Seasonal variation of platelet serotonin uptake and 3H-imipramine binding in normal and depressed subjects

Platelet 3H-imipramine binding in major depressive episodes

Density (Bmax) and affinity constant (Kd) values of tritiated imipramine binding sites were determined on platelets from patients suffering from major depression and from healthy, age-and sex-matched controls. Significantly lower Bmax values were found in the depressed patients, while the Kd values did not differ from those of controls. The results suggest that, in accordance with data from the literature, decrease in 3H-imipramine binding sites may be used as a state-dependent biological marker of depression in clinical practice.

Seasonality of cerebrospinal fluid monoamine metabolite concentrations and their associations with meteorological variables in humans

Seasonal variations in neurotransmitter parameters have been previously reported in humans. However, these studies have involved small sample sizes and have not examined possible relationships with meteorological variables. We compared cerebrospinal fluid (CSF) concentrations of the major monoamine neurotransmitter metabolites (5-HIAA, HVA, and MHPG) in 188 healthy controls (80 men, 108 women) in relationship to age, sex, BMI, and available meteorological variables. All subjects had a lumbar puncture (LP) performed at 9 a.m. after overnight stay. Meteorological data for the day prior to LP were obtained from the National Climatic Association and included the photoperiod, percent sunshine, temperature (max, min, mean), barometric pressure, relative humidity, amount of precipitation and sky cover. Results revealed differences across seasons and cross-seasons for CSF 5-HIAA (p ≤ .05), with post-hoc differences emerging between spring versus summer and fall and between x-spring and x-summer (p ≤ .05). Differences were also found across seasons for CSF HVA (p ≤ .05) with post-hoc differences between spring versus fall. CSF 5-HIAA was significantly inversely correlated with maximum (r = -.28, p ≤ .02), minimum (r = -.24, p ≤ .04), and mean temperature (r = -.28, p ≤ .02) in men. In women, 5-HIAA (r = -.22, p ≤ .02) and HVA (r = -.28, p ≤ .003) were significantly correlated with relative humidity. These data confirm previous findings of variations in serotonin and dopamine metabolites across the year and highlight possible underlying mechanisms involving meteorological changes, which may result in alterations in neurophysiology and behavior.

The influence of daylight exposure on platelet 5-HT levels in patients with major depression and schizophrenia

Platelet serotonin (5-HT) can be used as a limited, peripheral model for the central 5-HT synaptosomes. Altered platelet 5-HT concentrations have been associated with psychiatric disorders like depression and schizophrenia. The aim of the present study was to compare platelet 5-HT concentrations during long, medium and short period of natural daylight exposure in a large number of medication-free male and female schizophrenic and depressed patients and sex-matched healthy controls. Platelet 5-HT concentration was determined spectrofluorimetrically in 240 (97 female, 143 male) schizophrenic and 258 (153 female, 105 male) nonpsychotic, nonsuicidal depressed medication-free patients and 328 (149 women, 179 men) healthy subjects during periods with short (<12), long (>12) and medium (average 12) hours of the natural daylight. Platelet 5-HT concentration was significantly lower in women compared to men in all groups. Healthy male subjects had significantly higher (p=0.011) platelet 5-HT concentrations during long compared to medium period. There were no significant differences (p>0.05) in platelet 5-HT concentration between different periods in healthy women. The significant increase in platelet 5-HT values were found in female (p=0.01) and male (p=0.029) depressed patients during long compared to short period. There were no significant associations between platelet 5-HT concentrations and different periods in both male and female schizophrenic patients. The results indicate the sex-related differences in the serotonergic system. The alterations of platelet 5-HT concentrations, observed across period with different durations of daylight exposure, point to a direct or indirect effect of light on peripheral 5-HT system that could be related to different sensitivity of the pineal gland to light and/or melatonin influence on 5-HT metabolism.

Seasonal variations in [3H]citalopram platelet binding between healthy controls and violent offenders in Finland

Monthly binding densities (B(max)) of [3H]citalopram to the platelet serotonin transporter (SERT) was measured longitudinally over 1 year in a control group of 18 healthy Finnish male volunteers. Single platelet samples were also analysed from 33 men who were incarcerated for violent crimes during the same calendar year. A statistically significant seasonal variation in SERT B(max) was observed in both data sets, and bi-monthly floating averages for SERT B(max) were calculated and then fit to an annual sinusoidal curve for both groups. The B(max) for platelet [3H]citalopram binding showed a statistically significant (p = 0.001) seasonal variance between a winter (January-February) maximum of 1590 fmol/mg protein and a summer (July-August) minimum of 1216 fmol/mg protein for the control group, with an R2 of 70% for the annual sinusoidal curve fit. A statistically significant (p = 0.007) seasonal variance was also observed between a winter (January-February) maximum of 1980 fmol/mg protein and an autumnal (August-September) minimum of 1234 fmol/mg protein for the violent offenders, again with an R2 of 70% for the annual sinusoidal curve fit. This observation lends additional support to the idea that violent human behavior and impulsivity may be directly linked to values of SERT B(max), which can be affected by various psychoactive drugs and also varies with the natural change of seasons.

Actigraphy in patients with seasonal affective disorder and healthy control subjects treated with light therapy

BACKGROUND

Abnormalities of the circadian rest-activity cycle are hypothesized to accompany the clinical picture of seasonal affective disorder (SAD). The purpose of this study was to investigate if bright light therapy (BLT) is able to reverse these disturbances.

