Food, nutrition, and autism: from soil to fork

Food and nutrition-related factors have the potential to impact development of autism spectrum disorder (ASD) and quality of life for people with ASD, but gaps in evidence exist. On 10 November 2022, Tufts University's Friedman School of Nutrition Science and Policy and Food and Nutrition Innovation Institute hosted a 1-d meeting to explore the evidence and evidence gaps regarding the relationships of food and nutrition with ASD. This meeting report summarizes the presentations and deliberations from the meeting. Topics addressed included prenatal and child dietary intake, the microbiome, obesity, food-related environmental exposures, mechanisms and biological processes linking these factors and ASD, food-related social factors, and data sources for future research. Presentations highlighted evidence for protective associations with prenatal folic acid supplementation and ASD development, increases in risk of ASD with maternal gestational obesity, and the potential for exposure to environmental contaminants in foods and food packaging to influence ASD development. The importance of the maternal and child microbiome in ASD development or ASD-related behaviors in the child was reviewed, as was the role of discrimination in leading to disparities in environmental exposures and psychosocial factors that may influence ASD. The role of child diet and high prevalence of food selectivity in children with ASD and its association with adverse outcomes were also discussed. Priority evidence gaps identified by participants include further clarifying ASD development, including biomarkers and key mechanisms; interactions among psychosocial, social, and biological determinants; interventions addressing diet, supplementation, and the microbiome to prevent and improve quality of life for people with ASD; and mechanisms of action of diet-related factors associated with ASD. Participants developed research proposals to address the priority evidence gaps. The workshop findings serve as a foundation for future prioritization of scientific research to address evidence gaps related to food, nutrition, and ASD.

Sex Differences in the Allele Distribution of PGLYRP2 Variant rs892145 in Parkinson's Disease

Introduction

Parkinson's disease (PD) is a complex multifactorial disease, involving genetic susceptibility, environmental risk factors, and gene-environmental interactions. The microbiota-gut-brain axis is hypothesized to play a role in the pathophysiology of PD, and peptidoglycan recognition proteins (PGLYRPs), which modulate the gut microbiota, are, therefore, relevant candidate genes for PD.

Methods

Using quantitative real-time PCR, we genotyped three PGLYRP variants (rs892145, rs959117, and rs10888557) and performed an association analysis in 508 PD patients and 585 control individuals. We further conducted a meta-analysis of rs892145 and analyzed PGLYRP2 gene expression in lymphocytes from patients with PD and controls.

Results

Although initial analysis of the three variants rs892145, rs959117, and rs10888557 and a meta-analysis of rs892145 did not reveal any association between the selected variants and PD, we found an interaction between sex and genotype for rs892145, with a marked difference in the allele distribution of rs892145 between male and female patients. As compared to controls, the T allele was less common in female patients (odds ratio = 0.76, P = 0.04) and more common in male patients (odds ratio = 1.29, P = 0.04). No difference was found in PGLYRP2 gene expression between PD patients and controls (P = 0.38), nor between sexes (P = 0.07). Discussion. Overall, this genetic screening in Swedish PD patients does not support previous results demonstrating associations of PGLYRP variants with the risk of PD. Meta-analysis of rs892145 revealed pronounced heterogeneity between previously published studies which is likely to have influenced the results. Taken together, the genetic and gene expression analyses suggest a possible link between genetic variants in PGLYRP2 and sex differences in PD. Because of the limited sample size in our study, these results need to be verified in independent cohorts before concluding.

Cognitive Alterations in Old Mice Are Associated with Intestinal Barrier Dysfunction and Induced Toll-like Receptor 2 and 4 Signaling in Different Brain Regions

