Monika Hellstrand

Sex steroid-related genes and male-to-female transsexualism.

Transsexualism is characterised by lifelong discomfort with the assigned sex and a strong identification with the opposite sex. The cause of transsexualism is unknown, but it has been suggested that an aberration in the early sexual differentiation of various brain structures may be involved. Animal experiments have revealed that the sexual differentiation of the brain is mainly due to an influence of testosterone, acting both via androgen receptors (ARs) and--after aromatase-catalyzed conversion to estradiol--via estrogen receptors (ERs). The present study examined the possible importance of three polymorphisms and their pairwise interactions for the development of male-to-female transsexualism: a CAG repeat sequence in the first exon of the AR gene, a tetra nucleotide repeat polymorphism in intron 4 of the aromatase gene, and a CA repeat polymorphism in intron 5 of the ERbeta gene. Subjects were 29 Caucasian male-to-female transsexuals and 229 healthy male controls. Transsexuals differed from controls with respect to the mean length of the ERbeta repeat polymorphism, but not with respect to the length of the other two studied polymorphisms. However, binary logistic regression analysis revealed significant partial effects for all three polymorphisms, as well as for the interaction between the AR and aromatase gene polymorphisms, on the risk of developing transsexualism. Given the small number of transsexuals in the study, the results should be interpreted with the utmost caution. Further study of the putative role of these and other sex steroid-related genes for the development of transsexualism may, however, be worthwhile.

Association between a polymorphism of the 5-HT2C receptor and weight loss in teenage girls.

Receptors of the 5-HT2C subtype are assumed to be involved in the influence of serotonin on food intake. A polymorphism in the coding region of the gene for this receptor, resulting in a cysteine to serine substitution, has been reported. Fifty-seven somatically healthy teenage girls displaying weight loss and 91 normal-weight girls of the same age, all recruited by means of a population-based screening study, were compared with respect to this polymorphism. Subjects in the weight loss group displayed a higher frequency of the serine allele than those in the comparison group (23.7% vs. 7.7%, p = .0001). Seventy-two percent of the weight loss girls fulfilled the diagnostic criteria of anorexia nervosa, whereas 28% did not; when these two groups were separately analyzed, both differed significantly from controls with respect to serine allele frequency. The results support the notion that the studied gene may be involved in the regulation of food intake in young women.

Direct dopamine D2-receptor-mediated modulation of arachidonic acid release in transfected CHO cells without the concomitant administration of a Ca2+-mobilizing agent

In CHO cells transfected with the rat dopamine D2 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 (EC50=25 nM). The partial D2 receptor agonist, (−)‐(3‐hydroxyphenyl)‐N‐n‐propylpiperidine [(−)‐3‐PPP], also induced AA release, but with somewhat lower efficacy (maximal effect: 165%; EC50=91 nM). The AA‐releasing effect of dopamine was counteracted by pertussis toxin, by the inhibitor of intracellular Ca2+ release, 8‐(N N‐diethylamino)octyl‐3,4,5‐trimethoxybenzoate (TMB‐8), by excluding calcium from the medium, by the phospholipase A2 (PLA2) inhibitor, quinacrine, and by long‐term pretreatment with the phorbol ester, 12‐O‐tetradecanoylphorbol‐13‐acetate (TPA). In addition, it was antagonized by the D2 antagonists, raclopride and (−)‐sulpiride–but not by (+)‐sulpiride–and absent in sham‐transfected CHO cells devoid of D2 receptors. The results obtained contrast to the previous notion that dopamine and other D2 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.