METHODS

Seventeen SAD outpatients and 17 sex- and age-matched healthy control subjects were treated with BLT administered in the morning for 4 weeks. Activity levels were measured with wrist actigraphy.

RESULTS

SAD patients had 33% lower total (p = .031) and 43% lower daylight activity (p = .006) in week 1 compared with control subjects. The relative amplitude of the sleep-wake cycle was attenuated by 6% in patients (p = .025); they were phase delayed by 55 minutes (p = .023) and had significantly lower sleep efficiency (p = .030). Total (p = .002) and daylight activity (p = .001) increased after 4 weeks of treatment in SAD patients. Moreover, BLT led to increase of relative amplitude (p = .005), advance of delayed rhythms (p = .036), and improved sleep efficiency (p = .011) in patients. Intradaily stability, measuring the strength of coupling of the rhythm to external zeitgebers, increased by 9% both in patients and healthy control subjects (p = .032).

CONCLUSIONS

Treatment with BLT normalizes disturbed activity patterns and restores circadian rhythms in SAD patients. BLT might also stabilize the circadian rhythm in nondepressed individuals during the fall-winter season.

Serotonin transport kinetics correlated between human platelets and brain synaptosomes

RATIONALE

Blood platelets have been used extensively as a model system for investigating the role of the serotonin transporter (SERT) in various psychiatric disorders, especially depression. However, to date, it is not known whether platelet serotonin (5-HT) transport would be related to that in brain.

OBJECTIVES

We examined 5-HT transport kinetics simultaneously in human blood platelets and human cortical brain synaptosomes to determine whether they were correlated.

METHODS

Blood platelets and synaptosomes were obtained from 25 patients undergoing epileptic surgery. Synaptosomes were obtained from normal margins of surgical neuropathology specimens of anterotemporal cortex.

RESULTS

Platelet SERT V(max) was significantly correlated with brain SERT V(max) on linear regression (r=0.58, p<0.005), after controlling for the confounding effects of gender (t=-2.4, p=0.025) and time of day (t=2.1, p<0.05). Consistent with previous observations, there was a negative correlation between the maximum velocity (V(max)) of platelet 5-HT transport and pO2 (r=-0.52, p<0.01). Females had a significantly higher pO2 than males (F=4.9, p<0.05). After accounting for gender differences, addition of pO2 did not add further strength to the regression, given the aforementioned gender differences in pO2. The correlation between unadjusted values for platelet vs brain SERT V(max) was r=0.3, p=0.06.

CONCLUSIONS

These results suggest that a relationship may exist between 5-HT transport in platelets and cortical synaptosomes, when appropriate controls for confounding factors are employed.

Initial conditions of psychotropic drug response: studies of serotonin transporter long promoter region (5-HTTLPR), serotonin transporter efficiency, cytokine and kinase gene expression relevant to depression and antidepressant outcome

The Hypothesis of Initial Conditions posits that differences in psychotropic drug response result from individual differences in receptor site kinetics, and differences in the sensitivity of downstream receptor-linked responses. This work examines data consistent with the hypothesis, specific to genetic and kinetic differences of the serotonin (5-HT) transporter (SERT), as they may be linked to divergent antidepressant response (ADR). The mechanisms for divergent ADR in association with different initial SERT function are considered within the context of SERT trafficking as sensitive to various different kinase and cytokine signals, some of which are dependent on the 5-HTTLPR polymorphism of the SERT gene. Pilot data suggest that human lymphocytes show kinase changes similar to those found in rat brain with ADT. These studies additionally suggest that ADT prompts a shift in cytokine gene expression toward a greater anti-inflammatory/inflammatory ratio. These latter findings are discussed within the context of a literature suggesting increased inflammatory cytokine levels in depression, and recent observations of increased temperature associated with depression. In sum, the data suggest the opportunity to identify response dependent protein (RDP) expression patterns that may differ with dichotomous ADR, and suggest new insights into understanding the mechanisms of psychotropic drug response through an understanding of initial differences in potential for psychotropic drug target regulation during therapy.

Seasonal variations in the binding of [3H]paroxetine to the platelet serotonin transporter sites in African-American cocaine-dependent patients and healthy volunteers

Although seasonal fluctuations in several indices of serotonin function have been described, little is known about seasonality and serotonergic activity in substance abusers. We investigated whether there were seasonal differences in platelet serotonin transporter sites among cocaine dependent patients and controls. Platelet [(3)H]paroxetine binding, a measure of serotonin transporter sites, was assayed in 141 African-American cocaine-dependent subjects and in 60 race matched healthy volunteers who served as the control group. B(max) (density of serotonin transporter) and K(d) (affinity constant) values of [(3)H]paroxetine binding were compared during spring, summer, fall and winter. Consistent with our previous findings B(max) values were significantly lower in cocaine patients (639 +/- 234) than in controls (906 +/- 225) (t = 7.12, p < 0.001). Moreover, B(max) values showed a significant seasonal variation in controls with the highest values in summer and spring compared with fall and winter (F = 4.47, p < 0.01). However, there were no significant seasonal differences in B(max) values in cocaine patients. K(d) values did not show any seasonal changes in either group. There were no effects of age or gender on seasonal variations in B(max). The study demonstrates a seasonal effect on platelet serotonin uptake in healthy African-American volunteers. The lack of seasonal differences in transporter availability in cocaine patients indicates that the normal seasonal rhythm of serotonergic activity may be disturbed in cocaine abusers. Biological studies that employ platelet serotonin transporter sites as a marker of serotonin function should consider seasonal variations in these markers as a potential source of variance.

