Platelet imipramine binding in autistic subjects

The serotonin system in autism spectrum disorder: From biomarker to animal models

Elevated whole blood serotonin, or hyperserotonemia, was the first biomarker identified in autism spectrum disorder (ASD) and is present in more than 25% of affected children. The serotonin system is a logical candidate for involvement in ASD due to its pleiotropic role across multiple brain systems both dynamically and across development. Tantalizing clues connect this peripheral biomarker with changes in brain and behavior in ASD, but the contribution of the serotonin system to ASD pathophysiology remains incompletely understood. Studies of whole blood serotonin levels in ASD and in a large founder population indicate greater heritability than for the disorder itself and suggest an association with recurrence risk. Emerging data from both neuroimaging and postmortem samples also indicate changes in the brain serotonin system in ASD. Genetic linkage and association studies of both whole blood serotonin levels and of ASD risk point to the chromosomal region containing the serotonin transporter (SERT) gene in males but not in females. In ASD families with evidence of linkage to this region, multiple rare SERT amino acid variants lead to a convergent increase in serotonin uptake in cell models. A knock-in mouse model of one of these variants, SERT Gly56Ala, recapitulates the hyperserotonemia biomarker and shows increased brain serotonin clearance, increased serotonin receptor sensitivity, and altered social, communication, and repetitive behaviors. Data from other rodent models also suggest an important role for the serotonin system in social behavior, in cognitive flexibility, and in sensory development. Recent work indicates that reciprocal interactions between serotonin and other systems, such as oxytocin, may be particularly important for social behavior. Collectively, these data point to the serotonin system as a prime candidate for treatment development in a subgroup of children defined by a robust, heritable biomarker.

Altered serotonin, dopamine and norepinepherine levels in 15q duplication and Angelman syndrome mouse models

Childhood neurodevelopmental disorders like Angelman syndrome and autism may be the result of underlying defects in neuronal plasticity and ongoing problems with synaptic signaling. Some of these defects may be due to abnormal monoamine levels in different regions of the brain. Ube3a, a gene that causes Angelman syndrome (AS) when maternally deleted and is associated with autism when maternally duplicated has recently been shown to regulate monoamine synthesis in the Drosophila brain. Therefore, we examined monoamine levels in striatum, ventral midbrain, frontal cerebral cortex, cerebellar cortex and hippocampus in Ube3a deficient and Ube3a duplication animals. We found that serotonin (5HT), a monoamine affected in autism, was elevated in the striatum and cortex of AS mice. Dopamine levels were almost uniformly elevated compared to control littermates in the striatum, midbrain and frontal cortex regardless of genotype in Ube3a deficient and Ube3a duplication animals. In the duplication 15q autism mouse model, paternal but not maternal duplication animals showed a decrease in 5HT levels when compared to their wild type littermates, in accordance with previously published data. However, maternal duplication animals show no significant changes in 5HT levels throughout the brain. These abnormal monoamine levels could be responsible for many of the behavioral abnormalities observed in both AS and autism, but further investigation is required to determine if any of these changes are purely dependent on Ube3a levels in the brain.

Modeling rare gene variation to gain insight into the oldest biomarker in autism: construction of the serotonin transporter Gly56Ala knock-in mouse

Alterations in peripheral and central indices of serotonin (5-hydroxytryptamine, 5-HT) production, storage and signaling have long been associated with autism. The 5-HT transporter gene (HTT, SERT, SLC6A4) has received considerable attention as a potential risk locus for autism-spectrum disorders, as well as disorders with overlapping symptoms, including obsessive-compulsive disorder (OCD). Here, we review our efforts to characterize rare, nonsynonymous polymorphisms in SERT derived from multiplex pedigrees carrying diagnoses of autism and OCD and present the initial stages of our effort to model one of these variants, Gly56Ala, in vivo. We generated a targeting vector to produce the Gly56Ala substitution in the Slc6a4 locus by homologous recombination. Following removal of a neomycin resistance selection cassette, animals exhibiting germline transmission of the Ala56 variant were bred to establish a breeding colony on a 129S6 background, suitable for initial evaluation of biochemical, physiological and behavioral alterations relative to SERT Gly56 (wild-type) animals. SERT Ala56 mice were achieved and exhibit a normal pattern of transmission. The initial growth and gross morphology of these animals is comparable to wildtype littermate controls. The SERT Ala56 variant can be propagated in 129S6 mice without apparent disruption of fertility and growth. We discuss both the opportunities and challenges that await the physiological/behavioral analysis of Gly56Ala transgenic mice, with particular reference to modeling autism-associated traits.

