A Single High Dose of Methamphetamine Reduces Monoamines and Impairs Egocentric and Allocentric Learning and Memory in Adult Male Rats

Tests for learning and memory in rodent regulatory studies

For decades, regulatory guidelines for safety assessment in rodents for drugs, chemicals, pesticides, and food additives with developmental neurotoxic potential have recommended a single test of learning and memory (L&M). In recent years some agencies have requested two such tests. Given the importance of higher cognitive function to health, and the fact that different types of L&M are mediated by different brain regions assessing higher functions represents a step forward in providing better evidence-based protection against adverse brain effects. Given the myriad of tests available for assessing L&M in rodents this leads to the question of which tests best fit regulatory guidelines. To address this question, we begin by describing the central role of two types of L&M essential to all mammalian species and the regions/networks that mediate them. We suggest that the tests recommended possess characteristics that make them well suited to the needs in regulatory safety studies. By brain region, these are (1) the hippocampus and entorhinal cortex for spatial navigation, which assesses explicit L&M for reference and episodic memory and (2) the striatum and related structures for egocentric navigation, which assesses implicit or procedural memory and path integration. Of the tests available, we suggest that in this context, the evidence supports the use of water mazes, specifically, the Morris water maze (MWM) for spatial L&M and the Cincinnati water maze (CWM) for egocentric/procedural L&M. We review the evidentiary basis for these tests, describe their use, and explain procedures that optimize their sensitivity.

Glibenclamide alters serotonin and dopamine levels in the rat striatum and hippocampus, reducing cognitive impairment

RATIONALE

Glibenclamide (GD) is a widely used medical drug; therefore, identifying the mechanisms underlying its pleiotropic effects in the central nervous system is urgent.

OBJECTIVES

The aim of this work was to determine the ability of GD to modulate serotonin (5-hydroxytryptamine, 5-HT) and dopamine (DA) transmission and to assess the dose-dependent effect of GD on cognitive function in rats during natural ageing.

METHODS

In Experiment 1, rats received 10, 25, or 50 μg/kg GD intraperitoneally for 10 days. In Experiment 2, rats received 50 μg/kg GD intraperitoneally for 30 days. Spatial and working memory was assessed in the MWM and Y-maze tests, respectively. In both experiments, the levels of DA and 5-HT, their metabolites, and turnover rate were analysed by HPLC-ED in the rat hippocampus and striatum.

RESULTS

Changes in DA and 5-HT levels occurred only with a dose of 50 μg/kg GD. Therefore, in the second experiment, we administered a dose of 50 μg/kg GD. At this dose, GD prevented the development of impairments in spatial and working memory. The hippocampal concentrations of DA and DOPAC decreased, and the striatal concentrations of DA, DOPAC, 5-HT, and 5-HIAA increased.

CONCLUSION

One of the possible mechanisms of the precognitive effect of GD is its ability to modulate monoamine transmission. Thus, in translating our results to humans, GD can be recommended as a prophylactic agent for natural ageing to reduce the risk of developing cognitive impairments.

Hippocampal ischaemia from accidental 5-Hydroxytryptophan (5-HTP) overdose case report

We report severe reversible hippocampal ischaemia following an accidental 5-Hydroxytryptophan (5-HTP) overdose. Serious consequences from 5-HTP overdose have not been reported. A 44-year-old previously well man ingested ten times the recommended dose of 5-HTP powder. After four hours he developed marked antegrade and retrograde amnesia, disorientation and confusion in the absence of loss of consciousness, seizure activity or features of serotonin toxicity. Magnetic resonance imaging (MRI) of the brain on day two revealed extensive symmetrical restricted diffusion bilaterally in the hippocampi, suggestive of ischaemia or seizure. Electroencephalogram was normal. Short and long-term memory improved sufficiently to return to work after two months. MRI at eleven months was normal. The most likely mechanism is drug-induced hippocampal ischaemia resulting from marked increase in 5-HTP.

Effects of methamphetamine-induced neurotoxicity on striatal long-term potentiation

RATIONALE

Methamphetamine (METH) exposure is associated with damage to central monoamine systems, particularly dopamine signaling. Rodent models of such damage have revealed a decrease in the amplitude of phasic dopamine signals and significant striatal dysfunction, including changes in the molecular, system, and behavioral functions of the striatum. Dopamine signaling through D1 receptors promotes corticostriatal long-term potentiation (LTP), a critical substrate of these striatal functions.

OBJECTIVES

Therefore, the purpose of this study was to determine if METH-induced dopamine neurotoxicity would impair D1 receptor-dependent striatal LTP in mice.

