Dark Box Test Research Articles

Administration of aluminium to neonatal mice in vaccine-relevant amounts is associated with adverse long term neurological outcomes

Our previous ecological studies of autism spectrum disorder (ASD) has demonstrated a correlation between increasing ASD rates and aluminium (Al) adjuvants in common use in paediatric vaccines in several Western countries. The correlation between ASD rate and Al adjuvant amounts appears to be dose-dependent and satisfies 8 of 9 Hill criteria for causality. We have now sought to provide an animal model to explore potential behavioural phenotypes and central nervous system (CNS) alterations using s.c. injections of Al hydroxide in early postnatal CD-1 mice of both sexes. Injections of a “high” and “low” Al adjuvant levels were designed to correlate to either the U.S. or Scandinavian paediatric vaccine schedules vs. control saline-injected mice. Both male and female mice in the “high Al” group showed significant weight gains following treatment up to sacrifice at 6months of age. Male mice in the “high Al” group showed significant changes in light–dark box tests and in various measures of behaviour in an open field. Female mice showed significant changes in the light–dark box at both doses, but no significant changes in open field behaviours. These current data implicate Al injected in early postnatal life in some CNS alterations that may be relevant for a better understanding of the aetiology of ASD.

Selective deletion of leptin receptors in adult hippocampus induces depression-related behaviours

Previous studies have demonstrated that leptin and its receptors (LepRb) in the central nervous system play an important role in regulating depression- and anxiety-related behaviours. However, the physiological functions of LepRb in specific brain regions for mediating different emotional behaviours remain to be defined. In this study, we examined the behavioural effects of LepRb ablation in the adult hippocampus using a series of behavioural paradigms for assessing depression- and anxiety-related behaviours. Targeted deletion of LepRb was achieved using the Cre/loxP site-specific recombination system through bilateral stereotaxic delivery of an adeno-associated virus expressing Cre-recombinase (AAV-Cre) into the dentate gyrus of adult mice homozygous for a floxed leptin receptor allele. AAV-Cre-mediated deletion of the floxed region of LepRb was detected 2 wk after injection. In accordance with this, leptin-stimulated phosphorylation of Akt was attenuated in the hippocampus of AAV-Cre injected mice. Mice injected with AAV-Cre displayed normal locomotor activity and anxiety-like behaviour, as determined in the elevated plus-maze, light-dark box and open field tests, but showed increased depression-like behaviours in the tail suspension, saccharin preference and learned helplessness tests. Taken together, these data suggest that deletion of LepRb in the adult hippocampus is sufficient to induce depression-like behaviours. Our results support the view that leptin signalling in the hippocampus may be essential for positive mood states and active coping to stress.

Involvement of the α1-adrenoceptor in sleep–waking and sleep loss-induced anxiety behavior in zebrafish

Sleep is a universal phenomenon in vertebrates, and its loss affects various behaviors. Independent studies have reported that sleep loss increases anxiety; however, the detailed mechanism is unknown. Because sleep deprivation increases noradrenalin (NA), which modulates many behaviors and induces patho-physiological changes, this study utilized zebrafish as a model to investigate whether sleep loss-induced increased anxiety is modulated by NA. Continuous behavioral quiescence for at least 6s was considered to represent sleep in zebrafish; although some authors termed it as a sleep-like state, in this study we have termed it as sleep. The activity of fish that signified sleep–waking was recorded in light–dark, during continuous dark and light; the latter induced sleep loss in fish. The latency, number of entries, time spent and distance travelled in the light chamber were assessed in a light–dark box test to estimate the anxiety behavior of normal, sleep-deprived and prazosin (PRZ)-treated fish. Zebrafish showed increased waking during light and complete loss of sleep upon continuous exposure to light for 24h. PRZ significantly increased sleep in normal fish. Sleep-deprived fish showed an increased preference for dark (expression of increased anxiety), and this effect was prevented by PRZ, which increased sleep as well. Our findings suggest that sleep loss-induced anxiety-like behavior in zebrafish is likely to be mediated by NA’s action on the α1-adrenoceptor.

