Context-dependent efficacy of a counter-conditioning strategy with atypical neuroleptic drugs in mice previously sensitized to cocaine

RATIONALE

We have previously demonstrated that treatment with ziprasidone and aripiprazole selectively inhibit the development of behavioral sensitization to cocaine in mice. We now investigate their effects on a counter-conditioning strategy in mice and the importance of the treatment environment for this phenomenon.

OBJECTIVE

Evaluate the context-specificity of ziprasidone and aripiprazole on conditioned locomotion to cocaine and cocaine-induced hyperlocomotion and behavioral sensitization in a counter-conditioning strategy in mice.

METHODS

Animals were sensitized with saline or cocaine injections in the open-field apparatus in a 15-day intermittent treatment and subsequently treated with vehicle, 5mg/kg ziprasidone or 0.1mg/kg aripiprazole paired to the open-field or the home-cage for 4 alternate days. Mice were then challenged with saline and cocaine in the open-field apparatus on subsequent days.

RESULTS

While treatment with ziprasidone decreased spontaneous locomotion and conditioned locomotion alike, treatment with aripiprazole specifically attenuated the expression of conditioned hyperlocomotion to cocaine. Ziprasidone and aripiprazole had no effects on cocaine-induced conditioned hyperlocomotion observed during saline challenge after drug withdrawal. Treatment with either ziprasidone or aripiprazole when previously given in the cocaine-paired environment attenuated the subsequent expression of behavioral sensitization to cocaine. Animals treated with aripiprazole in the open-field, but not in the home-cage, showed a blunted response to cocaine when receiving a cocaine challenge for the first time.

CONCLUSIONS

Both neuroleptic drugs showed a context-dependent effectiveness in attenuating long-term expression of cocaine-induced behavioral sensitization when administered in the cocaine-associated environment, with aripiprazole also showing effectiveness in blocking the expression of acute cocaine effects.

Acute total sleep deprivation potentiates cocaine-induced hyperlocomotion in mice

Sleep deprivation is common place in modern society. Nowadays, people tend to self-impose less sleep in order to achieve professional or social goals. In the social context, late-night parties are frequently associated with higher availability of recreational drugs with abuse potential. Physiologically, all of these drugs induce an increase in dopamine release in the mesolimbic dopaminergic system, which leads to hyperlocomotion in rodents. Sleep deprivation also seems to play an important role in the events related to the neurotransmission of the dopaminergic system by potentiating its behavioral effects. In this scenario, the aim of the present study was to investigate the effects of total sleep deprivation (6h) on the acute cocaine-induced locomotor stimulation in male mice. Animals were sleep deprived or maintained in their home cages and subsequently treated with an acute i.p. injection of 15mg/kg cocaine or saline and observed in the open field. Total sleep deprivation for 6h potentiated the hyperlocomotion induced by acute cocaine administration. In addition, the cocaine sleep deprived group showed a decreased ratio central/total locomotion compared to the cocaine control group, which might be related to an increase in the impulsiveness of mice. Our data indicate that acute periods of sleep loss should be considered risk factors for cocaine abuse.

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.

Postnatal Transplantation of Interneuronal Precursor Cells Decreases Anxiety-Like Behavior in Adult Mice

The GABAergic system is critically involved in the modulation of anxiety levels, and dysfunction of GABAergic neurotransmission appears to be involved in the development of generalized anxiety disorder. Precursor cells from the medial ganglionic eminence (MGE) have the ability to migrate and differentiate into inhibitory GABAergic interneurons after being transplanted into the mouse brain. Thus, transplantation of interneuronal precursor cells derived from the MGE into a postnatal brain could modify the neuronal circuitry, increasing GABAergic tone and decreasing anxiety-like behavior in animals. Our aim was to verify the in vivo effects of transplanted MGE cells by evaluating anxiety-like behavior in mice. MGE cells from 14-day green fluorescent protein (GFP) embryos were transplanted into newborn mice. At 15, 30, and 60 days posttransplant, the animals were tested for anxiety behavior with the elevated plus maze (EPM) test. Our results show that transplanted cells from MGE were able to migrate to different regions of the brain parenchyma and to differentiate into inhibitory interneurons. The neuronal precursor cell transplanted animals had decreased levels of anxiety, indicating a specific function of these cells in vivo. We suggested that transplantation of MGE-derived neuronal precursors into neonate brain could strengthen the inhibitory function of the GABAergic neuronal circuitry related to anxiety-like behavior in mice.

