Mice deficient for corticotropin-releasing hormone receptor-2 display anxiety-like behaviour and are hypersensitive to stress.

Corticotropin-releasing hormone (Crh) is a critical coordinator of the hypothalamic-pituitary-adrenal (HPA) axis. In response to stress, Crh released from the paraventricular nucleus (PVN) of the hypothalamus activates Crh receptors on anterior pituitary corticotropes, resulting in release of adrenocorticotropic hormone (Acth) into the bloodstream. Acth in turn activates Acth receptors in the adrenal cortex to increase synthesis and release of glucocorticoids. The receptors for Crh, Crhr1 and Crhr2, are found throughout the central nervous system and periphery. Crh has a higher affinity for Crhr1 than for Crhr2, and urocortin (Ucn), a Crh-related peptide, is thought to be the endogenous ligand for Crhr2 because it binds with almost 40-fold higher affinity than does Crh. Crhr1 and Crhr2 share approximately 71% amino acid sequence similarity and are distinct in their localization within the brain and peripheral tissues. We generated mice deficient for Crhr2 to determine the physiological role of this receptor. Crhr2-mutant mice are hypersensitive to stress and display increased anxiety-like behaviour. Mutant mice have normal basal feeding and weight gain, but decreased food intake following food deprivation. Intravenous Ucn produces no effect on mean arterial pressure in the mutant mice.

Corticotropin releasing factor receptor 1-deficient mice display decreased anxiety, impaired stress response, and aberrant neuroendocrine development.

Corticotropin releasing factor (CRF) is a major integrator of adaptive responses to stress. Two biochemically and pharmacologically distinct CRF receptor subtypes (CRFR1 and CRFR2) have been described. We have generated mice null for the CRFR1 gene to elucidate the specific developmental and physiological roles of CRF receptor mediated pathways. Behavioral analyses revealed that mice lacking CRFR1 displayed markedly reduced anxiety. Mutant mice also failed to exhibit the characteristic hormonal response to stress due to a disruption of the hypothalamic-pituitary-adrenal (HPA) axis. Homozygous mutant mice derived from crossing heterozygotes displayed low plasma corticosterone concentrations resulting from a marked agenesis of the zona fasciculata region of the adrenal gland. The offspring from homozygote crosses died within 48 hr after birth due to a pronounced lung dysplasia. The adrenal agenesis in mutant animals was attributed to insufficient adrenocorticotropic hormone (ACTH) production during the neonatal period and was rescued by ACTH replacement. These results suggest that CRFR1 plays an important role both in the development of a functional HPA axis and in mediating behavioral changes associated with anxiety.

Macrophage/microglial-mediated primary demyelination and motor disease induced by the central nervous system production of interleukin-3 in transgenic mice.

Activated macrophage/microglia may mediate tissue injury in a variety of CNS disorders. To examine this, transgenic mice were developed in which the expression of a macrophage/microglia activation cytokine, interleukin-3 (IL-3), was targeted to astrocytes using a murine glial fibrillary acidic protein fusion gene. Transgenic mice with low levels of IL-3 expression developed from 5 mo of age, a progressive motor disorder characterized at onset by impaired rota-rod performance. In symptomatic transgenic mice, multi-focal, plaque-like white matter lesions were present in cerebellum and brain stem. Lesions showed extensive primary demyelination and remyelination in association with the accumulation of large numbers of proliferating and activated foamy macrophage/microglial cells. Many of these cells also contained intracisternal crystalline pole-like inclusions similar to those seen in human patients with multiple sclerosis. Mast cells were also identified while lymphocytes were rarely, if at all present. Thus, chronic CNS production of low levels of IL-3 promotes the recruitment, proliferation and activation of macrophage/microglial cells in white matter regions with consequent primary demyelination and motor disease. This transgenic model exhibits many of the features of human inflammatory demyelinating diseases including multiple sclerosis and HIV leukoencephalopathy.

Dissociation of locomotor activation and suppression of food intake induced by CRF in CRFR1-deficient mice.

Corticotropin-releasing factor (CRF) systems are involved in locomotor and feeding behaviors. Two distinct CRF receptor subtypes, CRFR1 and CRFR2, are thought to mediate CRF actions in the central nervous system. However, the role for each receptor in locomotor activity and feeding remains to be determined. Using CRFR1 null mutant mice, the present study examined the functional significance of this receptor in ambulation and feeding. CRF treatment of wild-type mice resulted in increased levels of locomotion whereas no change was observed in CRFR1-deficient mice as compared to vehicle-treated mutant mice. In contrast, CRF decreased food-water intake in both wild type and CRFR1-deficient mice equally. These results support an important role for CRFR1 in mediating CRF-induced locomotor activation, whereas other receptor subtypes, likely CRFR2, may mediate the appetite-suppressing effects of CRF-like peptides.

