Cannabidiol Recovers Dopaminergic Neuronal Damage Induced by Reserpine or α-synuclein in Caenorhabditis elegans

Progressive neurodegenerative disorders such as Parkinson Disease (PD) lack curative or long-term treatments. At the same time, the increase of the worldwide elderly population and, consequently, the extension in the prevalence of age-related diseases have promoted research interest in neurodegenerative disorders. Caenorhabditis elegans is a free-living nematode widely used as an animal model in studies of human diseases. Here we evaluated cannabidiol (CBD) as a possible neuroprotective compound in PD using the C. elegans models exposed to reserpine. Our results demonstrated that CBD reversed the reserpine-induced locomotor alterations and this response was independent of the NPR-19 receptors, an orthologous receptor for central cannabinoid receptor type 1. Morphological alterations of cephalic sensilla (CEP) dopaminergic neurons indicated that CBD also protects neurons from reserpine-induced degeneration. That is, CBD attenuates the reserpine-induced increase of worms with shrunken soma and dendrites loss, increasing the number of worms with intact CEP neurons. Finally, we found that CBD also reduced ROS formation and α-syn protein accumulation in mutant worms. Our findings collectively provide new evidence that CBD acts as neuroprotector in dopaminergic neurons, reducing neurotoxicity and α-syn accumulation highlighting its potential in the treatment of PD.

Harmine impairs memory performance of treated rats and nontreated cagemates

The interest in psychedelic substances as potential treatments for psychiatric disorders is increasing. The β-carboline harmine, an Ayahuasca component, presents hallucinogenic and antidepressant effects. Although Ayuahuasca-and consequently harmine-is usually consumed in rituals, the role of social contexts in the behavioral effects of harmine has not been investigated yet. In this sense, affective states may modulate cohabitants' behavior, including learning/memory. This work investigates the effects of harmine on the learning/memory performance of rats evaluated on the contextual and tone fear conditioning (CFC and TFC) and on the plus-maze discriminative avoidance (PMDAT) tasks. The possible influence of a harmine-treated cohabitant was assessed by evaluating rats housed in homogeneous cages-where all the animals were acutely administered with the same treatment (vehicle, 5, 10, or 15 mg/kg harmine), and in heterogeneous cages-where each animal received a different drug treatment. The main results are: (a) harmine impaired CFC (10 mg/kg) and PMDAT discrimination (all doses); and (b) harmine caused a memory deficit in CFC, TFC, and PMDAT of untreated rats kept in heterogeneous cages. Our results show that harmine induces a memory deficit in tasks with emotional contexts. Further, the cohabitation with animals treated with this drug also seems to impair memory performance of untreated animals. (PsycInfo Database Record (c) 2022 APA, all rights reserved).

Changes in the mesocorticolimbic pathway after low dose reserpine-treatment in Wistar and Spontaneously Hypertensive Rats (SHR): Implications for cognitive deficits in a progressive animal model for Parkinson's disease

Reserpine (RES) is an irreversible inhibitor of VMAT2 used to study Parkinson's disease (PD) and screening for antiparkinsonian treatments in rodents. Recently, the repeated treatment with a low dose of reserpine was proposed as a model capable of emulating progressive neurochemical, motor and non-motor impairments in PD. Conversely, compared to Wistar rats, Spontaneously Hypertensive Rats (SHR) are resistant to motor changes induced by repeated treatment with a low dose of RES. However, such resistance has not yet been investigated for RES-induced non-motor impairments. We aimed to assess whether SHR would have differential susceptibility to the object recognition deficit induced by repeated low-dose reserpine treatment. We submitted male Wistar and SHR rats to repeated RES treatment (15 s.c. injections of 0.1 mg/kg, every other day) and assessed object memory acquisition and retrieval 48 h after the 6^th RES injection (immediately before the appearance of motor impairments). Only RES Wistar rats displayed memory impairment after reserpine treatment. On the other hand, untreated SHR rats displayed object recognition memory deficit, but RES treatment restored such deficits. We also performed immunohistochemistry for tyrosine hydroxylase (TH) and α-synuclein (α-syn) 48 h after the last RES injection. In a different set of animals submitted to the same treatment, we quantified DA, 5-HT and products of lipid peroxidation in the prefrontal cortex (PFC) and hippocampus (HPC). SHR presented increased constitutive levels of DA in the PFC and reduced immunoreactivity to TH in the medial PFC and dorsal HPC. Corroborating the behavioral findings, RES treatment restored those constitutive alterations in SHR. These findings indicate that the neurochemical, molecular and genetic differences in the SHR strain are potentially relevant targets to the study of susceptibility to diseases related to dopaminergic alterations.

Cannabidiol Administered During Peri-Adolescence Prevents Behavioral Abnormalities in an Animal Model of Schizophrenia

Schizophrenia is considered a debilitating neurodevelopmental psychiatric disorder and its pharmacotherapy remains problematic without recent major advances. The development of interventions able to prevent the emergence of schizophrenia would therefore represent an enormous progress. Here, we investigated whether treatment with cannabidiol (CBD - a compound of Cannabis sativa that presents an antipsychotic profile in animals and humans) during peri-adolescence would prevent schizophrenia-like behavioral abnormalities in an animal model of schizophrenia: the spontaneously hypertensive rat (SHR) strain. Wistar rats and SHRs were treated with vehicle or CBD from 30 to 60 post-natal days. In experiment 1, schizophrenia-like behaviors (locomotor activity, social interaction, prepulse inhibition of startle and contextual fear conditioning) were assessed on post-natal day 90. Side effects commonly associated with antipsychotic treatment were also evaluated: body weight gain and catalepsy throughout the treatment, and oral dyskinesia 48 h after treatment interruption and on post-natal day 90. In experiment 2, serum levels of triglycerides and glycemia were assessed on post-natal day 61. In experiment 3, levels of BDNF, monoamines, and their metabolites were evaluated on post-natal days 61 and 90 in the prefrontal cortex and striatum. Treatment with CBD prevented the emergence of SHRs' hyperlocomotor activity (a model for the positive symptoms of schizophrenia) and deficits in prepulse inhibition of startle and contextual fear conditioning (cognitive impairments). CBD did not induce any of the potential motor or metabolic side effects evaluated. Treatment with CBD increased the prefrontal cortex 5-HIAA/serotonin ratio and the levels of 5-HIAA on post-natal days 61 and 90, respectively. Our data provide pre-clinical evidence for a safe and beneficial effect of peripubertal and treatment with CBD on preventing positive and cognitive symptoms of schizophrenia, and suggest the involvement of the serotoninergic system on this effect.

