Effects of reserpine on the plus-maze discriminative avoidance task: dissociation between memory and motor impairments

Fluoxetine rescues the depressive-like behaviour induced by reserpine and the altered emotional behaviour induced by nicotine withdrawal in zebrafish: Involvement of tyrosine hydroxylase

BACKGROUND

Nicotine cessation leads to anxiety and depression.

AIMS

The suitability of the zebrafish model of anhedonia using reserpine and fluoxetine was evaluated. Fluoxetine was also used to reduce nicotine withdrawal-induced anhedonic state.

METHODS

Zebrafish were exposed to reserpine (40 mg/l) and then to fluoxetine (0.1 mg/l) for 1 week. Anhedonia was evaluated in the Novel Tank Diving and Compartment Preference tests. Another group was exposed to nicotine (1 mg/l/2 weeks) and then exposed to fluoxetine. Anxiety and anhedonia were evaluated 2-60 days after. Tyrosine hydroxylase (TH) immunoreactivity and microglial morphology (labelled by 4C4 monoclonal antibody) in the parvocellular pretectal nucleus (PPN), dorsal part, and of calcitonin gene-related peptide (CGRP) in the hypothalamus were also analysed.

RESULTS

Less time in the top and increased latency to the top in reserpine compared to a drug-free group was found. Fluoxetine rescued reserpine-induced the reduced time in the top. Seven and 30 days after nicotine withdrawal more time in the bottom and similar time in the Compartment Preference test, rescued by fluoxetine, were shown. In the PPN, 30-day withdrawal induced an increase in TH immunoreactivity, but fluoxetine induced a further significant increase. No changes in PPN microglia morphology and hypothalamic CGRP were detected.

CONCLUSIONS

Our findings validate the suitability of the zebrafish model of anhedonia using the reserpine-induced depression-like behaviour and the predictivity using fluoxetine. Fluoxetine rescued nicotine withdrawal-induced anhedonic state, opening the possibility to screen new drugs to alleviate anxiety and depression in smokers during abstinence.

Effect of Hesperetin on the Antidepressant Activity of Electroconvulsive Therapy in an Enforced Reserpine Model of Depression in Male Rats

Background: Depression is a common and debilitating disorder of the brain. Many pharmacological therapies, including many plant components (such as flavonoids), are used to treat depression. Electroconvulsive therapy (ECT) is a useful method for depressed patients who do not respond to medication. However, this method has some side effects. Hence, investigators have tried to improve ECT’s positive points by diminishing its side effects. Objectives: We investigated the effect of hesperetin (a flavonoid component) on the antidepressant activity of ECT in an enforced reserpine model of depression in male rats. Methods: Eighty male rats (230 - 250 g) were randomly divided into control, ECT + reserpine (Res), Res + hesperetin (Hes; 10 or 20 mg/kg), Res + ECT, and Res + ECT + Hes (10 or 20 mg/kg) groups. The effects of hesperetin were evaluated by the forced swimming test (FST), sucrose preference test (SPT), open field test (OFT), elevated plus maze test (EPMT), as well as by measurement of the brain-derived neurotrophic factor (BDNF) and oxidative stress biomarkers [ie, malondialdehyde (MDA), superoxide dismutase (SOD), and glutathione (GSH)] in the prefrontal cortex area. Results: The outcomes of the behavioral experiments showed that Hes + ECT treatment could raise the percentage of open arm entrance in EPMT, anhedonia in SPT, and decrease immobilization time in FST compared to the groups treated with ECT (P < 0.05) or hesperetin alone. Our biochemical research also illustrated a significant reduction in MDA in the groups treated with ECT + Hes (10 or 20 mg/kg; P < 0.01 and P < 0.001) and ECT or hesperetin, as well as a significant increase in GSH, SOD, and BDNF in the ECT + Hes (20 mg/kg) animal group (P < 0.001). Conclusions: In depressed rats, the ECT linked to the application of hesperetin could significantly elevate BDNF, GSH, and SOD reduction in depressed male rats.

Visuo-spatial learning and memory impairments in the 5xFAD mouse model of Alzheimer's disease: Effects of age, sex, albinism, and motor impairments

The 5xFAD mouse model of Alzheimer's disease (AD) rapidly develops AD-related neuro-behavioral pathology. Learning and memory impairments in 5xFAD mice, however, are not always replicated and the size of impairments varies considerably across studies. To examine possible sources of this variability, we analyzed the effects of age, sex, albinism due to background genes (Tyrc , Oca2p ) and motor impairment on learning and memory performance of wild type and 5xFAD mice on the Morris water maze, from 3 to 15 months of age. The 5xFAD mice showed impaired learning at 6-9 months of age, but memory impairments were not detected with the test procedure used in this study. Performance of 5xFAD mice was profoundly impaired at 12-15 months of age, but was accompanied by slower swim speeds than wild-type mice and a frequent failure to locate the escape platform. Overall female mice performed worse than males, and reversal learning impairments in 5xFAD mice were more pronounced in females than males. Albino mice performed worse than pigmented mice, confirming that albinism can impair performance of 5xFAD mice independently of AD-related transgenes. Overall, these results show that 5xFAD mice have impaired learning performance at 6-9 months of age, but learning and memory performance at 12-15 months is confounded with motor impairments. Furthermore, sex and albinism should be controlled to provide an accurate assessment of AD-related transgenes on learning and memory. These results will help reduce variability across pre-clinical experiments with 5xFAD mice, and thus enhance the reliability of studies developing new therapeutics for AD.