Fish oil supplementation and physical exercise program: distinct effects on different memory tasks

Both fish oil supplementation and physical exercise are able to induce benefits to mental health by providing an improvement in cognitive performance and enhancing neuroplasticity and protection against neurological lesions. The aim of the present study was to investigate the cognitive effects in rats of the: (1) a diary and prolonged fish oil supplementation (85 mg/kg/day) initiated from prenatal period to the midlife (300 day/old); (2) moderate physical exercise in treadmill initiated from adolescent period to midlife and (3) association of fish oil supplementation and moderate physical exercise protocol during the same period. Animals were submitted to the habituation in the open-field, object recognition and to the plus-maze discriminative avoidance tasks. Our results demonstrated that a diary and prolonged fish oil supplementation can facilitate the persistence of the long-term habituation and recognition memories without, however, affecting the discriminative avoidance memory. Conversely, although the program of physical exercise exerted no effects on habituation or objects recognition, it was able to potentiate the persistence of the discriminative avoidance memory. Such promnestic effects (induced by both fish oil supplementation and physical exercise) were not accompanied by alterations in emotionality or locomotor activity. Our findings suggest that fish oil supplementation, initiated from prenatal period to midlife, and physical exercise program applied throughout the life induced distinctly a better cognitive performance.

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.

Association of paradoxical sleep deprivation and ecstasy (MDMA) enhances genital reflexes in male rats

Ecstasy ((+/-)3,4-methylenedioxymethamphetamine, MDMA) is a psychostimulant and a synthetic derivative of amphetamine that, according to its consumers, promotes the enhancement of sexual pleasure. This study sought to investigate the effects of ecstasy in the genital reflexes of paradoxical sleep deprived (PSD) male rats. Distinct groups of PSD rats were administered with saline or different doses of ecstasy. The incidence of genital reflexes was verified for 100 min. The four doses that were used induced genital reflexes in PSD animals and these significantly differed from their respective treated control groups. Under the influence of two intermediary doses (2.5 and 5mg/kg), all animals displayed erection and ejaculation. The frequency of genital reflexes was also significantly greater than in relation to the PSD-saline group. The comparison between cocaine and ecstasy in PSD rats revealed that ecstasy induced more erections and ejaculations than cocaine. Thus, the present results showed a great enhancement of the genital reflexes of PSD rats that might have occurred due to serotoninergic alterations induced by this illicit substance when associated to sleep deprivation.

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.

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.

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 morphine or naloxone on cocaine-induced genital reflexes in paradoxical sleep-deprived rats

The involvement of opioidergic neurotransmission in the modulation of genital reflexes induced by paradoxical sleep deprivation (PSD) and cocaine in rats was the aim of the present study. Morphine (0, 1, 5 and 10 mg/kg) and naloxone (0, 0.3, 3 and 30 mg/kg) were administered prior to saline or cocaine to rats that had been deprived of sleep and the incidence of penile erections (PE) and ejaculations (EJ) was measured. PSD alone induced PE in 50% and EJ in 20% of the rats, but these behaviors were not influenced by morphine or naloxone. Cocaine potentiated the incidence of genital reflexes in PSD rats to 90% (PE) and 70% (EJ). Morphine and not naloxone significantly reduced the percentage of rats displaying this response at the highest doses. Morphine also significantly reduced PE and EJ frequencies at 10 mg/kg. Furthermore, this inhibitory effect of morphine on genital reflexes was prevented by the prior injection of naloxone. Although a number of factors are involved in such a complex phenomenon as PE and EJ, our data show that activation of the opioidergic systems by the agonist morphine reduces genital reflexes-induced by cocaine in PSD males while the antagonist, naloxone, did not have any significant effect. The findings suggest that the stimulating effects of cocaine in potentiating genital reflexes in PSD rats can be unidirectionally modified by opioidergic systems.

