Developmental changes in brain serotonin synthesis capacity in autistic and nonautistic children

Serotonin content, serotonin uptake sites, and serotonin receptor binding measured in animal studies are all higher in the developing brain, compared with adult values, and decline before puberty. Furthermore, a disruption of synaptic connectivity in sensory cortical regions can result from experimental increase or decrease of brain serotonin before puberty. The purpose of the present study was to determine whether brain serotonin synthesis capacity is higher in children than in adults and whether there are differences in serotonin synthesis capacity between autistic and nonautistic children. Serotonin synthesis capacity was measured in autistic and nonautistic children at different ages, using alpha[11C]methyl-L-tryptophan and positron emission tomography. Global brain values for serotonin synthesis capacity (K complex) were obtained for autistic children (n = 30), their nonautistic siblings (n = 8), and epileptic children without autism (n = 16). K-complex values were plotted according to age and fitted to linear and five-parameter functions, to determine developmental changes and differences in serotonin synthesis between groups. For nonautistic children, serotonin synthesis capacity was more than 200% of adult values until the age of 5 years and then declined toward adult values. Serotonin synthesis capacity values declined at an earlier age in girls than in boys. In autistic children, serotonin synthesis capacity increased gradually between the ages of 2 years and 15 years to values 1.5 times adult normal values and showed no sex difference. Significant differences were detected between the autistic and epileptic groups and between the autistic and sibling groups for the change with age in the serotonin synthesis capacity. These data suggest that humans undergo a period of high brain serotonin synthesis capacity during childhood, and that this developmental process is disrupted in autistic children.

Cerebral imaging in paediatrics

Radioisotope brain imaging has focused mainly on regional cerebral blood flow (rCBF). However the use of ligands which go to specific receptor sites is being introduced in paediatrics, mainly psychiatry. rCBF is potentially available in many institutions, especially with the availability of multi-headed gamma cameras. The use of this technique in paediatrics requires special attention to detail in the manner of data acquisition and handling the child. The interpretation of the rCBF study in a child requires knowledge of normal brain maturation. The major clinical use in paediatrics is epilepsy because of the advances in surgery and the frequency of complex partial seizures. Other indications in paediatric neurology include brain death, acute neurological loss including stroke, language disorders, cerebral palsy, hypertension due to renovascular disease, traumatic brain injury and migraine. There are paediatric psychological conditions in which rCBF has been undertaken, these include anorexia nervosa, autism, Gilles de la Tourette syndrome (GTS) and attention deficit disorder-hyperactivity (ADHD). Research using different ligands to specific receptor sites will also be reviewed in paediatrics.

Impairment of dentato-thalamo-cortical pathway in autistic men: language activation data from positron emission tomography

Recent evidence suggests disturbances of serotonin synthesis affecting the dentato-thalamo-cortical pathway in autistic boys. We studied possible effects of such disturbances on brain activations for language in autistic adults. Four autistic and five normal men were studied while listening to, repeating, and generating sentences, using [15(O)]-water positron emission tomography (PET). Activation in the right dentate nucleus and in the left frontal area 46 was reduced during verbal auditory and expressive language and enhanced during motor speech functions in the autism as compared to the control group. The thalamus showed group differences concordant with area 46 for expressive language. The results may indicate atypical functional specialization of the dentato-thalamo-cortical pathway and are compatible with a model of region-specific biochemical disturbances in the developing autistic brain.

Structural neuroimaging in learning disability

BACKGROUND

Neuroimaging has proven useful in confirming diagnoses of certain neuropsychiatric conditions, but neuroimaging studies in learning disability are at an early stage.

METHOD

A review of recent structural neuroimaging research in relation to learning disability was carried out.

RESULTS

Brain abnormalities can be detected in cases of idiopathic and non-idiopathic learning disability, but their significance is not clear due to discrepancies in study findings and the small cohorts involved.

CONCLUSION

Although the role of structural neuroimaging in the assessment of people with learning disability is not clear, new magnetic resonance imaging technology holds great promise for future research.

Tuberous Sclerosis Complex: the role of neuroradiology

Tuberous Sclerosis Complex is the second commonest phakomatosis affecting between 1 in 70,00-10,000 live births. It is a multisystem disorder but neurological disturbances are often the presenting feature and cause major morbidity/mortality. In this paper the neuroradiological and clinical features are reviewed, focusing on a rational approach to imaging children with tuberous Sclerosis Complex.