Myrtenol complexed with β-cyclodextrin ameliorates behavioural deficits and reduces oxidative stress in the reserpine-induced animal model of Parkinsonism

Current pharmacological approaches to treat Parkinson's disease have low long-term efficacy and important adverse side effects. The development of new pharmacological therapies has focused on novel plant-derived phytochemicals. The alcoholic monoterpene myrtenol has been isolated from several plant species, and has anxiolytic, analgesic, anti-inflammatory and antioxidant actions. Our study evaluated the neuroprotective potential of myrtenol complexed with β-cyclodextrin (MYR) on a progressive parkinsonism model induced by reserpine (RES) in mice. The complexation with cyclodextrins enhances the pharmacological action of monoterpenes. Male Swiss mice were treated daily with MYR (5 mg/kg, p.o.) and with RES (0.1 mg/kg, s.c.) every other day during 28 days. Behavioural evaluations were conducted across treatment. At the end of the treatment, immunohistochemistry for tyrosine hydroxylase (TH) and oxidative stress parameters were evaluated. Chronic MYR-treatment protected against olfactory sensibility loss, restored short-term memory and decreased RES-induced motor impairments. Moreover, this treatment prevented dopaminergic depletion and reduced the oxidative status index in the dorsal striatum. Therefore, MYR ameliorated motor and non-motor impairments in the progressive animal model of parkinsonism, possibly by an antioxidant action. Additional research is needed to investigate the mechanisms involved in this neuroprotective effect.

The influence of early exposure to methylphenidate on addiction-related behaviors in mice

Methylphenidate (MET) has a putative cognitive enhancer effect that has led adolescents and young adults to increase and indiscriminate its use aiming to ameliorate their productivity. However, the impacts of MET on addiction-related behaviors, emotional levels, and cognition are still not fully understood. To investigate the influence of chronic treatment with MET during adolescence on addiction-like behaviors, memory, and anxiety in adult mice. Thirty-day-old female mice received i.p. 10 mg/kg MET or Veh injections for 10 consecutive days. Forty days after the treatment (mice were 70-days-old), animals were submitted to the behavioral evaluation under the effects of MET, which included: MET-induced conditioned place preference (CPP), behavioral sensitization, and plus-maze discriminative avoidance task. Pre-exposure to MET during adolescence promoted an early expression of CPP and also facilitated the development of MET-induced behavioral sensitization during adulthood. These addictive-like behaviors were accompanied by anxiogenic effects of MET but not by any memory-enhancing effect. We demonstrated that exposure to MET during adolescence can increase the vulnerability to addiction-like behaviors and anxiety during adulthood. Our results reinforce the necessity of a more efficient system to control MET indiscriminate use, thus avoiding its potential tardive addictive effects.

Impact of rasagiline nanoparticles on brain targeting efficiency via gellan gum based transdermal patch: A nanotheranostic perspective for Parkinsonism

Rasagiline mesylate is used as first line agent for early management of Parkinson's disease but its water soluble nature creates hurdles to cross blood brain barrier also its low oral bioavailability and rapid elimination requires frequent dosing. Thus present study aims to prepare rasagiline mesylate-nanoparticles (RM-NPs) loaded gellan gum transdermal film for non-invasive; self-administration in elderly patients. PLGA coated RM-NPs prepared by solvent evaporation technique were incorporated into film prepared by solvent casting method. Optimized films with 1.127 g gellan gum and 1.962 % linoleic acid showed enhanced ex-vivo diffusion over a period of 72 h. Comparative pharmacokinetic study revealed increased bioavailability of rasagiline on transdermal application compared to oral route. In-vivo anti-Parkinson activity estimated by behavioural and biochemical analysis indicate reserpine to interfere with monoamine storage hence resulting in development of akinesia and PD-like symptoms in rats. Brain targeting monitored by gamma imaging showed effective brain drug uptake from transdermal film which was also supported by increased brain targeting efficiency estimated from biodistribution study. Thus, the data support efficacy of gellan gum film to target drug to brain region compared to oral route and hence can be employed as a convenient approach for long-term treatment of Parkinson's disease in elderly patients.

Eplingiella fruticosa leaf essential oil complexed with β-cyclodextrin produces a superior neuroprotective and behavioral profile in a mice model of Parkinson's disease

Evidence indicates that oxidative stress has an important role in the onset and progression of Parkinson's disease (PD). Antioxidant agents from natural products have shown neuroprotective effects in animal models of PD. Eplingiella fruticosa is an aromatic and medicinal plant of the Lamiaceae family that include culinary herbs. The essential oil (EPL) has anti-inflammatory and antioxidant activities. Cyclodextrins are used to enhances pharmacological profile of essential oil. We obtained the EPL from leaves and complexed with β-cyclodextrin (EPL-βCD). Phytochemical analysis showed as main constituents: β-caryophyllene, bicyclogermacrene and 1,8-cineole. We evaluated the effects of EPL and EPL-βCD (5 mg/kg, p.o. for 40 days) on male mice submitted to the progressive reserpine PD model. Behavioral evaluations, lipid peroxidation quantification and immunohistochemistry for tyrosine hydroxylase were conducted. EPL delayed the onset of catalepsy and decreased membrane lipid peroxides levels in the striatum. EPL-βCD also delayed the onset of catalepsy, reduced the frequency of oral diskynesia, restored memory deficit, produced anxiolytic activity and protected against dopaminergic depletion in the striatum and SNpc. These findings showed that EPL has a potential neuroprotective effect in a progressive PD animal model. Further, EPL-βCD enhanced this protective effects, suggesting a novel therapeutic approach to ameliorate the symptoms of PD.

