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Molecular Neuropsychiatry Section, National Institute on Drug Abuse-Intramural Research Program, National Institutes of Health, Baltimore, Maryland, USA
1Correspondence: Molecular Neuropsychiatry Section, NIH/NIDA Intramural Research Program, 5500 Nathan Shock Dr., Baltimore, MD 21224, USA. E-mail: JCADET{at}intra.nida.nih.gov
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONCONCLUSIONREFERENCES |
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Key Words: amphetamine • neurotoxicity • Cu/Zn SOD • striatum • gene expression analysis
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONCONCLUSIONREFERENCES |
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, 2)
. Nevertheless, addiction to AMPH continues to be a major public health problem in the United States as well as in other countries throughout the world (3
4
5)
. In addition to its abuse potential, AMPH can cause neuronal damage in the mammalian brain. For example, administration of AMPH to rodents has been shown to cause decrease in activity of tyrosine hydroxylase (6)
, significant depletion of dopamine (DA) in the striatum of mice (7)
, loss of striatal DA transporters (8
, 9)
, as well as decreases in DA and vesicular monoamine transporter 2 proteins (8)
. Besides the changes in DA terminals, AMPH can cause degeneration of non-DA cell bodies via a process that resembles apoptosis (10)
. The molecular mechanisms underlying these distinct effects are not well understood but are thought to involve DA and vesicular monoamine transporters (11
, 12)
, nitric oxide (13)
, and the activation of genes related to cell death (10)
.
Reactive oxygen species (ROS) have been implicated in the mechanisms of AMPH neurotoxicity (8
, 14
; for a review, see ref 15
). Overproduction of ROS caused by drug administration that can exceed the capacity of antioxidant enzymes such as superoxide dismutases (SODs), catalase and glutathione peroxidase is indeed known to cause oxidative stress and cellular damage (15)
. In the case of AMPH, this idea is supported by the demonstration that overexpression of Cu/Zn SOD in transgenic mice is neuroprotective against AMPH-induced brain injury (8)
, observations that document a role for superoxide radicals in the neuronal damage caused by this illicit drug. Nevertheless, the complete molecular picture underlying the neuronal protection observed in SOD transgenic (SOD-tg) animals treated with AMPH remained to be drawn.
It is well established that ROS play a role in cellular signaling processes, including the regulation of transcriptional factors (16)
. Induction or suppression of transcription factors with subsequent activation or repression of genes that encode proteins involved in various neuronal functions might be critical steps in the AMPH-induced cascades of toxic events. Acute administration of AMPH does indeed cause the activation of c-fos (17
, 18)
, fos-related antigen (19)
, fosB and junB (17
, 20)
, c-jun (20)
, as well as of zif268 [erg-1, Krox-24, and NGF1A] (17
, 18)
in the mammalian striatum. Induction of several transcription factors, whose products may influence the transcription of other genes (for a review, see refs 21
, 22
), has been linked to conditions that lead to long-term, stimulant-induced degenerative changes in the brain (23
, 24)
.
When taken together, these studies have hinted at the possibility that AMPH administration might cause complex molecular events that might trigger the long-term effects of the drug. Therefore, as a further step toward clarifying the cellular and molecular events caused by AMPH treatment, we have made use of the comprehensive cDNA array approach in order to identify genes involved in the subacute effects of the drug in wild-type (WT) and Cu/Zn SOD-tg mice that have been shown to be protected against AMPH neurotoxicity (8)
. Our results show that AMPH can indeed cause superoxide-dependent transcriptional regulation of many genes whose products participate in stress responses or in cellular reactions to injury and inflammation.
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MATERIALS AND METHODS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONCONCLUSIONREFERENCES |
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. Male nontransgenic CD-1 mice (Charles River, Raleigh, NC) 9–12 wk old weighing 30–40 g were used as WT controls. Animals were housed three per cage and maintained in a temperature- (22±2°C) and light-controlled environment. Food and water were available ad libitum. All animal use procedures were according to the NIH Guide for the Care and Use of Laboratory Animals and were approved by the local NIDA Animal Care Committee. On the day of the experiment, groups of mice received four intraperitoneal injections of d-(+) AMPH sulfate, 10 mg/kg or saline every 2 h. At 30 min, 1, 2, 4, 8, 16, and 24 h after the last administration of AMPH or saline, mice were killed by cervical dislocation. Their brains were then removed and placed on an ice-cooled plate. Striata were dissected, immediately frozen on dry ice, and stored at -70°C until RNA extraction.