METHODS

Mice were treated with a METH binge regimen (4 × 10 mg/kg d,l-methamphetamine, s.c.) that recapitulates all of the known METH-induced neurotoxic effects observed in humans, including dopamine toxicity. Three weeks later, acute brain slices containing either the dorsomedial striatum (DMS) or dorsolateral striatum (DLS) were prepared, and plasticity was assessed using white matter, high-frequency stimulation (HFS), and striatal extracellular electrophysiology.

RESULTS

Under these conditions, LTP was induced in brain slices containing the DMS from saline-pretreated mice, but not mice with METH-induced neurotoxicity. Furthermore, the LTP observed in DMS slices from saline-pretreated mice was blocked by the dopamine D1 receptor antagonist SCH23390, indicating that this LTP is dopamine D1 receptor-dependent. Finally, acute in vivo treatment of METH-pretreated mice with bupropion (50 mg/kg, i.p.) promoted LTP in DMS slices.

CONCLUSIONS

Together, these studies demonstrate that METH-induced neurotoxicity impairs dopamine D1 receptor-dependent LTP within the DMS and that the FDA-approved drug bupropion restores induction of striatal LTP in mice with METH-induced dopamine neurotoxicity.

Methamphetamine abuse disturbs the dopaminergic system to impair hippocampal-based learning and memory: An overview of animal and human investigations

Diverse intellectual functions including memory are some important aspects of cognition. Dopamine is a neurotransmitter of the catecholamine family, which contributes to the experience of pleasure and/or emotional states but also plays crucial roles in learning and memory. Methamphetamine is an illegal drug, the abuse of which leads to long lasting pathological manifestations in the brain. Chronic methamphetamine-induced neurotoxicity results in an alteration of various parts of the memory systems by affecting learning processes, an effect attributed to the structural similarities of this drug with dopamine. An evolving field of research established how cognitive deficits in abusers arise and how they could possibly trigger neurodegenerative disorders. Thus, the drugs-induced tenacious neurophysiological changes of the dopamine system trigger cognitive deficits, thereby affirming the influence of this addictive drug on learning, memory and executive function in human abusers. Here we present an overview of the effects of methamphetamine abuse on cognitive functions, dopaminergic transmission and hippocampal integrity as they have been validated in animals and in humans during the past 20 years.

The Role of HSP90α in Methamphetamine/Hyperthermia-Induced Necroptosis in Rat Striatal Neurons

Methamphetamine (METH) is one of the most widely abused synthetic drugs in the world. The users generally present hyperthermia (HT) and psychiatric symptoms. However, the mechanisms involved in METH/HT-induced neurotoxicity remain elusive. Here, we investigated the role of heat shock protein 90 alpha (HSP90α) in METH/HT (39.5°C)-induced necroptosis in rat striatal neurons and an in vivo rat model. METH treatment increased core body temperature and up-regulated LDH activity and the molecular expression of canonical necroptotic factors in the striatum of rats. METH and HT can induce necroptosis in primary cultures of striatal neurons. The expression of HSP90α increased following METH/HT injuries. The specific inhibitor of HSP90α, geldanamycin (GA), and HSP90α shRNA attenuated the METH/HT-induced upregulation of receptor-interacting protein 3 (RIP3), phosphorylated RIP3, mixed lineage kinase domain-like protein (MLKL), and phosphorylated MLKL. The inhibition of HSP90α protected the primary cultures of striatal neurons from METH/HT-induced necroptosis. In conclusion, HSP90α plays an important role in METH/HT-induced neuronal necroptosis and the HSP90α-RIP3 pathway is a promising therapeutic target for METH/HT-induced neurotoxicity in the striatum.

URB597 abrogates anxiogenic and depressive behaviors in the methamphetamine-withdrawal mice: Role of the cannabinoid receptor type 1, cannabinoid receptor type 2, and transient receptor potential vanilloid 1 channels

BACKGROUND

Methamphetamine is an addictive stimulant that possesses toxicity in the brain when taken repeatedly or at higher doses. Methamphetamine neurotoxicity is associated with numerous forms of mental impairment, including depression and anxiety. Evidence has also demonstrated that the endocannabinoid system is involved in the regulation of anxiety and depression.

AIMS

This study was designed to determine the involvement of the endocannabinoid system in anxiety- and depression-related behaviors in methamphetamine-withdrawal male NMRI mice.

METHODS

The elevated plus maze and forced swim test were used to assess the level of anxiety and depression.