Cannabidiol as a Promising Strategy to Treat and Prevent Movement Disorders?

Movement disorders such as Parkinson's disease and dyskinesia are highly debilitating conditions linked to oxidative stress and neurodegeneration. When available, the pharmacological therapies for these disorders are still mainly symptomatic, do not benefit all patients and induce severe side effects. Cannabidiol is a non-psychotomimetic compound from Cannabis sativa that presents antipsychotic, anxiolytic, anti-inflammatory, and neuroprotective effects. Although the studies that investigate the effects of this compound on movement disorders are surprisingly few, cannabidiol emerges as a promising compound to treat and/or prevent them. Here, we review these clinical and pre-clinical studies and draw attention to the potential of cannabidiol in this field.

Spontaneously Hypertensive Rats (SHR) Are Resistant to a Reserpine-Induced Progressive Model of Parkinson's Disease: Differences in Motor Behavior, Tyrosine Hydroxylase and α-Synuclein Expression

Reserpine is an irreversible inhibitor of vesicular monoamine transporter-2 (VMAT2) used to study Parkinson’s disease (PD) and screening for antiparkinsonian treatments in rodents. Recently, the repeated treatment with a low-dose of reserpine was proposed as a progressive model of PD. Rats under this treatment show progressive catalepsy behavior, oral movements and spontaneous motor activity decrement. In parallel, compared to Wistar rats, spontaneously hypertensive rats (SHR) are resistant to acute reserpine-induced oral dyskinesia. We aimed to assess whether SHR would present differential susceptibility to repeated reserpine-induced deficits in the progressive model of PD. Male Wistar and SHR rats were administered 15 subcutaneously (s.c.) injections of reserpine (0.1 mg/kg) or vehicle, every other day and motor activity was assessed by the catalepsy, oral movements and open field tests. Only reserpine-treated Wistar rats presented increased latency to step down in the catalepsy test and impaired spontaneous activity in the open field. On the other hand, there was an increase in oral movements in both reserpine-treated strains, although with reduced magnitude and latency to instauration in SHR. After a 15-day withdrawn period, both strains recovered from motor impairment, but SHR animals expressed reduced latencies to reach control levels. Finally, we performed immunohistochemistry for tyrosine hydroxylase (TH) and α-synuclein (α-syn) 48 h after the last injection or 15 days after withdrawn. Reserpine-treated animals presented a reduction in TH and an increase in α-syn immunoreactivity in the substantia nigra and dorsal striatum (dSTR), which were both recovered after 15 days of withdraw. Furthermore, SHR rats were resistant to reserpine-induced TH decrement in the substantia nigra, and presented reduced immunoreactivity to α-syn in the dSTR relative to Wistar rats, irrespective of treatment. This effect was accompanied by increase of malondaldhyde (MDA) in the striatum of reserpine-treated Wistar rats, while SHR presented reduced MDA in both control and reserpine conditions relative to Wistar strain. In conclusion, the current results show that SHR are resilient to motor and neurochemical impairments induced by the repeated low-dose reserpine protocol. These findings indicate that the neurochemical, molecular and genetic differences in the SHR strain are potential relevant targets to the study of susceptibility to PD.

A current snapshot of common genomic variants contribution in psychiatric disorders

In the past decade, numerous advances were achieved in psychiatric genetics. Particularly, the genome wide association studies (GWAS) have contributed to uncovering new genes and pathways associated to psychiatric disorders (PDs). At the same time, with increasing sample sizes in the GWAS, the polygenic risk score (PRS) promoted an additional tool for identification and evaluation the genetic risk quantitatively in PDs. This concept review presents the state of the art GWAS analysis and PRS focusing on the genetic underpinnings of PDs. © 2016 Wiley Periodicals, Inc.

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.

Effects of cannabinoid and vanilloid drugs on positive and negative-like symptoms on an animal model of schizophrenia: the SHR strain

Studies have suggested that the endocannabinoid system is implicated in the pathophysiology of schizophrenia. We have recently reported that Spontaneously Hypertensive Rats (SHRs) present a deficit in social interaction that is ameliorated by atypical antipsychotics. In addition, SHRs display hyperlocomotion - reverted by atypical and typical antipsychotics. These results suggest that this strain could be useful to study negative symptoms (modeled by a decrease in social interaction) and positive symptoms (modeled by hyperlocomotion) of schizophrenia and the effects of potential drugs with an antipsychotic profile. The aim of this study was to investigate the effects of WIN55-212,2 (CB1/CB2 agonist), ACEA (CB1 agonist), rimonabant (CB1 inverse agonist), AM404 (anandamide uptake/metabolism inhibitor), capsaicin (agonist TRPV1) and capsazepine (antagonist TRPV1) on the social interaction and locomotion of control animals (Wistar rats) and SHRs. The treatment with rimonabant was not able to alter either the social interaction or the locomotion presented by Wistar rats (WR) and SHR at any dose tested. The treatment with WIN55-212,2 decreased locomotion (1mg/kg) and social interaction (0.1 and 0.3mg/kg) of WR, while the dose of 1mg/kg increased social interaction of SHR. The treatment with ACEA increased (0.3mg/kg) and decreased (1mg/kg) locomotion of both strain. The administration of AM404 increased social interaction and decreased locomotion of SHR (5mg/kg), and decreased social interaction and increased locomotion in WR (1mg/kg). The treatment with capsaicin (2.5mg/kg) increased social interaction of both strain and decreased locomotion of SHR (2.5mg/kg) and WR (0.5mg/kg and 2.5mg/kg). In addition, capsazepine (5mg/kg) decreased locomotion of both strains and increased (5mg/kg) and decreased (10mg/kg) social interaction of WR. Our results indicate that the schizophrenia-like behaviors displayed by SHR are differently altered by cannabinoid and vanilloid drugs when compared to control animals and suggest the endocannabinoid and the vanilloid systems as a potential target for the treatment of schizophrenia.

