Testosterone as well as estrogen increases serotonin2A receptor mRNA and binding site densities in the male rat brain

Alteration of behavioural phenotype in mice by targeted disruption of the progranulin gene

Sexual differentiation of the brain in rodents is achieved by estrogens, which are converted from androgens in the brain, during the perinatal period. We have identified the progranulin (PGRN) gene as one of the sex steroid-inducible genes that may be involved in masculinization of the rat brain. In the present study, we generated a line of mice with targeted disruption of the PGRN gene, and investigated male sexual behaviour, aggression and anxiety. PGRN-deficient mice exhibited a decrease in ejaculation incidence, while the latency and frequency of both mount and intromission were unchanged. For the aggressive behaviour test, the resident-intruder paradigm was used, and PGRN-deficient mice exhibited enhanced aggressiveness. In wild-type mice, males exhibited lower levels of anxiety than females by the open field test, while male PGRN-deficient mice exhibited an elevated level of anxiety and sex difference in anxiety was not observed. In addition, mRNA expression of the serotonergic receptor 5-HT1A, which could be related to the inhibition of aggression and anxiety, was significantly reduced in the hippocampus of PGRN-deficient mice after aggressive encounters. On the other hand, deficiency of the PGRN gene did not affect serum testosterone concentrations. These results suggest that PGRN gene plays a role in establishing sexual dimorphic behaviours at least partially by modulating the brain serotonergic system.

Influence of sex and estrous cycle on the effects of acute tryptophan depletion induced by a gelatin-based mixture in adult Wistar rats

Women are more vulnerable to develop depression and anxiety disorders than men. This may be related to higher serotonergic vulnerability in women. Serotonergic vulnerability entails that differences between people in the regulation of serotonin (5-HT) determine the vulnerability of an individual to develop depression or other 5-HT-related disorders. The aim of the present experiment was to evaluate whether male and female Wistar rats differ in serotonergic vulnerability. Here, a stronger behavioral response to acute tryptophan (TRP) depletion was assumed to reflect serotonergic vulnerability. Twenty-four male and 48 female rats were repeatedly subjected to treatment with a gelatin-based protein-carbohydrate mixture, either with or without L-tryptophan. Female estrous cycle phase was determined by means of vaginal smears and the females were divided into two groups based on their estrous cycle phase: pro-estrus/estrus and met-estrus/di-estrus. Blood samples showed stronger TRP depletion in males than females. There was no effect of estrous cycle on plasma TRP concentrations. In contrast, treatment effects on some brain TRP concentrations were influenced by estrous cycle phase, females in pro-estrus/estrus showed the strongest response to TRP depletion. In the open field test and home cage emergence test, females in pro-estrus/estrus also showed the strongest behavioral response to acute TRP depletion. In general, females showed more activity than males in anxiety-related situations and this effect appeared to be enhanced by TRP depletion. In the social interaction test, passive body contact in males and females in pro-estrus/estrus was decreased after TRP depletion whereas it was increased in females in the met-estrus/di-estrus phase. Acute TRP depletion affected object recognition, but did not affect behavior in the forced swimming test and a reaction time task. It is concluded that sex and estrous cycle phase can influence the behavioral response to TRP depletion, and that females in pro-estrus/estrus show the strongest behavioral response to acute TRP depletion.

Serotonergic vulnerability and depression: assumptions, experimental evidence and implications

In recent years, the term serotonergic vulnerability (SV) has been used in scientific literature, but so far it has not been explicitly defined. This review article attempts to elucidate the SV concept. SV can be defined as increased sensitivity to natural or experimental alterations of the serotonergic (5-HTergic) system. Several factors that may disrupt the 5-HTergic system and hence contribute to SV are discussed, including genetic factors, female gender, personality characteristics, several types of stress and drug use. It is explained that SV can be demonstrated by means of manipulations of the 5-HTergic system, such as 5-HT challenges or acute tryptophan depletion (ATD). Results of 5-HT challenge studies and ATD studies are discussed in terms of their implications for the concept of SV. A model is proposed in which a combination of various factors that may compromise 5-HT functioning in one person can result in depression or other 5-HT-related pathology. By manipulating 5-HT levels, in particular with ATD, vulnerable subjects may be identified before pathology initiates, providing the opportunity to take preventive action. Although it is not likely that this model applies to all cases of depression, or is able to identify all vulnerable subjects, the strength of the model is that it may enable identification of vulnerable subjects before the 5-HT related pathology occurs.

Sex-/Ovarian Steroid-Dependent Release of Endomorphin 2 from Spinal Cord

Mu-opioid receptor (MOR) agonists have been shown to be more potent analgesics in male than female rodents. Regulation of spinal MOR-coupled antinociception by 17beta-estradiol (estrogen, E2) and progesterone (P) is also sexually dimorphic; pregnancy levels of E2/P activate MOR-coupled analgesic pathways in male but not female rats. We hypothesized that the sexual dimorphic characteristics of MOR-coupled antinociception reflects sexual dimorphism in the regulation of the release from spinal cord of the endogenous MOR agonist, endomorphin 2 (EM2). Parameters of spinal EM2 release manifesting sexual dimorphism include its 1) magnitude: in vitro basal and K+-evoked release of EM2 from spinal tissue of male rats is approximately 50% greater than that observed from spinal cord of females; 2) modulation by ovarian sex steroids: E2/P treatment significantly enhanced K+-evoked EM2 release from spinal tissue of males, but not females; and 3) enhancement by opioid receptor blockade: naloxone enhanced stimulated EM2 release from spinal tissue of both males and females, but it augmented basal release from spinal tissue of only males. Enhancement of EM2 release by naloxone reflects negative coupling of MOR to EM2 release and hence its modulation by negative feedback since only activation of MOR, not kappa-or delta-opioid receptors, was able to inhibit evoked EM2 release. These data reveal that the EM2-MOR spinal analgesic system is more robust and "higher gain" in male versus female rodents. These findings could provide a mechanistic rubric for understanding the male female dichotomy in prevalence and intensity of chronic pain syndromes.

Raloxifene blocks estradiol induction of the serotonin transporter and 5-hydroxytryptamine2A receptor in female rat brain

Sex steroids have potent effects on mood, mental state and cognition. Our previous findings and those of others suggest that these effects may be due at least in part to estradiol actions on central serotonergic mechanisms. Specifically, estradiol-17beta in its acute positive feedback mode for gonadotropin release in the female rat induces expression of the genes for the 5-hydroxytryptamine(2A) receptor (5-HT(2A)R) and the serotonin transporter (SERT) in the dorsal raphe nucleus (DRN). This is accompanied by an increase in the densities of 5-HT(2A)R and the SERT in forebrain regions which in the human are concerned with the control of mood, mental state, cognition and emotion. Here we report that raloxifene, a benzothiophene and selective estrogen receptor modulator (SERM), completely blocked estradiol stimulation of brain 5-HT(2A)R and SERT expression in acutely ovariectomized rats. Raloxifene also blocked the estrogen-induced surge of luteinizing hormone. Treatment of acutely ovariectomized rats with raloxifene alone increased the density of SERT sites in the mid-frontal cortex and decreased the density of 5-HT(2A)R in the posterior olfactory tubercle. The inhibitory effects of raloxifene on acute estrogen-induction of central serotonergic mechanisms were similar to those of tamoxifen even though there are major differences between the two SERMs in their affinity for the two estrogen receptor subtypes and their actions on the uterus. These findings provide robust evidence that estradiol induction of the 5-HT(2A)R and the SERT in brain is mediated by nuclear estrogen receptors. Our data may provide the basis for obtaining a better understanding of the effects of sex steroids on mood and mental state in the human and the possible rational development of congeners of sex steroids for the treatment of mental disorders.