Pleiotropic effect of histamine H4 receptor modulation in the central nervous system

The histamine H4 receptor (H4R) is expressed primarily on cells involved in inflammation and immune responses. Recently, it has been reported the functional expression of H4R within neurons of the central nervous system, but their role has been poorly understood. The present study aimed to elucidate the physiopathological role of cerebral H4R in animal models by the intracerebroventricular administration of the H4R agonist VUF 8430 (20–40 μg per mouse). Selectivity of results was confirmed by the prevention of the effects produced by the H4R antagonist JNJ 10191584 (3–9 mg/kg p.o.). Neuronal H4R activation induced acute thermal antinociception, indicating that neuronal histamine H4R might be involved in the production of antinociception in the absence of an inflammatory process. An anxiolytic-like effect of intensity comparable to that exerted by diazepam, used as reference drug, was produced in the light–dark box test. VUF 8430 reversed the scopolamine-induced amnesia in the passive avoidance test and showed anorexant activity in food deprived mice. Conversely, the H4R activation did not modify the immobility time in the tail suspension test. Rotarod performance test was employed to demonstrate that the effects observed following the administration of VUF 8430 and JNJ 10191584 were not due to impaired motor function of animals. Furthermore, both compounds did not alter spontaneous mobility and exploratory activity in the hole board test. These results show the antinociceptive, antiamnesic, anxiolytic and anorexant effects induced by neuronal H4R agonism, suggesting that H4 modulators may have broader utility further the control of inflammatory and immune processes.

Behavioral Profile Assessment in Offspring of Swiss Mice Underwent to Neonatal Treatment with D‐fenfluramine

Serotonin (5‐HT) exerts an important role in the central nervous system embryogenesis of mammals, influencing directly several brain systems ontogeny. Therefore, we investigate the effect of neonatal D‐fenfluramine (D‐fen), a specific 5‐HT‐releasing agent, administration on the behavioral expression of adults male Swiss mice. For this purpose, three groups (n=6 each, and ~35g) of pregnant female Swiss mice were mated. The offsprings obtained were treated subcutaneously (s.c) with saline and D‐fenfluramine (1mg/kg or 3mg/kg) from the 5th at 21th post‐natal day. By completing 70 days of life, the animals underwent a behavioral assessment in open field, rotarod, light‐dark box, elevated plus maze and tail suspension test. Statistical analysis was performed by ANOVA one way and the means were considered significantly different when p<0.05. According to our results, the programmed animals had less time of immobility in tail suspension test (D‐fen 3mg/kg: 64.89±6.07; D‐Fen 1mg/kg: 94.15±9.67 vs. control: 130.6±13.26, p<0.001) and less time spent walking on rotarod (D‐fen 3mg/kg: 17.55±7.32; D‐Fen 1mg/kg: 22.75±7.90 vs. control: 189,7±52,33, p<0.001). In the dark light box test, the animals treated with D‐fen 3mg/kg had less time in the light side than the other groups (D‐fen 3mg/kg: 94,56±8.81 vs. D‐Fen 1mg/kg: 121.7±3.43; control: 133.9±8.01, p<0.01). These findings suggest that programming with D‐fenfluramine during the neonatal period alters neural circuits involved with coordination, anxiety and depression‐like behaviors in adults.Support: FAPERJ & CNPq.