Desipramine rescues emotional memory deficit induced by low doses of reserpine

Emotional memory deficit is a well-known complication in early Parkinson's disease. However, its molecular mechanism is still not well known. To address this issue, we examined the cue-related fear-conditioning task and long-term potentiation (LTP) of the thalamus to the lateral amygdala in rats treated with low doses of reserpine (Res). We found that low-dose Res treatment impaired emotional memory and LTP. We also found that exogenous upregulation of norepinephrine (NE) ameliorated the impairment of LTP by facilitating β-adrenergic receptors. Finally, acute treatment with NE or desipramine rescued the impaired emotional memory induced by a low-dose of Res. These results imply a pivotal role for NE in synaptic plasticity and associative fear memory in rats treated with low doses of Res and suggest that desipramine is a potential candidate for treating Parkinson's disease-related emotional memory deficit.

Long-term Potentiation Decay and Poor Long-lasting Memory Process in the Wild Rodents Proechimys from Brazil's Amazon Rainforest

Proechimys are small terrestrial rodents from Amazon rainforest. Each animal species is adapted to a specific environment in which the animal evolved therefore without comparative approaches unique characteristics of distinct species cannot be fully recognized. Laboratory rodents are exceedingly inbred strains dissociated from their native habitats and their fundamental ecological aspects are abstracted. Thus, the employment of exotic non-model species can be informative and complement conventional animal models. With the aim of promoting comparative studies between the exotic wildlife populations in the laboratory and traditional rodent model, we surveyed a type of synaptic plasticity intimately related to memory encoding in animals. Using theta-burst paradigm, in vitro long-term potentiation (LTP) in the CA1 subfield of hippocampal slices was assessed in the Amazon rodents Proechimys and Wistar rats. Memory, learning and anxiety were investigated through the plus-maze discriminative avoidance task (PM-DAT) and object recognition test. In PM-DAT, both animal species were submitted to two test sessions (3-h and 24-h) after the conditioning training. Proechimys exhibited higher anxiety-like behavior in the training session but during test sessions both species exhibited similar patterns of anxiety-related behavior. After 3-h of the training, Proechimys and Wistar spent significantly less time in the aversive enclosed arm than in the non-aversive arm. But, at 24-h after training, Wistar rats remained less time in the aversive closed arm in comparison with the non-aversive one, while Proechimys rodents spent the same amount of time in both enclosed arms. In the object recognition test, both species were evaluated at 24-h after the acquisition session and similar findings than those of the PM-DAT (24-h) were obtained, suggesting that long-term memory duration did not persist for 24-h in the Amazon rodent. Field excitatory post-synaptic potentials recordings revealed that LTP decays rapidly over time reaching basal levels at 90 min after theta-burst stimulation in Proechimys, contrasting to the stable LTP found in the Wistar rats which was observed throughout 3-h recording period. These findings suggest a link between the LTP decay and the lack of 24-h long-lasting memory process in Proechimys. Nevertheless, why early-phase LTP in Proechimys decays very rapidly remains to be elucidated.

Passiflora cincinnata Extract Delays the Development of Motor Signs and Prevents Dopaminergic Loss in a Mice Model of Parkinson's Disease

Passiflora cincinnata Masters is a Brazilian native species of passionflower. This genus is known in the American continent folk medicine for its diuretic and analgesic properties. Nevertheless, few studies investigated possible biological effects of P. cincinnata extracts. Further, evidence of antioxidant actions encourages the investigation of possible neuroprotective effects in animal models of neurodegenerative diseases. This study investigates the effect of the P. cincinnata ethanolic extract (PAS) on mice submitted to a progressive model of Parkinson's disease (PD) induced by reserpine. Male (6-month-old) mice received reserpine (0.1 mg/kg, s.c.), every other day, for 40 days, with or without a concomitant treatment with daily injections of PAS (25 mg/kg, i.p.). Catalepsy, open field, oral movements, and plus-maze discriminative avoidance evaluations were performed across treatment, and immunohistochemistry for tyrosine hydroxylase was conducted at the end. The results showed that PAS treatment delayed the onset of motor impairments and prevented the occurrence of increased catalepsy behavior in the premotor phase. However, PAS administration did not modify reserpine-induced cognitive impairments. Moreover, PAS prevented the decrease in tyrosine hydroxylase immunostaining in the substantia nigra pars compacta (SNpc) induced by reserpine. Taken together, our results suggested that PAS exerted a neuroprotective effect in a progressive model of PD.

