Parvalbumin neuron circuits and microglia in three dopamine-poor cortical regions remain sensitive to amphetamine exposure in the absence of hyperthermia, seizure and stroke

Characterization of status epilepticus induced by two organophosphates in rats

Organophosphates (OPs) inhibit the enzyme cholinesterase and cause accumulation of acetylcholine, and are known to cause seizures and status epilepticus (SE) in humans. The animal models of SE caused by organophosphate analogs of insecticides are not well characterized. SE caused by OPs paraoxon and diisopropyl fluorophosphate (DFP) in rats was characterized by electroencephalogram (EEG), behavioral observations and response to treatment with the benzodiazepine diazepam administered at various stages of SE. A method for SE induction using intrahippocampal infusion of paraoxon was also tested. Infusion of 200nmol paraoxon into the hippocampus caused electrographic seizures in 43/52 (82.7%) animals tested; and of these animals, 14/43 (30%) had self-sustaining seizures that lasted 4-18h after the end of paraoxon infusion. SE was also induced by peripheral subcutaneous injection of diisopropyl fluorophosphate (DFP, 1.25mg/kg) or paraoxon (1.00mg/kg) to rats pretreated with atropine (2mg/kg) and 2-pralidoxime (2-PAM, 50mg/kg) 30min prior to OP injection. SE occurred in 78% paraoxon-treated animals and in 79% of DFP-treated animals. Diazepam (10mg/kg) was administered 10min and 30min after the onset of continuous EEG seizures induced by paraoxon and it terminated SE in a majority of animals at both time points. DFP-induced SE was terminated in 60% animals when diazepam was administered 10min after the onset of continuous EEG seizure activity but diazepam did not terminate SE in any animal when it was administered 30min after the onset of continuous seizures. These studies demonstrate that both paraoxon and DFP can induce SE in rats but refractoriness to diazepam is a feature of DFP induced SE.

Implications of central immune signaling caused by drugs of abuse: mechanisms, mediators and new therapeutic approaches for prediction and treatment of drug dependence

In the past two decades a trickle of manuscripts examining the non-neuronal central nervous system immune consequences of the drugs of abuse has now swollen to a significant body of work. Initially, these studies reported associative evidence of central nervous system proinflammation resulting from exposure to the drugs of abuse demonstrating key implications for neurotoxicity and disease progression associated with, for example, HIV infection. However, more recently this drug-induced activation of central immune signaling is now understood to contribute substantially to the pharmacodynamic actions of the drugs of abuse, by enhancing the engagement of classical mesolimbic dopamine reward pathways and withdrawal centers. This review will highlight the key in vivo animal, human, biological and molecular evidence of these central immune signaling actions of opioids, alcohol, cocaine, methamphetamine, and 3,4-methylenedioxymethamphetamine (MDMA). Excitingly, this new appreciation of central immune signaling activity of drugs of abuse provides novel therapeutic interventions and opportunities to identify 'at risk' individuals through the use of immunogenetics. Discussion will also cover the evidence of modulation of this signaling by existing clinical and pre-clinical drug candidates, and novel pharmacological targets. Finally, following examination of the breadth of central immune signaling actions of the drugs of abuse highlighted here, the current known common immune signaling components will be outlined and their impact on established addiction neurocircuitry discussed, thereby synthesizing a common neuroimmune hypothesis of addiction.

Recommended Neuroanatomical Sampling Practices for Comprehensive Brain Evaluation in Nonclinical Safety Studies

Adequate tissue sampling is known to reduce the likelihood that the toxicity of novel biomolecules, chemicals, and drugs might go undetected. Each organ, and often specific structurally and functionally distinct regions within it, must be assessed to detect potential site-specific toxicity. Adequate sampling of the brain requires particular consideration because of the many major substructures and more than 600 subpopulations of generally irreplaceable cells with unique functions and vulnerabilities. All known neurotoxicants affect specific subpopulations (usually neurons) rather than damaging a certain percentage of cells throughout the brain; thus, all populations should be independently assessed for lesions. Historically, the affected neural cell subpopulation has not been predictable, but it is now clear that sampling selected populations (e.g., cerebral cortex, hippocampus, cerebellar folia) cannot forecast the health of other populations. This article reviews the neuroanatomical domains affected by several model neurotoxicants to illustrate the need for more comprehensive neurohistological evaluation during nonclinical development of novel compounds. The article also describes an easily executed, cost-effective method that uses a set number of evenly spaced coronal (cross) sections to accomplish this comprehensive brain assessment during nonclinical safety studies performed in rodents, dogs, and nonhuman primates.