Season of birth in panic disorder

Several studies have investigated the seasonal distribution of the birth dates of patients with psychiatric diseases. Our purpose was to verify if there is a specific distribution (by month) of birth dates in subjects with panic disorder (PD). The birth dates of 843 outpatients with a diagnosis of PD were compared with those of 1,181 subjects with other mental diseases. The birth dates of psychiatric patients were compared to those of the general Tuscane and Italian populations. The monthly distribution of birth in patients with PD (with and without comorbidity) peaked in September to December, while no relevant deviation in birth rate was observed in other mental diseases. Our results suggest a pathogenic role of birth seasonality in the development of PD.

Seasonal variation in plasma prolactin response to D-fenfluramine in healthy subjects

To assess dynamically a seasonal variation in the functioning of the central serotonin (5-HT) system, we investigated the prolactin (PRL) response to the specific serotonergic agent D-fenfluramine (D-FEN) in the different seasons of the year. Thirteen healthy women and 11 healthy men (six for each season), aged 20-50 years, received PO 30 mg D-FEN and placebo, according to a randomized double-blind design. As compared to placebo, D-FEN induced a clear-cut increase in plasma PRL levels in all the seasons; this response was higher in fall than in spring and summer (p < .01 and < .05, respectively). In all the subjects, as a group, the hormone response to the 5-HT probe was inversely correlated with the body weight and age. These results document a seasonal variability in the PRL response to D-FEN, which suggests a seasonal fluctuation in central 5-HT transmission in healthy humans.

Physiological characteristics of serotonin transporters on rat platelets

Physiological characteristics of serotonin (5-hydroxytryptamine, 5HT) transport through the platelet membrane was investigated in Wistar rats with our recently developed method permitting repetitive measurements of transporter kinetics in individual animals. Full kinetic analysis in the population of 91 animals revealed Michaelis constant (K(m)) of 0.158 +/- 0.025 microM and maximal velocity (Vmax) of 5HT uptake of 225 +/- 32 pmol per 10(8) platelets min-1 (mean +/- S.D.). Both kinetic parameters demonstrated normal distribution curves, which for Vmax were slightly skewed toward higher than average values. No gender effect was shown in frequency distributions, mean values and variability of kinetic parameters. A significant intraindividual correlation between kinetic parameters was found suggesting compensation at the level of the plasma membrane. Kinetic parameters were not influenced by age (until the middle age) or annual cycle (under laboratory conditions) and were shown to be fairly stable in time, supporting the view that platelet 5HT transport kinetics could be a useful biological trait marker.

Circannual variations in the binding of [3H]lysergic acid diethylamide to serotonin2A receptors and of [3H]paroxetine to serotonin uptake sites in platelets from healthy volunteers

BACKGROUND

Circannual variations occur in several serotonergic parameters, including platelet serotonin uptake and platelet [3H]imipramine binding.

METHODS

Binding of [3H]lysergic acid diethylamide ([3H]LSD) to platelet serotonin (5-HT)2A receptors and binding of [3H]paroxetine to platelet serotonin uptake sites were studied longitudinally for 1 year in 12 healthy volunteers.

RESULTS

For [3H]LSD, the number of binding sites (Bmax) showed no significant seasonal variation (two-way analysis of variance), although Bmax was significantly higher during the months October through February than during the months April through August (32.6 vs. 29.8 fmol/mg protein; p = .015). For [3H]paroxetine, Bmax showed a significant seasonal variation (p = .003) with maximum in August (1322 fmol/mg protein) and minimum in February (1168 fmol/mg protein). The affinity constant (Kd) showed a significant seasonal variation for [3H]LSD binding (p = .046), but not for [3H]paroxetine binding. The seasonal fluctuations in [3H]LSD binding and in paroxetine binding tended to be inversely correlated for Bmax (r = -.70; p = .08) and were significantly negatively correlated for Kd (r = -.88; p = .009).

CONCLUSIONS

The present study demonstrates a seasonal effect on platelet serotonin uptake site binding and indicates a possible seasonal effect on 5-HT2A receptor binding. The results imply that circannual fluctuations should be taken into account when these platelet serotonin markers are studied.

Seasonal influence on platelet 5-HT levels in patients with recurrent major depression and schizophrenia

The influence of seasons on platelet serotonin (5-HT) concentration was determined in 88 unipolar depressed and 117 schizophrenic male inpatients, and 90 normal male controls. Platelet 5-HT concentrations showed moderate, but insignificant intragroup seasonal variations in healthy controls and in the groups of depressed (psychotic and nonpsychotic) and schizophrenic (positive and negative) patients. In spring, platelet 5-HT concentrations were higher in schizophrenic patients than in normal controls or in depressed patients, while in other seasons platelet 5-HT concentrations were not significantly different between the groups. Higher platelet 5-HT concentrations were detected in psychotic when compared to nonpsychotic depressed patients in summer, fall, and winter. Increased platelet 5-HT concentrations observed in schizophrenic patients with positive symptoms clearly separated these patients from patients with negative schizophrenia, especially in spring, summer, and fall. Our results indicate the necessity to match patients with regard to the season of the sampling, and to divide depressed and schizophrenic patients into subtypes.

