Differential regulation of psychostimulant-induced gene expression of brain derived neurotrophic factor and the immediate-early gene Arc in the juvenile and adult brain

The neuropharmacological properties of α-pyrrolidinobutiothiophenone, a new synthetic cathinone, in rodents; role of the dopaminergic system

BACKGROUND AND PURPOSE

α-Pyrrolidinobutiothiophenone (α-PBT) is a chemical derivative of cathinone, a structural analogue of amphetamine. Until now, there have been a few previous neurochemical or neurobehavioural studies on the abuse potential of α-PBT.

EXPERIMENTAL APPROACH

We examined the abuse potential of α-PBT by measuring psychomotor, rewarding, and reinforcing properties and methamphetamine-like discriminative stimulus effects in rodents using locomotor activity, conditioned place preference, self-administration, and drug discrimination studies. To clarify the underlying neuropharmacological mechanisms, we measured dopamine levels and neuronal activation in the dorsal striatum. In addition, we investigated the role of the dopamine D1 receptor or D2 receptors in α-PBT-induced hyperlocomotor activity, conditioned place preference, and the methamphetamine-like discriminative stimulus effect of α-PBT in rodents.

KEY RESULTS

α-PBT promoted hyperlocomotor activity in mice. α-PBT induced drug-paired place preference in mice and supported self-administration in rats. In a drug discrimination experiment, α-PBT fully substituted for the discriminative stimulus effects of methamphetamine in rats. Furthermore, α-PBT increased dopamine levels and c-Fos expression in the dorsal striatum of mice, which was associated with these behaviours. Finally, pretreatment with the D1 receptor antagonist SCH23390 or the D2 receptors antagonist eticlopride significantly attenuated acute or repeated α-PBT-induced hyperlocomotor activity, place preference, and the methamphetamine-like discriminative stimulus effects in rodents.

CONCLUSIONS AND IMPLICATIONS

These findings suggest that α-PBT has abuse potential at the highest dose tested via enhanced dopaminergic transmission in the dorsal striatum of rodents. The results provide scientific evidence for the legal restrictions of the recreational use of α-PBT.

Effects of Methylphenidate on the Dopamine Transporter and Beyond

The dopamine transporter (DAT) is the main target of methylphenidate (MPH), which remains the number one drug prescribed worldwide for the treatment of Attention-Deficit Hyperactivity Disorder (ADHD). In addition, abnormalities of the DAT have been widely associated with ADHD. Based on clinical and preclinical studies, the direction of DAT abnormalities in ADHD are, however, still unclear. Moreover, chronic treatment of MPH has been shown to increase brain DAT expression in both animals and ADHD patients, suggesting that findings of overexpressed levels of DAT in ADHD patients are possibly attributable to the effects of long-term MPH treatment rather than the pathology of the condition itself. In this chapter, we will discuss some of the effects exerted by MPH, which are related to its actions on catecholamine protein targets and brain metabolites, together with genes and proteins mediating neuronal plasticity. For this purpose, we present data from biochemical, proton nuclear magnetic resonance spectroscopy (¹H-NMR) and gene/protein expression studies. Overall, results of the studies discussed in this chapter show that MPH has a complex biological/pharmacological action well beyond the DAT.

Prelimbic proBDNF Facilitates Retrieval-Dependent Fear Memory Destabilization by Regulation of Synaptic and Neural Functions in Juvenile Rats

Fear regulation changes as a function of the early life is a key developmental period for the continued maturation of fear neural circuitry. The mechanisms of fear retrieval-induced reconsolidation have been investigated but remain poorly understood. The involvement of prelimbic proBDNF in fear memory extinction and its mediated signaling have been reported previously. Specifically, blocking the proBDNF/p75^NTR pathway during the postnatal stage disrupts synaptic development and neuronal activity in adulthood. Given the inherent high expression of proBDNF during the juvenile period, we tested whether the prelimbic proBDNF regulated synaptic and neuronal functions allowing to influencing retrieval-dependent memory processing. By examining the freezing behavior of auditory fear-conditioned rats, we found the high level of the prelimbic proBDNF in juvenile rats enhanced the destabilization of the retrieval-dependent weak but not strong fear memory through activating p75^NTR-GluN2B signaling. This modification of fear memory traces was attributed to the increment in the proportion of thin-type spine and promotion in synaptic function, as evidenced by the facilitation of NMDA-mediated EPSCs and GluN2B-dependent synaptic depression at the prelimbic projection. Furthermore, the strong prelimbic theta- and gamma-oscillation coupling predicted the suppressive effect of juvenile proBDNF on the recall of postretrieval memory. Our results critically emphasize the importance of developmental proBDNF for modification of retrieval-dependent memory and provide a potential critical targeting to inhibit threaten memories associated with neurodevelopment disorders.

A view of response and resistance to atomoxetine treatment in children with ADHD: effects of CYP2C19 polymorphisms and BDNF levels

OBJECTIVE

Although several genes have previously been studied about the treatment of Attention Deficit Hyperactivity Disorder (ADHD), the number of studies investigating the effects of genes on atomoxetine (ATX) treatment is very limited. In this study, we aimed to investigate the effect of CYP2C19 polymorphisms, which have a role in ATX biotransformation, on the treatment response and also to assess whether there is a relationship between BDNF and treatment response in children and adolescents with ADHD.

METHODS

One hundred children with ADHD and 100 healthy controls (HCs) were included in this study. The treatment response was assessed 2 months after the start of the ATX treatment. DNA samples from peripheral venous blood were replicated using PCR and analyzed using the ILLUMINA next-generation sequencing method. The resulting fastqs were analyzed using Basespace's Variant Interpreter Program. Plasma BDNF levels were evaluated with ELISA kits.

RESULTS

Treatment response was found to be lower in both heterozygous and homozygous carriers of the c.681G > A (CYP2C19*2) polymorphism. When the BDNF level was compared, it was found to be significantly higher in the ADHD group compared to HCs. Also, BDNF has a stronger predictive value for assessing resistance to ATX treatment.

CONCLUSIONS

To our knowledge, this is the first study to assess the effects of CYP2C19 polymorphisms and BDNF levels together on ATX treatment in children. Further studies with an extensive population are needed to better understand the effects of CYP2C19 polymorphisms on treatment and side effects, as well as the effects of BDNF levels.