RNA preparation and array hybridization
Total RNA from striata of saline- and AMPH-treated WT and SOD-tg mice killed at the times listed after the last injection was isolated using Atlas Pure RNA Isolation Kit (BD Biosciences Clontech, Palo Alto, CA) according to the manufacturer’s protocol. RNA concentration was determined by UV spectrophotometry and RNA integrity was confirmed using denaturing 1.5% agarose-formaldehyde gel. Samples were stored at -70°C.
cDNA array analysis was performed by using Atlas Mouse 1.2 Cancer Arrays (Cat. #7858–1, BD Biosciences Clontech) containing a total of 1176 cDNA segments spotted on a nylon membrane. The identity of the genes can be found on the BD Biosciences Clontech web site (www.clontech.com). Probing of cDNA arrays was performed as described in Clontech Atlas cDNA Expression Arrays User Manual (PT3231–1). Total RNA (50 µg) from the striata of four mice was pooled for each experimental group and used for templates in a 20 µL reverse transcription reaction. A pooled set of primers complementary to the genes represented on the array (BD Biosciences Clontech) was used for the reverse transcription probe synthesis, which was radiolabeled with [32P]-dATP and purified by passage over CHROMA SPIN-200 columns (BD Biosciences Clontech).
Each membrane was prehybridized for 1 h at 68°C in 8 mL of hybridization solution (ExpressHyb, BD Biosciences Clontech) containing 0.1 mg/mL of sheared salmon testes DNA (Sigma, St. Louis) with continuous agitation. Hybridization with radiolabeled cDNA probes (
1x106 cpm/mL) was performed overnight in 8 mL of ExpressHyb at 68°C. The next day membranes were washed with continuous agitation at 68°C in 2x SSC, 1% SDS (4x30 min) in 0.1x SSC, 0.5% SDS (1x30 min), then at room temperature in 2x SSC (1x5 min). The membranes were mounted on the film, plastic-wrapped, and exposed to a PhosphorImager screen for 7 days at room temperature. The exposed screen was scanned on Storm 840 PhosphorImager (Molecular Dynamics, Sunnyvale, CA) at 100 µm resolution. All hybridization experiments were performed twice (with new sets of microarray membranes) using total RNA pooled from different sets of animals. Only gene expression changes observed consistently in both arrays were analyzed further.
Analysis of cDNA array
The array spots on the array images were analyzed using a theoretical pattern of template of Array Vision software for Windows NT (version 4, Imaging Research Inc., St. Catherine’s, ON, Canada). The template elements were aligned over the true array spot and the spot intensity value was quantified after subtraction of set background. Signals were normalized per array using median expression intensity.
For further analysis, the data were imported into GeneSpring (version 4.0.2, Silicon Genetics, Redwood City, CA) by Excel (Microsoft) spreadsheet formatted as a tab-delimited text file and ratio measures of AMPH-treated to saline-treated control were generated. A difference was considered eligible for further consideration if the ratio was >1.8 or <0.55 in two consecutive time points in both hybridization experiments in either WT or SOD-tg animals. Genes similarly regulated in both genotypes were excluded from the analysis. A hierarchical cluster analysis with standard correlation 0.95 and distance 0.1 (dendrogram) of the expression measure was generated using GeneSpring software (26)
.
Quantitative real-time RT-PCR
Real-time quantitative RT-PCR with gene-specific Custom Atlas Array primers obtained from BD Biosciences Clontech was used to confirm some of the results obtained with cDNA array. Total RNA (1 µg) was reversed transcribed with the poly dT primer using Advantage RT for PCR kit (BD Biosciences Clontech). Real-time quantitative RT-PCR was performed using LightCycler (Roche, Indianapolis, IN) and FastStart DNA master SYBR Green I ready-to-use PCR mix (Roche) according to the manufacturer’s protocol. cDNA was amplified in 20 µL total volume PCR reaction mixture with specific primers for c-jun, junB, c-fos, Fra2, heat shock cognate 70 (HSC70), heat shock protein 110 (HSP110), activin A, macrophage colony-stimulating factor (M-CSF), and ß-actin cDNAs. The sequences of the primers are given in Table 1
. The results are analyzed in real-time on the provided program of the LightCycler. Expression of each gene was normalized using values obtained for ß-actin.