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.

Monosialoganglioside (GM1) attenuates the behavioural effects of long-term haloperidol administration in supersensitive rats

In the present study we investigated the effects of co-administration of GM(1) (15.0 mg/kg, twice daily, for 30 days) and haloperidol (1.0 mg/kg, twice daily, for 30 days), as well as the effects of a 5-day treatment with this dose of GM(1) after withdrawal from haloperidol in rats. The animals were evaluated in the open-field test and apomorphine-induced stereotyped behaviour. The results show that GM(1) was able to attenuate dopaminergic supersensitivity evaluated by the locomotion frequency at 24 and 48 h after the withdrawal from haloperidol. On the other hand, rearing frequency was changed neither by haloperidol nor by GM(1.) In haloperidol-treated rats immobility time differs from 30 min observation session in comparison with the following sessions after the withdrawal from neuroleptic. Apomorphine-induced stereotyped behaviour produced a significant increase in scores of haloperidol-withdrawn rats. GM(1) did not modify the haloperidol effects and did not change the dopamine receptor affinity to apomorphine 100 h from abrupt neuroleptic withdrawal.

Mitochondrial calcium, oxidative stress and apoptosis in a neurodegenerative disease model induced by 3-nitropropionic acid

Intracellular calcium homeostasis is important for cell survival. However, increase in mitochondrial calcium (Ca2+m) induces opening of permeability transition pore (PTP), mitochondrial dysfunction and apoptosis. Since alterations of intracellular Ca2+ and reactive oxygen species (ROS) generation are involved in cell death, they might be involved in neurodegenerative processes such as Huntington's disease (HD). HD is characterized by the inhibition of complex II of respiratory chain and increase in ROS production. In this report, we studied the correlation between the inhibitor of the complex II, 3-nitropropionic acid (3NP), Ca2+ metabolism, apoptosis and behavioural alterations. We showed that 3NP (1 mm) is able to release Ca2+m, as neither Thapsigargin (TAP, 2 microm) nor free-calcium medium affected its effect. PTP inhibitors and antioxidants inhibited this process, suggesting an increase in ROS generation and PTP opening. In addition, 3NP (0.1 mm) also induces apoptotic cell death. Behavioural changes in animals treated with 3NP (20 mg/kg/day for 4 days) were also attenuated by pre- and co-treatment with vitamin E (VE, 20 mg/kg/day). Taken together, our results show that complex II inhibition could involve Ca2+m release, oxidative stress and cell death that may precede motor alterations in neurodegenerative processes such as HD.

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.

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

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

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.

Acute buspirone abolishes the expression of behavioral dopaminergic supersensitivity in mice

Previous studies have shown that rats withdrawn from long-term treatment with dopamine receptor blockers exhibit dopaminergic supersensitivity, which can be behaviorally evaluated by enhanced general activity observed in an open-field. Recently, it has been reported that co-treatment with the non-benzodiazepine anxiolytic buspirone attenuates the development of haloperidol-induced dopaminergic supersensitivity measured by open-field behavior of rats. The aims of the present study were: 1) to determine, as previously reported for rats, if mice withdrawn from long-term neuroleptic treatment would also develop dopaminergic supersensitivity using open-field behavior as an experimental paradigm, and 2) to examine if acute buspirone administration would attenuate the expression of this behavioral dopaminergic supersensitivity. Withdrawal from long-term haloperidol treatment (2.5 mg/kg, once daily, for 20 days) induced a significant (30%) increase in ambulation frequency (i.e., number of squares crossed in 5-min observation sessions) but did not modify rearing frequency or immobility duration in 3-month-old EPM-M1 male mice observed in the open-field apparatus. Acute intraperitoneal injection of buspirone (3.0 and 10 but not 1.0 mg/kg, 12-13 animals per group) 30 min before open-field exposure abolished the increase in locomotion frequency induced by haloperidol withdrawal. These data suggest that the open-field behavior of mice can be used to detect dopaminergic supersensitivity, whose expression is abolished by acute buspirone administration.