Anxiolytic-like effect of Shigyakusan extract with low side effects in mice

Shigyakusan is a traditional Japanese herbal (Kampo) medicine used to treat inflammatory conditions such as cholecystitis and gastritis as well as psychiatric disorders. This study examined the anxiolytic-like effect of Shigyakusan extract (SS), and evaluated the activity of the main compound. Three behavioral tests in mice were used to evaluate the activity of SS. Samples were administered orally over a 10-day period. A light and dark box (LDB) test was performed on the 8th day, while an open field (OF) test was done on the 9th day, and an elevated plus maze (EPM) test was performed on the 10th day. Diazepam (DZ), a typical anxiolytic drug, was used as the positive control. Administration of 10 mg/kg DZ resulted in a significant anxiolytic-like effect in the LDB and EPM tests, while administration of 0.3 g/kg SS resulted in a weak anxiolytic-like effect. In the OF test, while DZ caused a significant reduction of locomotor activity, SS did not cause any changes compared to the water controls. This suggests that locomotor activity may be a side effect of DZ, and thus SS, which lacks this response, may be a more useful treatment. Quantitative analysis performed to clarify the activity of the main compound also determined that SS contained 51.4 mg/g naringin, which also has been reported to have anxiolytic-like activity. Since these results suggested that this compound might be responsible for the activity of SS, we subsequently examined the oral administration of a similar dose of naringin. Although we observed a tendency for a weak anxiolytic-like effect, this effect was not greater than that seen for SS.

Evaluation of emotional behaviors in young offspring of C57BL/6J mice after gestational and/or perinatal exposure to nicotine in six different time-windows

Nicotine replacement treatments are being alternatively applied as an aid to smoking cessation during pregnancy. However, the effects of nicotine exposed at the prenatal stage on the emotional behaviors in offspring are not well understood due to the lack of systematic investigations. The current study has therefore initially aimed to evaluate emotional behaviors in young mouse offspring (postnatal day 28–36) which experienced gestational and/or perinatal nicotine exposure (GPNE) in six different time-windows. Pregnant C57BL/6J mice were exposed to nicotine via sweetened (2% sucrose) drinking water during 6 different time-windows including gestational day 0–day 13 (G0–G13), G14–perinatal day 0 (P0), G0–P0, G14–P7, G0–P7, and P0–P7. During P28–P36 days, both male and female offspring were given a battery of behavioral tests including light and dark box test, marble burying behavior test, novelty-suppressed feeding test, sociability and social novelty preference test, social avoidance tube test, and elevated plus maze test. GPNE during G0–P0, G14–P0, G14–P7, and G0–P7 induced abnormal behaviors in male and female offspring to different extent. Results indicated that nicotine at any time points of gestational and/or perinatal period impairs emotional behaviors in offspring, and suggested certain time-windows for further neurochemical or molecular studies in relation with GPNE-induced emotional abnormalities.

Inhibition of nitric oxide synthase accentuates endotoxin-induced sickness behavior in mice

Sickness behavior appears to be the expression of a central motivational state that reorganizes an organism's priorities to cope with infectious pathogens. To evaluate the possible participation of nitric oxide (NO) in lipopolysaccharide-induced sickness behaviors, mice were submitted to the forced swim test (FST), open field test and dark–light box test. Food intake and corticosterone plasma levels were evaluated. Lipopolysaccharide (LPS, 100μg/kg; i.p.) administration increased the time spent floating in the FST and decreased locomotor activity in the open field. Indeed, treatment with LPS decreased the total number of transitions between the dark and light compartments of the apparatus. In addition, LPS reduced food intake and increased corticosterone levels. Pretreatment with L-NAME (30mg/kg; i.p.) or aminoguanidine (50mg/kg; i.p.) accentuated the behavioral changes induced by LPS in the FST, open field and light–dark box tests as well as induced an increment in hypophagia and in corticosterone levels. These findings confirm previous observations that have reported LPS-induced sickness behaviors. In addition, they provide evidence that the synthesis of NO modulates changes in depressive-like and exploratory behaviors in mice, which is supported by the fact that NO synthase inhibitors also attenuate LPS-induced behavioral changes. In addition, the present study suggests that NO may have a protective role, acting in an inhibitory feedback manner to limit LPS-induced sickness behavior.

