Tolerance to the neurotoxic effect of methamphetamine in rats behaviorally sensitized to methamphetamine or amphetamine

Astrocytic clasmatodendrosis in the cerebral cortex of methamphetamine abusers

Postmortem investigation of methamphetamine (MA) abuse is an important task in forensic pathology. The present study investigated morphological changes in the astrocytes in the parietal cerebral cortex of MA abusers. Glial fibrillary acidic protein immunoreactivity in the cerebral cortex was examined in forensic autopsy cases for MA-detected group and control group. Clasmatodendrotic astrocytes (including those with swollen cell bodies and disintegrating distal processes) were frequently observed in the cerebral cortex of MA abusers. Quantitative analysis using a colour image processor showed a concomitant increase in the astrocyte area and astrocyte-to-vessel area ratio (size and number of astrocytes) in the grey matter in acute MA fatality and other MA-involved cases, although the astrocyte area (size) was also increased in cases of asphyxiation. The total astrocyte area (size) in the white matter was significantly higher in MA fatalities and asphyxia than in the other groups involving MA abusers. Those indices were independent of blood MA level, age, sex, survival or postmortem time. These observations suggest the increasing number and hypertrophic changes of astrocytes in the grey matter in MA abusers can be the outcome of long-term abuse, while disintegrating distal processes may exist only in acute fatal MA intoxication.

Tetrahydropalmatine protects against methamphetamine-induced spatial learning and memory impairment in mice

OBJECTIVE

The purpose of this study was to investigate the effect of methamphetamine (MA) on spatial learning and memory and the role of tetrahydropalmatine (THP) in MA-induced changes in these phenomena in mice.

METHODS

Male C57BL/6 mice were randomly divided into eight groups, according to different doses of MA, different doses of THP, treatment with both MA and THP, and saline controls. Spatial learning and memory were assessed using the Morris water maze. Western blot was used to detect the expression of extracellular signal-regulated protein kinase (ERK) in the mouse prefrontal cortex (PFC) and hippocampus.

RESULTS

Repeated MA treatment significantly increased the escape latency in the learning phase and decreased the number of platform site crossings in the memory-test phase. ERK1/2 expression was decreased in the PFC but not in the hippocampus of the MA-treated mice. Repeated THP treatment alone did not affect the escape latency, the number of platform site crossings or the total ERK1/2 expression in the brain. Statistically significantly shorter escape latencies and more platform site crossings occurred in MA+THP-treated mice than in MA-treated mice.

CONCLUSION

Repeated MA administration impairs spatial learning and memory in mice, and its co-administration with THP prevents this impairment, which is probably attributable to changed ERK1/2 expression in the PFC. This study contributes to uncovering the mechanism underlying MA abuse, and to exploring potential therapies.

Preconditioning provides neuroprotection in models of CNS disease: paradigms and clinical significance

Preconditioning is a phenomenon in which brief episodes of a sublethal insult induce robust protection against subsequent lethal injuries. Preconditioning has been observed in multiple organisms and can occur in the brain as well as other tissues. Extensive animal studies suggest that the brain can be preconditioned to resist acute injuries, such as ischemic stroke, neonatal hypoxia/ischemia, surgical brain injury, trauma, and agents that are used in models of neurodegenerative diseases, such as Parkinson's disease and Alzheimer's disease. Effective preconditioning stimuli are numerous and diverse, ranging from transient ischemia, hypoxia, hyperbaric oxygen, hypothermia and hyperthermia, to exposure to neurotoxins and pharmacological agents. The phenomenon of "cross-tolerance," in which a sublethal stress protects against a different type of injury, suggests that different preconditioning stimuli may confer protection against a wide range of injuries. Research conducted over the past few decades indicates that brain preconditioning is complex, involving multiple effectors such as metabolic inhibition, activation of extra- and intracellular defense mechanisms, a shift in the neuronal excitatory/inhibitory balance, and reduction in inflammatory sequelae. An improved understanding of brain preconditioning should help us identify innovative therapeutic strategies that prevent or at least reduce neuronal damage in susceptible patients. In this review, we focus on the experimental evidence of preconditioning in the brain and systematically survey the models used to develop paradigms for neuroprotection, and then discuss the clinical potential of brain preconditioning.