Neonatal Escherichia coli infection alters glial, cytokine, and neuronal gene expression in response to acute amphetamine in adolescent rats

Neonatal bacterial infection in rats alters the responses to a variety of subsequent challenges later in life. Here we explored the effects of neonatal bacterial infection on a subsequent drug challenge during adolescence, using administration of the psychostimulant amphetamine. Male rat pups were injected on postnatal day 4 (P4) with live Escherichia coli (E. coli) or PBS vehicle, and then received amphetamine (15mg/kg) or saline on P40. Quantitative RT-PCR was performed on micropunches taken from medial prefrontal cortex, nucleus accumbens, and the CA1 subfield of the hippocampus. mRNA for glial and neuronal activation markers as well as pro-inflammatory and anti-inflammatory cytokines were assessed. Amphetamine produced brain region specific increases in many of these genes in PBS controls, while these effects were blunted or absent in neonatal E. coli treated rats. In contrast to the potentiating effect of neonatal E. coli on glial and cytokine responses to an immune challenge previously observed, neonatal E. coli infection attenuates glial and cytokine responses to an amphetamine challenge.

Amphetamine and environmentally induced hyperthermia differentially alter the expression of genes regulating vascular tone and angiogenesis in the meninges and associated vasculature

An amphetamine (AMPH) regimen that does not produce a prominent blood-brain barrier breakdown was shown to significantly alter the expression of genes regulating vascular tone, immune function, and angiogenesis in vasculature associated with arachnoid and pia membranes of the forebrain. Adult-male Sprague-Dawley rats were given either saline injections during environmentally-induced hyperthermia (EIH) or four doses of AMPH with 2 h between each dose (5, 7.5, 10, and 10 mg/kg d-AMPH, s.c.) that produced hyperthermia. Rats were sacrificed either 3 h or 1 day after dosing, and total RNA and protein was isolated from the meninges, arachnoid and pia membranes, and associated vasculature (MAV) that surround the forebrain. Vip, eNos, Drd1a, and Edn1 (genes regulating vascular tone) were increased by either EIH or AMPH to varying degrees in MAV, indicating that EIH and AMPH produce differential responses to enhance vasodilatation. AMPH, and EIH to a lesser extent, elicited a significant inflammatory response at 3 h as indicated by an increased MAV expression of cytokines Il1b, Il6, Ccl-2, Cxcl1, and Cxcl2. Also, genes related to heat shock/stress and disruption of vascular homeostasis such as Icam1 and Hsp72 were also observed. The increased expression of Ctgf and Timp1 and the decreased expression of Akt1, Anpep, and Mmp2 and Tek (genes involved in stimulating angiogenesis) from AMPH exposure suggest that angiogenesis was arrested or disrupted in MAV to a greater extent by AMPH compared to EIH. Alterations in vascular-related gene expression in the parietal cortex and striatum after AMPH were less in magnitude than in MAV, indicating less of a disruption of vascular homeostasis in these two regions. Changes in the levels of insulin-like growth factor binding proteins Igfbp1, 2, and 5 in MAV, compared to those in striatum and parietal cortex, imply an interaction between these regions to regulate the levels of insulin-like growth factor after AMPH damage. Thus, the vasculature and meninges surrounding the surface of the forebrain may be an important region in which AMPHs can disrupt vascular homeostasis.

Neonatal status epilepticus alters prefrontal-striatal circuitry and enhances methamphetamine-induced behavioral sensitization in adolescence

Neonatal seizures may alter the developing neurocircuitry and cause behavioral abnormalities in adulthood. We found that rats previously subjected to lithium-pilocarpine (LiPC)-induced neonatal status epilepticus (NeoSE) exhibited enhanced behavioral sensitization to methamphetamine (MA) in adolescence. Neurochemically, dopamine (DA) and metabolites were markedly decreased in prefrontal cortex (PFC) and insignificantly changed in striatum by NeoSE, but were increased in both PFC and striatum by NeoSE+MA. Glutamate levels were increased in both PFC and striatum in the NeoSE+MA group. DA turnover, an index of utilization and activity, was increased by NeoSE but reversed by MA in PFC. Gene expression of the regulator of G-protein signaling 4 (RGS4) was downregulated in PFC and striatum by NeoSE and further suppressed by MA. These findings suggest NeoSE affects both dopaminergic and glutamatergic systems in the prefrontal-striatal circuitry that manifests as enhanced behavioral sensitization to MA in adolescence.

