Rhesus monkey cerebrospinal fluid amine metabolite changes following treatment with the reversible monoamine oxidase type-A inhibitor cimoxatone

Relationship of monoamine oxidase A binding to adaptive and maladaptive personality traits

BACKGROUND

Monoamine oxidase A (MAOA) is an important enzyme that metabolizes monoamines such as serotonin, norepinephrine and dopamine in the brain. In prefrontal cortex, low MAOA binding is associated with aggression and high binding is associated with major depressive disorder (MDD) and also risk for recurrence of depressive episodes. In rodent models, low MAOA levels are associated with increased aggression and fear conditioning, and decreased social and exploratory investigative behaviors. Our objective was to measure MAOA binding in prefrontal cortex and concurrently evaluate a broad range of validated personality traits. We hypothesized that prefrontal MAOA binding would correlate negatively with angry-hostility, a trait related to aggression/anger, and positively with traits intuitively related to adaptive investigative behavior.

METHOD

Participants were aged 19-49 years, healthy and non-smoking. MAOA binding was measured with [11C]harmine positron emission tomography (PET) in prefrontal brain regions and personality traits were measured with the NEO Personality Inventory Revised (NEO PI-R).

RESULTS

Prefrontal MAOA binding correlated negatively with angry-hostility (r=-0.515, p=0.001) and positively with deliberation (r=0.514, p=0.001). In a two-factor regression model, these facets explained 38% of variance in prefrontal MAOA binding. A similar relationship was found in prefrontal cortex subregions.

CONCLUSIONS

We propose a new continuum describing the relationship between personality and MAOA: deliberate/thoughtful contrasting aggressive/impulsive. Additionally, the association between high MAOA binding and greater deliberation may explain why some people have moderately high levels of MAOA, although very high levels occur during MDD. In health, higher MAOA binding is associated with an adaptive personality facet.

Toloxatone pharmacokinetics in the plasma and cerebrospinal fluid of the rabbit

The pharmacokinetics of toloxatone (5 and 10 mg kg-1, i.v.) was studied in anaesthetized rabbits. There was a biexponential decline in plasma concentration with time. No differences were observed in the pharmacokinetic parameters with the increase of the dose. The terminal half-life was short (47.4 +/- 2.8 and 41.5 +/- 4.2 min for 5 and 10 mg kg-1, respectively). The total clearance was 79 +/- 18 mL min-1 after a dose of 5 mg kg-1 and 106 +/- 40 mL min-1 after a dose of 10 mg kg-1. The volume of distribution was 5.8 +/- 2.8 (5 mg kg-1) and 5.4 +/- 1.8 L (10 mg kg-1). The average percentage of toloxatone bound to plasma protein was 30% and was not affected by concentrations within the investigated range. In cerebrospinal fluid (CSF), the highest concentrations of toloxatone were obtained within 15 min after the end of the injection. The CSF level of toloxatone was equal to that of plasma unbound toloxatone and declined at a rate similar to toloxatone in plasma. These results suggest that the toloxatone passage through the blood-brain barrier may be completed by passive diffusion. In addition, the unbound plasma concentration would accurately reflect the toloxatone concentration in CSF and could be a useful tool for drug monitoring.

