Effect of +-methamphetamine on path integration learning, novel object recognition, and neurotoxicity in rats

(+)-Methamphetamine-induced monoamine reductions and impaired egocentric learning in adrenalectomized rats is independent of hyperthermia

Methamphetamine (MA) is widely abused and implicated in residual cognitive deficits. In rats, increases in plasma corticosterone and egocentric learning deficits are observed after a 1-day binge regimen of MA (10 mg/kg x 4 at 2-h intervals). The purpose of this experiment was to determine if adrenal inactivation during and following MA exposure would attenuate the egocentric learning deficits in the Cincinnati water maze (CWM). In the first experiment, the effects of adrenalectomy (ADX) or sham surgery (SHAM) on MA-induced neurotoxicity at 72 h were determined. SHAM-MA animals showed typical patterns of hyperthermia, whereas ADX-MA animals were normothermic. Both SHAM-MA- and ADX-MA-treated animals showed increased neostriatal glial fibrillary acidic protein and decreased monoamines in the neostriatum, hippocampus, and entorhinal cortex. In the second experiment, SHAM-MA- and ADX-MA-treated groups showed equivalently impaired CWM performance 2 weeks post-treatment (increased latencies, errors, and start returns) compared to SHAM-saline (SAL) and ADX-SAL groups with no effects on novel object recognition, elevated zero maze, or acoustic startle/prepulse inhibition. Post-testing, monoamine levels remained decreased in both MA-treated groups in all three brain regions, but were not as large as those observed at 72-h post-treatment. The data demonstrate that MA-induced learning deficits can be dissociated from drug-induced increases in plasma corticosterone or hyperthermia, but co-occur with dopamine and serotonin reductions.

Comparative neuroscience of stimulant-induced memory dysfunction: role for neurogenesis in the adult hippocampus

The discovery that the addictive drugs impair neurogenesis in the adult hippocampus has prompted the elaboration of new biological hypotheses to explain addiction and drug-induced cognitive dysfunction. Considerable evidence now implicates the process of adult neurogenesis in at least some critical components of hippocampal-dependent memory function. In experimental models, psychomotor stimulant drugs produce alterations in the rate of birth, survival, maturation and functional integration of adult-born hippocampal neurons. Thus some of the deleterious consequences of drug abuse on memory could result from the neurotoxic actions of drugs on adult hippocampal neurogenesis. In this review, we will first summarize preclinical and clinical literature on the disruptive effects of drugs such as cocaine and ecstasy in the areas of learning, memory and attention. We will also summarize data that document the widespread effects of stimulant drugs on progenitor activity and precursor incorporation in the adult dentate gyrus. Finally, we will examine evidence that supports the involvement of hippocampal neurogenesis in specific aspects of learning and memory function and we will consider critically the hypothesis that some of the negative consequences of drug abuse on cognition might be ascribed to deficits in adult hippocampal neurogenesis. Evidence suggests that stimulant abuse impacts negatively on at least four areas of memory/cognitive function that may be influenced by adult hippocampal neurogenesis: contextual memory, spatial memory, working memory and cognitive flexibility.

Comparison of (+)-methamphetamine, ±-methylenedioxymethamphetamine, (+)-amphetamine and ±-fenfluramine in rats on egocentric learning in the Cincinnati water maze

