, constituting a physiopathological state commonly found in chronic-degenerative diseases. At the testicular level, aging is associated with tissue atrophy, decreased steroidogenesis and spermatogenesis, and sexual behavior disorders. This situation, in addition to the elevated generation of ROS in the testicular steroidogenesis, provides a critical cellular environment causing oxidative damage at diverse cellular levels. To assess the effects of a reduction in the levels of ROS, thiamine pyrophosphate (TPP) was chronically administered in senile Wistar rats. TPP causes an activation of intermediate metabolism routes, enhancing cellular respiration and decreasing the generation of ROS. Our results show an overall decrease of atrophic histological changes linked to aging, with higher levels of serum testosterone, sexual activity, and an increase in the levels of endogenous antioxidant enzymes in TPP-treated animals. These results suggest that TPP chronic administration decreases the progression of age-related atrophic changes by improving the intermediate metabolism, and by increasing the levels of antioxidant enzymes.

Involvement of the nucleus accumbens shell dopaminergic system in prelimbic NMDA-induced anxiolytic-like behaviors

BackgroundNucleus accumbens (NAc) and prefrontal cortex (PFC) dopaminergic and glutamatergic systems are involved in fear/anxiety-related behaviors; meanwhile NAc dopaminergic system activity is mediated by PFC via NAc glutamatergic projections. This study has investigated the involvement of NAc shell dopaminergic system in prelimbic NMDA-induced anxiolytic-like behaviors. MethodElevated plus-maze apparatus was employed to test parameters of anxiety-like behaviors in male Wistar rats. ResultsUnilateral intra-prelimbic injection of NMDA (0.9 μg/μl) but not D-AP7 (NMDA receptor antagonist; 0.25, 0.5 and 1 μg/μl) induced anxiolytic-like behaviors which was blocked by D-AP7. Moreover, unilateral infusion of SCH23390 (dopamine D1 receptor antagonist; 0.25, 0.5 and 1 μg/μl) and quinpirole (dopamine D2 receptor agonist; 0.125, 0.25 and 0.5 μg/μl) into the left NAc shell, did not alter anxiety-like behaviors. However, injection of SKF38393 (dopamine D1 receptor agonist; 3 μg/μl) and sulpiride (dopamine D2 receptor antagonist; 0.4 and 0.6 μg/μl) into the left NAc shell, likewise induced anxiolytic-like behaviors which were blocked by SCH23390 (0.25 μg/μl) and SKF96365 (Ca-channel blocker; 0.125 μg/μl)/SCH23390 (0.25 μg/μl), respectively. Furthermore, infusion of the subthreshold dose of SCH23390 (0.25 μg/μl) or quinpirole (0.25 μg/μl) into the left NAc shell, reduced while did not alter intra-prelimbic NMDA-induced anxiolytic-like behaviors, respectively. In addition, intra-NAc shell administration of the subthreshold dose of SKF38393 (1 μg/μl) or sulpiride (0.2 μg/μl), potentiated the lower dose response, while decreased the higher dose intra-left prelimbic NMDA response. ConclusionOur results suggested a modulatory effect of the NAc shell dopaminergic system on prelimbic NMDA-induced anxiolytic-like behaviors.

The effects of the time of the day and the pinealectomy on anxiety-like behaviour in male Wistar rats

The previous studies on the anxiety-like behaviour in rats by using elevated plus maze and open field have provided rather unequivocal results because they obtained data at different times of the day. These studies have never investigated the effects of the different times of day in a single research paradigm even though the results of such studies are generally attributed to the different measurement times. Thus, we aimed to examine the effects of the time of the day and the pinealectomy on anxiety-like behaviour in male Wistar albino rats by using elevated plus maze and open field in this study. Experiments were performed with control and pinealectomy groups at the four different time points (6:00, 12:00, 18:00 and 24:00 hr; LD 12:12, lights on at 6:00 h and off at 18:00 h). In open field, the main effect of the measurement time was significant on the total distance travelled, the mobility and the velocity. In elevated plus maze, the main effect of the measurement time was significant on the total distance travelled, the total entry to closed arms and mobility. The main effect of the pinealectomy was insignificant on all of the measured parameters in both open field and elevated plus maze except for the total entry to closed arms in elevated plus maze. The results of the present study showed for the first time that the time of the day when the measurements are performed is important on the anxiety-like behaviour of the Wistar albino rats.