Cannabidiol Prevents Motor and Cognitive Impairments Induced by Reserpine in Rats

Cannabidiol (CBD) is a non-psychotomimetic compound from Cannabis sativa that presents antipsychotic, anxiolytic, anti-inflammatory, and neuroprotective effects. In Parkinson's disease patients, CBD is able to attenuate the psychotic symptoms induced by L-DOPA and to improve quality of life. Repeated administration of reserpine in rodents induces motor impairments that are accompanied by cognitive deficits, and has been applied to model both tardive dyskinesia and Parkinson's disease. The present study investigated whether CBD administration would attenuate reserpine-induced motor and cognitive impairments in rats. Male Wistar rats received four injections of CBD (0.5 or 5 mg/kg) or vehicle (days 2-5). On days 3 and 5, animals received also one injection of 1 mg/kg reserpine or vehicle. Locomotor activity, vacuous chewing movements, and catalepsy were assessed from day 1 to day 7. On days 8 and 9, we evaluated animals' performance on the plus-maze discriminative avoidance task, for learning/memory assessment. CBD (0.5 and 5 mg/kg) attenuated the increase in catalepsy behavior and in oral movements - but not the decrease in locomotion - induced by reserpine. CBD (0.5 mg/kg) also ameliorated the reserpine-induced memory deficit in the discriminative avoidance task. Our data show that CBD is able to attenuate motor and cognitive impairments induced by reserpine, suggesting the use of this compound in the pharmacotherapy of Parkinson's disease and tardive dyskinesia.

Behavioral and neurochemical effects induced by reserpine in mice

RATIONALE

Reserpine, a monoamine-depleting agent, which irreversibly and non-selectively blocks the vesicular monoamine transporter, has been used as an animal model to study several neurological disorders, including tardive dyskinesia and Parkinson's disease.

OBJECTIVE

The purpose of this study was to examine if motor deficits induced by reserpine in mice could be related to alterations in the expression of dopaminergic system proteins such as tyrosine hydroxylase (TH) and dopamine transporter (DAT) and in the activity of monoamine oxidase (MAO).

METHODS

Mice received either vehicle or reserpine (0.1, 0.5, or 1 mg/kg, s.c.) for four consecutive days. Two, 20, or 60 days after reserpine withdrawal, behavioral, and neurochemical changes were evaluated.

RESULTS

Reserpine at a dose of 0.5 and 1 mg/kg increased vacuous chewing movements (VCMs) and reduced locomotion. Behavioral changes were accompanied by reduction in TH immunoreactivity in the striatum evaluated on days 2 and 20 after the last injection of 1 mg/kg reserpine. Furthermore, negative correlations were found between VCM and MAO-A or MAO-B on day 2 and TH striatal immunoreactivity on day 20 after the last injection of 1 mg/kg reserpine. A positive correlation was observed between VCMs and DAT immunoreactivity in the substantia nigra on day 2 after the last injection of 0.5 mg/kg reserpine.

CONCLUSIONS

These findings suggest that the pharmacological blockage of vesicular monoamine transporter (VMAT) by reserpine caused neurochemical and behavioral alterations in mice.

Effects of post-training modafinil administration in a discriminative avoidance task in mice

OBJECTIVE

Although the cognitive-enhancing abilities after modafinil have been demonstrated, its effects on memory consolidation remain overlooked. We investigated the effects of repeated modafinil administration on consolidation of a discriminative avoidance task.

METHODS

Mice were trained in the plus-maze discriminative avoidance task. After training, mice received intraperitonial modafinil (doses of 32, 64 or 128 mg/kg). Animals were treated for more 9 consecutive days; 30 min after the last injection, testing was performed. In addition, the effects of 32 mg/kg modafinil on consolidation at different time points were examined.

RESULTS

The smaller dose of modafinil (32 mg/kg) impaired memory consolidation, without modifying anxiety or locomotion. Still, modafinil post-training administration at 1 or 2 h impaired memory persistence.

CONCLUSIONS

Modafinil impaired memory consolidation in a dose- and time-dependent fashion.

Molecular, Neurochemical, and Behavioral Hallmarks of Reserpine as a Model for Parkinson's Disease: New Perspectives to a Long-Standing Model

The administration of reserpine to rodents was one of the first models used to investigate the pathophysiology and screening for potential treatments of Parkinson's disease (PD). The reserpine model was critical to the understanding of the role of monoamine system in the regulation of motor and affective disorders, as well as the efficacy of current PD treatments, such as L-DOPA and dopamine agonists. Nevertheless, with the introduction of toxin-induced and genetic models of PD, reserpine became underused. The main rationale to this drawback was the supposed absence of reserpine construct validity with PD. Here, we highlight classical and recent experimental findings that support the face, pharmacological, and construct validity of reserpine PD model and reason against the current rationale for its underuse. We also aim to shed a new perspective upon the model by discussing the main challenges and potentials for the reserpine model of PD.

Aquatic blues: modeling depression and antidepressant action in zebrafish

Depression is a serious psychiatric condition affecting millions of patients worldwide. Unipolar depression is characterized by low mood, anhedonia, social withdrawal and other severely debilitating psychiatric symptoms. Bipolar disorder manifests in alternating depressed mood and 'hyperactive' manic/hypomanic states. Animal experimental models are an invaluable tool for research into the pathogenesis of bipolar/unipolar depression, and for the development of potential treatments. Due to their high throughput value, genetic tractability, low cost and quick reproductive cycle, zebrafish (Danio rerio) have emerged as a promising new model species for studying brain disorders. Here, we discuss the developing utility of zebrafish for studying depression disorders, and outline future areas of research in this field. We argue that zebrafish represent a useful model organism for studying depression and its behavioral, genetic and physiological mechanisms, as well as for anti-depressant drug discovery.