(+)-Methamphetamine (MA), (±)-3,4-methylenedioxymethamphetamine (MDMA), (+)-amphetamine (AMPH), and (±)-fenfluramine (FEN) are phenylethylamines with CNS effects. At higher doses, each induces protracted reductions in brain dopamine (DA) and/or serotonin. Chronic MA and MDMA users show persistent monoamine reductions and cognitive impairments. In rats, similar neurochemical effects can be induced, yet cognitive impairments have been difficult to demonstrate. We recently showed that rats treated on a single day with MA (10 mg/kg x 4 at 2 h intervals) exhibit impaired egocentric learning (Cincinnati water maze [CWM]) without affecting spatial learning (Morris water maze [MWM]) (Herring et al., [2008] Psychopharmacology (Berl) 199:637–650). Whether this effect is unique to MA or is a general characteristic of these drugs is unknown. Accordingly, this experiment compared these drugs on CWM performance. Drugs were given s.c. in four doses at 2 h intervals. MA doses were 10 or 12.5 mg/kg/dose, AMPH 25 mg/kg/dose (to match MA12.5-induced hyperthermia), MDMA 15 mg/kg/dose (previously established hyperthermia-inducing dose), and FEN 16.5 mg/kg/dose (equimolar to MA12.5). Two weeks later, rats were tested in the CWM (2 trials/day, 21 days). AMPH and MA (both doses) induced significant increases in CWM errors and latency to reach the goal with no differences in swim speed. MDMA and FEN did not significantly alter learning. Given that FEN selectively and MDMA preferentially affect serotonin whereas AMPH selectively and MA preferentially affect DA, the data suggest that egocentric learning may be predominantly dopaminergically mediated.

A neurotoxic regimen of methamphetamine impairs novelty recognition as measured by a social odor-based task

Repeated administration of methamphetamine (mAMPH) to rodents in a single-day "binge" regimen damages forebrain monoaminergic nerve terminals and produces subsequent cognitive deficits. Here we investigate performance on a social odor-based task, demonstrating enduring mAMPH-induced deficits in recognition memory. Three weeks after a neurotoxic mAMPH regimen, singly-housed male Long-Evans rats had four wooden beads placed in their home cage: three beads containing odors from their home cage (HC beads) and one bead from a cage of a rat not present in the colony room (N1 bead). Exploration times for each bead were recorded during three 1-min habituation trials separated by 1-min intertrial intervals. Twenty-four hours later, a 1-min memory test was conducted, in which animals were presented with two HC beads, one N1 bead, and one bead from another novel animal (N2). Saline- and mAMPH-treated rats showed similar, progressive decreases in exploration time for the N1 bead during the habituation trials, indicating equivalent short-term olfactory habituation to the novel odor. By contrast, during the subsequent memory test, saline-treated rats showed a strong preference for the N2 bead over the N1 bead while mAMPH-treated rats showed no preference. The use of the rats' primary sensory modality (olfaction) coupled with the social significance (from conspecifics) of the odors produces strong, long-lasting memories. Our results show that prior treatment with a neurotoxic regimen of mAMPH impairs long-term memory for the previously experienced odors. As compared with previously employed object recognition tasks, this test may be advantageous for investigating mAMPH-induced memory impairments in rodents.

Autoradiographic study of serotonin transporter during memory formation

Serotonin transporter (SERT) has been associated with drugs of abuse like d-methamphetamine (METH). METH is well known to produce effects on the monoamine systems but it is unclear how METH affects SERT and memory. Here the effects of METH and the serotonin reuptake inhibitor fluoxetine (FLX) on autoshaping and novel object recognition (NOR) were investigated. Notably, both memory tasks recruit different behavioral, neural and cognitive demand. In autoshaping task a dose-response curve for METH was determined. METH (1.0mg/kg) impaired short-term memory (STM; lasting less of 90min) in NOR and impaired both STM and long-term memory (LTM; lasting 24 and 48h) in autoshaping, indicating that METH had long-lasting effects in the latter task. A comparative autoradiography study of the relationship between the binding pattern of SERT in autoshaping new untrained vs. trained treated (METH, FLX, or both) animals was made. Considering that hemispheric dominance is important for LTM, hence right vs. left hemisphere of the brain was compared. Results showed that trained animals decreased cortical SERT binding relative to untrained ones. In untrained and trained treated animals with the amnesic dose (1.0mg/kg) of METH SERT binding in several areas including hippocampus and cortex decreased, more remarkably in the trained animals. In contrast, FLX improved memory, increased SERT binding, prevented the METH amnesic effect and re-established the SERT binding. In general, memory and amnesia seemed to make SERT more vulnerable to drugs effects.

Effect of a neurotoxic dose regimen of (+)-methamphetamine on behavior, plasma corticosterone, and brain monoamines in adult C57BL/6 mice

RATIONALE

In rats, neurotoxic doses of methamphetamine (MA) induce astrogliosis, long lasting monoamine reductions, reuptake transporter down-regulation, and learning impairments.