Evidence That Methylphenidate Treatment Evokes Anxiety-Like Behavior Through Glucose Hypometabolism and Disruption of the Orbitofrontal Cortex Metabolic Networks

Methylphenidate (MPH) has been widely misused by children and adolescents who do not meet all diagnostic criteria for attention-deficit/hyperactivity disorder without a consensus about the consequences. Here, we evaluate the effect of MPH treatment on glucose metabolism and metabolic network in the rat brain, as well as on performance in behavioral tests. Wistar male rats received intraperitoneal injections of MPH (2.0 mg/kg) or an equivalent volume of 0.9% saline solution (controls), once a day, from the 15th to the 44th postnatal day. Fluorodeoxyglucose-18 was used to investigate cerebral metabolism, and a cross-correlation matrix was used to examine the brain metabolic network in MPH-treated rats using micro-positron emission tomography imaging. Performance in the light-dark transition box, eating-related depression, and sucrose preference tests was also evaluated. While MPH provoked glucose hypermetabolism in the auditory, parietal, retrosplenial, somatosensory, and visual cortices, hypometabolism was identified in the left orbitofrontal cortex. MPH-treated rats show a brain metabolic network more efficient and connected, but careful analyses reveal that the MPH interrupts the communication of the orbitofrontal cortex with other brain areas. Anxiety-like behavior was also observed in MPH-treated rats. This study shows that glucose metabolism evaluated by micro-positron emission tomography in the brain can be affected by MPH in different ways according to the region of the brain studied. It may be related, at least in part, to a rewiring in the brain the metabolic network and behavioral changes observed, representing an important step in exploring the mechanisms and consequences of MPH treatment.

Structure-Activity Relationship of Novel Second-Generation Synthetic Cathinones: Mechanism of Action, Locomotion, Reward, and Immediate-Early Genes

Several new synthetic cathinones, which mimic the effect of classical psychostimulants such as cocaine or MDMA, have appeared in the global illicit drug market in the last decades. In fact, the illicit drug market is continually evolving by constantly adding small modifications to the common chemical structure of synthetic cathinones. Thus, the aim of this study was to investigate the in vitro and in vivo structure–activity relationship (SAR) of six novel synthetic cathinones currently popular as recreational drugs, pentedrone, pentylone, N-ethyl-pentedrone (NEPD), N-ethyl-pentylone (NEP), 4-methyl-pentedrone (4-MPD), and 4-methyl-ethylaminopentedrone (4-MeAP), which structurally differ in the absence or presence of different aromatic substituents and in their amino terminal group. Human embryonic kidney (HEK293) cells expressing the human isoforms of SERT and DAT were used for the uptake inhibition and release assays. Moreover, Swiss CD-1 mice were used to investigate the psychostimulant effect, rewarding properties (3, 10, and 30 mg/kg, i.p.), and the induction of immediate-early genes (IEGs), such as Arc and c-fos in the dorsal striatum (DS) and ventral striatum (VS) as well as bdnf in the medial prefrontal cortex (mPFC), of the test compounds. Our results demonstrated that all tested synthetic cathinones are potent dopamine (DA) uptake inhibitors, especially the N-ethyl analogs, while the ring-substituted cathinones tested showed higher potency as SERT inhibitors than their no ring-substituted analogs. Moreover, unlike NEP, the remaining test compounds showed clear “hybrid” properties, acting as DAT blockers but SERT substrates. Regarding the locomotion, NEP and NEPD were more efficacious (10 mg/kg) than their N-methyl analogs, which correlates with their higher potency inhibiting the DAT and an overexpression of Arc levels in the DS and VS. Furthermore, all compounds tested induced an increase in c-fos expression in the DS, except for 4-MPD, the least effective compound in inducing hyperlocomotion. Moreover, NEP induced an up-regulation of bdnf in the mPFC that correlates with its 5-HTergic properties. Finally, the present study demonstrated for the first time that NEP, 4-MPD, and 4-MeAP induce reward in mice. Altogether, this study provides valuable information about the mechanism of action and psychostimulant and rewarding properties as well as changes in the expression of IEGs related to addiction induced by novel second-generation synthetic cathinones.

Primary role for melatonin MT2 receptors in the regulation of anhedonia and circadian temperature rhythm

Circadian rhythms disturbance is widely observable in patients with major depression (MD) and is also associated with depression vulnerability. Of them, disturbed melatonin secretion rhythm is particularly relevant to MD and is strongly phase-locked to core body temperature (CBT) rhythm. Here we aim to study the specific role of each melatonin receptor (MT₁ and MT₂) subtype in melatonin regulation of circadian CBT and its possible relationship with depressive-like behaviors. MT₁-/- , MT₂-/- and WT (C57BL/6) mice were used.  Anhedonia, using the sucrose intake test, circadian CBT, environmental place preference (EPP) conditioning and vulnerability to chronic social defeat stress (CSDS) procedure were studied. Moreover, the antidepressant effects of reboxetine (15 mg/kg/day, i.p.) for three weeks or ketamine (15 mg/kg i.p. every four days, 4 doses in total) were studied. Further, exposure to ultra-mild stress induced by individual housing for several weeks was also studied in these mice. MT₂-/- mice showed anhedonia and lower CBT compared to WT and MT₁-/-. In addition, while reward exposure raised nocturnal CBT in WT this increase did not take place in MT₂-/- mice. Further, MT₂-/- mice showed an enhanced vulnerability to stress-induced anhedonia and social avoidance as well as an impaired acquisition of novelty seeking behavior. Both reboxetine and ketamine reverted anhedonia and induced a clear anti-helpless behavior in the tail suspension test (TST). Reboxetine raised CBT in mice and reverted ultra-mild stress-induced anhedonia. Our findings show a primary role for MT₂ receptors in the regulation of circadian CBT as well as anhedonia and suggest that these receptors could be involved in depressive disorders associated to disturbed melatonin function.

Atomoxetine improves hippocampal cell proliferation but not memory in Doxorubicin-treated adult male rats

Atomoxetine (ATX) is a noradrenaline reuptake inhibitor used to treat Attention deficit hyperactive disorder (ADHD), or improve cognition in normal subjects. Cancer patients treated with systemic adjuvant chemotherapy have described experiencing deterioration in cognition. Doxorubicin (DOX, Adriamycin) is one of the anthracycline families used in chemotherapy, which has a deteriorating effect on both cognition and proliferation. The cognitive effects of ATX require inputs from the hippocampus. The aim of this study was to examine spatial memory and proliferation in the subgranular zone (SGZ) of the DG in adult Lister Hooded rats treated either alone or with a combination of Atomoxetine (30 mg kg⁻¹ day⁻¹, six i.p. doses, one injection every other day) and Doxorubicin (DOX) ( 2 mg kg⁻¹ day⁻¹, six i.p. doses, one injection every other day). Spatial memory was tested using the Novel location recognition (NLR) test, and proliferation of hippocampal cells was quantified using immunohistochemistry for the proliferative marker Ki67. Results showed that ATX treatment has improved the NLR task and increased cell proliferation in the SGZ of the DG, compared with saline‐treated controls. Animals treated with DOX only showed deficits in NLR task, and co‐administration of ATX along with DOX did not improve their performance. DOX chemotherapy caused a significant reduction in the number of proliferating cells in the SGZ of the DG compared with saline‐treated controls. This reduction was reversed by co‐administration of ATX. The above findings suggest that DOX can negatively affect both cell proliferation and memory and ATX co‐administration improves proliferation, but not memory in the adult male rat hippocampus.