Hyperserotonemia in autism: activity of 5HT-associated platelet proteins

Disturbances in serotonin (5HT) neurotransmission have been indicated as biological substrates in several neuropsychiatric disorders including autism. Blood 5HT concentrations, elevated in about one-third of autistic subjects, are regulated through the action of peripheral 5HT-associated proteins. We have measured the activity of two platelet 5HT-associated proteins: 5HT transporter (5HTT) and monoamine oxidase B (MAOB), and indirectly studied the activity of 5HT(2A) receptor (5HT(2A)r) in 15 hyperserotonemic (HS) and 17 normoserotonemic (NS) autistic subjects, and 15 healthy controls (C). While mean velocities of 5HTT kinetics did not significantly differ among the groups, significant elevation in the mean velocity of MAOB kinetics was observed in NS subjects and was even more pronounced in HS subjects in comparison to controls. Also, a decrease in adenosine 5'-diphosphate-induced platelet aggregation of borderline significance was observed in NS subjects, compared to C subjects. The results suggest a possibility of upregulation of monoaminergic synthesis/degradation and, probably consequential, downregulation of 5HT(2A)r in autistic subjects.

Biochemical effects of antidepressant treatment--studies of monoamine metabolites in cerebrospinal fluid and platelet [3H]imipramine binding

Two putative markers of serotonergic function, the concentrations of the serotonin metabolite 5-hydroxyindoleacetic acid (5-HIAA) and the binding parameters of [3H]imipramine to blood platelets, are discussed. Pretreatment concentrations of 5-HIAA in the cerebrospinal fluid (CSF) are lower in depressed patients than in normal controls, and a low concentration of the metabolite is associated with an increased risk of suicide. Many studies have attempted to use pretreatment concentrations of 5-HIAA, of the noradrenaline metabolite 3-methoxy-4-hydroxyphenylglycol (MHPG) and of the dopamine metabolite homovanillic acid (HVA) as predictors of therapeutic effect. On the whole, HVA appears to predict the effects of diverse treatments rather better than 5-HIAA. Treatment with antidepressant drugs changes the amine metabolite concentrations in the CSF in a relatively predictable way. Thus, administration of selective inhibitors of serotonin uptake has a more profound effect on CSF 5-HIAA, while noradrenaline uptake inhibitors preferentially reduce CSF MHPG concentrations. The Bmax of [3H]imipramine binding to blood platelets has been found to be lower in untreated depressed patients than in healthy controls in several studies. In a study from our group, three weeks' treatment with the serotonin uptake blockers zimeldine and alaproclate increased Bmax, while neither nortriptyline nor electroconvulsive treatment caused any change in Bmax after this time period. One year after initiation of treatment, patients who had clinically recovered and were no longer taking drugs still had a low Bmax of [3H]imipramine platelet binding. Prophylactic lithium caused a significant, but transient decrease in the Bmax of platelet [3H]imipramine binding in euthymic bipolar patients.