Altered serotonin synthesis in the dentatothalamocortical pathway in autistic boys

Based on reports of increased platelet serotonin in 30 to 50% of autistic subjects, abnormal serotonergic neurotransmission may be important in the pathogenesis of autism. However, serotonin metabolite measurements in cerebrospinal fluid of autistic subjects have failed to demonstrate consistent abnormalities. Using alpha-[11C]methyl-L-tryptophan as a tracer for serotonin synthesis with positron emission tomography, we now report unilateral alterations of serotonin synthesis in the dentatothalamocortical pathway in autistic boys. Asymmetries of serotonin synthesis were found in frontal cortex, thalamus, and dentate nucleus of the cerebellum in all 7 boys, but not in the 1 autistic girl studied. Decreased serotonin synthesis was found in the left frontal cortex and thalamus in 5 of the 7 boys and in the right frontal cortex and thalamus in the 2 remaining autistic boys. In all 7 cases, elevated serotonin synthesis in the contralateral dentate nucleus was observed. Statistically significant differences between autistic boys and their nonautistic siblings (n = 5) were obtained when comparing asymmetry indices for frontal cortex, thalamus, and dentate nucleus combined as well as individually for frontal cortex and thalamus. These serotonergic abnormalities in a brain pathway, important for language production and sensory integration, may represent one mechanism underlying the pathophysiology of autism.

Anterior cingulate gyrus volume and glucose metabolism in autistic disorder

OBJECTIVE

This study reports the first paired measurements of glucose metabolism and volume of the anterior cingulate gyrus in autism.

METHOD

Magnetic resonance imaging (MRI) and positron emission tomography (PET) scans of seven high-functioning autistic patients and seven sex- and age-matched normal volunteers were coregistered. After the anterior cingulate gyri were outlined on the MRI images, the volumes of the structures were measured and corrected for brain volume. The volumes were then applied to the PET images and metabolic maps were obtained.

RESULTS

Right anterior cingulate area 24' was significantly smaller in relative volume, and both area 24 and area 24' were metabolically less active, in the autistic patients than in the normal subjects.

CONCLUSIONS

Autism may be characterized by structural and functional alterations in the anterior cingulate gyrus.

Possible effects of tetrahydrobiopterin treatment in six children with autism--clinical and positron emission tomography data: a pilot study

Six children, between 3 and 5 years of age, having infantile autism according to DSM-III-R, were treated for 3 months with 6R-L-erythro-5,6,7,8-tetrahydrobiopterin (R-BH4), a cofactor for tyrosine hydroxylases in the biosynthetic pathway of catecholamines and serotonin. A criterion for inclusion in the study was a relatively low level of R-BH4 in the cerebrospinal fluid. For clinical evaluation, the Parental Satisfaction Survey (PASS) was used every fourth week and the Griffiths Developmental Scales were used before starting and 3 months after completing the treatment. During the treatment period, all parents reported improvements in the child's social functioning-mainly eye contact and desire to interact-and in the number of words or sounds which the child used. Small positive changes were noted on the Griffiths Developmental Scales between the two testing occasions. R-BH4 levels in CSF increased significantly after treatment. The positron emission tomography (PET) study showed that the high value of dopamine D2 receptor binding in the caudate and putamen decreased by about 10% towards the normal level after treatment with R-BH4. The observations in this open study indicate that the drug might be useful for a subgroup of children with autism, but there is a need for a larger double-blind study with a longer treatment period.

Normal fusion for three-dimensional integrated visualization of SPECT and magnetic resonance brain images

Multimodality visualization aims at efficiently presenting integrated information obtained from different modalities, usually combining a functional modality (SPECT, PET, functional magnetic resonance imaging) with an anatomical modality [CT, magnetic resonance imaging (MRI)]. This paper presents a technique for three-dimensional integrated visualization of SPECT and magnetic resonance brain images, where MRI is used as a framework of reference for the display of the SPECT data.

METHODS

A novel technique for three-dimensional integrated visualization of functional and anatomical information, called normal fusion, is presented. With this technique, local functional information is projected onto an anatomic structure.

RESULTS

The normal fusion technique is applied to three cases of SPECT/MRI integration. The results are presented, discussed and evaluated for clinical relevance.

CONCLUSION

The results for three-dimensional integrated display of SPECT and MR brain images indicate that the normal fusion technique provides a potentially comprehensive and diagnostically valuable presentation of cerebral blood perfusion in relation to the anatomy of the brain.