Repeated Use of the Psychoactive Substance Ethylphenidate Impacts Neurochemistry and Reward Learning in Adolescent Male and Female Mice

Schedule II prescription psychostimulants, such as methylphenidate (MPH), can be misused as nootropic drugs, i.e., drugs that enhance focus and cognition. When users are unable to obtain these prescribed medications, they may seek out novel psychoactive substances (NPSs) that are not yet scheduled. An example of a NPS reportedly being abused is ethylphenidate (EPH), a close analog of MPH but with a higher preference for the dopamine transporter compared with the norepinephrine transporter. Therefore, based upon this pharmacological profile and user self-reports, we hypothesized that repeated EPH exposure in adolescent mice may be rewarding and alter cognition. Here, we report that repeated exposure to 15 mg/kg EPH decreased spatial cognitive performance as assessed by the Barnes maze spatial learning task in adolescent male C57Bl/6 mice; however, male mice did not show alterations in the expression of mature BDNF - a protein associated with increased cognitive function - in key brain regions. Acute EPH exposure induced hyperlocomotion at a high dose (15 mg/kg, i.p.), but not a low dose (5 mg/kg, i.p.). Interestingly, mice exhibited significant conditioned place preference at the low EPH dose, suggesting that even non-stimulating doses of EPH are rewarding. In both males and females, repeated EPH exposure increased expression of deltaFosB - a marker associated with increased risk of drug abuse - in the dorsal striatum, nucleus accumbens, and prefrontal cortex. Overall, our results suggest that repeated EPH use in adolescence is psychostimulatory, rewarding, increases crucial brain markers of reward-related behaviors, and may negatively impact spatial performance.

Neurogenesis within the hippocampus after chronic methylphenidate exposure

Methylphenidate is a psychostimulant used to treat attention deficit hyperactivity disorder. Neurogenesis occurs throughout adulthood within the dentate gyrus of the hippocampus and can be altered by psychoactive medications; however, the impact of methylphenidate on neurogenesis is not fully understood. We investigated the effects of chronic low (1 mg/kg) and high (10 mg/kg) intraperitoneal doses of methylphenidate on neurogenesis in mouse hippocampus following 28 days and 56 days of treatment. Interestingly, methylphenidate, at both doses, increased neurogenesis. However, if methylphenidate treatment was not continued, the newly generated cells did not survive after 28 days. If treatment was continued, the newly generated neurons survived only in the mice receiving low-dose methylphenidate. To investigate the mechanism for this effect, we examined levels of proteins linked to cell proliferation in the hippocampus, including brain-derived neurotrophic factor (BDNF), glial cell line-derived neurotrophic factor (GDNF), vascular endothelial growth factor (VEGF), tropomyosin receptor kinase B (TrkB), and beta-catenin. BDNF or GDNF levels were not significantly different between groups. However, hippocampal VEGF, TrkB, and beta-catenin were significantly increased in mice receiving low-dose methylphenidate for 28 days compared to controls. Interestingly, high-dose methylphenidate significantly decreased beta-catenin after 28 days and decreased VEGF, beta-catenin, and TrkB after 56 days compared to controls. Thus, low-dose methylphenidate appears to increase cell proliferation and cell survival in the hippocampus, and these effects may be mediated by increase in VEGF, TrkB, and beta-catenin. While high dose methylphenidate may initially increase neuronal proliferation, newly generated neurons are unable to survive long-term, possibly due to decrease in VEGF, TrkB and beta-catenin.

Methylphenidate disrupts cytoskeletal homeostasis and reduces membrane-associated lipid content in juvenile rat hippocampus

Although methylphenidate (MPH) is ubiquitously prescribed to children and adolescents, the consequences of chronic utilization of this psychostimulant are poorly understood. In this study, we investigated the effects of MPH on cytoskeletal homeostasis and lipid content in rat hippocampus. Wistar rats received intraperitoneal injections of MPH (2.0 mg/kg) or saline solution (controls), once a day, from the 15th to the 44th day of age. Results showed that MPH provoked hypophosphorylation of glial fibrillary acidic protein (GFAP) and reduced its immunocontent. Middle and high molecular weight neurofilament subunits (NF-M, NF-H) were hypophosphorylated by MPH on KSP repeat tail domains, while NFL, NFM and NFH immunocontents were not altered. MPH increased protein phosphatase 1 (PP1) and 2A (PP2A) immunocontents. MPH also decreased the total content of ganglioside and phospholipid, as well as the main brain gangliosides (GM1, GD1a, and GD1b) and the major brain phospholipids (sphingomyelin, phosphatidylcholine, phosphatidylethanolamine, phosphatidylinositol, and phosphatidylserine). Total cholesterol content was also reduced in the hippocampi of juvenile rats treated with MPH. These results provide evidence that disruptions of cytoskeletal and lipid homeostasis in hippocampus of juvenile rats are triggers by chronic MPH treatment and present a new basis for understanding the effects and consequences associated with chronic use of this psychostimulant during the development of the central nervous system.

Differential Behavioral and Biochemical Responses to Caffeine in Male and Female Rats from a Validated Model of Attention Deficit and Hyperactivity Disorder

Epidemiological studies suggest sex differences in attention deficit and hyperactivity disorder (ADHD) symptomatology. The potential benefits of caffeine have been reported in the management of ADHD, but its effects were not properly addressed with respect to sex differences. The present study examined the effects of caffeine (0.3 g/L) administered since childhood in the behavior and brain-derived neurotrophic factor (BDNF) and its related proteins in both sexes of a rat model of ADHD (spontaneously hypertensive rats-SHR). Hyperlocomotion, recognition, and spatial memory disturbances were observed in adolescent SHR rats from both sexes. However, females showed lack of habituation and worsened spatial memory. Although caffeine was effective against recognition memory impairment in both sexes, spatial memory was recovered only in female SHR rats. Besides, female SHR rats showed exacerbated hyperlocomotion after caffeine treatment. SHR rats from both sexes presented increases in the BDNF, truncated and phospho-TrkB receptors and also phospho-CREB levels in the hippocampus. Caffeine normalized BDNF in males and truncated TrkB receptor at both sexes. These findings provide insight into the potential of caffeine against fully cognitive impairment displayed by females in the ADHD model. Besides, our data revealed that caffeine intake since childhood attenuated behavioral alterations in the ADHD model associated with changes in BDNF and TrkB receptors in the hippocampus.

Methamphetamine binge administration during late adolescence induced enduring hippocampal cell damage following prolonged withdrawal in rats

A recent study from our laboratory demonstrated that binge methamphetamine induced hippocampal cell damage (i.e., impaired cell genesis) in rats when administered specifically during late adolescence (postnatal day, PND 54-57) and evaluated 24 h later (PND 58). The results also suggested a possible role for brain-derived neurotrophic factor (BDNF) regulating cell genesis and survival. This subsequent study evaluated whether these effects persisted in time as measured following prolonged withdrawal. Male Sprague-Dawley rats were treated (i.p.) with BrdU (2 × 50 mg/kg, 3 days, PND 48-50) followed by a binge paradigm (3 pulses/day, every 3 h, 4 days, PND 54-57) of methamphetamine (5 mg/kg, n = 14, M) or saline (0.9% NaCl, 1 ml/kg, n = 12, C). Following 34 days of forced withdrawal (PND 91), rats were killed 45 min after a challenge dose of saline (Sal: C-Sal, n = 6; M-Sal, n = 7) or methamphetamine (Meth: C-Meth, n = 6; M-Meth, n = 7). Neurogenesis markers (Ki-67: cell proliferation; NeuroD: early neuronal survival; BrdU: prolonged cell survival, 41-43 days old cells) were evaluated by immunohistochemistry while neuroplasticity markers (BDNF and Fos forms) were evaluated by Western blot. The main results showed that a history of methamphetamine administration (PND 54-57) induced enduring hippocampal cell damage (i.e., observed on PND 91) by decreasing cell survival (BrdU + cells) and mature-BDNF (m-BDNF) protein content, associated with neuronal survival, growth and differentiation. Interestingly, m-BDNF regulation paralleled hippocampal c-Fos protein content, indicating decreased neuronal activity, and thus reinforcing the persisting negative effects induced by methamphetamine in rat hippocampus following prolonged withdrawal.

