Neonatal dopamine depletion induces changes in morphogenesis and gene expression in the developing cortex

Benefits of exercise on cognitive impairment in alcohol use disorder following alcohol withdrawal

Although most cognitive impairments induced by prolonged alcohol consumption tend to improve within the initial months of abstinence, there is evidence suggesting certain cognitive deficits may persist. This study aimed to investigate the impact of aerobic exercise on learning and memory in alcohol use disorder (AUD) mice following a period of abstinence from alcohol. We also sought to assess the levels of monoamine neurotransmitters in the hippocampus. To this end, we established an AUD mouse model through a two-bottle choice (sucrose fading mode and normal mode) and chronic intermittent alcohol vapor (combined with intraperitoneal injection) and randomly allocated mice into exercise groups to undergo treadmill training. Learning and memory abilities were assessed through the Morris water maze test and spontaneous activity was evaluated using the open field test. The levels of dopamine, norepinephrine, serotonin, and brain-derived neurotrophic factor in the hippocampus were quantified using enzyme-linked immunoassay (ELISA) kits. The findings reveal that after cessation of alcohol consumption, learning and memory abilities in AUD mice did not completely return to normal levels. The observed enhancement of cognitive functions in AUD mice through aerobic exercise may be attributed to restoring levels of monoamine neurotransmitters in the hippocampus, boosting brain-derived neurotrophic factor (BDNF) concentrations, and facilitating an increase in hippocampal mass. These results offer empirical evidence to support aerobic exercise as a viable therapeutic strategy to alleviate cognitive deficits associated with AUD.

Behavioral and Neuroanatomical Consequences of Cell-Type Specific Loss of Dopamine D2 Receptors in the Mouse Cerebral Cortex

Developmental dysregulation of dopamine D2 receptors (D2Rs) alters neuronal migration, differentiation, and behavior and contributes to the psychopathology of neurological and psychiatric disorders. The current study is aimed at identifying how cell-specific loss of D2Rs in the cerebral cortex may impact neurobehavioral and cellular development, in order to better understand the roles of this receptor in cortical circuit formation and brain disorders. We deleted D2R from developing cortical GABAergic interneurons (Nkx2.1-Cre) or from developing telencephalic glutamatergic neurons (Emx1-Cre). Conditional knockouts (cKO) from both lines, Drd2^fl/fl, Nkx2.1-Cre⁺ (referred to as GABA-D2R-cKO mice) or Drd2^fl/fl, Emx1-Cre⁺ (referred to as Glu-D2R-cKO mice), exhibited no differences in simple tests of anxiety-related or depression-related behaviors, or spatial or nonspatial working memory. Both GABA-D2R-cKO and Glu-D2R-cKO mice also had normal basal locomotor activity, but GABA-D2R-cKO mice expressed blunted locomotor responses to the psychotomimetic drug MK-801. GABA-D2R-cKO mice exhibited improved motor coordination on a rotarod whereas Glu-D2R-cKO mice were normal. GABA-D2R-cKO mice also exhibited spatial learning deficits without changes in reversal learning on a Barnes maze. At the cellular level, we observed an increase in PV+ cells in the frontal cortex of GABA-D2R-cKO mice and no noticeable changes in Glu-D2R-cKO mice. These data point toward unique and distinct roles for D2Rs within excitatory and inhibitory neurons in the regulation of behavior and interneuron development, and suggest that location-biased D2R pharmacology may be clinically advantageous to achieve higher efficacy and help avoid unwanted effects.

Increased novelty-induced locomotion, sensitivity to amphetamine, and extracellular dopamine in striatum of Zdhhc15-deficient mice

Novelty-seeking behaviors and impulsivity are personality traits associated with several psychiatric illnesses including attention deficits hyperactivity disorders. The underlying neural mechanisms remain poorly understood. We produced and characterized a line of knockout mice for zdhhc15, which encodes a neural palmitoyltransferase. Genetic defects of zdhhc15 were implicated in intellectual disability and behavioral anomalies in humans. Zdhhc15-KO mice showed normal spatial learning and working memory but exhibited a significant increase in novelty-induced locomotion in open field. Striatal dopamine content was reduced but extracellular dopamine levels were increased during the habituation phase to a novel environment. Administration of amphetamine and methylphenidate resulted in a significant increase in locomotion and extracellular dopamine levels in the ventral striatum of mutant mice compared to controls. Number and projections of dopaminergic neurons in the nigrostriatal and mesolimbic pathways were normal. No significant change in the basal palmitoylation of known ZDHHC15 substrates including DAT was detected in striatum of zdhhc15 KO mice using an acyl-biotin exchange assay. These results support that a transient, reversible, and novelty-induced elevation of extracellular dopamine in ventral striatum contributes to novelty-seeking behaviors in rodents and implicate ZDHHC15-mediated palmitoylation as a novel regulatory mechanism of dopamine in the striatum.