Emerging evidence implicate the 'microbiota-gut-brain axis' in cognitive aging and neuroinflammation; however, underlying mechanisms still remain to be elucidated. Here, we assessed if potential alterations in intestinal barrier function and microbiota composition as well as levels of two key pattern-recognition receptors namely Toll-like receptor (TLR) 2 and TLR4, in blood and different brain regions, and depending signaling cascades are paralleling aging associated alterations of cognition in healthy aging mice. Cognitive function was assessed in the Y-maze and intestinal and brain tissue and blood were collected in young (4 months old) and old (24 months old) male C57BL/6 mice to determine intestinal microbiota composition by Illumina amplicon sequencing, the concentration of TLR2 and TLR4 ligands in plasma and brain tissue as well as to determine markers of intestinal barrier function, senescence and TLR2 and TLR4 signaling. Cognitive function was significantly impaired in old mice. Also, in old mice, intestinal microbiota composition was significantly altered, while the relative abundance of Gram-negative or Gram-positive bacteria in the small and large intestines at different ages was not altered. Moreover, intestinal barrier function was impaired in small intestine of old mice, and the levels of TLR2 and TLR4 ligands were also significantly higher in both portal and peripheral blood. Furthermore, levels of TLR2 and TLR4 ligands, and downstream markers of TLR signaling were higher in the hippocampal and prefrontal cortex of old mice compared to young animals. Taken together, our results suggest that even in 'healthy' aging, cognitive function is impaired in mice going along with an increased intestinal translocation of TLR ligands and alterations of TLR signaling in several brain regions.

Early-life differences in the gut microbiota composition and functionality of infants at elevated likelihood of developing autism spectrum disorder

Evidence from cross-sectional human studies, and preliminary microbial-based intervention studies, have implicated the microbiota-gut-brain axis in the neurobiology of autism spectrum disorder (ASD). Using a prospective longitudinal study design, we investigated the developmental profile of the fecal microbiota and metabolome in infants with (n = 16) and without (n = 19) a family history of ASD across the first 36 months of life. In addition, the general developmental levels of infants were evaluated using the Mullen Scales of Early Learning (MSEL) test at 5 and 36 months of age, and with ADOS-2 at 36 months of age. At 5 months of age, infants at elevated-likelihood of ASD (EL) harbored less Bifidobacterium and more Clostridium and Klebsiella species compared to the low-likelihood infants (LL). Untargeted metabolic profiling highlighted that LL infants excreted a greater amount of fecal γ-aminobutyric acid (GABA) at 5 months, which progressively declined with age. Similar age-dependent patterns were not observed in the EL group, with GABA being consistently low across all timepoints. Integrated microbiome-metabolome analysis showed a positive correlation between GABA and Bifidobacterium species and negative associations with Clostridium species. In vitro experiments supported these observations demonstrating that bifidobacteria can produce GABA while clostridia can consume it. At the behavioral level, there were no significant differences between the EL and LL groups at 5 months. However, at 36 months of age, the EL group had significantly lower MSEL and ADOS-2 scores compared to the LL group. Taken together, the present results reveal early life alterations in gut microbiota composition and functionality in infants at elevated-likelihood of ASD. These changes occur before any behavioral impairments can be detected, supporting a possible role for the gut microbiota in emerging behavioral variability later in life.

Perturbation of maternal gut microbiota in mice during a critical perinatal window influences early neurobehavioral outcomes in offspring

The gut microbiota is increasingly recognized as a key environmental factor that shapes host development and physiology, including neural circuits formation and function. Concurrently, there has been growing concern that early-life antibiotic exposure may alter brain developmental trajectories, increasing the risk for neurodevelopmental disorders such as autism spectrum disorder (ASD). Here, we assessed whether perturbation of the maternal gut microbiota in mice during a narrow critical perinatal window (last week of pregnancy and first three postnatal days), induced by exposure to a commonly used broad-spectrum oral antibiotic (ampicillin), influences offspring neurobehavioral outcomes relevant to ASD. Our results demonstrate that neonatal offspring from antibiotic-treated dams display an altered pattern of ultrasonic communication, which was more pronounced in males. Moreover, juvenile male, but not female, offspring from antibiotic-treated dams showed reduced social motivation and social interaction, as well as context-dependent anxiety-like behavior. However, no changes were observed in locomotor or exploratory activity. This behavioral phenotype of exposed juvenile males was associated with reduced gene expression of the oxytocin receptor (OXTR) and several tight-junction proteins in the prefrontal cortex, a key region involved in the regulation of social and emotional behaviors, as well as a mild inflammatory response in the colon. Further, juvenile offspring from exposed dams also showed distinct alterations in several gut bacterial species, including, Lactobacillus murinus, and Parabacteroides goldsteinii. Overall, this study highlights the importance of the maternal microbiome in early-life, and how its perturbation by a widely used antibiotic could contribute to atypical social and emotional development of offspring in a sex-dependent manner.