Low concentrations of methamphetamine can protect dopaminergic cells against a larger oxidative stress injury: mechanistic study

Mild stress can protect against a larger insult, a phenomenon termed preconditioning or tolerance. To determine if a low intensity stressor could also protect cells against intense oxidative stress in a model of dopamine deficiency associated with Parkinson disease, we used methamphetamine to provide a mild, preconditioning stress, 6-hydroxydopamine (6-OHDA) as a source of potentially toxic oxidative stress, and MN9D cells as a model of dopamine neurons. We observed that prior exposure to subtoxic concentrations of methamphetamine protected these cells against 6-OHDA toxicity, whereas higher concentrations of methamphetamine exacerbated it. The protection by methamphetamine was accompanied by decreased uptake of both [(3)H] dopamine and 6-OHDA into the cells, which may have accounted for some of the apparent protection. However, a number of other effects of methamphetamine exposure suggest that the drug also affected basic cellular survival mechanisms. First, although methamphetamine preconditioning decreased basal pERK1/2 and pAkt levels, it enhanced the 6-OHDA-induced increase in these phosphokinases. Second, the apparent increase in pERK1/2 activity was accompanied by increased pMEK1/2 levels and decreased activity of protein phosphatase 2. Third, methamphetamine upregulated the pro-survival protein Bcl-2. Our results suggest that exposure to low concentrations of methamphetamine cause a number of changes in dopamine cells, some of which result in a decrease in their vulnerability to subsequent oxidative stress. These observations may provide insights into the development of new therapies for prevention or treatment of PD.

Methamphetamine-induced behavioral and physiological effects in adolescent and adult HIV-1 transgenic rats

We recently reported that six consecutive days of treatment with a moderate dose of methamphetamine (METH) induced greater behavioral sensitization in adult HIV-1 transgenic (HIV-1 Tg) rats than in adult Fischer 344/NHsd (F344) non-transgenic, wild-type control animals. In the present study, we evaluated the effects of a moderate dose of METH on the brains of adolescent versus adult HIV-1 Tg male rats using both behavioral (METH-induced, stereotypic head movement) and physiological (rectal body temperature) parameters. We found that both the acute and behavior-sensitizing effects of METH were greater in HIV-1 Tg rats compared with controls and also in adolescent rats compared with adult animals, regardless of HIV-1 status. We determined that acute hyperthermic effects of METH as well as tolerance to METH-induced hyperthermia were greater in HIV-1 Tg rats than in controls. Taken together, these results suggest that both the neuroadaptations seen in HIV infection and the immaturity of the adolescent brain are associated with increased sensitivity to the psychoactive and behavior-sensitizing properties of METH. Thus, HIV-infected individuals and adolescents may be more vulnerable to the development of METH abuse and dependence than non-infected individuals and adults.

Neuroprotective effect of atypical antipsychotics in cognitive and non-cognitive behavioral impairment in animal models

Antipsychotic drugs are divided into two groups: typical and atypical. Recent clinical studies show atypical antipsychotics have advantages over typical antipsychotics in a wide variety of neuropsychiatric conditions, in terms of greater efficacy for positive and negative symptoms, beneficial effects on cognitive functioning, and fewer extra pyramidal side effects in treating schizophrenia. As such, atypical antipsychotics may be effective in the treatment of depressive symptoms associated with psychotic and mood disorders, posttraumatic stress disorder and psychosis in Alzheimer disease. In this paper, we describe the effects and potential neurochemical mechanisms of action of atypical antipsychotics in several animal models showing memory impairments and/or non-cognitive behavioral changes. The data provide new insights into the mechanisms of action of atypical antipsychotics that may broaden their clinical applications.

