Methylphenidate Restores Ventral Tegmental Area Dopamine Neuron Activity in Prenatal Ethanol-Exposed Rats by Augmenting Dopamine Neurotransmission

Characterisation of methylphenidate-induced excitation in midbrain dopamine neurons, an electrophysiological study in the rat brain

Methylphenidate (MPH) is a drug routinely used for patients with attention deficit and hyperactivity disorder (ADHD). Concerns arise about psychostimulant use, with dramatic increases in prescriptions. Besides, antipsychotic drugs are often administered in combination with MPH. In this study, we examine the consequences of MPH exposure in combination with dopamine D₂ receptor antagonism (eticlopride) on midbrain dopaminergic neurons in anaesthetised rodents, using in vivo extracellular single-cell electrophysiology. As expected, we show that methylphenidate (2 mg/kg, i.v.) decreases the firing and bursting activities of ventral tegmental area (VTA) dopamine neurons, an effect that is reversed with eticlopride (0.2 mg/kg, i.v.). However, using such a paradigm, we observed higher firing and bursting activities than under baseline conditions. Furthermore, we demonstrate that such an effect is dependent on dual alpha-1 and dopamine D₁ receptors, as well as glutamatergic transmission, through glutamate N-Methyl-D-aspartate (NMDA) receptor activation. Chronic MPH treatment during adolescence greatly dampens MPH-induced excitatory effects measured at adulthood. To conclude, we demonstrated here that a combination of methylphenidate and a dopamine D₂ receptor antagonist produced long-lasting consequences on midbrain dopamine neurons, via glutamatergic-dependent mechanisms.

Prenatal Alcohol Exposure in Rats Diminishes Postnatal Cxcl16 Chemokine Ligand Brain Expression

Maternal ethanol consumption during pregnancy is one of the main causes of Neurodevelopmental disorders (NDD). Prenatal alcohol exposure (PAE) produces several adverse manifestations. Even low or moderate intake has been associated with long-lasting behavioral and cognitive impairment in offspring. In this study we examined the gene expression profile in the rat nucleus accumbens using microarrays, comparing animals exposed prenatally to ethanol and controls. Microarray gene expression showed an overall downward regulatory effect of PAE. Gene cluster analysis reveals that the gene groups most affected are related to transcription regulation, transcription factors and homeobox genes. We focus on the expression of the C-X-C motif chemokine ligand 16 (Cxcl16) which was differentially expressed. There is a significant reduction in the expression of this chemokine throughout the brain under PAE conditions, evidenced here by quantitative polymerase chain reaction qPCR and immunohistochemistry. Chemokines are involved in neuroprotection and implicated in alcohol-induced brain damage and neuroinflammation in the developing central nervous system (CNS), therefore, the significance of the overall decrease in Cxcl16 expression in the brain as a consequence of PAE may reflect a reduced ability in neuroprotection against subsequent conditions, such as excitotoxic damage, inflammatory processes or even hypoxic-ischemic insult.

Modafinil reduces choice impulsivity while increasing motor activity in preadolescent rats treated prenatally with alcohol

Rats exposed prenatally to alcohol show a reduction in the spontaneous activity of dopaminergic neurons of the ventral tegmental area (VTA), as well as greater impulsive behavior and motor activity, behavioral alterations that have been related to dopaminergic dysfunction. Modafinil (MOD) is a dopamine (DA) reuptake blocker prescribed to treat sleep disorders; however, in recent years it has been used for the treatment of ADHD with positive results. Also, studies in humans and rodents show beneficial effects on learning and attention; however, studies evaluating MOD effects on impulsivity are few and show contradictory results. The purpose of this work was to evaluate the effect of a daily dose of MOD (60 mg/kg i.g.) on cognitive (or choice) impulsivity and motor activity in male preadolescent rats exposed prenatally to alcohol or sucrose (isocaloric control). MOD reduced the impulsive responses in a delay discounting task (DDT) at the same time that increased the motor activity, in both healthy and prenatal alcohol treated rats; however, MOD reduced the response latency in DDT only in prenatal alcohol treated rats. This differential effect of DA activation on impulsivity and motor activity show that the MOD dose that improves the impulse control, does not necessarily decrease motor activity, and suggests a possible differential neural mechanism underlying the expression of these behaviors. On the other hand, the changes in the response latency, only in prenatal alcohol treated groups, suggest that decision-making in animals with a dopaminergic dysfunction is more susceptible to be affected by MOD action.