Developmental Signatures of Microbiota-Derived Metabolites in the Mouse Brain

The gut microbiome is recognized to exert a wide-ranging influence on host health and disease, including brain development and behavior. Commensal bacteria can produce bioactive molecules that enter the circulation and impact host physiology and homeostasis. However, little is known about the potential for these metabolites to cross the blood–brain barrier and enter the developing brain under normal physiological conditions. In this study, we used a liquid chromatography–mass spectrometry-based metabolomic approach to characterize the developmental profiles of microbial-derived metabolites in the forebrains of mice across three key postnatal developmental stages, co-occurring with the maturation of the gut microbiota. We demonstrate that direct metabolites of the gut microbiome (e.g., imidazole propionate) or products of the combinatorial metabolism between the microbiome and host (e.g., 3-indoxyl-sulfate, trimethylamine-N-oxide, and phenylacetylglycine) are present in the forebrains of mice as early as the neonatal period and remain into adulthood. These findings demonstrate that microbial-associated molecules can cross the BBB either in their detected form or as precursor molecules that undergo further processing in the brain. These chemical messengers are able to bind receptors known to be expressed in the brain. Alterations in the gut microbiome may therefore influence neurodevelopmental trajectories via the regulation of these microbial-associated metabolites.

Bacterial peptidoglycans as novel signaling molecules from microbiota to brain

Mounting evidence indicates that gut microbiota exerts a broad range of effects on host physiology and development beyond the gastrointestinal tract, including the modulation of brain development. However, the mechanisms mediating the interactions between the microbiota and the developing brain are still poorly understood. Pattern recognition receptors of the innate immune system that recognize microbial products, such as peptidoglycans have emerged as potential key regulators of gut microbiome-brain interactions. Peptidoglycan-sensing molecules are expressed in the placenta and brain during specific time windows of development. Moreover, peptidoglycans are ubiquitously present in circulation and can cross the blood brain barrier. This review brings together the current evidence supporting a broad function of peptidoglycans well beyond host's immunity, extending to neurodevelopment and behavior.

Can Neonatal Systemic Inflammation and Hypoxia Yield a Cerebral Palsy-Like Phenotype in Periadolescent Mice?

Cerebral palsy (CP) is one of the most common childhood-onset motor disabilities, attributed to injuries of the immature brain in the foetal or early postnatal period. The underlying mechanisms are poorly understood, rendering prevention and treatment strategies challenging. The aim of the present study was to establish a mouse model of CP for preclinical assessment of new interventions. For this purpose, we explored the impact of a double neonatal insult (i.e. systemic inflammation combined with hypoxia) on behavioural and cellular outcomes relevant to CP during the prepubertal to adolescent period of mice. Pups were subjected to intraperitoneal lipopolysaccharide (LPS) injections from postnatal day (P) 3 to P6 followed by hypoxia at P7. Gene expression analysis at P6 revealed a strong inflammatory response in a brain region-dependent manner. A comprehensive battery of behavioural assessments performed between P24 and P47 showed impaired limb placement and coordination when walking on a horizontal ladder in both males and females. Exposed males also displayed impaired performance on a forelimb skilled reaching task, altered gait pattern and increased exploratory activity. Exposed females showed a reduction in grip strength and traits of anxiety-like behaviour. These behavioural alterations were not associated with gross morphological changes, white matter lesions or chronic inflammation in the brain. Our results indicate that the neonatal double-hit with LPS and hypoxia can induce subtle long-lasting deficits in motor learning and fine motor skills, which partly reflect the symptoms of children with CP who have mild gross and fine motor impairments.

Brief Report: Association Between Autism Spectrum Disorder, Gastrointestinal Problems and Perinatal Risk Factors Within Sibling Pairs

Autism spectrum disorder (ASD) has been associated with gastrointestinal (GI) problems, but the nature of this association is unclear. Parents to siblings, concordant or discordant for ASD (N = 217), participated in a web survey covering mother's weight gain during pregnancy, maternal viral/bacterial infection and use of antibiotics, duration of breastfeeding, mode of delivery, birth weight and child GI problems. ASD was associated with GI problems and perinatal environmental risk, based on a summation of maternal infection and antibiotic use during pregnancy and/or the breastfeeding period. The association between GI problems and ASD remained within the sibling pairs (β = 1.23; p < .001) in the adjusted model. Our results indicate non-shared environmental effects on the ASD/GI association, but none of the factors examined explained the link.