Persistence of tolerance to methamphetamine-induced monoamine deficits

Methamphetamine is a highly addictive and potent stimulant, the use of which has increased significantly in recent years. In addition to the severe behavioral and societal consequences associated with methamphetamine abuse, methamphetamine can cause persistent damage to monoaminergic nerve terminals in rats, as measured by either monoamine concentrations or activity of the rate limiting synthetic enzymes, tyrosine hydroxylase and tryptophan hydroxylase. Repeated, sub-neurotoxic doses of methamphetamine, however, can cause rats to become resistant to the neurotoxic effects of multiple high-dose administrations of methamphetamine; a phenomenon known as tolerance. This study investigates the persistence of tolerance evoked by pretreatment with escalating-dose administrations of methamphetamine. Rats were pretreated over several days with low, escalating doses of methamphetamine, followed by high-dose methamphetamine challenge after variable recovery periods. Results revealed that tolerance to monoaminergic deficits persisted for at least one week, but was completely eliminated by 31 days. There were no differences in the distribution of methamphetamine or its major metabolite, amphetamine, between methamphetamine-pretreated animals and saline-pretreated animals 2 h after the final methamphetamine challenge injection, and there were no regional differences in methamphetamine concentrations between the frontal cortex, hippocampus or striatum. We also observed that while methamphetamine pretreatment attenuated the hyperthermia caused by the high-dose methamphetamine challenge, significant reductions in methamphetamine-induced hyperthermia were not required for the development of tolerance with this regimen.

The effects of chronic administration of quetiapine on the methamphetamine-induced recognition memory impairment and dopaminergic terminal deficit in rats

Previous studies have suggested that quetiapine, a new atypical antipsychotic drug, may have beneficial effects on cognitive impairment and be a neuroprotectant in treating neurodegenerative diseases. In the present study, we investigated the therapeutic effects of chronic administration of quetiapine on methamphetamine (METH)-induced recognition memory impairment and dopaminergic terminal neurotoxicity in rats. Rats were pretreated with METH (5 mg/kg; s.c.) four times at 2-h intervals while their body temperature was monitored. Fifteen minutes after the last METH injection, rats were administered quetiapine (10 mg/kg/day; i.p.) for 28 days. One day after the last quetiapine injection, rats were trained and tested on an object recognition task on days 29 and 30. Finally, on day 31, rats were sacrificed for immunohistochemistry, 1 day after the object recognition task. METH induced hyperthermia, recognition memory impairment and a decrease of tyrosine hydroxylase immunoreactivity in the caudate putamen (CPu) of striatum. Quetiapine attenuated the METH-induced hyperthermia. Furthermore, chronic post-treatment of quetiapine reversed the METH-induced memory impairment and dopaminergic terminal deficit. These findings suggest that quetiapine may have therapeutic effects in the treatment of cognitive impairment and neurodegeneration induced by METH.

Chronic administration of quetiapine alleviates the anxiety-like behavioural changes induced by a neurotoxic regimen of dl-amphetamine in rats

We have demonstrated that the atypical antipsychotic drugs prevent cell death in PC12 cells induced by various cytotoxins and have protective effects on methamphetamine-induced neurotoxcity in rats. The present study was designed to examine the possible effects of chronic administration of quetiapine, an atypical antipsychotic drug, on the anxiety-like behavioural consequences of a neurotoxic regimen of dl-amphetamine. Rats were treated with quetiapine (10 mg/kg/day; i.p.) for 33 days. During days 15-19 of this period, the animals were given dl-amphetamine (20 mg/kg/day; s.c.) 1 h after the administration of quetiapine. The repeated administration of dl-amphetamine resulted in a decrease of tyrosine hydroxylase (TH) immunostaining in the caudate putamen, hyperthermia, and anxiety-like behavioural changes. The behavioural changes were indicated by a significant increase in the time spent in the light box in the light/dark box test, an increase in the ratios of ambulation distance inside the inner circle over the total ambulation distance and rearings inside the inner circle over the total rearings in the open field test, and an increase in the time spent in open arms in the elevated plus-maze test. Chronic administration of quetiapine significantly attenuated the dl-amphetamine-induced hyperthermia, and the anxiety-like behavioural changes in the light/dark box and in the open field tests. These results suggest that quetiapine can normalize the dl-amphetamine-induced anxiety-like behavioural changes, and might be helpful in the treatment for amphetamine-induced emotional changes.