Schizophrenia: What's Arc Got to Do with It?

Human studies of schizophrenia are now reporting a previously unidentified genetic convergence on postsynaptic signaling complexes such as the activity-regulated cytoskeletal-associated (Arc) gene. However, because this evidence is still very recent, the neurobiological implication of Arc in schizophrenia is still scattered and unrecognized. Here, we first review current and developing findings connecting Arc in schizophrenia. We then highlight recent and previous findings from preclinical mouse models that elucidate how Arc genetic modifications might recapitulate schizophrenia-relevant behavioral phenotypes following the novel Research Domain Criteria (RDoC) framework. Building on this, we finally compare and evaluate several lines of evidence demonstrating that Arc genetics can alter both glutamatergic and dopaminergic systems in a very selective way, again consistent with molecular alterations characteristic of schizophrenia. Despite being only initial, accumulating and compelling data are showing that Arc might be one of the primary biological players in schizophrenia. Synaptic plasticity alterations in the genetic architecture of psychiatric disorders might be a rule, not an exception. Thus, we anticipate that additional evidence will soon emerge to clarify the Arc-dependent mechanisms involved in the psychiatric-related dysfunctional behavior.

The Transitional Age Brain: "The Best of Times and the Worst of Times"

Over the past two decades, there have been substantial developments in the understanding of brain development and the importance of environmental inputs and context. This paper focuses on the neurodevelopmental mismatch that occurs during the epoch we term the 'transitional age brain' (ages 13-25) and the collateral behavioral correlates. We summarize research findings supporting the argument that, because of this neurodevelopmental mismatch, transitional age youth are at high risk for engaging in behaviors that lead to negative outcomes, morbidity, and mortality. We highlight the need to develop new, neuroscience-inspired health promotion and illness prevention approaches for transitional age youth.

1H NMR-based metabolomics reveals neurochemical alterations in the brain of adolescent rats following acute methylphenidate administration

The psychostimulant methylphenidate (MPH) is increasingly used in the treatment of attention deficit hyperactivity disorder (ADHD). While there is little evidence for common brain pathology in ADHD, some studies suggest a right hemisphere dysfunction among people diagnosed with the condition. However, in spite of the high usage of MPH in children and adolescents, its mechanism of action is poorly understood. Given that MPH blocks the neuronal transporters for dopamine and noradrenaline, most research into the effects of MPH on the brain has largely focused on these two monoamine neurotransmitter systems. Interestingly, recent studies have demonstrated metabolic changes in the brain of ADHD patients, but the impact of MPH on endogenous brain metabolites remains unclear. In this study, a proton nuclear magnetic resonance (¹H NMR)-based metabolomics approach was employed to investigate the effects of MPH on brain biomolecules. Adolescent male Sprague Dawley rats were injected intraperitoneally with MPH (5.0 mg/kg) or saline (1.0 ml/kg), and cerebral extracts from the left and right hemispheres were analysed. A total of 22 variables (representing 13 distinct metabolites) were significantly increased in the MPH-treated samples relative to the saline-treated controls. The upregulated metabolites included: amino acid neurotransmitters such as GABA, glutamate and aspartate; large neutral amino acids (LNAA), including the aromatic amino acids (AAA) tyrosine and phenylalanine, both of which are involved in the metabolism of dopamine and noradrenaline; and metabolites associated with energy and cell membrane dynamics, such as creatine and myo-inositol. No significant differences in metabolite concentrations were found between the left and right cerebral hemispheres. These findings provide new insights into the mechanisms of action of the anti-ADHD drug MPH.

Epigenetic and gene expression changes in the adolescent brain: What have we learned from animal models?

Adolescence is defined as the gradual period of transition between childhood and adulthood that is characterized by significant brain maturation, growth spurts, sexual maturation, and heightened social interaction. Although originally believed to be a uniquely human aspect of development, rodent and non-human primates demonstrate maturational patterns that distinctly support an adolescent stage. As epigenetic processes are essential for development and differentiation, but also transpire in mature cells in response to environmental influences, they are an important aspect of adolescent brain maturation. The purpose of this review article was to examine epigenetic programming in animal models of brain maturation during adolescence. The discussion focuses on animal models to examine three main concepts; epigenetic processes involved in normal adolescent brain maturation, the influence of fetal programming on adolescent brain development and the epigenome, and finally, postnatal experiences such as exercise and drugs that modify epigenetic processes important for adolescent brain maturation. This corollary emphasizes the utility of animal models to further our understanding of complex processes such as epigenetic regulation and brain development.

The Impact of Chronic Early Administration of Psychostimulants on Brain Expression of BDNF and Other Neuroplasticity-Relevant Proteins

ABSRACT

Frequently, healthy individuals, children, and students are using stimulants to treat attention deficit hyperactivity disorder (ADHD)-like symptoms or to enhance cognitive capacity, attention and concentration. Methylphenidate, the most common treatment for ADHD, similarly to cocaine, blocks the dopamine reuptake, leading to increase in dopamine level in the synaptic cleft. Brain-derived neurotrophic factor (BDNF) and other neuroplasticity-relevant proteins have a major role in cellular plasticity during development and maturation of the brain. Young Sprague Dawley rats (postnatal days (PND) 14) were treated chronically with either cocaine or methylphenidate. The rats were examined behaviorally and biochemically at several time points (PND 35, 56, 70, and 90). We found age-dependent, but stimulant-independent, alterations in the mRNA expression levels of microtubule-associated protein tau, doublecortin, and synaptophysin. The PND 90 rats, treated with methylphenidate at an early age, exhibited increased BDNF protein levels in the prefrontal cortex compared to the saline-treated group. Despite the treatment effects at the biochemical level, cocaine and methylphenidate treatments at an early age had only minor effects on the behavioral parameters measured at older ages. The biochemical alterations may reflect neuroprotective or neuroplastic effects of chronic methylphenidate treatment at an early age.