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RESULTS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONCONCLUSIONREFERENCES |
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, 9)
. In contrast, SOD-tg mice do not develop hyperthermia after AMPH treatment and show significant attenuation in the drug-induced neurotoxicity (8)
. The levels of AMPH were comparable in the two genotypes (8)
. Gene expression changes in the striata of these animals were compared to controls treated with saline. To ensure the reliability of the data, all hybridization experiments were done in duplicate (two independent pools of mRNAs; two sets of microarray membranes were used). Only gene expression changes observed consistently in both arrays were further analyzed. To select genes for future analysis, we used the criteria of 1.8-fold changes in gene expression at two consecutive time points after AMPH treatment in either of the two genotypes. Genes similarly regulated in both genotypes were excluded from further analysis as they were not thought to be involved in the superoxide-mediated neurotoxic effects of the drug.
cDNA array findings
Of 1176 genes detected, 42 were differentially regulated in WT and SOD-tg mice. Of those, 37 were consistently affected in WT but not SOD-tg mice, whereas 5 were changed in SOD-tg but not in WT animals. Figure 1
shows a scatter plot of the 42 genes affected by AMPH in the two genotypes. The scatter shows the relationship in baseline gene expression between the two groups of mice. The majority of the genes had similar expression at baseline. However, three genes showed 1.8-fold higher expression in WT than in SOD-tg mice. Those genes include signal transducer and activator of transcription 4 (STAT4) and adenosine A2b receptor (ARA2b), which belong to intra/extracellular signaling pathways, as well as cytochrome P450 IIF2 (CYP2F2), which participates in xenobiotic metabolism (Table 2
). These differences in the baseline expression of these genes may be due in part to the fact ROS are known to play physiological roles in cell signaling (27)
.
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Using hierarchical cluster analysis (GeneSpring, Silicon Genetics), the AMPH-regulated genes were profiled based on the similarity between their temporal expression patterns (Fig. 2
). A dendrogram constructed during the clustering algorithm is shown on the left of Fig. 2
and describes the relationship between the genes. Because genes with similar patterns of expression in response to AMPH are grouped together by common branches of the dendrogram (see ref 28
for a more extensive discussion), we were able to further divide the large cluster into five main subclusters, which are described in detail below. These genes could be grouped into functional classes (Table 2)
. Table 2
provides fold increases in gene expression in AMPH- over saline-treated WT and SOD-tg animals and their GenBank accession numbers.
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Cluster A (Fig. 2)
consists of 12 genes that showed overall consistent increased expression in WT mice 30 min to 4 h after drug treatment, then returned to control values at 8–24 h. These genes show no AMPH-induced differences from control values in SOD-tg mice. This list includes junB, which belongs to the AP-1 family of transcription factors (22)
. Some members of this cluster, such as HSC70 and HSP110, are involved in response to heat, toxins, ischemia, and other stressors (29)
. Moreover, M-CSF (30)
and interleukin 10 (IL-10) (31)
are involved in microglial immune responses to neuronal damage. Others are occludin and N-cadherin, which code for cell adhesion molecules, and p18-INK4C and BUB1, involved in cell cycle regulation.
The 10 genes that form cluster B showed increased expression in the WT mice at 30 min to 2 h and returned to control values by 8–24 h. In SOD-tg mice, those genes had smaller increases that did not meet the 1.8 exclusion criteria. Some of these genes represent growth factors and cytokines that participate in the response of the brain to injury. These include fibroblast growth factor 8 (FGF8), FGF10, FGF15, and activin A. Other genes of interest are c-fos, Fra2, and c-jun, all members of the AP-1 family of transcription factors (22)
. The AMPH-induced changes in the AP-1 family in WT mice are consistent with data from other investigators (17
, 19
, 20)
.