Brain region-specific neurodegenerative profiles showing the relative importance of amphetamine dose, hyperthermia, seizures, and the blood-brain barrier

Understanding the neurotoxic effects of acute high-dose exposures of laboratory animals to methamphetamine (METH) and amphetamine (AMPH) is of relevance to understanding the neurotoxicity incurred in humans from overdose or abuse of these substances. We present recent findings on the neurodegenerative effects of both a single high dose of 40 mg/kg and a 4-dose exposure to AMPH in the rat. Comparing these results with those we have previously observed in rodents exposed to either AMPH or METH helps further address how dose, hyperthermia, seizures and blood-brain barrier (BBB) disruption interact to produce neurodegeneration. With regard to the 4-dose paradigm of AMPH exposure in the rat, our recent data, combined with previous findings, clearly show the importance of dose and hyperthermic interactions in producing neurodegeneration. The single high AMPH dose invariably resulted in extreme hyperthermia and brief episodes of clonic-tonic seizure activity in many rats. However, motor behavior indicative of status epilepticus was not observed in rats receiving the 40 mg/kg AMPH, which contrasts with what we have previously seen with 40 mg/kg METH dose in the mouse. This may explain why, unlike the mice given METH, there was minimal BBB disruption in the amygdala of rats. Nonetheless, in some of the surviving rats there was extensive neurodegeneration in the hippocampus and intralaminar and ventromedial/lateral thalamic nuclei. Early BBB disruption was seen in the hippocampus and may play an important role in the subsequent neurodegeneration. The fact that status epilepticus does not occur in rats that have major hippocampal and thalamic degeneration indicates that such damage may also occur in humans exposed to high doses of AMPH or METH in the absence of status epilepticus or prominent motor manifestations of seizure activity.

Amphetamine causes dopamine depletion and cell death in the mouse olfactory bulb

Amphetamine is a neurotoxic psychostimulant that causes dopamine depletion and neuronal death in the rodent striatum. In the present study, we sought to determine if toxic doses of the drug can also induce pathological changes in the mouse olfactory bulb. We found that injections of amphetamine (10 mg/kg x 4, given 2 h apart) caused significant decreases in dopamine levels in that structure. This dose of the drug also induced substantial increases in the number of terminal deoxynucleotidyl transferase-mediated deoxyribonucleotide triphosphate (dNTP) nick end labeling (TUNEL)-positive cells in the olfactory bulb indicative of elevated DNA fragmentation. These results show that the toxic effects of amphetamine involve the olfactory bulb in addition to the striatum. These observations need to be taken into consideration when discussing the clinical course of amphetamine addiction.

Neurotoxicity of substituted amphetamines: Molecular and cellular mechanisms

The amphetamines, including amphetamine (AMPH), methamphetamine (METH) and 3,4-methylenedioxymethamphetamine (MDMA), are among abused drugs in the US and throughout the world. Their abuse is associated with severe neurologic and psychiatric adverse events including the development of psychotic states. These neuropsychiatric complications might, in part, be related to drug-induced neurotoxic effects, which include damage to dopaminergic and serotonergic terminals, neuronal apoptosis, as well as activated astroglial and microglial cells in the brain. The purpose of the present review is to summarize the toxic effects of AMPH, METH and MDMA. The paper also presents some of the factors that are thought to underlie this toxicity. These include oxidative stress, hyperthermia, excitotoxicity and various apoptotic pathways. Better understanding of the cellular and molecular mechanisms involved in their toxicity should help to generate modern therapeutic approaches to prevent or attenuate the long-term consequences of amphetamine use disorders in humans.