Neurobehavioral changes arising from early life dopamine signaling perturbations

Dopamine (DA) signaling is critical to the modulation of multiple brain functions including locomotion, reinforcement, attention and cognition. The literature provides strong evidence that altered DA availability and actions can impact normal neurodevelopment, with both early and enduring consequences on anatomy, physiology and behavior. An appreciation for the developmental contributions of DA signaling to brain development is needed to guide efforts to preclude and remedy neurobehavioral disorders, such as attention-deficit/hyperactivity disorder, addiction, bipolar disorder, schizophrenia and autism spectrum disorder, each of which exhibits links to DA via genetic, cellular and/or pharmacological findings. In this review, we highlight research pursued in preclinical models that use genetic and pharmacological approaches to manipulate DA signaling at sensitive developmental stages, leading to changes at molecular, circuit and/or behavioral levels. We discuss how these alterations can be aligned with traits displayed by neuropsychiatric diseases. Lastly, we review human studies that evaluate contributions of developmental perturbations of DA systems to increased risk for neuropsychiatric disorders.

Methamphetamine addiction: involvement of CREB and neuroinflammatory signaling pathways

RATIONALE AND OBJECTIVES

Addiction to psychostimulant methamphetamine (METH) remains a major public health problem in the world. Animal models that use METH self-administration incorporate many features of human drug-taking behavior and are very helpful in elucidating mechanisms underlying METH addiction. These models are also helping to decipher the neurobiological substrates of associated neuropsychiatric complications. This review summarizes our work on the influence of METH self-administration on dopamine systems, transcription and immune responses in the brain.

METHODS

We used the rat model of METH self-administration with extended access (15 h/day for eight consecutive days) to investigate the effects of voluntary METH intake on the markers of dopamine system integrity and changes in gene expression observed in the brain at 2 h-1 month after cessation of drug exposure.

RESULTS

Extended access to METH self-administration caused changes in the rat brain that are consistent with clinical findings reported in neuroimaging and postmortem studies of human METH addicts. In addition, gene expression studies using striatal tissues from METH self-administering rats revealed increased expression of genes involved in cAMP response element binding protein (CREB) signaling pathway and in the activation of neuroinflammatory response in the brain.

CONCLUSION

These data show an association of METH exposure with activation of neuroplastic and neuroinflammatory cascades in the brain. The neuroplastic changes may be involved in promoting METH addiction. Neuroinflammatory processes in the striatum may underlie cognitive deficits, depression, and parkinsonism reported in METH addicts. Therapeutic approaches that include suppression of neuroinflammation may be beneficial to addicted patients.

Postnatal exposure to PFOS, but not PBDE 99, disturb dopaminergic gene transcription in the mouse CNS

The CNS of breast feeding infants and toddlers may be exposed to persistent organic pollutants via lactational transfer. Here, 10 days old mice were exposed to single oral doses of either PFOS, PBDE99 or vehicle control and were examined for changes in dopaminergic gene transcription in CNS tissue collected at 24h or 2 months post exposure.qPCR analyses of brain tissue from mice euthanized 24h post exposure revealed that PFOS affected transcription of Dopamine receptor-D5 (DRD5) in cerebral cortex and Tyrosine hydroxylase (TH) in the hippocampus. At 2 months of age, mice neonatally exposed to PFOS displayed decreased transcription of Dopamine receptor-D2 (DRD2) and TH in hippocampus. No significant changes in any of the tested genes were observed in PBDE99 exposed mice. This indicates that PFOS, but not PBDE99, affects the developing cerebral dopaminergic system at gene transcriptional level in cortex and hippocampus, which may account for some of the mechanistic effects behind the aetiology of neuropsychiatric disorders.

