The longitudinal behavioral effects of acute exposure to galactic cosmic radiation in female C57BL/6J mice: implications for deep space missions, female crews, and potential antioxidant countermeasures.

Galactic cosmic radiation (GCR) is an unavoidable risk to astronauts that may affect mission success. Male rodents exposed to 33-beam-GCR (33-GCR) show short-term cognitive deficits but reports on female rodents and long-term assessment is lacking. Here we asked: What are the longitudinal behavioral effects of 33-GCR on female mice? Also, can an antioxidant/anti-inflammatory compound mitigate the impact of 33-GCR? Mature (6-month-old) C57BL/6J female mice received the antioxidant CDDO-EA (400 µg/g of food) or a control diet (vehicle, Veh) for 5 days and either Sham-irradiation (IRR) or whole-body 33-GCR (0.75Gy) on the 4th day. Three-months post-IRR, mice underwent two touchscreen-platform tests: 1) location discrimination reversal (which tests behavior pattern separation and cognitive flexibility, two abilities reliant on the dentate gyrus) and 2) stimulus-response learning/extinction. Mice then underwent arena-based behavior tests (e.g. open field, 3-chamber social interaction). At the experiment end (14.25-month post-IRR), neurogenesis was assessed (doublecortin-immunoreactive [DCX+] dentate gyrus neurons). Female mice exposed to Veh/Sham vs. Veh/33-GCR had similar pattern separation (% correct to 1st reversal). There were two effects of diet: CDDO-EA/Sham and CDDO-EA/33-GCR mice had better pattern separation vs. their respective control groups (Veh/Sham, Veh/33-GCR), and CDDO-EA/33-GCR mice had better cognitive flexibility (reversal number) vs. Veh/33-GCR mice. Notably, one radiation effect/CDDO-EA countereffect also emerged: Veh/33-GCR mice had worse stimulus-response learning (days to completion) vs. all other groups, including CDDO-EA/33-GCR mice. In general, all mice show normal anxiety-like behavior, exploration, and habituation to novel environments. There was also a change in neurogenesis: Veh/33-GCR mice had fewer DCX+ dentate gyrus immature neurons vs. Veh/Sham mice. Our study implies space radiation is a risk to a female crew's longitudinal mission-relevant cognitive processes and CDDO-EA is a potential dietary countermeasure for space-radiation CNS risks.

The P7C3 class of neuroprotective compounds exerts antidepressant efficacy in mice by increasing hippocampal neurogenesis.

Augmenting hippocampal neurogenesis represents a potential new strategy for treating depression. Here we test this possibility by comparing hippocampal neurogenesis in depression-prone ghrelin receptor (Ghsr)-null mice to that in wild-type littermates and by determining the antidepressant efficacy of the P7C3 class of neuroprotective compounds. Exposure of Ghsr-null mice to chronic social defeat stress (CSDS) elicits more severe depressive-like behavior than in CSDS-exposed wild-type littermates, and exposure of Ghsr-null mice to 60% caloric restriction fails to elicit antidepressant-like behavior. CSDS resulted in more severely reduced cell proliferation and survival in the ventral dentate gyrus (DG) subgranular zone of Ghsr-null mice than in that of wild-type littermates. Also, caloric restriction increased apoptosis of DG subgranular zone cells in Ghsr-null mice, although it had the opposite effect in wild-type littermates. Systemic treatment with P7C3 during CSDS increased survival of proliferating DG cells, which ultimately developed into mature (NeuN+) neurons. Notably, P7C3 exerted a potent antidepressant-like effect in Ghsr-null mice exposed to either CSDS or caloric restriction, while the more highly active analog P7C3-A20 also exerted an antidepressant-like effect in wild-type littermates. Focal ablation of hippocampal stem cells with radiation eliminated this antidepressant effect, further attributing the P7C3 class antidepressant effect to its neuroprotective properties and resultant augmentation of hippocampal neurogenesis. Finally, P7C3-A20 demonstrated greater proneurogenic efficacy than a wide spectrum of currently marketed antidepressant drugs. Taken together, our data confirm the role of aberrant hippocampal neurogenesis in the etiology of depression and suggest that the neuroprotective P7C3-compounds represent a novel strategy for treating patients with this disease.