Prenatal and postnatal alcohol exposure increases vulnerability to cocaine addiction in adult mice

BACKGROUND AND PURPOSE

Alcohol exposure in utero may lead to a wide range of long-lasting morphological and behavioural deficiencies known as fetal alcohol spectrum disorders (FASD), associated with a higher risk of later developing neuropsychiatric disorders. However, little is known about the long-term consequences of cocaine use and abuse in individuals with FASD. This study aimed to investigate the effects of maternal binge alcohol drinking during prenatal and postnatal periods on cocaine reward-related behaviours in adult offspring.

EXPERIMENTAL APPROACH

Pregnant C57BL/6 female mice were exposed to an experimental protocol of binge alcohol consumption (drinking-in-the-dark test) from gestation to weaning. Male offspring were subsequently left undisturbed until reaching adulthood and were tested for cocaine-induced motivational responses (conditioned place preference, behavioural sensitization and operant self-administration). Protein expression of dopamine- and glutamate-related molecules was assessed following cocaine-induced reinstatement.

KEY RESULTS

The results show that prenatal and postnatal alcohol exposure enhanced the preference for the cocaine-paired chamber in the conditioned place preference test. Furthermore, early alcohol-exposed mice displayed attenuated cocaine-induced behavioural sensitization but also higher cocaine self-administration. Furthermore, alterations in glutamatergic excitability (GluA1/GluA2 ratio) and ΔFosB expression were found in the prefrontal cortex and the striatum of alcohol-exposed mice after cocaine-primed reinstatement.

CONCLUSION AND IMPLICATIONS

Our findings demonstrate that maternal binge-like alcohol consumption during gestation and lactation alters sensitivity to the reinforcing effects of cocaine in adult offspring mice. Together, such data suggest that prenatal and postnatal alcohol exposure may underlie an enhanced susceptibility of alcohol-exposed offspring to develop drug addiction later in adulthood.

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.

Environmental enrichment reverses increased addiction risk caused by prenatal ethanol exposure

Prenatal ethanol exposure (PE) leads to multiple cognitive and behavioral deficits including increased drug addiction risk. Previous studies have shown that rearing environment plays a significant role in impacting addiction risk. In the present study, we investigated if environmental enrichment during development could be effective in lowering the PE-induced increase in addiction risk. To simulate heavy drinking during pregnancy in humans, pregnant Sprague-Dawley rats received ethanol (6 g/kg/day) or vehicle through intragastric gavage on gestation days 8-20. After weaning, the offspring were reared in either an enriched environment (EE) including neonatal handling and complex housing or an impoverished environment (IE) consisting of barren, single housing. Adult male offspring were then tested for locomotion, performance on the elevated plus maze, and amphetamine self-administration under a progressive ratio reinforcement schedule. Overall, EE rats, compared to IE rats, showed reduced locomotor activity in a novel environment and lower levels of anxiety, irrespective of prenatal treatments. Prenatal ethanol exposure increased amphetamine self-administration at both doses tested (0.02 and 0.05 mg/kg/infusion) and in each case EE, relative to IE, reversed this effect. These findings suggest that postnatal environmental complexity plays a determining role in addiction risk after PE.