Selective loss of dentate hilar interneurons contributes to reduced synaptic inhibition of granule cells in an electrical stimulation-based animal model of temporal lobe epilepsy

Neuropeptide-containing hippocampal interneurons and dentate granule cell inhibition were investigated at different periods following electrical stimulation-induced, self-sustaining status epilepticus (SE) in rats. Immunohistochemistry for somatostatin (SOM), neuropeptide Y (NPY), parvalbumin (PV), cholecystokinin (CCK), and Fluoro-Jade B was performed on sections from hippocampus contralateral to the stimulated side and studied by confocal laser scanning microscopy. Compared to paired age-matched control animals, there were fewer SOM and NPY-immunoreactive (IR) interneurons in the hilus of the dentate gyrus in animals with epilepsy (40-60 days after SE), and 1, 3, and 7 days following SE. In the hilus of animals that had recently undergone SE, some SOM-IR and NPY-IR interneurons also stained for Fluoro-Jade B. Furthermore, there was electron microscopic evidence of the degeneration of SOM-IR interneurons following SE. In contrast, the number of CCK and PV-IR basket cells in epileptic animals was similar to that in controls, although it was transiently diminished following SE; there was no evidence of degeneration of CCK or PV-IR interneurons. Patch-clamp recordings revealed a diminished frequency of inhibitory postsynaptic currents in dentate granule cells (DGCs) recorded from epileptic animals and animals that had recently undergone SE compared with controls. These results confirm the selective vulnerability of a particular subset of dentate hilar interneurons after prolonged SE. This loss may contribute to the reduced GABAergic synaptic inhibition of granule cells in epileptic animals.

High doses of methamphetamine that cause disruption of the blood-brain barrier in limbic regions produce extensive neuronal degeneration in mouse hippocampus

Histological examination of brain after a single high (40 mg/kg) dose of D-methamphetamine (METH) was used to determine the relationships between blood-brain barrier (BBB) disruption, hyperthermia, intense seizure activity, and extensive degeneration that this exposure often produces. In very hyperthermic mice (body temperatures > 40.5 degrees C) exhibiting status epilepticus, increase in mouse IgG immunoreactivity (IgGIR) in the medial and ventral amygdala was observed within 90 min after METH exposure. In a few instances, where body temperature was in the 40.0 degrees C range, such IgGIR was also seen in animals that had exhibited status epilepticus. Variable increases in IgGIR, which correlated with neurodegeneration, also occurred within 12 h in the hippocampus, indicating BBB disruption in this region also. Degenerating neurons, Fluoro-Jade C (FJ-C) labeled, were first detected 4 h after METH in the amygdala and hippocampus. Extensive neurodegeneration occurred in the amygdaloid and hippocampal pyramidal cell regions in animals with marked IgGIR increase in these regions by 12 and 24 h after METH. A very rapid activation of brain microglia and/or infiltration of macrophages in regions of notable IgGIR increase with intense neurodegeneration were seen within 24 h. The phagocytosis rate of neurons in the hippocampus was so rapid that FJ-C labeling was virtually nonexistent 3 days after METH. METH did not produce IgGIR increase or neurodegeneration in the limbic regions in the absence of hyperthermia and seizures. Thus, high doses of METH can cause damage to the BBB when hyperthermia occurs, resulting in rapid and extensive hippocampal and amygdalar damage. The BBB disruption in the medial amygdala occurs first, and may well be contributing to the induction and severity of seizures, while BBB disruption in the hippocampus is likely a result of the seizures and hyperthermia. This hippocampal damage should be sufficient to compromise learning and memory.

A threshold neurotoxic amphetamine exposure inhibits parietal cortex expression of synaptic plasticity-related genes

Compulsive drug abuse has been conceptualized as a behavioral state where behavioral stimuli override normal decision making. Clinical studies of methamphetamine users have detailed decision making changes and imaging studies have found altered metabolism and activation in the parietal cortex. To examine the molecular effects of amphetamine (AMPH) on the parietal cortex, gene expression responses to amphetamine challenge (7.5 mg/kg) were examined in the parietal cortex of rats pretreated for nine days with either saline, non-neurotoxic amphetamine, or neurotoxic AMPH dosing regimens. The neurotoxic AMPH exposure [three doses of 7.5 mg/kg/day AMPH (6 h between doses), for nine days] produced histological signs of neurotoxicity in the parietal cortex while a non-neurotoxic dosing regimen (2.0 mg/kg/day x 3) did not. Neurotoxic AMPH pretreatment resulted in significantly diminished AMPH challenge-induced mRNA increases of activity-regulated cytoskeletal protein (ARC), nerve growth-factor inducible protein A (NGFI-A), and nerve growth-factor inducible protein B (NGFI-B) in the parietal cortex while neither saline pretreatment nor non-neurotoxic AMPH pretreatment did. This effect was specific to these genes as tissue plasminogen activator (t-PA), neuropeptide Y (NPY) and c-jun expression in response to AMPH challenge was unaltered or enhanced by amphetamine pretreatments. In the striatum, there were no differences between saline, neurotoxic AMPH, and non-neurotoxic AMPH pretreatments on ARC, NGFI-A or NGFI-B expression elicited by the AMPH challenge. These data indicate that the responsiveness of synaptic plasticity-related genes is sensitive to disruption specifically in the parietal cortex by threshold neurotoxic AMPH exposures.