Serotonin genes and attention deficit/hyperactivity disorder in a Brazilian sample: preferential transmission of the HTR2A 452His allele to affected boys

Attention-deficit hyperactivity disorder (ADHD) is one of the most common psychiatric disorders of childhood. The role of genetic factors in its etiology is strongly supported by family, adoption, and twin studies. Low serotonin activity has been associated in both animal and human studies with measures of impulsivity, aggression, and disinhibited behaviors, which make genes from the serotonin system reasonable candidates for ADHD susceptibility. In the present study, we investigated a polymorphism in the promoter region of the serotonin transporter (SLC6A4) and two polymorphisms (-1438 A > G and His452Tyr) in the serotonin 5-HTR2A receptor gene using family based association analyses in a sample of 243 Brazilian ADHD children and adolescents and their parents. No linkage disequilibrium between the two HTR2A polymorphisms was detected in this sample (P = 0.76). Considering several evidences from animal models for sexual dimorphism in serotonin genes expression, analyses were performed separately for the whole sample and for male probands. No evidences for biased transmissions of both HTR2A -1438 A > G and SLC6A4 polymorphisms to ADHD youths were observed. Preferential transmission of the HTR2A His452 allele was observed only in families with affected boys (P = 0.04). Our results suggest that findings from ADHD association studies for serotonin genes might be understood in the context of a gender effect, which may help to explain conflicting results in these association studies.

Total testosterone, androgen receptor polymorphism, and depressive symptoms in young black and white men: the CARDIA Male Hormone Study

Androgen receptor (AR) CAG repeat length (RL) might modify the relationship between endogenous testosterone (T) and depressive symptoms in men on average over age 50 years. We hypothesized that CAG RL modifies the association between T and depressive symptoms in 525 black and 721 white men under age 40 years participating in the CARDIA Male Hormone Study. We assessed cross-sectional associations of quartiles of total and bioavailable T and tertiles of CAG RL with depressive symptoms, defined as Center for Epidemiologic Studies Depression Scale (CES-D) score > or=16, in 1995-1996. The interaction of CAG RL and total T on depressive symptoms was statistically significant for blacks, whites, and both groups combined. In the combined analysis, the odds ratios (OR) (95% confidence intervals (CI)) across the quartiles of total T were 1.00, 0.17 (95% CI=0.07-0.43), 0.31 (95% CI=0.14-0.70), and 0.49 (95% CI=0.22-1.09) for the shortest RL group. The interaction of CAG RL and bioavailable T on depressive symptoms was statistically significant for black men only, and nonsignificant in a combined analysis. For black men in the shortest RL group, the ORs for the quartiles of bioavailable T were 1.00, 0.41 (95% CI=0.16-1.05), 0.10 (95% CI=0.03-0.38), and 0.35 (95% CI=0.14-0.90). In other CAG groups, there were no relationships of total or bioavailable T with depressive symptoms. CAG RL might modify the association between endogenous total and bioavailable T and depressive symptoms in younger black men. Clinical trials assessing the effects of T replacement therapy on depressive symptoms in hypogonadal men should consider including CAG RL in their design and/or analysis.

Puberty, hormones, and sex differences in alcohol abuse and dependence

Sex differences in patterns of drinking and rates of alcohol abuse and dependence begin to emerge during the transition from late puberty to young adulthood. Increases in pubertal hormones, including gonadal and stress hormones, are a prominent developmental feature of adolescence and could contribute to the progression of sex differences in alcohol drinking patterns during puberty. This paper reviews experimental and correlational studies of gonadal and stress-related hormone changes and their effects on alcohol drinking and other associated actions of alcohol. Mechanisms are suggested by which reproductive hormones and stress-related hormones may modulate neural circuits within the brain reward system to produce sex differences in alcohol drinking patterns and vulnerability to alcohol abuse and dependence which become apparent during the late pubertal period.

Effects of the 5-HT2A antagonist mirtazapine in rat models of thermoregulation

Thermoregulation is a complex intercommunicative function requiring coordination between core body temperature (CBT), the central nervous system, and peripheral vasculature. In menopausal women, dysregulation of thermoregulatory mechanisms leads to hot flushes and night sweats. A previous study in ovariectomized (OVX) rats has suggested that mirtazapine can alleviate thermoregulatory dysfunction by blocking 5-HT(2A) receptor signaling. This is in opposition to other work in which 5-HT(2A) receptor blockade appeared to exacerbate thermoregulatory dysfunction in OVX rats. Thus, the goals of the present study were to reexamine the effects of mirtazapine on temperature regulation in OVX rat models and explore further the role of 5-HT(2A) receptor blockade. Mirtazapine exhibited potent functional antagonism (EC(50)=0.62 nM) at the cloned human 5-HT(2A) receptor. In the morphine-dependent model of thermoregulatory dysfunction, mirtazapine (10 mg/kg, i.p.) induced an increase in tail-skin temperature (TST) prior to naloxone administration. In the telemetry model, mirtazapine (0.3-3 mg/kg, i.p.) caused an increase in TST. However, at the highest dose tested (10 mg/kg, i.p.), mirtazapine induced a small but significant decrease in TST followed by an increase in TST. To examine this finding further, mirtazapine's effect on CBT was determined. Administration of mirtazapine (1-3 mg/kg, i.p.) resulted in a slight decrease in CBT but at the 10 mg/kg dose a dramatic decrease (-3.6 degrees C) in CBT was observed. These data support the concept that 5-HT(2A) receptors play a role in temperature regulation but that functional blockade of these receptors by mirtazapine is not a likely mechanism for restoring thermoregulatory processes in OVX rats.

Aging of Brain: Role of Estrogen

The brain undergoes many structural and functional changes during aging. Some of these changes are regulated by estrogens which act mainly through their intracellular receptors, estrogen receptor ERalpha and ERbeta. The expression of these receptors is regulated by several factors including their own ligand estrogen, and others such as growth hormone and thyroid hormone. The levels of these factors decrease during aging which in turn influence estrogen signaling leading to alterations in brain functions. In the present paper, we review the effects of aging on brain structure and function, and estrogen action and signaling during brain aging. The findings suggest key role of estrogen in the maintenance of brain functions during aging.

Expression of the transcriptional coactivator CITED1 in the adult and developing murine brain

The transcription coactivator CITED1 is an important mediator of transcriptional events regulated by estrogen or TGF-beta. We used in situ hybridization to delineate the distribution of CITED1 mRNA in the adult and developing murine brain and found robust CITED1 expression in ventral hypothalamus and midbrain raphe. The distribution of CITED1 in these regions overlapped the reported expression of estrogen receptors alpha and beta. Less intense expression of CITED1 was also evident in medial preoptic area, subfornical organ, thalamus and cerebral cortex. CITED1 mRNA in the arcuate nucleus (an area of active transcriptional modulation by TGF-beta) was evident in postmigratory neurons as early as embryonic day 16. Expression of CITED1 in arcuate continued throughout postnatal development. CITED1 in developing cerebellum was first evident in external granule cells and was transiently expressed in the Purkinje cell/granule cell layer in a temporal pattern similar to estrogen receptor-beta. The spatial and temporal distribution of CITED1 mRNA reported here is consistent with a role for CITED1 in the modulation of transcriptional events mediated by steroid hormone and cytokine signaling pathways.