Synaptic Cytoskeletal Plasticity in the Prefrontal Cortex Following Psychostimulant Exposure

Addiction is characterized by maladaptive decision-making, a loss of control over drug consumption and habit-like drug seeking despite adverse consequences. These cognitive changes may reflect the effects of drugs of abuse on prefrontal cortical neurobiology. Here, we review evidence that amphetamine and cocaine fundamentally remodel the structure of excitatory neurons in the prefrontal cortex. We summarize evidence in particular that these psychostimulants have opposing effects in the medial and orbital prefrontal cortices ('mPFC' and 'oPFC', respectively). For example, amphetamine and cocaine increase dendrite length and spine density in the mPFC, while dendrites are impoverished and dendritic spines are eliminated in the oPFC. We will discuss evidence that certain cytoskeletal regulatory proteins expressed in the oPFC and implicated in postnatal (adolescent) neural development also regulate behavioral sensitivity to cocaine. These findings potentially open a window of opportunity for the identification of novel pharmacotherapeutic targets in the treatment of drug abuse disorders in adults, as well as in drug-vulnerable adolescent populations. Finally, we will discuss the behavioral implications of drug-related dendritic spine elimination in the oPFC, with regard to reversal learning tasks and tasks that assess the development of reward-seeking habits, both used to model aspects of addiction in rodents.

The Physiology of BDNF and Its Relationship with ADHD

Brain-derived neurotrophic factor (BDNF) is a major neurotrophin in the central nervous system that plays a critical role in the physiological brain functions via its two independent receptors: tropomyosin-related kinase B (TrkB) and p75, especially in the neurodevelopment. Disrupting of BDNF and its downstream signals has been found in many neuropsychological diseases, including attention-deficit hyperactivity disorder (ADHD), a common mental disorder which is prevalent in childhood. Understanding the physiological functions of BDNF during neural development and its potential relationship with ADHD will help us to elucidate the possible mechanisms of ADHD and to develop therapeutic approaches for this disease. In this review, we summarized the important literatures for the physiological functions of BDNF in the neurodevelopment. We also performed an association study on the functional genetic variation of BDNF and ADHD by a case-control study in the Chinese mainland population and revealed the potential correlation between BDNF and ADHD which needs further research to confirm.

Long-term effects of gestational nicotine exposure and food-restriction on gene expression in the striatum of adolescent rats

Gestational exposure to environmental toxins such as nicotine may result in detectable gene expression changes in later life. To investigate the direct toxic effects of prenatal nicotine exposure on later brain development, we have used transcriptomic analysis of striatal samples to identify gene expression differences between adolescent Lister Hooded rats exposed to nicotine in utero and controls. Using an additional group of animals matched for the reduced food intake experienced in the nicotine group, we were also able to assess the impact of imposed food-restriction on gene expression profiles. We found little evidence for a role of gestational nicotine exposure on altered gene expression in the striatum of adolescent offspring at a significance level of p<0.01 and |log2 fold change >0.5|, although we cannot exclude the possibility of nicotine-induced changes in other brain regions, or at other time points. We did, however, find marked gene expression differences in response to imposed food-restriction. Food-restriction resulted in significant group differences for a number of immediate early genes (IEGs) including Fos, Fosb, Fosl2, Arc, Junb, Nr4a1 and Nr4a3. These genes are associated with stress response pathways and therefore may reflect long-term effects of nutritional deprivation on the development of the stress system.

Changes in plasma Brain-derived neurotrophic factor (BDNF) levels induced by methylphenidate in children with Attention deficit-hyperactivity disorder (ADHD)

OBJECTIVES

It has been suggested that BDNF may play a role in the pathogenesis of ADHD. Our aim is to determine whether methylphenidate can induce changes in plasma BDNF levels of children with ADHD.

METHODS

We assessed levels of plasma BDNF in 28 ADHD patients (age range = 3.5-10 years) before and after 6 weeks treatment with effective dosages of methylphenidate. Then we evaluated the correlation of levels of plasma BDNF with clinical variables, especially ADHD Conner's parents rating scale.

RESULTS

According to the paired sample T-test, the mean plasma BDNF level in the baseline was 193.06 pg/ml, whereas 271.06 pg/ml in the end point, thus showing significantly higher mean plasma BDNF levels in the post-treatment situation than in the pretreatment (t = -3.393, df = 27, p = 0.002). Pearson's correlation test revealed that there was also significant negative correlation between levels of BDNF in the plasma of ADHD patients before treatment and improvement in hyperactivity symptoms with treatment (Pearson's correlation = -0.395, p = 0.037).

CONCLUSION

The mean plasma BDNF levels increased after 6 weeks of treatment with methylphenidate. Also, we found an improvement in hyperactivity symptoms with decreasing baseline plasma BDNF levels. We recommend that more studies should be conducted in order to assess the possible roles of plasma BDNF levels in treatment response prediction and prognosis.

Methylphenidate place conditioning in adolescent rats: an analysis of sex differences and the dopamine transporter

In two experiments, we analyzed the effects of methylphenidate (MPH) on conditioned place preference (CPP) in adolescent male and female rats, and the effects of MPH on the dopamine transporter (DAT). In Experiment 1, male and female rats were conditioned for 5 consecutive days from postnatal day (P)44 to P48 with saline, 1, or 5mg/kg MPH. On the post conditioning preference test, the group administered the 1mg/kg dose of MPH resulted in no significant preference compared to controls, whereas the 5mg/kg dose of MPH produced a robust significant preference for the paired context, but there were no sex differences. Analysis of the DAT revealed that animals conditioned with the 5mg/kg dose of MPH demonstrated a significant decrease of the dopamine transporter (DAT) in the nucleus accumbens and striatum compared to controls. In Experiment 2, animals were conditioned using an every second day paradigm from P33-41 to model a previous MPH treatment regimen that had revealed sex differences in behavioral sensitization. MPH produced an increased preference for the paired context on a post-conditioning preference test in Experiment 2, but as in Experiment 1, no sex differences were observed. These data show that a relatively high dose of MPH has rewarding associative effects in both adolescent male and female rats reliably across two different conditioning paradigms and ages in adolescence, but no sex difference. In addition, MPH results in a significant decrease of the DAT in drug reward brain areas which has implications toward plasticity of the brain's reward system.

Sex and dose-related differences in methylphenidate adolescent locomotor sensitization and effects on brain-derived neurotrophic factor

This study analyzed repeated methylphenidate (MPH) administration and its effects on brain-derived neurotrophic factor (BDNF) in the dorsal striatum and nucleus accumbens of male and female adolescent rats. In Experiment 1, rats were administered intraperitoneal (ip) saline, 1, 3, or 5 mg/kg dose of MPH every second day from postnatal day (P)33-P49. Locomotor activity was analyzed for 10 min after each administration. Results revealed that the 1 mg/kg dose of MPH produced locomotor suppression, however, the 5 mg/kg dose of MPH produced locomotor sensitization and robust behavioral activation in females as compared to males. In Experiment 2, animals were administered ip saline or the 5 mg/kg dose of MPH using an identical regimen but a 30 min behavioral test was employed. Dorsal striatum and nucleus accumbens tissue was assayed for BDNF at P50. Females demonstrated sensitization to MPH and increased locomotor activation compared to males. Interestingly, females given MPH demonstrated a significant 42% decrease of striatal BDNF whereas males administered MPH demonstrated a significant 50.4% increase of striatal BDNF compared to controls. There were no effects on accumbal BDNF. This report demonstrates robust sex differences in the behavioral response, but sex-dependent changes in striatal BDNF in response to MPH in adolescence.