Evidence of astrogliosis in rat hippocampus after d-amphetamine exposure

INTRODUCTION

Psychostimulants such as amphetamine (AMPH) induce manic-like symptoms in humans and studies have suggested that bipolar disorder (BD) may be associated to dopamine dysfunction. Glial fibrillary acidic protein (GFAP) up-regulation is considered a marker of astrogliosis, and it has been associated to behavioral sensitization.

PURPOSE

We aimed to investigate the behavioral effects of acute and chronic AMPH on rat locomotion and assess GFAP levels in rat cortex and hippocampus.

METHODS

Rats were administered either acute (single dose) or chronic (seven days) d-amphetamine IP injection. Locomotion was assessed with an open-field test and GFAP immunoquantity was measured using ELISA.

RESULTS

Chronic, but not acute, administration of AMPH increased GFAP levels in rat hippocampus. No differences were observed in rat cortex.

CONCLUSIONS

Repeated exposure to AMPH leads to an astroglial response in the hippocampus of rats.

Damage of serotonergic axons and immunolocalization of Hsp27, Hsp72, and Hsp90 molecular chaperones after a single dose of MDMA administration in Dark Agouti rat: Temporal, spatial, and cellular patterns

3,4-Methylenedioxymethamphetamine (MDMA, "ecstasy") causes long-term disturbance of the serotonergic system. We examined the temporal, spatial, and cellular distribution of three molecular chaperones, Hsp27, Hsp72, and Hsp90, 3 and 7 days after treatment with 7.5, 15, and 30 mg/kg single intraperitoneal (i.p.) doses of MDMA in Dark Agouti rat brains. Furthermore, we compared the immunostaining patterns of molecular chaperones with serotonergic axonal-vulnerability evaluated by tryptophan-hydroxylase (TryOH) immunoreactivity and with astroglial-activation detected by GFAP-immunostaining. There was a marked reduction in TryOH-immunoreactive axon density after MDMA treatment in all examined areas at both time points. Three days after treatment, a significant dose-dependent increase in Hsp27-immunoreactive protoplasmic astrocytes was found in the cingulate, frontal, occipital, and pyriform cortex, and in the hippocampus CA1. However, there was no increase in astroglial Hsp27-immunoreactivity in the caudate putamen, lateral septal nucleus, or anterior hypothalamus. A significant increase in the GFAP immunostaining density of protoplasmic astrocytes was found only in the hippocampus CA1. In addition, numerous strong Hsp72-immunopositive neurons were found in some brain areas only 3 days after treatment with 30 mg/kg MDMA. Increased Hsp27-immunoreactivity exclusively in the examined cortical areas reveals that Hsp27 is a sensitive marker of astroglial response to the effects of MDMA in these regions of Dark Agouti rat brain and suggests differential responses in astroglial Hsp27-expression between distinct brain areas. The co-occurrence of Hsp27 and GFAP response exclusively in the hippocampus CA1 may suggest the particular vulnerability of this region. The presence of strong Hsp72-immunopositive neurons in certain brain areas may reflect additional effects of MDMA on nonserotonergic neurons.