RESULTS

We found that methamphetamine (30 mg/kg, intraperitoneal) evoked depressive- and anxiogenic-like effects at 3 days post-administration. Injection of URB597 (5-10 ng/mouse, intracerebroventricular), 10 min before the test, prevented the emotional deficits induced by methamphetamine withdrawal. Moreover, the cannabinoid receptor type 1 antagonist AM251 (1 μg/mouse) or cannabinoid receptor type 2 antagonist AM630 (5 and 10 μg/mouse) suppressed the antidepressant activity in the methamphetamine-withdrawal mice treated with URB597. The transient receptor potential vanilloid 1 antagonist capsazepine (25 μg/mouse) prevented while capsazepine (100 μg/mouse) potentiated the antidepressant efficacy in the methamphetamine-withdrawal mice treated with URB597. The higher dose of AM630 and two higher doses of capsazepine had antidepressant efficacy, by themselves. Furthermore, capsazepine (50 μg/mouse) increased locomotion in the methamphetamine-withdrawal mice treated with URB597.

CONCLUSIONS

The results suggest that URB597 has a potential for preventing methamphetamine withdrawal-evoked anxiety and depression. Cannabinoid type 1 receptors, cannabinoid type 2 receptors and transient receptor potential vanilloid 1 differently affect depression-related behaviors in methamphetamine-withdrawal mice treated with URB597.

Whole brain proton irradiation in adult Sprague Dawley rats produces dose dependent and non-dependent cognitive, behavioral, and dopaminergic effects

Proton radiotherapy causes less off-target effects than X-rays but is not without effect. To reduce adverse effects of proton radiotherapy, a model of cognitive deficits from conventional proton exposure is needed. We developed a model emphasizing multiple cognitive outcomes. Adult male rats (10/group) received a single dose of 0, 11, 14, 17, or 20 Gy irradiation (the 20 Gy group was not used because 50% died). Rats were tested once/week for 5 weeks post-irradiation for activity, coordination, and startle. Cognitive assessment began 6-weeks post-irradiation with novel object recognition (NOR), egocentric learning, allocentric learning, reference memory, and proximal cue learning. Proton exposure had the largest effect on activity and prepulse inhibition of startle 1-week post-irradiation that dissipated each week. 6-weeks post-irradiation, there were no effects on NOR, however proton exposure impaired egocentric (Cincinnati water maze) and allocentric learning and caused reference memory deficits (Morris water maze), but did not affect proximal cue learning or swimming performance. Proton groups also had reduced striatal levels of the dopamine transporter, tyrosine hydroxylase, and the dopamine receptor D1, effects consistent with egocentric learning deficits. This new model will facilitate investigations of different proton dose rates and drugs to ameliorate the cognitive sequelae of proton radiotherapy.

Oxytocin inhibits methamphetamine-associated learning and memory alterations by regulating DNA methylation at the Synaptophysin promoter

Methamphetamine (METH) causes memory changes, but the underlying mechanisms are poorly understood. Epigenetic mechanisms, including DNA methylation, can potentially cause synaptic changes in the brain. Oxytocin (OT) plays a central role in learning and memory, but little is known of the impact of OT on METH-associated memory changes. Here, we explored the role of OT in METH-induced epigenetic alterations that underlie spatial and cognitive memory changes. METH (2.0 mg/kg, i.p.) was administered to male C57BL/6 mice once every other day for 8 days. OT (2.5 μg, i.c.v.) or aCSF was given prior to METH. Spatial and cognitive memory were assessed. In Hip and PFC, synaptic structures and proteins were examined, levels of DNA methyltransferases (DNMTs) and methyl CpG binding protein 2 (MECP2) were determined, and the DNA methylation status at the Synaptophysin (Syn) promoter was assessed. METH enhanced spatial memory, decreased synapse length, downregulated DNMT1, DNMT3A, DNMT3B, and MECP2, and induced DNA hypomethylation at the Syn promoter in Hip. In contrast, METH reduced cognitive memory, increased synapse thickness, upregulated DNMT1, DNMT3A, and MECP2, and induced DNA hypermethylation at the Syn promoter in PFC. OT pretreatment specifically ameliorated METH-induced learning and memory alterations, normalized synapse structures, and regulated DNMTs and MECP2 to reverse the DNA methylation status changes at the Syn promoter in Hip and PFC. DNA methylation is an important gene regulatory mechanism underlying METH-induced learning and memory alterations. OT can potentially be used to specifically manipulate METH-related memory changes.