Prefrontal cortical dopamine from an evolutionary perspective

In this article, we propose the hypothesis that the prefrontal cortex (PFC) acquired neotenic development as a consequence of mesocortical dopamine (DA) innervation, which in turn drove evolution of the PFC into becoming a complex functional system. Accordingly, from the evolutionary perspective, decreased DA signaling in the PFC associated with such adverse conditions as chronic stress may be considered as an environmental adaptation strategy. Psychiatric disorders such as schizophrenia and attention deficit/hyperactivity disorder may also be understood as environmental adaptation or a by-product of such a process that has emerged through evolution in humans. To investigate the evolutionary perspective of DA signaling in the PFC, domestic animals such as dogs may be a useful model.

Developmental origins of brain disorders: roles for dopamine

Neurotransmitters and neuromodulators, such as dopamine, participate in a wide range of behavioral and cognitive functions in the adult brain, including movement, cognition, and reward. Dopamine-mediated signaling plays a fundamental neurodevelopmental role in forebrain differentiation and circuit formation. These developmental effects, such as modulation of neuronal migration and dendritic growth, occur before synaptogenesis and demonstrate novel roles for dopaminergic signaling beyond neuromodulation at the synapse. Pharmacologic and genetic disruptions demonstrate that these effects are brain region- and receptor subtype-specific. For example, the striatum and frontal cortex exhibit abnormal neuronal structure and function following prenatal disruption of dopamine receptor signaling. Alterations in these processes are implicated in the pathophysiology of neuropsychiatric disorders, and emerging studies of neurodevelopmental disruptions may shed light on the pathophysiology of abnormal neuronal circuitry in neuropsychiatric disorders.

CREB phosphorylation regulates striatal transcriptional responses in the self-administration model of methamphetamine addiction in the rat

Neuroplastic changes in the dorsal striatum participate in the transition from casual to habitual drug use and might play a critical role in the development of methamphetamine (METH) addiction. We examined the influence of METH self-administration on gene and protein expression that may form substrates for METH-induced neuronal plasticity in the dorsal striatum. Male Sprague-Dawley rats self-administered METH (0.1mg/kg/injection, i.v.) or received yoked saline infusions during eight 15-h sessions and were euthanized 2h, 24h, or 1month after cessation of METH exposure. Changes in gene and protein expression were assessed using microarray analysis, RT-PCR and Western blots. Chromatin immunoprecipitation (ChIP) followed by PCR was used to examine epigenetic regulation of METH-induced transcription. METH self-administration caused increases in mRNA expression of the transcription factors, c-fos and fosb, the neurotrophic factor, Bdnf, and the synaptic protein, synaptophysin (Syp) in the dorsal striatum. METH also caused changes in ΔFosB, BDNF and TrkB protein levels, with increases after 2 and 24h, but decreases after 1month of drug abstinence. Importantly, ChIP-PCR showed that METH self-administration caused enrichment of phosphorylated CREB (pCREB), but not of histone H3 trimethylated at lysine 4 (H3K4me3), on promoters of c-fos, fosb, Bdnf and Syp at 2h after cessation of drug intake. These findings show that METH-induced changes in gene expression are mediated, in part, by pCREB-dependent epigenetic phenomena. Thus, METH self-administration might trigger epigenetic changes that mediate alterations in expression of genes and proteins serving as substrates for addiction-related synaptic plasticity.

Effects of brief stress exposure during early postnatal development in balb/CByJ mice: I. Behavioral characterization

Early life stress has been linked to the etiology of mental health disorders. Rodent models of neonatal maternal separation stress frequently have been used to explore the long-term effects of early stress on changes in affective and cognitive behaviors. However, most current paradigms risk metabolic deprivation, due to prolonged periods of pup removal from the dam. We have developed a new paradigm in Balb/CByJ mice, that combines very brief periods of maternal separation with temperature stress to avoid the confound of nutritional deficiencies. We have also included a within-litter control group of pups that are not removed from the dam. The present experiments provide an initial behavioral characterization of this new model. We show that neonatally stressed mice display increased anxiety and aggression along with increased locomotion but decreased exploratory behavior. In contrast, littermate controls show increased exploration of novelty, compared to age-matched, colony-reared controls. Behavioral changes in our briefly stressed mice substantially concur with the existing literature, except that we were unable to observe any cognitive deficits in our paradigm. However, we show that within litter control pups also sustain behavioral changes suggesting complex and long-lasting interactions between different environmental factors in early postnatal life.