Factors producing a menopausal depressive-like state in mice following ovariectomy

RATIONALE

Bilateral ovariectomy in female mice produces a menopausal depressive-like state but the factors responsible for the phenomenon are unknown.

OBJECTIVES

We elucidated methodological issues related to establishing this mouse model and investigated a possible mechanism underlying the depressive-like state of ovariectomized mice.

METHODS

We removed both ovaries of female ICR mice at 9 weeks of age. Changes in the immobility time during the forced swimming test as a function of the time interval between ovariectomy and behavioral testing were determined on nine different days after surgery. To assess behavioral specificity, the elevated plus-maze (EPM) behavior and spontaneous activity were measured. With respect to the effect of ovariectomy on the immobility time, we compared ICR mice with three other strains of mice (C57BL/6J, DBA/2N, and CD-1). Finally, we investigated the effects of (-)-2,5-dimethoxy-4-iodoamphetamine (DOI) and (+/-)-8-hydroxy-2-(N,N-di-n-propylamino) tetralin (8-OH-DPAT) on the immobility time of ovariectomized mice.

RESULTS

A significant effect on the prolongation of immobility was observed between 12 and 18 days after ovariectomy. Ovariectomy did not alter either the EPM behavior or spontaneous activity. Of the four strains of mice, only DBA mice did not show any significant prolongation of immobility after ovariectomy. Acute or chronic treatment with DOI (0.5 or 1.0 mg kg(-1)) significantly prevented the prolongation of immobility time, whereas acute and chronic treatments with 8-OH-DPAT (0.05, 0.5, or 1.0 mg kg(-1)) were ineffective.

CONCLUSION

The present findings have potentially important implications for evaluating a candidate substance for the management of mood disorders in menopausal women.

Androgen deprivation impairs memory in older men

Androgen deprivation leads to a profound loss of synaptic density in the hippocampus and changes in learning and memory in animal models. The authors examined group differences in verbal memory between men on androgen deprivation therapy (ADT), a commonly used treatment for prostate cancer, and healthy men. The authors found that men on ADT have a specific impairment of retention but normal encoding and retrieval processes on a word list-learning task. Speed and accuracy for both perceptual and semantic encoding, as well as retrieval at a very short retention interval, were not affected; however, recognition fell to chance after a 2-min retention interval in men on ADT. Healthy men showed only moderate forgetting, and performance was still above chance at 12 min. This pattern of preserved encoding and retrieval but impaired retention suggests that androgens play a role in hippocampally mediated memory processes, possibly having a specific affect on consolidation.

Gonadal and Adrenal Abnormalities in Drug Users: Cause or Consequence of Drug Use Behavior and Poor Health Outcomes

Opiates and cocaine both have effects on adrenal and gonadal function. Opiates suppress the hypothalamic-pituitary adrenal (HPA) axis, whereas cocaine leads to HPA activation. Opiates also cause gonadal dysfunction in both men and women. During withdrawal from opiates and cocaine, the HPA axis is activated which may reinforce relapse behavior. This review describes these hormonal effects and explores the potential consequences, including the effects on mood cognition and cardiovascular risk. Modification of the drug-induced hormonal dysfunction may represent a treatment strategy for drug rehabilitation.

Regulation of sexual behaviour in male macaques by sex steroid modulation of the serotonergic system

The view that androgen action is the primary impetus underlying male-typical behaviour has been irrevocably altered by the profound perturbations in social and sexual behaviour observed in recent models of oestrogen insufficiency in male mice. Evidence is also accumulating for an involvement of oestrogens in the modulation of neural systems that are thought to play important roles in male reproductive functioning. Specifically, the serotonergic system is implicated in diverse autonomic functions, most or all of which are sensitive to oestradiol as well. Although their interaction domains have yet to be examined in male primates, roles have been established for both oestrogen and serotonin in the regulation of male sexual behaviour. We used a blinded, sham-treated and self-controlled, randomized, multitreatment cross-over design to test the hypothesis that male sexual behaviour is regulated by oestrogen modulation of the serotonergic system in intact male Japanese macaques. Regression analysis revealed that oestradiol and whole blood tryptophan, but not testosterone or 5alpha-dihydrotestosterone, had additive, independent effects on male potentia over a range of hormone concentrations, whereas androgens were confirmed to be the primary determinants of sexual motivation. We suggest that modulation of the serotonergic system by 'female hormones' may be fundamental to the regulation of male mating success in higher primates. This might also explain, at least in part, why significant correlations between steroid hormones and male copulatory behaviour have traditionally proven so elusive in this order, thereby warranting a re-evaluation of the current notion that male sexual behaviour has been emancipated from activational hormonal control in higher primates.

5-Hydroxytryptamine2C receptors on pudendal motoneurons innervating the external anal sphincter

The aim of this study was to determine the localization of 5-hydroxytryptamine2C (5-HT2C) receptors on the motoneurons innervating the external anal sphincter (EAS) of male rats. Motoneurons were retrogradely labeled after percutaneous intramuscular injection of Fluorogold (FG) into the EAS. Using fluorescent immunohistochemistry, FG-positive EAS motoneurons that were immunoreactive for the 5-HT2C receptor (5-HT2C-IR) were targeted for specific examination with widefield microscopy or confocal laser scanning microscopy with spectral separation. Widefield microscopy revealed distributions of FG-positive EAS motoneurons in the L5-S1 gray matter corresponding to the dorsomedial cell group. 5-HT2C-IR positive cells were distributed in the intermediolateral cell column and the ventral horn. Ventral horn 5-HT2C-IR labeling included the dorsomedial cell group as well as the dorsolateral, ventromedial and ventrolateral areas. Confocal analysis of FG-positive EAS motoneurons and 5-HT2C-IR positive motoneuron profiles adjacent to EAS motoneurons that were not labeled with FG but presumably innervate the bulbospongiosus muscle confirmed that EAS motoneurons were immunopositive for the 5-HT2C receptor. These data suggest that previously identified descending serotonergic immunopositive fibers observed terminating on EAS motoneurons might mediate their input through the activation of 5-HT2C receptors.

Neuroactive steroid effects on cognitive functions with a focus on the serotonin and GABA systems

This article will review neuroactive steroid effects on serotonin and GABA systems, along with the subsequent effects on cognitive functions. Neurosteroids (such as estrogen, progesterone, and allopregnanolone) are synthesized in the central and peripheral nervous system, in addition to other tissues. They are involved in the regulation of mood and memory, in premenstrual syndrome, and mood changes related to hormone replacement therapy, as well as postnatal and major depression, anxiety disorders, and Alzheimer's disease. Estrogen and progesterone have their respective hormone receptors, whereas allopregnanolone acts via the GABA(A) receptor. The action of estrogen and progesterone can be direct genomic, indirect genomic, or non-genomic, also influencing several neurotransmitter systems, such as the serotonin and GABA systems. Estrogen alone, or in combination with antidepressant drugs affecting the serotonin system, has been related to improved mood and well being. In contrast, progesterone can have negative effects on mood and memory. Estrogen alone, or in combination with progesterone, affects the brain serotonin system differently in different parts of the brain, which can at least partly explain the opposite effects on mood of those hormones. Many of the progesterone effects in the brain are mediated by its metabolite allopregnanolone. Allopregnanolone, by changing GABA(A) receptor expression or sensitivity, is involved in premenstrual mood changes; and it also induces cognitive deficits, such as spatial-learning impairment. We have shown that the 3beta-hydroxypregnane steroid UC1011 can inhibit allopregnanolone-induced learning impairment and chloride uptake potentiation in vitro and in vivo. It would be important to find a substance that antagonizes allopregnanolone-induced adverse effects.