Infantile spasms: III. Prognostic implications of bitemporal hypometabolism on positron emission tomography

Positron emission tomography (PET) of brain glucose utilization is highly sensitive in detecting focal cortical abnormalities in patients with infantile spasms even when the computed tomographic (CT) and magnetic resonance imaging (MRI) scans are normal. Of 110 infants with spasms evaluated for potential surgical intervention during an 8-year period, we encountered 18 infants (7 males, 11 females; age range, 10 mo to 5 yr) with a common metabolic pattern on positron emission tomography (PET) consisting of bilateral hypometabolism in the temporal lobes. CT and MRI scans did not reveal any focal abnormalities in the 18 infants. Video-electroencephalographic monitoring indicated either bilateral or multifocal epileptogenicity, or failed to show any epileptic focus, so that none of the 18 infants were considered candidates for resective surgery. These patients were then enrolled in a prospective study aimed at determining long-term outcome in the presence of bilateral temporal PET hypometabolism. Analysis of outcome in 14 of the 18 subjects (follow-up period, 10 mo to 10 yr 5 mo; mean, 3 yr 11 mo +/- 2 yr 4 mo [SD]) revealed the following: (1) all had severe developmental delay and had failed to gain significant milestones; (2) language development had been minimal or absent; (3) 10 of the 14 met the DSM-IV criteria for autistic disorder. Our findings indicate that patients with infantile spasms and bitemporal glucose hypometabolism on PET comprise a relatively homogeneous group and are typically not candidates for cortical resection. The long-term outcome of these infants is particularly poor and the majority are autistic.

SPECT of the brain in childhood autism: evidence for a lack of normal hemispheric asymmetry

Autism is thought to be associated with abnormal hemispheric specialization and left-hemispheric dysfunction. Brain functional imaging using 133Xe-SPECT (single photon emission computed tomography) was used to measure left/right asymmetry and absolute values of regional cerebral blood flow (rCBF) in 18 children with autism aged from four to 17 years and 10 age-matched controls. All controls but only 10 children with autism were right-handed. The left-to-right indices, both hemispheric and regional, were positive in controls, indicating higher left than right rCBF values, but were negative in patients with autism. This inversion was statically significant for total hemispheres, sensorimotor and language-related cortex and was explained by a significant decrease of the left absolute rCBF values in these regions in the patients with autism. The inversion was independent of handedness, sex and age. These results confirm the existence of left-hemispheric dysfunction in childhood autism, especially in the cortical areas devoted to language and handedness, leading to anomalous hemispheric specialization.

Glucose metabolic correlates of continuous performance test performance in adults with a history of infantile autism, schizophrenics, and controls

Twenty-five schizophrenic patients, fourteen adults with a history of infantile autism, and twenty normal controls performed a test of sustained attention, the degraded stimulus continuous performance test (CPT), during the 35 minute 18-fluoro-2-deoxyglucose uptake period preceding positron emission tomographic (PET) scan acquisition. This is the first analysis comparing correlations between glucose metabolic rate (GMR) for selected regions and CPT performance. CPT performance differed in controls and schizophrenics, but autistics did not differ from either group. In controls and schizophrenic patients, task performance correlated with GMR in medial superior frontal gyrus and lateral inferior temporal gyrus, suggesting that activation of those regions is important in the normal performance of the task and that damage to those regions, which also showed low GMR in schizophrenics, contributes to the attentional dysfunction in schizophrenia. Also, schizophrenics showed negative correlations of task performance with anterior cingulate activity suggesting that overactivity of that region, which is involved in mental effort and whose GMR was low in our larger study of schizophrenia, impairs task performance in schizophrenics. Autistic patients showed negative correlations of medial frontal cortical GMR with attentional performance, suggesting that neuronal inefficiency in that region may contribute to poor performance.

Functional deficits in autistic disorder: characterization by technetium-99m-HMPAO and SPECT

Autistic disorder is an early and severe developmental disorder characterized by deficits in verbal and nonverbal language, social skills, cognitive functioning and an abnormal repertoire of behaviors. Current research, however, has failed to identify the neurobiological mechanisms that underlie autism or those cortical brain regions, if any, that are abnormal.

METHODS

We examined regional cerebral blood flow (rCBF) in six young, severely autistic patients. High-resolution brain SPECT with 99mTc-HMPAO was performed while five of the six patients were under general anesthesia. The scans reflected the subjects' rCBF in their usual alert behavioral state, since the tracer was injected at least 15 min prior to anesthesia and is rapidly extracted and fixed in the brain. A computer-automated cortical region of interest (ROI) generator was used to define 12 annular cortical regions (region 1 = left frontal, clockwise to region 12 = right frontal) for count data acquisition. The ratio of average counts in each ROI to whole-slice counts for the autistic patients was compared to age-matched controls using repeated measures (splt-plot) ANOVA statistical analysis for three representative brain levels.