Effects of brief stress exposure during early postnatal development in Balb/CByJ mice: II. Altered cortical morphology

Early life experience can significantly determine later mental health status and cognitive function. Neonatal stress, in particular, has been linked to the etiology of mental health disorders as divergent as mood disorder, schizophrenia, and autism. Our study uses a Balb/CByJ mouse model to test the hypothesis, that neonatal stress will alter development and subsequent environmental modulation of neocortex. Using a split litter design, we generated stressed mice (STR) and within litter controls (LMC) along with age-matched, untreated animals (AMC), to serve as across litter controls. Short, daily exposure to a psychosocial/physical stressor, during the first week of life, resulted by adulthood in significant changes in neocortical thickness and architecture, which were further modulated by exposure to behavioral testing. Surprisingly, cortical size in LMC mice was also affected. These observations were compared to the effects of environmental enrichment in the same mouse strain. Our data indicate that LMC and STR males share with environmentally enriched males, an increase in thickness in infra-granular cortical layers, while STR also display a stress selective decrease in supragranular layers, in response to behavioral training as adults.

Neurotrophic actions of dopamine on the development of a serotonergic feeding circuit in Drosophila melanogaster

BACKGROUND

In the fruit fly, Drosophila melanogaster, serotonin functions both as a neurotransmitter to regulate larval feeding, and in the development of the stomatogastric feeding circuit. There is an inverse relationship between neuronal serotonin levels during late embryogenesis and the complexity of the serotonergic fibers projecting from the larval brain to the foregut, which correlate with perturbations in feeding, the functional output of the circuit. Dopamine does not modulate larval feeding, and dopaminergic fibers do not innervate the larval foregut. Since dopamine can function in central nervous system development, separate from its role as a neurotransmitter, the role of neuronal dopamine was assessed on the development, and mature function, of the 5-HT larval feeding circuit.

RESULTS

Both decreased and increased neuronal dopamine levels in late embryogenesis during development of this circuit result in depressed levels of larval feeding. Perturbations in neuronal dopamine during this developmental period also result in greater branch complexity of the serotonergic fibers innervating the gut, as well as increased size and number of the serotonin-containing vesicles along the neurite length. This neurotrophic action for dopamine is modulated by the D2 dopamine receptor expressed during late embryogenesis in central 5-HT neurons. Animals carrying transgenic RNAi constructs to knock down both dopamine and serotonin synthesis in the central nervous system display normal feeding and fiber architecture. However, disparate levels of neuronal dopamine and serotonin during development of the circuit result in abnormal gut fiber architecture and feeding behavior.

CONCLUSIONS

These results suggest that dopamine can exert a direct trophic influence on the development of a specific neural circuit, and that dopamine and serotonin may interact with each other to generate the neural architecture necessary for normal function of the circuit.

GluA3-deficiency in mice is associated with increased social and aggressive behavior and elevated dopamine in striatum

Glutamate signaling has been implicated in the regulation of social behavior. AMPA-glutamate receptors are assembled from four subunits (GluA1-4) of mainly GluA1/2 and GluA2/3 tetramers that form ion channels of distinct functional properties. Mice lacking GluA1 showed a reduced anxiety and male aggression. To understand the role of GluA3 in modulating social behavior, we investigated GluA3-deficient mice (Gria3-/Y) on C57BL/6J background. Compared to wild type (WT) littermates (n=14), Gria3-/Y mice (n=13) showed an increase in isolation-induced male aggression (p=0.011) in home cage resident-intruder test; an increase in sociability (p=0.01), and increase in male-male social interactions in neutral arena (p=0.005); an increase in peripheral activities in open field test (p=0.037) with normal anxiety levels in elevated plus maze and light-dark box; and minor deficits in motor and balance function in accelerating rotarod test (p=0.016) with normal grip strength. Gria3-/Y mice showed no significant deficit in spatial memory function in Morris-water maze and Y-maze tests, and normal levels of testosterone. Increased dopamine concentrations in stratum (p=0.034) and reduced serotonin turnover in olfactory bulb (p=0.002) were documented in Gria3-/Y mice. These results support a role of GluA3 in the modulation of social behavior through brain dopamine and/or serotonin signaling and different AMPA receptor subunits affect social behavior through distinct mechanisms.