Serotonin transporter promoter variants in autism: functional effects and relationship to platelet hyperserotonemia

The well-replicated platelet hyperserotonemia of autism has stimulated interest in serotonin (5-HT) in autism. We have examined the effects of the serotonin transporter gene (5-HTT, locus SLC6A4) promoter polymorphism (5-HTTLPR) on platelet 5-HT physiology in autism. Platelet 5-HT uptake rates and affinities (V(max) and K(m)), uptake site densities (B(max)) and 5-HT levels were examined in 31 French individuals with autism genotyped with respect to the 5-HTTLPR. Platelet 5-HT uptake and 5-HT levels were measured using HPLC; uptake sites were determined by radioligand binding. A 1.5-fold increased rate (V(max)) of platelet 5-HT uptake was observed in ll genotype individuals compared to those with ls and ss genotypes (Mann- Whitney U-test, P = 0.022). However, no significant relationship was observed between genotype and uptake site density (U-test, P = 0.51). Although median levels of platelet 5-HT in platelet-rich plasma were higher in the ll group, only trend level significance was observed (U-test, P= 0.069); platelet 5-HT content measured in whole blood was similar across genotypes. Uptake rates were well correlated with B(max) values (r = 0.66, P = 0.002); correlations between uptake and platelet 5-HT levels and between B(max) values and 5-HT levels were somewhat lower. While 5-HTTLPR alleles had an appreciable effect on platelet 5-HT uptake rates, effects on 5-HT levels and uptake site density were smaller or absent. Based on these preliminary data and prior studies of allele frequencies, we conclude that the 5-HTTLPR is not a major determinant of the group mean platelet serotonin elevation seen in autism. However, a role for increased uptake in the hyperserotonemia of autism can not be ruled out. In addition, it appears that studies of platelet 5-HT measures in autism and other disorders should take account of the effects of 5-HTTLPR genotype on 5-HT uptake

Adenosine diphosphate inhibits the serotonin transporter

Adenosine 5'-diphosphate (ADP) caused rapid and significant reductions in the rates of [3H]serotonin uptake observed for human platelets, human platelet vesicles, and rat brain synaptic vesicles. Estimated Vmax values in platelets (N = 15). platelet vesicles (N = 3), and synaptic vesicles (N = 3) exposed to 100 microM ADP were 42.3 +/- 11.4%, 78.8 +/- 1.4%, and 56.8 +/- 9.9% of control values, respectively. The EC50 values observed for ADP in platelets and platelet vesicles were 10-24 microM. Exposure to 100 microM ADP had small, inconsistent effects on KM values observed for the platelet transporter. ADP (100 microM) caused only a slight competitive inhibition of the platelet membrane binding of [3H]citalopram, a ligand for the 5HT uptake site of the transporter (5.0% displacement of 1.0 nM [3H]citalopram, 13% increase in apparent KD). The ADP analogue 2-methylthioADP caused similar decreases in the rates of platelet [3H]serotonin uptake, while a number of other related compounds had little or no effect on rates of platelet uptake. The ADP-effect on uptake was rapid, occurring in less than 2.5 s. and was additive with reductions produced by protein kinase C (PKC) activation. The ADP-induced decreases in uptake did not appear to occur through the ADP receptor or known platelet second messenger systems. The exact mechanism of the ADP-effect and its functional significance remain to be determined.

Platelet imipramine binding in depressed children and adolescents

Kinetic constants of platelet imipramine binding were determined in youths with major depression, and a contrast group. Subjects actively depressed (N = 10) had significantly fewer imipramine binding sites (Bmax) (877 +/- 148 fmol/mg protein) than recovering depressives (N = 12) (1220 +/- 428 fmol/mg protein) and contrasts (N = 10) (1270 +/- 230 fmol/mg protein). Affinity constants (Kd) (1.14 +/- 0.36 nM, 0.97 +/- 0.31 nM, and 1.17 +/- 0.39 nM, respectively) were similar among the groups. Actively depressed males but not females had fewer imipramine binding sites than both their sex-matched comparison groups. Although actively depressed females' Bmax was significantly lower than recovering depressed and nondepressed males, neither age, Tannner stage, nor circannual rhythms influenced Bmax, but suicidality may be associated with low Bmax. A decrease in Bmax may be a state-specific marker of major depression in boys or associated with a depressive disorder with a suicidal history.

