Low dopamine D5 receptor density in hippocampus in an animal model of attention-deficit/hyperactivity disorder (ADHD).

A state of low dopaminergic activity has been implicated in attention-deficit/hyperactivity disorder (ADHD). The clinical symptoms of ADHD include inattention, impulsivity and hyperactivity, as well as impaired learning; dopaminergic modulation of the functions in the hippocampus is important to both learning and memory. To determine dopamine receptor (DR) density in a well-established animal model for ADHD, we quantified the dopamine D5 receptors in the hippocampus in the spontaneously hypertensive rat. We used immunofluorescence microscopy and immunogold electron microscopy to quantify the dopamine D5 receptor density on CA1 pyramidal cell somas and dendrites and dendritic spines in the stratum radiatum and stratum oriens. The density of the dopamine D5 receptors was significantly lower in the cytoplasm of pyramidal cell somas in the spontaneously hypertensive rat compared to the control, indicating a reduced reservoir for insertion of receptors into the plasma membrane. DRs are important for long-term potentiation and long-term depression, hence the deficit may contribute to the learning difficulties in individuals with the diagnosis of ADHD.

Dopamine D5 receptors are localized at asymmetric synapses in the rat hippocampus.

Functional studies indicate that the dopamine D5 receptor is involved in synaptic transmission in the hippocampus. However, previous anatomical studies have detected D5 receptor labelling primarily on the soma and main dendrites of CA1 pyramidal cells and on dendritic spines in monkey but not in rats. In order to get a better understanding of putative dopamine function in the hippocampus, we quantified the D5 receptor immunoreactivity on the pyramidal cell somas and on spines and dendrites in stratum radiatum and stratum oriens in the hippocampal CA1 region of rats by quantitative immunofluorescence and immunogold electron microscopy. The quantitative immunogold results revealed a higher labelling density on dendritic spines, notably at their synaptic membranes, compared to pyramidal cell somas and dendrites. Hence, dopamine could have effects on spines as well as on somas and dendrites. The labelling density was similar on spines in stratum oriens and stratum radiatum, but the presence of labelling varied between the spines within each stratum, indicating that the effect of dopamine could be diverse between different spines.

Intra-individual variability in genetic and environmental models of attention-deficit/hyperactivity disorder.

The frequent observation of intra-individual variability (IIV) in the expression of ADHD symptoms suggest that IIV is an integral component of the disorder. We tested IIV in ADHD-like phenotype from five different studies of rodent models of ADHD, including studies with Spontaneous Hypertensive Rats (SHR/NCrl and SHR/N), Wistar-Kyoto Hyperactive Rats (WKHA/N), Wistar-Kyoto Hypertensive rat (WKHT), PCB-126 and -153-treated Lewis rats and behaviorally normal Wistar/Mol, Wistar-Kyoto (WKY/N and WKY/NMol), and untreated Lewis rats. Averages of the absolute residual deviation of ADHD-like behavior from individual means ("individual phenotypic dispersion," PD(i)) were used to represent IIV in the fixed-interval (FI) and extinction (EXT) phases of operant behavioral activity. Across all studies, SHR rats had higher PD(i) than WKY rats (P < 0.0001) for all ADHD-like traits, and higher PD(i) for hyperactivity than WKHT and WKHA/N rats. Male SHR rats in particular had higher PD(i) for hyperactivity than male or female WKYs, SHR females for EXT hyperactivity, and higher dispersion for inattention than WKY females. These findings strongly suggest the genetic control of IIV, and suggest that the SHR may be a useful model for the identification of genes for IIV in human ADHD. These findings also obliquely support the SHR as a useful model for ADHD overall.

Methylphenidate normalizes elevated dopamine transporter densities in an animal model of the attention-deficit/hyperactivity disorder combined type, but not to the same extent in one of the attention-deficit/hyperactivity disorder inattentive type.