Genetic Variation in the Dopamine System Influences Intervention Outcome in Children with Cerebral Palsy

Background

There is large variation in treatment responses in children with cerebral palsy. Experimental and clinical results suggest that dopamine neurotransmission and brain-derived neurotrophic factor (BDNF) signalling are involved in motor learning and plasticity, which are key factors in modern habilitation success. We examined whether naturally occurring variations in dopamine and BDNF genes influenced the treatment outcomes.

Methods

Thirty-three children (18–60 months of age) with spastic unilateral cerebral palsy were enrolled in the study. Each child had participated in a training programme consisting of active training of the involved hand for 2 h every day during a 2-month training period. The training outcome was measured using Assisting Hand Assessment before and after the training period. Saliva was collected for genotyping of COMT, DAT, DRD1, DRD2, DRD3, and BDNF. Regression analyses were used to examine associations between genetic variation and training outcome.

Findings

There was a statistically significant association between variation in dopamine genes and treatment outcome. Children with a high polygenic dopamine gene score including polymorphisms of five dopamine genes (COMT, DAT, DRD1, DRD2, and DRD3), and reflecting higher endogenous dopaminergic neurotransmission, had the greatest functional outcome gains after intervention.

Interpretation

Naturally occurring genetic variation in the dopamine system can influence treatment outcomes in children with cerebral palsy. A polygenic dopamine score might be valid for treatment outcome prediction and for designing individually tailored interventions for children with cerebral palsy.

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Naturally occurring variation of dopamine genes is associated with treatment outcomes in children with cerebral palsy.

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Children with polymorphisms reflecting higher endogenous dopaminergic neurotransmission had the greatest functional gains.

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A polygenic dopamine score might be valid to predict treatment outcome.

New evidence-based therapies including active motor learning and training for children with cerebral palsy improve motor function at a group level, but there are also large inter-individual variations. Naturally occurring variations in dopamine and BDNF genes affect motor learning and cortical plasticity.

This study showed that naturally occurring genetic variation of five dopamine genes was associated with the outcome of a 2-month long active upper limb motor training intervention in children with unilateral cerebral palsy. The results suggest that a polygenic dopamine gene score can be used to predict the outcome of motor training programmes for children with cerebral palsy.

Sex-dependent alterations in motor and anxiety-like behavior of aged bacterial peptidoglycan sensing molecule 2 knockout mice

Peptidoglycan recognition proteins (PGRPs) are key sensing-molecules of the innate immune system that specifically detect bacterial peptidoglycan (PGN) and its derivates. PGRPs have recently emerged as potential key regulators of normal brain development and behavior. To test the hypothesis that PGRPs play a role in motor control and anxiety-like behavior in later life, we used 15-month old male and female peptidoglycan recognition protein 2 (Pglyrp2) knockout (KO) mice. Pglyrp2 is an N-acetylmuramyl-l-alanine amidase that hydrolyzes PGN between the sugar backbone and the peptide chain (which is unique among the mammalian PGRPs). Using a battery of behavioral tests, we demonstrate that Pglyrp2 KO male mice display decreased levels of anxiety-like behavior compared with wild type (WT) males. In contrast, Pglyrp2 KO female mice show reduced rearing activity and increased anxiety-like behavior compared to WT females. In the accelerated rotarod test, however, Pglyrp2 KO female mice performed better compared to WT females (i.e., they had longer latency to fall off the rotarod). Further, Pglyrp2 KO male mice exhibited decreased expression levels of synaptophysin, gephyrin, and brain-derived neurotrophic factor in the frontal cortex, but not in the amygdala. Pglyrp2 KO female mice exhibited increased expression levels of spinophilin and alpha-synuclein in the frontal cortex, while exhibiting decreased expression levels of synaptophysin, gephyrin and spinophilin in the amygdala. Our findings suggest a novel role for Pglyrp2asa key regulator of motor and anxiety-like behavior in late life.

Fetal, neonatal, and infant microbiome: Perturbations and subsequent effects on brain development and behavior

The human gastrointestinal tract harbors a diverse and complex community of microbes, termed gut microbiota, that normally assemble during the first postnatal years of life. This evolution-driven process has been shown to contribute to the developmental programming of epithelial barrier function, gut homeostasis, and angiogenesis, as well as the development and function of the immune system. Research over the last few years has revealed that the actions of the gut microbiota have much wider effects on host physiology and development than originally believed, including the modulation of brain development and behavior. This article briefly reviews recent findings on the impact of the gut microbiota on brain development, and how disturbances in the assembly and maturation of the gut microbiota may impact development of motor, social, and cognitive functions. The potential link between microbiota and metabolic requirements of the developing brain is also considered.