GWAS findings for human iris patterns: associations with variants in genes that influence normal neuronal pattern development

Human iris patterns are highly variable. The origins of this variation are of interest in the study of iris-related eye diseases and forensics, as well as from an embryological developmental perspective, with regard to their possible relationship to fundamental processes of neurodevelopment. We have performed genome-wide association scans on four iris characteristics (crypt frequency, furrow contractions, presence of peripupillary pigmented ring, and number of nevi) in three Australian samples of European descent. Both the discovery (n = 2121) and replication (n = 499 and 73) samples showed evidence for association between (1) crypt frequency and variants in the axonal guidance gene SEMA3A (p = 6.6 × 10(-11)), (2) furrow contractions and variants within the cytoskeleton gene TRAF3IP1 (p = 2.3 × 10(-12)), and (3) the pigmented ring and variants in the well-known pigmentation gene SLC24A4 (p = 7.6 × 10(-21)). These replicated findings individually accounted for around 1.5%-3% of the variance for these iris characteristics. Because both SEMA3A and TRAFIP1 are implicated in pathways that control neurogenesis, neural migration, and synaptogenesis, we also examined the evidence of enhancement among such genes, finding enrichment for crypts and furrows. These findings suggest that genes involved in normal neuronal pattern development may also influence tissue structures in the human iris.

Chronic methamphetamine administration causes differential regulation of transcription factors in the rat midbrain

Methamphetamine (METH) is an addictive and neurotoxic psychostimulant widely abused in the USA and throughout the world. When administered in large doses, METH can cause depletion of striatal dopamine terminals, with preservation of midbrain dopaminergic neurons. Because alterations in the expression of transcription factors that regulate the development of dopaminergic neurons might be involved in protecting these neurons after toxic insults, we tested the possibility that their expression might be affected by toxic doses of METH in the adult brain. Male Sprague-Dawley rats pretreated with saline or increasing doses of METH were challenged with toxic doses of the drug and euthanized two weeks later. Animals that received toxic METH challenges showed decreases in dopamine levels and reductions in tyrosine hydroxylase protein concentration in the striatum. METH pretreatment protected against loss of striatal dopamine and tyrosine hydroxylase. In contrast, METH challenges caused decreases in dopamine transporters in both saline- and METH-pretreated animals. Interestingly, METH challenges elicited increases in dopamine transporter mRNA levels in the midbrain in the presence but not in the absence of METH pretreatment. Moreover, toxic METH doses caused decreases in the expression of the dopamine developmental factors, Shh, Lmx1b, and Nurr1, but not in the levels of Otx2 and Pitx3, in saline-pretreated rats. METH pretreatment followed by METH challenges also decreased Nurr1 but increased Otx2 and Pitx3 expression in the midbrain. These findings suggest that, in adult animals, toxic doses of METH can differentially influence the expression of transcription factors involved in the developmental regulation of dopamine neurons. The combined increases in Otx2 and Pitx3 expression after METH preconditioning might represent, in part, some of the mechanisms that served to protect against METH-induced striatal dopamine depletion observed after METH preconditioning.

Methamphetamine-induced dopamine-independent alterations in striatal gene expression in the 6-hydroxydopamine hemiparkinsonian rats

Unilateral injections of 6-hydroxydopamine into the medial forebrain bundle are used extensively as a model of Parkinson's disease. The present experiments sought to identify genes that were affected in the dopamine (DA)-denervated striatum after 6-hydroxydopamine-induced destruction of the nigrostriatal dopaminergic pathway in the rat. We also examined whether a single injection of methamphetamine (METH) (2.5 mg/kg) known to cause changes in gene expression in the normally DA-innervated striatum could still influence striatal gene expression in the absence of DA. Unilateral injections of 6-hydroxydopamine into the medial forebrain bundle resulted in METH-induced rotational behaviors ipsilateral to the lesioned side and total striatal DA depletion on the lesioned side. This injection also caused decrease in striatal serotonin (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) levels. DA depletion was associated with increases in 5-HIAA/5-HT ratios that were potentiated by the METH injection. Microarray analyses revealed changes (±1.7-fold, p<0.025) in the expression of 67 genes on the lesioned side in comparison to the intact side of the saline-treated hemiparkinsonian animals. These include follistatin, neuromedin U, and tachykinin 2 which were up-regulated. METH administration caused increases in the expression of c-fos, Egr1, and Nor-1 on the intact side. On the DA-depleted side, METH administration also increased the expression of 61 genes including Pdgf-d and Cox-2. There were METH-induced changes in 16 genes that were common in the DA-innervated and DA-depleted sides. These include c-fos and Nor-1 which show greater changes on the normal DA side. Thus, the present study documents, for the first time, that METH mediated DA-independent changes in the levels of transcripts of several genes in the DA-denervated striatum. Our results also implicate 5-HT as a potential player in these METH-induced alterations in gene expression because the METH injection also caused significant increases in 5-HIAA/5-HT ratios on the DA-depleted side.