Addiction-related gene regulation: risks of exposure to cognitive enhancers vs. other psychostimulants

The psychostimulants methylphenidate (Ritalin, Concerta), amphetamine (Adderall), and modafinil (Provigil) are widely used in the treatment of medical conditions such as attention-deficit hyperactivity disorder and narcolepsy and, increasingly, as "cognitive enhancers" by healthy people. The long-term neuronal effects of these drugs, however, are poorly understood. A substantial amount of research over the past two decades has investigated the effects of psychostimulants such as cocaine and amphetamines on gene regulation in the brain because these molecular changes are considered critical for psychostimulant addiction. This work has determined in some detail the neurochemical and cellular mechanisms that mediate psychostimulant-induced gene regulation and has also identified the neuronal systems altered by these drugs. Among the most affected brain systems are corticostriatal circuits, which are part of cortico-basal ganglia-cortical loops that mediate motivated behavior. The neurotransmitters critical for such gene regulation are dopamine in interaction with glutamate, while other neurotransmitters (e.g., serotonin) play modulatory roles. This review presents (1) an overview of the main findings on cocaine- and amphetamine-induced gene regulation in corticostriatal circuits in an effort to provide a cellular framework for (2) an assessment of the molecular changes produced by methylphenidate, medical amphetamine (Adderall), and modafinil. The findings lead to the conclusion that protracted exposure to these cognitive enhancers can induce gene regulation effects in corticostriatal circuits that are qualitatively similar to those of cocaine and other amphetamines. These neuronal changes may contribute to the addiction liability of the psychostimulant cognitive enhancers.

Reduced striatal dopamine D1-D2 receptor heteromer expression and behavioural subsensitivity in juvenile rats

In adult rat striatum the dopamine D1-D2 receptor heteromer is expressed selectively in a subset of medium spiny neurons (MSNs) that coexpress the dopamine D1 and D2 receptors (D1R and D2R) as well as dynorphin (DYN) and enkephalin (ENK), with higher coexpression in nucleus accumbens (NAc) and much lower in the caudate putamen (CP). In the present study we showed that in neonatal striatal cultured neurons >90% exhibited the D1R/D2R-DYN/ENK phenotype. Similarly, in the striatum of juvenile rats (age 26-28 days) coexpression of D1R and D2R was also coincident with the expression of both DYN and ENK. Quantification of the number of striatal MSNs exhibiting coexpression of D1R and D2R in juvenile rats revealed significantly lower coexpression in NAc shell, but not core, and CP than in adult rats. However, within MSNs that coexpressed D1R and D2R, the propensity to form the D1-D2 receptor heteromer did not differ between age groups. Consistent with reduced coexpression of the D1R and D2R, juvenile rats exhibited subsensitivity to D1-D2 receptor heteromer-induced grooming following activation by SKF 83959. Given the proposed role of D1R/D2R-coexpressing MSNs in the regulation of thalamic output, and the recent discovery that these MSNs exhibit both inhibitory and excitatory capabilities, these findings suggest that the functional regulation of neurotransmission by the dopamine D1-D2 receptor heteromer within the juvenile striatum may be significantly different than in the adult.

Gestational IV nicotine produces elevated brain-derived neurotrophic factor in the mesocorticolimbic dopamine system of adolescent rat offspring

Maternal smoking during pregnancy is associated with enduring psychopathology, such as increased likelihood of substance use, in offspring. Various animal models demonstrate that continuous nicotine exposure produces teratogenic effects in offspring, as well. In this experiment, a novel intravenous (IV) exposure model was used to determine if gestational nicotine (GN) treatment produced alterations in methamphetamine-induced sensitization and the expression of brain-derived neurotrophic factor (BDNF) in the mesocorticolimbic dopamine (DA) system of adolescent offspring. Dams were injected with IV saline or nicotine (0.05 mg/kg/injection) three times per day on gestational days 8-21. Habituation was measured on postnatal day (PND) 25-27 and baseline activity on PND 28. On PND 29-35, offspring were injected with saline or methamphetamine (0.3 mg/kg) and locomotor activity was measured after the first and seventh injections. On PND 36, brains were removed, flash frozen, and BDNF protein levels in the nucleus accumbens (NAcc), dorsal striatum (Str), frontal cortex (FC), and hippocampus (Hipp) were analyzed. GN did not affect habituation or the induction of methamphetamine-induced sensitization. Interestingly, GN, but not adolescent methamphetamine treatment, elevated levels of BDNF in the NAcc and Str; however, the GN-induced increase in BDNF in the FC was attenuated by adolescent methamphetamine treatment. Both GN and adolescent methamphetamine treatment increased BDNF in the Hipp. These findings indicate that GN exposure will result in increased levels of BDNF protein throughout the mesocorticolimbic DA system during adolescent development and suggests that methamphetamine abuse will modulate the expression of BDNF in motivational circuitries of adolescent offspring exposed to GN.

Effects of ADHD therapeutic agents, methylphenidate and atomoxetine, on hippocampal neurogenesis in the adolescent mouse dentate gyrus

Methylphenidate (MPH) and atomoxetine (ATX) are commonly used as attention-deficit/hyperactivity disorder (ADHD) therapeutic agents. In the present study, we investigated the effects of MPH and ATX on cell proliferation and neuronal differentiation in the dentate gyrus (DG) of the adolescent mouse by 5-bromo-2'-deoxyuridine (BrdU) and doublecortin (DCX) immunohistochemistry. BrdU-positive ((+)) cells, DCX(+) cells and BrdU(+)/NeuN(+) neurons (BrdU(+) cells with NeuN immunoreaction) were easily detected in the subgranular zone (SGZ) of the DG in the vehicle-, MPH- and ATX-treated groups. Among them, only in the 10mg/kg MPH-treated group, the numbers of BrdU(+), DCX(+) and BrdU(+)/NeuN(+) cells were significantly increased compared to those in the vehicle-treated group. In addition, brain-derived neurotrophic factor (BDNF) level was significantly increased in 10mg/kg MPH-treated group, not in the other experimental groups, compared to the vehicle-treated group. These results indicate that MPH, not ATX, can enhance cell proliferation and neuroblast differentiation in the SGZ of the DG via increasing BDNF level.