The spontaneously hypertensive rat (SHR/NCrl) is a validated model of attention-deficit/hyperactivity disorder (ADHD) combined subtype, whereas a recently identified substrain of the Wistar Kyoto rat (WKY/NCrl) is a model of ADHD inattentive subtype. In this study, we first examined the expression of genes involved in dopamine signaling and metabolism in the dorsal striatum and ventral mesencephalon of these two rat strains, as well as three reference control strains (WKY/NHsd, WK/HanTac, and SD/NTac) using quantitative real time RT-PCR. Next, striatal dopamine transporter (DAT) density was determined by ligand binding assay in the two ADHD-like strains at different developmental stages and after methylphenidate treatment. In adult rats, the mRNA expression of DAT and tyrosine hydroxylase was elevated in SHR/NCrl and WKY/NCrl rats compared to control strains, with differences between SHR/NCrl and WKY/NCrl rats also evident. During normal development, changes of striatal DAT densities occurred in both strains with lower densities in WKY/NCrl compared to SHR/NCrl after day 25. Two-weeks methylphenidate treatment during different developmental stages was associated with decreased striatal DAT density in both rat strains compared to the non-treated rats with more pronounced effects followed prepubertal treatment. These results suggest differences in the pathophysiology of the combined versus the predominantly inattentive animal model of ADHD. Finally, treatment with methylphenidate might reduce elevated DAT levels more effectively in the combined subtype especially when applied before puberty.

N-methyl-D-aspartate receptor subunit dysfunction at hippocampal glutamatergic synapses in an animal model of attention-deficit/hyperactivity disorder.

Attention-deficit/hyperactivity disorder (ADHD) is the most common neurobehavioural disorder among children. ADHD children are hyperactive, impulsive and have problems with sustained attention. These cardinal features are also present in the best validated animal model of ADHD, the spontaneously hypertensive rat (SHR), which is derived from the Wistar Kyoto rat (WKY). Current theories of ADHD relate symptom development to factors that alter learning. N-methyl-D-aspartate receptor (NMDAR) dependent long term changes in synaptic efficacy in the mammalian CNS are thought to represent underlying cellular mechanisms for some forms of learning. We therefore hypothesized that synaptic abnormality in excitatory, glutamatergic synaptic transmission might contribute to the altered behavior in SHRs. We studied physiological and anatomical aspects of hippocampal CA3-to-CA1 synapses in age-matched SHR and WKY (controls). Electrophysiological analysis of these synapses showed reduced synaptic transmission (reduced field excitatory postsynaptic potential for a defined fiber volley size) in SHR, whereas short-term forms of synaptic plasticity, like paired-pulse facilitation, frequency facilitation, and delayed response enhancement were comparable in the two genotypes, and long-term potentiation (LTP) of synaptic transmission was of similar magnitude. However, LTP in SHR was significantly reduced (by 50%) by the NR2B specific blocker CP-101,606 (10 microM), whereas the blocker had no effect on LTP magnitude in the control rats. This indicates that the SHR has a functional predominance of NR2B, a feature characteristic of early developmental stages in these synapses. Quantitative immunofluorescence and electron microscopic postembedding immunogold cytochemistry of the three major NMDAR subunits (NR1, NR2A; and NR2B) in stratum radiatum spine synapses revealed no differences between SHR and WKY. The results indicate that functional impairments in glutamatergic synaptic transmission may be one of the underlying mechanisms leading to the abnormal behavior in SHR, and possibly in human ADHD.

Behavioral and genetic evidence for a novel animal model of Attention-Deficit/Hyperactivity Disorder Predominantly Inattentive Subtype.