Effect of antidepressant treatment on platelet 5-HT content and relation to therapeutic outcome in unipolar depressive patients

Platelet 5-HT levels and scores on the 17-item Hamilton Rating Scale for Depression (HRS) were studied in patients with unipolar depression before and after antidepressant treatment. Before treatment there were no differences in platelet 5-HT values or in HRS scores between patients who showed a good and a poor therapeutic response. Repeated administration of 5-HT uptake inhibitors (amitriptyline, clovoxamine, fluvoxamine) for 28 days markedly decreased platelet 5-HT levels. Chronic treatment with trazodone or maprotiline (weak inhibitors of platelet 5-HT uptake) produced no changes in platelet 5-HT levels. No significant correlation was observed between platelet 5-HT concentrations and the HRS scores before or during treatment. The findings suggest that the changes in platelet 5-HT levels after antidepressant treatment are mainly due to the effects of antidepressants on the 5-HT uptake system.

Aggression, hyperactivity and platelet imipramine binding

We measured platelet 3H-imipramine binding parameters in 16 subjects affected by different types of mental deficiency, all characterized by hyperactive and/or aggressive behaviour, and in 16 healthy controls. The patients had a lower maximum binding capacity than the controls, with no difference in Kd, irrespectively of the type of mental disorder. These findings suggest a link between 5-HT disturbances, reflected by reduced imipramine binding sites, and behavioural dyscontrol, expressed as hyperactivity and aggression.

Signal-to-noise optimization of HPLC-fluorometric systems and their application to the analysis of indoles

The signal-to-noise optimization of high performance liquid chromatographic (HPLC) flow-cell fluorometric systems is described and the possibilities for further improving limits of detection for indoles is discussed. Application of HPLC-fluorometry to analyses in rat cerebrospinal fluid (CSF), human lumbar CSF, and human blood is presented. Finally, the intriguing clinical finding of hyperserotonemia in autism is discussed.

The hyperserotonemia of autism

The planned and ongoing studies of platelet function and composition should allow us to better define the alteration which we presume to be present in platelets of autistic subjects. Although much of the research focuses on serotonergic aspects, the more general research should permit a better delineation of the extent of the alteration and will protect against a premature narrowing of the inquiry. The methodological development which has been a necessary aspect of the work should contribute to an improved understanding of platelet function and composition, as well as result in improved clinical tools for the assessment of platelet functioning in neuropsychiatric disorders and hematology. As an example, improvements in short-term in vitro storage conditions to stabilize aggregation and shape change responses over time were found to be necessary, and are probably critical to an optimal comparison of these phenomena across groups. The identification of the platelet alteration which is responsible for the hyperserotonemia of autism should prove useful in several ways. It would be expected that assessment of the altered function would provide a marker with less overlap with the normal population than the multidetermined measure of blood 5-HT. Determination of the specific protein(s) involved in the altered platelet should lead directly to gene probes and chromosomal location. These, in turn, should prove useful for neonatal screening, subtyping, and more powerful genetic and family studies. Work of this sort might also allow early intervention and improved treatment. Finally, characterization of the physiological alteration would provide a basis for focusing studies of brain neurochemistry and should, as well, suggest modes of neuropharmacological intervention. The confidence that one can have in the basic finding of hyperserotonemia in autism and the potential benefits to be derived from its explication make further research in this area of great interest.

Platelet imipramine binding in endogenous depressed patients and controls: relationship to platelet MAO and 5HT uptake during successful imipramine treatment

Platelet imipramine binding was measured in 25 unmedicated depressed patients and 25 age- and sex-matched healthy controls. In the patients, the measurement was repeated after 3 weeks and 2 months of imipramine treatment leading to clinical recovery. No significant differences in imipramine binding were found between controls and unmedicated patients. In the latter, imipramine administration produced a progressive change in the binding characteristics, increasing the apparent Kd and decreasing the number of binding sites (Bmax). The results suggest that platelet imipramine binding is not altered in depression and that changes in this parameter are the consequence of the presence of imipramine in the blood stream. However, such changes accompany changes in other biological parameters, such as platelet monoamine oxidase and serotonin uptake, seen in the same patients throughout imipramine treatment, suggesting that the drug acts on a wide range of normal or altered serotonin-related cellular mechanisms while it accelerates the clinical recovery from depression.