Anxiogenic-like effects limit rewarding effects of cocaine in balb/cbyj mice.

Previous studies have reported intravenous cocaine self-administration behavior in several strains of mice with the exception of BALB/cByJ, a strain considered a mouse model of high emotional reactivity. The present experiments further investigated acquisition of self-administration in BALB/cByJ mice using a low dose and a habituation session. Following evidence of an initial drug-seeking behavior, we observed a progressive decline of intravenous self-administration. Pretreatment with diazepam (0.5 mg/kg, IP), reinstated cocaine-maintained responding. To test the hypothesis that injections directly into a reward-relevant brain region might support consistent cocaine-seeking behavior, BALB/cByJ mice implanted in the nucleus accumbens (NAc) or the caudate-putamen nucleus (CPu) were trained to discriminate between the arm enabling a microinjection of cocaine (30 pmol/50 nl or 150 pmol/50 nl) and the neutral arm of a Y-maze. Only NAc subjects exhibited a spatial discrimination toward the cocaine-reinforced arm and the D2 antagonist, sulpiride (50 mg/kg, IP) eliminated intra-NAc cocaine self-administration. However, after several days of cocaine self-injection, animals developed an approach/avoidance-like behavior between the start box and the reinforced arm. This behavior was suppressed by systemic diazepam (1 mg/kg, IP) pretreatment. We conclude that: (1) medio-ventral NAc is involved both in the rewarding (via a D2 dopaminergic mechanism) and aversive effects of cocaine in mice; and (2) anxiolytic pretreatment (diazepam) indirectly enhanced the reinforcing properties of cocaine in BALB/cByJ, suggesting that emotionality can act as a protective mechanism against stimulant abuse.

Functional consequences of repeated (+/-)3,4-methylenedioxymethamphetamine (MDMA) treatment in rhesus monkeys.

Six rhesus monkeys were trained to stable performance on neuropsychological tests of memory, reinforcer efficacy, reaction time and bimanual motor coordination. Three monkeys were then exposed to a high-dose, short course regimen of (+/-)3,4-Methylenedioxymethamphetamine (MDMA, "Ecstasy") (4 days, 10 mg/kg i.m., b.i.d.). Following treatment, concentrations of 5-hydroxyindoleacetic acid (5-HIAA) in cerebrospinal fluid (CSF) were reduced by approximately 50% in the treated animals, and this effect persisted for approximately three months post-MDMA. Behavioral performance was disrupted during acute MDMA treatment but returned to baseline within one week following treatment. MDMA also produced persistent alterations in late peak latencies of brainstem auditory evoked potentials (BSAEP), lasting three months post-MDMA. Both CSF 5-HIAA concentrations and evoked potential latencies were normalized four months after treatment. These findings indicate that serotonergic alterations associated with MDMA use may result in persisting changes in brain function.

Learning impairment in transgenic mice with central overexpression of corticotropin-releasing factor.

The present studies were designed to test the learning and memory capacities of transgenic mice with central overexpression of corticotropin-releasing factor in a forced alternation water T-maze task and in the Morris water maze. In T-maze testing, littermate control mice reached a criterion of 70% correct responses after five days of trials, while the performance of transgenic subjects was still random after the same training. In Morris maze testing, control subjects reached the submerged platform significantly faster (F(1.48) = 4.51, P < 0.05) after three days of trials, while the performance of transgenic mice was unimproved over the same period. The deficit in Morris maze performance in transgenic mice was reversed when the platform was visible above the surface of the water. Pre-test administration of the benzodiazepine anxiolytic, chlordiazepoxide (10 mg/kg), before acquisition training also produced a significant (F(4.40) = 16.61, P < 0.001) and persistent improvement in Morris maze performance in transgenic mice when compared to vehicle-treated transgenic litter mates. Finally, there was no evidence of hippocampal cell loss in transgenic brains. The results suggest that corticotropin-releasing factor-overexpressing mice exhibit a profound learning deficit without sensory or motor-related impairments, and that memory plasticity can be restored by anxiolytic pre-treatment. Thus, constitutive overabundance of brain corticotropin-releasing factor may produce hyperemotionality that interferes with learned behaviors. Stress-related disorders characterized by co-morbid deficits in learning/memory may benefit from pharmacological normalization of brain corticotropin-releasing factor systems.