Molecular endocrinology and physiology of the aging central nervous system

Aging is associated with a progressive decline in physical and cognitive functions. The impact of age-dependent endocrine changes regulated by the central nervous system on the dynamics of neuronal behavior, neurodegeneration, cognition, biological rhythms, sexual behavior, and metabolism are reviewed. We also briefly review how functional deficits associated with increases in glucocorticoids and cytokines and declining production of sex steroids, GH, and IGF are likely exacerbated by age-dependent molecular misreading and alterations in components of signal transduction pathways and transcription factors.

Oestrogen and testosterone modulate the firing activity of dorsal raphe nucleus serotonergic neurones in both male and female rats

Women are twice as likely to suffer from mood disorders than men. Moreover, a growing body of evidence suggests a reciprocal modulation between sex steroids and the serotonin (5-HT) system. A previous study from our laboratory has shown that the progesterone metabolites 5beta-pregnane-3,20-dione (5beta-DHP) and 5alpha-pregnan-3alpha-ol,20-one (3alpha,5alpha-THP), as well as dehydroepiandrosterone (DHEA), increase the firing activity of dorsal raphe nucleus (DRN) 5-HT neurones in female rats. The present study was undertaken to assess the effects of these steroids in male rats, as well as the effects of testosterone and 17beta-oestradiol (17beta-E) in both sexes, and finally to evaluate gender differences in the modulation of the 5-HT neuronal firing activity by these different neuroactive steroids. Male rats were treated i.c.v., for 7 days, with a dose of 50 microg/kg/day of one of the following steroids: progesterone, 5beta-DHP, 3alpha,5alpha-THP, DHEA, testosterone, 17beta-hydroxy-5alpha-androstan-3-one (5alpha-DHT) and 17beta-E. Some rats also received a 3-day administration of testosterone (50 microg/kg/day, i.c.v). Females were treated in the same fashion with testosterone and 17beta-E. Extracellular unitary recordings of 5-HT neurones, obtained in vivo in the DRN of these rats, revealed that testosterone and 17beta-E increased the firing activity of 5-HT neurones in both males and females. In males, the effect of testosterone could already be seen after 3 days of treatment. Neither castration nor any treatment with other steroids significantly modified the firing rate of male 5-HT neurones. Taken together with previous findings, the results of the present study indicate both similarities and differences between sexes in the modulation of 5-HT neurones by some steroids. This could prove important in understanding gender differences in mood disorders.

Serotonin 2A receptors modulate tail-skin temperature in two rodent models of estrogen deficiency-related thermoregulatory dysfunction

Menopause-associated thermoregulatory dysfunction, including hot flushes and night sweats, is effectively treated by hormonal therapies that include estrogens. Evidence suggests that estrogen regulates serotonin 2A (5-HT(2A)) receptor expression and that 5-HT(2A) receptors are involved in thermoregulation. Therefore, the role of 5-HT(2A) receptors in thermoregulation was assessed in two rat models of ovariectomy-induced thermoregulatory dysfunction. The first model is based on measurement of the tail-skin temperature (TST) increase following naloxone-induced withdrawal in morphine-dependent ovariectomized (OVX) rats (MD model), while the second model relies on telemetric assessment of diurnal TST changes in ovariectomized rats (telemetry model). Treatment with a 5-HT(2A/2C) receptor agonist, (-)-2,5-dimethoxy-4-iodoamphetamine hydrochloride (DOI), prevented the naloxone-induced TST increase in the MD model and restored normal active-phase TST in the telemetry model. The selective 5-HT(2A) receptor antagonist, MDL-100907, had no effect on the naloxone-induced flush when administered alone in the MD model, but it decreased DOI's ability to abate the flush. In the telemetry model, MDL-100907 attenuated the DOI-induced decrease in active-phase TST. Interestingly, MDL-100907 increased TST in both models when given alone, with the TST increase occurring prior to the naloxone-induced flush in the MD model. To evaluate the role of central nervous system (CNS) 5-HT(2A) receptors in TST regulation, DOI was administered in combination with a known peripheral 5-HT(2A/2C) receptor antagonist, xylamidine, in the MD model. Xylamidine had no effect on DOI's ability to abate the naloxone-induced flush. These results indicate that activation of central 5-HT(2A) receptors restores temperature regulation in two rodent models of ovariectomy-induced thermoregulatory dysfunction.

The relationship of sex hormones and cortisol with cognitive functioning in Schizophrenia

Gonadal as well as stress hormones have recently been implicated in pathophysiology and sex differences in onset, prognosis and treatment of schizophrenia. The present study investigated the effects of serum levels of oestrogen, progesterone, testosterone and cortisol on neuropsychological functioning and psychopathology in a group of 37 patients (17 women, 20 men) with schizophrenia. Neuropsychological measures included tests of attention, verbal abilities, language, memory, executive functioning, motor and speed of information processing. The results showed that oestrogen and age was associated with low positive symptom scores, and within gender, cortisol predicted poor performance on the information processing domain in men. These findings demonstrate that cortisol, in addition to the commonly reported effects of oestrogen, influences neuropsychological functioning in schizophrenia with differential effects on specific domains of cognitive functioning and underscore the need for further investigation of the modulating role of hormones on neuropsychological functioning in schizophrenia.

Expression of estrogen receptors (alpha, beta) and androgen receptor in serotonin neurons of the rat and mouse dorsal raphe nuclei; sex and species differences

Sex steroids have been inferred to be involved in the regulation of affective status at least partly through the serotonergic (5-HT) system, particularly in the dorsal raphe nucleus (DRN), which innervates enormous projections to the cerebral cortex and limbic system. In the present study, the expression of estrogen receptors-alpha and -beta (ERalpha, ERbeta), androgen receptor (AR) and 5-HT was examined immunohistochemically in the rat and mouse DRN in both sexes. The results showed that large numbers of ERalpha- and/or ERbeta-immunoreactive (ERalpha-I, ERbeta-I) cells were found in the DRN of both male and female mice, whereas only small numbers of ERalpha-I cells and no ERbeta-I cells were seen in the rat DRN of each sex. With respect to AR-immunoreactive (AR-I) cells, moderate numbers of such cells were present only in male rats and mice, and no or very few could be observed in female ones. The ERalpha-I, ERbeta-I, and AR-I cells were mainly distributed in the rostral DRN. In double-immunostaining, many 5-HT-I neurons were found to show ERalpha and/or ERbeta expression specifically in the rostral DRN (particularly dorsal, ventral and interfascicular parts) of mice of both sexes, but not in that of rats. In contrast, only a few 5-HT neurons were observed to show AR expression in the DRN of both rodents. The current results strongly suggest that sex steroids can modulate the affective regulation of the serotonergic system through ERalpha and/or ERbeta in 5-HT neurons of the mouse rostral DRN (but not so much through AR), and that such effects might be different depending on the sex and species, as shown by the prominent sex differences in AR expression and prominent species differences in ERalpha and ERbeta expression.