Prenatal ethanol exposure increases risk of psychostimulant addiction

Prenatal ethanol exposure (PE) causes many cognitive and behavioral deficits including increased drug addiction risk, demonstrated by enhanced ethanol intake and behavioral phenotypes associated with addiction risk. Additionally, preclinical studies show that PE persistently changes the function of dopaminergic neurons in the ventral tegmental area, a major neural substrate for addiction, and alters these neurons' responses to psychostimulants. Accordingly, PE could also lead to increased risk of addiction to drugs of abuse, other than ethanol. In the present study, addiction risk was examined utilizing paradigms of amphetamine conditioned place preference (CPP) and intravenous self-administration. Ethanol was administered to pregnant dams via intragastric gavage (6  g/kg, during gestational days 8-20). Behavioral tests were conducted in adult male offspring. Amphetamine at a low dose (0.3  mg/kg, i.p.) induced CPP in PE but not control rats, whereas at a higher dose (0.6  mg/kg, i.p.) both groups acquired CPP. There was no group difference in amphetamine-induced CPP reinstatement. Furthermore, PE rats self-administered more amphetamine at a low dose (0.02  mg/kg/infusion) than controls, while no group differences were observed at a higher dose (0.1  mg/kg/infusion). Rats with PE also exhibited greater reactivity to contextual drug cues after extended abstinence and amphetamine-induced reinstatement of drug seeking. These results support that PE persistently leads to increased psychostimulant addiction risk later in life, manifested in many elements of addictive behavior following limited psychostimulant exposure. The observations provide insights into prevention strategies for drug addiction in individuals with fetal alcohol spectrum disorders.

Excitatory synaptic function and plasticity is persistently altered in ventral tegmental area dopamine neurons after prenatal ethanol exposure

Prenatal ethanol exposure (PE) is one of the developmental factors leading to increased addiction propensity (risk). However, the neuronal mechanisms underlying this effect remain unknown. We examined whether increased excitatory synaptic transmission in ventral tegmental area (VTA) dopamine (DA) neurons, which is associated with drug addiction, was impacted by PE. Pregnant rats were exposed to ethanol (0 or 6 g/kg/day) via intragastric intubation from gestational day 8-20. Amphetamine self-administration, whole-cell recordings, and electron microscopy were performed in male offspring between 2 and 12-week-old. The results showed enhanced amphetamine self-administration in PE animals. In PE animals, we observed a persistent augmentation in calcium-permeable AMPA receptor (CP-AMPAR) expression, indicated by increased rectification and reduced decay time of AMPAR-mediated excitatory postsynaptic currents (AMPAR-EPSCs), enhanced depression of AMPAR-EPSCs by NASPM (a selective CP-AMPAR antagonist), and increased GluA3 subunits in VTA DA neuron dendrites. Increased CP-AMPAR expression in PE animals led to enhanced excitatory synaptic strength and the induction of CP-AMPAR-dependent long-term potentiation (LTP), an anti-Hebbian form of LTP. These observations suggest that, in PE animals, increased excitatory synaptic strength in VTA DA neurons might be susceptible to further strengthening even in the absence of impulse flow. The PE-induced persistent increase in CP-AMPAR expression, the resulting enhancement in excitatory synaptic strength, and CP-AMPAR-dependent LTP are similar to effects observed after repeated exposure to drugs of abuse, conditions known to increase addiction risk. Therefore, these mechanisms could be important neuronal substrates underlying PE-induced enhancement in amphetamine self-administration and increased addiction risk in individuals with fetal alcohol spectrum disorders.

Prenatal alcohol exposure and adolescent stress - unmasking persistent attentional deficits in rats