BACKGROUND: According to DSM-IV there are three subtypes of Attention-Deficit/Hyperactivity Disorder, namely: ADHD predominantly inattentive type (ADHD-PI), ADHD predominantly Hyperactive-Impulsive Type (ADHD-HI), and ADHD combined type (ADHD-C). These subtypes may represent distinct neurobehavioral disorders of childhood onset with separate etiologies. The diagnosis of ADHD is behaviorally based; therefore, investigations into its possible etiologies should be based in behavior. Animal models of ADHD demonstrate construct validity when they accurately reproduce elements of the etiology, biochemistry, symptoms, and treatment of the disorder. Spontaneously hypertensive rats (SHR) fulfill many of the validation criteria and compare well with clinical cases of ADHD-C. The present study describes a novel rat model of the predominantly inattentive subtype (ADHD-PI). METHODS: ADHD-like behavior was tested with a visual discrimination task measuring overactivity, impulsiveness and inattentiveness. Several strains with varied genetic background were needed to determine what constitutes a normal comparison. Five groups of rats were used: SHR/NCrl spontaneously hypertensive and WKY/NCrl Wistar/Kyoto rats from Charles River; SD/NTac Sprague Dawley and WH/HanTac Wistar rats from Taconic Europe; and WKY/NHsd Wistar/Kyoto rats from Harlan. DNA was analyzed to determine background differences in the strains by PCR genotyping of eight highly polymorphic microsatellite markers and 2625 single nucleotide polymorphisms (SNPs). RESULTS: Compared to appropriate comparison strains (WKY/NHsd and SD/NTac rats), SHR/NCrl showed ADHD-C-like behavior: striking overactivity and poor sustained attention. Compared to WKY/NHsd rats, WKY/NCrl rats showed inattention, but no overactivity or impulsiveness. WH/HanTac rats deviated significantly from the other control groups by being more active and less attentive than the WKY/NHsd and SD/NTac rats. We also found substantial genomic differences between the WKY/NCrl and WKY/NHsd rats for eight short tandem repeat loci and 2625 SNPs. About 33.5 percent of the genome differs between the two WKY rat substrains, with large stretches of divergence on each chromosome. DISCUSSION: These data provide solid behavioral and genetic evidence that the WKY/NCrl and WKY/NHsd rats should be considered as separate substrains. Moreover, the behavioral features of the WKY/NCrl rat indicate that it should be a useful model for ADHD-PI, the primarily inattentive subtype of ADHD. The SD/NTac and the WH/HanTac rats show significant genetic and/or behavioral differences from WKY/NHsd rats and appear not to be appropriate controls in studies using the SHR/NCrl. The present results support the conclusion that SHR/NCrl is the best validated animal model of ADHD-C. The overactivity, impulsiveness and deficient sustained attention of the SHR/NCrl strain are independent behaviors. Thus, overactivity does not account for this strain's impulsiveness and deficient sustained attention. Finally, the present study shows that great care has to be exercised to select the model and comparison groups.

Guidelines and algorithms for the use of methylphenidate in children with Attention-Deficit/ Hyperactivity Disorder.

OBJECTIVE: To review published algorithms for guiding the use of methylphenidate (MPH) in the treatment of Attention-Deficit/Hyperactivity Disorder (ADHD) in children and adolescents. METHODS: A consensus roundtable of 12 experts was convened to review the evidence for the safety and efficacy of MPH in the treatment of ADHD, as well as the published algorithms and practice guidelines for using MPH. The experts reviewed the algorithms for practicality and acceptability by clinicians. RESULTS: Algorithms that included MPH commonly selected it as the initial medication to be employed in the treatment of children with ADHD. Factors involved included its high efficacy, good safety record, and the ubiquitous nature of its appearance in the ADHD treatment literature. CONCLUSIONS: MPH should be considered as the first medication to be used in a treatment algorithm for children and adolescents with ADHD.

Methylphenidate affects striatal dopamine differently in an animal model for attention-deficit/hyperactivity disorder--the spontaneously hypertensive rat.

The spontaneously hypertensive rat (SHR) is used as a model for attention-deficit/hyperactivity disorder (ADHD) because it has behavioural characteristics (hyperactivity, impulsiveness, poorly sustained attention) similar to those of ADHD. ADHD children have been shown to have reduced striatal activation in certain tasks. SHR have reduced striatal dopamine release in response to electrical stimulation. The present study set out to investigate possible long-term effects of methylphenidate treatment on dopaminergic function in striatal slices of SHR compared to their normotensive Wistar-Kyoto (WKY) control rats. Methylphenidate treatment (3 mg/kg daily for 14 days) did not normalize the decreased electrically-stimulated release of [(3)H]dopamine from SHR caudate-putamen slices nor did it affect postsynaptic D(2) receptor function. However, the second electrical stimulus caused a relatively greater release of [(3)H]dopamine from caudate-putamen slices of methylphenidate-treated SHR than from vehicle-treated SHR, suggesting that presynaptic mechanisms controlling dopamine release had been altered. Interestingly, [(3)H]dopamine release from WKY caudate-putamen slices in response to D(2) autoreceptor blockade by the antagonist, sulpiride, was selectively increased by methylphenidate treatment. This effect was not seen in SHR possibly because D(2) autoreceptor function had already been up-regulated. The results show that methylphenidate is unable to enhance D(2) autoreceptor function in SHR.