Resistance to change and vulnerability to stress: autistic-like features of GAP43-deficient mice.

There is an urgent need for animal models of autism spectrum disorder (ASD) to understand the underlying pathology and facilitate development and testing of new treatments. The synaptic growth-associated protein-43 (GAP43) has recently been identified as an autism candidate gene of interest. Our previous studies show many brain abnormalities in mice lacking one allele for GAP43 [GAP43 (+/-)] that are consistent with the disordered connectivity theory of ASD. Thus, we hypothesized that GAP43 (+/-) mice would show at least some autistic-like behaviors. We found that GAP43 (+/-) mice, relative to wild-type (+/+) littermates, displayed resistance to change, consistent with one of the diagnostic criteria for ASD. GAP43 (+/-) mice also displayed stress-induced behavioral withdrawal and anxiety, as seen in many autistic individuals. In addition, both GAP43 (+/-) mice and (+/+) littermates showed low social approach and lack of preference for social novelty, consistent with another diagnostic criterion for ASD. This low sociability is likely because of the mixed C57BL/6J 129S3/SvImJ background. We conclude that GAP43 deficiency leads to the development of a subset of autistic-like behaviors. As these behaviors occur in a mouse that displays disordered connectivity, we propose that future anatomical and functional studies in this mouse may help uncover underlying mechanisms for these specific behaviors. Strain-specific low sociability may be advantageous in these studies, creating a more autistic-like environment for study of the GAP43-mediated deficits of resistance to change and vulnerability to stress.

Effect of chronic morphine on the dentate gyrus neurogenic microenvironment.

Opiates, such as morphine, decrease neurogenesis in the postnatal hippocampal subgranular zone (SGZ) by inhibiting progenitor proliferation and maturation. However, it is not known how morphine influences the growth factors and vasculature that encompass the neurogenic SGZ microenvironment. We examined morphine's effect on pro- and anti-proliferative factors in the dentate gyrus (DG; Experiment 1) as well as the DG neurovasculature itself (Experiment 2). For Experiment 1, mice were implanted with subcutaneous sham or morphine pellets (0 and 48 h) and were decapitated 24 or 96 h later. One brain hemisphere was postfixed to examine proliferation by immunohistochemistry, and a DG-enriched sample was dissected from the other hemisphere to examine the neurogenic microenvironment via immunoblotting for known pro- and anti-proliferative factors. Consistent with previous results, morphine decreased the number of proliferating cells in the SGZ, as the number of Ki67-immunoreactive (IR) cells was decreased at 96 h. Morphine did not alter DG levels of the pro-proliferative factor brain-derived neurotrophic factor, anti-proliferative factor interleukin-1 beta, or their receptors TrkB and IL1R1 at either time point. However, morphine increased the pro-proliferative factor vascular endothelial growth factor (VEGF) at 96 h. Given that VEGF is also a potent angiogenic factor, Experiment 2 examined whether the morphine-induced increase in VEGF correlated with altered DG neurovasculature. Mice were implanted with morphine pellets as in Experiment 1, and 2 h before perfusion (24 or 96 h) were administered bromodeoxyuridine (BrdU; intraperitoneal, 150 mg/kg). Tissue was co-stained for BrdU and the endothelial cell marker endoglin to enable examination of DG vessels and proximity of BrdU-IR cells to endoglin-IR vessels. At 96 h, endoglin-IR vessel area and perimeter were increased, but proximity of BrdU-IR cells to endoglin-IR vessels remained unchanged. These data suggest that following chronic morphine exposure, factors within the neurogenic microenvironment are maintained or upregulated to compensate for decreased SGZ proliferation.

Time course of morphine's effects on adult hippocampal subgranular zone reveals preferential inhibition of cells in S phase of the cell cycle and a subpopulation of immature neurons.