3H-imipramine binding in the blood platelets of normal twins

3H-Imipramine binding (IB) was studied in the blood platelets of 13 pairs of monozygotic (MZ) and dizygotic (DZ) twins, and 15 pairs of unrelated normal volunteers, to determine if IB is under genetic control. The intrapair variance of Bmax (the maximum number of 3H-IB sites) was significantly smaller in MZ twins and unrelated control pairs than in DZ twins. The intraclass correlations (ICC) of Bmax were significant for all the pairs with no difference between these correlations. The ICC of the Kd (inversely related to the affinity for 3H-imipramine) of IB was significant only for the normal control pairs and the DZ twins. These results suggest that the kinetic constants of IB in blood platelets are not under genetic control and that interassay variance significantly affects the absolute values for Kd and Bmax of 3H-IB. The environmental and assay factors that influence 3H-IB may account for the numerous discrepancies in platelet 3H-IB between various research reports.

Influence of protein concentration on platelet 3H-imipramine binding

1. The effects of protein concentration in the assay mixture on platelet 3H-imipramine binding were studied in normal controls. 2. Increasing protein concentrations (76-926 micrograms/ml) were found to alter estimates of binding affinity (Kd) but not the number of binding sites (Bmax). 3. Increasing Kd estimates were protein dependent at concentrations in excess of ca. 200 micrograms/ml but were not protein dependent at lower concentrations. 4. A comparison of the present results with previous reports suggests that widespread interlaboratory differences in reported Bmax values for normal controls cannot be attributed to differences in the protein content of incubated samples. Rather these differences may be due to the inclusion of non-membrane protein in the assayed material.

Autism: review of neurochemical investigation

The neurochemistry of autism, the most well-validated childhood neuropsychiatric disorder, has been studied extensively over the past three decades. Autism is of interest neurochemically because it represents a relatively homogeneous disorder with a triad of social, communicative, and intellectual developmental disturbance. Because a sufficient animal model has been lacking and relatively few diagnosed people with autism have died, most investigation has been of peripheral fluids and tissues. The most consistent finding has been that over 25% of autistic children and adolescents are hyperserotonemic. However, after 29 years of investigation, the mechanism of hyperserotonemia has not been determined. Hyperserotonemia has been found to be familial. Elevated plasma norepinephrine has also been a replicated finding. Cerebrospinal fluid (CSF) opiate activity has been found to be elevated in two studies. Plasma cyclic adenosine monophosphate (cAMP) has been found to be elevated in autistic children. A high rate of nonsuppression after dexamethasone and blunted or delayed growth hormone response to L-dopa have been found. Abnormal cell-mediated immunity has been replicated consistently in autism. Although several pharmacological trials have been conducted and shown promise in initial open trials, only "typical" antipsychotic drugs have shown replicable chronic ameliorating effects in double-blind trials. However, chronic neurotoxicity (tardive dyskinesia) has also been revealed. Findings of morphological changes in the cerebellum have been replicated. Findings in need of replication include diminished platelet function, increased baseline CSF homovanillic acid, decreased nerve cell adhesion molecule serum fragment, blunted prolactin response to fenfluramine, amelioration of symptoms by naltrexone and bromocriptine, reduced electroretinographic (ERG) b-wave amplitude, and morphological changes in the hippocampus, amygdala, and septal nuclei. In addition to refining and replicating past findings, future directions that may be fruitful include investigation of neurochemical aspects of platelet function, of interactions between monoaminergic systems, of phosphatidylinositides, and of pharmacological response to "atypical" antipsychotic agents and relatively selective serotonin receptor subtype agonists or antagonists.