Estrogen levels modify scopolamine-induced amnesia in gonadally intact rats

Previous studies suggested that estrogen plays a role in cognitive function by modulating the cholinergic transmission. However, most of the studies dealing with this subject have been conducted using ovariectomized rats. In the present study we evaluated the effects of physiological and supra-physiological variation of estrogen levels on scopolamine-induced amnesia in gonadally intact female rats. We used the plus-maze discriminative avoidance task (PMDAT) in order to evaluate anxiety levels and motor activity concomitantly to the memory performance. In experiment 1, female Wistar rats in each estrous cycle phase received scopolamine (1 mg/kg) or saline i.p. 20 min before the training session in the PMDAT. In experiment 2, rats in diestrus received estradiol valerate (1 mg/kg) or sesame oil i.m., and scopolamine (1 mg/kg) or saline i.p., 45 min and 20 min before the training, respectively. In experiment 3, rats in diestrus received scopolamine (1 mg/kg) or saline i.p. 20 min before the training, and estradiol valerate (1 mg/kg) or sesame oil i.m. immediately after the training session. In all experiments, a test session was performed 24 h later. The main results showed that: (1) scopolamine impaired retrieval and induced anxiolytic and hyperlocomotor effects in all experiments; (2) this cholinergic antagonist impaired acquisition only in animals in diestrus; (3) acute administration of estradiol valerate prevented the learning impairment induced by scopolamine and (4) interfered with memory consolidation process. The results suggest that endogenous variations in estrogen levels across the estrous cycle modulate some aspects of memory mediated by the cholinergic system. Indeed, specifically in diestrus, a stage with low estrogen levels, the impairment produced by scopolamine on the acquisition was counteracted by exogenous administration of the hormone, whereas the posttraining treatment potentiated the negative effects of scopolamine during the consolidation phase of memory.

Food restriction increases long-term memory persistence in adult or aged mice

Food restriction (FR) seems to be the unique experimental manipulation that leads to a remarkable increase in lifespan in rodents. Evidences have suggested that FR can enhance memory in distinct animal models mainly during aging. However, only few studies systemically evaluated the effects FR on memory formation in both adult (3-month-old) and aged (18-24-month-old) mice. Thus, the aim of the present study was to investigate the effects of acute (12h) or repeated (12h/day for 2days) FR protocols on learning and memory of adult and aged mice evaluated in the plus-maze discriminative avoidance task (PM-DAT), an animal model that concurrently (but independently) evaluates learning and memory, anxiety and locomotion. We also investigated the possible role of FR-induced stress by the corticosterone concentration in adult mice. Male mice were kept at home cage with food ad libitum (CTRL-control condition) or subjected to FR during the dark phase of the cycle for 12h/day or 12h/2days. The FR protocols were applied before training, immediately after it or before testing. Our results demonstrated that only FR for 2days enhanced memory persistence when applied before training in adults and before testing in aged mice. Conversely, FR for 2days impaired consolidation and exerted no effects on retrieval irrespective of age. These effects do not seem to be related to corticosterone concentration. Collectively, these results indicate that FR for 2days can promote promnestic effects not only in aged mice but also in adults.

Short-term sleep deprivation reinstates memory retrieval in mice: the role of corticosterone secretion

While the effects of sleep deprivation (SD) on the acquisition and consolidation phases of memory have been extensively characterized, its effects on memory retrieval remain overlooked. SD alone is a stressor, and stress-activated glucocorticoids promote bimodal effects on memory. Because we have recently demonstrated that 72h SD impairs memory retrieval in the plus-maze discriminative avoidance task (PM-DAT) in mice, this study investigated whether shorter SD periods would facilitate retrieval. In Experiment I, the temporal forgetting curve of the PM-DAT was determined and an interval between training/testing in which retrieval was no longer present was used in all subsequent experiments. In Experiments II and III, retrieval performance and corticosterone concentration, respectively, were quantified in mice that were sleep deprived for 12 or 24h before testing. In Experiments IV and V, the effects of the corticosterone synthesis inhibitor metyrapone were evaluated on 12h SD-induced retrieval reinstatement and corticosterone concentration enhancement, respectively. Experiment VI determined whether pre-test acute administration of exogenous corticosterone would mimic the facilitatory effects of 12h SD on retrieval. Thirty days after training, mice presented poor performance of the task; however, SD for 12h (but not for 24) before testing reinstated memory retrieval. This facilitatory effect was accompanied by increased corticosterone concentration, abolished by metyrapone, and mimicked by pre-test acute corticosterone administration. Collectively, short-term SD can facilitate memory retrieval by enhancing corticosterone secretion. This facilitatory effect is abolished by longer periods of SD.