Cluster C shows a group of genes that exhibit up-regulation in WT mice at 8 and 16 h after AMPH treatment. Expression of these genes was not different from control levels in SOD-tg mice. These include glutathione S-transferase 
2 (GSTA2) and monoamine oxidase type B (see Table 2
for classification). The somewhat delayed changes in the expression suggest they might be involved in secondary responses of the organism to AMPH-induced superoxide production in the brain. Cluster D contains 6 genes that show down-regulation at 2 and 4 h after treatment and return to basal levels at 8, 16, and 24 h in WT mice. Overall, they show no differences from baseline expression in SOD-tg mice. This list includes genes that code for CYP2F2 and cytochrome P450 VIIIB1 (CYP8B1), which are involved in xenobiotic metabolism and are members of a class of genes that have been shown to be down-regulated by oxidative stress (32)
. The apoptosis-associated protein TNF--induced protein 3 (TNFAIP3) and other genes involved in intra/extracellular signaling also belong in this cluster (see Table 2
). Cluster E consists of five genes that are up-regulated in SOD-tg mice 30 min to 4 h after AMPH injections. They show a tendency to be down-regulated in WT mice (see Fig. 2
). Among those are genes that code for transcription factors A-MYB and activating transcription factor 1 (ATF1), and the growth factor bone morphogenetic protein 4 (BMP4). Other genes are STAT4 and talin, which are known to be involved in intra/extracellular signaling and regulation of cytoskeleton, respectively. They might participate in the protection observed in the SOD-tg mice (8)
.
Quantitative RT-PCR analysis
To confirm some of the cDNA array data, real-time RT-PCR analyses of c-jun, junB, c-fos, Fra2, activin A, M-CSF, HSC70, and HSP110 were performed in WT and SOD-tg mice using a time course similar to that used for the array analyses. As shown in Fig. 3
, AMPH-induced expression profiles of these genes in WT and SOD-tg mice were similar to those obtained after cDNA array hybridization. AMPH caused significant biphasic induction of c-jun mRNA in WT and SOD-tg mice (Fig. 3A
). However, c-jun expression was significantly higher and lasted longer (up to+110% at 1–4 h and +101% at 8 h) in WT than in SOD-tg mice (+70% at 30 min-1 h,+59% at 8 h). The effects of the drug on the expression of junB in WT mice, which increased (+81%) at 30 min-4 h after treatment, was completely blocked in the striatum of SOD-tg mice (Fig. 3B
), thus suggesting a direct role of superoxide radicals in the AMPH-induced junB expression. Expression of c-fos mRNA showed different profiles in the two genotypes. In WT mice, AMPH resulted in very early increases (+239%) in c-fos mRNA at 30 min-4 h, with gradual decreases reaching -44% at 24 h after treatment (Fig. 3C
). In contrast, SOD-tg mice showed biphasic responses in the expression of c-fos, with early increases at 30 min to 2 h (+92%) significantly lower than in WT mice. This was followed by a second but smaller peak at 8–16 h (+60%) that was not apparent in WT mice. AMPH-induced expression of Fra2 in WT mice had a profile similar to that of c-fos: early increases at 30 min-2 h (+82%) with gradual decreases and significant reduction (-45%) at 24 h (Fig. 3D
). However, SOD-tg mice showed only very brief (30 min-1 h) increases (+58%) in Fra2 expression.
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Activin A mRNA was dramatically increased in WT mice, reaching its peak (+474%) at 1 h. The values returned to control levels 8 h after AMPH (Fig. 3E
). A similar profile of changes of smaller magnitude (+217%) occurred in SOD-tg mice. AMPH caused significant increases in M-CSF transcript levels in WT mice 4–16 h after treatment, with a maximal increase +123% at 8 h (Fig. 3F
). In SOD-tg mice, this induction was significantly lower (+71%) and shorter (only at 8 h) than in non-tg animals. HSC70 mRNA showed significant AMPH-induced increases (+85%) at 30 min to 4 h in WT, but its levels were not affected in SOD-tg mice (Fig. 3G
). As shown in Fig. 3H
, AMPH administration resulted in long-lasting (1–16 h) increases (+175%) in HSP110 mRNA in WT mice but showed biphasic responses in SOD-tg mice, reaching a large peak at 2 h (+177%) and a smaller one at 8 h (+48%) after drug administration.