Complications associated with thoracocentesis.

In order to determine the spectrum and frequency of complications associated with thoracocentesis, we decided to audit prospectively all thoracocentesis performed in the medical service at our institution. Over a ten-month interval, 125 procedures were performed. We identified 114 (91 percent) prospectively, 11 retrospectively by a computer-assisted review of discharge summaries. Forty-six percent of the procedures were complicated by at least one adverse occurrence. Complications considered major occurred in 14 percent, minor in 33 percent. The major complications included 14 pneumothoraces (three required tube thoracostomies and one percutaneous aspiration), one splenic laceration, one sheared-off catheter, and one pneumohemothorax. The minor complications included pain in 28, persistent cough in 14, dry taps in 16, and subcutaneous fluid collections in four patients. We conclude that thoracocentesis can carry the risk of frequent morbidity even when a lecture and printed guidelines on performing thoracocentesis have been given and experienced individuals are in attendance during the performance of the procedure. Our study suggests a portion of this morbidity may be from poor technique, inability to adequately identify landmarks, and improper utilization of a needle-catheter apparatus. Suggestions for correction of these problems are made.

The role of mesolimbic dopamine in conditioned locomotion produced by amphetamine.

Daily administration of psychomotor stimulants in a distinctive environment can impart on the environment stimulantlike properties. Rats injected with amphetamine (0.75 mg/kg, sc) daily for 5 days exhibited a robust unconditioned locomotor response, measured in photocell cages, and showed a conditioned locomotor response when treated with saline on the 6th day. This conditioned locomotor response was found to be significantly attenuated by 6-hydroxydopamine (6-OHDA) lesions of the nucleus accumbens when the lesion was made either pre- or postconditioning. Similarly, although rats with 6-OHDA lesions of the nucleus accumbens exhibited a robust supersensitive unconditioned locomotor hyperactivity in response to apomorphine (0.1 mg/kg, sc), they did not show a conditioned response on the test day. These results suggest that the mesolimbic dopamine system may be responsible for both the unconditioned and conditioned locomotor responses to psychomotor stimulant drugs. Further, conditioned locomotion depends on a critical interaction between the physiological release of presynaptic dopamine and occupation of postsynaptic receptors.

Strain distribution of mice in discriminated Y-maze avoidance learning: genetic and procedural differences.

The current study was conducted to characterize discriminated avoidance learning in mice by using a Y-maze task. In Experiment 1, the task parameters were manipulated, including the amount of time spent in the start arm, the amount of time to make the avoidance response, and the intertrial interval (ITI) using C57 x SJL F1 hybrid mice. Avoidance performance was significantly improved with longer times to avoid the shock and longer ITIs. In Experiment 2, mice from 4 inbred strains (BALB/cByJ, DBA/2J, C57BL/6J, and SJL/J), an F1 hybrid (C57 x SJL), and 1 outbred strain (CD1) were tested with various ITIs. Strain differences were observed in avoidance learning, with BALB, DBA, C57 x SJL and CD1 mice showing significantly better avoidance learning than C57 mice, which were better than SJL mice. These data demonstrate that Y-maze performance is significantly influenced by the genetic background of the mouse and the parameters of the task.

MDMA produces stimulant-like conditioned locomotor activity.

Daily administration of a drug in a distinctive environment establishes contingencies that support Pavlovian conditioning. Environmental cues that are paired with the drug injection and that predict the onset of drug action can become conditioned stimuli. Ultimately, the conditioned stimuli come to predict the availability of drug and develop the potential to engender conditioned drug responses. Various psychostimulant drugs can produce conditioned locomotion when tested in the presence of environmental cues that were repeatedly associated with the drug experience. The ability of amphetamine and cocaine to produce conditioned locomotion was demonstrated in the present study. Stimulant-like properties of methylenedioxy-methamphetamine (MDMA) have been reported in locomotor paradigms, drug discrimination procedures, and human subjective questionnaires. MDMA (5 mg/kg), paired for 5 days to a distinct environment signalled by the presence of a distinct odor, produced enhanced locomotion during a test probe with the odor alone indicating that MDMA can also produce conditioned locomotion. The observation that the stimulus properties of MDMA can also become associated with environmental cues supports the hypothesis that some of the behavioral effects of MDMA resemble those of other classical psychostimulants such as amphetamine and cocaine.