The usefulness of olfactory fear conditioning for the study of early emotional and cognitive impairment in reserpine model

Due to the ability for depleting neuronal storages of monoamines, the reserpine model is a suitable approach for the investigation of the neurobiology of neurodegenerative diseases. However, the behavioral effects of low doses of reserpine are not always detected by classic animal tests of cognition, emotion, and sensory ability. In this study, the effects of reserpine (0.5-1.0mg/kg) were evaluated in olfactory fear conditioning, inhibitory avoidance, open-field, elevated plus-maze, and olfactory discrimination. Possible protective effects were also investigated. We found that single administration of reserpine impaired the acquisition of olfactory fear conditioning (in both doses) as well as olfactory discrimination (in the higher dose), while no effects were seen in all other tests. Additionally, we demonstrated that prior exposure to environmental enrichment prevented effects of reserpine in animals tested in olfactory fear conditioning. Altogether, these findings suggest that a combined cognitive, emotional and sensory-dependent task would be more sensitive to the effects of the reserpine model. In addition, the present data support the environmental enrichment as an useful approach for the study of resilience mechanisms in neurodegenerative processes.

Role of state-dependent learning in the cognitive effects of caffeine in mice

Caffeine is the most widely used psychoactive substance in the world and it is generally believed that it promotes beneficial effects on cognitive performance. However, there is also evidence suggesting that caffeine has inhibitory effects on learning and memory. Considering that caffeine may have anxiogenic effects, thus changing the emotional state of the subjects, state-dependent learning may play a role in caffeine-induced cognitive alterations. Mice were administered 20 mg/kg caffeine before training and/or before testing both in the plus-maze discriminative avoidance task (an animal model that concomitantly evaluates learning, memory, anxiety-like behaviour and general activity) and in the inhibitory avoidance task, a classic paradigm for evaluating memory in rodents. Pre-training caffeine administration did not modify learning, but produced an anxiogenic effect and impaired memory retention. While pre-test administration of caffeine did not modify retrieval on its own, the pre-test administration counteracted the memory deficit induced by the pre-training caffeine injection in both the plus-maze discriminative and inhibitory avoidance tasks. Our data demonstrate that caffeine-induced memory deficits are critically related to state-dependent learning, reinforcing the importance of considering the participation of state-dependency on the interpretation of the cognitive effects of caffeine. The possible participation of caffeine-induced anxiety alterations in state-dependent memory deficits is discussed.

Short-term social isolation induces depressive-like behaviour and reinstates the retrieval of an aversive task: mood-congruent memory in male mice?

BACKGROUND

Although mood-congruent memory (MCM), or the tendency to recall information consistent with one's mood, is a robust phenomenon in human depression, to our knowledge, it has never been demonstrated in animals.

METHODS

Mice were subjected to social isolation (SI) or crowding for 12 hours and had their depressive-like behaviour (evaluated by the forced swim, tail suspension, sucrose preference and splash tests) or their serum corticosterone concentrations evaluated. In addition, we determined the temporal forgetting curve of the plus-maze discriminative avoidance task (PM-DAT) and examined the effects of SI or crowding on memory retrieval in the PM-DAT. Finally, we verified the effects of metyrapone pretreatment on reinstatement of memory retrieval or on the increase of corticosterone levels induced by SI.

RESULTS

Twelve hours of SI produced depressive-like behaviour, enhanced corticosterone concentration and reinstated retrieval of a forgotten discriminative aversive (i.e., negatively valenced) task. Depressive-like behaviour was critical for this facilitative effect of SI because 12 hours of crowding neither induced depressive-like behaviour nor enhanced retrieval, although it increased corticosterone levels at the same magnitude as SI. However, corticosterone increase was a necessary condition for MCM in mice, in that the corticosterone synthesis inhibitor metyrapone abolished SI-induced retrieval reinstatement.

LIMITATIONS

Our study did not investigate the effects of the social manipulations proposed here in a positively valenced task.

CONCLUSION

To our knowledge, the present paper provides the first evidence of MCM in animal models.

Behavioral effects of bidirectional modulators of brain monoamines reserpine and d-amphetamine in zebrafish

Brain monoamines play a key role in the regulation of behavior. Reserpine depletes monoamines, and causes depression and hypoactivity in humans and rodents. In contrast, d-amphetamine increases brain monoamines' levels, and evokes hyperactivity and anxiety. However, the effects of these agents on behavior and in relation to monoamine levels remain poorly understood, necessitating further experimental studies to understand their psychotropic action. Zebrafish (Danio rerio) are rapidly emerging as a promising model organism for drug screening and translational neuroscience research. Here, we have examined the acute and long-term effects of reserpine and d-amphetamine on zebrafish behavior in the novel tank test. Overall, d-amphetamine (5 and 10mg/L) evokes anxiogenic-like effects in zebrafish acutely, but not 7 days later. In contrast, reserpine (20 and 40 mg/L) did not evoke overt acute behavioral effects, but markedly reduced activity 7 days later, resembling motor retardation observed in depression and/or Parkinson's disease. Three-dimensional 'temporal' (X, Y, time) reconstructions of zebrafish locomotion further supports these findings, confirming the utility of 3D-based video-tracking analyses in zebrafish models of drug action. Our results show that zebrafish are highly sensitive to drugs bi-directionally modulating brain monoamines, generally paralleling rodent and clinical findings. Collectively, this emphasizes the potential of zebrafish tests to model complex brain disorders associated with monoamine dysregulation.