Effects of amphetamine on the plus-maze discriminative avoidance task in mice

RATIONALE

The contradictory amphetamine effects on memory could be due to different protocols of amphetamine administration or the well-known anxiogenic effect of the drug.

OBJECTIVE

The effects of different protocols of administration of amphetamine were investigated on mice tested in the plus-maze discriminative avoidance task (DAT), which provides simultaneous information about memory and anxiety.

METHODS

Acutely pre- or post-training, 0.3, 1.0, or 3.0 mg/kg amphetamine-treated, 10-day chronically 3.0 mg/kg amphetamine-treated, 0.3 mg/kg amphetamine plus 0.25 mg/kg scopolamine and 3.0 mg/kg amphetamine plus 3.0 mg/kg tacrine-treated mice were conditioned to choose between two enclosed arms (one of which was aversive) while avoiding two open arms. Learning/memory was evaluated by the percentage time in the aversive enclosed arm (PTAV), and anxiety by the percentage time in the open arms (PTO).

RESULTS

Given acutely before conditioning, amphetamine significantly decreased PTO in training, suggesting an anxiogenic effect, and significantly increased PTAV in the test, suggesting an amnestic action. Given acutely after the conditioning, no action of this drug on memory was found. After repeated treatment, the anxiogenic effect disappeared, while the amnestic effect remained. While no effects of subeffective doses of amphetamine and scopolamine co-administration were detected, tacrine attenuated the amnestic effect of amphetamine.

CONCLUSIONS

Amphetamine has different effects on DAT when given pre- or post-training. While acute pre-training amnestic action is temporally correlated with an anxiogenic effect, there is tolerance to the anxiogenic but not to the amnestic effect after repeated administration. Because this acute amnestic effect of amphetamine is attenuated by tacrine, a possible relationship with cholinergic system cannot be discarded as a mechanism to amphetamine-induced amnesia in DAT.

The neurotensin receptor antagonist, SR48692, attenuates the expression of amphetamine-induced behavioural sensitisation in mice

The effects of acute administration of the neurotensin receptor antagonist, SR48692 (2-[[1-(7-chloroquinolin-4-yl)-5-(2,6-dimethoxyphenyl)-1H-pyrazol-3-carbonyl]amino]adamantane-2-carboxylic acid), on amphetamine-induced behavioural sensitisation were studied with the locomotor activity of mice in an open-field as an experimental parameter. The animals were repeatedly pretreated with saline or amphetamine (2.0 mg/kg, i.p. once a day, every other day for 13 days) and 2, 9 and 16 days after the last injection they received an acute i.p. administration of saline or 0.3 mg/kg SR48692 15 min before a challenge i.p. injection of 2.0 mg/kg amphetamine. Locomotor activity of the amphetamine-challenged mice was significantly higher in amphetamine-pretreated animals than in saline-pretreated mice on days 9 and 16 after withdrawal. SR48692 prevented the expression of this behavioural sensitisation. In addition, in saline-pretreated mice, the first two challenge injections of amphetamine sufficed to induce a sensitized locomotor response to the third challenge injection of the drug. SR48692 administration before amphetamine challenge injections prevented the development of this challenge injection-induced sensitisation in saline-pretreated mice but not in amphetamine-pretreated animals. In order to determine the effects of SR48692 on the expression of amphetamine-induced behavioural sensitisation in the absence of this challenge injection-induced sensitisation, the experiment was redone with a single challenge test 9 days after pretreatment. Once again, SR48692 prevented the expression of amphetamine-induced behavioural sensitisation. These results suggest that neurotensinergic transmission has a critical role in both the initiation and expression of locomotor sensitisation to amphetamine.