Prenatal alcohol exposure (PAE) can produce a myriad of deficits. Unfortunately, affected individuals may also be exposed to the stress of an adverse home environment, contributing to deficits of attentional processes that are the hallmark of optimal executive function. Male offspring of ad-libitum-fed Control (Con), Pairfed (PF), and PAE dams were randomly assigned to either a 5-day period of variable chronic mild stress (CMS) or no CMS in adolescence. In adulthood, rats were trained in a non-match to sample task (T-maze), followed by extensive assessment in the five-choice serial reaction time task. Once rats acquired the five-choice serial reaction time task (stable accuracy), they were tested in three challenge conditions: (i) increased sustained attention, (ii) selective attention and, (iii) varying doses of d-amphetamine, an indirect dopamine and norepinephrine agonist. At birth and throughout the study, PAE offspring showed reduced body weight. Moreover, although PAE animals were similar to Con animals in task acquisition, they were progressively less proficient with transitions to shorter stimulus durations (decreased accuracy and increased omissions). Five days of adolescent CMS increased basal corticosterone levels in adolescence and disrupted cognitive performance in adulthood. Further, CMS augmented PAE-related disturbances in acquisition and, to a lesser extent, also disrupted attentional processes in Con and PF animals. Following task acquisition, challenges unmasked persistent attentional difficulties resulting from both PAE and adolescent CMS. In conclusion, PAE, adolescent CMS, and their interaction produced unique behavioural profiles that suggest vulnerability in select neurobiological processes at different stages of development.

Prefrontal grey and white matter neurometabolite changes after atomoxetine and methylphenidate in children with attention deficit/hyperactivity disorder: a (1)H magnetic resonance spectroscopy study

Attention deficit/hyperactivity disorder (ADHD) is the most common neurobehavioral childhood disorder. Dysfunction of prefrontal neural circuits which are responsible for executive and attentional functions has been previously shown in ADHD. We investigated the neurometablite changes in areas included in dorsolateral prefrontal neural circuits after 2 months of long-acting methylphenidate or atomoxetine medication in children with ADHD who were responders to treatment. Twenty-one ADHD children were examined by single voxel (1)H-magnetic resonance spectroscopy (MRS) before and after 2 months of medication with OROS methylphenidate (n=10) or atomoxetine (n=11). The spectra were taken from the dorsolateral prefrontal cortex (DLPFC, 8ml) and white matter behind the DLPFC (anterior semioval center, 7.5ml), bilaterally. NAA and NAA/Cr (N-acetylaspartate/creatine) decreased in the left DLPFC and Cho/Cr (choline/creatine) increased in the right DLPFC after atomoxetine medication. Glu+Gln and Glu+Gln/Cr (glutamate/glutamine) increased in the left white matter after methylphenidate medication. We hypothesize that atomoxetine could decrease hyperactivation of DLPFC neurons and methylphenidate could lead to increased activation of cortical glutamatergic projections with the consequences of increased tonic dopamine release in the mesocortical system.

The effects of prenatal alcohol exposure on behavior: rodent and primate studies

The use of alcohol by women during pregnancy is a continuing problem. In this review the behavioral effects of prenatal alcohol from animal models are described and related to studies of children and adults with FASD. Studies with monkeys and rodents show that prenatal alcohol exposure adversely affects neonatal orienting, attention and motor maturity, as well as activity level, executive function, response inhibition, and sensory processing later in life. The primate moderate dose behavioral findings fill an important gap between human correlational data and rodent mechanistic research. These animal findings are directly translatable to human findings. Moreover, primate studies that manipulated prenatal alcohol exposure and prenatal stress independently show that prenatal stress exacerbates prenatal alcohol-induced behavioral impairments, underscoring the need to consider stress-induced effects in fetal alcohol research. Studies in rodents and primates show long-term effects of prenatal and developmental alcohol exposure on dopamine system functioning, which could underpin the behavioral effects.

Fetal alcohol-induced hyperactivity is reversed by treatment with the PPARα agonist fenofibrate in a rat model

INTRODUCTION

Exposure to alcohol in utero is linked to the development of a wide range of psychobehavioral changes, notably hyperactivity and attention deficit, with complex underlying pathological and functional mechanisms. Although the currently available treatments for hyperactivity have been studied in children exposed to alcohol in utero, the efficacy of these compounds is subject to debate and has prompted efforts to identify new pharmacological targets.

METHOD

In a rat model of early alcohol exposure (i.e., in utero and during lactation), we studied the effect of the lipid-lowering peroxisome proliferator-activated receptor (PPAR) alpha activator fenofibrate on psychobehavioral impairments.

