Platelet dopamine uptake in autistic and other psychotic children. Inhibition by imipramine

Tricyclic antidepressants for autism spectrum disorders (ASD) in children and adolescents

BACKGROUND

Autism spectrum disorders (ASD) are a heterogeneous group of neurodevelopmental disorders, ranging in severity and characterised by early onset of delay and deviance in the development of social interaction, and verbal and nonverbal communication. ASD is associated with restricted and/or stereotyped interests or behaviours. Tricyclic antidepressants (TCAs) block noradrenaline and serotonin reuptake, increasing the availability of these neurotransmitters in the central nervous system. Via their impact on serotonin, TCAs have been used in the treatment of autistic symptoms and comorbidities in individuals with ASD.  

OBJECTIVES

To determine if treatment with tricyclic antidepressants:1) improves the core features of autism, including restricted social interaction, restricted communication, and stereotypical and repetitive behaviours; 2) improves non-core features such as challenging behaviours; 3) improves comorbid states, such as depression and anxiety; 4) causes adverse effects.

SEARCH METHODS

We ran the latest searches for this review on 23 May 2011. We searched: Cochrane Central Register of Controlled Trials (CENTRAL), 2011 Issue 2, MEDLINE (1948 to May Week 2, 2011), EMBASE (1980 to 2011 Week 2), PsycINFO (1887 to current), CINAHL (1937 to current). We also searched Dissertation Abstracts International via Dissertation Express, and the metaRegister of Controlled Trials.

SELECTION CRITERIA

Randomised controlled trials of any dose, duration and frequency of oral TCAs compared with placebo, in children and adolescents with a diagnosis of ASD, where at least one standardised outcome measure had been used.

DATA COLLECTION AND ANALYSIS

Two review authors independently selected and appraised the studies for inclusion and risk of bias. All data were continuous.

MAIN RESULTS

Three studies met the inclusion criteria for this review. Two studies used clomipramine and one used tianeptine. All three trials were small, with between 12 and 32 participants. One of the clomipramine trials involved children and young adults, while the other two trials enrolled only children. Due to heterogeneity in study participant characteristics, the TCA medications investigated and the outcome measures used, we were not able to perform any meta-analysis.In only one of the three studies was there any indication that giving children tianeptine could be effective in the short term. In this study, parents and teachers reported that it reduced irritability, hyperactivity, inadequate eye contact and inappropriate speech, but clinician ratings found no significant impact on these symptoms. There were also significant adverse effects, including increased drowsiness and reduced activity levels in these individuals while being treated with tianeptine. The evidence of the impact of clomipramine in the two studies is contradictory. There was evidence of improvement in autistic symptoms, irritability and obsessive-compulsive disorder type symptoms, but conflicting evidence in relation to hyperactivity across the two studies, and no significant changes found with inappropriate speech. There were also adverse effects reported with the use of clomipramine. Although side effect ratings were not significantly different to placebo, there were significant dropout rates in the clomipramine arm of one study.

AUTHORS' CONCLUSIONS

Clinicians considering the use of TCAs need to be aware of the limited and conflicting evidence of effect and the side effect profile when discussing this treatment option with people who have ASD and their carers. Further research is required before TCAs can be recommended for treatment of individuals with ASD.

Platelets and biogenic amines. 1. Platelets are poor investigative models for dopamine re-uptake

The uptake of 14C-dopamine (DA) by human platelets at 10(-7) -2.5 X 10(-4) M of labelled amine concentration was studied in human platelet-rich plasma. The total uptake could be resolved into two components, one of which was saturable and completely inhibited by 10(-5) imipramine and another which was unsaturable but temperature-dependent. The saturable uptake of DA had an apparent Km of 75 X 10(-6) M and Vmax of 1.34 pmol/10(6) platelets/min. The uptake of unsaturable DA was 1.33 pmol/10(6) platelets/min at 10(-4) M DA. Dopamine exerted a mixed non-competitive inhibition of the saturable 5-HT transport and vice versa. Thus the increase in Km was paralleled by a decrease in Vmax. The low-affinity transport of DA by the human platelets does not share any of the dopamine uptake characteristics found in neuronal tissue. The platelet therefore seems to be a poor model for the presynaptic function of the dopamine neurons.

Blood platelets in psychopharmacological research

Blood platelets are a very good model for nerve endings, for study of serotonin uptake and imipramine binding. The efficiency of various drugs, mainly antidepressants, can be evaluated using blood platelets instead of synaptosomes. A few neuronal active compounds are effective in inducing platelet secretion and shape change reaction. Platelet MAO and c-AMP levels are not yet established as useful in psychopharmacological studies.

The active uptake of serotonin by platelets of schizophrenic patients and their families: possibility of a genetic marker

The active uptake of serotonin (5-HT) blood platelets of 20 schizophrenic patients and their families was studied. The uptake was studied over a wide range of 5-HT concentrations (0.1-20 microM), and Km and Vmax of the uptake process were calculated. Of 20 patients, 18 exhibited a lower rate of uptake than the family average at 5-HT concentrations lower than the Km value. At a 5-HT concentration of 0.1 microM, the average 5-HT uptake of patients was 2.15 pmol/10(8) platelets/min, while that of families was 2.99 pmol/10(8) platelets/min (33% difference). At a high 5-HT concentration, only the drug-treated patients had lower Vmax than the family average, and this might be attributed to the effect of the drugs. Km of patients and families were very similar. In eight families, one or more of the family members showed 5-HT uptake patterns very similar to that of the patient. We termed these healthy family members "schizophrenic risks". Our findings indicate the involvement of some genetic factors in this disease.