Host microbiota modulates development of social preference in mice

BACKGROUND

Mounting evidence indicates that the indigenous gut microbiota exerts long-lasting programming effects on brain function and behaviour.

OBJECTIVE

In this study, we used the germ-free (GF) mouse model, devoid of any microbiota throughout development, to assess the influence of the indigenous microbiota on social preference and repetitive behaviours (e.g. self-grooming).

METHODS AND RESULTS

Using the three-chambered social approach task, we demonstrate that when adult GF mice were given a choice to spend time with a novel mouse or object, they spent significantly more time sniffing and interacting with the stimulus mouse compared to conventionally raised mice (specific pathogen-free, SPF). Time spent in repetitive self-grooming behaviour, however, did not differ between GF and SPF mice. Real-time PCR-based gene expression analysis of the amygdala, a key region that is part of the social brain network, revealed a significant reduction in the mRNA levels of total brain-derived neurotrophic factor (BDNF), BDNF exon I-, IV-, VI-, IX-containing transcripts, and NGFI-A (a signalling molecule downstream of BDNF) in GF mice compared to SPF mice.

CONCLUSION

These results suggest that differential regulation of BDNF exon transcripts in the amygdala by the indigenous microbes may contribute to the altered social development of GF mice.

Translational studies exploring neuroplasticity associated with motor skill learning and the regulatory role of the dopamine system

Cerebral palsy (CP) is a heterogeneous group of neurodevelopmental disorders associated with lifelong motor impairment and disability. Current intervention programmes aim to capitalize on the neuroplasticity of the undamaged part of the brain to improve motor functions, by engaging individuals in active motor learning and training. In this review, we highlight recent animal studies (1) exploring cellular and molecular mechanisms contributing to neuroplasticity during motor training, (2) assessing the functional role of the mesocortical dopaminergic system in motor skill learning, and (3) exploring the impact of naturally occurring genetic variation in dopamine-related gene expression on the acquisition and performance of fine motor skills. Finally, the potential influence of the dopamine system on the outcome of motor learning interventions in cerebral palsy is discussed.

Cognitive outcome in adolescents and young adults after repeat courses of antenatal corticosteroids

OBJECTIVE

To investigate whether repeat courses of antenatal corticosteroids have long-term effects on cognitive and psychological functioning.

STUDY DESIGN

In a prospective cohort study, 58 adolescents and young adults (36 males) who had been exposed to 2-9 weekly courses of betamethasone in utero were assessed with neuropsychological tests and behavior self-reports. Unexposed subjects (n = 44, 25 males) matched for age, sex, and gestational age at birth served as a comparison group. In addition, individuals exposed in utero to a single course (n = 25, 14 males) were included for dose-response analysis. Group differences were investigated using multilevel linear modeling.

RESULTS

Mean scores obtained in 2 measures of attention and speed were significantly lower in subjects exposed to 2 or more antenatal corticosteroids courses (Symbol Search, P = .009; Digit Span Forward, P = .02), but these were not dose-dependent. Exposure to repeat courses of antenatal corticosteroids was not associated with general deficits in higher cognitive functions, self-reported attention, adaptability, or overall psychological function.

CONCLUSIONS

Although this study indicates that repeat exposure to antenatal corticosteroids may have an impact on aspects of executive functioning, it does not provide support for the prevailing concern that such fetal exposure will have a major adverse impact on cognitive functions and psychological health later in life.

Antenatal corticosteroids for preterm birth: dose-dependent reduction in birthweight, length and head circumference

AIM

This study was undertaken to evaluate the effects of repeated courses of antenatal corticosteroids (ACS) on foetal growth.

METHODS

We studied 94 infants exposed to 2-9 courses of ACS. Mean gestational age (GA) at first exposure was 29 and at birth 34 weeks. Exposure data were retrieved from case record files. Information on potential confounders was collected from the Swedish Medical Birth Registry. Standard deviation scores (SDS) for birthweight (BW), birthlength (BL) and head circumference (HC) were calculated and considered as outcomes.