OBJECTIVE

We tested whether comparable effects occur in C57BL/6 mice.

METHOD

C57BL/6 mice were treated with 10mg/kgs.c.x4 MA on a single day and evaluated at various intervals thereafter.

RESULTS

The neurotoxic dose regimen of MA caused the predicted acute hyperthermia and increased striatal glial fibrillary acidic protein and reduced neostriatal dopamine. The MA-treated mice were hypoactive 24h later but not 48h later. MA-treated mice also showed exaggerated initial hyperactivity after a pharmacological dose of MA used to stimulate locomotion followed by a later phase of hypoactivity compared to saline-treated mice. No differences were observed on learning or memory tests (novel object recognition, egocentric, or spatial learning/memory). MA-treated mice showed a trend toward increased prepulse inhibition but not baseline acoustic startle reactivity. After testing, MA-treated mice showed reduced neostriatal dopamine and increased basal plasma corticosterone.

CONCLUSIONS

A neurotoxic/binge regimen of MA in mice that produces the typical pattern of neurotoxic changes to those seen in rats, results in few behavioral changes. This may limit the utility of C57BL/6 mice for modeling the cognitive and behavioral effects described in human MA users who show such changes even after prolonged abstinence.

Reversal-specific learning impairments after a binge regimen of methamphetamine in rats: possible involvement of striatal dopamine

A growing body of evidence indicates that protracted use of methamphetamine (mAMPH) causes long-term impairments in cognitive function in humans. Aside from the widely reported problems with attention, mAMPH users exhibit learning and memory deficits, particularly on tasks requiring response control. Although binge mAMPH administration to animals results in cognitive deficits, few studies have attempted to test behavioral flexibility in animals after mAMPH exposure. The aim of this study was to evaluate whether mAMPH would produce impairments in two tasks assessing flexible responding in rats: a touchscreen-based discrimination-reversal learning task and an attentional set shift task (ASST) based on a hallmark test of executive function in humans, the Wisconsin Card Sort. We treated male Long-Evans rats with a regimen of four injections of 2 mg/kg mAMPH (or vehicle) within a single day, a dosing regimen shown earlier to produce object recognition impairments. We then tested them on (1) reversal learning after pretreatment discrimination learning or (2) the ASST. Early reversal learning accuracy was impaired in mAMPH-treated rats. MAMPH pretreatment also selectively impaired reversal performance during ASST testing, leaving set-shifting performance intact. Postmortem analysis of [(125)I]RTI-55 binding revealed small (10-20%) but significant reductions in striatal dopamine transporters produced by this mAMPH regimen. Together, these results lend new information to the growing field documenting impaired cognition after mAMPH exposure, and constitute a rat model of the widely reported decision-making deficits resulting from mAMPH abuse seen in humans.

Methamphetamine self-administration and the effect of contingency on monoamine and metabolite tissue levels in the rat

A number of studies have shown that exposure to high doses of methamphetamine (MA) is toxic to central dopamine (DA) and serotonin (5-HT) neurons. In most of those studies, however, high doses of MA were experimenter-administered during a short exposure time. Because contingency is a determinant for many effects of drug exposure, the present objective was to investigate the effects of self-administered MA on tissue monoamine levels following a short (24 hours) or longer (7 days) withdrawal period. As previously reported, a noncontingent "binge" high-dose treatment regimen (4 injections of 10 mg/kg MA administered every 2 hours) produced persistent depletion of cortical 5-HT and striatal DA. Effects of self-administered MA (0.1 mg/kg/infusion) were then determined following a 20-day duration where a yoked design was employed such that some rats received MA contingent on an operant lever press and others received either MA or saline dependent on the responses of the contingent rat. Self-administered MA produced a transient striatal DA depletion with a more persistent increase in DA turnover, indicating the presence of some lasting adaptations. Furthermore, the yoked design revealed that there was no effect of contingency on these parameters.