Effects of cannabinoid drugs on the deficit of prepulse inhibition of startle in an animal model of schizophrenia: the SHR strain

Clinical and neurobiological findings suggest that the cannabinoids and the endocannabinoid system may be implicated in the pathophysiology and treatment of schizophrenia. We described that the spontaneously hypertensive rats (SHR) strain presents a schizophrenia behavioral phenotype that is specifically attenuated by antipsychotic drugs, and potentiated by proschizophrenia manipulations. Based on these findings, we have suggested this strain as an animal model of schizophrenia. The aim of this study was to evaluate the effects of cannabinoid drugs on the deficit of prepulse inhibition (PPI) of startle, the main paradigm used to study sensorimotor gating impairment related to schizophrenia, presented by the SHR strain. The following drugs were used: (1) WIN55212,2 (cannabinoid agonist), (2) rimonabant (CB1 antagonist), (3) AM404 (anandamide uptake inhibitor), and (4) cannabidiol (CBD; indirect CB1/CB2 receptor antagonist, among other effects). Wistar rats (WRs) and SHRs were treated with vehicle (VEH) or different doses of WIN55212 (0.3, 1, or 3 mg/kg), rimonabant (0.75, 1.5, or 3 mg/kg), AM404 (1, 5, or 10 mg/kg), or CBD (15, 30, or 60 mg/kg). VEH-treated SHRs showed a decreased PPI when compared to WRs. This PPI deficit was reversed by 1 mg/kg WIN and 30 mg/kg CBD. Conversely, 0.75 mg/kg rimonabant decreased PPI in SHR strain, whereas AM404 did not modify it. Our results reinforce the role of the endocannabinoid system in the sensorimotor gating impairment related to schizophrenia, and point to cannabinoid drugs as potential therapeutic strategies.

Cannabidiol exhibits anxiolytic but not antipsychotic property evaluated in the social interaction test

Cannabidiol (CBD), a non-psychotomimetic compound of the Cannabis sativa, has been reported to have central therapeutic actions, such as antipsychotic and anxiolytic effects. We have recently reported that Spontaneously Hypertensive Rats (SHRs) present a deficit in social interaction that is ameliorated by atypical antipsychotics. In addition, SHRs present a hyperlocomotion that is reverted by typical and atypical antipsychotics, suggesting that this strain could be useful to study negative symptoms (modeled by a decrease in social interaction) and positive symptoms (modeled by hyperlocomotion) of schizophrenia as well as the effects of potential antipsychotics drugs. At the same time, an increase in social interaction in control animals similar to that induced by benzodiazepines is used to screen potential anxiolytic drugs. The aim of this study was to investigate the effects of CBD on social interaction presented by control animals (Wistar) and SHRs. The lowest dose of CBD (1mg/kg) increased passive and total social interaction of Wistar rats. However, the hyperlocomotion and the deficit in social interaction displayed by SHRs were not altered by any dose of CBD. Our results do not support an antipsychotic property of cannabidiol on symptoms-like behaviors in SHRs but reinforce the anxiolytic profile of this compound in control rats.

Amnestic effect of cocaine after the termination of its stimulant action

The effects of cocaine on memory are controversial. Furthermore, the psychostimulant action of cocaine can be a critical issue in the interpretation of its effects on learning/memory models. The effects of a single administration of cocaine on memory were investigated during the presence of its motor stimulating effect or just after its termination. The plus-maze discriminative avoidance task (PM-DAT) was used because it provides simultaneous information about memory, anxiety and motor activity. In Experiment I, mice received saline, 7.5, 10, 15 or 30 mg/kg cocaine 5 min before the training session. In Experiment II, mice were trained 30 min after the injection of saline, 7.5, 10, 15 or 30 mg/kg cocaine. In Experiment III, mice received 30 mg/kg cocaine 30 min pre-training and pre-test. In Experiment IV, mice received 30 mg/kg cocaine immediately post-training. Tests were always conducted 24 h following the training session. Given 5 min before training, cocaine promoted a motor stimulant effect at the highest dose during the training session but did not impair memory. When cocaine was injected 30 min pre-training, the drug did not modify motor activity, but produced marked amnestic effects at all doses tested. This amnesia induced by cocaine given 30 min pre-training was not related to a state-dependent learning because it was not abolished by pre-test administration of the drug. Post-training cocaine administration did not induce memory deficits either. Our results suggest that the post-stimulant phase is the critical moment for cocaine-induced memory deficit in a discriminative task in mice.

Dissociation of the effects of ethanol on memory, anxiety, and motor behavior in mice tested in the plus-maze discriminative avoidance task

RATIONALE

Several studies have shown the amnestic effects of ethanol (ETOH). However, while memory tasks in rodents can be markedly influenced by anxiety-like behavior and motor function, ETOH induces anxiolysis and different effects on locomotion, depending on the dose.

OBJECTIVE

Verify the effects of ETOH in mice tested in the plus-maze discriminative avoidance task (PMDAT) concomitantly evaluating memory, anxiety-like behavior, and motor behavior.

METHODS

ETOH acutely or repeatedly treated mice were submitted to the training session in a modified elevated plus-maze with two open and two enclosed arms, aversive stimuli in one of the enclosed arms, and tested 24 h later without aversive stimuli. Learning/memory, locomotion, and anxiety-related behavior were evaluated by aversive arm exploration, number of entries in all the arms and open arms exploration, respectively.

RESULTS

Acute ETOH: (1) either increased (1.2-1.8 g/kg) or decreased (3.0 g/kg) locomotion; (2) decreased anxiety levels (1.2-3.0 g/kg); and (3) induced learning deficits (1.2-3.0 g/kg) and memory deficits (0.3-3.0 g/kg). After repeated treatment, sensitization and tolerance to hyperlocomotion and anxiolysis induced by 1.8 g/kg ETOH were observed, respectively, and tolerance to the amnestic effect of 0.6 (but not 1.8) g/kg ETOH occurred.

CONCLUSION

Neither the anxiolytic nor the locomotor effects of ETOH seem to be related to its amnestic effect in the PMDAT. Additionally, data give support to the effectiveness of the PMDAT in simultaneously evaluating learning, memory, anxiety-like behavior, and motor activity by different parameters. Possible relationships between the behavioral alterations found are discussed.

Effects of 3-nitropropionic acid administration on memory and hippocampal lipid peroxidation in sleep-deprived mice

Numerous studies have described memory deficits following sleep deprivation. There is also evidence that the absence of sleep increases brain oxidative stress. The present study investigates the effects of a pro-oxidant agent--3-nitropropionic acid (3-NP)--on hippocampal oxidative stress and passive avoidance performance of sleep-deprived mice. Mice were repeatedly treated i.p. with saline or 5 or 15 mg/kg 3-NP and sleep-deprived for 24 h by the multiple platform method--groups of 4-5 animals placed in water tanks, containing 12 platforms (3 cm in diameter) surrounded by water up to 1 cm beneath the surface or kept in their home cage (control groups). The results showed that: (1) neither a 24 h sleep deprivation period nor 3-NP repeated treatment alone were able to induce memory deficits and increased hippocampal lipid peroxidation; (2) this same protocol of sleep deprivation, combined with 15 mg/kg 3-NP repeated treatment, induced memory deficits and an increase in hippocampal lipid peroxidation. The results support the involvement of hippocampal oxidative stress in the memory deficits induced by sleep deprivation and the hypothesis that normal sleep would prevent oxidative stress.