3H-imipramine binding to freshly prepared platelet membranes in depression

3H-Imipramine binding was measured in freshly prepared platelet membranes from 47 drug-free major depressives and 46 healthy controls. Where possible, platelet binding in depressed subjects was repeated following treatment. A significant negative correlation was found between Bmax and assay protein concentration and Bmax values were corrected for this effect. Adjusted Bmax was significantly lower (by 14%) in female depressed patients than in female control subjects, and the difference was of similar magnitude premenopausally and postmenopausally. No such difference was found in males. Kd did not differ significantly between depressed and control subjects. Multiple regression analysis confirmed significant effects on Bmax of presence of depressive illness, age (positive correlation), and season (higher in summer). Within the depressed sample, Bmax was significantly lower in those subjects with obsessional features. Endogenicity (Research Diagnostic Criteria or Newcastle), dexamethasone suppression test result, drug-free interval, family history of depression, depressive psychosis, suicidal ideation, and past history of suicide attempts were not significantly related to Bmax. Paired comparisons revealed no significant effect on Bmax of 6 weeks' treatment with imipramine, maprotiline, or BRL 14342 or of a course of electroconvulsive therapy.

Whole blood serotonin and tryptophan in autism: temporal stability and the effects of medication

Whole blood serotonin (5-HT) was significantly increased in a drug-free autistic group (n = 17) compared to age- and sex-matched normal control (n = 20). Blood tryptophan (TRP) values and platelet counts were similar in unmedicated autistics and normal subjects; but whole blood concentrations of TRP were significantly lower, and 5-HT values tended to be lower in the medicated group compared to unmedicated autistics. Highly significant intraclass correlation coefficients and low mean percentage differences were found for repeated measures over a year's period of whole blood 5-HT and the platelet count in the unmedicated but not in the medicated group. Blood TRP values were highly variable over time in both the medicated and drug-free autistic groups.

Differences between sodium-dependent and desipramine-defined [3H]imipramine binding in intact human platelets

Measurements of sodium-dependent [3H]imipramine binding to intact human platelets from 20 human volunteers were made and compared to desipramine-defined binding, a method commonly employed in population studies of platelet [3H]imipramine sites. The density (Bmax) of sodium-dependent [3H]imipramine sides in platelets was significantly lower (449 +/- 36 sites/platelet) and the affinity (Kd) significantly higher (1.15 +/- 0.12 nM) than those obtained when excess desipramine was used to define specific binding (Bmax 654 +/- 33 sites/platelet, p less than 0.001; Kd 1.52 +/- 0.11 nM, p less than 0.001). There was no significant correlation between the density (Bmax) of sodium-dependent and desipramine-defined binding in individual subjects, suggesting that a different proportion of sites are labeled under the two assay conditions. No age-dependent variation was found in either Kd or Bmax values of sodium-dependent or desipramine-defined [3H]imipramine binding. The results suggest determination of sodium-dependent [3H]imipramine binding to intact platelets may be a useful measure for the estimation of [3H]imipramine recognition sites relevant to the serotonin uptake in studies of patients with affective disorders.

Effects of antidepressants on monoamine transporters

1. Using [3H]antidepressants, high affinity binding sites associated with the neuronal transporter for serotonin, noradrenaline, dopamine and adrenaline have been identified. 2. The association of high affinity [3H]imipramine binding with the serotonin transporter in brain and platelets is well established. Although the exact relationship between the [3H]imipramine recognition site and the serotonin transporter remains to be elucidated, it appears that the [3H]imipramine labelled component of the serotonin transporter represents a novel receptor that functions to modulate serotonin uptake. 3. Most data available to date support the hypothesis that [3H]imipramine binding to platelet represents a biological marker in depression. The majority of studies indicate that the Bmax of platelet [3H]imipramine binding is lower in depressed, untreated patients than in the control population and that this finding is relatively specific to depression. 4. Among the [3H]antidepressant binding sites associated with the other monoaminergic transporters, the recent identification of [3H]desipramine binding to the neuronal transporter for adrenaline offers novel perspectives. Thus, given the high affinity for [3H]desipramine binding to the adrenaline transporter in the frog heart for not only desipramine but also imipramine and the atypical antidepressants mianserin and iprindol, it is possible that an interaction with the adrenaline transporter is of significance to the clinical effects of antidepressant drugs.