Behavioral validation of the spontaneously hypertensive rat (SHR) as an animal model of attention-deficit/hyperactivity disorder (AD/HD).

A good model of a disorder is one that: (a) mimics, although in a simpler form than the full-blown clinical case, the fundamentals of the behavioral characteristics, in this case of people with Attention-Deficit/Hyperactivity Disorder (AD/HD;face validity); (b) conforms with a theoretical rationale for the disorder (construct validity); and (c) is able to predict aspects of behavior, genetics and neurobiology previously uncharted in the clinics (predictive validity). This article discusses the Spontaneously Hypertensive Rat (SHR) and some other putative animal models of AD/HD. It is argued that although other strains and species may be hyperactive and/or show attention deficits following genetic, environmental or pharmacological interventions, the SHR is presently the only strain shown to have the major behavioral symptoms of AD/HD. This does not mean that investigating other models cannot give valuable information.

Behavioural effects in female rats of postnatal exposure to sub-toxic doses of polychlorinated biphenyl congener 153.

Polychlorinated biphenyls (PCBs) are widespread environmental contaminants that are also present in human tissues and breast milk. Behavioural disturbances have been reported in both children and animals exposed perinatally to PCBs. The present study assessed the behavioural consequences in female rats of postnatal exposure to the di-ortho-substituted 2,2',4,4',5,5'-hexachlorobiphenyl (IUPAC no. 153), which is one of the PCB congeners most frequently detected in human milk. The different groups of mothers were dosed via gavage with 5 mg/kg bodyweight of PCB 153 in corn oil or 5 ml/kg bodyweight corn oil vehicle every second day from day 3 to day 13 after delivery. The exposure did not affect the bodyweight of the dams nor the physical development of the pups. Operant behavioural testing of the female offspring by two different schedules of reinforcement was performed. First, the animals were tested by a multiple schedule with two components: fixed interval (FI) and extinction (EXT), which has proved sensitive in revealing changes in activity level. There were no statistically significant differences in frequency or interresponse times of lever pressing between the PCB-exposed female rats and the controls. These results were in contrast to a previous, analogous study where PCB 153 produced an increased frequency of lever presses during the FI in male rats, indicating a sex-specific behavioural effect of PCB 153. The female offspring was also tested by a conjunctive schedule with two components: variable interval (VI) and differential reinforcement of low rate (DRL). This schedule revealed slower acquisition of time discrimination in the PCB 153-exposed females as compared with the controls. The VI-DRL results showed that PCB 153 may also produce long-lasting behavioural effects in female rats following postnatal exposure through the mother's milk.

Attention deficit/hyperactivity disorder--from brain dysfunctions to behaviour.

This special issue represents an attempt to answer fundamental brain and behaviour issues in attention-deficit hyperactivity disorder (ADHD). The European network on hyperkinetic disorders (Eunethydis) is trying to develop a novel, testable theory of ADHD, giving an account of its causes, its development from brain dysfunctions to behavioural symptoms and co-morbidity and explaining why no current therapy produces long-lasting improvements. The combined insights of the articles presented here suggest that there is no brain damage in ADHD, but hypo-efficient dopamine systems which give rise to neurochemical imbalances. These cause behavioural problems: deficits in sustained attention, overactivity and impulsiveness. Impulsiveness is increasingly being seen as a key characteristic of the disorder. None of these symptoms are necessarily primary, but may be secondary to an underlying deficit in reinforcement processes seen particularly in a greater than normal sensitivity to variations in the timing of stimulus presentation. Other symptoms can also be seen: altered effects of reinforcers, increased behavioural variance and motor co-ordination problems. Medication produces temporary, plastic changes in cellular components like receptors and transduction mechanisms normalising dopamine functions and behaviour. reserved.

Altered reinforcement mechanisms in attention-deficit/hyperactivity disorder.

