Methylphenidate has long-lasting metaplastic effects in the prefrontal cortex of adolescent rats

Methylphenidate Restores Behavioral and Neuroplasticity Impairments in the Prenatal Nicotine Exposure Mouse Model of ADHD: Evidence for Involvement of AMPA Receptor Subunit Composition and Synaptic Spine Morphology in the Hippocampus

In ADHD treatment, methylphenidate (MPH) is the most frequently used medication. The present work provides evidence that MPH restored behavioral impairments and neuroplasticity due to changes in AMPAR subunit composition and distribution, as well as maturation of dendritic spines, in a prenatal nicotine exposure (PNE) ADHD mouse model. PNE animals and controls were given a single oral dose of MPH (1 mg/kg), and their behavior was tested for attention, hyperactivity, and working memory. Long-term potentiation (LTP) was induced and analyzed at the CA3/CA1 synapse in hippocampal slices taken from the same animals tested behaviorally, measuring fEPSPs and whole-cell patch-clamp EPSCs. By applying crosslinking and Western blots, we estimated the LTP effects on AMPAR subunit composition and distribution. The density and types of dendritic spines were quantified by using the Golgi staining method. MPH completely restored the behavioral impairments of PNE mice. Reduced LTP and AMPA-receptor-mediated EPSCs were also restored. EPSC amplitudes were tightly correlated with numbers of GluA1/GluA1 AMPA receptors at the cell surface. Finally, we found a lower density of dendritic spines in hippocampal pyramidal neurons in PNE mice, with a higher fraction of thin-type immature spines and a lower fraction of mushroom mature spines; the latter effect was also reversed by MPH.

DCC-related developmental effects of abused- versus therapeutic-like amphetamine doses in adolescence

The guidance cue receptor DCC controls mesocortical dopamine development in adolescence. Repeated exposure to an amphetamine regimen of 4 mg/kg during early adolescence induces, in male mice, downregulation of DCC expression in dopamine neurons by recruiting the Dcc microRNA repressor, microRNA-218 (miR-218). This adolescent amphetamine regimen also disrupts mesocortical dopamine connectivity and behavioral control in adulthood. Whether low doses of amphetamine in adolescence induce similar molecular and developmental effects needs to be established. Here, we quantified plasma amphetamine concentrations in early adolescent mice following a 4 or 0.5 mg/kg dose and found peak levels corresponding to those seen in humans following recreational and therapeutic settings, respectively. In contrast to the high doses, the low amphetamine regimen does not alter Dcc mRNA or miR-218 expression; instead, it upregulates DCC protein levels. Furthermore, high, but not low, drug doses downregulate the expression of the DCC receptor ligand, Netrin-1, in the nucleus accumbens and prefrontal cortex. Exposure to the low-dose regimen did not alter the expanse of mesocortical dopamine axons or their number/density of presynaptic sites in adulthood. Strikingly, adolescent exposure to the low-dose drug regimen does not impair behavioral inhibition in adulthood; instead, it induces an overall increase in performance in a go/no-go task. These results show that developmental consequences of exposure to therapeutic- versus abused-like doses of amphetamine in adolescence have dissimilar molecular signatures and opposite behavioral effects. These findings have important clinical relevance since amphetamines are widely used for therapeutic purposes in youth.