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

We investigated the effects of reserpine (0.1-0.5 mg/kg) on the performance of mice in the plus-maze discriminative avoidance task (DAVT), which simultaneously evaluates memory and motor activity. All doses induced memory impairment (increased aversive arm time) but only 0.5 mg/kg reserpine decreased locomotion (entries in enclosed arms). The results suggest that the DAVT evaluation in reserpine-treated mice can be a useful model for studying cognitive deficits accompanied by motor impairments.

Bovine brain phosphatidylserine attenuates scopolamine induced amnesia in mice

This study verifies the effects of bovine brain phosphatidylserine (PS) on passive avoidance (PA) and contextual fear conditioning (CFC) tests in scopolamine-treated mice. Mice received daily i.p. 50 mg/kg PS or 0.2 M Tris pH 7.4 (TRIS) for 5 days. On day 6, mice received saline (TRIS-SAL and PS-SAL) or 1 mg/kg SCO (TRIS-SCO and PS-SCO) i.p. After 20 min, the animals were submitted to PA (experiment 1) or CFC (experiment 2) training sessions, and tests were performed 24 h later. Latency in entering the dark chamber of the PA apparatus presented by TRIS-SCO (but not PS-SCO) group in the test was significantly higher than those presented by controls. Except for TRIS-SCO, all the groups presented higher latencies in the test compared to the training session. In experiment 2, the TRIS-SCO (but not PS-SCO) group presented significantly lower freezing duration than that presented by the TRIS-SAL group in the test. Animals treated with PS alone presented higher freezing duration than that presented by the TRIS-SAL group. The results demonstrate that PS attenuates SCO-induced amnesia in both PA and CFC tests. In addition, PS per se improves retention in the CFC test.

Drug-induced home cage conspecifics' behavior can potentiate behavioral sensitization in mice

The effect of home cage conspecifics' behavior on locomotor sensitization to amphetamine (AMP) or ethanol (ETOH) were investigated. Female mice were repeatedly treated with saline or AMP (2.0 mg/kg for 13 days--Experiment 1) or saline or ETOH (1.8 g/kg for 21 days--Experiment 2) in home cages where all the animals had the same treatment (homogeneous home cages--HOM-HC) or in home cages where half of the animals were drug-treated and half of them were saline-treated (heterogeneous home cages--HET-HC). Behavioral sensitization was evaluated by the quantification of open-field locomotor activity after AMP or ETOH challenge injection, respectively. In both experiments, behavioral sensitization was potentiated in HOM-HC maintained animals. These results suggest that the behavioral sensitization phenomenon can be modified by home cage conspecifics' behavior.

Sleep deprivation abolishes the locomotor stimulant effect of ethanol in mice

The present study aimed to investigate the effects of sleep deprivation (SD) on the dose-dependent stimulant effect of ethanol (ETOH) on the open-field behavior of female and male mice. Sleep-deprived (48 h, multiple platforms method) or home-cage control female mice were treated with saline (SAL) or 1.4, 1.8 or 2.2g/kg ETOH 5 min before behavioral testing. ETOH produced a dose-dependent increase in open-field locomotor behavior. This locomotor stimulant effect did not reflect a general stimulation in motor activity, since it was accompanied by a simultaneous decrease in rearing frequency as well as by no modification in immobility duration. The effects of ETOH on these three behavioral parameters were specifically modified by SD: the locomotor stimulant effect was abolished, the rearing inhibitory effect was potentiated and the lack of effect on immobility was changed to increase in immobility. Similar results were obtained for male mice although the effects of SD had a lower magnitude. The present findings demonstrate that the acute effect of ETOH on mice's motor activity are behaviorally complex and can be specifically modulated by SD.

Effects of baclofen on reserpine-induced vacuous chewing movements in mice

We have described that GABA mimetic drugs present the ability to inhibit the expression of reserpine-induced oral movements. In this respect, oral movements is associated with important neuropathologies. This study investigates the effects of an acute or a repeated treatment of different doses of the GABA(B) agonist baclofen, as well as withdrawal from these treatments, on the development and/or expression of reserpine-induced vacuous chewing movements (VCM). Male mice received two injections of vehicle or of 1mg/kg reserpine separated by 48 h. In the first experiment, 24h later, animals were acutely treated with vehicle or baclofen (1, 2 or 4 mg/kg). In the second experiment, animals were treated with vehicle or baclofen (1 or 4 mg/kg) for four consecutive days receiving a concomitant injection of 1mg/kg reserpine (or vehicle) on Days 2 and 4. Twenty-four hours later, animals received vehicle or baclofen. Thirty minutes after the last injection, they were observed for quantification of VCM and open-field general activity. The acute administration of all the doses of baclofen abolished the manifestation of reserpine-induced VCM. Repeated treatment with 1mg/kg baclofen induced tolerance to the ability of an acute injection of this dose to reduce VCM. Treatment with baclofen (4 mg/kg) did not modify spontaneous VCM. Acute administration of the highest dose induced a decrease in general motor activity and a potentiation of the reserpine-induced decrease in general activity. These results reinforce the involvement of GABAergic hypofunction in the expression of oral movements and suggest that a repeated treatment with baclofen induces compensatory changes in GABAergic transmission that can attenuate its acute property to decrease VCM.

Effects of morphine on the plus-maze discriminative avoidance task: role of state-dependent learning

RATIONALE

The amnesic effects of morphine may be related to its action on nociception, anxiety, or locomotion. This effect is also suggested to be related to state dependency.

OBJECTIVES

The aims of this study were to verify the effects of morphine on mice tested in the plus-maze discriminative avoidance task (DAT) that uses light and noise as aversive stimuli and allows the concomitant evaluation of learning, memory, anxiety, and locomotion and also to verify the possible role of state-dependent learning in the effects of morphine.