Methamphetamine treatment causes delayed decrease in novelty-induced locomotor activity in mice

Methamphetamine (METH) is a psychostimulant that causes damage to dopamine (DA) axons and to non-monoaminergic neurons in the brain. The aim of the present study was to investigate short- and long-term effects of neurotoxic METH treatment on novelty-induced locomotor activity in mice. Male BALB/c mice, 12-14 weeks old, were injected with saline or METH (i.p., 7.5 mg/kg x 4 times, every 2 h). Behavior and neurotoxic effects were assessed at 10 days, 3 and 5 months following drug treatment. METH administration caused marked decreases in DA levels in the mouse striatum and cortex at 10 days post-drug. However, METH did not induce any changes in novelty-induced locomotor activity. At 3 and 5 months after treatment METH-exposed mice showed significant recovery of DA levels in the striatum and cortex. In contrast, these animals demonstrated significant decreases in locomotor activity at 5 months in comparison to aged-matched control mice. Further assessment of METH toxicity using TUNEL staining showed that the drug induced increased cell death in the striatum and cortex at 3 days after administration. Taken together, these data suggest that delayed deficits in novelty-induced locomotor activity observed in METH-exposed animals are not due to neurodegeneration of DA terminals but to combined effects of METH and age-dependent dysfunction of non-DA intrinsic striatal and/or corticostriatal neurons.

Comparison of the developmental effects of 5-methoxy-N,N-diisopropyltryptamine (Foxy) to (+/-)-3,4-methylenedioxymethamphetamine (ecstasy) in rats

RATIONALE

We have previously shown that (+/-)-3,4-methylenedioxymethamphetamine (MDMA) treatment from postnatal days (P)11 to P20 leads to learning and memory deficits when the animals are tested as adults. Recently, the club drug 5-methoxy-N,N-diisopropyltryptamine (5-MeO-DIPT) has gained popularity.

OBJECTIVE

Due to the similarities between MDMA and 5-MeO-DIPT and the substitution of 5-MeO-DIPT for MDMA, the purpose of this study was to compare the developmental effects of these drugs.

METHODS

Within a litter, animals were treated from P11 to P20 with either MDMA, 5-MeO-DIPT, or saline.

RESULTS

MDMA-treated animals showed increased anxiety in a measure of defensive marble burying, as well as deficits in spatial and path integration learning. 5-MeO-DIPT-treated animals showed spatial learning deficits; however, there were no deficits observed in spatial memory or path integration learning. 5-MeO-DIPT-treated animals also showed hyperactivity in response to a challenge dose of methamphetamine.

CONCLUSIONS

The results show that treatment with either 5-MeO-DIPT or MDMA during development results in cognitive deficits and other behavioral changes but the pattern of effects is distinct for each drug.

(+/-)-3,4-Methylenedioxymethamphetamine treatment in adult rats impairs path integration learning: a comparison of single vs once per week treatment for 5 weeks

3,4-Methlylenedioxymethamphetamine (MDMA) administration (4 x 15 mg/kg) on a single day has been shown to cause path integration deficits in rats. While most animal experiments focus on single binge-type models of MDMA use, many MDMA users take the drug on a recurring basis. The purpose of this study was to compare the effects of repeated single-day treatments with MDMA (4 x 15 mg/kg) once weekly for 5 weeks to animals that only received MDMA on week 5 and saline on weeks 1-4. In animals treated with MDMA for 5 weeks, there was an increase in time spent in the open area of the elevated zero maze suggesting a decrease in anxiety or increase in impulsivity compared to the animals given MDMA for 1 week and saline treated controls. Regardless of dosing regimen, MDMA treatment produced path integration deficits as evidenced by an increase in latency to find the goal in the Cincinnati water maze. Animals treated with MDMA also showed a transient hypoactivity that was not present when the animals were re-tested at the end of cognitive testing. In addition, both MDMA-treated groups showed comparable hyperactive responses to a later methamphetamine challenge. No differences were observed in spatial learning in the Morris water maze during acquisition or reversal but MDMA-related deficits were seen on reduced platform-size trials. Taken together, the data show that a single-day regimen of MDMA induces deficits similar to that of multiple weekly treatments.