Whole blood serotonin in autistic and normal subjects

Whole blood serotonin and tryptophan were measured in 87 normal subjects and in 40 autistic subjects. Whole blood serotonin concentrations (mean +/- SE) were significantly higher in drug-free (N = 21) autistics (205 +/- 16 ng/ml) than in normals (136 +/- 5.4 ng/ml). The Gaussian distribution of serotonin levels in the unmedicated autistic group suggests the elevation was not due to a subgroup of autistic subjects. Autistics medicated with anticonvulsants or neuroleptics had significantly lower serotonin levels than did drug-free autistic subjects. Whole blood tryptophan levels and platelet counts were similar in the autistic and normal groups. The possible causes of the hyperserotonemia of autism are discussed.

Urinary 5-hydroxyindoleacetic acid and whole blood serotonin and tryptophan in autistic and normal subjects

Urinary 5-hydroxyindoleacetic acid (5-HIAA) excretion in two consecutive collection periods (5:00 PM-11:00 PM and 11:00 PM-8:00 AM) and whole blood serotonin (5-HT) and tryptophan (TRP) were measured in groups of unmedicated autistics (n = 16), medicated autistics (n = 20), and normal controls (n = 27). Whole blood 5-HT values were significantly higher in unmedicated autistics compared to normal controls. No significant differences were found in 5-HIAA excretion (microgram/mg creatinine, mean +/- SD) between unmedicated autistics (4.07 +/- 1.52) and normal controls (3.50 +/- 1.07), or between medicated (5.35 +/- 2.93) and drug-free autistic individuals. No correlations were found between 5-HT values and urinary 5-HIAA excretion. Urinary 5-HIAA (microgram/mg creatinine, mean +/- SD) was significantly greater in hyperserotonemic autistic subjects (4.88 +/- 0.87) compared to normal controls (3.50 +/- 1.07, total collection period; p = 0.002). The relevance of these findings to the possibility that increased gut production of 5-HT might cause the elevated whole blood 5-HT levels seen in autism is discussed.

Platelet [3H]imipramine binding in autism and schizophrenia

[3H]Imipramine binding to platelet membranes was evaluated in ten autistics, eight schizophrenics and seven normal controls. The schizophrenics and eight out of the ten autistics were maintained on chronic neuroleptic treatment. Diagnosis of autism and schizophrenia was established according to the DSM-III criteria. No significant difference in the maximal binding capacity of [3H]imipramine (Bmax) and Kd values could be found among the three groups. It seems that the imipramine binding site is intact both in autism and schizophrenia.

Association of [3H]-imipramine and [3H]-paroxetine binding with the 5HT transporter in brain and platelets: relevance to studies in depression

[3H]-Imipramine and [3H]-paroxetine label with high affinity a site which is associated with the serotonergic transporter in brain and platelets. The pharmacological profile of inhibition by drugs of [3H]-imipramine and [3H]-paroxetine binding is highly correlated with the potency of the drugs to inhibit the uptake of 5HT. Denervation of serotonergic neurons by electrolytic lesions or with 5,7-dihydroxytryptamine produces marked decreases in the density of [3H]-imipramine as well as [3H]-paroxetine binding. Dissociation kinetic experiments support the view that the substrate recognition site for 5HT is different from the modulatory site which is labelled by [3H]-imipramine or [3H]-paroxetine. The existence of an endogenous ligand acting on the [3H]-imipramine recognition site to modulate the 5HT transporter was proposed by several laboratories. [3H]-Imipramine binding in platelets appears to be a biological marker in depression. Studies carried out in several laboratories report a significant decrease in the Bmax of platelet [3H]-imipramine binding without changes in Kd, when severely depressed untreated patients are compared with healthy volunteers matched for age and sex. The Bmax of platelet [3H]-imipramine binding appears to be a state-dependent biological marker in depression. It is tempting to speculate that the endocoid of the [3H]-imipramine recognition site may play a role in the pathogenesis of depression.