Androgens, ApoE, and Alzheimer's Disease

Increasing evidence indicates that there are reductions in estrogen and androgen levels in aged men and women. These hormonal reductions might be risk factors for cognitive impairments and the development of Alzheimer's disease (AD). Aged people show improved cognition after treatments with sex steroids. Therefore, ongoing clinical AD trials have been designed to evaluate the potential benefits of estrogen therapy in women and testosterone therapy in men. Apolipoprotein E (apoE) plays an important role in the metabolism and redistribution of lipoproteins and cholesterol. The three major human apoE isoforms, apoE2, apoE3, and apoE4, differ in their effects on AD risk and pathology. Here I review various mechanisms proposed to mediate the differential effects of apoE isoforms on brain function and highlight the potential contribution of detrimental isoform-dependent effects of apoE on androgen- and androgen receptor (AR)-mediated pathways. I also discuss potential interactions of androgens with other AD-related factors.

Diurnal rhythms of free estradiol and cortisol during the normal menstrual cycle in women with major depression

To investigate whether depression is accompanied by changes in diurnal rhythms of free estradiol and cortisol in different phases of the menstrual cycle, we measured these two hormone levels in saliva samples collected every 2 h for 24 h from 15 healthy normally cycling women and 12 age-matched normally cycling women suffering from major depression taking antidepressants. The assessments were repeated four times over one menstrual cycle: during menstruation and in the late follicular/peri-ovulating, early to mid-luteal and late luteal phases, respectively. Quantification with a nonlinear periodic regression model revealed distinct diurnal rhythms in free estradiol and free cortisol in all subjects. For the diurnal cortisol rhythm, significant differences were found in the peak-width and ultradian amplitude among different menstrual phases, both in controls and depressed patients, while no significant differences were found between the two groups. The diurnal estradiol rhythm, on the other hand, was quite consistent among different menstrual phases within both groups, while the depressed patients had overall larger amplitudes than controls, which is negatively correlated with disease duration. Significant positive correlations between the two hormone rhythms were found for 24-h mean level (mesor), peak, and trough in late luteal phase, and for ultradian harmonics in early to mid-luteal phase in controls, but only for ultradian harmonics in late follicular/peri-ovulating phase and for acrophase in the menstruation phase in depressed patients. A sub-analysis was also performed in patients who received Fluoxetine (n = 7). The findings implicate a close correlation between the hypothalamic-pituitary-adrenal axis and the hypothalamic-pituitary-gonadal axis, both of which may be involved in depression.

Management of the negative symptoms of schizophrenia: new treatment options

This article presents a systematic review of pharmacological treatment for negative symptoms of schizophrenia, based on MEDLINE searches from 1995 to September 2002 to identify pertinent clinical trials. The pharmacotherapy of negative symptoms in schizophrenia includes novel/atypical antipsychotics and classical antipsychotics, as well as antidepressants, glutamatergic compounds, antiepileptic drugs and estrogens. In the assessment of therapy for negative symptoms of schizophrenia, it is imperative that better studies of sound methodology are performed. In such studies, some important aspects to be considered include an accurate definition and assessment of negative symptoms (including well designed, valid and reliable rating scales), the differentiation between primary and secondary negative symptoms, an appropriate selection of standard comparators, adequate dosages of comparators (e.g. haloperidol dosages) and an overall optimal study design. Most of the available studies on treating negative symptoms in schizophrenia have focused on the atypical antipsychotics, while other potential candidates, mostly in the context of add-on therapy, have not been so intensively investigated. Atypical antipsychotics have been proven in placebo-controlled trials to be effective in treating negative symptoms of acute schizophrenic episodes. In many of the comparator studies, they showed efficacy in treating negative symptoms that was superior to that of typical antipsychotics. Data on stable, predominant negative symptoms in subchronic or chronic cases of schizophrenia, although limited, have demonstrated the efficacy of atypical antipsychotics. If the beneficial tolerability profile with respect to extrapyramidal symptoms is also taken into account during clinical decision making, the atypical antipsychotics should be preferred for the treatment of negative symptoms. It is also worth noting that the traditional antipsychotics have the risk of inducing negative symptoms in the context of akinesia. The benefits of add-on therapy with SSRIs or a glutamatergic compound are well documented. Estrogen add-on therapy seems promising. Other traditionally suggested approaches, such as comedication with an antiepileptic drug, lithium or beta-adrenoceptor antagonist, cannot generally be recommended on the basis of the available data.

Interaction of nitric oxide and serotonin in aggressive behavior

Nitric oxide (NO) modulates many behavioral and neuroendocrine responses. Genetic or pharmacological inhibition of the synthetic enzyme that produces NO in neurons evokes elevated and sustained aggression in male mice. Recently, the excessive aggressive and impulsive traits of neuronal NO synthase knockout (nNOS-/-) mice were shown to be caused by reductions in serotonin (5-HT) turnover and deficient 5-HT1A and 5-HT1B receptor function in brain regions regulating emotion. The consistently high levels of aggression observed in nNOS-/- mice could be reversed by 5-HT precursors and by treatment with specific 5-HT1A and 5-HT1B receptor agonists. The expression of the aggressive phenotype of nNOS-/- knockout mice requires isolated housing prior to testing. The effects of social factors such as housing condition and maternal care can affect 5-HT and aggression, but the interaction among extrinsic factors, 5-HT, NO, and aggression remains unspecified. Taken together, NO appears to play an important role in normal brain 5-HT function and may have significant implications for the treatment of psychiatric disorders characterized by aggressive and impulsive behaviors.

Cognitive changes associated with supplementation of testosterone or dihydrotestosterone in mildly hypogonadal men: a preliminary report

This study prospectively examined changes in cognition in hypogonadal men given testosterone (T) or older hypogonadal men given dihydrotestosterone (DHT) gel. A battery of cognitive tests assessing verbal and spatial memory, language, and attention was administered at baseline (prior to medication) and again at days 90 and 180 of treatment for men receiving T gel and at baseline and days 30 and 90 of treatment for men receiving DHT gel. For men receiving T gel, circulating total T and estradiol (E(2)) were significantly raised compared with baseline, and a significant improvement in verbal memory was observed. For men receiving DHT gel, serum DHT levels increased and T levels decreased significantly compared with baseline, and a significant improvement in spatial memory was observed. The results suggest that beneficial changes in cognition can occur in hypogonadal men using T replacement levels and DHT treatment, and these changes in cognition can be reliably measured during a relative steady-state dose level. Further, our results suggest that aromatization of T to E(2) may regulate verbal memory in men, whereas nonaromatizable androgens may regulate spatial memory.

Influence of estradiol, stress, and 5-HT2A agonist treatment on brain-derived neurotrophic factor expression in female rats

BACKGROUND

Estradiol affects neuronal plasticity, mood, and cognition. We examined the effects of the estrous cycle, acute and chronic estradiol treatments on BDNF mRNA expression in the hippocampus and cortex of female rats. The roles of 5-HT2A receptors and of stress on the BDNF mRNA regulation were also explored.

METHODS

BDNF mRNA levels were measured using in situ hybridization at proestrus and estrus, and following acute and chronic estradiol treatment of acutely and chronically ovariectomized (OVX) female rats. Some rats were pretreated with 5-HT2A agonist and antagonist, and another group was subjected to two-hour immobilization stress.