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DISCUSSION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONCONCLUSIONREFERENCES |
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, 15)
. These studies have suggested that oxidative mechanisms might play important roles in stimulant-induced neurodegeneration. As a step toward dissecting these pathways further, we combined cDNA array and genetic approaches by assessing AMPH-induced changes in transcript levels in SOD-tg mice that have been shown to be protected against AMPH toxicity (8)
. To compile a list of genes that were consistently affected by AMPH, we used stringent criteria and selected for analysis only genes with > 1.8-fold induction or repression in at least two consecutive time points in duplicate experiments. Using ‘subtractive’ cDNA array approaches (by eliminating from consideration the genes whose expression changed at least 1.8-fold when AMPH is administered to SOD-tg mice), we were able to identify 37 genes that exhibit superoxide-mediated responses. The expression of these genes is indeed likely to be mediated by AMPH-induced generation of superoxide radicals because of their differential expression in the two genotypes and because AMPH shows a similar time course of entry and reaches similar levels in the brains of these two groups of mice (8)
, thus eliminating the possibility of differential pharmacokinetics of the drug between the two genotypes. These 37 genes encode for transcription factors, cytokines and chemokines, heat shock proteins, cytoskeleton/motility proteins, cell adhesion molecules, as well as proteins involved in cell cycle, intra/extracellular signaling pathways, and xenobiotic metabolism. In contrast, only five genes were affected by AMPH in SOD-tg but not in WT mice. Those genes belong to classes of transcription factors, growth factors, and cytoskeleton/motility proteins. In what follows, we describe possible superoxide-dependent scenarios that might account for the long-term changes observed in the striatum after toxic doses of this stimulant.
AMPH causes regulation of transcription factors
As stated above, studies on the mechanisms underlying the neurotoxic effects of AMPH and its substituted analogs had led to the conclusion that oxidative stress might play important roles in the degeneration of striatal systems caused by these drugs (for a review, see ref 15
). This is supported by the demonstration that hydroxyl (14)
and superoxide (8)
radicals are involved in AMPH neurotoxicity. Because ROS such as hydroxyl and superoxide radicals can induce the expression of many genes via their regulation of the AP-1 family of transcription factors (16)
, the presently observed early AMPH-induced up-regulation of the AP-1 members, c-jun, junB, c-fos and Fra2 in WT mice may be due in part to AMPH-induced ROS formation. This idea is supported by our observations that mice overexpressing Cu/Zn SOD enzyme in their brains show no increase in junB and decreased activation of c-jun, c-fos, and Fra2 in response to AMPH administration. Although these data identify superoxides as potential mediators of AMPH-induced AP-1 expression, the observation that only partial attenuation in the expression of c-fos, Fra2, and c-jun mRNA occurred in SOD-tg mice suggests that AMPH may be causing these effects through both superoxide-dependent and -independent pathways. Indeed, another possibility for the AMPH-induced activation of those transcription factors includes stimulation of DA D1 receptors, because the DA D1 antagonist SCH 23390 attenuates AMPH-induced striatal AP-1 activation (17)
. Last, AMPH may interact directly with the nucleus in a fashion similar to what was recently described in the case of methamphetamine (33)
.
In our study, AMPH caused biphasic increase in the expression of c-jun in both strains, although c-jun overexpression in WT mice was significantly higher and lasted longer than that observed in SOD-tg animals. The persistent increases observed in c-jun transcript levels in non-tg mice suggest that c-Jun might participate in AMPH-induced toxicity. Stimulation of c-Jun activity in response to oxidative stimuli may involve at least two distinct steps, which consist of early activation of endogenous c-Jun protein by increases in its phosphorylation with a secondary autoinduction of its own transcription via a positive autoregulatory loop (34)
. These AMPH-induced increases observed in c-jun transcript levels are consistent with the idea that c-Jun may be a positive modulator of cell death (35)
. For example, overexpression of c-Jun is sufficient to induce apoptosis in endothelial cells (36)
and sympathetic neurons (37)
whereas microinjection of an antibody specific for c-Jun inhibited cell death caused by nerve growth factor deprivation (38)
. In addition to a proapoptotic role in endothelial cells and sympathetic neurons, the c-Jun transduction pathway has been shown to promote apoptosis of striatal neurons treated with toxic doses of DA (39
, 40)
. The increased resistance to kainic acid-induced cell death in the hippocampus of c-JunAA knockin mice bearing a mutant c-jun gene (41)
supports this proposition. JunB, whose AMPH-induced activation was completely blocked in SOD-tg mice, might be a member of AMPH-induced protoxic cascades because inactivation of JunB in myeloma cells protects against cell death caused by withdrawal of survival factors (42)
.