Opiates, such as morphine, decrease neurogenesis in the adult hippocampal subgranular zone (SGZ), raising the possibility that decreased neurogenesis contributes to opiate-induced cognitive deficits. However, there is an incomplete understanding of how alterations in cell cycle progression and progenitor maturation contribute to this decrease. The present study examined how morphine regulates progenitor cell cycle, cell death and immature SGZ neurons (experiment 1) as well as the progression of SGZ progenitors through key stages of maturation (experiment 2). In experiment 1, mice received sham or morphine pellets (s.c., 0 and 48 h) and bromodeoxyuridine (BrdU) 2 h prior to sacrifice (24, 72 or 96 h). Morphine decreased both the number of S phase and total cycling cells, as there were fewer cells immunoreactive (IR) for the S phase marker BrdU and the cell cycle marker Ki67. The percentage of Ki67-IR cells that were BrdU-IR was decreased after 24 but not 96 h of morphine, suggesting a disproportionate effect on S phase cells relative to all cycling cells at this time point. Cell death (activated caspase-3 counts) was increased after 24 but not 96 h. In experiment 2, nestin-green fluorescent protein (GFP) mice given BrdU 1 day prior to morphine or sham surgery (0 and 48 h, sacrifice 96 h) had fewer Ki67-IR cells, but no change in BrdU-IR cell number, suggesting that this population of BrdU-IR cells was less sensitive to morphine. Interestingly, examination of key stages of progenitor cell maturation revealed that morphine increased the percent of BrdU-IR cells that were type 2b and decreased the percent that were immature neurons. These data suggest that chronic morphine decreases SGZ neurogenesis by inhibiting dividing cells, particularly those in S phase, and progenitor cell progression to a more mature neuronal stage.

Morphine blood levels, dependence, and regulation of hippocampal subgranular zone proliferation rely on administration paradigm.

Chronic morphine, administered via s.c. pellet, decreases the number of proliferating cells in the dentate gyrus subgranular zone (SGZ) in both rats and mice. This robust morphine-induced decrease could be used to better understand mechanisms regulating adult hippocampal neurogenesis, as well as to explore the relationship between neurogenesis and drug dependence, withdrawal, and relapse behaviors. Such research would benefit enormously from identifying a route of morphine administration that produces addiction-relevant blood levels of morphine, results in a high degree of dependence, translates to both rat and mouse, and is free of the behavioral confounds of s.c. pellets. Therefore, we examined a classic chronic morphine pellet paradigm (two s.c. pellets over 5 days) versus three chronic morphine injection paradigms (escalating dose i.p. injections over 2, 5, or 10 days) for their effect in adult male C57BL/6J mice. We assessed blood morphine levels, SGZ proliferation, and drug dependence as assessed by tolerance to locomotion sensitization and naloxone-precipitated withdrawal. The pellet paradigm produced high and relatively stable blood levels of morphine, a high degree of dependence, and a significant decrease in SGZ proliferation. In contrast, the three injection paradigms produced transient spikes in morphine blood levels, significantly less dependence than the pellet paradigm, and no significant decrease in SGZ proliferation. These data show that regulation of mouse SGZ proliferation requires high and relatively stable blood levels of morphine, and provide critical knowledge for the design of future studies to probe the relationship between addiction and neurogenesis.

Determination of key aspects of precursor cell proliferation, cell cycle length and kinetics in the adult mouse subgranular zone.

Neurogenesis studies on the adult mouse hippocampal subgranular zone (SGZ) typically report increases or decreases in proliferation. However, key information is lacking about these proliferating SGZ precursors, from the fundamental--what dose of bromodeoxyuridine (BrdU) is appropriate for labeling all S phase cells?--to the detailed--what are the kinetics of BrdU-labeled cells and their progeny? To address these questions, adult C57BL/6J mice were injected with BrdU and BrdU-immunoreactive (IR) cells were quantified. Initial experiments with a range of BrdU doses (25-500 mg/kg) suggested that 150 mg/kg labels all actively dividing precursors in the mouse SGZ. Experiments using a saturating dose of BrdU suggested BrdU bioavailability is less than 15 min, notably shorter than in the developing mouse brain. We next explored precursor division and maturation by tracking the number of BrdU-IR cells and colabeling of BrdU with other cell cycle proteins from 15 min to 30 days after BrdU. We found that BrdU and the Gap2 and mitosis (G2/M) phase protein pHisH3 maximally colocalized 8 h after BrdU, indicating that the mouse SGZ precursor cell cycle length is 14 h. In addition, triple labeling with BrdU and proliferating cell nuclear antigen (PCNA) and Ki-67 showed that BrdU-IR precursors and/or their progeny express these endogenous cell cycle proteins up to 4 days after BrdU injection. However, the proportion of BrdU/Ki-67-IR cells declined at a greater rate than the proportion of BrdU/PCNA-IR cells. This suggests that PCNA protein is detectable long after cell cycle exit, and that reliance on PCNA may overestimate the length of time a cell remains in the cell cycle. These findings will be critical for future studies examining the regulation of SGZ precursor kinetics in adult mice, and hopefully will encourage the field to move beyond counting BrdU-IR cells to a more mechanistic analysis of adult neurogenesis.

