On the influence of serotonin- and sex steroid-related genetic variation on mood, anxiety, personality, autism and transsexualism

Background: The neurotransmitter serotonin has been related to mood and anxiety, and variation in genes that encode important members of the serotonergic system may hence affect mood- and anxiety-related traits. Sex steroids influence brain development, and variation in genes encoding androgen and estrogen receptors, or enzymes needed for sex steroid synthesis, may be of importance for both personality traits and risk for psychiatric disorders. The specific aims of this thesis were: (i) to investigate the possible influence of serotonin-related genetic variation on the neural correlates of anxiety, and on mood- and anxiety-related phenotypes, including premenstrual dysphoric disorder (PMDD), depression and anxiety-related personality traits, (ii) to investigate the possible influence of sex steroid-related genetic variation on personality, autism spectrum disorder and transsexualism, and (iii) to try to ameliorate the chance of detecting effects of combinations of genetic variations by restricting the statistical analysis to particular patterns. Results: (i) The serotonin transporter (5-HTT) linked polymorphic region (5-HTTLPR) and a polymorphism in an important enzyme for serotonin synthesis (tryptophan hydroxylase 2; TPH2) were associated with amygdala response during presentation of angry faces in subjects with social phobia and controls. (ii) The same polymorphisms were associated with response to placebo and also with placebo-induced changes in amygdala activity during public speaking in subjects with social phobia. (iii) In men, genetic variation in the neurotrophic factor BDNF, which is closely related to the serotonergic system, was associated with the amount of serotonin transporter in the brain. (iv) Polymorphisms in genes that encode proteins important for the development of the serotonergic system (GATA2), for serotonin synthesis (TPH2) and for serotonergic transmission (5-HT3B) were associated with PMDD. (v) The 5-HTTLPR was shown to influence reports of controllable stressful life events in combination with the BDNF Val66Met polymorphism or anxiety-related personality traits in non-depressed men. (vi) Variants that may increase the function of the androgen receptor were associated with extraversion and spiritual acceptance in men. (vii) A variant that is associated with increased androgen receptor function was more common in women with autism spectrum disorder than in controls. (viii) The same androgen receptor polymorphism was associated with transsexualism in combination with polymorphisms in the genes encoding the estrogen receptor β or the testosterone-converting aromatase enzyme. (ix) A method that restricts the search for genetic combinations to monotone effect patterns was shown to increase the probability of finding gene-gene effects. Conclusions: The results support the notion that variation in genes that encode serotonin-related and sex steroid-related proteins are of importance for the psychiatric traits studied in this thesis

Dopamine D2 and D3 receptors. Studies on transduction mechanisms and on the role of a D3 gene polymorphism

The neurotransmitter dopamine has been implicated in the pathophysiology of, e.g., Parkinson s disease and schizophrenia, and dopamine receptor-active compounds are commonly employed therapeutically in these and other disorders. An overall aim of this thesis was to illuminate how the signal transduction system involving arachidonic acid (AA) and its metabolite, prostaglandin E2 (PGE2), is influenced by D2 and D3 dopamine receptors, respectively, and to what extent assessment of the effects of ligands with affinity for these receptors on the AA pathway may serve to study phenomena such as partial and inverse agonism. In addition, the possible functional importance of a polymorphism in the gene encoding the D3 receptor was assessed both in vitro, using cAMP and PGE2 as markers of receptor activation, and in vivo, by means of an association study.The results presented in paper I suggest that dopamine potently increases AA formation in D2 receptor-transfected Chinese hamster ovary (CHO) cells. Challenging previous reports, this effect was observed also in the absence of the concomitant administration of a Ca2+-mobilizer. Paper I also outlined the respective roles of G-proteins, Ca2+, and phospholipases for this effect to occur. Whereas ( )-3-PPP, in line with previous studies, displayed the properties of a partial D2 receptor agonist, the alleged dopamine receptor antagonist haloperidol displayed the profile of an inverse agonist. Paper II extends the findings of paper I by showing that the D2-induced induction of AA leads to the formation of PGE2 as the result of the catalytic action of cyclooxygenase 2 (COX-2). In this paper, we also present data supporting the notion that the D2-induced AA mobilization is catalyzed by the cPLA2 phospholipase subtype. Paper III shows that dopamine at low, but not high, concentrations inhibits AA formation in CHO cells transfected with the rat D3 receptor, i.e. an effect opposite to that observed in cells expressing D2 receptors. The dopamine receptor ligand PNU-99194A, which previously has been regarded as a D3 receptor antagonist, displayed agonist-like properties.Paper IV was an attempt to clarify the functional role of a polymorphism in the dopamine D3 receptor gene, the ser9gly polymorphism, using CHO cells transfected with either the ser9 or the gly9 variant of this receptor. The ser9gly polymorphism was found to alter the effect of dopamine on cellular transduction from inhibition of cyclic AMP (ser9) to inhibition of PGE2 (gly9). Haloperidol displayed antagonist properties at ser9-type receptors, and agonist-like properties at gly9 receptors. Finally, paper V aimed at further exploring the notion that the ser9gly polymorphism is functionally important by assessing its possible association with personality traits in healthy humans. The results suggest that the ser9gly polymorphism may be weakly linked to neuroticism in males and females, and to non-conformity traits in women.The main conclusions are (i) that the AA/PGE2 pathway is a useful marker for assessment of D2 and D3 receptor activity in vitro, (ii) that compounds previously assumed to act as neutral antagonists at D2 or D3 receptors may display agonism or inverse agonism vis-à-vis these receptors, hence illustrating the difficulties associated with the characterization of a receptor ligand in terms of intrinsic activity, and (iii) that the ser9gly polymorphism may influence D3 receptor function by means of a hitherto unknown mechanism, i.e. by shifting cellular transduction from one second messenger system (cAMP) to another (PGE2)

Direct dopamine D(2)-receptor-mediated modulation of arachidonic acid release in transfected CHO cells without the concomitant administration of a Ca(2+)-mobilizing agent

1. In CHO cells transfected with the rat dopamine D(2) receptor (long isoform), administration of dopamine per se elicited a concentration-dependent increase in arachidonic acid (AA) release. The maximal effect was 197% of controls (EC(50)=25 nM). The partial D(2) receptor agonist, (−)-(3-hydroxyphenyl)-N-n-propylpiperidine [(−)-3-PPP], also induced AA release, but with somewhat lower efficacy (maximal effect: 165%; EC(50)=91 nM). 2. The AA-releasing effect of dopamine was counteracted by pertussis toxin, by the inhibitor of intracellular Ca(2+) release, 8-(N N-diethylamino)octyl-3,4,5-trimethoxybenzoate (TMB-8), by excluding calcium from the medium, by the phospholipase A(2) (PLA(2)) inhibitor, quinacrine, and by long-term pretreatment with the phorbol ester, 12-O-tetradecanoylphorbol-13-acetate (TPA). In addition, it was antagonized by the D(2) antagonists, raclopride and (−)-sulpiride–but not by (+)-sulpiride–and absent in sham-transfected CHO cells devoid of D(2) receptors. 3. The results obtained contrast to the previous notion that dopamine and other D(2) receptor agonists require the concomitant administration of calcium-mobilizing agents such as ATP, ionophore A-23187 (calcimycin), thrombin, and TRH, to influence AA release from various cell lines