RESULTS

In the young rat, early exposure to alcohol perturbs locomotor behavior and induces prepubertal hyperactivity and postpubertal hypoactivity. The hyperactivity, usually observed at the end of the fifth week of life, was prevented by the administration of fenofibrate, which also had a beneficial effect on the accompanying attention deficit by reinforcing sustained attention.

CONCLUSION

Our results with fenofibrate suggest that the pharmacological modulation of nuclear receptors such as PPAR-alpha may constitute a new therapeutic approach to managing the psychobehavioral disorders associated with early alcohol exposure.

Early life experience alters behavioral responses to sweet food and accumbal dopamine metabolism

Neonatal handling in rats persistently alters behavioral parameters and responses to stress. Such animals eat more sweet food in adult life, without alterations in lab chow ingestion. Here, we show that neonatally handled rats display greater incentive salience to a sweet reward in a runway test; however they are less prone to conditioned place preference and show less positive hedonic reactions to sweet food. When injected with methylphenidate (a dopamine mimetic agent), non-handled rats increase their sweet food ingestion in the fasted state, while neonatally handled rats do not respond. We did not observe any differences regarding baseline general ambulatory activity between the groups. A lower dopamine metabolism in the nucleus accumbens was observed in handled animals, without differences in norepinephrine content. We suggest that early handling leads to a particular response to positive reinforcers such as palatable food, in a very peculiar fashion of higher ingestion but lower hedonic impact, as well as higher incentive salience, but diminished dopaminergic metabolism in the nucleus accumbens.

Effects of prenatal and postnatal maternal ethanol on offspring response to alcohol and psychostimulants in long evans rats

An important factor that may influence addiction liability is exposure during the early life period. Exposure to ethanol, early in life, can have long-lasting implications on brain function and drugs of abuse response later in life. In the present study we investigated the behavioral responses to ethanol and to psychostimulants in Long Evans rats that have been exposed to pre- and postnatal ethanol. Since a relationship between heightened drug intake and susceptibility to drug-induced locomotor activity/sensitization has been demonstrated, we tested these behavioral responses, in control and early life ethanol-exposed animals. The young adult male and female progeny were tested for locomotor response to alcohol, cocaine and d-amphetamine. Sedative, rewarding effects of alcohol and alcohol consumption were measured. Our results show that early life ethanol exposure behaviorally sensitized animals to subsequent ethanol and psychostimulants exposure. Ethanol-exposed animals were also more sensitive to the hyperlocomotor effects of all drugs of abuse tested and to those of the dopamine receptor agonist apomorphine. Locomotor sensitization to repeated injections of cocaine was facilitated in ethanol-exposed animals. Ethanol-induced conditioned place preference was also facilitated in ethanol-exposed animals. Ethanol consumption and preference were increased after early life ethanol exposure and this was associated with decreased sensitivity to the sedative effects of ethanol. The altered behavioral responses to drugs of abuse were associated with decreased striatal dopamine transporter and hippocampal NMDAR binding. Our results outline an increased vulnerability to rewarding and stimulant effects of ethanol and psychostimulants and support the epidemiological and clinical data that suggested that early chronic exposure to ethanol may increase the propensity for later self-administration of ethanol or other substances.

Motivational effect of nomifensine in the intracranial self-stimulation behavior using a runway method

Intracranial self-stimulation (ICSS) behavior is an experimental methodology to study reward and motivational effects. We have established a new paradigm to evaluate enhancing motivation by drugs in the runway method using the priming stimulation of ICSS. In the present study, we investigated the effects of nomifensine on the experimental extinction process of non-reinforcing reward and pre-trial electric priming stimulations in lateral hypothalamic self-stimulation. In this study, the experimental extinction process of the non-reinforcing reward means the experimental method of excluding reward effect in ICSS behavior. The extinction process in the runway method consisted of these 15 trials. Nomifensine, an antidepressant drug, delayed the running speed of the extinction process at doses of 5 and 10 mg/kg (i.p.) compared with the vehicle alone. This result suggests that the delay in the running speed of the extinction process promotes a motivational effect in rats. Previously, priming stimulation in the runway method was found to affect motivational function of ICSS. Therefore, our findings suggest the possible application of nomifensine for improving motivation.