The present study tested eight boys with attention-deficit/hyperactivity disorder (ADHD) and 12 normal boys (comparison group), aged 7-12 years, to investigate the hypothesis that ADHD is associated with a steeper and shorter delay-of-reinforcement gradient than is normal. A two-component schedule of reinforcement was used to deliver trinkets or coins as reinforcers in a game-like test. One component was marked by a signal. During this period reinforcers (coins or trinkets) were delivered every 30 s. This component is called a 30-s fixed interval (FI) schedule of reinforcement and measures changes in reactivity to reinforcers. The other component was in effect when the signal was turned off. Then no reinforcer was ever delivered. This is called an extinction (EXT) component and measures primarily sustained attention. The ADHD children gradually developed hyperactivity to a large extent consisting of bursts of responses with short interresponse times (IRTs) during both schedule components. The response bursts not only constituted a substantial portion of the ADHD overactivity, but may well be a key component of the behaviour commonly described as impulsiveness, the key behavioural characteristic of ADHD. In addition, the ADHD children showed behaviour during the extinction component that may well be described as a sustained-attention deficit: initially stopping when the signal was turned off and then resuming responding some time thereafter as if the signal had been turned on again. The comparison group ceased responding during extinction and did not show impulsiveness. The findings were in accordance with a steeper and shorter delay gradient in ADHD.

Sex differences in operant discrimination behaviour in an animal model of attention-deficit hyperactivity disorder.

The present study was aimed at determining whether the behaviour of the spontaneously hypertensive rat (SHR), an animal model of attention-deficit hyperactivity disorder (ADHD), showed sex differences parallel to those seen in ADHD children. The experimental protocol contained an operant discrimination task, a two-component multiple (mult) 2-min fixed interval (FI) 5-min extinction (EXT) schedule of water reinforcement, a reliable behavioural paradigm for testing activity levels, discrimination behaviour and impulsiveness. The results indicated that both male and female SHRs show some of the most important behavioural traits of ADHD. Both were hyperactive and showed discrimination problems in terms of a behavioural extinction deficit towards the end of the EXT component. Still their behaviour differed markedly, which was probably due to quite different underlying mechanisms. The behavioural characteristics of the female SHRs may be compatible with an attention-deficit interpretation, whereas the behavioural characteristics of the male SHRs may be due to a shorter than normal delay-of-reinforcement gradient. The present study strengthens the position of SHR as an animal model of ADHD for future studies that may elucidate details in the underlying neurobiological deficits and for testing various treatment strategies.

Chronic L-deprenyl treatment alters brain monoamine levels and reduces impulsiveness in an animal model of Attention-Deficit/Hyperactivity Disorder.

Effects of chronic L-deprenyl administration on hyperactive behaviour and brain monoamine levels were studied in spontaneously hypertensive rats (SHR) and Wistar-Kyoto (WKY) rats. SHR were hyperactive, impulsive and had impaired sustained attention when tested with a multiple 2-min fixed interval (FI) 5-min extinction (EXT) schedule of reinforcement. Even low, 0.25 mg/kg, doses of chronically-administered L-deprenyl reduced the impulsiveness (bursts of responses with short interresponse times) of SHR, without altering the general hyperactivity or the impaired sustained attention. The drug had no effect on WKY behaviour. The levels of noradrenaline (NA), dopamine (DA), serotonin (5-hydroxytryptamine, 5-HT) and their metabolites, measured in neostriatum, nucleus accumbens and frontal cortex, showed that L-deprenyl effectively inhibited monoamine oxidase (MAO) activity. These results suggest that impulsiveness is a behavioural component that may be operating independent of the other components, like hyperactivity and deficient sustained attention, and that can be reduced by chronic MAO-B inhibition with L-deprenyl in this strain of rats. The positive effect of L-deprenyl on impulsiveness is discussed as due either to normalization of an asymmetric dopaminergic activity in the nucleus accumbens, or to a restoration of normal DA function in the prefrontal cortex.

Differences between electrically-, ritalin- and D-amphetamine-stimulated release of [3H]dopamine from brain slices suggest impaired vesicular storage of dopamine in an animal model of Attention-Deficit Hyperactivity Disorder.