METHODS AND RESULTS

The DAT was conducted in a modified elevated plus-maze. In the training, the aversive stimuli were applied when mice entered in one of the enclosed arms, whereas in the test, no stimuli were applied. The main results showed that (1) pretraining morphine (5-20 mg/kg i.p.) induced retrieval deficits (evaluated by the time spent in the aversive arm in the test) but not acquisition deficits (evaluated by the decrease in aversive arm exploration along the training); (2) pretest morphine (5-10 but not 20 mg/kg) counteracted this deficit; (3) morphine induced hypolocomotion (decreased number of entries in the arms), irrespective of memory alterations; and (4) morphine did not alter anxiety-like behavior (evaluated by the time spent in the open arms) during the training.

CONCLUSIONS

Morphine given before training induces retrieval deficits in mice tested in the DAT, and these deficits could be related to morphine-induced state-dependent learning. Neither the memory deficit induced by pretraining morphine nor the reversal of this deficit by pretest morphine seems to be related to anxiety levels or locomotor alterations.

Effects of long-term continuous exposure to light on memory and anxiety in mice

The studies on the relationship between the light/dark cycle and memory function mostly used protocols of acute disruption of the circadian rhythm. The aim of the present study is to verify the effects of long-term continuous exposure to light on memory, anxiety and motor parameters of mice tested in the plus-maze discriminative avoidance task. Mice were conditioned to choose between the two enclosed arms (one aversive and one non-aversive) while avoiding the open arms of a modified elevated plus-maze apparatus. Memory was evaluated by the time spent in the aversive enclosed arm, anxiety was evaluated by the time spent in the open arms and locomotor behavior was evaluated by number of entries in the arms of the maze. The results showed that long-term (35-42 days) continuous light exposure did not modify memory or anxiety parameters but increased locomotor activity. While the increase in locomotor behavior is in line with previous studies, the unexpected absence of alterations in memory and anxiety (reported to be influenced by the circadian rhythm) is discussed.

Effects of social isolation on aging-induced orofacial movements in rats

World population is becoming older, and aging is a common risk factor for a number of pathologies. In this respect, it is important to study possible factors that could modify alterations implicated in the process of aging. The aim of the present study is to verify the effects of social isolation on the expression of orofacial movements in adult and old rats. Adult and old rats were housed isolated for 5 days or kept in their home cages in groups of six. Before and after this period, orofacial movements and open-field general activity were evaluated. Aging-induced orofacial movements were abolished by isolation. On the other hand, isolated adult rats presented an increase in orofacial movements. General activity was decreased by aging but was not modified by isolation. Our results indicate that social isolation produces different effects in adult and old rats, and these effects are specific for orofacial movements and not related to a decrease in general motor activity.

The importance of housing conditions on behavioral sensitization and tolerance to ethanol

The differential outcomes of social isolation and crowding environment on the effects of single or repeated administration of ethanol on open-field behavior were examined in female mice. Whereas housing conditions did not alter the increase in locomotor activity induced by ethanol single administration, behavioral sensitization (a progressive increase of a drug effect following repeated drug administration) to the locomotor activating effect of ethanol was significantly greater in crowded mice as compared to isolated and control groups. Single administration of ethanol significantly decreased rearing frequency and increased immobility duration, there being tolerance to these ethanol behavior effects after repeated treatment. Social isolation attenuated the increase in immobility behavior induced by single administration of ethanol and potentiated the tolerance of ethanol-induced rearing decrease, verified after repeated treatment. These results point out that both sensitization and tolerance to the behavioral effects of ethanol can be critically influenced by housing conditions.

Behavioral characterization of morphine effects on motor activity in mice

A biphasic effect of morphine on locomotion has been extensively described. Nevertheless, the effects of this opioid on other behavioral parameters have been overlooked. The aim of the present study was to verify the effects of different doses of morphine on motor behaviors observed in an open-field. Adult female mice were injected with saline or morphine (10, 15 and 20 mg/kg, i.p.) and observed in an open-field for quantification of locomotor and rearing frequencies as well as duration of immobility and grooming. The lowest dose of morphine decreased locomotion (and increased immobility duration) while the highest dose increased it. All doses tested decreased rearing and grooming. Thus, the effects of morphine on locomotion do not parallel to its effects on rearing and grooming. Our results indicate that locomotion not always reflects the effect of drugs on motor activity, which can be better investigated when other behavioral parameters are concomitantly taken into account.

Effects of gabaergic drugs on reserpine-induced oral dyskinesia

Recently we have described the antidyskinetic property of the GABA mimetic drugs valproic acid and topiramate on reserpine-induced oral dyskinesia. In this respect, oral dyskinesia has been associated with important neuropathologies. The present study investigates the effects of different doses of the GABA(A) agonist tetrahydroisoxazolopyridine (THIP), of the GABA(B) agonist baclofen as well as of the GABA(A) modulator diazepam on the manifestation of reserpine-induced orofacial dyskinesia. Male Wistar rats received two injections of vehicle or of 1mg/kg reserpine separated by 48 h. Twenty-four hours later, animals were acutely treated with vehicle or THIP (2, 4 or 8 mg/kg), baclofen (1, 2 or 4 mg/kg) or diazepam (1, 2 or 4 mg/kg) and were observed for quantification of oral dyskinesia and open-field general activity. In order to verify the effects of these drugs per se on spontaneous oral movements, male Wistar rats were acutely treated with vehicle, 8 mg/kg THIP, 4 mg/kg baclofen or 4 mg/kg diazepam and observed for quantification of oral dyskinesia. The two highest doses of THIP or of baclofen abolished the manifestation of reserpine-induced oral dyskinesia while the lowest dose of baclofen attenuated it. Diazepam did not modify reserpine-induced oral dyskinesia at any dose tested. The highest doses of these drugs did not modify spontaneous oral movements. Reserpine-induced decrease in open-field general activity was not modified by any of the doses of THIP and diazepam or by the two lowest doses of baclofen. The highest dose of baclofen potentiated the increase in the duration of immobility induced by reserpine. These results reinforce the involvement of GABAergic hypofunction in the expression of oral dyskinesias, and support the potential therapeutic use of THIP and baclofen in the treatment of oral dyskinesias.