In addition to triggering protoxic mechanisms, AMPH administration causes increases in the levels of transcripts thought to participate in protective mechanisms. For example, c-fos, which is activated early after AMPH treatment in WT mice and shows biphasic activation in SOD-tg animals, is induced in CNS neurons by nontraumatic stimuli (i.e., learning) and traumatic stimuli (i.e., quinolinic acid administration) (for review, see ref 22
). Several studies using c-fos-deficient mouse fibroblasts have documented protective roles of c-Fos against cytostatic drugs, UV light, and ionizing radiation (43
, 44)
. The observations that c-fos knockout mice are more susceptible to neurotoxic effects of methamphetamine (45)
support this protective proposition for c-Fos. It is thus possible that the secondary increase in c-fos expression observed in SOD-tg, but not in WT mice, might contribute to the protection against AMPH neurotoxicity observed in these SOD-tg mice (8)
. Although the basis for the second peak in c-fos transcript levels in SOD-tg mice is not clear, it might be related to changes observed in ATF1, a member of the CREB/ATF transcription factor family (22)
. ATF1 was indeed up-regulated at 30 min-4 h after AMPH administration in SOD-tg but not in WT mice. This line of reasoning is supported by observations that ATF1 participates in the mediation of the protective effects of iron chelators against oxidative stress-induced apoptosis in cortical neurons (46)
and by the report that ATF1 can regulate c-fos expression in the brain (47)
. When taken together, our findings suggest that AMPH-induced overproduction of superoxide radicals might mediate the increased transcription of several members of the AP-1 family of genes. These in turn might play either protoxic or protective roles in the brain’s multifaceted responses to this illicit stimulant.
AMPH causes activation of growth factors and heat shock proteins
Several lines of evidence indicate that neuronal damage is associated with initiation and the elaboration of neuroprotective signaling pathways that function to attenuate damage, prevent apoptosis, and/or increase functional recovery after brain injury (48
, 49)
. These include increased synthesis and release of growth factors and cytokines such as the neuronal protein activin A, which is a protective component of the early CNS response to injury inflicted by kainic acid, hypoxia/ischemia, and mechanical irritation (50)
. Activin A protects DA neurons in vitro from MPP+-induced cellular damage (51)
and rat striatal neuronal cell bodies against the toxic effects of quinolinic acid (52)
. Thus, it can be concluded that the AMPH-induced greater activation of activin A in WT mice might constitute a partial response to the oxidative load generated by administration of this drug.
Another AMPH-responsive superoxide-mediated gene is M-CSF, which is induced in neurons during the early phase after focal brain injury (30)
. M-CSF is thought to be one of the most important inducers of proliferation and migration of activated microglia to the site of brain injuries (48)
. The greater induction of M-CSF in the WT mice may serve to induce the proliferation of microglial cells that participate in the elimination of cells damaged by AMPH. Consistent with this reasoning are studies using op/op mice that carry a mutation in the coding region for M-CSF, which show that M-CSF is involved in neuronal protection against ischemic injury and is required for microglial response to neuronal damage (53)
.
Additional genes whose transcript levels are induced by AMPH code for heat shock proteins that are ROS responsive and are known to protect cells against oxidative damage (29
, 54)
and stress-induced cell death (55)
. Activation of HSC70 and HSP110 in WT mice may work concomitantly with other trophic substances in an attempt to protect against AMPH-induced damage because they have been shown to prevent the formation of abnormal protein conformation (56
, 57)
. Recent studies have shown that in addition to its protein binding properties, HSP110 preferentially binds AU-rich regions of RNA in vitro, thus suggesting that HSP110 may have in vivo RNA chaperoning properties, perhaps through the regulation of mRNA degradation and/or translation (58)
. Thus, AMPH-induced increases in the transcripts of these chaperones may result in the stabilization of mRNAs, which are important for the restoration of normal neuronal functions during and/or subsequent to AMPH assaults on the brain.
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CONCLUSION |
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Received for publication October 3, 2001.
Revision received March 21, 2002.
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| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