Baicalin regulates the dopamine system to control the core symptoms of ADHD

We aimed to test the therapeutic effects of baicalin on attention deficit hyperactivity disorder (ADHD) in an animal model and to explain the potential mechanism. We investigated the therapeutic effects and mechanisms of baicalin in a spontaneously hypertensive rat (SHR) model of ADHD depending on the dopamine (DA) deficit theory. In this study, fifty SHRs were randomly divided into five groups: methylphenidate (MPH), baicalin (50 mg/kg, 100 mg/kg, or 150 mg/kg), and saline-treated. Ten Wistar Kyoto (WKY) rats were used as controls. All rats were orally administered the treatment for four weeks. Motor activity, spatial learning and memory ability were assessed with the open-field and Morris water-maze tests. The mRNA and protein levels of tyrosine hydroxylase (TH), vesicular monoamine transporter 2 (VMAT2), synaptosomal-associated protein of molecular mass 25kD (SNAP25) and synataxin 1a in synaptosomes were detected with real-time polymerase chain reaction (PCR) and Western blot. In addition, DA levels were measured in the prefrontal cortex and striatum. The results indicated that both MPH and baicalin at doses of 150 mg/kg and 100 mg/kg significantly decreased the hyperactivity and improved the spatial learning memory deficit in the SHRs and increased the synaptosomal mRNA and protein levels of TH, SNAP25, VMAT2 and synataxin 1a compared with saline treatment. MPH significantly increased DA levels in both the prefrontal cortex (PFC) and striatum, while baicalin significantly increased DA levels only in the striatum. The results of the present study showed that baicalin treatment was effective for controlling the core symptoms of ADHD. Baicalin increased DA levels only in the striatum, which suggested that baicalin may target the striatum. The increased DA levels may partially be attributed to the increased mRNA and protein expression of TH, SNAP25, VMAT2, and syntaxin 1a. Therefore, these results suggested that the pharmacological effects of baicalin were associated with the synthesis, vesicular localization, and release of DA and might be effective in treating ADHD. However, further studies are required to better understand the molecular mechanisms underlying these findings.

Chronic methylphenidate treatment during adolescence has long-term effects on monoaminergic function

BACKGROUND

Psychostimulants like methylphenidate or D-amphetamine are often prescribed for attention deficit and hyperactivity disorders in children. Whether such drugs can be administered into a developing brain without consequences in adulthood is still an open question.

METHODS

Here, using in vivo extracellular electrophysiology in anesthetised preparations, combined with behavioural assays, we have examined the long-term consequences in adulthood of a chronic methylphenidate oral administration (5 mg/kg/day, 15 days) in early adolescent (post-natal day 28) and late adolescent (post-natal day 42) rats, by evaluating body weight change, sucrose preference (indicator of anhedonia), locomotor sensitivity to D-amphetamine and electrical activities of ventral tegmental area dopamine and dorsal raphe nucleus serotonin neurons.

RESULTS

Chronic methylphenidate treatment during early or late adolescence did not induce weight deficiencies and anhedonia-like behaviours at adulthood. However, it increased bursting activities of dorsal raphe nucleus serotonin neurons. Furthermore, chronic methylphenidate treatment during early but not during late adolescence enhanced D-amphetamine-induced rearing activity, as well as ventral tegmental area dopamine cell excitability (firing, burst and population activity), associated with a partial desensitisation of dopamine D₂ auto-receptors.

CONCLUSIONS

We have demonstrated here that early, but not late, adolescent exposure to oral methylphenidate may induce long-lasting effects on monoamine neurotransmission. The possible clinical implication of these data will be discussed.

Single and Repeated Administration of Methylphenidate Modulates Synaptic Plasticity in Opposite Directions via Insertion of AMPA Receptors in Rat Hippocampal Neurons

Methylphenidate (MPH) is widely used in the treatment of Attention Deficit Hyperactivity Disorder. Several lines of evidence support that MPH can modulate learning and memory processes in different ways including improvement and impairment of test performances. A relevant factor in the efficacy of treatment is whether administration is performed once or several times. In this study we demonstrate opposite effects of MPH on performance of preadolescent rats in the Morris Water Maze test. Animals treated with a single dose (1 mg/kg) performed significantly better compared to controls, while in animals treated with repetitive administration at the same concentration performance was reduced. We found that hippocampal LTP in slices from rats treated with a single dose was increased, while LTP from rats treated with repetitive injections of MPH was lower than in controls. Using Western blot of CA1 areas from potentiated slices of rats treated with a single dose we found a significant increase of phosphorylation at Ser845 of GluA1 subunits, associated to an increased insertion of GluA1-containing AMPARs in the plasma membrane. These receptors were functional, because AMPA-dependent EPSCs recorded on CA1 were enhanced, associated to a significant increase in short-term plasticity. In contrast, CA1 samples from rats injected with MPH during six consecutive days, showed a significant decrease in the phosphorylation at Ser845 of GluA1 subunits associated to a lower insertion of GluA1-containing AMPARs. Accordingly, a reduction of the AMPA-mediated EPSCs and short-term plasticity was also observed. Taken together, our results demonstrate that single and repeated doses with MPH can induce opposite effects at behavioral, cellular, and molecular levels. The mechanisms demonstrated here in preadolescent rats are relevant to understand the effects of this psychostimulant in the treatment of ADHD.