Role of anxiety levels in memory performance of spontaneously hypertensive rats

Spontaneously hypertensive rats (SHR) show behavioural differences when compared to their strain-matched controls. These differences include decreased anxiety-like behaviour in SHR, while both improved performance and behavioural deficits have been reported in learning/memory studies. Considering that alterations in anxiety levels during the training session can modify retention performance in animal models of memory, the aim of the present study was to investigate the role of anxiety levels in the performance of SHR rats in the plus-maze discriminative avoidance task (PM-DAT), in which memory and anxiety are evaluated simultaneously. Adult (5-month-old) and young (45-day-old) SHR and normotensive Wistar rats (NWR) were treated with chlordiazepoxide (CDZ) or saline. Thirty minutes later, rats were submitted to the PM-DAT training session. After 24 h, the test session was performed. The results showed that: (1) adult SHR showed lower anxiety levels compared to adult NWR; (2) adult SHR and NWR, as well as young NWR, showed significant retention of the task, while young SHR showed impaired performance; (3) 5.0 mg/kg CDZ decreased anxiety levels in adult NWR and young and adult SHR; (4) 5.0 mg/kg CDZ impaired retention in adult SHR and NWR and increased retention in young SHR. Our data suggest an important role of anxiety levels in the performance of SHR in a plus-maze discriminative avoidance task.

Role of learning of open arm avoidance in the phenomenon of one-trial tolerance to the anxiolytic effect of chlordiazepoxide in mice

A single exposure to the elevated plus-maze (EPM) test of anxiety reduces or abolishes the anxiolytic efficacy of benzodiazepines on a second trial. Some possible explanations to the occurrence of this phenomenon (one-trial tolerance-OTT) involve behavioral modifications thought to be consequence of some kind of learning in the first trial. In the present study, the influence of learning-impairing situations on the effects of the benzodiazepine chlordiazepoxide on mice re-tested in the EPM is investigated. The results showed that: (1) as expected, the administration of chlordiazepoxide to mice re-tested in the EPM- under the same conditions of the first trial- failed to induce anxiolysis; (2) a decreased percent time in the open arms was observed on the second trial of mice exposed to both trials under the same experimental conditions; (3) neither the increase in open arm avoidance by mice re-exposed to the EPM nor the OTT to chlordiazepoxide effect were modified by administration of the amnestic agent scopolamine; (4) the decrement of the duration of the first trial to 1 min or the change in light and noise conditions in both trials counteracted the increase in open arm avoidance on trial 2; (5) none of the later procedures modified the phenomenon of OTT. Although not discarding the modulation exerted by other memory processes in the OTT phenomenon, the results indicate that situations that impair the learned avoidance response to the open arms in the EPM do not modify the phenomenon of OTT.

Effects of topiramate on oral dyskinesia induced by reserpine

Recently, we have described the antidyskinetic property of the GABA mimetic drug valproic acid on reserpine-induced oral dyskinesia, an animal model that has been related to tardive as well as acute dyskinesias, which are associated with important neuropathologies. The present study investigates the effects of different doses of the GABA mimetic anticonvulsant topiramate on the manifestation of reserpine-induced orofacial dyskinesia. Female EPM-M1 mice received two injections of control solution or of 0.5 mg/kg reserpine separated by 48 h. Twenty-four hours after the second reserpine or control solution injection, animals were acutely treated with control solution or topiramate (1, 3, 10 or 30 mg/kg) and were observed for quantification of oral dyskinesia or general activity in an open-field. In order to verify the effects of topiramate per se on oral dyskinesia or general activity, female EPM-M1 mice were acutely treated with control solution or 1, 3, 10 or 30 mg/kg topiramate and observed for quantification of oral dyskinesia and general activity. The highest dose of topiramate completely abolished the manifestation of reserpine-induced oral dyskinesia whereas the doses of 3 and 10 mg/kg significantly attenuated it. None of the doses of the anticonvulsant modified spontaneous locomotion frequency or oral movements, whereas spontaneous rearing frequency was decreased by 3, 10 and 30 mg/kg topiramate. The highest dose of topiramate did not modify general activity in reserpine-treated mice. These results support the potential therapeutic use of topiramate in the treatment of oral dyskinesias.

Anxiogenic effect of sleep deprivation in the elevated plus-maze test in mice

RATIONALE

Several clinical studies demonstrate that the absence of periods of sleep is closely related to occurrence of anxiety symptoms. However, the basis of these interactions is poorly understood. Studies performed with animal models of sleep deprivation and anxiety would be helpful in the understanding of the mechanisms underlying this relationship, but some animal studies have not corroborated clinical data, reporting anxiolytic effects of sleep deprivation.

OBJECTIVES

The aim of the present study was to verify the effects of different protocols of sleep deprivation in mice tested in the elevated plus-maze and to assess the effect of chlordiazepoxide and clonidine.

METHODS

Three-month-old male mice were sleep-deprived for 24 or 72 h using the methods of single or multiple platforms in water tanks. Mice kept in their home cages were used as controls. Plus-maze behavior was observed immediately after the deprivation period.

RESULTS

Mice that were sleep-deprived for 72 h spent a lower percent time in the open arms of the apparatus than control animals. This sleep deprivation-induced anxiety-like behavior was unaffected by treatment with chlordiazepoxide (5.0 and 7.5 mg/kg IP), but reversed by an administration of 5 or 10 microg/kg IP clonidine.

CONCLUSION

The results indicate that under specific methodological conditions sleep deprivation causes an increase in anxiety-like behavior in mice exposed to the elevated plus-maze.

Effects of pre- or post-training paradoxical sleep deprivation on two animal models of learning and memory in mice

The aim of the present study was to verify the effects of pre- or post-training paradoxical sleep (PS) deprivation in mice tested in the passive and the plus-maze discriminative avoidance tasks. Three-month-old Swiss male mice were placed in narrow platforms in a water tank for 72 h to prevent the occurrence of PS. Control animals were kept in the same room, but in their home cages. Before or after this period, the animals were submitted to the training session of one of the behavioral tasks. The test sessions were performed 3 and 10 days after the training. The animals that were PS-deprived before the training session showed retention deficits in the test sessions performed 3 days later in both tasks (decreased latency to enter the dark chamber of the passive avoidance apparatus or increased percent time spent in the aversive arm of the plus-maze discriminative avoidance apparatus). Animals that were PS deprived after the training session showed no differences from control animals in the test sessions performed 3 days after the training in any of the tasks, but showed passive and discriminative avoidance retention deficits in the test performed 10 days after the training. The results suggest that both pre- and post-training paradoxical sleep deprivation produce memory deficits in mice. However, these effects have different temporal characteristics.