Knockout of the mu opioid receptor enhances the survival of adult-generated hippocampal granule cell neurons.

Recent evidence suggests that mu opioid receptors (MOR) are key regulators of hippocampal structure and function. For example, exogenous MOR agonists morphine and heroin negatively impact hippocampal function and decrease adult hippocampal neurogenesis. Here we explored the role of MOR in the birth and survival of hippocampal progenitor cells by examining adult neurogenesis in mice that lack MOR. Adult male mice lacking exon 1 of MOR were injected with the S phase marker bromodeoxyuridine (BrdU) and killed either 2 hours or 4 weeks later to evaluate proliferating and surviving BrdU-immunoreactive (IR) cells, respectively, in the adult hippocampal granule cell layer. Wild-type (WT), heterozygote, and homozygote mice did not differ in the number of BrdU-IR cells at a proliferation time point. However, 4 weeks after BrdU injection, heterozygote and homozygote mice had 57% and 54% more surviving BrdU-IR cells in the hippocampal granule cell layer as compared with WT mice. A decrease in apoptosis in the heterozygote and homozygote mice did not account for the difference in number of surviving BrdU-IR cells since there were no alterations in number of pyknotic, terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL)-positive, or activated caspase 3-IR cells compared with WT. In concordance with the increased numbers of granule cells maturing into neurons, heterozygote and homozygote mice had larger hippocampal granule cell layers and increased numbers of granule cells. These findings indicate that MOR may play a role in regulating progenitor cell survival and more generally encourage further exploration of how MOR activation can influence hippocampal structure and function.

[Neurogenesis. Relevance for pathophysiology and pharmacotherapy of psychiatric diseases]. / Neuroneogenese. Relevanz für Pathophysiologie und Pharmakotherapie psychiatrischer Erkrankungen.

Research into neurogenesis, i.e., the growth of new neurons in the adult brain, is leaving the area of pure basic science and gaining relevance for clinical disciplines such as psychopharmacology and molecular psychiatry. Neurogenesis is proposed to play a crucial role in psychiatric disorders which exhibit degenerative alterations, neural maldevelopment, and changes in neural plasticity as potentially important pathophysiological factors. Especially in dementia, drug addiction, and schizophrenic and affective psychoses, disruption of adult neurogenesis could thus represent a considerable pathogenetic element. Interestingly, several psychotropic drugs (e.g., antidepressants, atypical antipsychotics) are able to modify neurogenesis significantly. Further elucidation of the importance and implications of neurogenesis may concomitantly result in better understanding of the etiopathogenesis of mental disorders and increased knowledge of the mechanisms of action of psychotropic substances. Furthermore, this may support the development of promising innovative therapeutic approaches in clinical practice.

Dopamine receptor regulating factor, DRRF: a zinc finger transcription factor.

Dopamine receptor genes are under complex transcription control, determining their unique regional distribution in the brain. We describe here a zinc finger type transcription factor, designated dopamine receptor regulating factor (DRRF), which binds to GC and GT boxes in the D1A and D2 dopamine receptor promoters and effectively displaces Sp1 and Sp3 from these sequences. Consequently, DRRF can modulate the activity of these dopamine receptor promoters. Highest DRRF mRNA levels are found in brain with a specific regional distribution including olfactory bulb and tubercle, nucleus accumbens, striatum, hippocampus, amygdala, and frontal cortex. Many of these brain regions also express abundant levels of various dopamine receptors. In vivo, DRRF itself can be regulated by manipulations of dopaminergic transmission. Mice treated with drugs that increase extracellular striatal dopamine levels (cocaine), block dopamine receptors (haloperidol), or destroy dopamine terminals (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine) show significant alterations in DRRF mRNA. The latter observations provide a basis for dopamine receptor regulation after these manipulations. We conclude that DRRF is important for modulating dopaminergic transmission in the brain.