Biomarkers of adult and developmental neurotoxicity

Neurotoxicity may be defined as any adverse effect on the structure or function of the central and/or peripheral nervous system by a biological, chemical, or physical agent. A multidisciplinary approach is necessary to assess adult and developmental neurotoxicity due to the complex and diverse functions of the nervous system. The overall strategy for understanding developmental neurotoxicity is based on two assumptions: (1) significant differences in the adult versus the developing nervous system susceptibility to neurotoxicity exist and they are often developmental stage dependent; (2) a multidisciplinary approach using neurobiological, including gene expression assays, neurophysiological, neuropathological, and behavioral function is necessary for a precise assessment of neurotoxicity. Application of genomic approaches to developmental studies must use the same criteria for evaluating microarray studies as those in adults including consideration of reproducibility, statistical analysis, homogenous cell populations, and confirmation with non-array methods. A study using amphetamine to induce neurotoxicity supports the following: (1) gene expression data can help define neurotoxic mechanism(s), (2) gene expression changes can be useful biomarkers of effect, and (3) the site-selective nature of gene expression in the nervous system may mandate assessment of selective cell populations.

The modulation effects of d-amphetamine and procaine on the spontaneously generated action potentials in the central neuron of snail, Achatina fulica Ferussac

The modulation effects of d-amphetamine and procaine on the spontaneously generated action potentials were studied on the RP1 central neuron of giant African snails (Achatina fulica Ferussac). Extra-cellular application of d-amphetamine or procaine reversibly elicited bursts of potential (BoP). Prazosin, propranolol, atropine or d-tubocurarine did not alter the BoP elicited by either d-amphetamine or procaine. KT-5720 or H89 (protein kinase A inhibitors) blocked d-amphetamine-elicited BoP, whereas they did not block the procaine-elicited BoP. U73122, neomycin (phospholipase C inhibitors) blocked the procaine-elicited BoP, whereas they did not block the d-amphetamine-elicited BoP in the same neuron. These results suggest that BoP elicited by d-amphetamine or procaine were associated with protein kinase A and phospholipase C activity in the neuron.

Multiple-testing strategy for analyzing cDNA array data on gene expression

An objective of many functional genomics studies is to estimate treatment-induced changes in gene expression. cDNA arrays interrogate each tissue sample for the levels of mRNA for hundreds to tens of thousands of genes, and the use of this technology leads to a multitude of treatment contrasts. By-gene hypotheses tests evaluate the evidence supporting no effect, but selecting a significance level requires dealing with the multitude of comparisons. The p-values from these tests order the genes such that a p-value cutoff divides the genes into two sets. Ideally one set would contain the affected genes and the other would contain the unaffected genes. However, the set of genes selected as affected will have false positives, i.e., genes that are not affected by treatment. Likewise, the other set of genes, selected as unaffected, will contain false negatives, i.e., genes that are affected. A plot of the observed p-values (1 - p) versus their expectation under a uniform [0, 1] distribution allows one to estimate the number of true null hypotheses. With this estimate, the false positive rates and false negative rates associated with any p-value cutoff can be estimated. When computed for a range of cutoffs, these rates summarize the ability of the study to resolve effects. In our work, we are more interested in selecting most of the affected genes rather than protecting against a few false positives. An optimum cutoff, i.e., the best set given the data, depends upon the relative cost of falsely classifying a gene as affected versus the cost of falsely classifying a gene as unaffected. We select the cutoff by a decision-theoretic method analogous to methods developed for receiver operating characteristic curves. In addition, we estimate the false discovery rate and the false nondiscovery rate associated with any cutoff value. Two functional genomics studies that were designed to assess a treatment effect are used to illustrate how the methods allowed the investigators to determine a cutoff to suit their research goals.

Amphetamine induces apoptosis of medium spiny striatal projection neurons via the mitochondria‐dependent pathway

Amphetamine (AMPH) is a psychostimulant whose chronic abuse may cause impairments in attention and memory in humans. These cognitive deficits might be related to neurotoxic effects of the drug. One such toxic effect is the well-described destruction of striatal dopaminergic terminals in mammals. In the present study, we investigated the possibility that AMPH might also cause neuronal apoptosis in the rodent striatum. Administration of a dose of the drug (10 mg/kg, 4 times, every 2 h) that is toxic to dopaminergic terminals resulted in the appearance of striatal cells that were positive for cleaved caspase-3 and for terminal deoxynucleotidyl transferase-mediated biotin-dUTP nick-end labeling (TUNEL), observations that are indicative of an ongoing apoptotic process. Dual immunofluorescence staining revealed that cleaved caspase-3-positive cells express calbindin and DARPP-32, but not somatostatin, parvalbumin, or cholinergic markers. In addition, AMPH also caused increased expression of p53 and Bax at both transcript and protein levels; in contrast, Bcl-2 levels were decreased after the AMPH injections. Moreover, Bax knockout mice showed resistance to AMPH-induced apoptotic cell death but not to AMPH-induced destruction of dopaminergic terminals. When taken together, these observations indicate that injections of doses of AMPH that are known to destroy striatal dopamine terminals can also cause apoptotic death of postsynaptic medium spiny projection neurons via mitochondria-dependent mechanisms.