Important role of striatal catalase in aging- and reserpine-induced oral dyskinesia

Tardive dyskinesia, the most serious iatrogenic movement disorder, has been tentatively associated with nigrostriatal dopaminergic supersensitivity and with oxidative stress. It is also suggested that long-term neuroleptic treatment does not cause oral dyskinesia (OD), but interacts with some substrate of brain aging, resulting in the premature emergence of OD, that can occur spontaneously with aging. In order to investigate a possible role of nigrostriatal dopaminergic supersensitivity and of oxidative stress in aging- and reserpine-induced OD, the stereotyped behavior induced by dopaminergic agonists, a functional index of dopaminergic striatal activity, as well as the striatal antioxidant enzymes glutathione peroxidase and catalase were assessed. We demonstrate that, opposite to normotensive Wistar rats (NWR), spontaneously hypertensive rats (SHR) do not develop aging- or reserpine-OD. There were no differences between NWR and SHR in stereotyped behavior or in striatal glutathione peroxidase activity. Adult and old SHR presented higher striatal catalase activity relative to NWR, and aging increased it only in SHR. The catalase inhibitor aminotriazole reverted the absence of aging- and reserpine-induced OD in SHR. Our results suggest an important role of striatal catalase in the development of reserpine- and aging-induced OD.

Role of hippocampal oxidative stress in memory deficits induced by sleep deprivation in mice

Numerous animal and clinical studies have described memory deficits following sleep deprivation. There is also evidence that the absence of sleep increases brain oxidative stress. The present study investigates the role of hippocampal oxidative stress in memory deficits induced by sleep deprivation in mice. Mice were sleep deprived for 72 h by the multiple platform method-groups of 4-6 animals were placed in water tanks, containing 12 platforms (3 cm in diameter) surrounded by water up to 1 cm beneath the surface. Mice kept in their home cage or placed onto larger platforms were used as control groups. The results showed that hippocampal oxidized/reduced glutathione ratio as well as lipid peroxidation of sleep-deprived mice was significantly increased compared to control groups. The same procedure of sleep deprivation led to a passive avoidance retention deficit. Both passive avoidance retention deficit and increased hippocampal lipid peroxidation were prevented by repeated treatment (15 consecutive days, i.p.) with the antioxidant agents melatonin (5 mg/kg), N-tert-butyl-alpha-phenylnitrone (200 mg/kg) or vitamin E (40 mg/kg). The results indicate an important role of hippocampal oxidative stress in passive avoidance memory deficits induced by sleep deprivation in mice.

Effects of valproic acid on an animal model of tardive dyskinesia

GABAergic hypofunction in the basal ganglia is stated as an important mechanism underlying the pathophysiology of tardive dyskinesia. The present study investigates the effects of the GABA-mimetic drug valproic acid (VA) on the manifestation of reserpine-induced orofacial movements, an animal model of tardive dyskinesia. Male Wistar rats received two injections of control solution or of 1 mg/kg reserpine separated by 48 h. Twenty-four hours later, animals were acutely treated with 50, 100, or 200 mg/kg VA or control solution and were observed for quantification of orofacial movements and of open-field general activity. The highest dose of VA inhibited the manifestation of reserpine-induced orofacial movements but none of the VA doses modified reserpine-induced decrease in open-field general activity. These results support the potential of VA as an effective pharmacological tool in the treatment of tardive dyskinesia.

Effects of melatonin on behavioral dopaminergic supersensitivity

This study examines the effects of melatonin on dopaminergic supersensitivity induced by long-term treatment with haloperidol in rats. Enhancements of spontaneous general activity in an open-field and of stereotyped behavior induced by apomorphine after abrupt withdrawal from long-term treatment with haloperidol were used as experimental parameters for dopaminergic supersensitivity. Experiment 1 was conducted to investigate the effects of melatonin on the development of dopaminergic supersensitivity, and experiment 2 was conducted to investigate the effects of melatonin on the development as well as on expression of dopaminergic supersensitivity. Rats of both experiments were long-term treated with saline or haloperidol concomitant to saline or melatonin. In experiment 1 behavioral observations were performed after abrupt withdrawal from long-term treatment. In experiment 2 behavioral observations were performed 1 hour after an acute injection of saline or melatonin, administered after the abrupt withdrawal from long-term treatment. Both behavioral parameters used showed the development of central dopaminergic supersensitivity in rats treated with haloperidol since 24 hours after abrupt withdrawal. Concomitant treatment with melatonin intensified haloperidol-induced dopaminergic supersensitivity, observed 72 hours after withdrawal. Melatonin treatment per se also induced behavioral supersensitivity evaluated by both open-field and stereotyped behaviors, although it was more fugacious than that presented by haloperidol. Acute treatment with melatonin reverted the enhancement of the haloperidol-induced dopaminergic supersensitivity produced by concomitant long-term treatment with melatonin, as well as melatonin-induced dopaminergic supersensitivity per se. Our results support previous evidence of antidopaminergic effects of melatonin and demonstrate that repeated administration of this hormone modifies the plasticity of behaviors mediated by central dopaminergic systems.

Antidyskinetic effects of risperidone on animal models of tardive dyskinesia in mice

The effects of risperidone, an atypical neuroleptic, were investigated on two animal models of tardive dyskinesia (TD). The repeated administration of reserpine (1.0mg/kg) or haloperidol (2.0mg/kg) induces orofacial movements in mice, which are very similar to those observed in humans presenting TD. The effects of acute or repeated treatment with several doses of risperidone (0.1; 0.5; 2.0 or 4.0) on the expression and development of orofacial movements in reserpine- and haloperidol-treated male mice were investigated. The results showed that risperidone per se did not induce the development of orofacial movements. In addition, this drug was able to attenuate the expression and the development of reserpine-as well as haloperidol-induced orofacial movements. These results are in line with several clinical studies that suggest not only a lower incidence of TD in schizophrenic patients treated with risperidone, but also an antidyskinetic effect of this drug in patients previously treated with classical neuroleptics.

Vitamin E attenuates reserpine-induced oral dyskinesia and striatal oxidized glutathione/reduced glutathione ratio (GSSG/GSH) enhancement in rats

The effects of a previous and concomitant treatment with vitamin E (VE) were studied on an animal model of tardive dyskinesia, i.e., the frequency of spontaneous tongue protrusions in rats treated with reserpine (RE). VE (5, 10, 20 or 40 mg/kg administered intraperitoneally, daily, for 19 days) attenuated the increase in tongue protrusion frequency induced by RE (1 mg/kg administered subcutaneously, on Days 16 and 18, 1 h after VE), which was quantified on Day 19. In a second experiment, a similar treatment with 20 mg/kg VE attenuated RE-induced increase in the striatal ratio of oxidized/reduced glutathione (GSSG/GSH), an index of the oxidative stress process. These results support the free radical hypothesis of tardive dyskinesia.