Attenuated microglial activation mediates tolerance to the neurotoxic effects of methamphetamine

Methamphetamine causes persistent damage to dopamine nerve endings of the striatum. Repeated, intermittent treatment of mice with low doses of methamphetamine leads to the development of tolerance to its neurotoxic effects. The mechanisms underlying tolerance are not understood but clearly involve more than alterations in drug bioavailability or reductions in the hyperthermia caused by methamphetamine. Microglia have been implicated recently as mediators of methamphetamine-induced neurotoxicity. The purpose of the present studies was to determine if a tolerance regimen of methamphetamine would attenuate the microglial response to a neurotoxic challenge. Mice treated with a low-dose methamphetamine tolerance regimen showed minor reductions in striatal dopamine content and low levels of microglial activation. When the tolerance regimen preceded a neurotoxic challenge of methamphetamine, the depletion of dopamine normally seen was significantly attenuated. The microglial activation that occurs after a toxic methamphetamine challenge was blunted likewise. Despite the induction of tolerance against drug-induced toxicity and microglial activation, a neurotoxic challenge with methamphetamine still caused hyperthermia. These results suggest that tolerance to methamphetamine neurotoxicity is associated with attenuated microglial activation and they further dissociate its neurotoxicity from drug-induced hyperthermia.

Neuroprotective effects of olanzapine on methamphetamine-induced neurotoxicity are associated with an inhibition of hyperthermia and prevention of Bcl-2 decrease in rats

It is hypothesized that atypical antipsychotic drugs have neuroprotective effects which may be one of the mechanisms in treatment of schizophrenia. We investigated the neuroprotective effects of olanzapine (OLA), an atypical antipsychotic drug, on methamphetamine (METH)-induced neurotoxicity in rats. After pretreatment with OLA (2 mg/kg/day) by intraperitoneal injection for 2 weeks, rats were administered METH (7.5 mg/kg, four times at 2-h intervals) by subcutaneous injection while their body temperature was monitored. The rats were sacrificed 24 h after the last injection of METH for immunohistochemistry. METH-induced 24 h mortality was effectively reduced and METH-induced decrease of tyrosine hydroxylase immunoreactivity in caudate putamen (CPu) was significantly attenuated by OLA chronic pretreatment. Furthermore, we showed that the above neuroprotective potential of OLA might be associated with its attenuating effects on METH-induced hyperthermia and with its preventative actions on METH-induced decrease of Bcl-2, an anti-apoptotic gene product, in the CPu. Our results suggest that OLA may be a neuroprotective agent and that its neuroprotective potential may contribute to its therapeutic effects in treatment of schizophrenia.

Amphetamine neurotoxicity: accomplishments and remaining challenges

In addition to the social, cultural and indirect medical complications of amphetamine analog abuse, this class of drugs is also known to have the potential to damage brain monoaminergic cells directly. Using methamphetamine as a prototype, this article provides a brief review of the history of amphetamine neurotoxicity research and the progress that has been made toward defining its characteristics. Remaining challenges for this line of investigation are outlined, and suggested avenues for addressing these challenges are provided.

Physiological and behavioral effects of methamphetamine in a mouse model of endotoxemia: a preliminary study

We investigated the effects of methamphetamine (METH) on core body temperature (Tb) and motor activity (MA) with or without exposure to a peripheral immune challenge. Mice were exposed to an escalating METH treatment and then to a METH treatment known to cause neurotoxicity (binge METH treatment). This was followed by a challenge with lipopolysaccharide (LPS). Three days later, METH and saline-treated control groups were challenged with an acute test dose of METH (METH test). Animals exposed to the escalating METH treatment exhibited a significant increase in Tb only after the initial exposure to METH (Day 1) and following the METH test (Day 7). The hyperthermic effect produced by the METH test (Day 7) was reduced in mice previously exposed to combined exposure to binge METH and LPS treatments. The escalating METH treatment produced MA sensitization to the METH test. Animals treated with the binge METH, LPS injection or both treatments combined prevented MA sensitization to the METH test. These findings suggest that induction of peripheral endotoxemia in animals with a history of METH reduced the hyperthermic response to a subsequent challenge with METH.