Monoamine oxidases regulate telencephalic neural progenitors in late embryonic and early postnatal development

Monoamine neurotransmitters play major roles in regulating a range of brain functions in adults and increasing evidence suggests roles for monoamines in brain development. Here we show that mice lacking the monoamine metabolic enzymes MAO A and MAO B (MAO AB-deficient mice) exhibit diminished proliferation of neural stem cells (NSC) in the developing telencephalon beginning in late gestation [embryonic day (E) 17.5], a deficit that persists in neonatal and adult mice. These mice showed significantly increased monoamine levels and anxiety-like behaviors as adults. Assessments of markers of intermediate progenitor cells (IPC) and mitosis showed that NSC in the subventricular zone (SVZ), but not in the ventricular zone, are reduced in MAO AB-deficient mice. A developmental time course of monoamines in frontal cortical tissues revealed increased serotonin levels as early as E14.5, and a further large increase was found between E17.5 and postnatal day 2. Administration of an inhibitor of serotonin synthesis (parachlorophenylalanine) between E14.5 and E19.5 restored the IPC numbers and SVZ thickness, suggesting the role of serotonin in the suppression of IPC proliferation. Studies of neurosphere cultures prepared from the telencephalon at different embryonic and postnatal ages showed that serotonin stimulates proliferation in wild-type, but not in MAO AB-deficient, NSC. Together, these results suggest that a MAO-dependent long-lasting alteration in the proliferation capacity of NSC occurs late in embryonic development and is mediated by serotonin. Our findings reveal novel roles for MAOs and serotonin in the regulation of IPC proliferation in the developing brain.

A53T-alpha-synuclein overexpression impairs dopamine signaling and striatal synaptic plasticity in old mice

Background

Parkinson's disease (PD), the second most frequent neurodegenerative disorder at old age, can be caused by elevated expression or the A53T missense mutation of the presynaptic protein alpha-synuclein (SNCA). PD is characterized pathologically by the preferential vulnerability of the dopaminergic nigrostriatal projection neurons.

Methodology/Principal Findings

Here, we used two mouse lines overexpressing human A53T-SNCA and studied striatal dysfunction in the absence of neurodegeneration to understand early disease mechanisms. To characterize the progression, we employed young adult as well as old mice. Analysis of striatal neurotransmitter content demonstrated that dopamine (DA) levels correlated directly with the level of expression of SNCA, an observation also made in SNCA-deficient (knockout, KO) mice. However, the elevated DA levels in the striatum of old A53T-SNCA overexpressing mice may not be transmitted appropriately, in view of three observations. First, a transcriptional downregulation of the extraneural DA degradation enzyme catechol-ortho-methytransferase (COMT) was found. Second, an upregulation of DA receptors was detected by immunoblots and autoradiography. Third, extensive transcriptome studies via microarrays and quantitative real-time RT-PCR (qPCR) of altered transcript levels of the DA-inducible genes Atf2, Cb₁, Freq, Homer1 and Pde7b indicated a progressive and genotype-dependent reduction in the postsynaptic DA response. As a functional consequence, long term depression (LTD) was absent in corticostriatal slices from old transgenic mice.

Conclusions/Significance

Taken together, the dysfunctional neurotransmission and impaired synaptic plasticity seen in the A53T-SNCA overexpressing mice reflect early changes within the basal ganglia prior to frank neurodegeneration. As a model of preclinical stages of PD, such insights may help to develop neuroprotective therapeutic approaches.

Methamphetamine preconditioning causes differential changes in striatal transcriptional responses to large doses of the drug

Methamphetamine (METH) is a toxic drug of abuse, which can cause significant decreases in the levels of monoamines in various brain regions. However, animals treated with progressively increasing doses of METH over several weeks are protected against the toxic effects of the drug. In the present study, we tested the possibility that this pattern of METH injections might be associated with transcriptional changes in the rat striatum, an area of the brain which is known to be very sensitive to METH toxicity and which is protected by METH preconditioning. We found that the presence and absence of preconditioning followed by injection of large doses of METH caused differential expression in different sets of striatal genes. Quantitative PCR confirmed METH-induced changes in some genes of interest. These include small heat shock 27 kD proteins 1 and 2 (HspB1 and HspB2), brain derived neurotrophic factor (BDNF), and heme oxygenase-1 (Hmox-1). Our observations are consistent with previous studies which have reported that ischemic or pharmacological preconditioning can cause reprogramming of gene expression after lethal ischemic insults. These studies add to the growing literature on the effects of preconditioning on the brain transcriptome.