Effects of buspirone and gepirone on i.v. cocaine self-administration in rhesus monkeys.

Buspirone and gepirone were evaluated as potential pharmacotherapies for cocaine abuse by studying the effects of acute and repeated treatment on IV cocaine self-administration in rhesus monkeys. Chlorpromazine was also evaluated as a positive control. Effects of IV drug pretreatments were tested during daily 60-min sessions with lever-pressing reinforced under a fixed-ratio 10 schedule of 0.02 or 0.05 mg/kg cocaine infusions. Acute pretreatment with buspirone (0.1 and 0.3 mg/kg, IV) increased rates of cocaine self-administration without disrupting food pellet consumption. Some doses of buspirone also produced changes in rates of cocaine self-administration without altering the within-session pattern of responding. In contrast, acute doses of gepirone had little effect on rates of cocaine self-administration, while disruptions in food consumption and changes in the within-session pattern of cocaine self-administration were obtained at the highest dose of gepirone tested (1.0 mg/kg). When either buspirone (0.1 and 0.3 mg/kg, IV) or gepirone (0.1 mg/kg, IV) were administered daily for 10 days, consistent effects on cocaine self-administration were not observed. Thus, the effects of acute buspirone administration on cocaine-maintained behavior were similar to the effects produced by chlorpromazine and other dopaminergic antagonists, whereas, gepirone was ineffective. These results provide some support for further evaluation of buspirone as a potential pharmacotherapy for cocaine abuse, although its lack of efficacy with repeated treatment is not encouraging. The negative results with gepirone provide less rationale for continued investigations with this drug, possibly because of its lesser involvement than buspirone with dopaminergic neurotransmission.

d-Amphetamine in squirrel monkeys of different social status: effects on social and agonistic behavior, locomotion, and stereotypies.

The influences of social status on amphetamine-induced behavioral effects in squirrel monkeys were investigated. Social status was determined by constructing a sociogram. d-Amphetamine (0.3--1.0 mg/kg orally, 0.3 and 0.6 mg/kg IM) increased stereotyped head movements and reduced the time spent in the sitting posture in all monkeys (N = 25) regardless of sex, age, or social status. The high levels of locomotor activity in dominant and juvenile monkeys were decreased at higher amphetamine doses (0.6 mg/kg IM, 0.6 and 1.0 mg/kg orally), whereas the same doses increased locomotion in otherwise less active subdominant and submissive animals. Low doses of amphetamine (0.1, 0.3 mg/kg) decreased the incidence of agonistic behavior initiated by dominant monkeys, and higher doses (0.6, 1.0 mg/kg) caused these monkeys to change from predominant initiators of agonistic behavior into recipients. At 2 h after amphetamine administration (0.3 mg/kg IM), the high levels of locomotor behavior had returned to baseline, the social isolation began to disappear, and the disrupted agonistic behavior of dominant monkeys returned to control levels, yet the stereotyped head movements continued to occur with high frequency. In half of the monkeys, amphetamine produced a large increase in distress-like vocalizations. Amphetamine-mediated motor stereotypies may be mediated by mechanisms different than those responsible for agonistic behavior. The selective changes in agonistic behavior by dominant monkeys when challenged with amphetamine may reflect a status-related functional alteration of catecholaminergic processes upon which the drug acts.

The effects of dopaminergic agents on reaction time in rhesus monkeys.

Many CNS pathologies, including Parkinson's, Alzheimer's and Huntington's diseases, as well as AIDS dementia complex, involve some degree of movement dysfunction. Reaction time (RT) performance has been shown to be a sensitive measure of motor function for these disorders. Useful models of RT performance exist in a variety of species, but few are performed in the same manner as with humans. To facilitate species comparisons, the present RT task was developed from a human RT task. Dopaminergic drugs were then used to characterize the sensitivity of the model to CNS changes and to investigate their effects on RT performance in intact rhesus monkeys. With cumulative dosing, the selective dopamine receptor antagonists (D1) SCH 39166 and (D2) raclopride produced dose-dependent slowing of RT performance. Results following bolus administration of these drugs were consistent with the cumulative dosing procedure, although of smaller magnitude and higher variability. Amphetamine had no significant effect on group RT performance with either dosing scheme, but RT performance in individual monkeys was either speeded or slowed by d-amphetamine. The present results suggest that blockade of either D1-like or D2-like dopamine receptors can slow RT performance in rhesus monkeys and that this paradigm may be useful to study movement dysfunction in non-human primates.