Mild acute stress reactivates memory of a discriminative avoidance task in mice

Previous studies have demonstrated that stress or glucocorticoids impair the retrieval of spatial memory in rodents and declarative memory in humans. However, the effects on memory retrieval of stress introduced a long time after learning have not been well studied. We investigated whether a mild, extrinsic stressor (1-s 0.1 or 0.3 mA foot shock) would reactivate low baseline retrieval of an aversive memory [the plus-maze discriminative avoidance task (PM-DAT)] and if it would be modulated by glucocorticoids. In Experiment 1, male Swiss mice received pre-test foot shock (n = 10 mice/group) 7 days after training and just before testing. A time-retrieval curve for low baseline retrieval for the subsequent experiments was also determined (Experiment 2, n = 10 mice/group). We investigated if pre-test foot shock could modify corticosterone release (Experiment 3, n = 8-9 mice/group) and reinstate retrieval in the PM-DAT (Experiment 4, n = 15 mice/group). The effects of metyrapone (100 mg/kg) on retrieval reinstatement (Experiment 5, n = 15 mice/group) and serum corticosterone enhancement (Experiments 6, n = 7-9 mice/group) induced by foot shock were analyzed. Finally, the effects of foot shock itself on PM-DAT exploration were verified (Experiment 7, n = 10 mice/group). We demonstrated here that foot shock reinstated the retrieval of a low baseline, discriminative avoidance task 30 (but not 7) days after training. This facilitative effect was not dependent on corticosterone secretion because metyrapone abolished the enhancement of corticosterone concentration but did not reverse the stress-induced reinstatement of retrieval.

Effects of zolpidem on sedation, anxiety, and memory in the plus-maze discriminative avoidance task

RATIONALE

Zolpidem (Zolp), a hypnotic drug prescribed to treat insomnia, may have negative effects on memory, but reports are inconsistent.

OBJECTIVES

We examined the effects of acute doses of Zolp (2, 5, or 10 mg/kg, i.p.) on memory formation (learning, consolidation, and retrieval) using the plus-maze discriminative avoidance task.

METHODS

Mice were acutely treated with Zolp 30 min before training or testing. In addition, the effects of Zolp and midazolam (Mid; a classic benzodiazepine) on consolidation at different time points were examined. The possible role of state dependency was investigated using combined pre-training and pre-test treatments.

RESULTS

Zolp produced a dose-dependent sedative effect, without modifying anxiety-like behavior. The pre-training administration of 5 or 10 mg/kg resulted in retention deficits. When administered immediately after training or before testing, memory was preserved. Zolp post-training administration (2 or 3 h) impaired subsequent memory. There was no participation of state dependency phenomenon in the amnestic effects of Zolp. Similar to Zolp, Mid impaired memory consolidation when administered 1 h after training.

CONCLUSIONS

Amnestic effects occurred when Zolp was administered either before or 2-3 h after training. These memory deficits are not related to state dependency. Moreover, Zolp did not impair memory retrieval. Notably, the memory-impairing effects of Zolp are similar to those of Mid, with the exception of the time point at which the drug can modify consolidation. Finally, the memory effects were unrelated to sedation or anxiolysis.

Acute treatment with bis selenide, an organic compound containing the trace element selenium, prevents memory deficits induced by reserpine in rats

Taking into account the promising pharmacological actions of (Z)-2,3-bis(4-chlorophenylselanyl) prop-2-en-1-ol) (bis selenide), an organic compound containing the trace element selenium, and the constant search for drugs that improve the cognitive performance, the objective of the present study was to investigate whether bis selenide treatment ameliorates memory deficits induced by reserpine in rats. For this aim, male adult rats received a single subcutaneous injection of reserpine (1 mg/kg), a biogenic amine-depleting agent used to induce memory deficit. After 24 h, bis selenide at doses of 25 and 50 mg/kg was administered to rats by intragastric route, and 1 h later, the animals were submitted to behavior tasks. The effects of acute administration of bis selenide on memory were evaluated by social recognition, step-down passive avoidance, and object recognition paradigms. Exploratory and locomotor activities of rats were determined using the open-field test. Analysis of data revealed that the social memory disruption caused by reserpine was reversed by bis selenide at both doses. In addition, bis selenide, at the highest dose, prevented the memory deficit resulting from reserpine administration to rats in step-down passive avoidance and object recognition tasks. No significant alterations in locomotor and exploratory behaviors were found in animals treated with reserpine and/or bis selenide. Results obtained from distinct memory behavioral paradigms revealed that an acute treatment with bis selenide attenuated memory deficits induced by reserpine in rats.

Role of state-dependency in memory impairment induced by acute administration of midazolam in mice

Although the memory deficits produced by pre-training benzodiazepines administration have been extensively demonstrated both in humans and in animal studies, there is considerable controversy about the involvement of the state-dependency phenomenon on benzodiazepines-induced anterograde amnesia. The present study aimed to characterize the role of state-dependency on memory deficits induced by the benzodiazepine midazolam (MID) in mice submitted to the plus-maze discriminative avoidance task (PM-DAT). This animal model concomitantly evaluates learning and retention of discriminative avoidance task, exploratory habituation as well as anxiety-like behavior and motor activity. Mice received 2mg/kg MID before training and/or before testing in the PM-DAT. Pre-training (but not pre-test) MID administration impaired the retention of the discriminative avoidance task, which was not counteracted by a subsequent pre-test administration of this drug, thus refuting the role of state-dependency. Conversely, the pre-training administration of MID also led to an impairment of the habituation of exploration in the PM-DAT (an animal model of non-associative memory). This habituation deficit was state-dependent since it was absent in pre-training plus pre-test MID treated mice. Concomitantly, MID pre-training administration induced anxiolytic effects and diminished the aversive effectiveness of the aversive stimuli of the task, leading to an impairment of the acquisition of the discriminative avoidance task. Our findings suggest that pre-training benzodiazepine administration can impair the retention of different types of memory by producing specific deleterious effects on learning or by inducing state-dependent memory deficits.