Unique and potent effects of acute ibogaine on zebrafish: The developing utility of novel aquatic models for hallucinogenic drug research

An indole alkaloid, ibogaine is the principal psychoactive component of the iboga plant, used by indigenous peoples in West Africa for centuries. Modulating multiple neurotransmitter systems, the drug is a potent hallucinogen in humans, although its psychotropic effects remain poorly understood. Expanding the range of model species is an important strategy for translational neuroscience research. Here we exposed adult zebrafish (Danio rerio) to 10 and 20mg/L of ibogaine, testing them in the novel tank, light–dark box, open field, mirror stimulation, social preference and shoaling tests. In the novel tank test, the zebrafish natural diving response (geotaxis) was reversed by ibogaine, inducing initial top swimming followed by bottom dwelling. Ibogaine also attenuated the innate preference for dark environments (scototaxis) in the light–dark box test. While it did not exert overt locomotor or thigmotaxic responses in the open field test, the drug altered spatiotemporal exploration of novel environment, inducing clear preference of some areas over others. Ibogaine also promoted ‘mirror’ exploration in the mirror stimulation test, disrupted group cohesion in the shoaling test, and evoked strong coloration responses due to melanophore aggregation, but did not alter brain c-fos expression or whole-body cortisol levels. Overall, our results support the complex pharmacological profile of ibogaine and its high sensitivity in zebrafish models, dose-dependently affecting multiple behavioral domains. While future investigations in zebrafish may help elucidate the mechanisms underlying these unique behavioral effects, our study strongly supports the developing utility of aquatic models in hallucinogenic drug research. High sensitivity of three-dimensional phenotyping approaches applied here to behavioral effects of ibogaine in zebrafish provides further evidence of how 3D reconstructions of zebrafish swimming paths may be useful for high-throughput pharmacological screening.

Impact of the time in an animal model of mood disorder

The objective of the study is to evaluate whether intervening and testing in different rest-activity periods of the day would produce different measurements in animal behavior studies. Methodology: Thirty-five, 60-day-old male Wistar rats were submitted to an inescapable foot shock (IFS) stress model and behavioral tests (Light–Dark Box test). The animals received intervention and were tested in both light and dark phases, resulting in the following groups: control L (tested in the light), control D (tested in the dark), LL (IFS and tested in the light), LD (IFS in the light and tested in the dark), DL (IFS in the dark and tested in the light), and DD (IFS and tested in the dark). Results: The Light–Dark Box test showed that control L was not significantly different from other groups in any of the parameters. However, when comparing control D with the intervention groups, we observed a difference in the mean length of time spent in the light compartment (t=2.56; p=0.045). A significant difference in the number of crossings into the light compartment was only observed between the control D and the LL and LD groups (t=−2.608; p=0.028; t=−2.571; p=0.030, respectively). The latency time for the control D group was significantly lower than that of the DD group (t=−2.556; p=0.043). Conclusions: These results show that behavior testing during the animal's period of highest activity (dark period) revealed differences caused by the intervention, whereas no differences were apparent when the control group was observed during the day.

Gabra5-gene haplotype block associated with behavioral properties of the full agonist benzodiazepine chlordiazepoxide

The gabra5 gene is associated with pharmacological properties (myorelaxant, amnesic, anxiolytic) of benzodiazepines. It is tightly located (0.5cM) close to the pink-eyed dilution (p) locus which encodes for fur color on mouse chromosome 7. We tested the putative role of the gabra5 gene in pharmacological properties of the full non specific agonist chlordiazepoxide (CDP), using behavioral and molecular approaches in mutated p/p mice and wild type F2 from crosses between two multiple markers inbred strain ABP/Le and C57BL/6By strain. From our results, using rotarod, light–dark box, elevated maze and radial arm maze tests, we demonstrate that p/p mice are more sensitive than WT to the sensory motor, anxiolytic and amnesic effect of CDP. This is associated with the presence of a haplotypic block on the murine chromosome 7 and with an up regulation of gabra5 mRNAs in hippocampi of p/p F2 mice.