Evaluation of the cocaine-like discriminative stimulus effects and reinforcing effects of modafinil.

Modafinil [(diphenyl-methyl)sulphinyl-2-acetamide] is a novel psychostimulant drug which is effective in the treatment of narcolepsy and idiopathic hypersomnia. It also has neuroprotective effects in animal models of striatal neuropathology. Although the cellular mechanisms of action of modafinil are poorly understood, it has been shown to have a profile of pharmacological effects that differs considerably from that of amphetamine-like stimulants. There is some evidence that modafinil has central alpha 1-adrenergic agonist effects. In the present study modafinil was evaluated for cocaine-like discriminative stimulus effects in rats and for reinforcing effects in rhesus monkeys maintained on intravenous cocaine self-administration. Modafinil, l-ephedrine and d-amphetamine all produced dose dependent increases in cocaine-lever responding, with maximal levels of 67%, 82% and 100%, respectively. Modafinil produced full substitution in four out of the six rats tested while the highest levels of substitution were associated with substantial response rate decreasing effects. Little evidence was obtained that the discriminative stimulus effects of modafinil were produced by alpha 1-adrenergic activation, based upon results of tests performed in combination with prazosin. In the self-administration procedure, modafinil and l-ephedrine functioned as reinforcers in rhesus monkeys. The reinforcing and discriminative stimulus effects of modafinil-required very high doses: modafinil was over 200 times less potent than d-amphetamine and was also less potent than l-ephedrine. These results show that modafinil has some cocaine-like discriminative stimulus effects and, like other abused stimulants, can serve as a reinforcer at high doses.

A role for the mesolimbic dopamine system in the psychostimulant actions of MDMA.

Methylenedioxymethamphetamine (MDMA) is a phenylethylamine with a chemical structure that resembles both the amphetamines and mescaline and has both stimulant and perception altering properties. The stimulant properties of MDMA were assessed in photocell cages designed to measure locomotor activity in rats. MDMA, over a range of doses (2.5-10.0 mg/kg, SC) produced locomotor hyperactivity which lasted up to 4 h. Further studies examined the role of the mesolimbic dopamine system in the hyperactivity induced by MDMA. 6-Hydroxydopamine lesions of the Nucleus accumbens attenuated the locomotor response produced by MDMA. The well characterized attenuation of the locomotor response produced by amphetamine was also demonstrated in the same rats. The present study demonstrates similarities in the stimulant properties of MDMA and amphetamine, and also suggests that as with amphetamine, the locomotor activation associated with MDMA may involve the presynaptic release of dopamine in the region of the Nucleus accumbens. However, MDMA may have a more unusual pharmacological profile because of its longer duration of action, neurotoxic potential, and differences in the qualitative aspects of its psychoactive effects.

Evidence for separate neuronal mechanisms for the discriminative stimulus and catalepsy induced by delta 9-THC in the rat.

The cataleptogenic effect of delta 9-THC was compared to its discriminative stimulus effects in rats. The ED50s for the discriminative stimulus and catalepsy were 0.8 and 4.0 mg/kg, respectively, while their time courses were very similar. The ED50 of delta 9-THC for catalepsy in experimentally naive rats was not different from that in rats trained with the drug discrimination procedure, indicating that the cataleptogenic effect was not appreciably attenuated by long-term exposure to low doses of delta 9-THC. Pharmacologically, the catalepsy produced by delta 9-THC more closely resembled that of haloperidol than of morphine, since anticholinergic pretreatment eliminated the delta 9-THC-induced catalepsy while pre-treatment with naloxone had no effect. Although the cataleptogenic effect of delta 9-THC could be pharmacologically manipulated by anticholinergic pre-treatment, its discriminative stimulus effects were not changed in the same animals. These results demonstrate that distinctive mechanisms of action exist for these cannabinoid-induced behaviors.

The acoustic startle response as a measure of behavioral dependence in rats.