RESULTS

BDNF mRNA levels in the dentate gyrus and the medial prefrontal cortex were decreased during estrus, when estradiol levels are highest. Acute estradiol treatment decreased hippocampal BDNF mRNA in acutely OVX rats, but neither acute nor chronic estradiol had effect in chronically OVX rats. Estradiol pretreatment reduced the 5-HT2A receptor-mediated cortical upregulation in BDNF mRNA and did not effect the stress-induced down-regulation of BDNF mRNA in the dentate gyrus.

CONCLUSIONS

The duration of the estradiol treatment and the duration of the ovarian hormone deprivation are important factors in the regulation of BDNF synthesis and possibly in the functional outcome of estrogen treatment.

Effects of estrogen on brain development and neuroprotection--implications for negative symptoms in schizophrenia

Increasing evidence during the last few years suggests that there are gender-specific differences in schizophrenia, influencing the age of onset, treatment outcome and the prevalence of negative symptoms. With respect to the latter in postmortem brain and cerebrospinal fluid of schizophrenic patients with negative symptoms a reduction of dopaminergic activity became evident. Measures of noradrenergic activity, dopamine beta-hydroxylase and the metabolite MHPG, appear to decrease with brain atrophy seen in patients with negative symptoms. Serotonergic activity tends to be low in patients with impaired cognitive function as is seen in negative schizophrenia. In these patients ventricular enlargement is associated with the severity of negative symptoms, low monoamine activity and low cerebral glucose metabolism. On the other hand atypical antipsychotic drugs that modulate also glutamate receptor activity, suggest an additional alternative mechanism of antipsychotic action beyond aminergic neurotransmitters. These drugs improve glutamatergic transmission and decrease negative symptoms; this suggests a glutamatergic deficiency as an extension of the dopamine model. The glutamate-dopamine interaction illustrates the importance of cross-talk between projections to the cortex, striatum, and lower brainstem for the expression of negative symptomatology. On the other hand, estradiol-17beta the most potent female sex hormone influences not only primary and secondary sexual characteristics but also embryonal and fetal growth as well as development of the brain aminergic networks, which are involved in schizophrenia. Estradiol-l7beta possesses neuroprotective properties, which are relevant for the course of schizophrenia and this may explain the pronounced gender differences with respect to progression and therapeutic response of schizophrenia. The present review attempts an update and synthesis of the information about the hormonal influence on neuronal pathways in negative symptoms of schizophrenia. It shows that estradiol-l7beta influences transporters and receptors as well as the morphological appearance of neuronal systems and that it may be an integral part of the neuroprotective system ameliorating schizophrenia.

Association study of oestrogen receptor alpha gene polymorphism and suicidal behaviours in major depressive disorder

OBJECTIVE

Gender comparison in epidemiological studies has consistently demonstrated a greater prevalence for major depressive disorders (MDD) in females. Several lines of evidence have implicated oestrogen pathways in this gender difference. Furthermore, there is evidence that attempted suicides are more frequent in women. A population-based association study was used to test the hypothesis that the genetic variants ( II and I polymorphisms) of the oestrogen receptor alpha gene (ER-alpha) confer susceptibility to MDD.

METHODS

The ER-alpha was genotyped for 154 patients with MDD and 226 controls in a Chinese population.

RESULTS

Statistical analysis showed a significant difference in the II genotype and allele frequencies between the female MDD patients and the female controls ( P=0.010 and P=0.004, respectively). However, no significant differences in ER-alpha genotype or allele frequencies were found between male MDD patients and male controls. Furthermore, the ER-alpha genotypes were not associated with suicide-attempt history for MDD cases.

CONCLUSIONS

Our results suggest that the ER-alpha may play a role in the susceptibility of MDD in females.

Testosterone and child and adolescent adjustment: the moderating role of parent-child relationships

In a sample of established middle- and working-class families with normally developing children and adolescents ranging in age from 6 to 18 years, sons' and daughters' testosterone levels showed little direct connection to risk behavior or symptoms of depression. In contrast, testosterone's positive relation with risk behavior and negative relation with depression were conditional on the quality of parent-child relations. As parent-child relationship quality increased, testosterone-related adjustment problems were less evident. When relationship quality decreased, testosterone-linked risk-taking behavior and symptoms of depression were more in evidence. Few relations were found between parents' testosterone and child behavior. Boys' and girls' ages and stages of pubertal development were important for understanding the expression of hormone-related problem behavior in some cases but not in others.

Lack of effect of testosterone and dihydrotestosterone compared to 17beta-oestradiol in 1-methyl-4-phenyl-1,2,3,6, tetrahydropyridine-mice

Previous work from our laboratory has demonstrated prevention of 1-methyl-4-phenyl-1,2,3,6, tetrahydropyridine (MPTP)-induced striatal dopamine depletion in C57Bl/6 mice by 17beta-oestradiol, progesterone and raloxifene. The activity of androgenic compounds in MPTP mice has received less attention and was the object of the present investigation. The effects of 17beta-oestradiol (2 microg/day), testosterone (100 microg/day) and dihydrotestosterone (DHT) (2 microg/day or 100 microg/day) were studied during 5 days before and after an acute treatment of four MPTP (10 mg/kg) injections in male C57Bl/6 mice. Striatal concentrations of dopamine and its metabolites dihydroxyphenylacetic acid and homovanillic acid were measured by high-performance liquid chromatography. MPTP mice treated with saline showed large decreases in dopamine and its metabolites compared to control mice. 17beta-oestradiol partially spared this decrease whereas testosterone and DHT did not. Striatal specific binding to the dopamine transporter (DAT) and to the vesicular monoamine transporter (VMAT2) were measured using [125I] RTI-121 and [3H] dihydrotetrabenazine autoradiography, respectively. As with striatal dopamine concentrations, MPTP treatment caused a decrease in DAT and VMAT2 specific binding. 17beta-oestradiol partially spared this decrease, whereas androgens did not. In the substantia nigra, DAT mRNA was measured by in situ hybridization. MPTP treatment induced a significant, but smaller decrease in substantia nigra DAT mRNA than striatal DAT protein. In addition, 17beta-oestradiol completely prevented the MPTP-induced decrease of DAT mRNA, whereas androgens did not. The present results show that androgens are unable to protect against MPTP-induced dopaminergic toxicity.

5HT and 5HIAA dialysate levels within the arcuate nucleus of the hypothalamus: relationship with photoperiod-driven differences in serum prolactin and luteinizing hormone in the Siberian hamster

This study examined the relationship between dialysate levels of serotonin (5HT), and its major metabolite 5HIIAA within the arcuate nucleus of the hypothalamus (ARC) and serum gonadotropin levels under two different in vivo paradigms. Experiment 1 evaluated the relationship between dialysate levels of 5HT and 5HIAA within the ARC and circulating prolactin (PRL) and lutenizing hormone (LH) levels under long- and short-day photoperiod conditions. In experiment 2, the profile of 5HT and 5HIAA dialysate levels within the ARC on the afternoon of proestrous was investigated to determine if changes in serotonergic neurotransmission are correlated with preovulatory surges in LH and PRL. Adult male and female Siberian hamsters were housed either in long-day (16L:8D) or short-day (10L:14D) photoperiods for 8 weeks. Dialysis samples were collected every hour for 5 h (12.00-17.00 h) and blood samples were collected via a jugular cannula every hour for analysis of LH and PRL levels. ARC 5HT and 5HIAA dialysate levels were significantly higher in short-day exposed female hamsters, correlating with suppressed basal LH and PRL secretion when compared to their long-day counterparts. Short-day housed male hamsters displayed significantly higher dialysate levels of 5HIAA than males exposed to a long-day photoperiod-5HT was below the lower limit of detection regardless of photoperiod exposure. Long-day females in proestrus showed no change in dialysate levels of 5HT or 5HIAA within the ARC just prior to the onset of the afternoon surge of LH and PRL. Our results indicate that elevated 5HT and 5HIAA dialysate levels within the ARC may regulate photoperiod effects upon LH and PRL secretion, but not the preovulatory surges of LH and PRL.