The spontaneously hypertensive rat (SHR) has behavioural characteristics which make it a suitable animal model for Attention-Deficit Hyperactivity Disorder (ADHD). The drugs of choice in the treatment of ADHD are methylphenidate and D-amphetamine. Using an in vitro superfusion system, we showed that both drugs released [3H]dopamine (DA) (and metabolites) from prefrontal cortex, nucleus accumbens and caudate-putamen slices, but methylphenidate was from 7- to 17-fold less potent than D-amphetamine. The similarity in the drug effects on SHR and WKY [3H]DA release is in accordance with the fact that there is no 'paradoxical effect' of psychomotor stimulants on ADHD behaviour. Methylphenidate released significantly less [3H]DA from nucleus accumbens slices obtained from SHR than from their normotensive Wistar-Kyoto (WKY) controls. Electrical stimulation released less [3H]DA from prefrontal cortex and caudate-putamen slices of SHR, while D-amphetamine, in contrast to methylphenidate, released more [3H]DA from prefrontal cortex, nucleus accumbens and caudate-putamen slices of SHR compared to WKY. Inhibition of the DA uptake carrier by low concentrations of methylphenidate increased the electrically-stimulated release of [3H]DA to the same extent in SHR and WKY tissue, suggesting that the DA transporter was not responsible for the differences between SHR and WKY. The present results suggest that SHR may have impaired vesicular storage of DA causing leakage of DA into the cytoplasm, since SHR released less [3H]DA from vesicular stores in response to methylphenidate or electrical stimulation and released more [3H]DA from cytoplasmic stores via the uptake carrier in response to D-amphetamine. Methylphenidate might be the drug of choice in the treatment of ADHD because it releases DA from vesicular stores only and is less potent than D-amphetamine, thus making it possible to adjust the dose and thereby 'normalise' reduced DA function more precisely than is possible with D-amphetamine. There was no difference between SHR and WKY with respect to D-amphetamine-stimulated release of [14C]acetylcholine (ACh) or methylphenidate-induced inhibition of the electrically-stimulated release of [14C]ACh from nucleus accumbens or caudate-putamen slices, suggesting that there is no major change in cholinergic transmission in SHR.

Behavioural hyperactivity in rats following postnatal exposure to sub-toxic doses of polychlorinated biphenyl congeners 153 and 126.

Rats were exposed through mother's milk either to the di-ortho-substituted polychlorinated biphenyl (PCB) congener 2,2',4,4',5,5'-CB (IUPAC no. 153) or to the non-ortho-substituted PCB congener 3,3',4,4',5-CB (IUPAC no. 126). The different groups of mothers were dosed via gavage with corn oil vehicle, 5 mg/kg b.w. of PCB 153 or 2 microg/kg b.w. of PCB 126 every second day from day 3 to 13 after delivery. The exposure did not affect the body weight (b.w.) of the dams or the physical development of the pups. A two-component schedule of reinforcement was used to study behavioural effects of the PCB exposures in male offspring. One component was operating when the house light was turned on. Then a reinforcer, a drop of water, was delivered every 2-min. This component is called a 2-min fixed interval (FI) schedule of reinforcement. The other component was in effect when the house light was turned off. Then no reinforcer was ever delivered. This is called an extinction (EXT) component. It was shown that the PCB-exposed offspring were hyperactive as they had an increased frequency of lever presses. In addition, the PCB 153-exposed male pups showed a behavioural pattern similar to that observed in spontaneously hypertensive rats (SHR), an animal model of attention-deficit hyperactivity disorder (ADHD). This behaviour is characterized by 'burst' of lever presses with short interresponse times (IRT) just before the next reinforcer is given. These results show that both PCBs 153 and 126 may produce significant neurotoxic effects following postnatal exposure through mother's milk.

A quantitative cytochrome oxidase mapping study, cross-regional and neurobehavioural correlations in the anterior forebrain of an animal model of Attention Deficit Hyperactivity Disorder.