Cognitive and emotional behavioural changes associated with methylphenidate treatment: a review of preclinical studies

There is evidence from animal studies that repeated exposure to methylphenidate (MPH), a widely used psychostimulant for the treatment of attention deficit hyperactivity disorder (ADHD), produces behavioural, structural and neurochemical changes that persist long after drug administration has ended. However, the translational utility of much of this work is compromised by the use of drug doses and routes of administration that produce plasma and brain MPH levels that fall outside the clinical range, i.e. experimental parameters more relevant to drug abuse than ADHD. We used PubMed to identify pre-clinical studies that employed repeated MPH administration at low doses in young rodents and examined long-term effects on cognition, emotion, and brain structure and function. A review of this work suggests that repeated MPH treatment during early development can modify a number of cognitive, behavioural and brain processes, but these are reduced when low therapeutic doses are employed. Moreover, MPH sites of action extend beyond those implicated in ADHD. Studies that combined neurobiological and behavioural approaches provide important insights into the mechanisms underlying MPH-produced effects on cognitive and behavioural processes, which may be relevant to MPH therapeutic efficacy. There is an emerging consensus that pharmacological treatment of childhood psychiatric disorders produces persistent neuroadaptations, highlighting the need for studies that assess long-term effects of early developmental pharmacotherapy. In this regard, studies that mimic clinical therapy with rodents are useful experimental approaches for defining the behavioural and neural plasticity associated with stimulant therapy in paediatric populations.

Brain processes in discounting: consequences of adolescent methylphenidate exposure

Traits of inattention, impulsivity, and motor hyperactivity characterize children diagnosed with attention-deficit/hyperactivity disorder (ADHD), whose inhibitory control is reduced. In animal models, crucial developmental phases or experimental transgenic conditions account for peculiarities, such as sensation-seeking and risk-taking behaviors, and reproduce the beneficial effects of psychostimulants. An "impulsive" behavioral profile appears to emerge more extremely in rats when forebrain dopamine (DA) systems undergo remodeling, as in adolescence, or with experimental manipulation tapping onto the dopamine transporter (DAT). Ritalin(®) (methylphenidate, MPH), a DAT-blocking drug, is prescribed for ADHD therapy but is also widely abused by human adolescents. Administration of MPH during rats' adolescence causes a long-term modulation of their self-control, in terms of reduced intolerance to delay and diminished proneness for risk when reward is uncertain. Exactly the opposite profile emerges when exogenous alteration of DAT levels is achieved via lentiviral transfection. Both adolescent MPH exposure and DAT-targeting transfection lead to enduring hyperfunction of dorsal striatum and hypofunction of ventral striatum. Together with upregulation of prefronto-cortical phospho-creatine, striatal upregulation of selected genes (like serotonin 7 receptor gene) suggests that enhanced inhibitory control is generated by adolescent MPH exposure. Operant tasks, which assess the balance between motivational drives and inhibitory self-control, are thus useful for investigating reward-discounting processes and their modulation by DAT-targeting tools. In summary, due to the complexity of human studies, preclinical investigations of rodent models are necessary to understand better both the neurobiology of ADHD-like symptoms' etiology and the long-term therapeutic safety of adolescent MPH exposure.

Val/Val genotype of brain-derived neurotrophic factor (BDNF) Val⁶⁶Met polymorphism is associated with a better response to OROS-MPH in Korean ADHD children

Research on psychostimulants, analysis of animal models and genetic association studies all suggest that the brain-derived neurotrophic factor gene (BDNF) may be a good candidate for pharmacogenetic studies of attention deficit hyperactivity disorder (ADHD). Yet to date there have been no pharmacogenetic studies of BDNF in ADHD. A total of 102 drug-naive ADHD children (8.7±2.1 yr) were treated with osmotic release oral system-methylphenidate (OROS-MPH) for 12 wk, and four kinds of response criteria were applied, based first, on a combined threshold of the ADHD Rating Scale - IV (ARS) and the Clinical Global Impression - Improvement scale (CGI-I); second, on scores of 1 or 2 vs. 3-7 on the CGI - Severity scale; third, on a >50% reduction in ARS scores; and fourth, on satisfaction of all of the aforementioned criteria. The Val⁶⁶Met polymorphism of BDNF and six single nucleotide polymorphisms from the SLC6A2, ADRA2A and NTF-3 genes were tested for association with each criterion. Relative to other genotypes, homozygosity for the Val allele of the BDNF Val⁶⁶Met polymorphism was associated with a greater relative frequency of good response under all four response criteria (after controlling for baseline ARS score, age, gender, final dose (mg/kg) of OROS-MPH at 12 wk, and level of academic functioning). This association was significant at the uncorrected level for the first and third response criteria (p=0.013 and p=0.018, respectively) and significant at a Bonferroni-corrected level for the second and fourth response criteria (p=0.0002, p=0.0003, respectively). Our findings support an association between homozygosity for the Val allele of BDNF and better response to OROS-MPH in Korean ADHD children as assessed by four different response criteria.

Annual Research Review: New frontiers in developmental neuropharmacology: can long-term therapeutic effects of drugs be optimized through carefully timed early intervention?

Our aim is to present a working model that may serve as a valuable heuristic to predict enduring effects of drugs when administered during development. Our primary tenet is that a greater understanding of neurodevelopment can lead to improved treatment that intervenes early in the progression of a given disorder and prevents symptoms from manifesting. The immature brain undergoes significant changes during the transitions between childhood, adolescence, and adulthood. Such changes in innervation, neurotransmitter levels, and their respective signaling mechanisms have profound and observable changes on typical behavior, but also increase vulnerability to psychiatric disorders when the maturational process goes awry. Given the remarkable plasticity of the immature brain to adapt to its external milieu, preventive interventions may be possible. We intend for this review to initiate a discussion of how currently used psychotropic agents can influence brain development. Drug exposure during sensitive periods may have beneficial long-term effects, but harmful delayed consequences may be possible as well. Regardless of the outcome, this information needs to be used to improve or develop alternative approaches for the treatment of childhood disorders. With this framework in mind, we present what is known about the effects of stimulants, antidepressants, and antipsychotics on brain maturation (including animal studies that use more clinically-relevant dosing paradigms or relevant animal models). We endeavor to provocatively set the stage for altering treatment approaches for improving mental health in non-adult populations.

Ciproxifan, a histamine H₃-receptor antagonist / inverse agonist, modulates methamphetamine-induced sensitization in mice

The role of histamine neurons in schizophrenia and psychostimulant abuse remains unclear. Behavioural sensitization to psychostimulants is a cardinal feature of these disorders. Here, we have explored the ability of imetit and ciproxifan (CPX), a reference H₃-receptor agonist and inverse agonist, respectively, to modulate locomotor sensitization induced in mice by methamphetamine (MET). Mice received saline, CPX (3 mg/kg) or imetit (3 mg/kg) 2 h before MET (2 mg/kg), once daily for 12 days, and were killed after a 2-day wash out. Imetit had no effect, but CPX induced a decrease of MET-induced locomotor activity, which became significant at Day 5, and even more at Day 10. Quantitative polymerase chain reaction was used in the sensitized mice to quantify brain-derived neurotrophic factor (BDNF) and N-methyl-D-aspartate (NMDA)-receptor subunit 1 (NR1) mRNAs, two factors that are altered in both schizophrenia and drug abuse. Imetit and CPX used alone had no effect on any marker. Sensitization by MET decreased BDNF mRNAs by 40% in the hippocampus. This decrease was reversed by CPX. Sensitization by MET also induced strong decreases of NR1 mRNAs in the cerebral cortex, hippocampus and striatum, but not hypothalamus. These decreases were also reversed by CPX. The strong modulator effect of CPX in mice sensitized to MET may result from its modulator effect on NR1 mRNAs in the cerebral cortex and striatum. The reversal by CPX of BDNF and NR1 mRNAs in the hippocampus of sensitized animals further strengthens the interest of H₃-receptor inverse agonists for the long-term treatment of cognitive deficits of patients with schizophrenia.