Sex differences in the human brain's response to hunger and satiation

BACKGROUND

Sex differences in eating behavior are well documented, but it is not known whether these differences have neuroanatomical correlates. Recent neuroimaging studies have provided functional maps of the human cerebral areas activated in response to hunger and satiation.

OBJECTIVE

The objective of this study was to assess whether the brain's response to a meal is sex-specific.

DESIGN

Using positron emission tomography, we measured regional cerebral blood flow, a marker of neuronal activity, to investigate the functional neuroanatomy of hunger (36-h fast) and satiation (in response to a liquid meal) in 22 women and 22 men.

RESULTS

We observed extensive similarities, as well as some differences, between the sexes. In response to hunger, the men tended to have greater activation in the frontotemporal and paralimbic areas than did the women (P < 0.005). In response to satiation, the women tended to have greater activation in the occipital and parietal sensory association areas and in the dorsolateral prefrontal cortex than did the men (P < 0.005); in contrast, the men tended to have greater activation in the ventromedial prefrontal cortex than did the women (P < 0.005).

CONCLUSIONS

Despite extensive similarities in the brain responses to hunger and satiation between the men and women, our study showed sex-specific brain responses to a meal that indicate possible differences between men and women in the cognitive and emotional processing of hunger and satiation. This study provides a foundation for investigating the brain regions and cognitive processes that distinguish normal and abnormal eating behavior in men and women.

Effects of gonadectomy on immunoreactivity for choline acetyltransferase in the cortex, hippocampus, and basal forebrain of adult male rats

Androgens are known to affect cognitive and mnemonic aspects of spatial processing. The cholinergic system is thought to play an important role in cognition and memory, but little is known about the interaction between androgen and cholinergic neurons. The present study focused on the effects of testosterone on the cholinergic neurons in the anterior cingulate cortex, the posterior parietal cortex, the hippocampus, and the basal forebrain including the medial septum, i.e., regions related to spatial processing. We examined choline acetyltransferase (ChAT) immunoreactivity in three groups of adult male rats: sham-operated (Sham), 28-day gonadectomized (GDX), and 28-day gonadectomized with immediate implantation of testosterone propionate (GDX+TP). Comparison of the Sham and GDX+TP groups demonstrated that the GDX group had significantly decreased cell counts of ChAT-immunoreactive neurons in anterior cingulate cortex layer II/III, posterior parietal cortex layer II/III, and the medial septum, but not in the other basal forebrain subregions examined (the horizontal part of the diagonal band of Broca and the substantia innominata). The GDX group also had significantly reduced hippocampal ChAT-immunoreactive fiber pixel density. The GDX+TP group maintained ChAT-immunoreactive cell counts in the anterior cingulate cortex, posterior parietal cortex, and medial septum equivalent to those in the Sham group. Less than 1% of identified cells showed colocalization of immunoreactivity for ChAT and androgen receptor in the cell bodies of the cortex and basal forebrain. Our observations demonstrate that the presence or absence of testosterone for 4 weeks influenced the cholinergic population region-specifically in the adult rat brain.

Ovarian hormone effects on 5-hydroxytryptamine(2A) and 5-hydroxytryptamine(2C) receptor mRNA expression in the ventral hippocampus and frontal cortex of female rats

Alterations in female gonadal hormones are associated with anxiety and mood changes. The aim of the present study was to determine influences of chronic gonadal hormone supplementation on 5-HT(2A) and 5-HT(2C) receptor mRNA levels in the ventral hippocampus and the frontal cerebral cortex. Ovariectomized adult female Sprague-Dawley rats (n=37) received implantation of subcutaneous pellets containing different dosages of 17beta-estradiol alone or in combination with progesterone, or placebo pellets, for 2 weeks. Serotonin receptor mRNA levels were analyzed by in situ hybridization in the ventral hippocampus and 5-HT(2A) receptor mRNA also in the frontal cortex. Estradiol treatment in combination with low-dose progesterone increased 5-HT(2A) receptor mRNA by 43% in the CA2 region of the ventral hippocampus, while estradiol combined with high-dose progesterone increased the expression of this gene by 84% in ventral CA1. 5-HT(2A) mRNA expression in the frontal cortex was not influenced by hormone manipulation. 5-HT(2C) receptor gene expression was in the ventral hippocampus decreased in the CA2, ventral CA1 and the subiculum subregions by high-dose estradiol treatment (8-20% decreases). Effects on mood by gonadal hormones can be mediated, at least partly, through influences on 5-HT(2A) and 5-HT(2C) receptor expression.

Invited review: Estrogens effects on the brain: multiple sites and molecular mechanisms

Besides their well-established actions on reproductive functions, estrogens exert a variety of actions on many regions of the nervous system that influence higher cognitive function, pain mechanisms, fine motor skills, mood, and susceptibility to seizures; they also appear to have neuroprotective actions in relation to stroke damage and Alzheimer's disease. Estrogen actions are now recognized to occur via two different intracellular estrogen receptors, ER-alpha and ER-beta, that reside in the cell nuclei of some nerve cells, as well as by some less well-characterized mechanisms. In the hippocampus, such nerve cells are sparse in number and yet appear to exert a powerful influence on synapse formation by neurons that do not have high levels of nuclear estrogen receptors. However, we also find nonnuclear estrogen receptors outside of the cell nuclei in dendrites, presynaptic terminals, and glial cells, where estrogen receptors may couple to second messenger systems to regulate a variety of cellular events and signal to the nuclear via transcriptional regulators such as CREB. Sex differences exist in many of the actions of estrogens in the brain, and the process of sexual differentiation appears to affect many brain regions outside of the traditional brain areas involved in reproductive functions. Finally, the aging brain is responsive to actions of estrogens, which have neuroprotective effects both in vivo and in vitro. However, in an animal model, the actions of estrogens on the hippocampus appear to be somewhat attenuated with age. In the future, estrogen actions over puberty and in pregnancy and lactation should be further explored and should be studied in both the hypothalamus and the extrahypothalamic regions.

Molecular basis of aggression

Recent pharmacological and genetic studies have dramatically expanded the list of neurotransmitters, hormones, cytokines, enzymes, growth factors, and signaling molecules that influence aggression. In spite of this expansion, serotonin (5-HT) remains the primary molecular determinant of inter-male aggression, whereas other molecules appear to act indirectly through 5-HT signaling. We review evidence of interactions among these molecules and aggressive behavior. Slight modulations in 5-HT levels, turnover, and metabolism, or in receptor subtype activation, density, and binding affinity affect aggression. Activation of specific 5-HT receptors evokes distinct, but highly interacting, second messenger systems and multiple effectors. Understanding the interactions between 5-HT receptor subtypes should lead to novel insights into the molecular mechanisms of aggression.