The plus-maze discriminative avoidance task: a new model to study memory-anxiety interactions. Effects of chlordiazepoxide and caffeine

The plus-maze discriminative avoidance paradigm is a new animal model of learning/memory that provides simultaneous information about anxiety. Mice are conditioned to choose between the two enclosed arms (in one of which light and noise are presented as aversive stimuli) while avoiding the two open arms of the apparatus. The test has the advantage of measuring, at the same time and in the same animals, learning/memory (by the percent time spent in aversive enclosed arm - PTAV) and anxiety (by the percent time spent in the open arms - PTO). The effects of chlordiazepoxide and caffeine on learning/memory and anxiety of mice tested in this paradigm were investigated. Chlordiazepoxide (5 mg/kg) significantly increased and caffeine (20 mg/kg) significantly decreased PTO during the training session, suggesting an anxiolytic and an anxiogenic effect, respectively. In the test session, chlordiazepoxide- or caffeine-treated mice presented higher PTAV, suggesting amnestic effects. Given together, chlordiazepoxide plus caffeine did not alter PTO, and the amnesic effect produced by each drug was no longer observed. It is concluded that learning/memory depends on an optimum emotional level. The plus-maze discriminative avoidance model appears to be a useful test to investigate this critical relationship between learning/memory and anxiety.

Effects of neonatal ganglioside GM1 administration on memory in adult and old rats

Numerous investigations have been reporting the involvement of GM1 ganglioside in central nervous system development and memory formation. The effects of neonatal treatment with GMI ganglioside on the performance of adult rats in a plus-maze discriminative avoidance task and old rats in a step-down passive avoidance task were investigated. Rats were injected subcutaneously from day 3 to 15 after birth with 10 mg/kg GM1 or saline. GM1 treatment did not modify indicative landmarks of physical and motor development. Behavioural tasks were carried out when the animals were 4 (discriminative avoidance) or 24 (passive avoidance) months old. Discriminative avoidance conditioning was performed in a modified elevated plus-maze. During the training session, the animals received aversive stimulation (light and hot air blow) in one of the enclosed arms. Tests were performed 7, 14 and 21 days after conditioning (tests 1, 2 and 3), in the absence of the aversive stimulation. In all tests, GM1-treated animals spent less time in the aversive arm than in the non-aversive enclosed arm. Control animals, however, spent a shorter time in the aversive arm only in tests 1 and 2. Passive avoidance conditioning was performed in an acrylic box with a grid floor, that was partially covered by an inclined platform. Animals were placed on the platform and received a 0,5 mA foot shock when stepped down. A test was performed 48 hr later. Latency to step down presented by GM 1-treated animals was significantly higher in the test session, whereas no significant increase in latency to step down was found for control animals. The results suggest a possible action of GM1 on the maturation of the central nervous system that persists during adulthood and ageing.

MK-801 blocks the development of behavioral sensitization to the ethanol

BACKGROUND

Studies have indicated that MK-801 (a noncompetitive N-methyl-D-aspartate receptor antagonist) participates in the long-term neural changes responsible for sensitization to stimulant drugs. It is known that repeated administration of low doses of ethanol sensitizes animals to its stimulant effect. In this work we investigated whether MK-801 alters the development of behavioral sensitization to ethanol.

METHODS

Groups of male Swiss mice were treated with saline or ethanol (2.0 g/kg) plus saline or MK-801 (0.25 mg/kg) for 21 days. On day 25, all animals received an ethanol challenge injection (2.0 g/kg). We measured locomotor activity on days 1, 7, 14, 21) and 25. In addition, we assessed the effects of different doses of MK-801 on the response to a low dose of ethanol (2.0 g/kg).