Regulation of GFRalpha-1 and GFRalpha-2 mRNAs in rat brain by electroconvulsive seizure.

The influence of both acute and chronic electroconvulsive seizure (ECS) or antidepressant drug treatments on expression of mRNAs encoding glial cell line-derived neurotrophic factor (GDNF) and its receptors, GFRalpha-1, GFRalpha-2, and c-Ret proto-oncogene (RET) in the rat hippocampus was examined by in situ hybridization. Two hours after acute ECS, levels of GFRalpha-1 mRNA in the dentate gyrus were significantly increased. This increase peaked to nearly 3-fold at 6 h after acute ECS and returned to basal levels 24 h after treatment. Chronic (once daily for 10 days) ECS significantly increased the expression of GFRalpha-1 mRNA nearly 5-fold after the last treatment. Levels of GFRalpha-2 mRNA in the dentate gyrus were also significantly increased by acute and chronic ECS, although this effect was less than that observed for GFRalpha-1. Maximum induction of GFRalpha-2 was 30% and 70% compared to sham in response to acute or chronic ECS, respectively. Levels of GDNF and RET mRNAs were not significantly changed following either acute or chronic ECS treatment at the time points examined. Chronic (14 days) administration of different classes of antidepressant drugs, including tranylcypromine, desipramine, or fluoxetine, did not significantly affect the GDNF, GFRalpha-1, GFRalpha-2, or RET mRNA levels in CA1, CA3, and dentate gyrus areas of hippocampus. The results demonstrate that acute ECS increases the expression of GFRalpha-1 and GFRalpha-2 and that these effects are enhanced by chronic ECS. The results also imply that regulation of the binding components of GDNF receptor complex may mediate the adaptive responses of the GDNF system to acute and chronic stimulation.

Cloning and localization of the hyperpolarization-activated cyclic nucleotide-gated channel family in rat brain.

Rhythmic firing in brain and heart is mediated by pacemaker channels that are activated by hyperpolarization and regulated directly by cyclic nucleotides. Recent work has identified a new gene family that encodes such channels, which are termed hyperpolarization-activated, cyclic nucleotide-gated (HCN) channels. In this study, we report the molecular cloning and localization by in situ hybridization of HCN1-4 in adult rat brain. The rat HCN1-4 clones show high homology to the deduced amino acid sequence of the mouse channels (>97% identity). The mRNA expression of the four channels in adult brain was evaluated in a systematic manner from the olfactory bulb to lower brain stem nuclei. Each mRNA demonstrated a unique pattern of distribution. HCN1 expression is highly enriched in cerebral cortex, hippocampus, cerebellum, and facial motor nucleus; HCN2 is highly abundant in mamillary bodies, pontine nucleus, ventral cochlear nucleus, and nucleus of the trapezoid body; HCN3 expression is most pronounced in supraoptic nucleus of hypothalamus; and HCN4 expression is most abundant in medial habenula and anterior and principal relay nuclei of the thalamus. These variations in regional specificity of HCN channels could generate important differences in neuronal pacemaker activity across brain systems.

Opiates inhibit neurogenesis in the adult rat hippocampus.

Recent work implicates regulation of neurogenesis as a form of plasticity in the adult rat hippocampus. Given the known effects of opiates such as morphine and heroin on hippocampal function, we examined opiate regulation of neurogenesis in this brain region. Chronic administration of morphine decreased neurogenesis by 42% in the adult rat hippocampal granule cell layer. A similar effect was seen in rats after chronic self-administration of heroin. Opiate regulation of neurogenesis was not mediated by changes in circulating levels of glucocorticoids, because similar effects were seen in rats that received adrenalectomy and corticosterone replacement. These findings suggest that opiate regulation of neurogenesis in the adult rat hippocampus may be one mechanism by which drug exposure influences hippocampal function.

Role for GDNF in biochemical and behavioral adaptations to drugs of abuse.