Reversal of memory deficits by ethanolic extract of Mimusops elengi Linn. in mice

Background: Management of cognitive disorders like dementia and Alzheimer's disease has been challenging since no potential drug is available with proved efficacy. Some nootropic drugs like piracetam, aniracetam and cholinesterase inhibitors such as Donepezil® have found to exhibit severe toxic effects in elderly. Objective: The present study was designed to investigate the reversal of memory deficits by ethanol extract of Mimusops elengi Linn. in mice. Methods: M. elengi [100 and 200 mg/kg] was administered orally for 8 successive days to both young and aged mice. Elevated plus maze and Passive avoidance paradigm were employed to assess short term and long term memory respectively. Light and dark box test, Open field test and Social interaction test were used to assess the possible anxiolytic potentials of M. Elengi. To delineate the possible mechanism through which M. elengi elicits the anti-amnesic effect, we investigated its influence on central cholinergic activity by estimating the whole brain acetylcholinesterase activity. Results: M. elengi [100 and 200 mg/kg, p.o.] significantly attenuated amnesic deficits induced by diazepam [1 mg/kg, i.p.], scopolamine [0.4 mg/kg, i.p.] and natural aging. M. elengi [100 and 200 mg/kg] decreased transfer latencies and increased step down latencies significantly in the aged mice. It also reversed amnesia induced by diazepam and scopolamine in young mice. M. elengi exhibited significant anxiolytic activity in mice. It also decreased whole brain acetyl cholinesterase activity significantly. Conclusion: M. elengi can be useful in restoring memory in the treatment of various types of dementia.

Central pharmacological activity of a new piperazine derivative: 4-(1-Phenyl-1h-pyrazol-4-ylmethyl)-piperazine-1-carboxylic acid ethyl ester

AimsOur study focuses on the design and synthesis of a new piperazinic derivate, 4-(1-phenyl-1h-Pyrazol-4-Ylmethyl)-Piperazine-1-Carboxylic Acid Ethyl ester (LQFM008), and evaluation of its anxiolytic-like profile in Swiss mice. Main methodsLQFM008 was evaluated in a screening test of the central nervous system including the rota-rod, sodium pentobarbital-induced sleep, open field, elevated plus maze and light–dark box tests. Key findingsLQFM008 induced convulsions at the dose of 1.1mmol/kg (i.p., s.c. or p.o.). LQFM008 up to 400μmol/kg had no effect in the rota rod test. In the open field test, LQFM008 increased the number of crossings and the time spent at the central area as well as the sleeping time in sodium pentobarbital-induced sleep. In the elevated plus maze and light–dark box tests, this compound showed an anxiolytic-like activity. This anxiolytic-like activity was antagonized by NAN-190 (5-HT1A antagonist) but not by flumazenil (benzodiazepine antagonist). SignificanceThe compound LQFM008 showed anxiolytic-like activity which may involve serotonergic pathway.

Dipyrone attenuates acute sickness response to lipopolysaccharide in mice

Sickness behavior appears to be the expression of a central motivational state that reorganizes the organism's priorities to cope with infectious pathogens. To evaluate the effect of dipyrone in lipopolysaccharide (LPS)-induced sickness behavior, mice were subjected to the forced swim test (FST), tail suspension test (TST), dark–light box test, open field test, sucrose preference intake test and food intake test. LPS administration increased the immobility time in the TST, increased the time spent floating in the FST, and depressed locomotor activity in the open field test. Treatment with LPS decreased the total number of transitions made between the dark and light compartments of the apparatus and induced anhedonia and anorexia. Pre-treatment with dipyrone (10, 50, or 200mg/kg) attenuated behavioral changes induced by LPS in the FST, TST, open field and light–dark box tests. In addition, dipyrone prevented anhedonia and anorexia in mice challenged with LPS. Considering that dipyrone attenuates LPS-induced behavioral changes, it is proposed that LPS-induced sickness behavior is dependent on the COX pathway.

