Correlation of platelet MAO activity with introversion: a study on a German rural population

Sensation seeking: A comparative approach to a human trait

A comparative method of studying the biological bases of personality compares human trait dimensions with likely animal models in terms of genetic determination and common biological correlates. The approach is applied to the trait of sensation seeking, which is defined on the human level by a questionnaire, reports of experience, and observations of behavior, and on the animal level by general activity, behavior in novel situations, and certain types of naturalistic behavior in animal colonies. Moderately high genetic determination has been found for human sensation seeking, and marked strain differences in rodents have been found in open-field behavior that may be related to basic differences in brain neurochemistry. Agonistic and sociable behaviors in both animals and humans and the trait measure of sensation seeking in humans have been related to certain common biological correlates such as gonadal hormones, monoamine oxidase (MAO), and augmenting of the cortical evoked potential.

The monoamine systems in the rodent brain are involved in general activity, exploratory behavior, emotionality, socialization, dominance, sexual and consummately behaviors, and intracranial self-stimulation. Preliminary studies have related norepinephrine and enzymes involved in its production and degradation to human sensation seeking. A model is suggested that relates mood, behavioral activity, sociability, and clinical states to activity of the central catecholamine neurotransmitters and to neuroregulators and other transmitters that act in opposite ways on behavior or stabilize activity in the arousal systems. Stimulation and behavioral activity act on the catecholamine systems in a brain–behavior feedback loop. At optimal levels of catecholamine systems activity (CSA) mood is positive and activity and sociability are adaptive. At very low or very high levels of CSA mood is dysphoric, activity is restricted or stereotyped, and the organism is unsocial or aggressively antisocial. Novelty, in the absence of threat, may be rewarding through activation of noradrenergic neurons.

Relationship between depression and borderline personality disorder

The frequent occurrence of depressive symptoms in patients with borderline personality disorder has generated considerable interest in the nature of the relationship between borderline personality disorder and the depressive disorders. Data from the perspectives of phenomenology, biology, family history, course of illness, comorbidity patterns, and treatment response have been brought to bear on the question. Reviews based on research available by 1985 and 1991, respectively, arrived at differing conclusions: (1) that both disorders shared common but non-specific sources, and (2) that the two disorders were unrelated but co-occurred because of the high prevalence of each. Since the time of these reviews, additional evidence has become available from a wider range of biological investigations, better controlled comorbidity studies, studies of the relationship of psychosocial stressors to the course of each disorder and neuroimaging studies. In reviewing the more recent findings, we propose the less parsimonious hypothesis that the disorders co-occur, both because they share some common biological features and because the psychosocial sequella of each can contribute to the development of the other.

Low platelet monoamine oxidase activity in borderline personality disorder

Platelet monoamine oxidase (MAO) activity was significantly lower in nonpsychotic, nonorganic, unmedicated male inpatients with DSM-III-R borderline personality disorder (BPD) than in nonpsychiatric controls. Patients with BPD who also met DSM-III-R criteria for antisocial personality disorder had significantly lower MAO activity than those with BPD alone. Low MAO activity in this sample did not appear to be related to the comorbid presence of major depressive disorder or a history of substance abuse.

Markers for vulnerability to psychopathology: temperament traits associated with platelet MAO activity

The functional linkage between platelet MAO activity and psychopathology was explored by analyzing temperamental correlates in 40 male subjects by means of scales from the Eysenck Personality Questionnaire (EPQ), the Zuckerman Sensation Seeking Inventory, and the Karolinska Scales of Personality (KSP). Linear correlations were found with two sensation seeking scales, replicating earlier findings. However, nonlinear correlations predominated. Subjects with intermediate platelet MAO activity had higher scores in conformity scales and lower scores in anxiety and hostility scales than low and high MAO subgroups. Low MAO subjects showed a pattern of higher scores in KSP Impulsiveness, EPQ Neuroticism, and KSP Somatic Anxiety and Irritability and lower scores in KSP Socialization, in line with personality profiles found in alcoholics, psychopaths, and suicide attempters who also tend to have low platelet MAO activity. High MAO subjects scored lower in sensation seeking and conformity scales and higher in KSP Psychasthenia, Muscular Tension and Suspicion scales, consistent with clinical links between high platelet MAO activity and anxiety and paranoia.