RESULTS

GA at start of ACS did not affect outcome. BW-SDS, BL-SDS and HC-SDS were -0.21, -0.19 and +0.25 in infants exposed to two courses, compared to -1.01, -1.04 and -0.23 in infants exposed to ≥ 4 courses of ACS (p = 0.04-0.07). In multiple regression analyses, ≥ 4 courses were associated with lower BW-SDS, BL-SDS and HC-SDS (p = 0.007-0.04) compared to SDS after 2-3 courses. The effects from ≥ 4 courses on BW and BL were comparable to reduction in birth size seen in twins and on HC to that observed after maternal smoking.

CONCLUSIONS

Multiple courses of ACS are associated with a dose-dependent decline in foetal growth, which may affect later development and health.

Deficits in fine motor skills in a genetic animal model of ADHD

Background

In an attempt to model some behavioral aspects of Attention Deficit/Hyperactivity Disorder (ADHD), we examined whether an existing genetic animal model of ADHD is valid for investigating not only locomotor hyperactivity, but also more complex motor coordination problems displayed by the majority of children with ADHD.

Methods

We subjected young adolescent Spontaneously Hypertensive Rats (SHRs), the most commonly used genetic animal model of ADHD, to a battery of tests for motor activity, gross motor coordination, and skilled reaching. Wistar (WIS) rats were used as controls.

Results

Similar to children with ADHD, young adolescent SHRs displayed locomotor hyperactivity in a familiar, but not in a novel environment. They also had lower performance scores in a complex skilled reaching task when compared to WIS rats, especially in the most sensitive measure of skilled performance (i.e., single attempt success). In contrast, their gross motor performance on a Rota-Rod test was similar to that of WIS rats.

Conclusion

The results support the notion that the SHR strain is a useful animal model system to investigate potential molecular mechanisms underlying fine motor skill problems in children with ADHD.

Effects of antenatal dexamethasone treatment on glucocorticoid receptor and calcyon gene expression in the prefrontal cortex of neonatal and adult common marmoset monkeys

BACKGROUND

Synthetic glucocorticoids such as dexamethasone (DEX) are commonly used to promote fetal lung maturation in at-risk preterm births, but there is emerging evidence of subsequent neurobehavioral abnormalities in these children e.g. problems with inattention/hyperactivity. However, molecular pathways mediating effects of glucocorticoid overexposure on motor and cognitive development are poorly understood.

METHODS

In this study with common marmoset monkeys, we investigated for neonatal and adulthood effects of antenatal DEX treatment on the expression of the corticosteroid receptors and also calcyon, a risk gene for attention-deficit/hyperactivity disorder, in the prefrontal cortex (PFC). Pregnant marmosets were exposed to DEX (5 mg/kg body weight) or vehicle during early (days 42-48) or late (days 90-96) stages of the 144-day pregnancy.

RESULTS

In neonates, relative to controls, glucocorticoid receptor (GR) mRNA levels were significantly reduced after the late DEX treatment in the medial, orbital and dorsal PFC and after the early DEX treatment in the dorsal PFC. The early DEX exposure, specifically, resulted in significant reduction in calcyon mRNA expression in the medial, orbital, dorsal and lateral PFC relative to controls. Mineralocorticoid receptor (MR) mRNA levels were not significantly affected by DEX treatment. In adults, PFC GR, calcyon, and MR mRNA levels were not significantly affected by early or late prenatal DEX treatment.

CONCLUSION

These findings indicate that antenatal DEX treatment could lead to short-term alterations in PFC expression of the GR and calcyon genes, with possible neurodevelopmental functional consequences.

Calcyon mRNA expression in the frontal-striatal circuitry and its relationship to vesicular processes and ADHD

Background

Calcyon is a single transmembrane protein predominantly expressed in the brain. Very recently, calcyon has been implicated in clathrin mediated endocytosis, a critical component of synaptic plasticity. At the genetic level, preliminary evidence supports an association between attention-deficit/hyperactivity disorder (ADHD) and polymorphisms in the calcyon gene. As little is known about the potential role of calcyon in ADHD, animal models may provide important insights into this issue.

Methods

We examined calcyon mRNA expression in the frontal-striatal circuitry of three-, five-, and ten-week-old Spontaneously Hypertensive Rats (SHR), the most commonly used animal model of ADHD, and Wistar-Kyoto (WKY; the strain from which SHR were derived). As a complement, we performed a co-expression network analysis using a database of mRNA gene expression profiles of multiple brain regions in order to explore potential functional links of calcyon to other genes.