Escalating dose methamphetamine pretreatment alters the behavioral and neurochemical profiles associated with exposure to a high-dose methamphetamine binge

The neurotoxic effects of methamphetamine (METH) have been characterized primarily from the study of high-dose binge regimens in rodents. However, this drug administration paradigm does not include a potentially important feature of stimulant abuse in humans, that is, the gradual escalation of stimulant doses that frequently occurs prior to high-dose exposure. We have argued that pretreatment with escalating doses (EDs) might significantly alter the neurotoxic profile produced by a single high-dose binge. In the present study, we tested this hypothesis by pretreating rats with saline or gradually increasing doses of METH (0.1-4.0 mg/kg over 14 days), prior to an acute METH binge (4 x 6 mg/kg at 2 h intervals). These animals, whose behavior was continuously monitored throughout drug treatment, were then killed 3 days later for determination of caudate-putamen dopamine (DA) content, levels of [(3)H]WIN 35,428 binding to the DA transporter, and levels of [(3)H]dihydrotetrabenazine ([(3)H]DTBZ) binding to the vesicular monoamine transporter. ED pretreatment markedly attenuated the stereotypy response, as well as the hyperthermia and indices of sympathetic activation associated with the acute binge. In addition, ED pretreatment prevented the decline in [(3)H]WIN 35,428 binding, and significantly diminished the decrease in DA levels, but did not affect the decrease in [(3)H]DTBZ binding associated with the acute binge. We suggest that further study of the effects produced by a regimen which includes a gradual escalation of doses prior to high-dose METH binge exposure could more accurately identify the neurochemical and behavioral changes relevant to those that occur as a consequence of high-dose METH abuse in humans.

Tolerance to the neurotoxic effects of methamphetamine in young rats

The present study examined whether exposure to methamphetamine during adolescence (as determined in post-natal day 40 rats) might alter its effects when used in young adulthood (as assessed in post-natal day 90 rats). Results confirm that high-dose methamphetamine administration (4x10 mg/kg/injection, s.c., 2-h intervals) decreases striatal dopamine uptake and transporter ligand binding in post-natal day 90 rats; effects that were blocked if animals received six biweekly methamphetamine pretreatments (15 mg/kg; s.c.) beginning at post-natal day 40. This neuroprotection was not likely due to pharmacokinetic tolerance, since brain methamphetamine concentrations did not differ 1 h after the high-dose methamphetamine regimen among treated rats regardless of pretreatment. The methamphetamine biweekly pretreatment attenuated the hyperthermia caused by the neurotoxic methamphetamine regimen; a phenomenon that may have contributed to the neuroprotection.

Striatal dopamine depletion and behavioural sensitization induced by methamphetamine and 3-nitropropionic acid

The neurotoxic effects of methamphetamine (4 x 5 mg/kg i.p. at 2-h intervals) and 3-nitropropionic acid (20 mg/kg i.p. on days 1-4 and 6-9, saline on day 5), administered alone or in combination (3-nitropropionic acid as above and methamphetamine on day 5), were investigated in rats 1 week after the last injection. Neither methamphetamine nor 3-nitropropionic acid on their own altered brain dopamine levels, but in combination, they selectively lowered dopamine in the terminal regions of the corpus striatum and nucleus accumbens. Methamphetamine depleted 5-hydroxytryptamine (5-HT) in the striatum, while 3-nitropropionic acid depleted 5-HT in the accumbens and substantia nigra, but a combination of the two toxins failed to lower 5-HT in any of these brain regions. Measurements of aromatic L-amino acid decarboxylase activity disclosed no change in the capacity to decarboxylate L-3,4-dihydroxyphenylalanine in any region with any of the treatments, but a lowered capacity to decarboxylate 5-hydroxytryptophan in the nigra after all three treatments. Methamphetamine evoked characteristic hyperactivity and stereotypy in the animals, whereas 3-nitropropionic gave rise to early hypermotility followed by hypoactivity. At 1 week after treatment with 3-nitropropionic/methamphetamine, rats exhibited normal spontaneous motor behaviour, a poor response to dopamine D(1) receptor stimulation and an exaggerated response to dopamine D(2) receptor agonists. These results show that combined systemic treatment with methamphetamine and 3-nitropropionic acid partially depletes dopamine in the basal ganglia, rendering the animals supersensitive to dopamine D(2) receptor activation without altering their spontaneous locomotion.