Inverse agonism at dopamine D2 receptors : Haloperidol-induced prolactin release from GH4C1 cells transfected with the human D2 receptor is antagonized by R(-)-n-propylnorapomorphine, raclopride, and phenoxybenzamine

Our earlier observation that the antipsychotic drug haloperidol in the absence of dopamine increases cAMP formation and prolactin release in two prolactin-producing cell lines expressing rat dopamine D2 receptors (GH3, GH4ZR7), but not in similar cells devoid of D2 receptors (GH4C1), prompted us to suggest that haloperidol may act as an inverse (or negative) agonist, rather than as a neutral antagonist, at the D2 receptor (Nilsson and Eriksson 1993). In the present study it is shown that haloperidol elicits a dose-dependent increase in prolactin release also in prolactin-producing GH4C1 cells transfected with the human dopamine D2 receptor (short isoform) (GH4C1-hD2s); in addition, it is shown that another antipsychotic drug, flupenthixol, also causes prolactin release per se in this cell line. The effect of haloperidol on prolactin release in GH4C1-hD2s is calcium dependent and counteracted by pretreatment either with the D2 receptor agonist R(−)-n-propylnorapomorphine or with a D2 receptor antagonist that does not affect prolactin release per se (raclopride). In addition, pretreatment with the alkylating compound phenoxybenzamine at a concentration causing a marked reduction of D2 receptor density in GH4C1-hD2s cells significantly counteracted haloperidol-induced prolactin release.

The ser9gly SNP in the dopamine D3 receptor causes a shift from cAMP related to PGE2 related signal transduction mechanisms in transfected CHO cells

The dopamine D3 receptor is a member of the D2 family of dopamine receptors. Several investigators have suggested that D3 receptors are involved in the regulation of locomotion,1 in the pathophysiology of schizophrenia,2 and in drug abuse.3 Dopamine enhances basal and stimulus evoked release of arachidonic acid, as well as the production of one of its metabolites, prostaglandin E2 (PGE2), in CHO (Chinese hamster ovary) cells transfected with the D2 receptor.4–6 In contrast, dopamine does not influence basal arachidonic acid release7–9 but inhibits stimulus evoked release in cells transfected with the rat D3 receptor.10 On the other hand, with respect to cAMP production, the effect of dopamine is similar in CHO cells transfected with either D2 or D3 receptors, both receptor subtypes mediating a reduction in forskolin induced cAMP formation.11,12 A single nucleotide polymorphism (SNP) in the first exon of the dopamine D3 receptor gene, the ser9gly polymorphism, leads to a serine to glycine amino acid substitution in the N -terminal extracellular domain of the receptor protein.13 An association between this polymorphism and schizophrenia has been suggested, but also questioned,14,15 a meta-analysis suggesting the effect to be small but real in white subjects.16 Other investigators have suggested that the gly-9 allele may be associated with an increased risk of developing antipsychotic induced tardive dyskinesia rather than with schizophrenia per se17; this finding also gained support from a report containing both pooled analyses of original data and a meta-analysis,18 and also from a recent primate study19 (see also a recent report by Lohmueller and coworkers20). In addition, the ser9gly polymorphism has been reported to be associated with therapeutic response to atypical antipsychotic agents, …

Verified hormone therapy improves episodic memory performance in healthy postmenopausal women.

ABSTRACT Studies of hormone therapy (HT) and cognition have yielded conflicting results. The aim of this observational study was to examine the effect of estradiol, via serum verified HT (estradiol, estriol, progesterone) and endogenous estradiol, on 108 healthy postmenopausal womens cognitive performance. The results demonstrated that the 43 HT-users performed at a significantly higher level than non-users on episodic memory tasks and on a verbal fluency task, whereas HT-users and non-users did not differ on tasks assessing semantic memory and spatial visualization. In addition, there was a positive relationship between serum estradiol level and episodic memory performance, indicating that postmenopausal HT is associated with enhanced episodic memory and verbal fluency, independent of age and education. These observational results suggest that HT use may be sufficient to exert small, yet positive effects on female sensitive cognitive tasks. Hormone therapy compliance and formulation is discussed as confounding factors in previous research.

Phenotypic and genotypic characteristics of women in relation to personality traits.