Results

In all age groups, SHR expressed significantly more calcyon mRNA in the medial prefrontal and orbital frontal cortices than WKY rats. In contrast, in the motor cortex, dorsal striatum and nucleus accumbens, calcyon mRNA expression was only significantly elevated in SHR in younger animals. In both strains, calcyon mRNA levels decreased significantly with age in all regions studied. In the co-expression network analysis, we found a cluster of genes (many of them poorly studied so far) strongly connected to calcyon, which may help elucidate its role in the brain. The pair-wise relations of calcyon with other genes support its involvement in clathrin mediated endocytosis and, potentially, some other membrane/vesicular processes. Interestingly, no link was found between calcyon and the dopamine D1 receptor, which was previously shown to interact with the C-terminal of calcyon.

Conclusion

The results indicate an alteration in calcyon expression within the frontal-striatal circuitry of SHR, especially in areas involved in cognitive processes. These findings extend our understanding of the molecular alterations in SHR, a heuristically useful model of ADHD.

Motor inhibitory role of dopamine D1 receptors: implications for ADHD

Dysregulation of dopamine (DA) neurotransmission in frontal-striatal circuitry has been hypothesized to underlie several neurodevelopmental disorders, including attention-deficit/hyperactivity disorder (ADHD). The actions of DA are mediated by five distinct receptor subtypes that belong to the G-protein-coupled receptor super-family and are divided into two major classes, D1-like (D1 and D5) and D2-like (D2, D3, and D4). Accumulating evidence implicates the D1 receptor subtype (D1R) in the regulation of motor and cognitive processes. It is generally assumed that D1R is linked to motor activity in a stimulatory fashion. However, recent findings in rodents suggest a potential role of D1R on motor inhibition, which emerges during late postnatal development. Several lines of evidence indicate that the locus of the inhibitory effects involve subregions of the prefrontal cortex (PFC). These results may be relevant for understanding the neurobiology of ADHD.

Alteration of dopamine D1 receptor-mediated motor inhibition and stimulation during development in rats is associated with distinct patterns of c-fos mRNA expression in the frontal-striatal circuitry

Dopamine D1 receptors have been implicated in various neurodevelopmental disorders, including attention-deficit/hyperactivity disorder. However, little is known about potential late maturational changes of the motor inhibitory and stimulatory role of these receptors. Here, we investigated the effects of a full and selective D1 receptor agonist, SKF-81297, on motor activity and expression of the plasticity-associated gene, c-fos, in the prefrontal cortex and striatum of juvenile and adolescent male rats. In general, SKF-81297 produced a biphasic effect on motor activity (locomotor and rearing activity), which consisted of an initial short inhibition followed by a long-lasting stimulation. These effects were dose- and age- dependent. The inhibitory phase was more pronounced in adolescent than in juvenile rats whereas the opposite was true for the stimulatory phase. During the initial inhibitory phase of the drug, c-fos mRNA expression was increased in the prefrontal cortex of juvenile rats but reduced in adolescent rats. There was also an increase in c-fos mRNA expression in the medial-dorsal striatum and olfactory tubercle, which was more evident in juvenile rats. In contrast, during the stimulatory phase, c-fos mRNA expression was increased in both the dorsal and ventral striatum, especially in the nucleus accumbens, as well as in the prefrontal cortex, in both age groups. The increase of c-fos mRNA in the dorsal striatum, however, was more pronounced in juvenile rats. These results indicate the presence of two distinct D1 receptor populations within the frontal-striatal circuitry, which have opposite effects on motor activity, and which have different maturational profiles.

Can a therapeutic dose of amphetamine during pre-adolescence modify the pattern of synaptic organization in the brain?