The new generation of monoamine oxidase inhibitors

Irreversible and unspecific inhibitors of MAO were the first modern antidepressants, but after an initial success they fell into discredit due to adverse side effects. In the past two decades interest in MAO inhibitors has been renewed because of progress in basic research, a milestone being the finding that there are two subtypes of MAO, MAO-A and MAO-B. These are distinct proteins with high amino acid homology, coded by separate genes both located on the short arm of the human chromosome X. The enzyme subforms show different substrate specificities in vitro and different distributions within the central nervous system and in peripheral organs. In the central nervous system of man MAO-A seems to be mainly involved in the metabolism of 5 HT and noradrenaline, whereas 2-phenylethylamine and probably dopamine are predominantly deaminated by MAO-B. In the intestinal tract tyramine is mainly metabolized by MAO-A. These characteristics indicate distinct physiological functions of the two MAO-subforms. Several irreversible and reversible non-hydrazine inhibitors with relative selectivities for one of the MAO-subforms have been developed. They belong to various chemical classes with different modes of enzyme inhibition. These range from covalent mechanism based interaction (e.g. by propargyl- and allylamine derivatives) to pseudosubstrate inhibition (e.g. by 2-aminoethyl-carboxamides) and non-covalent interaction (e.g. by brofaromine, toloxatone and possibly moclobemide). The most important pharmacological effects of the new types of MAO inhibitors are those observed in neuropsychiatric disorders. The inhibitors of MAO-A show a favorable action in various forms of mental depression. The drugs seem to have about the same activity as other types of antidepressants, including tricyclic and related compounds as well as classical MAO inhibitors. The onset of action of the MAO-A inhibitors is claimed to be relatively fast. Other possible indications of these drugs include disorders with cognitive impairment, e.g. dementia of the Alzheimer type. In subjects with Parkinson's disease the MAO-B inhibitor L-deprenyl exerts a L-dopa-sparing effect, prolongs L-dopa action and seems to have a favorable influence regarding on-off disabilities. The action is in general transitory (months to several years). In addition L-deprenyl has been shown to delay the necessity for L-dopa treatment in patients with early parkinsonism. Whether the drug influence the progression of the disease is still a matter of debate. L-deprenyl also appears to have some antidepressant effect (especially in higher doses) and to exert a beneficial influence in other disorders, e.g. dementia of the Alzheimer type.(ABSTRACT TRUNCATED AT 400 WORDS)

The behavioral neurobiology of self-injurious behavior in rhesus monkeys

1. Self-injurious behavior (SIB) is prevalent among institutionalized children, but the efficacy of current behavioral and pharmacological treatments is marginal. 2. There is evidence that SIB in humans has a neurobiological basis. A better understanding of the neurobiological factors that may promote or cause SIB is necessary for the development of effective pharmacologic treatments. 3. SIB that is similar in some respects to SIB in humans occurs in nonhuman primates that have been deprived of social experience early in life. An analysis of the "cause" of SIB suggests that it is a relatively straight-forward example of the development of neurobiological and behavioral aspects of aggressive behavior in the absence of social factors that would normally bring the behavior under environmental control. Once induced, however, it becomes environmentally autonomous and its proximal cause is neurobiological in nature. 4. There are three lines of evidence that nonhuman primate SIB is linked to malfunctions in the norepinephrine (NE) and serotonin (5HT) neurotransmitter systems. The activity of these systems appears to be altered by psychosocial deprivation. The functional relationship between the two systems appears to be altered or absent in socially deprived monkeys. Pharmacologic agents that act on these systems alter SIB in monkeys. 5. Preliminary data from socially deprived rhesus monkeys are consistent in major respects with studies linking altered serotonin systems to self-injurious behavior and suicidal motivation in humans who also probably suffer from social deprivation. 6. Taken together, these findings indicate that developmental study of biogenic amine systems, particularly finding ways to circumvent deficits in, or restore functional linkages between, the 5HT and NE systems, will lead to a greater understanding of the neurobiologic basis of SIB in humans and animals and will enable us to develop more effective treatments of SIB.

The effects of amiflamine on cerebrospinal fluid amine metabolites in the rhesus monkey

Amiflamine, a drug reported to be a reversible inhibitor of monoamine oxidase type A (MAO-A) selective for serotonergic neurons in rodents, was administered to rhesus monkeys over a 12-fold dosage range (0.5-6 mg/kg). Amiflamine produced small, essentially equivalent reductions in cerebrospinal fluid (CSF) 5-hydroxyindoleacetic acid (5-HIAA, 1-28%), 3-methoxy-4-hydroxyphenylglycol (MHPG, 4-26%), and homovanillic acid (HVA, 7-29%), suggesting that the effects of amiflamine are approximately equal on serotonin, norepinephrine and dopamine metabolism in nonhuman primates. Concentrations of amiflamine were very low in CSF 3-6 h after drug administration (less than 7 nmol/l), while those of its two major, biologically active metabolites were higher (22-150 nmol/l) and varied in relative proportions among the monkeys. Further investigation is required of some preliminary observations of a possible association between drug metabolite variations and the substantial individual differences in the amine metabolite changes following amiflamine treatment. MAO-B in platelets was not inhibited by 6 mg/kg amiflamine, indicating that MAO-A selectivity was maintained. At low amiflamine doses, early and transient increases in CSF 5-HIAA and HVA concentrations were observed, suggesting an amine-releasing effect of the drug within brain serotonergic and dopaminergic neurons.