Effects of the alpha- and gamma-polymorphs of glycine on the behavior of catalepsy prone rats

Glycine is used to treat various health problems and is efficient in the treatment of the negative symptoms of schizophrenia. Since glycine exists as a few polymorphs, the aim of this work is to compare the effects of the alpha- and gamma-forms of glycine on the behavior of the genetic catalepsy (GC) strain of rats. Both polymorphs of glycine have been administered to rats orally as pure solid chemicals, and cataleptic behavior and behaviors in the open-field, elevated plus-maze, and light–dark box tests were studied. Both the alpha- and gamma-polymorphs of glycine increased exploratory activity in the open-field test, but only the gamma-polymorph had beneficial effects on catalepsy and exploratory activity in the light–dark box and reduced anxiety in the elevated plus-maze.

Prostaglandins mediate depressive-like behaviour induced by endotoxin in mice

Sickness behaviour appears to be the expression of a central motivational state that reorganises the organism's priorities to cope with infectious pathogens. To evaluate the possible participation of prostaglandins in lipopolysaccharide-induced sickness behaviours, mice were submitted to the tail suspension test (TST), forced swim test (FST), open field test and dark–light box test. Lipopolysaccharide (LPS, 100 μg/kg; i.p.) administration increased the time spent immobile in the TST, increased the time spent floating in the FST, and depressed locomotor activity in the open field. Indeed, treatment with LPS decreased the total number of transitions made between the dark and light compartments of the apparatus. Pretreatment with indomethacin (10 mg/kg; i.p.) or nimesulide (5 mg/kg) blocked behavioural changes induced by LPS in the FTS, TST, open field and light–dark box test. This effect was similar to pretreatment with dexamethasone (1 mg/kg), which is a steroidal drug that inhibits immune and inflammatory responses, including cytokine production. These findings confirm previous observations that have reported LPS-induced sickness behaviours. In addition, they provide evidence that the synthesis of prostaglandins is necessary for changes in depressive-like and exploratory behaviours in mice, which is supported by the fact that COX inhibitors also attenuate LPS-induced behavioural changes.

Translating rodent behavioral repertoire to zebrafish ( Danio rerio): Relevance for stress research

The current study provides a detailed description of the pattern of exploratory behaviors encountered in adult zebrafish when exposed to a novel/unfamiliar environment using the light/dark box and open field tests. We also document the impact of an acute stressor ( restraint stress) given just prior the onset of behavioral testing. We report the following main findings: (1) zebrafish display anxiety-like behaviors including dark-avoidance (in light/ dark box test) and thigmotaxis (in open field test), (2) upon exposure to a novel environment (first 2 min), zebrafish display place preference for the outer zone of the testing apparatus where they seek escape via the transparent wall, and exhibit high locomotor activity accompanied by high swimming speed, (3) thigmotaxis, behavioral hyperactivity, and swimming speed habituate (decrease) over time, (4) prior history of stress attenuates the natural tendency to engage in dark-avoidance behavior and thigmotaxis, reduces attempts to escape via the transparent wall, and greatly increased behavioral hyperactivity and swimming speed. Stress-induced patterns of behavior normalize to levels comparable to that of non-stressed controls by the end of the 5-min test session. Taken together, these findings suggest that novel environment can elicit anxiety-like behaviors in zebrafish such as dark-avoidance and thigmotaxis and the prior history of stress greatly affects patterns of exploration, defensive behaviors, and coping strategies in the light/ dark box and open field tests. These findings are consistent with previous findings in rodents and support the usefulness of such behavioral paradigms in zebrafish.