Neuronal and peripheral damages induced by synthetic psychoactive substances: an update of recent findings from human and animal studies

Preclinical and clinical studies indicate that synthetic psychoactive substances, in addition to having abuse potential, may elicit toxic effects of varying severity at the peripheral and central levels. Nowadays, toxicity induced by synthetic psychoactive substances poses a serious harm for health, since recreational use of these substances is on the rise among young and adult people. The present review summarizes recent findings on the peripheral and central toxicity elicited by “old” and “new” synthetic psychoactive substances in humans and experimental animals, focusing on amphetamine derivatives, hallucinogen and dissociative drugs and synthetic cannabinoids.

Time-dependent impairments in learning and memory in Streptozotocin-induced hyperglycemic rats

The sedentary lifestyle is responsible for the high prevalence of diabetes which also impairs cognition including learning and memory. Various studies have highlighted the learning and memory impairments in rodent models but data regarding the timeline of their development and their correlation to biochemical parameters are scarce. So, the present study was designed to investigate the type of memory which is more susceptible to hyperglycemia and its correlation with biochemical parameters such as inflammatory cytokines, cAMP response element binding (CREB) and protein kinase B (Akt) activation. Hyperglycemia was induced using streptozotocin (STZ, 45 mg/kg i.p.) and confirmed by measuring fasting blood glucose levels after 1 week of STZ injection. Learning and memory deficits were evaluated using the Novel Object Recognition Test (NORT) and Morris water maze (MWM), and correlated with biochemical parameters (TNF-α, IL-1β, and dopamine) at 3, 6 and 9 weeks. STZ-injected rats after 3 weeks of injection demonstrated moderate hyperglycemia (blood glucose = 7.99 ± 0.62 mM) with intact learning and reference memory; however, their working memory was impaired in MWM. Severe hyperglycemia (blood glucose = 11.51 ± 0.69 mM) accompanied by impaired short, long, and working memory was evident after 6 weeks whereas learning was intact. After 9 weeks of STZ injection, hyperglycemia was more pronounced (13.69 ± 1.43 mM) and accompanied by a learning deficit in addition to short, long, and working memory impairments. The extent of hyperglycemia either in terms of duration or severity resulted in enhanced inflammation, down-regulation of the level of dopamine, protein expression of AKT and CREB, which possibly affected learning and memory negatively.

Methamphetamine regulation of activity and topology of ventral midbrain networks

The ventral midbrain supports a variety of functions through the heterogeneity of neurons. Dopaminergic and GABA neurons within this region are particularly susceptible targets of amphetamine-class psychostimulants such as methamphetamine. While this has been evidenced through single-neuron methods, it remains unclear whether and to what extent the local neuronal network is affected and if so, by which mechanisms. Both GABAergic and dopaminergic neurons were heavily featured within the primary ventral midbrain network model system. Using spontaneous calcium activity, our data suggest methamphetamine decreased total network output via a D2 receptor-dependent manner. Over culture duration, functional connectivity between neurons decreased significantly but was unaffected by methamphetamine. However, across culture duration, exposure to methamphetamine significantly altered changes in network assortativity. Here we have established primary ventral midbrain networks culture as a viable model system that reveals specific changes in network activity, connectivity, and topology modulation by methamphetamine. This network culture system enables control over the type and number of neurons that comprise a network and facilitates detection of emergent properties that arise from the specific organization. Thus, the multidimensional properties of methamphetamine can be unraveled, leading to a better understanding of its impact on the local network structure and function.

Effects of Molecular Hydrogen on Methamphetamine-Induced Neurotoxicity and Spatial Memory Impairment

Methamphetamine (METH) is a highly addictive stimulant, and METH exposure can induce irreversible neuronal damage and cause neuropsychiatric and cognitive disorders. The ever-increasing levels of METH abuse worldwide have necessitated the identification of effective intervention strategies to protect the brain against METH-induced neurotoxicity. The protective effects of molecular hydrogen on oxidative stress and related neurodegenerative diseases have been recently elucidated. Herein, we investigated whether treatment with molecular hydrogen ameliorated the METH-induced neurotoxicity and spatial learning and memory impairments. Male C57BL/6 mice received four intraperitoneal METH injections (10 mg/kg, 3-h interval), and stereotypic behaviors and hyperthermia were observed. After METH treatment and behavioral observation, the mice were returned to their home cages, where they received water or hydrogen-rich water (HRW) ad libitum for 7 days. We found that the molecular hydrogen delivered by ad libitum HRW consumption significantly inhibited the METH-induced spatial learning impairment and memory loss evidenced in the Barnes maze and Morris water maze tests. Furthermore, molecular hydrogen significantly restrained the neuronal damage in the hippocampus after high-dose METH exposure. Ad libitum HRW consumption also had an inhibitory effect on the METH-induced increase in the expression of Bax/Bcl-2, cleaved caspase-3, glucose-related protein 78 (GRP 78), CCAAT/enhancer-binding protein homologous protein (CHOP), and p-NF-kB p65 expression and elevation of interleukin (IL)-6 and tumor necrosis factor (TNF)-α levels in the hippocampus. These are the first findings to indicate that hydrogen might ameliorate METH-induced neurotoxicity and has a potential application in reducing the risk of neurodegeneration frequently observed in METH abusers.

