Platelet Serotonin Level and Impulsivity in Human Self-destructive Behavior: A Biological and Psychological Study

Platelet serotonin estimation

Enzyme immunometric assay was carried out on the kit obtained from M/s Enzo Life Sciences, PA, USA. Blood samples were collected after informed consent under full aseptic conditions. The samples were labeled by alphanumeric code to maintain confidentiality. After collection of blood, it was centrifuged at 16000 ×g for 15 min, and the white buffy coat was collected. The platelets were washed twice using physiological saline and centrifuged at 2000 ×g for 10 min and again washed. Platelet pellet was resuspended using distilled water. Suspension thus obtained was frozen and thawed shortly before carrying final assay.

The samples were stored at −20°C before final estimation at the facilities provided at the Interactive Research School for Health Affairs, an autonomous research institute of the Parent University.

The structured interview for impulsivity is a 25 item structured interview that is taken out of the diagnostic interview for borderlines (DIB) by Zanarini et al.[6] It has been translated and back translated into Marathi at Maharashtra Institute of Mental Health by Chitalkar and Phadke.[7] Up to two marks can be given for each positive answer. The maximum score is 50.

Gender

Maharashtra is one of the leading suicide states of India. Among the completed suicides in our country, a male:female ratio of 65:35 has been reported.[13] As far as attempted suicides are concerned a reverse trend has been reported by various workers.[141516] In India, Srivastava and Kulshreshtha reported male under 35 were at risk.[16] While Lal and Sethi reported homemakers below 30 years of age were at risk.[15] No official figures for suicide attempts are available. There is no epidemiological data on attempted suicides. In the present study, females outnumbered males by 2:1 which perhaps reflect the present trend.

Age

Globally, parasuicide is generally considered as a problem in the young (under 35 years) while suicide as a problem in the old.[2] The mean age of the patients in the present study was 30.6 years. There was no difference in the mean age of male and female persons. Hence, it appears that mean age reflects the general trend. In India, even completed suicide appears to be a problem of young as 70.1% of suicide victims are below 44 years of age.[13]

Human self-destructive behavior and psychiatric diagnosis

It is reported that 90%–94% of people who completed suicide had mental illness[1718] and mood disorders were reported in 45%–77% of suicides;[19] the figures for suicidal attempts are not known. However, adjustment disorders and personality disorders reported to be more likely in suicidal attempts while mood disorder, psychosis, and substance use predominate in completed suicides.[2] In the present study, 51% had depression that corresponds to Barraclough et al.[19] and Bagadia et al.[20] In 19% of cases, no diagnoses could be made. In both sexes, the absence of psychosis and substance use is quite striking. Seventy-one percent of females had depression or adjustment disorder with depressed mood, while 50% of the males had a depression 25% of the females had no diagnosable disorder. Thirty percent of the males had a personality disorder, and 5% of males had no diagnosable disorder. In this way, attempted suicide seems to be similar to mood disorders in some ways and differ in other respects. The differences between male and female found to be significant (P = 0.0037).

Two putative factors are assumed to be underlying suicide. A common genetic factor predisposing for mental illness in general and an independent risk factor for suicide of which the biological factor may be related to the serotonergic system while the psychological factors were found to be impulsivity and aggression.[1]

Human self-destructive behavior and impulsivity

Impulsivity may be made up of several independent factors, and there is little unanimity what these factors are. There is no consensus on the best way to measure impulsivity.[21] To circumvent the problem of translating and standardizing the Barrat Impulsiveness scale,[22] we utilized the 25 items on impulsivity from the DIB[6] that was translated into Marathi by Chitalkar and Phadke.[7] These 25 items appear to give adequate coverage to tap various aspects of impulsivity. Norms for the scale obviously are not available. The possible maximum marks are fifty. The mean score for the study population was 5.45, and that of males and females were 7.6 and 4.39, respectively. However, the difference in the means was not significant. Among the diagnostic categories, personality disorder patients had the highest mean impulsivity score of 13, which was significantly high (P < 0.001) than other diagnoses. Personality disorder patients are known to have high impulsivity scores.[9]

Human self-destructive behavior and platelet serotonin

The mean platelet serotonin levels of the total study samples were 51.3 ng/ml, which in males was 57.3 ng/ml, and in females, it was 56.05 ng/ml. Only one study has quoted platelet Serotonin levels in normal individuals. Ghosh correlated little finger length and platelet serotonin levels in 48 healthy subjects. He postulated that little finger length was related to neuroticism, which is known to be associated with depression and anxiety.[11] In his study, serotonin levels in the males were 160.57 (nonneuroticism) and 86.38 (neuroticism). While in females, they were 182.76 (nonneuroticism) and 126.16 (neuroticism). The platelet serotonin levels of the present study are lower than those reported by Ghosh.[11] Perhaps, it can be understood from the fact that his sample consisted of healthy individuals. Comparison with platelet serotonin levels of Ghosh study brings out of the fact that all attempted suicides have low platelet serotonin levels. Walderhaug et al.[23] reported reduced serotonin levels (by tryptophan depletion) caused increased impulsivity in healthy individuals and impulsivity is associated with suicidality.[1] In the present study, no difference in platelet Serotonin levels between males and females was found.

Correlation of impulsivity and platelet 5-hydroxytryptamine

Contrary findings have been reported about the relationship between impulsivity and platelet serotonin levels.[24252627282930] In the present study, platelet serotonin levels when compared with that of healthy normal patients of Ghosh study[11] found to be quite low in the sample. The issue could have been put across more emphatically had there been a sample of healthy controls in this study. Platelet serotonin levels were found to be low in suicidal patients, and this corresponds to other studies.[24252628] However, Askenazy et al. found elevated 5HT levels in platelets of suicidal attempt patients.[27]

Given the low levels of platelet serotonin in the study sample and the reported association of impulsivity and suicidality[31] an attempt was made to correlate the impulsivity scores with platelet serotonin levels. A significant negative correlation (r = −0.32, t = 2.173, P < 0.05) was obtained.

On analyzing if impulsivity associated with gender, it was observed that a significant negative association between platelet serotonin and impulsivity was present in males (r = −0.31, t = 2.27, P < 0.05) and not in females (r = 0.026, t = 0.12, P > 0.05). This divergent finding is not due to high serotonin content in females as found by Le Quan-Bui et al.[32] because platelet serotonin levels in females were actually marginally higher in females in this study. It appears that low impulsivity scores (mean 4.39) in females in comparison to males (mean 7.60) have contributed to this gender specific correlation of impulsivity with platelet serotonin. The worker is not aware of any study showing similar finding.