3H-imipramine binding in blood platelets of schizophrenic patients

3H-Imipramine binding was studied in the blood platelets of 51 unmedicated chronic schizophrenic patients. Univariate analyses of log-transformed data revealed that Bmax was significantly lower in schizophrenic patients than normal volunteers; Kd was nonsignificantly higher in the schizophrenics. A multivariate analysis of variance indicated the Kd and Bmax both differ significantly between normal controls and schizophrenic patients in the direction of increased Kd and decreased Bmax in the schizophrenics. These results indicate that decreased platelet imipramine binding is not specific for major depression.

The organic etiology of infantile autism: a critical review of the literature

Various theories have been provided in the literature regarding the etiology of infantile autism. It seems that the biological causation dominates the thinking of mental health practitioners and researchers irrespective of discipline. Areas of research include the following: neuropathological studies of the brain, autopsies, electroencephalograms, epileptic seizures, brain lateralization, studies in asymmetry; neurochemistry; genetics; and pre-, peri- and postnatal factors. A critical analysis of these studies has indicated that the evidence of organic factors tends to be rather weak and furthermore has been found to be contradictory. It is felt that the major problem lies in the fact that a large number of investigators include in their sampling children with various mental and physical disabilities and label them autistic. In general, there seems to be little information regarding the selection and little background information is offered on these children. It is suggested that a standardized and world wide diagnostic system be constructed which will provide objective etiological results.

Platelet 3H-imipramine binding in bipolar patients

Platelet 3H-imipramine binding was investigated in 31 control subjects and 19 hospitalized bipolar patients, either in the hypomanic or the depressed phase of illness. The mean Bmax value in the bipolar depressed patients did not differ significantly from that in the control subjects or the hypomanic patients. Differences in timing of the assay after blood collection, membrane preparation, protein content used in the assay, or binding of radioactive ligand to the equipment do not appear to explain the discrepancy between these results and previous findings.

Effect of adrenalectomy and corticosterone on [3H]imipramine binding in rat blood platelets and brain

The effect of adrenalectomy and administration of glucocorticoids on [3H]imipramine binding (IB) of rat blood platelets and brain was investigated. Adrenalectomy significantly increased both Kd and Bmax of IB in the blood platelets but not the brain of male Sprague-Dawley rats. Administration of corticosterone acetate, 1 mg/kg i.p. for 7 days, decreased both Kd and Bmax in the blood platelets of sham-operated rats, but only Bmax in adrenalectomized rats. Corticosterone administration also decreased Bmax in frontal cortex and hypothalamus of sham and adrenalectomized rats but had no effect on Kd. These results suggest that glucocorticoids may modulate imipramine binding.

The role of the central monoaminergic system and rapid eye movement sleep in development

Transmission of information in the brain is of a chemical nature. Neurotransmitters are present at very early stages of brain development, having trophic effects on maturation of target neurons as well as mediating the behavioral repertoire of the immature brain. Many centrally acting psychoactive drugs which are commonly used (also during pregnancy) for treatment of depression, asthma, hypertension, epilepsy, parkinsonism, hyperkinetism and other neurological and psychiatric disorders act directly on brain neurotransmitters (in particular monoamines) and behavioral states. Disturbances observed later in life in animals and man, as a result of early interference with brain neurotransmitters, using these drugs, are not gross physical malformations but are in fact subtle behavioral and neurological symptoms such as hyperactivity, emotional lability, attentional distractability and sleep disturbances, similar to symptoms observed in the minimal brain dysfunction syndrome.

Lower 3H-imipramine binding in platelets from untreated depressed patients compared to healthy controls

3H-Imipramine binding in platelets was measured in 63 severely depressed hospitalized patients, who had been drug free (with the exception of moderate doses of benzodiazepines) for at least 1 month, and in 53 healthy control subjects of comparable age and sex distribution. Bmax of 3H-imipramine binding was significantly lower in the depressed subjects (1012 +/- SD 295 vs. 1123 +/- SD 178 fmole/mg protein). Depressed patients who had attempted suicide by violent means tended to have higher Bmax than nonviolent attempters.