RESULTS

Ethanol-treated mice developed sensitization to the locomotor-stimulating effect of the drug, whereas those concomitantly receiving ethanol and MK-801 did not. All doses of MK-801 that were used stimulated the locomotor activity of both ethanol and saline-treated animals.

CONCLUSIONS

The findings support the hypothesis that N-methyl-D-aspartate receptors have an important role in the development of sensitization to drugs of abuse.

Conditioning to injection procedures and repeated testing increase SCH 23390-induced catalepsy in mice

The cataleptic behavior induced by the dopamine D1 antagonist SCH 23390 (SCH) has proven to be a useful assay for investigating the sensitivity of D1-like dopamine receptor-mediated effects during chronic drug administration. A fundamental flaw in most of these studies may be the involvement of the "repeated measures effect," a behavioral phenomenon well demonstrated for neuroleptic-induced catalepsy but not yet investigated for dopamine D1 antagonists. In this study, mice exposed for various sessions to the bar test presented a strong sensitization to the cataleptic behavior induced by repeated SCH treatment. Conversely, single tested animals exhibited a trend toward decreased catalepsy after repeated SCH treatment, which was in line with the development of a D1-like dopamine receptor supersensitivity suggested by an increase in SKF 38393-induced grooming behavior. Surprisingly, a challenge intraperitoneal saline injection increased the cataleptic behavior of single tested mice after long-term SCH treatment. This "injection-conditioned catalepsy" was also observed after repeated treatment with the dopamine D2 antagonists, haloperidol and metoclopramide. While these findings seem to explain some important contradictory data in the literature, they provide a new and simple animal model of the placebo effect.

Effects of buspirone on an animal model of tardive dyskinesia

1. The effects of buspirone were studied on an animal model of tardive dyskinesia, i.e., the quantification of orofacial dyskinesia in rats repeatedly treated with reserpine. 2. Rats were co-treated with saline [SAL] or buspirone [BUS] (3.0 mg/kg, i.p., twice daily) and vehicle [VEH] or reserpine [RES] (0.1 mg/kg, s.c., once every other day) for 19 days. On the day 20, the animals were observed for quantification of the behavioral parameters of orofacial dyskinesia: tongue protrusion and vacuous chewing movements frequencies and duration of twitching of the facial musculature. 3. Rats of the SAL + RES group exhibited a significant increase in the three behavioral parameters of orofacial dyskinesia relative to the rats of the SAL + VEH group. However, animals of the BUS + RES group showed only an increased frequency of vacuous chewing movements when compared to animals of the SAL + VEH group. In addition, the duration of the facial twitching was significantly decreased in the BUS + RES group in relation to rats of the SAL + RES group. There were no significant differences in the orofacial parameters between the BUS + VEH and the SAL + VEH groups. 4. Because it was also verified that chronic buspirone treatment was able to increase apomorphine-induced yawning behavior, the possibility is raised that buspirone attenuates reserpine-induced orofacial dyskinesia through the development of dopamine autoreceptor supersensitivity.

Naltrexone potentiates the anxiolytic effects of chlordiazepoxide in rats exposed to novel environments

RATIONALE

Both novelty and naloxone have been reported to modify the anxiolytic-like effect of benzodiazepines in the elevated plus maze. In addition, it has been largely demonstrated that novelty alters endogenous opioid activity.

OBJECTIVES

The present study was designed to examine a possible interaction between novelty and naltrexone effects on the behavior of chlordiazepoxide-treated rats in two animal models of anxiety.

METHODS

Thirty minutes after acute intraperitoneal treatment with saline or naltrexone and saline or chlordiazepoxide, male Wistar rats were exposed for the first time to the elevated plus maze apparatus or the social interaction arena for the quantification of the percentage of time spent in the open arms or the time of active social interaction, respectively. The effects of naltrexone and/or chlordiazepoxide on the plus maze and the social interaction tests were also evaluated after previous exposure to the respective apparatus.