Serotonin and gender-specific psychiatric disorders

The serotonergic system has been linked to the etiology of several, albeit disparate, psychiatric disorders. The accumulation of many lines of evidence support the view that there are gender differences in the serotonergic system in humans. It is further proposed that a gender differentiated serotonergic system acts as the nidus for the development of gender-specific psychiatric disorders. Depression, anxiety and eating disorders are largely seen in females, whereas alcoholism, aggressivity and suicide predominate in males. Evidence from both animal and human studies suggesting that the serotonergic system mediates between social-environmental experience and biological states is presented and reviewed. A reconceptualization of the serotonergic system as a gender-specific psychobiological interface is proposed. (Int J Psych Clin Prac 1997; 1: 3-13).

Seasonal variability in blood platelet 3H-imipramine binding in healthy controls: age and gender effects

Binding of 3H-imipramine to blood platelet membranes was determined four times (once each season) in 26 healthy volunteers (11 men and 15 women), over the course of 1 year to determine possible seasonal variations. Blood platelets were obtained in April-May, July-August, October-November, and January-February. Significant seasonal variations in the maximum number of binding sites were found in women but not in men, with circannual peak in summer and a nadir in spring. The pattern of seasonal variations was not the same in men and women. The present results highlight the importance of monitoring for gender and season in binding studies. We found no significant correlation between 3H-imipramine binding parameters and age.

Seasonal patterns in platelet ligand binding are related to membrane proteins

A seasonal pattern of platelet [3H]imipramine (3H-IMI) binding was explained by a similar but inverted pattern in membrane protein levels in repeated measures of 20 normal volunteers. No seasonal pattern was evident when 3H-IMI binding was expressed on the basis of surface area rather than membrane protein. Platelet Bmax levels in 50 depressed patients were lower than those of controls when values were expressed in terms of platelet surface area. The results support previous reports of low Bmax values in unipolar major depression, but indicate that seasonal changes in 3H-IMI binding are due to fluctuations in membrane protein and not to changes in the number of receptive sites. The present findings also have similar implications for other platelet measures expressed in terms of membrane protein.

Seasonal pattern of posttraumatic stress disorder admissions

Seasonal influences in some psychiatric disorders have been reported. Therefore, we examined whether a seasonal variation exists in posttraumatic stress disorder (PTSD). Charts of Vietnam veterans with PTSD (N = 160) admitted to a Veterans Administration Medical Center during a 3-year period were reviewed for season of admission. We found that admissions for PTSD were significantly more frequent in spring and summer. These preliminary results suggest the possibility that seasonal factors may influence PTSD.

Changes in platelet 3-H-imipramine binding: influences of protein concentration of varying proportions of cytosol or intact platelets and displacing agents used

Platelet 3-H-imipramine binding exhibits considerable variation, both interindividually and between several groups. The aim of this study was to measure 3-H-imipramine binding, simultaneously in platelet membranes vs. intact platelets vs. cytosol or intracytosolic protein in order to determine their effect on Bmax and Kd values. 3-H-imipramine binding was carried out at different protein concentrations. Our results indicate that the affinity constant is heavily influenced by the presence of cytosol and intact platelets in membrane preparations. Finally, we demonstrate a negative correlation between Bmax and protein concentration. Only perfect analytical conditions will allow platelet 3-H-imipramine binding to be a biological marker for affective disorders.

Platelet [3H]paroxetine binding, 5-HT-stimulated Ca2+ response, and 5-HT content in winter seasonal affective disorder

The present study was designed to evaluate cellular serotonergic functions in winter seasonal affective disorder (SAD) using serotonin (5-HT)-stimulated Ca2+ response as an integrated measure of 5-HT2 receptor function in platelets, [3H]paroxetine binding to characterize the platelet 5-HT transporter and 5-HT content as an index of the platelet storage capacity for this neurotransmitter amine. Purified density-dependent subpopulations of platelets in untreated and light-treated SAD patients and matched controls were investigated in order to control for possible variations in platelet turnover. We found no differences between SAD patients and controls on any of the measures, nor between light therapy conditions in SAD patients, although we found a higher Bmax of [3H]paroxetine binding and 5-HT content in heavy platelets compared to light platelets. Although the validity of platelet serotonergic measures as a model for brain serotonergic systems still remains to be elucidated, we found no evidence of platelet serotonergic abnormalities in our sample of SAD patients.

Platelet serotonin transporter in drug-naive migrainous children and adolescents

Platelet [3H]imipramine binding was measured in 17 children and adolescents suffering from common (n = 10) and classical (n = 7) migraine and 10 healthy control subjects. All patients had more than a 1-year history of the disease and suffered at least one attack per month. All subjects had been drug-free for at least 4 weeks prior to the study and had never been treated with drugs active at the serotonergic system. An increased density in [3H]imipramine binding sites was detected in the migraine patients (+51%; p < 0.05). The increase in maximal binding was more prominent in the classical migraine group (+63%) than in the common migraine group (+43%). These results disagree with previous studies that reported decreased platelet imipramine binding in adult migraine patients. The discrepancy may be related to chronicity of drug treatment, long-term duration of disease and comorbidity of depression and anxiety disorders in adult migrainous patients.