Methamphetamine self-administration is associated with persistent biochemical alterations in striatal and cortical dopaminergic terminals in the rat

Methamphetamine (meth) is an illicit psychostimulant that is abused throughout the world. Repeated passive injections of the drug given in a single day or over a few days cause significant and long-term depletion of dopamine and serotonin in the mammalian brain. Because meth self-administration may better mimic some aspects of human drug-taking behaviors, we examined to what extent this pattern of drug treatment might also result in damage to monoaminergic systems in the brain. Rats were allowed to intravenously self-administer meth (yoked control rats received vehicle) 15 hours per day for 8 days before being euthanized at either 24 hours or at 7 and 14 days after cessation of drug taking. Meth self-administration by the rats was associated with a progressive escalation of daily drug intake to 14 mg/kg per day. Animals that self-administered meth exhibited dose-dependent decreases in striatal dopamine levels during the period of observation. In addition, there were significant reductions in the levels of striatal dopamine transporter and tyrosine hydroxylase proteins. There were also significant decreases in the levels of dopamine, dopamine transporter, and tyrosine hydroxylase in the cortex. In contrast, meth self-administration caused only transient decreases in norepinephrine and serotonin levels in the two brain regions, with these values returning to normal at seven days after cessation of drug taking. Importantly, meth self-administration was associated with significant dose-dependent increases in glial fibrillary acidic protein in both striatum and cortex, with these changes being of greater magnitude in the striatum. These results suggest that meth self-administration by rats is associated with long-term biochemical changes that are reminiscent of those observed in post-mortem brain tissues of chronic meth abusers.

Aminochrome induces disruption of actin, alpha-, and beta-tubulin cytoskeleton networks in substantia-nigra-derived cell line

In previous studies, we observed that cells treated with aminochrome obtained by oxidizing dopamine with oxidizing agents dramatically changed cell morphology, thus posing the question if such morphological changes were dependent on aminochrome or the oxidizing agents used to produce aminochrome. Therefore, to answer this question, we have now purified aminochrome on a CM-Sepharose 50-100 column and, using NMR studies, we have confirmed that the resulting aminochrome was pure and that it retained its structure. Fluorescence microscopy with calcein-AM and transmission electron microscopy showed that RCSN-3 cells presented an elongated shape that did not change when the cells were incubated with 50 muM aminochrome or 100 muM dicoumarol, an inhibitor of DT-diaphorase. However, the cell were reduced in size and the elongated shape become spherical when the cells where incubated with 50 muM aminochrome in the presence of 100 muM dicoumarol. Under these conditions, actin, alpha-, and beta-tubulin cytoskeleton filament networks became condensed around the cell membrane. Actin aggregates were also observed in cells processes that connected the cells in culture. These results suggest that aminochrome one-electron metabolism induces the disruption of the normal morphology of actin, alpha-, and beta-tubulin in the cytoskeleton, and that DT-diaphorase prevents these effects.

Methamphetamine treatment causes delayed decrease in novelty-induced locomotor activity in mice

Methamphetamine (METH) is a psychostimulant that causes damage to dopamine (DA) axons and to non-monoaminergic neurons in the brain. The aim of the present study was to investigate short- and long-term effects of neurotoxic METH treatment on novelty-induced locomotor activity in mice. Male BALB/c mice, 12-14 weeks old, were injected with saline or METH (i.p., 7.5 mg/kg x 4 times, every 2 h). Behavior and neurotoxic effects were assessed at 10 days, 3 and 5 months following drug treatment. METH administration caused marked decreases in DA levels in the mouse striatum and cortex at 10 days post-drug. However, METH did not induce any changes in novelty-induced locomotor activity. At 3 and 5 months after treatment METH-exposed mice showed significant recovery of DA levels in the striatum and cortex. In contrast, these animals demonstrated significant decreases in locomotor activity at 5 months in comparison to aged-matched control mice. Further assessment of METH toxicity using TUNEL staining showed that the drug induced increased cell death in the striatum and cortex at 3 days after administration. Taken together, these data suggest that delayed deficits in novelty-induced locomotor activity observed in METH-exposed animals are not due to neurodegeneration of DA terminals but to combined effects of METH and age-dependent dysfunction of non-DA intrinsic striatal and/or corticostriatal neurons.