The present study examined a role for GDNF in adaptations to drugs of abuse. Infusion of GDNF into the ventral tegmental area (VTA), a dopaminergic brain region important for addiction, blocks certain biochemical adaptations to chronic cocaine or morphine as well as the rewarding effects of cocaine. Conversely, responses to cocaine are enhanced in rats by intra-VTA infusion of an anti-GDNF antibody and in mice heterozygous for a null mutation in the GDNF gene. Chronic morphine or cocaine exposure decreases levels of phosphoRet, the protein kinase that mediates GDNF signaling, in the VTA. Together, these results suggest a feedback loop, whereby drugs of abuse decrease signaling through endogenous GDNF pathways in the VTA, which then increases the behavioral sensitivity to subsequent drug exposure.

Chronic antidepressant treatment increases neurogenesis in adult rat hippocampus.

Recent studies suggest that stress-induced atrophy and loss of hippocampal neurons may contribute to the pathophysiology of depression. The aim of this study was to investigate the effect of antidepressants on hippocampal neurogenesis in the adult rat, using the thymidine analog bromodeoxyuridine (BrdU) as a marker for dividing cells. Our studies demonstrate that chronic antidepressant treatment significantly increases the number of BrdU-labeled cells in the dentate gyrus and hilus of the hippocampus. Administration of several different classes of antidepressant, but not non-antidepressant, agents was found to increase BrdU-labeled cell number, indicating that this is a common and selective action of antidepressants. In addition, upregulation of the number of BrdU-labeled cells is observed after chronic, but not acute, treatment, consistent with the time course for the therapeutic action of antidepressants. Additional studies demonstrated that antidepressant treatment increases the proliferation of hippocampal cells and that these new cells mature and become neurons, as determined by triple labeling for BrdU and neuronal- or glial-specific markers. These findings raise the possibility that increased cell proliferation and increased neuronal number may be a mechanism by which antidepressant treatment overcomes the stress-induced atrophy and loss of hippocampal neurons and may contribute to the therapeutic actions of antidepressant treatment.

In vivo regulation of glial cell line-derived neurotrophic factor-inducible transcription factor by kainic acid.

A putative transcription factor induced in vitro by glial cell line-derived neurotrophic factor (GDNF) and transforming growth factor-beta was recently cloned and characterized [Yajima S. et al. (1997) J. Neurosci. 17, 8657-8666]. The messenger RNA of this protein, termed murine GDNF-inducible transcription factor (mGIF, hereafter referred to as GIF), is localized within cortical and hippocampal regions of brain, suggesting that GIF might be regulated by perturbations of these brain regions. In an effort to learn more about the role of GIF in vivo, we examined GIF messenger RNA in the brains of rats treated with the glutamatergic agonist kainic acid. This treatment is known to induce seizures and alter the messenger RNA expression of several growth factors, including GDNF, in several brain regions. Rats were given intraperitoneal saline (1 ml/kg) or kainic acid (15 mg/kg) and were killed at various time-points for in situ hybridization of brain sections with a GIF messenger RNA riboprobe. In saline-treated rats, GIF messenger RNA was present at low levels in cerebral cortex, hippocampus and hippocampal remnants such as the taenia tecta. Kainic acid treatment induced robust increases in GIF messenger RNA in several brain regions, including cerebral cortex, hippocampus, caudate-putamen, nucleus accumbens, and several nuclei of the amygdala and hypothalamus. Most brain regions showed the greatest increase in GIF messenger RNA 4-6 h after kainic acid administration and a return towards normal levels at 48 h. The CA3 region of hippocampus, however, showed a more rapid increase in GIF messenger RNA that was also evident 48 h after kainic acid administration. These results demonstrate that GIF messenger RNA can be regulated in vivo, and that this novel factor warrants further study as a central mediator of GDNF and perhaps other neurotrophic factors.

Methamphetamine neurotoxicity: dissociation of striatal dopamine terminal damage from parietal cortical cell body injury.