Effects of intracisternally injected serotonin on cerebral blood flow in cats during winter and summer, and after dark exposure

This investigation reports on two experiments: (a) The examination of the effects of intracisternally injected serotonin on cerebral blood flow and systemic pressure in cats during winter (1/10-3/7) and summer (7/6-9/3) at a latitude of 39' 40", and (b) the effects of similarly injected serotonin on the same parameters in 11 cats after exposure to 3 days of continuous darkness during the summer months. Serotonin (5 mg) injected intracisternally produced significant decreases in cerebral blood flow and systemic pressure that lasted from 60 to 180 min after injection. Blood flow decreases, expressed as percentage change from baseline, seen during winter (n = 24) periods were significantly greater [analysis of variance (ANOVA), p < 0.02] from decreases seen during summer (n = 25) periods. Following serotonin injection, systemic pressure decreases between the winter and summer cats were not significantly different. Eleven summer cats were subjected to 3 days of continuous darkness before being injected with serotonin. Blood flow decreases in the dark-exposed cats were significantly (p < 0.05) greater than those seen in normal light-exposed cats, whereas systemic pressure changes were not different. These studies suggest that the seasonal photoperiod may affect the sensitivity of cerebral vessels to intracisternally injected serotonin in cats.

Seasonality in psychiatry--a review

This paper reviews the literature pertaining to seasonal patterns in psychiatric illnesses. Evidence on the season of birth phenomenon suggests that a greater risk of pre-, peri-, or post-natal damage is associated with the winter months. There is currently insufficient evidence to pinpoint the exact mechanism involved or to ascertain whether the mechanism is common to each condition. Studies of seasonal patterns of incidence of psychiatric disorders have highlighted the role of seasonally regulated environmental factors on internal biological processes. There is growing evidence that serotonin is involved in a variety of psychiatric disorders. Seasonal patterns have been observed in processes involving serotonergic functioning. Furthermore, it has been postulated that these processes may be influenced by photoperiod, suggesting that the seasonal patterns of incidence of several psychiatric conditions may share a common neurophysiological substrate.

Clinical and biochemical aspects of depressive disorders: II. Transmitter/receptor theories

The present document is the second of three parts in a review that focuses on recent data from clinical and animal research concerning the biochemical bases of depressive disorders, diagnosis, and treatment. Various receptor/transmitter theories of depressive disorders are discussed in this section. Specifically, data supporting noradrenergic, serotonergic, cholinergic, dopaminergic, GABAergic, and peptidergic theories, as well as interactions between noradrenergic and serotonergic, or cholinergic and catecholaminergic systems are presented. Problems with the data and future directions for research are also discussed. A previous publication, Part I of this review, dealt with the classification of depressive disorders and research techniques for studying the biochemical mechanisms of these disorders. A future publication, Part III of this review, discusses treatments for depression and some of the controversies in this field.

Effect of phototherapy on 3H-imipramine binding sites in patients with SAD, non-SAD and in healthy controls

The effect of incandescent light treatment on the density of 3H-imipramine binding sites (Bmax) was investigated in 17 patients with seasonal affective disorder, in eight patients with non-seasonal depression and in six healthy volunteers. A significant increase in mean Bmax value parallel to a marked improvement of the depressive symptoms was found only in patients with SAD. No effect was observed either on mean Bmax value or on clinical symptoms in patients with non-SAD and on mean Bmax value in healthy volunteers.

Decreased seasonal mesor of platelet 3H-imipramine binding in depression

Seasonal cycles of platelet 3H-imipramine binding were compared in 49 endogenous unipolar depressed patients and 20 normal volunteers. A significant sinusoidal component was detected in the Bmax of binding in both patients and controls with similar amplitudes and seasonal peaks. However, the yearly average (mesor) of the patient group was significantly lower (20.0%) than that of the normal controls. The results support earlier claims of a diminished platelet binding in endogenous depression and indicate that this decrease was still evident in the presence of a 48.2% (controls) to 65.8% (patients) seasonal variation. Control Bmax values were normally distributed about a best-fit mean (cosinor fit). In contrast, patient values appeared to be bimodally distributed with one mode that was similar to controls and one mode that was substantially lower. In general, psychiatric symptoms failed to distinguish between patients with high and low platelet binding and no correlation was found between Bmax and severity of illness (HAM-D).

Effect of various factors on serotonin-induced Ca2+ response in human platelets

Serotonin (5-HT)-stimulated intracellular Ca2+ concentration change was studied in the platelets of healthy subjects, using fluorescent Ca indicator fura-2. 5-HT increased the Ca2+ response in a concentration-dependent manner. 10 microM of 5-HT induced the maximal response and its EC50 value was 0.4 microM. This response was potently inhibited by selective 5-HT2 antagonists, suggesting that 5-HT-induced Ca2+ mobilization in human platelets is mediated by 5-HT2 receptors. This 5-HT2-mediated Ca2+ response was not significantly affected by the time of blood sampling, gender, meal or exercise. However, this response declined with time after blood drawing, suggesting that it must be measured as soon as possible after sampling. These results indicate that 5-HT-stimulated Ca2+ response in human platelets is a stable parameter and that it will be suitable for assessing 5-HT2 receptor function in depressed patients.

Relationship between seasonal patterns of platelet serotonin uptake and 3H-imipramine binding in depressed patients and normal controls

1. Significant seasonal variations were found in the velocity of serotonin (Vmax) uptake and the density of 3H-imipramine binding sites (Bmax) in blood platelets from normal controls. 2. Peak 3H-imipramine (3H-IMI) binding was found in February whereas peak serotonin (5HT) uptake was found in June and these measures were not correlated in paired comparisons. 3. Both Vmax and Bmax values of depressed patients deviated from the normal seasonal pattern with lower uptake and binding in the patient group. 4. A comparison of Vmax and Bmax deviations from the normal patterns of uptake and binding revealed a significant correlation between these measures such that patients with low Vmax values were the same as those with low Bmax values. 5. The results support previous claims that the 3H-IMI binding site may be closely associated with, or identical to, a 5HT transport carrier. 6. A significant correlation between uptake and binding further suggests that a common defect may be responsible for observed decreases in Vmax and Bmax values of depressed patients.