Platelet monoamine oxidase: low activity in cigarette smokers

Platelet monoamine oxidase (MAO) activity and plasma thiocyanate concentration (an index of smoking behavior) were measured in 109 normal male and female volunteers. MAO activity was significantly lower and plasma thiocyanate concentration significantly higher in smoking volunteers than in nonsmoking volunteers. A significant negative correlation between MAO activity and thiocyanate concentration was observed in female smokers (rs = 0.43, n = 36) but not for male smokers (rs = 0.02, n = 31). In nine smokers who gave up smoking, mean (+/- SD) platelet MAO activity increased significantly (17.5 +/- 4.1 nmole/mg/hour to 24.6 +/- 4.2 nmole/mg/hour). At the same time, mean (+/- SD) plasma thiocyanate concentrations decreased significantly (144 +/- 41 microM to 50 +/- 12 microM). These data suggest that smoking directly or indirectly reduced platelet MAO activity.

Platelet MAO activity and psychosis proneness in college students

A population of individuals potentially at risk for psychiatric disorders was identified by screening 633 college students using the Wisconsin Scales for psychosis proneness. Platelet monoamine oxidase (MAO) activity was measured in high-scoring individuals and controls using 14C-benzylamine. Males with deviant scores on the Perceptual Aberration-Magical Ideation Scale showed a bimodal distribution of platelet MAO activity. Kinetic analysis of platelets from probands with the highest and lowest levels of MAO activity in this group revealed differences in Vmax but not in Km. Since abnormal platelet MAO activity has been linked to psychiatric vulnerability, the results provide further support for the validity of the Wisconsin Scales as predictors of psychopathology.

CSF dopamine levels correlate with extraversion in depressed patients

Cerebrospinal fluid (CSF) dopamine levels were studied in 16 male patients who also were tested for self-reported extraversion using the Eysenck Personality Inventory. Log CSF dopamine was significantly correlated with extraversion as predicted by recent theoretical work integrating mesolimbic dopamine function and active responding to external incentives as psychobiological traits. CSF dopamine levels were uncorrelated with the total score on the Hamilton Rating Scale for Depression, self-reported neuroticism, and age. The results are discussed in relation to other biological models of extraversion such as the construct of sensation-seeking behavior.

Urinary phenylethylamine correlates positively with hypomania, and negatively with depression, paranoia, and social introversion on the MMPI

It has been suggested that phenylethylamine (PEA) may play a role in the modulation of affective behavior. The aim of the present study was to test this hypothesis. Urinary PEA excretion was determined in 32 drug-free healthy volunteers, and the MMPI was used for personality assessment. In support of this hypothesis, a significant positive correlation between PEA and hypomania (r = 0.50; P less than 0.05) and a significant negative correlation between PEA and depression (r = -0.58; P less than 0.01) was observed in the female subgroup. Furthermore, PEA correlated significantly negatively with hypochondriasis (r = -0.65; P less than 0.01), paranoia (r = 0.49; P less than 0.05), and social introversion (r = -0.60; P less than 0.05). These results are the first evidence in normal individuals either that PEA itself might play a role in the modulation of affective behavior, or alternatively that PEA could be related to mechanisms responsible for the modulation of affective behavior.

Personality traits and platelet monoamine oxidase in tobacco smokers

A study was made of the smoking habits of an unselected series of 1129 18-year-old men from the general population. Their smoking habits were related to personality traits, intellectual level and platelet monoamine oxidase (MAO). Regular smokers were found to be extraverts, sensation seekers who were easily bored and with a strong tendency to avoid monotony. They also had a lower than average intellectual level, and were more prone to the abuse of alcohol, glue, cannabis, amphetamine and morphine. Furthermore, they had a low platelet MAO. The results are discussed in relation to the pharmacological reasons for smoking and favour the hypothesis that tobacco smoking is related to arousal-seeking behaviour. Ex-smokers had personality traits, intellectual levels and platelet MAO of the same magnitude as non-smokers: this may be the reason why they were able to give up smoking.