The aim of this study was to trace by molecular imaging techniques the neural substrates of attention deficit hyperactivity disorder (ADHD) using the spontaneously hypertensive rat (SHR) as animal model. Adult SHR and Wistar-Kyoto (WKY) controls were used throughout this study. In experiment 1, naive male SHR and WKY were used, whereas in experiment 2 SHR and WKY rats of both genders were trained on a multiple fixed interval (FI (120 s for water, 5-min extinction)) paradigm and sacrificed 6 months later. In both experiments coronal sections of the anterior forebrain were processed for quantitative cytochrome oxidase (COase) histochemistry by the method of Gonzalez-Lima. Optical density values were transformed into actual enzyme activity units by using tissue-calibrated standards. In experiment 1, non-trained male rats of the SHR line showed lower COase activity in the medial and lateral prefrontal cortices, compared with WKY controls. In experiment 2, there was a line x treatment interaction effect in the pole of the nucleus accumbens (ACB). Regional correlative analyses revealed that: (i) under basal conditions, SHR are more synchronized than WKY rats in the COase level of different brain regions; and (ii) the training desynchronizes COase activity in the WKY, further synchronizes it and increases the cross-talk between hemispheres in male SHR only. Neurobehavioral covariations between behavioural scores and metabolic capacity in the medial and lateral prefrontal/frontal cortices, the caudate-putamen complex (CPU), the pole, core, and shell of the accumbal complex (ACB), and the ventral pallidum (VP), indicated that, in the WKY rats, the frequency of lever pressing covaried positively with the COase activity in the CPU, whereas in the SHR covaried with both medial and lateral prefrontal/frontal cortices. The bursts of activity during the 1-1.33-s segment was positively correlated, in the WKY rats only, with the core and shell of the ACB, and with the VP. Finally, the correlative profiles showed significant gender differences with effects in male SHR only. Thus, the results lend support to the involvement of the cortico-striato-pallidal system in ADHD.

Short term storage of samples containing monoamines: ascorbic acid and glutathione give better protection against degradation than perchloric acid.

In order to study the protection of monoamines from degradation during short-time storage, the effect of three different antioxidants on the degradation of dopamine, dihydroxyphenylacetic acid (DOPAC), and 5-hydroxyindoleacetic acid (5-HIAA) was analyzed after 5 and 20 h. The results showed that dopamine was still quite stable after 20 h storage at room temperature, but that about 95% of 5-HIAA had disappeared. The best protection against degradation of all three substances was achieved when 15% v/v of a solution containing 1-2 mM ascorbic acid or 40 mM glutathione was added to the sample, resulting in near 100% protection after 20 h. Perchloric acid actually accelerated the degradation of 5-HIAA.

Reduced CaMKII-positive neurones in the accumbens shell of an animal model of attention-deficit hyperactivity disorder.

THIS study aimed at investigating putative neural substrates of attention-deficit hyperactivity disorder in children using the spontaneously hypertensive rat (SHR) as animal model and the Ca2+/calmodulin-dependent protein kinase II (CaMKII) as a marker in the nucleus accumbens, an interface between limbic and motor systems. In prehypertensive male SHR and Wistar-Kyoto rats image analysis of CaMKII immunocytochemistry showed more positive elements in the shell than in the core, and in the former a lower level in SHR. The data indicate a reduced number of nucleus accumbens modules available for limbic-motor integration revealing putative substrates of the altered attentional and reinforcement mechanisms demonstrated in the SHR and in children with attention-deficit hyperactivity disorder.

NMDA and non-NMDA sensitive [L-3H]glutamate receptor binding in the brain of the Naples high- and low-excitability rats: an autoradiographic study.

The Naples high-excitability (NHE) and low-excitability (NLE) rat lines, selectively bred for high and low activity in a Làt maze, respectively, are used as an animal model in the study of hippocampal functions. The aim of this study was to investigate the anatomical distribution of N-methyl-D-aspartate (NMDA) and non-NMDA sensitive [3H]glutamate receptor binding by quantitative autoradiography in the brain of the NHE and NLE rats with a randomly bred line (NRB) as controls. Twenty-micron-thick cryostat sagittal sections were incubated at 4 degrees C with 150 nM [L-3H]glutamate alone or in the presence of 100 microM NMDA or 2.5 microM quisqualate (QA). Non-specific binding was determined in the presence of 1 mM of non-labeled glutamate. The sections were exposed to tritium-sensitive films for 3 weeks at 4 degrees C. Quantitative analysis revealed: (1) higher levels of total binding in NHE than in NRB and NLE rats in all areas but the cerebellum; (2) fewer binding sites for both NMDA and QA receptors and larger binding sites for QA receptors in the hippocampus of NLE and NHE rats, respectively; (3) a positive correlation between total binding sites and activity level in a Làt maze in all areas, except the cerebellar molecular layer with NLE < NHE, which was due to differential contribution from NMDA and non-NMDA types. Thus, the brain of the NHE rats shows an imbalance between NMDA and non-NMDA sensitive [L-3H]glutamate receptors.