Effects of sleep deprivation on memory in mice: role of state-dependent learning

STUDY OBJECTIVES

A considerable amount of experimental evidence suggests that sleep plays a critical role in learning/memory processes. In addition to paradoxical sleep, slow wave sleep is also reported to be involved in the consolidation process of memories. Additionally, sleep deprivation can induce other behavioral modifications, such as emotionality and alternations in locomotor activity in rodents. These sleep deprivation-induced alterations in the behavioral state of animals could produce state-dependent learning and contribute, at least in part, to the amnestic effects of sleep deprivation. The aim of the present study was to examine the participation of state-dependent learning during memory impairment induced by either paradoxical sleep deprivation (PSD) or total sleep deprivation (TSD) in mice submitted to the plus-maze discriminative avoidance or to the passive avoidance task.

DESIGN

Paradoxical sleep deprivation (by the multiple platform method) and total sleep deprivation (by the gentle handling method) were applied to animals before training and/or testing.

CONCLUSIONS

Whereas pre-training or pre-test PSD impaired retrieval in both memory models, pre-training plus pre-test PSD counteracted this impairment. For TSD, pre-training, pre-test, and pre-training plus pre-test TSD impaired retrieval in both models. Our data demonstrate that PSD- (but not TSD-) memory deficits are critically related to state-dependent learning.

A rodent model of appetitive discrimination with concomitant evaluation of anxiety-like behavior

The plus-maze discriminative avoidance paradigm has been used to study the relationship between aversive memory and anxiety. The present study aims to verify if the elevated plus-maze can provide information about appetitive memory and anxiety-like behavior, through a task motivated by food reward. Animals were allowed to explore an elevated plus-maze and received reinforcement in one of the enclosed arms. In a test session performed 24h later, in the absence of reward, rats showed preference for the previously rewarded enclosed arm over the neutral enclosed arm. The administration of diazepam and pentylenetetrazole before training induced, respectively, anxiolytic and anxiogenic effects (as evaluated by open-arm exploration). Both drugs induced amnestic effects, i.e., lack of preference for the rewarded arm in the test session. The results suggest that appetitive memory can be influenced by anxiety levels as well. The plus-maze appetitive discrimination task seems to be a useful model to investigate the relationship between memory and anxiety.

Memory impairment induced by low doses of reserpine in rats: possible relationship with emotional processing deficits in Parkinson disease

We have recently verified that the monoamine-depleting drug reserpine--at doses that do not modify motor function--impairs memory in a rodent model of aversive discrimination. In this study, the effects of reserpine (0.1-0.5 mg/kg) on the performance of rats in object recognition, spatial working memory (spontaneous alternation) and emotional memory (contextual freezing conditioning) tasks were investigated. While object recognition and spontaneous alternation behavior were not affected by reserpine treatment, contextual fear conditioning was impaired. Together with previous studies, these results suggest that low doses of reserpine would preferentially induce deficits in tasks involved with emotional contexts. Possible relationships with cognitive and emotional processing deficits in Parkinson disease are discussed.

Cyclic and sleep-like spontaneous alternations of brain state under urethane anaesthesia

Background

Although the induction of behavioural unconsciousness during sleep and general anaesthesia has been shown to involve overlapping brain mechanisms, sleep involves cyclic fluctuations between different brain states known as active (paradoxical or rapid eye movement: REM) and quiet (slow-wave or non-REM: nREM) stages whereas commonly used general anaesthetics induce a unitary slow-wave brain state.

Methodology/Principal Findings

Long-duration, multi-site forebrain field recordings were performed in urethane-anaesthetized rats. A spontaneous and rhythmic alternation of brain state between activated and deactivated electroencephalographic (EEG) patterns was observed. Individual states and their transitions resembled the REM/nREM cycle of natural sleep in their EEG components, evolution, and time frame (∼11 minute period). Other physiological variables such as muscular tone, respiration rate, and cardiac frequency also covaried with forebrain state in a manner identical to sleep. The brain mechanisms of state alternations under urethane also closely overlapped those of natural sleep in their sensitivity to cholinergic pharmacological agents and dependence upon activity in the basal forebrain nuclei that are the major source of forebrain acetylcholine. Lastly, stimulation of brainstem regions thought to pace state alternations in sleep transiently disrupted state alternations under urethane.

Conclusions/Significance

Our results suggest that urethane promotes a condition of behavioural unconsciousness that closely mimics the full spectrum of natural sleep. The use of urethane anaesthesia as a model system will facilitate mechanistic studies into sleep-like brain states and their alternations. In addition, it could also be exploited as a tool for the discovery of new molecular targets that are designed to promote sleep without compromising state alternations.