The contribution of fetal drug exposure to temperament: potential teratogenic effects on neuropsychiatric risk

BACKGROUND

Preliminary evidence indicates that fetal drug exposure may be associated with alterations in temperament. However, studies often do not dissociate the potential effects of drug exposure from other perinatal or environmental factors that could influence temperament phenotypes.

METHODS

High risk children (n = 120) were followed from birth to 6 months of age to determine the effects of fetal drug exposure on temperament, after controlling for the child's gender, gestational age, medical morbidity, ethnicity, and maltreatment as well as the mother's stress, income adequacy, and quality of caregiving. Methods included medical chart review, questionnaires, and videotapes of mother-child interaction.

RESULTS

Preliminary analyses indicated that fetal drug exposure was associated with both distractibility and intensity of children's responses to the environment at 6 months of age. After adjusting for potentially confounding variables, drug exposure accounted for 12% of the variance in distractibility but was not a significant predictor in the regression model for intensity.

CONCLUSIONS

Findings suggest that drug-exposed children may experience difficulty sustaining their focus of attention and be more easily distracted by environmental stimuli than non-drug-exposed children. Results converge with previous research to implicate cortical hyperarousal, stemming from teratogenic effects on the dopaminergic system during fetal development.

Effects of Prenatal Ethanol Exposure on the Excitability of Ventral Tegmental Area Dopamine Neurons in Vitro

Prenatal ethanol exposure leads to a persistent reduction in the number of spontaneously active dopaminergic (DA) neurons (DA neuron population activity) in the ventral tegmental area (VTA) in developing and adult animals. This effect might contribute to the dysfunction of the mesolimbic/cortical DA system and attention problems in children with fetal alcohol spectrum disorders. To characterize the underlying cellular mechanism for prenatal ethanol exposure-induced reduction in VTA DA neuron population activity, we used the whole-cell patch-clamp technique to study the membrane properties of putative VTA DA neurons in brain slices in 2- to 3-week-old control and prenatal ethanol-exposed animals. The results show that prenatal ethanol exposure did not impair the spontaneous pacemaker activity in putative VTA DA neurons but reduced the frequency of evoked action potentials. In addition, prenatal ethanol exposure led to a reduction in hyperpolarization-induced cation current (I(h)) and an up-regulation of somatodendritic DA autoreceptors. The above prenatal ethanol exposure-induced changes could decrease the excitability of VTA DA neurons. However, they do not seem to play a role in reduced VTA DA neuron population activity in vivo, an effect thought to be mediated by excessive excitation leading to depolarization inactivation. Taken together, the above results indicate that prenatal ethanol exposure-induced reduction in VTA DA neuron population activity in vivo is not caused by changes in the intrinsic pacemaker activity or other membrane properties and could instead be caused by altered inputs to VTA DA neurons.

Perspectives on cognitive domains, H3 receptor ligands and neurological disease

Histamine H(3) receptor agonists and antagonists have been evaluated in numerous in vitro and in vivo animal models to better understand how H(3) receptors modulate neurotransmitter function in the central nervous system. Likewise, behavioural models have explored the hypothesis that changes in neurotransmitter release could enhance cognitive function in human diseases. This review examines the reported effects of H(3) receptor ligands and how they influence cognitive behaviour. These data are interpreted on the basis of different cognitive domains that are relevant to neuropsychiatric diseases. Because of the diversity of H(3) receptors, their function and their influence on neurotransmitter systems, considerable promise exists for H(3) ligands to treat diseases in which aspects of learning and memory are impaired. However, because of the complexities of the histaminergic system and H(3) receptors and the lack of clinical data so far, proof of principle for use in human disease remains to be established.