Seasonal changes in cyanoimipramine specific platelet 3H-imipramine binding in depression

Seasonal variations in cyanoimipramine (CNIMI) sensitive and CNIMI resistant subclasses of platelet 3H-imipramine (3H-IMI) binding sites were studied in depressed patients and normal volunteers. Sinusoidal rhythms of the binding of both subclasses were found in patients and controls with peak levels in mid-February. Patient values of CNIMI sensitive binding fluctuated about a yearly average that was 32% lower than the average of controls. Patient deviations from the normal pattern were apparently bimodally distributed, whereas those of controls were normally distributed. CNIMI resistant binding was also normally distributed in controls, but not in depressed patients, although patient mesor values were not lower than those of controls. Platelet binding was not correlated with the severity of illness as measured by the Hamilton Rating Scale for Depression, and individual symptoms failed to discriminate between patients with high and low Bmax values.

Platelet tritiated imipramine binding in psychiatric patients: relationship to symptoms and severity of depression

The clinical and research significance of reduced imipramine binding has remained unclear despite considerable investigation. This study used an assay of demonstrated reliability to investigate the clinical correlates of imipramine binding to platelets in 63 depressed and 33 nondepressed psychiatric patients and 40 healthy control subjects. Both patient groups had Bmax values significantly lower than those of the healthy controls. Unequivocal associations between binding parameters and individual symptoms or groups of symptoms were not established, but a negative correlation between Kd and the number of adverse life events experienced in the preceding 6 months was apparent. These findings provide no support for the view that reduced binding is a trait marker for susceptibility to depression and cast doubt on its specificity as a state marker for the syndrome of depression.

Seasonal variations in binding of 3H-paroxetine to blood platelets in healthy volunteers: indications for a gender difference

Binding of paroxetine to blood platelet membranes was studied longitudinally in 20 healthy volunteers (11 men and 9 women) in order to determine seasonal and gender variations. Blood samples were obtained in September, December, March, and June, and repeated in September. A significant seasonal variation in the maximal number of binding sites (Bmax) was found. Men were found to have significantly lower (Bmax) values than women. Although the pattern of seasonal variation was not identical in men and women, no significant differences were detected. The affinity constant (KD) of paroxetine binding showed a significant seasonal variation. Men were found to have a significantly higher KD (lower affinity) than women. The pattern of seasonal variation was identical in men and women. These data support the evidence indicating a substantial seasonal effect on the serotonergic system, and show that in paroxetine binding studies, groups of subjects should be matched for season and gender.

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 to previously frozen platelet membranes from depressed patients, before and after treatment

3H-imipramine binding in 39 drug-free patients with major depression and 44 healthy controls did not differ significantly between the two groups, in male or female subjects or in subgroups of depressed patients divided by endogenicity or dexamethasone suppression test result. 3H-imipramine binding in depressed patients drug-free for less than three weeks did not differ from those drug-free for longer intervals or from controls. A significant seasonal variation of 3H-imipramine Bmax was found, with lower values in summer and autumn. Treatment of depressed patients with imipramine or lofepramine for six weeks increased KD and Bmax. Methodological modification (in preparation and storage of platelets) does not explain the major differences in results between this study (using frozen platelets), a previous one (using freshly prepared platelets) and others in general, although it might contribute to the range of values reported.

Monoamines: biochemical markers of suicide?

The purpose of this article is to give the clinician not proficient in biochemistry an understanding of the biochemical research data on neurotransmitters and suicide. This literature review reports the current findings on serotonin (5-HT), dopamine (DA), and norepinephrine (NE) as possible biochemical markers of depression and suicide. In conjunction with known environmental and behavioral indicators of suicide, neurotransmitter balance could be a factor in determining the severity of depression and the possible suicidal ideation in patients. Numerous studies have been performed on the monoamines: Serotonin, Dopamine and Norepinephrine, neurotransmitters that innervate parts of the spinal cord and all areas of the brain. Studies appear to suggest a relationship among monoamine levels, depression, and suicide. Significantly low levels of serotonin and the neurotransmitter metabolite (5-HIAA) may be correlated with suicidal behavior.

Seasonal changes of plasma serotonin and related parameters: correlation with environmental measures

Seasonal changes of several serotonin-related measures in plasma and whole blood of healthy individuals were determined every 4 weeks. Plasma serotonin (5-HT) shows very marked changes throughout the year, with maximum values during the summer and lowest values in the fall, whereas its metabolite 5-hydroxyindoleacetic acid (5-HIAA) follows a somewhat contrary pattern. The sum of 5-HT plus 5-HIAA in plasma thus does not change significantly during the year and follows the evolution of total plasma tryptophan (TP). The difference of 5-HIAA minus 5-HT in plasma, which is indicative of the efficacy of degradative processes of 5-HT in the periphery, is strongly dependent on the season and suggests a higher degradation of 5-HT during fall-winter. Unlike plasma TP and whole blood 5-HT, significant correlations among plasma 5-HT, 5-HIAA, and the ambient temperature were found. The possible significance and relationship of these findings to the seasonality of major depression is discussed.