Microglial activation is a pharmacologically specific marker for the neurotoxic amphetamines

Neurotoxic amphetamines cause damage to monoamine nerve terminals of the striatum by unknown mechanisms. Microglial activation contributes to the neuronal damage that accompanies injury, disease, and inflammation, but a role for these cells in amphetamine-induced neurotoxicity has received little attention. We show presently that D-methamphetamine, 3,4-methylenedioxymethamphetamine (MDMA), D-amphetamine, and p-chloroamphetamine, each of which has been linked to dopamine (DA) or serotonin nerve terminal damage, result in microglial activation in the striatum. The non-neurotoxic amphetamines l-methamphetamine, fenfluramine, and DOI do not have this effect. All drugs that cause microglial activation also increase expression of glial fibrillary acidic protein (GFAP). At a minimum, microglial activation serves as a pharmacologically specific marker for striatal nerve terminal damage resulting only from those amphetamines that exert neurotoxicity. Because microglia are known to produce many of the reactive species (e.g., nitric oxide, superoxide, cytokines) that mediate the neurotoxicity of the amphetamine-class of drugs, their activation could represent an early and essential event in the neurotoxic cascade associated with high-dose amphetamine intoxication.

Glutamate N-methyl-d-aspartate and dopamine receptors have contrasting effects on the limbic versus the somatosensory cortex with respect to amphetamine-induced neurodegeneration

The roles that glutamate N-methyl-D-aspartate (NMDA) and dopamine D1-like and D2-like receptors play in the cortical neurotoxicity occurring in rats exposed to multiple doses of amphetamine (AMPH) for 2 days was evaluated. Neurodegeneration in rats that did not become hyperthermic during AMPH exposure was quantified by counting isolectin B4-labeled phagocytic microglia and Fluoro-Jade (F-J)-labeled neurons in the somatosensory parietal cortex, piriform cortex and posterolateral cortical amygdaloid nucleus (PLCo). The NMDA receptor antagonist, dizocilpine (0.63 mg/kg day) blocked AMPH-induced neurodegeneration in the somatosensory cortex. However, it did not affect degeneration in the piriform cortex and PLCo indicating that limbic degeneration was not NMDA-mediated. The dopamine antagonists, eticlopride (D2/3, 0.25 mg/kg day) and SCH-23390 (D1, 0.25 mg/kg day), blocked the stereotypic behavior and neurodegeneration in the somatosensory cortex. However, eticlopride had a lesser protective effect in the limbic regions. As well, the dopamine D2/D3 agonist quinpirole (1.5 mg/kg day) protected against cortical neurodegeneration when it was given during AMPH exposure and continued until sacrifice. The dopamine D1 agonist (SKF-38393, 12.5 mg/kg day) had no significant effect on neurodegeneration. These data indicate that there are significant differences in NMDA and dopamine D2 modulation of AMPH-induced neurodegeneration in the somatosensory cortex compared to the limbic cortices, and limbic cortical degeneration is not necessarily dependent on excessive stimulation of NMDA receptors as it is in the somatosensory cortex. Although excessive dopamine receptor stimulation during amphetamine exposure may trigger the neurodegenerative processes, continued D2 stimulation after AMPH exposure is neuroprotective in the cortex.

Selective Changes in Gene Expression in Cortical Regions Sensitive to Amphetamine During the Neurodegenerative Process