The associations were examined in women between personality traits and steroid hormones, particularly androgens, as well as polymorphisms in genes regulating androgen concentration and effects. Women, all 42 years of age and premenopausal (n = 270), were recruited randomly. Conventional “masculine” and “feminine” personality traits were examined by questionnaire and set in relation to psychosocial and socioeconomic conditions, behavior in childhood, hormones, risk factors for disease, and polymorphisms in microsatellites in the CYP aromatase and the androgen receptor gene. The proportions of personality traits considered as being dominated by “masculinity” (M) or “femininity” (F) were 44.9%, respectively 15.0%, the rest consisting of a combination of M and F (33.2%) or “undifferentiated” (6.9%). M characteristics were positively associated with education, sporting, self-confidence, and good adaptation to work situation. M scores correlated with reports of “tomboyism” as girls. There was essentially no difference in hormones or disease risk factors between M and F women. The number of (CAG) repeats in the microsatellite of the transactivating domain of the androgen receptor was 19 (2.3; M and SD). M characteristics were more pronounced in the presence of longer repeat stretches (n > 20). No associations were found with F scores. There were no significant associations to the number of tetranucleotide repeats (TTTA) in the fourth introne of the aromatase gene. It was concluded that a majority of women showed M type of personality traits, associated with normal hormones, somatic health, and a long microsatellite in the transactivating domain of the AR gene.

Both dopamine and the putative dopamine D3 receptor antagonist PNU-99194A induce a biphasic inhibition of phorbol ester-stimulated arachidonic acid release from CHO cells transfected with the dopamine D3 receptor.

In Chinese hamster ovary (CHO) cells transfected with the cDNA for the dopamine D3 receptor, low concentrations of dopamine (IC50: 0.5 nM) counteracted the release of arachidonic acid (AA) induced by the protein kinase C activator TPA (maximal inhibition: 15% at 10 - 30 nM). The effect of dopamine -- which was antagonized by pretreatment with pertussis toxin (PTX) or by the dopamine receptor antagonist haloperidol -- was biphasic; thus, at increasing concentrations of dopamine (100 nM - 1 microM), AA levels approached baseline. The preferential dopamine D3 receptor ligand PNU-99194A displayed an effect similar to that of dopamine; thus, whereas low concentrations of PNU-99194A (IC50: 1.9 nM) reduced TPA-induced AA release (maximal inhibition: 15% at 30 - 100 nM), higher concentrations (> or =1 microM) were ineffective. When dopamine and PNU-99194A were administered together at concentrations yielding maximal inhibition of AA release, no additive effect was observed; moreover, a high concentration of dopamine counteracted the AA-reducing effect of a low concentration of PNU-99194A and vice versa. It is suggested that D3 receptors in transfected CHO cells may exert mainly an inhibitory, but also a stimulatory influence on TPA-induced AA release, and that PNU-99194A acts as an agonist in this system.

The intrinsic activity of (−)-3-PPP vis-à-vis prolactin-suppressing dopamine D2 receptors in transfected GH4C1 cells is dependent on which secretagogue that is used to provoke prolactin release

The abilities of dopamine (DA) and the partial DA D2 receptor agonist (-)-(3-hydroxyphenyl)-N-n-propylpiperidine, (-)-3-PPP, to suppress prolactin (PRL) release induced by any of five different PRL secretagogues in GH4C1 cells transfected with the human D2 receptor (short isoform) were investigated. Whereas DA reduced the response to all five secretagogues. (-)-3-PPP reduced the response to vasoactive intestinal peptide (VIP) and thyrotropin-releasing hormone (TRH), but not to high medium potassium (K+) or to the potassium channel antagonist tetraethylammonium (TEA). (-)-3-PPP tended to reduce the PRL release induced by the Ca2+ channel agonist BAY K-8644 (BAY); however, this effect of the partial agonist was modest and not significant. Whereas the effects of both DA and (-)-3-PPP on the PRL response to VIP and TRH were counteracted by co-incubation with the D2 antagonist raclopride, the effects of DA on the PRL response to K+, BAY, and TEA were antagonized by co-incubation with either raclopride or (-)-3-PPP. The results show that, at a given receptor density, the intrinsic activity of a partial D2 agonist with respect to D2-mediated suppression of PRL release may vary from agonism to antagonism depending on which intracellular transduction systems that are being concomitantly activated.