RESULTS

In the autistic patients, cortical regions 3, 4, and 10 were abnormally low at the cortical level canthomeatal (CM) + 3.5 cm. At level CM + 5.5 cm, regions 3, 4, 5 and 10 were abnormally low, and at level CM + 7.5 cm, regions 7 and 9 were also abnormally low. These regions correspond to abnormally low rCBF values located predominately in the temporal and parietal lobes, with the left cerebral hemisphere showing greater rCBF abnormalities than the right.

CONCLUSION

Our findings suggest that the temporal and parietal lobes have abnormal rCBF in autism. HMPAO brain SPECT in combination with general anesthesia is particularly useful for imaging severely noncompliant patients.

Delayed maturation of the frontal cortex in childhood autism

OBJECTIVE

The authors investigated the metabolic maturation of the frontal cortex in pre-school autistic children.

METHOD

Regional cerebral blood flow (CBF) in five children with primary autism diagnosed according to the DSM-III-R criteria was studied longitudinally. Regional CBF in each of the autistic children was measured with single photon emission computed tomography twice during their development: at the age of 3-4 years and 3 years later. At each stage, the autistic children were compared to an age-matched comparison group of five nonautistic children with normal development.

RESULTS

A transient frontal hypoperfusion was found in the autistic children at ages 3-4 years; this corresponded to the pattern of perfusion observed in much younger normal children. By the ages of 6-7, the autistic children's frontal perfusion had attained normal values.

CONCLUSIONS

Since CBF patterns in children are related to maturational changes in brain function, these results indicate a delayed frontal maturation in childhood autism. Such a delayed brain maturational process is consistent with the clinical data and cognitive performance of autistic children.

Neuroimaging in infantile autism

Metabolic findings using [18F]fluorodeoxyglucose (FDG) with positron emission tomography (PET) and correlative anatomic findings with computed tomography (CT) or magnetic resonance imaging (MRI) were characterized in 13 children with infantile autism. Four of 13 patients had both an abnormal FDG-PET and an abnormal MRI, whereas seven of 13 patients had both a normal FDG-PET and a normal CT or MRI. Sixteen of a total of 195 brain areas qualitatively examined with FDG-PET had a hypometabolic abnormality on PET. Three of the five abnormal structural imaging studies revealed neuronal migrational anomalies (focal pachygyria). In two of the five patients with anatomic abnormalities, these were noted only after knowledge of the FDG-PET findings. Our experience reveals that anatomic and metabolic abnormalities can be found in children who exhibit autistic behavior. An FDG-PET study may provide evidence of metabolic dysfunction after an initially unremarkable MRI scan because subtle anatomic abnormalities (as those seen with neuronal migrational anomalies) may be found only after knowledge of a regional metabolic abnormality.

[Does juvenile autism have a morphologic basis?]

In the world literature findings of morphological abnormalities in the area of the brain and cerebellum in children with pervasive developmental disorders are encountered. The authors of the present article describe in three case-records morphological abnormalities of the brain and cerebellum found in subjects with markedly expressed or only indicated signs of child autism. At the same time they draw attention to the possible determination of experience and behaviour of subjects with discrete morphological abnormalities, even when the pervasive developmental disorder was not diagnosed but where specific determination of premorbid experience and behaviour, as well as the clinical picture of a possible mental disorder or disease.

Blood flow response to auditory stimulations in normal, mentally retarded, and autistic children: a preliminary transcranial Doppler ultrasonographic study of the middle cerebral arteries

Using the noninvasive transcranial ultrasonic Doppler method, flow dynamics of the middle cerebral arteries were investigated in relation to auditory stimulations in 12 children with autistic behavior compared with 12 normal controls and 10 mentally retarded children. In normal children, auditory stimulation evoked lateralized modifications: blood flow increased and resistance index decreased on the left side; such modifications were not recorded on the right side. This pattern should indicate vasodilatation mechanisms induced by changes in the metabolism of the brain areas supplied by the left middle cerebral arteries (MCA). Although less asymmetrical, this pattern was also found in the mentally retarded children. Autistic children significantly differed from these two groups. They displayed a symmetric pattern of responses with a blood flow decrease and resistance-index increase on both sides; this could suggest abnormal metabolic mechanisms induced by auditory stimulation in autistic children and could be related to the previous hypothesis of impairment in the development of cerebral lateralization in autism. These preliminary results show that transcranial Doppler ultrasonography may be a valuable and practicable tool for the noninvasive study of evoked blood flow responses in psychopathology.