Gene expression profiles in several brain regions of adult male rats were evaluated following a d-amphetamine (AMPH) exposure paradigm previously established to produce AMPH neurotoxicity. Escalating doses of AMPH (5-30 mg/kg) were given over the course of 16 h per day in an 18 degrees C environment for 2 days. This paradigm produces neurotoxicity but eliminates or minimizes the hyperthermia and seizure activity that might influence gene expression in a manner unrelated to the neurotoxic effects of AMPH. The expression of 1185 genes was monitored in the striatum, parietal cortex, piriform cortex and posteriolateral cortical amygdaloid nucleus (PLCo) using cDNA array technology, and potentially significant changes were verified by RT-PCR. Gene expression was determined at time points after AMPH when neurodegeneration was beginning to appear (16 h) or maximal (64 h). Expression was also determined 14 days after AMPH to find long-term changes in gene expression that might be biomarkers of a neurotoxic event. In the parietal cortex there was a two-fold increase in neuropeptide Y precursor protein mRNA whereas nerve growth factor-induced receptor protein I-A and I-B mRNA decreased 50% at 16 h after the end of AMPH exposure. Although these changes in expression were not observed in the PLCo, insulin-like growth factor binding protein 1 mRNA was increased two-fold in the PLCo at 16 and 64 h after AMPH. Changes in gene expression in the cortical regions were all between 1.2- and 1.5-fold 14 days after AMPH but some of these changes, such as annexin V increases, may be relevant to neurotoxicity. Gene expression was not affected by more than 1.5-fold at the time points in the striatum, although 65% dopamine depletions occurred, but the plasma membrane-associated dopamine transporter and dopamine D2 receptor were decreased about 40% in the substantia nigra at 64 h and 14 days post-AMPH. Thus, the 2-day AMPH treatment produced a few changes in gene expression in the two-fold range at time points 16 h or more after exposure but the majority of expression changes were less than 1.5-fold of control. Nonetheless, some of these lesser fold-changes appeared to be relevant to the neurotoxic process.

Serotonin neurotoxins--past and present

Autoxidation pathways and redox reactions of dihydroxytryptamines (5,6- and 5,7-DHT) and of 6-hydroxydopamine (6-OH-DA) are illustrated, and their potential role in aminergic neurotoxicity is discussed. It is proposed that certain aspects of the cytotoxicity of 6-OH-DA and of the DHTs, namely redox cycling of their quinone- and quinoneimine-intermediates as a source of free radicals, may also apply to quinoidal reactive intermediates and to glutathionyl- or cysteinyl conjugates ("thioether adducts") of o-dihydroxylated (catechol-like) metabolites of certain substituted amphetamines (of methylenedioxymethamphetamine (MDMA) and of methylenedioxyamphetamine (MDA)). Despite similarities in their primary interaction with the plasmalemmal (serotonergic transporter/dopamine transporter, SERT/DAT) and vesicular monoamine transporters (VMAT2), MDMA and fenfluramine (N-ethyl-meta-trifluoromethamphetamine, Fen) differ substantially in many aspects of their metabolism, pharmacokinetics, pharmacology, and neurotoxicology profile; the consequences of these differences for neuronal response patterns and long-term survival prospects are not yet fully understood. However, sustained hyperthermia appears to be a critical factor in these differences. Methodological requirements for adequate detection and description of pre- and postsynaptic forms of drug-induced neurotoxicity are exemplified using recently published accounts. The inclusion of microglial markers into research strategies has widened contemporary pathogenetic concepts on methamphetamine (MA)-induced neurotoxicity as an example of inflammatory neurodegeneration, thus complementing the traditional ROS and RNS-dependent stress models. Amphetamine-type neurotoxicity studies may assist in elaborating of preventive strategies for human neurodegenerative disorders.

A statistical approach in using cDNA array analysis to determine modest changes in gene expression in several brain regions after neurotoxic insult

Modest changes in gene expression of three-fold or less might be expected after mild to moderate neurotoxic exposure to classes of compounds, such as the substituted amphetamines, or at time points that are weeks after more severe neurotoxic exposures. When many genes appear to change expression by less than two-fold, it is crucial to run several pairs of arrays and use statistical analysis to determine which genes are really changing. This limits the number of genes that have to undergo the time consuming task of performing RT-PCR to validate change in expression levels. We describe here methods for statistically determining which genes are being expressed above background levels. These methods are used to compare expression differences among the striatum, parietal cortex, posterior lateral amygdaloid nucleus, and substantia nigra brain regions, all of which differ significantly in their gene expression profiles. In these comparisons, it was possible to distinguish differences among hundreds of genes with manageable estimated false discovery rates. The effect of amphetamine treatment on gene expression in posterior lateral amygdaloid nucleus was also evaluated. The expression data indicate that many genes have changed, but in this case it is more difficult to separate affected genes from false positives. The optimum list has 50 genes, of which 32% are expected to be false positives.