Lack of promoter IV‐driven BDNF transcription results in depression‐like behavior

Transcription of Bdnf is controlled by multiple promoters, in which promoter IV contributes significantly to activity-dependent Bdnf transcription. We have generated promoter IV mutant mice [brain-derived neurotrophic factor (BDNF)-KIV] in which promoter IV-driven expression of BDNF is selectively disrupted by inserting a green fluorescent protein (GFP)-STOP cassette within the Bdnf exon IV locus. BDNF-KIV animals exhibited depression-like behavior as shown by the tail suspension test (TST), sucrose preference test (SPT) and learned helplessness test (LHT). In addition, BDNF-KIV mice showed reduced activity in the open field test (OFT) and reduced food intake in the novelty-suppressed feeding test (NSFT). The mutant mice did not display anxiety-like behavior in the light and dark box test and elevated plus maze tests. Interestingly, the mutant mice showed defective response inhibition in the passive avoidance test (PAT) even though their learning ability was intact when measured with the active avoidance test (AAT). These results suggest that promoter IV-dependent BDNF expression plays a critical role in the control of mood-related behaviors. This is the first study that directly addressed the effects of endogenous promoter-driven expression of BDNF in depression-like behavior.

Restraint stress-induced brain activation patterns in two strains of mice differing in their anxiety behaviour

Genetically identical inbred mouse strains are one of the most useful tools in dissecting the genetic basis of complex disorders. C57BL/6 and BALB/c mice differ markedly in emotionality. In particular, BALB/c mice are more stress-sensitive and have been proposed to be a model of pathological anxiety. There is a paucity of studies investigating whether brain activation in response to a stressor is different in these two strains. To this end, having confirmed that the strains differ in anxiety responses in a light–dark box test, we then examined if restraint stress induced increases in c-Fos protein expression in selective regions of the mouse brain. The areas of interest analysed were the paraventricular nucleus (PVN) of the hypothalamus, prefrontal cortex (PFC), the paraventricular thalamic nucleus (PV) and the hippocampus. These areas were chosen due to their known involvement in stress response. Our data demonstrate that BALB/c showed a similar cellular activation pattern to stress, with respect to c-Fos expression, in the PVN, PV and in the hippocampus. On the other hand, BALB/c showed markedly blunted stress-induced brain activation compared with stressed C57BL/6 mice in both the CG1 and CG2 regions of the PFC. The lower levels of stress-induced activity in high anxiety BALB/c mice, possibly indicate a circuit dysregulation at the cortico-limbic level in response to stress.

Effects of dietary extra-virgin olive oil on behaviour and brain biochemical parameters in ageing rats

The aim of the present study was to verify whether extra-virgin olive oil, a dietary component naturally containing phenolic antioxidants, has the potential to protect the brain from the deleterious effects of ageing. To accomplish this goal, we used male rats fed a high-energy diet containing either maize oil, or extra-virgin olive oil with high or low phenol content (720 or 10 mg total phenols/kg oil, corresponding to a daily dose of 4 or 0.05 mg total phenols/kg body weight, respectively) from age 12 months to senescence. The measured endpoints were biochemical parameters related to oxidative stress and functional tests to evaluate motor, cognitive and emotional behaviour. Olive oil phenols did not exert major protective actions on motor and cognitive function, as we observed only a tendency to improved motor coordination on the rotarod in the old animals treated with the oil rich in phenols (40 % average increase in the time to first fall; P = 0.18). However, an interesting finding of the present study was a reduced step-through latency in the light-dark box test, found in the older animals upon treatment with the oil rich in antioxidant phenols, possibly indicating an anxiety-lowering effect. This effect was associated with decreased glutathione reductase activity and expression in the brain, a phenomenon previously associated with decreased anxiety in rodents. These results indicate a previously undetected effect of a diet containing an olive oil rich in phenols. Further studies are warranted to verify whether specific food antioxidants might also have an effect on emotional behaviour.