Effects of melatonin on orofacial movements in rats

RATIONALE

While reserpine-induced oral movements (OM), an animal model of tardive dyskinesia, are more persistent in old than in adult rats, old animals present spontaneous OM, which are phenomenologically similar to those presented by reserpine-treated adult rats. We postulate that these OM may be the result of oxidative stress induced by both age and reserpine treatment.

OBJECTIVES

We intended to determine the preventative effects of exogenous melatonin (one of the most important endogenous antioxidants) as well as suppression of endogenous melatonin via continuous exposure to light on reserpine- or age-induced OM in rats.

METHODS

Adult (4 months of age) male Wistar rats were repeatedly treated with saline or melatonin (5 mg/kg, IP) and saline or reserpine and kept under a 12-h light/dark cycle for quantification of reserpine-induced OM as well as oxidative stress (via quantification of lipid peroxidation). To verify the effects of endogenous melatonin suppression on reserpine-induced OM, adult rats were repeatedly treated with saline or reserpine and continuously exposed to light. To verify the effects of exogenous melatonin on age-induced OM older (20 months of age) rats were long-term treated with saline or melatonin and kept under a 12-h light/dark cycle.

RESULTS

Melatonin attenuated both reserpine- and age-induced OM. Reserpine enhanced striatal lipid peroxidation, that was prevented by melatonin co-administration. Continuous exposure to light increased spontaneous as well as reserpine-induced OM, indicating that endogenous melatonin may be involved in this movement disorder.

CONCLUSIONS

We suggested that melatonin attenuates both reserpine- and age-induced OM in rats.

Concomitant development of oral dyskinesia and memory deficits in reserpine-treated male and female mice

It has been suggested that reserpine-induced oral dyskinesia in rats may provide a new animal model of tardive dyskinesia. Both cognitive deficits and gender have been associated with the development of tardive dyskinesia. The aim of the present study was to investigate the effects of reserpine administration on the development of orofacial dyskinesia and on plus-maze discriminative avoidance task (DAT-an animal model of associative learning) in male and female mice. Male and female mice received 1.0 mg/kg reserpine or saline subcutaneously on day 1. On days 3, 6 and 8, the frequency of vacuous chewing movements (VCM) was quantified. On day 6, the DAT conditioning was performed, in a modified elevated plus-maze. In one of the enclosed arms, the animals received aversive stimulation (light and noise). On day 8, a test session was performed and the time spent by the animals in each of the enclosed arms was recorded. Our results showed that reserpine-treated male and female mice presented significantly higher VCM when compared with respective control groups in all observation days. On day 6, reserpine-treated female mice presented significantly higher VCM when compared with male mice injected with this drug. The DAT test performed on day 8 showed that the time spent in the aversive arm by saline-treated mice was significantly lower than the time spent in the non-aversive arm. This difference was not observed for reserpine-treated mice. Our results demonstrate the development of reserpine-induced oral dyskinesia in both male and female mice. While this oral dyskinesia is accompanied by a cognitive deficit in both genders, female mice tended to have more severe oral dyskinesia. It is suggested that reserpine-induced oral dyskinesia may provide a quick, simple and efficient mouse model of tardive dyskinesia.

Effects of continuous exposure to light on behavioral dopaminergic supersensitivity

BACKGROUND

This study examines the effects of long-term continuous exposure to light on dopaminergic supersensitivity induced by repeated treatment with haloperidol in rats.

METHODS

Spontaneous general activity in an open-field (SGA) and stereotyped behavior induced by apomorphine (SB-APO) or amphetamine (SB-AMP) were used as experimental parameters. Rats were allocated to four groups in each experiment: saline-treated animals kept under a 12-hour light/dark cycle (LD) or 24-hour light/light cycle (LL), and 2 mg/kg haloperidol-treated animals kept under the above cycles. Plasma corticosterone concentration was also measured by radioimmunoassay in saline-treated rats kept under a LD or LL cycle.

RESULTS

All the behavioral parameters used showed the development of central dopaminergic supersensitivity in rats kept under both cycles. Continuous exposure to light enhanced SGA and SB-AMP in both saline- and haloperidol-treated rats, but did not modify SB-APO. Animals kept under the LL cycle presented an increased plasma corticosterone concentration.

CONCLUSIONS

Our results suggest that continuous exposure to light leads to an increase in dopaminergic function in both normal and "supersensitive" rats. This effect seems to be mediated by a presynaptic mechanism possibly involving corticosterone actions.

Effects of age on a new animal model of tardive dyskinesia

The effects of age were studied on a new animal model of tardive dyskinesia, i.e., the quantification of oral dyskinesia in rats repeatedly treated with reserpine. Adult and old rats received two injections of reserpine (0.5 or 1.0 mg/kg s.c.) or vehicle, separated by 48 h. One, 10, 25 and 40 days after the second injection of reserpine or vehicle, the animals were observed for quantification of the behavioral parameters of oral dyskinesia: tongue protrusion and vacuous chewing movement frequencies and duration of twitching of the facial musculature. Phenomenologically, control old rats and reserpine-treated adult animals showed very similar oral dyskinesia. When compared to control adult rats, the significant increase in tongue protrusion frequency induced by reserpine treatment was more persistent in the old rats than in the adult animals. Because it is well known that age increases the persistence of tardive dyskinesia, our data provide further support for the validation of reserpine-induced oral dyskinesia as an animal model of tardive dyskinesia. In addition, the possibility is raised that a common pathophysiological mechanism may underlie tardive dyskinesia and age- and reserpine-induced oral dyskinesia.

Behavioural subsensitivity induced by long-term administration of a low dose of haloperidol to rats

This study examines the effects on open-field and stereotyped behaviour of rats of abrupt withdrawal from repeated treatment with a low (0.03 mg kg-1) dose of haloperidol. Single administration of this low dose of haloperidol significantly increased open-field locomotion without modifying apomorphine (0.5 or 2.0 mg kg-1)-induced stereotyped behaviour. Forty-eight hours after abrupt withdrawal from 0.03 mg kg-1 haloperidol (twice daily for 15 days) a significant decrease in locomotion frequency was observed, but no change was observed in apomorphine-induced stereotypy. Our results suggest that dopamine autoreceptor supersensitivity might be evaluated in a behavioural situation of absence of postsynaptic dopamine receptor supersensitivity.