[3H]yohimbine binding to platelet alpha 2-adrenoceptors in depression

[3H]Yohimbine binding to platelet alpha 2-adrenoceptors was studied in depressed patients and healthy volunteers. Where possible platelet binding measurement was repeated in depressed patients following treatment. Bmax of [3H]yohimbine binding did not differ significantly between depressed patients and control subjects and did not change with treatment in depressed patients. KD was significantly lower in female depressed patients, particularly in those who were post-menopausal. Multivariate analysis showed significant effects on KD of depression, season of testing and assay protein concentration.

Seasonal rhythm of platelet 3H-imipramine binding in normal controls

The densities of platelet 3H-imipramine sites were determined by repetitive measures of 11 normal controls over the course of 1 year. A significant seasonal variation was found, with a circannual peak on February 17 and a nadir on August 18. The estimated amplitude of this rhythm was +/- 599.54 fmol/mg, which fluctuated about a yearly mean of 2647.5 fmol/mg. The present results underscore the importance of including seasonally matched controls in the evaluation of potential patient differences in platelet binding.

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.

Platelet serotonin uptake dynamic changes in depression: effects of long-term imipramine treatment and clinical recovery

The characteristics of the serotonin uptake mechanism were measured in blood platelets of depressed patients before treatment and after 3 weeks and 2 months of imipramine therapy. The results were then compared with data from normal volunteers. In the unmedicated, depressed patients, platelets showed two affinity components of serotonin uptake. Both affinity states differed, in opposite directions, from the platelet serotonin uptake in normal volunteers. In the latter, a two-state model was more difficult to establish. Successful imipramine treatment progressively normalized the platelet serotonin uptake changes seen in unmedicated patients. Those changes allowed the membrane to deal with a wider than normal range of extracellular serotonin concentration; they might reflect neuronal compensatory changes resulting from altered extraneuronal serotonin concentrations and leading, directly or via presynaptic receptors, to balancing them. Imipramine treatment assists the adaptive process and accelerates the clinical recovery.

Phototherapy increases platelet 3H-imipramine binding in patients with winter depression

The density of platelet 3H-imipramine binding sites (Bmax) was investigated in seven inpatients with winter depression before and after incandescent light treatment and in seven healthy volunteers within a 7-day interval without light exposure. A significantly lower mean Bmax value was found in the depressed patients compared to the controls. After light treatment, parallel to a marked clinical improvement, Bmax increased in each patient and reached or even exceeded the mean values of the controls. These results indicate that in patients with winter depression the decreased Bmax value is state-dependent. The incandescent light treatment has beneficial effect in winter depressives and can influence Bmax values.

Effect of different photoperiod exposure on [3H]imipramine binding and serotonin uptake in the rat brain

Seasonal rhythmicity in the occurrence of acute depressive episodes and the therapeutic efficacy of light exposure suggest the possible involvement of the pineal gland or other biological oscillators in the pathophysiology of depressive illness. We have performed studies to clarify whether different light/dark (LD) cycle schedules may induce changes in the biochemical targets of antidepressants in the rat CNS. In particular, we have investigated the effect of short- (LD 8:16) or long-day (LD 14:10) photoperiods on different biochemical parameters of serotonergic neurons. A significant increase in the density of [3H]imipramine ([3H]IMI) binding and in the Vmax of 5-[3H]hydroxytryptamine (5-[3H]HT) uptake was found in the hypothalamus of LD 8:16-with respect to LD 14:10-exposed rats, whereas no difference was found in the kinetic properties of postsynaptic 5-HT receptors and in 5-HT metabolism in the hypothalami and cerebral cortices of rats exposed to the two different photoperiods. A seasonal rhythm of [3H]IMI binding sites and 5-HT uptake seems to exist only in certain brain areas, such as the hypothalamus, because no differences were found in the cerebral cortex of LD 14:10- and LD 8:16-accustomed rats. [3H]IMI binding and 5-HT uptake were significantly increased in the hypothalamus of rats accustomed to a light/dark-inverted cycle (DL 10:14) and killed 6 h after the stopping of lighting in comparison to rats exposed to normal LD 14:10 cycles and killed 6 h after the beginning of lighting. Therefore, a circadian modification of the serotonergic presynaptic sites seems to be present and related to light/dark exposure. Because the existence of endogenous compounds able to modulate [3H]IMI binding and 5-HT uptake, other than 5-HT, has been postulated in the mammalian brain, the involvement of these substances in the periodic changes observed could be suggested.

A longitudinal study of intact platelet 3H-imipramine binding in 12 normal human subjects

Most investigators have measured binding of 3H-imipramine to platelet membranes, but some of the preparations may have contained varying proportions of intracellular protein because of contamination with incompletely lysed platelets. Since binding to membranes has been expressed with reference to the amount of protein in the membrane preparation, it is not surprising that there are discrepancies and a wide range of reported values for platelet imipramine binding in the literature. We have now completed a 9-month study of the binding of 3H-imipramine to intact platelets obtained monthly from 12 normal subjects. Using the intact platelet assay, as described by Friedl and Propping, we found that both Bmax and Kd for 3H-imipramine binding exhibited large month-to-month variations and no consistent seasonal trend was observed. The substantial variation in both Bmax and Kd among normal subjects and among samples obtained from the same individual at different times may limit the clinical usefulness of these measurements. A single blood sample is unlikely to give reliable values for Bmax and Kd for comparison purposes.