Methamphetamine (m-AMPH) administration injures both striatal dopaminergic terminals and certain nonmonoaminergic cortical neurons. Fluoro-Jade histochemistry was used to label cortical cells injured by m-AMPH in order to identify factors that contribute to the cortical cell body damage. Rats given four injections of m-AMPH (4 mg/kg) at 2-h intervals showed hyperthermia (mean = 40.0 +/- 0.10 degrees C) and increased behavioral activation relative to animals given saline (SAL). Three days later, m-AMPH-treated animals showed indices of injury to striatal DA terminals (depletion of tyrosine hydroxylase immunoreactivity) and parietal cortical cell bodies (appearance of Fluoro-Jade stained cells). Pretreatment with a dopamine (DA) D1, D2, or N-methyl-D-aspartate (NMDA) receptor antagonist, or administration of m-AMPH in a 4 degrees C environment, prevented or attenuated m-AMPH-induced hyperthermia, behavioral activation, and injury to striatal DA terminals and parietal cortical cell bodies. Animals pretreated with a DA transport inhibitor prior to m-AMPH showed hyperthermia, behavioral activation, and parietal cortical cell body injury, but they did not show striatal DA terminal injury. Pretreatment with a 5HT transport inhibitor failed to prevent m-AMPH-induced damage to striatal DA terminals or parietal cortical cell bodies. Animals given four injections of SAL in a 37 degrees C environment became hyperthermic, but showed no injury to striatal DA terminals or cortical cell bodies. The ability of the DA transport inhibitor to block m-AMPH-induced striatal DA damage, but not cortical injury, and the inability of hyperthermia alone to cause the cortical cell body injury suggests that m-AMPH-induced behavioral activation and hyperthermia may both be necessary for the subsequent parietal cortical cell body damage.

Characterizing cortical neuron injury with Fluoro-Jade labeling after a neurotoxic regimen of methamphetamine.

We used Fluoro-Jade, a recently-developed fluorescent indicator of neuronal damage, to identify neurons injured 1-21 days after repeated injections of methamphetamine (m-AMPH) or saline. The m-AMPH-treated rats showed Fluoro-Jade positive neurons in parietal cortex (layers III and IV) and had less striatal tyrosine hydroxylase immunoreactivity than did saline-injected controls. Fluoro-Jade positive neurons were greatest in number 3 days post-treatment; some fluorescent neurons displayed bud-like surface protrusions. These observations support the hypothesis that certain neocortical neurons degenerate after m-AMPH.

Striatal and cortical NMDA receptors are altered by a neurotoxic regimen of methamphetamine.

Methamphetamine (m-AMPH) treatment produces long-lasting damage to striatal and cortical monoaminergic terminals and may also injure nonmonoaminergic cortical neurons. Evidence suggests that both dopamine (DA) and glutamate (GLU) play crucial roles in producing this damage. We used quantitative autoradiography to examine [3H]mazindol ([3H]MAZ) binding to striatal DA transporters and [3H]GLU binding to N-methyl-D-aspartate (NMDA) receptors in the striatum and cortex 1 week and 1 month after a neurotoxic regimen of m-AMPH. Rats received m-AMPH (4 mg/kg) or saline (SAL) (1 ml/kg) in four s.c. injections separated by 2 h intervals. One week after m-AMPH, the ventral and lateral sectors of the striatum showed the greatest decreases in both [3H]MAZ and [3H]GLU binding, while the nucleus accumbens (NA) showed no significant decreases. One month after m-AMPH, striatal [3H]MAZ binding was still significantly decreased, while NMDA receptor binding had recovered. Surprisingly, the parietal cortex showed a m-AMPH-induced increase in NMDA receptor binding in layers II/III and IV 1 week after m-AMPH and only in layers II/III 1 month after m-AMPH. The prefrontal cortex showed no m-AMPH-induced changes in NMDA receptor binding at either time point. This is the first demonstration that a regimen of m-AMPH that results in long-lasting damage to DA terminals can alter forebrain NMDA receptor binding. Thus, repeated m-AMPH treatments may produce changes in glutamatergic transmission in selected striatal and cortical regions.

Striatal subregions are differentially vulnerable to the neurotoxic effects of methamphetamine.

Methamphetamine (m-AMPH) or saline was repeatedly administered to rats. One week later, the caudate-putamen of the m-AMPH-treated rats revealed a decrease in both [3H]mazindol-labeled dopamine uptake sites and tissue dopamine content. Moreover, the resulting pattern of decline in these measures was regionally heterogeneous. The ventral caudate-putamen displayed the greatest decrease in both [3H]mazindol binding and dopamine content while the neighboring nucleus accumbens and the dorsal caudate-putamen remained relatively intact. These results indicate a regional difference in the susceptibility of striatal dopaminergic terminals to the neurotoxic effects of methamphetamine.