RESULTS

Naltrexone dose dependently increased the percentage of time spent in the open arms of the elevated plus maze in chlordiazepoxide-treated (5 mg/kg i.p.) rats exposed for the first time to the apparatus. Similarly, naltrexone (5 mg/kg i.p.) increased the time spent in active social interaction by chlordiazepoxide-treated rats exposed to an unfamiliar arena. In both experiments, naltrexone had no effect when administered alone. When both the plus maze and the social interaction tests were conducted after previous exposure to the respective apparatus, naltrexone did not modify the behavior of chlordiazepoxide- or saline-treated rats.

CONCLUSIONS

These data suggest that the anxiolytic-like effects of chlordiazepoxide can be modified by opioid mechanisms in novel environments.

Bovine brain phosphatidylserine attenuates scopolamine-induced amnesia

The effects of bovine cerebral cortex phosphatidylserine (BCPS) on the memory impairment induced by scopolamine in mice tested in the plus-maze discriminative avoidance task were investigated. Swiss male mice received daily i.p. 50 mg/kg BCPS or 0.2 M Tris pH 7.4 (TRIS) for 5 days. Twenty-four hours after the last injection, the animals received 1 mg/kg scopolamine (BCPS-SCO and TRIS-SCO) or saline (BCPS-SAL and TRIS-SAL) i.p. After 20 min, the animals were submitted to discriminative avoidance conditioning. In the test, performed 24 h later, BCPS-SCO, BCPS-SAL, and TRIS-SAL (but not TRIS-SCO) mice spent significantly less time in the aversive enclosed arm of the discriminative avoidance apparatus when compared to the time spent in the nonaversive enclosed arm. The results suggest that BCPS attenuates scopolamine-induced amnesia in a discriminative avoidance task.

Effect of a submaxillary gland extract on Ehrlich tumor growth in mice

Ablation of host submaxillary glands modifies Ehrlich tumor growth and tumor-infiltrating leukocytes, possibly by modifications in the serum level of growth factors produced by this gland. To extend this research, 7-month-old male EPM-1 mice (N = 30) were divided into two groups: 1) inoculated with tumor cells previously incubated with submaxillary salivary gland extract (SGE) in PBS for 30 min at 37%; 2) inoculated with tumor cells previously incubated with PBS, under the same conditions. Animals were inoculated into the footpad with 40 microl of a suspension containing 4.5 x 10(7) tumor cells/ml, and footpad thickness was measured daily for 10 days. Sections and smears of tumor cells were prepared from the tumor mass to determine mitosis frequency, percent of tumor cells immunopositive to nerve (NGF) and epidermal (EGF) growth factors and percent of tumor-infiltrating leukocytes. The incubation of tumor cells with SGE produced a tumor reduction of about 30% in size (P<0.01). This effect was not related to loss of cell viability during incubation, but a 33% increase (P<0.05) in the percentage of dead or dying tumor cells and a 15% increase in the percent of NGF/EGF-positive tumor cells (P<0.01) were observed in vivo at the end of experiment. Tumor-infiltrating lymphocytes and mitosis frequency did not differ between groups. These data suggest a direct effect of factors present in SGE on tumor cells, which induce degeneration of tumor cells.

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

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

Haloperidol increases spreading and nitric oxide production in macrophages from tumor-bearing mice: a possible mechanism for its antitumoral effect

Subcutaneous treatment with haloperidol (2.0 mg/kg) was found to increase both the percent of macrophage spreading and nitric oxide (NO) release in peritoneal macrophage from animals inoculated intraperitoneally with 5.0 x 10(6) Ehrlich ascites cells. This haloperidol-induced macrophage activation seems to be involved in its antitumoral effect since cotreatment with the iNOS inhibitor aminoguanidine was able to reverse the inhibitory effect of haloperidol on the development of the Ehrlich solid carcinoma.