Age-dependent effects of methylphenidate in the prefrontal cortex: evidence from electrophysiological and Arc gene expression measurements

Methylphenidate, a drug widely used for attention deficit hyperactivity disorder in children, may affect neuronal function differently in young and adult subjects, particularly in the prefrontal cortex, a brain structure that does not fully develop until adulthood. We compared the impact of development on the effects of methylphenidate on single unit electrical activity and mRNA expression of the effector immediate early gene activity-regulated cytoskeletal-associated protein (Arc) following methylphenidate in the prefrontal cortex in adult (more than 60 days old) and juvenile (25-35 days old) rats. Methylphenidate, administered under urethane anaesthesia to adult rats, at doses ranging from 1 mg/kg to 3 mg/kg intravenously, exerts a progressive activation of firing of prefrontal cortex neurones (30% to 84% from baseline). This activation was significantly lower in the juvenile rats, reaching only 37% of baseline levels at the highest dose (3 mg/kg, intravenous). In adults, methylphenidate (4 mg/kg intraperitoneal) produced marked increases in Arc mRNA levels compared with saline controls by 123% and 164% in cingulated and orbital cortex, respectively. Corresponding values for the juvenile rats were significantly lower (42% and 79%). In summary, this multi-approach investigation showed that the reactivity of prefrontal cortex neurones to methylphenidate differs markedly in juvenile and adult rats.

Sub-chronic exposure to atomoxetine up-regulates BDNF expression and signalling in the brain of adolescent spontaneously hypertensive rats: comparison with methylphenidate

The stimulant methylphenidate and the non-stimulant atomoxetine are widely used for the treatment of Attention-Deficit/Hyperactivity Disorder (ADHD), but the molecular mechanisms of their therapeutic action are not fully understood. The aim of our study was to investigate, in adolescent rats, the sub-chronic effect of these two drugs on neuronal plasticity, through a detailed analysis of BDNF expression and signalling in order to establish the contribution of these mechanisms in the pharmacotherapy of ADHD. Atomoxetine (ATX) up-regulated BDNF mRNA levels in the hippocampus whereas methylphenidate (MPH) increased BDNF gene expression in the nucleus accumbens and caudate-putamen. Opposite effects were seen in the prefrontal cortex, a critical region in attention disorders, where ATX increased while MPH reduced total and exon IV BDNF mRNA levels. Analysis of BDNF-mediated signalling in the prefrontal cortex revealed that ATX enhanced AKT and GSK3β phosphorylation whereas MPH reduced the synaptic levels of trkB, the high-affinity BDNF receptor, and ERK1/2 activation. Our findings show that ATX and MPH exert an opposite modulation of the BDNF system, primarily in prefrontal cortex that, independently from the behavioral control exerted by the two drugs, may be important for long-term consequences on cognitive function.

Perinatal asphyxia: current status and approaches towards neuroprotective strategies, with focus on sentinel proteins

Delivery is a stressful and risky event menacing the newborn. The mother-dependent respiration has to be replaced by autonomous pulmonary breathing immediately after delivery. If delayed, it may lead to deficient oxygen supply compromising survival and development of the central nervous system. Lack of oxygen availability gives rise to depletion of NAD⁺ tissue stores, decrease of ATP formation, weakening of the electron transport pump and anaerobic metabolism and acidosis, leading necessarily to death if oxygenation is not promptly re-established. Re-oxygenation triggers a cascade of compensatory biochemical events to restore function, which may be accompanied by improper homeostasis and oxidative stress. Consequences may be incomplete recovery, or excess reactions that worsen the biological outcome by disturbed metabolism and/or imbalance produced by over-expression of alternative metabolic pathways. Perinatal asphyxia has been associated with severe neurological and psychiatric sequelae with delayed clinical onset. No specific treatments have yet been established. In the clinical setting, after resuscitation of an infant with birth asphyxia, the emphasis is on supportive therapy. Several interventions have been proposed to attenuate secondary neuronal injuries elicited by asphyxia, including hypothermia. Although promising, the clinical efficacy of hypothermia has not been fully demonstrated. It is evident that new approaches are warranted. The purpose of this review is to discuss the concept of sentinel proteins as targets for neuroprotection. Several sentinel proteins have been described to protect the integrity of the genome (e.g. PARP-1; XRCC1; DNA ligase IIIα; DNA polymerase β, ERCC2, DNA-dependent protein kinases). They act by eliciting metabolic cascades leading to (i) activation of cell survival and neurotrophic pathways; (ii) early and delayed programmed cell death, and (iii) promotion of cell proliferation, differentiation, neuritogenesis and synaptogenesis. It is proposed that sentinel proteins can be used as markers for characterising long-term effects of perinatal asphyxia, and as targets for novel therapeutic development and innovative strategies for neonatal care.

Chronic low dose Adderall XR down-regulates cfos expression in infantile and prepubertal rat striatum and cortex

We previously reported that treatment of prepubertal male rats with low, injected or oral, doses of methylphenidate stimulated cfos, fosB and arc expression in many areas of the developing brain. In the present study our objective was to determine whether the widely prescribed psychostimulant Adderall XR (ADD) exerted similar effects in infantile and prepubertal rat brain. We report here, for the first time, that low threshold doses of oral ADD, an extended-release mixture of amphetamine salts, now routinely used for the treatment of Attention Deficit Hyperactivity Disorder (ADHD), also increased cfos expression in infantile (postnatal day 10; PD10) and prepubertal (PD24) rat brain. These threshold doses were correlated with blood levels of amphetamine determined by liquid chromatography-mass spectrometry. Moreover, we observed that chronic treatment with oral ADD (1.6 mg/kg; x 14 days) not only significantly down-regulated cfos expression following a final challenge dose of ADD in prepubertal (PD24) rat striatum and cortex, quantified in terms of FOS immunoreactivity (FOS-ir), but did so at a daily dose that was without effect with methylphenidate (MPH); that is a much higher oral dose of MPH (7.5 mg/kg; x 14 days) failed to induce down-regulation of cfos expression. Similar experiments in infantile rats (PD10), but using a threshold injected dose of ADD (1.25 mg/kg sc) also significantly reduced striatal and cingulate cortical FOS-ir. An additional finding in the prepubertal rats was that oral ADD-induced FOS-ir was observed in the cerebral cortex following doses lower than the threshold dose necessary to increase FOS-ir in the striatum. This was not the case in the PD10 rats. In conclusion, our efforts to calibrate biological responses, such as immediate early gene expression, to clinically relevant blood levels of stimulants confirmed that expression of cfos is very sensitive to repeated low doses of Adderall XR. It is now feasible to examine whether other genes are also affected in these young rats and if the changes we report are reversible. The implications of such studies should be relevant to the putative effects of psychostimulant treatment of very young children.