Effects of intrastriatal dopamine D1 or D2 antagonists on methamphetamine-induced egocentric and allocentric learning and memory deficits in Sprague-Dawley rats

RATIONALE

Methamphetamine (MA) is an abused psychostimulant that causes cognitive deficits after chronic use. Neostriatal dopamine receptors play a role in MA monoamine neurotoxicity. Blocking dopamine receptors prior to MA exposure in adult rats attenuates monoamine reductions and reactive gliosis.

OBJECTIVES

We tested whether blocking dopamine receptors protects against cognitive deficits.

METHODS

First, we determined the effects of MA alone versus MA in combination with the dopamine receptor D1 antagonist SCH-23390 or the dopamine receptor D2 antagonist sulpiride on cFos expression and monoamines at the age when rats in the cognitive experiment were to begin testing and monoamines in rats after cognitive testing.

RESULTS

SCH-23390 infused into the neostriatum prior to systemic administration of MA attenuated MA-induced cFos activation while sulpiride induced cFos activation. Two weeks after MA, rats had dopamine and serotonin reductions that were attenuated by each antagonist. Other rats treated the same way, were tested for egocentric learning and memory in the Cincinnati water maze, for navigational strategy in a star water maze, and spatial learning and memory in a Morris water maze. Pre-treatment with SCH-23390 or sulpiride attenuated the effects of MA on egocentric and spatial learning and memory. MA-treated rats showed a shift from an egocentric to a disorganized strategy in the star maze that was less disorganized in groups receiving MA and an antagonist. Post-behavior monoamine reductions remained but were attenuated by the antagonists but not identically to what was seen in rats not behaviorally tested.

CONCLUSIONS

The results show for the first time that dopamine receptors are mediators of MA-induced cognitive deficits.

Mouse knockout of guanylyl cyclase C: Recognition memory deficits in the absence of activity changes

Guanylyl cyclase C (GC-C) is found in brain regions where dopamine is expressed. We characterized a mouse in which GC-C was knocked out (KO) that was reported to be a model of attention deficit hyperactivity disorder (ADHD). We re-examined this model and controlled for litter effects, used 16 to 23 mice per genotype per sex and assessed an array of behavioral and neurochemical outcomes. GC-C KO mice showed no phenotypic differences from wild-type mice on most behavioral tests, or on striatal or hippocampal monoamines, and notably no evidence of an ADHD-like phenotype. KO mice were impaired on novel object recognition, had decreased tactile startle but not acoustic startle, and females had increased latency on cued training trials in the Morris water maze, but not hidden platform spatial learning trials. Open-field activity showed small differences in females but not males. The data indicate that the GC-C KO mouse with proper controls and sample sizes has a moderate cognitive and startle phenotype but has no ADHD-like phenotype.

Sex differences in memory and intracellular signaling after methamphetamine binge treatment

Methamphetamine is a neurotoxic psychostimulant known to cause cell death and terminal degradation of dopaminergic neurons in the striatum concomitant with memory deficits. However, most of the research studies have not examined the influence of sex on these changes. In this study we compared the effects of a binge regimen of methamphetamine (four injections of 4 mg/kg) on male, female, and ovariectomized (OVX) female Sprague-Dawley rats. We show that male and OVX female animals had a deficit in a novel object recognition task, while intact females did not show this deficit. Neurochemical analysis of the same animals indicated higher levels of FosB protein in caudate-putamen (CPu) and nucleus accumbens (NAc) of the male animals than intact or OVX females. Methamphetamine also increased Bcl-2 protein levels in CPu of all the cohorts. We did not find a significant effect of methamphetamine on the dopamine neuron markers tyrosine hydroxylase (TH) or dopamine transporter (DAT) 7 days after methamphetamine administrations. Our behavioral and neurochemical studies indicate that methamphetamine differentially affects male and female animals and shows sex differences in memory and molecular mechanisms in the striatum of these animals.