Ascorbic acid and alpha-tocopherol attenuate methylmalonic acid-induced convulsions

The effects of chronic administration of alpha-tocopherol or melatonin, or acute ascorbic acid administration on the convulsant action of methylmalonic acid (MMA) were investigated in adult male rats. Animals were chronically injected with alpha-tocopherol (40 mg kg(-1), i.p.), melatonin (5 mg kg(-1), i.p.) or vehicle for 7 days. Buffered MMA (6 micromol/2 microl) or NaCl (9 micromol/2 microl) was injected intrastriatally and the animals were observed for the appearance of clonic or tonic-clonic convulsions and rotational behavior. Ascorbic acid (100 mg kg(-1), s.c.) was administered 30 min before MMA injection. Alpha-tocopherol and ascorbic acid pretreatment decreased the duration of the convulsive episodes and the rotational behavior elicited by MMA. This study provides evidence that free radical generation may participate in the convulsant effects of methylmalonic acid.

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.

Kinetic analysis of GM1 effects on haloperidol-induced dopaminergic supersensitivity

The relative affinity of metoclopramide as indicated by K(B) values was calculated in control and in haloperidol-withdrawn rats treated or not with monosialoganglioside-1 (GM1) by using dose-response curves constructed for apomorphine-induced stereotyped behavior. Haloperidol withdrawal decreased K(B) data--that is, increased the D2-receptor affinity for metoclopramide. GM1 treatment per se did not modify K(B) values but, when given in combination with haloperidol, GM1 induced a decrease in K(B) values. No differences were found in K(B) data when GM1 was administered after withdrawal from haloperidol.

Ganglioside GM1 attenuates scopolamine-induced amnesia in rats and mice

Some experimental evidence suggests that the beneficial effects of monosialoganglioside GM1 on learning and memory could be related to an improving effect in central cholinergic function. The present study investigates the effects of GM1 on the memory impairment induced by scopolamine in rats or mice tested in passive (PA) and discriminative avoidance (DA) tasks, respectively. Wistar EPM-1 male rats and Swiss EPM-M1 male mice were treated daily IP with 50 mg/kg GM1 or saline for 7 or 14 days, respectively. Twenty-four hours after the last injection, GM1-treated animals received 1 mg/kg scopolamine (GM1-SCO) and saline-treated animals received 1 mg/kg scopolamine (SAL-SCO) or saline (SAL-SAL) IP. Twenty minutes later, the animals were submitted to PA or DA conditioning, and tests were performed 24 h later. The latency in entering the dark chamber of the PA apparatus (LD) presented by SAL-SCO rats was significantly decreased when compared to that presented by SAL-SAL animals. GM1-SCO animals showed an increased LD when compared to SAL-SCO animals and were not significantly different from SAL-SAL rats. GM1-SCO and SAL-SAL (but not SAL-SCO) mice spent significantly less time in the aversive enclosed arm of the discriminative avoidance apparatus when compared to the time spent in the non-aversive enclosed arm. The results are consistent with the interpretation that GM1 attenuates scopolamine-induced amnesia. Although not eliminating the participation of other transmitter systems, the present study indicates a possible role of central cholinergic transmission in the action of this compound on learning and memory.

Reserpine does not induce orofacial dyskinesia in spontaneously hypertensive rats

The nigrostriatal dopaminergic system seems to be involved in both reserpine-induced orofacial dyskinesia in normal rats and in the pathogenesis of hypertension in spontaneously hypertensive rats. In the present study, repeated reserpine administration (1.0 mg/kg, s.c., every other day, for 3 days) increased tongue protrusion and vacuous chewing frequencies as well as the duration of facial twitching in Wistar normotensive but not in spontaneously hypertensive rats. These results suggest that genetic hypertension and drug-induced orofacial movements may be inversely modulated by similar mechanisms in the nigrostriatal dopaminergic system.