A series of experiments was conducted to assess the sensitivity of the acoustic startle response to chronic morphine administration and naloxone-precipitated withdrawal. Rats were implanted with two subcutaneous pellets containing either 75 mg each of morphine or containing only placebo. In experiment 1, withdrawal induced by 0.05-0.2 mg/kg naloxone dose-dependently decreased the magnitude of the startle response. Physical dependence was confirmed by a naloxone-induced acute weight loss seen in morphine-implanted rats, but naloxone had no effect on startle or body weight in non-dependent animals. In experiment 2, a modified procedure with fewer trials per session and fewer test days was employed. Naloxone (0.2 mg/kg) given 4-5 days after implantation induced large startle-response decreases in morphine-dependent rats while having no effect in placebo-implanted rats. Post-naloxone saline tests revealed no significant differences in startle between morphine and placebo groups. Startle scores were significantly higher in morphine-implanted rats than in placebo rats during a saline test given 3 days following pellet implantation. In a separate group of animals, however, acute IP injections of morphine from 0.3-10 mg/kg had no significant effect on startle amplitude. The effect of repeated pairings of withdrawal with the startle environment was assessed in experiment 3. Morphine-dependent rats startled significantly less if naloxone injections were given before the startle session than if they were administered 4 h later. Conditioned withdrawal effects, expressed during a final test session when all rats received saline, were observed for the body-weight measure but not for the startle response.(ABSTRACT TRUNCATED AT 250 WORDS)

Animal models of drug craving.

Drug craving, the desire to experience the effect(s) of a previously experienced psychoactive substance, has been hypothesized to contribute significantly to continued drug use and relapse after a period of abstinence in humans. In more theoretical terms, drug craving can be conceptualized within the framework of incentive motivational theories of behavior and be defined as the incentive motivation to self-administer a psychoactive substance. The incentive-motivational value of drugs is hypothesized to be determined by a continuous interaction between the hedonic rewarding properties of drugs (incentive) and the motivational state of the organism (organismic state). In drug-dependent individuals, the incentive-motivational value of drugs (i.e., drug craving) is greater compared to non-drug-dependent individuals due to the motivational state (i.e., withdrawal) developed with repeated drug administration. In this conceptual framework, animal models of drug craving would reflect two aspects of the incentive motivation to self-administer a psychoactive substance. One aspect would be the unconditioned incentive (reinforcing) value of the drug itself. The other aspect would be relatively independent of the direct (unconditioned) incentive value of the drug itself and could be reflected in the ability of previously neutral stimuli to acquire conditioned incentive properties that could elicit drug-seeking and drug-taking behavior. Animal models of drug craving that permit the investigation of the behavioral and neurobiological components of these two aspects of drug craving are reviewed and evaluated. The models reviewed are the progressive ratio, choice, extinction, conditioned reinforcement and second-order schedule paradigms. These animal models are evaluated according to two criteria that are established herein as necessary and sufficient criteria for the evaluation of animal models of human psychopathology: reliability and predictive validity. The development of animal models of drug craving will have heuristic value and allow a systematic investigation of the neurobiological mechanisms of craving.

Amphetamine derivatives induce locomotor hyperactivity by acting as indirect serotonin agonists.

Derivatives of amphetamine are potent releasers of both dopamine (DA) and serotonin (5-HT), but the relative contributions of DA and 5-HT release to the behavioral effects of these drugs have not been established. Previously, S-(+)3,4-methylenedioxymethamphetamine (S-(+)MDMA) was found to produce locomotor hyperactivity in rats which was dependent on 5-HT release. The present study found that MBDB (1.25, 2.5, 5.0 or 10.0 mg/kg), the alpha-ethyl derivative of MDMA that produces little or no direct DA release, also induced locomotor hyperactivity that lasted for greater than 60 min after the 5.0 and 10.0 mg/kg doses. MBDB produced spatial patterns of locomotor hyperactivity and suppression of exploratory activity (holepokes and rearings) very similar to the behavioral syndrome produced by MDMA. MBDB-induced hyperactivity was blocked by pretreatment with the selective 5-HT uptake inhibitor fluoxetine (2.5 or 10 mg/kg), suggesting that MBDB produced behavioral effects via uptake-carrier mediated release of 5-HT. Similarly, fluoxetine pretreatment blocked the locomotor hyperactivity produced by S-(+)3,4-methylenedioxyamphetamine (3.0 mg/kg) or p-chloroamphetamine (2.5 mg/kg), supporting a serotonergic basis for the action of these drugs. Tissue levels of 5-HT and its metabolite 5-HIAA were decreased 40 min after administration of S-(+)MDMA (3.0 mg/kg) or MBDB (5.0 mg/kg), and these decreases were prevented by fluoxetine pretreatment. S-(+)MDMA also produced a fluoxetine-sensitive increase of tissue DA levels, suggesting that 5-HT release may indirectly result in increased DA release, although MBDB did not significantly increase DA levels.(ABSTRACT TRUNCATED AT 250 WORDS)