Adolescent Exposure to Methylphenidate Increases Impulsive Choice Later in Life

Background: The psychostimulant methylphenidate (MPH) is known to temporarily reduce impulsive choice and promote self-control. What is not sufficiently understood is how repeated treatment with MPH affects impulsive choice in the long run, and whether any such effect is contingent on exposure at certain developmental stages. Methods: Using an animal model for impulsive choice, we examined first whether giving MPH through early adolescence alters delay discounting, an operational measure of impulsive choice, later in adulthood. We then tested whether equivalent long-term effects are observed if exposure to the drug occurred during adulthood. Starting on postnatal day 25 or postnatal day 60, male rats received one of a range of doses of MPH for 10 consecutive days. Twenty-six days later, all rats were trained to choose between a lever that produced a small immediate reward and a lever that produced a large reward after a range of delays. Results: Rats showed a long-term decrease in the selection of the delayed larger reward when treated with moderate doses of MPH during early adolescence, but not when treated with the lower or higher doses. In contrast, no differences were observed in the selection of the delayed larger reward in animals that were treated with various doses of MPH during adulthood. Conclusions: Our findings suggest effects of MPH on impulsive choice that are contingent on dosage and on the developmental period of exposure. When administered during adolescence, moderate doses of MPH increase impulsive choice long after the end of treatment, whereas these same doses administered during adulthood were without effect.

Synaptic functions of endocannabinoid signaling in health and disease

Endocannabinoids (eCBs) are a family of lipid molecules that act as key regulators of synaptic transmission and plasticity. They are synthetized "on demand" following physiological and/or pathological stimuli. Once released from postsynaptic neurons, eCBs typically act as retrograde messengers to activate presynaptic type 1 cannabinoid receptors (CB₁) and induce short- or long-term depression of neurotransmitter release. Besides this canonical mechanism of action, recent findings have revealed a number of less conventional mechanisms by which eCBs regulate neural activity and synaptic function, suggesting that eCB-mediated plasticity is mechanistically more diverse than anticipated. These mechanisms include non-retrograde signaling, signaling via astrocytes, participation in long-term potentiation, and the involvement of mitochondrial CB₁. Focusing on paradigmatic brain areas, such as hippocampus, striatum, and neocortex, we review typical and novel signaling mechanisms, and discuss the functional implications in normal brain function and brain diseases. In summary, eCB signaling may lead to different forms of synaptic plasticity through activation of a plethora of mechanisms, which provide further complexity to the functional consequences of eCB signaling. This article is part of the Special Issue entitled "A New Dawn in Cannabinoid Neurobiology".

Acute and long-term effects of adolescent methylphenidate on decision-making and dopamine receptor mRNA expression in the orbitofrontal cortex

Though commonly used as a treatment for ADHD, the psychostimulant methylphenidate (MPH) is also misused and abused in adolescence in both clinical and general populations. Although MPH acts via pathways activated by other drugs of abuse, the short- and long-term effects of MPH on reward processing in learning and decision-making are not clearly understood. We examined the effect of adolescent MPH treatment on a battery of reward-directed behaviors both in adolescence during its administration and in adulthood after its discontinuation. We further measured whether MPH had lasting effects on dopamine receptor mRNA expression in orbitofrontal cortex (OFC) that may correspond with behavior. Long-Evans rats were injected with MPH (0, 1, 2.5, or 5mg/kg IP) twice daily from middle to late adolescence (PD38-57). During adolescence, the high dose of MPH reduced preference for large rewards in a Reward Magnitude Discrimination task, but did not affect preference for smaller-sooner rewards in a Delay Discounting task. In adulthood, after discontinuation of MPH, animals previously treated with the moderate dose of MPH showed improved acquisition, but not reversal, in a Reversal Learning task. MPH exposure did not increase preference for large-risky rewards in a Risk task in adulthood. We then quantified mRNA expression of D1, D2, and D3 receptors in the OFC using qPCR. MPH increased mRNA expression of dopamine D3 receptor subtype, but not D1 or D2. Overall, these results indicate that MPH has both immediate and lasting effects on reward-dependent learning and decisions, as well as dopaminergic function in rodents.