Methamphetamine preconditioning: differential protective effects on monoaminergic systems in the rat brain

Pretreatment with methamphetamine (METH) can attenuate toxicity due to acute METH challenges. The majority of previous reports have focused mainly on the effects of the drug on the striatal dopaminergic system. In the present study, we used a regimen that involves gradual increases in METH administration to rats in order to mimic progressively larger doses of the drug used by some human METH addicts. We found that this METH preconditioning was associated with complete protection against dopamine depletion caused by a METH challenge (5 mg/kg x 6 injections given 1 h apart) in the striatum and cortex. In contrast, there was no preconditioning-mediated protection against METH-induced serotonin depletion in the striatum and hippocampus, with some protection being observed in the cortex. There was also no protection against METH-induced norepinephrine (NE) depletion in the hippocampus. These results indicate that, in contrast to the present dogmas, there might be differences in the mechanisms involved in METH toxicity on monoaminergic systems in the rodent brain. Thus, chronic injections of METH might activate programs that protect against dopamine toxicity without influencing drug-induced pathological changes in serotoninergic systems. Further studies will need to evaluate the cellular and molecular bases for these differential responses.

The val158met COMT polymorphism's effect on atrophy in healthy aging and Parkinson's disease

We investigated whether the val(158)met functional polymorphism of catechol-o-methyltransferase influenced age-related changes in grey matter density and volume, both in healthy individuals (n=80, ages 18-79) and those with Parkinson's disease (n=50). Global grey matter volumes and voxelwise estimates of grey matter volume and density were determined from structural magnetic resonance images at 3T. Male and female ValVal homozygotes (low prefrontal cortical dopamine) had more grey matter in early adulthood, but this difference disappeared with increasing age. The insula and ventral prefrontal cortex had higher grey matter volume in younger, but not older, ValVal homozygotes. Conversely, the dominant premotor cortex revealed genotypic differences in grey matter density in later life. There were no global or local interactions between Parkinson's disease and COMT val(158)met genotype on morphometry. Since the val(158)met polymorphism is associated with differences in cortical dopamine metabolism, our data suggest a role for dopamine in cortical development followed by differential vulnerability to cortical atrophy across the adult life span.

Neonatal 6-hydroxydopamine lesions of the frontal cortex in rats: persisting effects on locomotor activity, learning and nicotine self-administration

Dopaminergic innervation of the frontal cortex in adults is important for a variety of cognitive functions and behavioral control. However, the role of frontal cortical dopaminergic innervation for neurobehavioral development has received little attention. In the current study, rats were given dopaminergic lesions in the frontal cortex with local micro-infusions of 6-hydroxydopamine (6-OHDA) at 1 week of age. The long-term behavioral effects of neonatal frontal cortical 6-OHDA lesions were assessed in a series of tests of locomotor activity, spatial learning and memory, and i.v. nicotine self-administration. In addition, neurochemical indices were assessed with tissue homogenization and HPLC in the frontal cortex, striatum, and nucleus accumbens of neonatal and adult rats after neonatal 6-OHDA lesions. In neonatal rats, frontal 6-OHDA lesions as intended caused a significant reduction in frontal cortical dopamine without effects on frontal cortical 5-HT and norepinephrine. The frontal cortical dopamine depletion increased 5-HT and norepinephrine levels in the nucleus accumbens. Locomotor activity assessment during adulthood in the figure-8 maze showed that lesioned male rats were hyperactive relative to sham-lesioned males. Locomotor activity of female rats was not significantly affected by the neonatal frontal 6-OHDA lesion. Learning and memory in the radial-arm maze was also affected by neonatal frontal 6-OHDA lesions. There was a general trend toward impaired performance in early maze acquisition and a paradoxical improvement at the end of cognitive testing. Nicotine self-administration showed significant lesion x sex interactions. The sex difference in nicotine self-administration with females self-administering significantly more nicotine than males was reversed by neonatal 6-OHDA frontal cortical lesions. Neurochemical studies in adult rats showed that frontal cortical dopamine and DOPAC levels significantly correlated with nicotine self-administration in the 6-OHDA-lesioned animals but not in the controls. Frontal cortical 5-HT and 5HIAA showed inverse correlations with nicotine self-administration in the 6-OHDA-lesioned animals but not in the controls. These results show that interfering with normal dopamine innervation of the frontal cortex during early postnatal development has persisting behavioral effects, which are sex-specific.