Stimulant drugs such as amphetamine have, for many decades, been the drugs of choice in the treatment of children with attention-deficit/hyperactivity disorder. However, little is known about their therapeutic mechanisms or about the consequences of their long-term exposure. In the present study we investigated whether repeated exposure of a low dose of amphetamine (0.5 mg/kg) to juvenile rats could induce long-term morphological alterations in the prefrontal cortex. In addition, to assess possible behavioural consequences of prolonged exposure to this drug, we examined whether changes in the motor response to various dopamine agonists occurred after this treatment. We found that this dose of amphetamine promotes plasma concentrations of amphetamine sulphate in juvenile rats to levels corresponding to the clinical range used for children with attention-deficit/hyperactivity disorder. Amphetamine (0.5 mg/kg; s.c.) was administered twice daily during postnatal days 22-34, and then the brains of the animals were evaluated 2 weeks later. This treatment produced an increase in dendritic length and branches of pyramidal neurons of the medial prefrontal cortex, but not in the nucleus accumbens. These changes were associated with an increase in the expression of calcium/calmodulin-dependent protein kinase II, a highly abundant signalling protein in the postsynaptic densities of excitatory synapses. Interestingly, amphetamine pre-treatment did not alter the motor response to various dopamine agonists, including amphetamine. These data suggest that clinical doses of stimulant drugs may be acting as a trophic support at the glutamatergic synapses, thereby enhancing dopamine-glutamate interactions in the prefrontal cortex.

Sex differences in the motor inhibitory and stimulatory role of dopamine D1 receptors in rats

We investigated sex differences in the motor responses to the full and selective dopamine D1-like receptor agonist, (+/-)-6-chloro-7,8-dihydroxyl-1-phenyl-2,3,4,5-tetrahydro-1H-3-benzazepine hydrobromide (SKF-81297; 0.3, 3, and 10 mg/kg, s.c.), in non-habituated adult rats. In general, SKF-81297 produced a biphasic effect on motor activity (including locomotion, rearing and exploratory activity) which consisted of an initial short inhibition followed by a long-lasting stimulation. These effects were dose- and sex-dependent. The inhibitory phase was more pronounced in males than females while the opposite was true for the stimulatory phase. Importantly, the motor inhibitory effects of SKF-81297 were not due to an increase in stereotypy (e.g., grooming activity). These biphasic effects on several motor parameters suggest the presence of two distinct dopamine D1 receptor populations which have opposite effects on motor activity and which are, in part, sexually dimorphic.

Calcyon in the rat brain: cloning of cDNA and expression of mRNA

Calcyon is a 24 kD protein recently cloned from a human brain cDNA library and shown to interact with the dopamine receptor 1 (D1R) of D1-like receptors. This interaction shifts the effector coupling of D1R to stimulate a calcium signaling pathway, without influencing the D1R-adenylyl-cAMP pathway. To obtain more knowledge about the potential role of calcyon in the brain, we cloned rat calcyon cDNA and studied its distribution in the brain. Northern blot analysis and RT-PCR revealed that rat calcyon mRNA was expressed only in the brain. With the use of the in situ hybridization technique, we studied rat calcyon mRNA distribution in the brain and related it to the distribution of D1R and dopamine receptor 5 (D5R) mRNAs. Prominent calcyon mRNA signals were found in several brain regions, including hippocampus, hypothalamus, cerebellum, and medial prefrontal cortex. Less abundant calcyon mRNA expression was observed in the dorsal striatum region, where D1R mRNA is highly expressed and where D1R/cAMP-DARPP-32 signaling pathway is of great functional importance. The strongest expression of D5R mRNA was found in the hippocampus and cerebellum, where D1R mRNA expression was relatively low. In conclusion, rat calcyon appears to be a brain specific protein. There is a certain overlap between calcyon mRNA distribution and that of the D1R and D5 mRNAs, indicating that calcyon might be associated not only with D1R but also with D5R.

Ontogeny of the motor inhibitory role of dopamine D(3) receptor subtype in rats

We have examined the motor responses to the dopamine D(3) receptor-preferring agonist, S(+)-(4aR,10bR)-3,4,4a, 10b-tetrahydro-4-propyl-2H,5H-1-benzopyranol[4,3-b]-1,4-oxazin+ ++-9-ol ((+)-PD128,907), by non-habituated male rats during postnatal development. (+)-PD128,907 (0.025 and 0.1 mg/kg) increased motor activity (rearing, motility and locomotion) in 14-day-old rats without inducing oral stereotypies. However, in 21-, 28- and 70-day-old rats, (+)-PD128,907 caused a significant reduction in motor activity. This reduction was most pronounced in 70-day-old rats. In addition, the stimulatory effects of (+)-PD128,907 in 14-day-old rats were fully blocked by the dopamine D(3) receptor antagonist 5,6-dimethoxy-2-(di-u-propylamino) indan (U99194A). These results suggest that the motor inhibition mediated by the activation of the dopamine D(3) receptors develops between the second and the third postnatal weeks.