Different adaptations in ventral tegmental area dopamine neurons in control and ethanol exposed rats after methylphenidate treatment

BACKGROUND

Methylphenidate (MPH) is a psychostimulant effective in treating attention-deficit/hyperactivity disorder (ADHD). Repeated MPH treatment may increase substance abuse risk because of adaptations in dopaminergic (DA) function associated with sensitization to subsequent stimulant exposure. However, this possibility is based on observations in normal animals and may not apply to animals with attention problems linked to compromised DA function such as prenatal ethanol exposed (PE) animals.

METHODS

The electrical activity of ventral tegmental area (VTA) DA neurons was studied after the cessation of repeated MPH treatment at a threshold dose (1 mg/kg/day for 3 weeks) in PE and control rats.

RESULTS

In control rats, there was a continuous increase in VTA DA neuron excitability post-MPH treatment, characterized by a transient increase in population activity (1 day posttreatment) followed by decreased population activity (30-60 days posttreatment) in most of the animals due to depolarization inactivation. In PE rats, MPH treatment decreased the excessive excitability of VTA DA neurons and resulted in prolonged normalization in the population activity (1-60 days posttreatment). These changes were not mediated by altered sensitivity of somatodendritic DA autoreceptors.

CONCLUSIONS

Repeated MPH treatment produced distinctly different effects on VTA DA neuron activity in control and PE animals. These results suggest that repeated MPH treatment for ADHD may not lead to increased substance abuse risk in special populations such as individuals with fetal alcohol spectrum disorder.

Moderate-level prenatal alcohol exposure alters striatal dopamine system function in rhesus monkeys

BACKGROUND

Moderate prenatal alcohol exposure can cause impairments even in the absence of gross morphological defects associated with fetal alcohol syndrome. The basal ganglia, which include the dopamine-rich striatum, are sensitive to fetal alcohol-induced injury. In this study, we manipulated the timing of moderate-level alcohol exposure and compared the risk of adverse effects on striatal dopamine (DA) system function in rhesus monkeys.

METHODS

Thirty-five young adult rhesus monkeys (Macaca mulatta) from four groups of females were assessed: (1) an early alcohol-exposed group (n=9), in which mothers voluntarily consumed 0.6 g/kg alcohol solution on gestational days 0 through 50; (2) a middle-to-late gestation alcohol-exposed group (n=7), in which mothers voluntarily consumed 0.6 g/kg alcohol solution on gestational days 50 through 135; (3) a continuous-exposure group (n=9), in which mothers voluntarily consumed 0.6 g/kg alcohol solution on days 0 through 135; and (4) controls (n=10), in which mothers voluntarily consumed an isocaloric control solution on gestational days 0 through 50, 50 through 135, or 0 through 135. We studied striatal DA system function by positron emission tomography in separate scans for trapping of [(18)F]fallypride and 6-[(18)F]fluoro-m-tyrosine to assess striatal DA D2 receptor (D2R) binding and DA synthesis, respectively, via dopadecarboxylase activity.

RESULTS

Moderate-level alcohol exposure during early gestation and continuous exposure throughout gestation (early + middle-to-late exposure) reduced the striatal D2R binding to DA synthesis ratio, whereas middle-to-late alcohol gestation exposure increased the striatal D2R binding to DA synthesis ratio. The continuous-exposure group showed the largest effect. Moreover, the D2R binding/DA synthesis ratio was related to neonatal neurobehavior measures in control monkeys, but these relationships were disrupted in the fetal alcohol-exposed monkeys.

CONCLUSION

These results suggest that the vulnerability of the DA system to the effects of moderate doses of alcohol during gestation depend on the timing of the alcohol exposure. Early-gestation moderate alcohol exposure resulted in a reduction or blunting of dopaminergic function in adulthood, whereas middle to late exposure (without early exposure) either induced the opposite pattern or heightened dopaminergic function. Continuously exposed monkeys showed the largest effect, suggesting that the sooner women stop drinking, the better it is for the fetus.