Cerebral blood flow abnormalities in adults with infantile autism

Structural brain abnormalities have recently been discovered using magnetic resonance imaging in infantile autism, a neurodevelopmental disorder of unknown etiology. However, functional neuroimaging studies in autism using positron emission tomography have had conflicting results and have not explained how the known structural brain abnormalities in autism act in a functioning brain to produce autistic behavior. Using a new technology, high-resolution brain single photon emission tomography, we studied and scanned four young adults with infantile autism and four age-matched controls using the labeled ligand 99mTc-D,L-hexamethyl-propylene amine oxime (99mTc-HMPAO). Total brain perfusion was significantly decreased in autism subjects (range, 58% to 72% of controls, p less than or equal to .02). In addition to the globally decreased perfusion, the autism group also had regionally decreased flow in the right lateral temporal and right, left, and midfrontal lobes compared with controls (p less than or equal to .02, Mann-Whitney t-test).

Regional cerebral blood flow in childhood autism: a SPECT study

OBJECTIVE

The authors investigated a possible cortical brain dysfunction associated with infantile autism.

METHOD

They measured regional cerebral blood flow with single photon emission computed tomography (SPECT) and xenon-133 in 21 children with primary autism (according to DSM-III-R criteria). Five cortical brain areas including frontal, temporal, and sensory association cortices were examined in order to test the recent hypothesis of cerebral dysfunction in primary autism. Anatomical references for each subject were obtained with computerized tomography or magnetic resonance imaging and were used to delimit the regions of interest for SPECT analysis.

RESULTS

When the results from the group with primary autism were compared with an age-matched group of nonautistic children with slight to moderate language disorders (N = 14), no cortical regional abnormalities were found.

CONCLUSIONS

It appears that there is no regional cortical dysfunction in primary autism; however, in light of methodological limitations, one cannot exclude the possibility of more localized or subcortical brain dysfunctions in autism.

Autistic symptoms in children with infantile hydrocephalus

From a population-based series of children with Infantile Hydrocephalus (IH) 69 patients (mean age 11.7 years) were examined with respect to the occurrence of autistic symptoms. Autistic symptomatology was evaluated according to a modified short Swedish version of the so-called Autism Behavior Checklist. Sixteen of the 69 IH children (23%) reached a score which was considered indicative of autistic symptoms (AS) in the child. This group was compared with the remaining 53 IH children without autistic symptoms (non AS). Significant differences were found between these two groups with respect to aetiological and clinical data. In the AS group 44% were born preterm as compared to 9% in the non AS group. CT scan showed major abnormalities in 64% of the AS children while this was present in 28% in the non AS group. The occurrence of major neuroimpairments--epilepsy, mental retardation and cerebral palsy--was 50%, 88% and 50% in the AS group as compared to 9%, 23% and 19% respectively in the non AS group. It was concluded that the more severe the brain damage in children with IH the more likely that autistic symptomatology would ensue. This implies that specific neuropsychiatric services to these families are required.

Infantile autism and computerized tomography brain-scan findings: specific versus nonspecific abnormalities

The hypothesis that specific computerized tomography brain-scan findings are associated with infantile autism was tested in 45 cases and 19 controls. The autistic group was subdivided into serious and less-serious language-impaired subgroups. The analysis of Euclidean Distances, a type of cluster analysis, showed that neuroradiological parameters of cases and controls, including ventricular sizes, were on the whole significantly different, but no statistically significant difference appeared between the two autistic subgroups. But the analysis of variance of each neuroradiological parameter did not show any significant difference between autistics and controls. It was concluded that autism is nonspecifically associated with brain-scan abnormalities, and that other nonorganic, as well as organic, factors should be taken into account.

Positron emission tomography of the cerebellum in autism

On the basis of neurological evidence that autistic patients have fewer Purkinje and granule cells in the cerebellum as well as vermal cerebellar hypoplasia, the authors tested the hypothesis that autistic patients have cerebellar hypofunctioning. They used positron emission tomography of the cerebellum with 18F-labeled 2-deoxyglucose to study seven autistic patients and eight age-matched control subjects. The results showed no significant difference in mean cerebellar glucose metabolism between the two groups, but all mean glucose rates of the autistic patients were either equal to or greater than those of the control subjects. The implications of these findings are discussed.