Sleep deprivation and imipramine binding sites in depressed patients and healthy subjects

The influence of sleep deprivation on 3H imipramine binding was investigated in blood platelets of 32 depressed patients and 15 healthy subjects. The effect of sleep deprivation was not statistically different in either group. Changes of Bmax associated with sleep deprivation were compensated for by reciprocal changes of Kd in the group of patients, suggesting altered regulatory mechanisms. A comparison of binding characteristics of responders and nonresponders to sleep deprivation revealed no difference between groups. If the patients were divided by a biological criterion (number of binding sites), a prediction of clinical response to sleep deprivation was possible.

Regional and subcellular localization in human brain of [3H]paroxetine binding, a marker of serotonin uptake sites

The characteristics of the binding of [3H]paroxetine, a selective serotonin (5-HT) uptake blocker, were investigated in human brain. The Kd value was 0.23 +/- 0.07 nM, and the Bmax value was 190 +/- 39 fmol/mg protein in the putamen. The capacity of various antidepressive drugs to inhibit [3H]paroxetine-specific binding in human brain was well correlated with their capacity to inhibit [3H]5-HT uptake in rat brain. The highest concentrations of [3H]paroxetine-specific binding sites were found in the substantia nigra, hypothalamus, and hippocampus. Lower values were obtained in the basal ganglia and the thalamus. The specific binding was very low in cerebral and cerebellar cortices. The regional distribution of [3H]paroxetine binding sites differs from that of [3H]ketanserin binding to S2 serotonin receptors. The subcellular distribution of the [3H]paroxetine-specific binding sites obtained by differential centrifugation revealed a synaptosomal enrichment in the frontal cortex and striatum, whereas an enrichment in the microsomal fraction was found in striatum. The results show that [3H]paroxetine is a ligand of choice to label the 5-HT uptake molecular complex in human brain.

Analysis of seasonal fluctuations of CSF monoamine metabolites and neuropeptides in normal controls: findings with 5HIAA and HVA

Seasonal variations of certain cerebrospinal fluid (CSF) parameters have been reported in several psychiatric patient groups, but there is little or no available information on such variations in normal individuals. To evaluate possible circannual variations in the major CSF monoamine metabolites and an array of neuropeptide measures, we analyzed data from 20 to 34 normal volunteers studied over a 3-year period. Data were analyzed for seasonal and cross-seasonal fluctuations by one-way analysis of variance (ANOVA) followed by Bonferroni t tests when appropriate. The only statistically significant findings by ANOVA were for CSF 5-hydroxyindoleacetic acid (5HIAA) and homovanillic acid (HVA), both of which were lowest during spring and highest during summer. These spring-summer differences were statistically significant following Bonferroni t tests. These data support a growing body of evidence indicating a substantial seasonal effect on the serotonin system and suggest that any group analysis of CSF 5HIAA, and perhaps HVA, should take into account circannual variability.

Platelet research in psychiatry

The platelet is one of the most researched biological markers in psychiatry. Characteristics of MAO activity, 5-HT uptake, imipramine and alpha 2-adrenergic receptor binding, for example, are similar in platelet and CNS. Methodological factors are not negligible, and range from diagnostic specificity and drug effects to the normal physiological variability of age and hormone-related changes, circadian and seasonal rhythms. As yet, there are no clear state or trait platelet markers in affective disorders and schizophrenia that can be unequivocally used to detect vulnerability to the illness, predict therapeutic response, define clinical diagnostic entities or follow the course of the illness. However, platelet markers are increasingly being used in careful studies to monitor psychopharmacological effects (an in vivo assay of all active metabolites), different ligands can be specific markers for certain aspects of a psychiatric illness (e.g. alpha 2-adrenergic receptors and weight loss), and this homogeneous preparation of human cells is an increasingly important tool in studying mechanisms in pathophysiology. More longitudinal studies are required to establish functional relationships between platelet variables and psychopathology.

Time course of schizophrenia and platelet 5-HT level

The concentration of platelet serotonin (5-HT) and the simultaneous uptake of 5-HT into platelets have been investigated in schizophrenic patients with (A) intermittent time course of illness (complete remission), (B) chronic time course (partial remission and residual symptoms), and (C) intermittent-chronic time course (good remission at the beginning of illness with gradual progression to chronic stage). An increased platelet 5-HT concentration (i.e., hyperserotoninemia) of unknown etiology was observed, especially in the group with chronic time course of disease as compared to the normal controls. At the same time, kinetic constants Km and Vmax of 5-HT uptake into platelets were unchanged in all patients. Neuroleptic treatment did not produce any significant change either in platelet 5-HT level or in the uptake of 5-HT. These results provide further support for the possible 5-HT dysfunction in schizophrenia.

Seasonal variation of imipramine binding in the blood platelets of normal controls and depressed patients

Imipramine binding (IB) was studied in the blood platelets from normal controls and depressed patients over a 4-year period (1981-1984) to determine if seasonal variation was present in Bmax or KD. Bimonthly variation in the Bmax of IB was found in normal controls studied longitudinally. No such variation was found when individual values from normal controls were examined on a monthly or seasonal basis. Bmax in depressed patients showed a significant seasonal, but not monthly, variation. KD of IB varied in normal controls using monthly or seasonal data, but not in the probably more reliable bimonthly data. These results suggest that IB studies comparing groups of subjects should match groups for season of the year or, for greater accuracy, month of the year.