Early postnatal ethanol administration does not affect prepulse inhibition in rats

Human prenatal ethanol exposure is associated with relatively widespread cognitive deficits but it is unclear whether general deficits in responsivity to sensory stimuli contribute to or underlie the deficits in later or more complex stages of information processing. The present experiment assessed the effects of early postnatal ethanol administration in rats on prepulse inhibition, with animals tested in adolescence (postnatal day (PD) 35) and early adulthood (PD 70). Animals were assigned to receive ethanol (5.25 g/kg) via intragastric intubation on PD 4-9, sham-intubation, or to a naive control group. Pre-exposure to ethanol did not differentially affect the magnitude of the response to the startle stimulus alone nor did it affect the percent inhibition of the startle response on trials with a prepulse stimulus. Male rats exhibited a greater percent inhibition than female rats on PD 35 at all interstimulus intervals (ISIs) except the shortest, 4 ms. Female rats exhibited a greater percent inhibition than male rats at all ISIs on PD 70. Collectively, these data demonstrate that cognitive deficits associated with early exposure to ethanol may not be attributable to deficits in sensorimotor gating, at least to the extent this construct is measured by prepulse inhibition.

Actions of methylphenidate on dopaminergic neurons of the ventral midbrain

BACKGROUND

Methylphenidate has been suggested to exert its therapeutic effect mainly by blocking the dopamine transporter. In spite of the importance of this interaction, no detailed information is available yet on its actions on single dopaminergic neurons.

METHODS

We examined the effects of methylphenidate on dopaminergic neurons using electrophysiological recordings from rat midbrain slices.

RESULTS

Methylphenidate inhibited spontaneous firing and caused a membrane hyperpolarization in current clamp or an outward current in voltage clamp. These effects were antagonized by the D(2) receptor antagonist sulpiride. An acute dopamine-depleting treatment of the slices with the dopa-decarboxylase inhibitor carbidopa significantly reduced the effects of methylphenidate. This drug potentiated, in a concentration-dependent manner, cellular responses to exogenous dopamine application.

CONCLUSIONS

Our electrophysiological data are consistent with the hypothesis that methylphenidate inhibits dopamine transporter and suggest that the depression of firing is mediated by the release of newly synthesized dopamine which accumulates extracellularly due to inhibition of its reuptake.

Prenatal ethanol exposure alters the postnatal development of the spontaneous electrical activity of dopamine neurons in the ventral tegmental area

Prenatal ethanol exposure causes a persistent reduction in the spontaneous electrical activity of dopamine (DA) neurons in the ventral tegmental area (VTA) in adult animals. Because DA neuron activity matures into adult pattern during postnatal development, it is possible that reduced activity in VTA DA neurons after prenatal ethanol exposure is caused by impaired postnatal development. This possibility was investigated in the present study using the in vivo extracellular single-unit recording and brain stimulation techniques. The results show an age-dependent decrease in the number of spontaneously active VTA DA neurons from 2 to 4 weeks of age in both the control and prenatal ethanol-exposed animals. In ethanol-exposed animals, the age-dependent decrease was more prominent after 3 weeks of age, resulting in lower numbers of spontaneously active VTA DA neurons in 4-week-old and adult animals. In both the control and ethanol-exposed animals, there were age-dependent increases in the firing rates and burst firing activity of VTA DA neurons after 2 weeks of age. Ethanol exposure led to slightly lower firing rates in 4-week-old and adult animals and did not impact the burst firing pattern in any age groups. There were no changes in axon conduction velocity and antidromic spike characteristics of VTA DA neurons. These results indicate that reduced activity of VTA DA neurons during adulthood after prenatal ethanol exposure does not begin prenatally. Instead, it is a result of impaired postnatal development manifested only when animals reach 4 weeks of age. These results suggest that early intervention may be an effective treatment strategy for attention deficit/hyperactivity disorder, a behavioral dysfunction related to the abnormalities of DA systems and often observed in children with fetal alcohol spectrum disorder.