Expression of serotonin 5-HT(2A) receptors in the human cerebellum and alterations in schizophrenia

The occurrence of human cerebellar serotonin 5-HT(2A) receptors (5-HT(2A)R) is equivocal and their status in schizophrenia unknown. Using a range of techniques, we investigated cerebellar 5-HT(2A)R expression in 16 healthy subjects and 16 subjects with schizophrenia. Immunocytochemistry with a monoclonal antibody showed labelling of Purkinje cell bodies and dendrites, as well as putative astrocytes. Western blots showed a major band at approximately 45 kDa. Receptor autoradiography and homogenate binding with [(3)H]ketanserin revealed cerebellar 5-HT(2A)R binding sites present at levels approximately a third of that in prefrontal cortex. 5-HT(2A)R mRNA was detected by reverse transcriptase-polymerase chain reaction, with higher relative levels in men than women. Several aspects of 5-HT(2A)R expression were altered in schizophrenia. 5-HT(2A)R immunoreactivity in Purkinje cells was partially redistributed from soma to dendrites and was increased in white matter. 5-HT(2A)R mRNA was decreased in the male patients. 5-HT(2A)R measured by dot blots and [(3)H]ketanserin binding (B(max) and K(d)) were not significantly altered in schizophrenia. These data show that 5-HT(2A)R gene products (mRNA, protein, binding sites) are expressed in the human cerebellum at nonnegligible levels; this bears upon 5-HT(2A)R imaging studies which use the cerebellum as a reference region. 5-HT(2A)R expression is altered in schizophrenia; the shift of 5-HT(2A)R from soma to dendrites is noteworthy since atypical antipsychotics have the opposite effect. Finally, the results emphasise that expression of a receptor gene is a mutifaceted process. Measurement of multiple parameters is necessary to give a clear picture of the normal situation and to show the profile of alterations in a disease.

Estrogen increases prepulse inhibition of acoustic startle in rats

Epidemiological studies have shown gender differences in the age of onset and symptoms of schizophrenia. Because sensorimotor gating mechanisms are deficient in schizophrenia, we studied the effect of administration of estrogen on prepulse inhibition of startle in rats, an animal model of sensorimotor gating. Rats were tested in an automated startle apparatus for their responses to random combinations of 115-dB sound pulses and prepulses of various intensity. Startle responses were reduced by increasing intensities of prepulses, indicating prepulse inhibition. Repeated administration of startle pulses caused gradual habituation of startle responses. Ovariectomy did not induce significant changes in either habituation of the startle response or prepulse inhibition of startle. Treatment with 17beta-estradiol caused an increase in percentage prepulse inhibition at all prepulse intensities at 18 h, but only at higher prepulse intensities at 30 min after injection. Habituation of startle responses was not affected. The enhancing effect of estradiol on prepulse inhibition was mimicked by testosterone, but not by dihydrotestosterone. Estradiol treatment increased prepulse inhibition similarly in controls or after disruption of prepulse inhibition induced by treatment with apomorphine or dizocilpine (MK-801). Our results may help to explain gender differences in schizophrenia and some of the beneficial clinical effects of estrogen treatment in this disease.

Analysis of steroid-induced genes in the rat preoptic area-anterior hypothalamus using a differential-display reverse transcriptase-polymerase chain reaction

Steroid hormones modulate a variety of physiological functions in the hypothalamus. We attempted to identify steroid-regulated genes in the rat preoptic area-anterior hypothalamus by comparing differentially expressed mRNAs. Adult female rats were ovariectomized and, 1 week later, a silastic capsule containing 17beta-oestradiol (180 microg/ml) was subcutaneously implanted. After 2 days, a single injection of progesterone (1 mg) was administered at 10.00 h and rats were killed at 17.00 h on the same day. Differential-display polymerase chain reaction followed by Northern blot analysis showed that 10 clones were differentially regulated. Using homology search in Genbank, three genes were identified as sodium, potassium-ATPase beta1, protein kinase C-binding Nell-homologue protein and evectin-1. Further characterization of 10 clones showed that the expression patterns were tissue-specific and differentially regulated during puberty. Among these, mRNAs for protein kinase C-binding Nell-homologue protein, evectin-1 and human CGI-118 protein-like gene were induced after vagina opening, and differentially expressed during the oestrous cycle. Taken together, several steroid-regulated genes identified in the present study may play an important role in regulating hypothalamic functions, including puberty and the oestrous cycle.

Estrogen receptor alpha gene polymorphism in schizophrenia: frequency, age at onset, symptomatology and prognosis

Schizophrenic disorders are equally distributed for both sexes; however, later onset, milder psychopathology and better outcome are associated with the female gender. This sex difference is thought to be partly due to the estrogen system. Recent studies have determined that estrogen receptor alpha subtype (ER alpha) genetic polymorphisms may affect the expression of ER alpha, and are associated with Alzheimer's disease. For this study, we investigated the association of ER alpha polymorphisms for 125 schizophrenic patients and 142 control subjects. No significant differences for genotype distribution or allele frequency were revealed comparing controls and schizophrenic patients. The ER alpha genotypes were not associated with onset age, psychiatric symptoms or outcome for schizophrenic cases. With new research highlighting the prominent role of sex hormones in neurological and psychological dysfunction, further study is needed to explore the genetic effect of the sex hormone receptor gene on susceptibility mental disorders and associations with different phenotypes.

Schizophrenia and liver dysfunction

It is suggested that a non-hepatocellular liver dysfunction, caused by the presence of a congenital or acquired portal-systemic shunt, constitutes a major predisposing factor in the pathogenesis of schizophrenia. In addition to the common occurrence of schizophrenic reactions observed in liver disease, this suggestion is supported by autoptic findings in addition to the fact that a considerable number of abnormal biochemical and biological phenomena are shared by patients suffering from schizophrenia and portal-systemic shunting. The frequency of abnormal portal-systemic shunts in schizophrenia is unknown. Recent advances in non-invasive Doppler-sonographic techniques should enable an elucidation of this question.

Estrogen - a potential treatment for schizophrenia

Estrogen has been shown in animal studies to modulate both the dopamine and serotonin neurotransmitter systems - the main neurotransmitters implicated in the pathogenesis of schizophrenia. A double blind, 28 day, placebo-controlled study was conducted with three groups of women of child-bearing age (N=12 in each group) who received standardized antipsychotic medication plus 50mcg transdermal estradiol or 100mcg transdermal estradiol or transdermal placebo. Analyses show that women receiving 100mcg of estradiol made greater improvements in the symptoms of schizophrenia than both the 50mcg estradiol and placebo groups. Women receiving 50mcg estradiol had more improvement in their symptoms compared with the placebo group. The 100mcg estradiol group had significantly lower mean lutenizing hormone (LH) and higher mean prolactin levels across the study period compared with both the 50mcg and placebo groups. The addition of 100mcg adjunctive transdermal estrogen significantly enhanced the treatment of acute, severe psychotic symptoms in women with schizophrenia. The differential response of adding 50mcg versus 100mcg estradiol on the types of symptom affected may be related to the estrogen effect on LH and prolactin. The positive impact of estrogen treatment on psychotic symptoms by a direct effect on dopamine and serotonin systems or via an indirect prolactin-mediated effect may be very useful in the overall treatment of women with schizophrenia.

Prolonged ovarian sex steroid treatment of male rats produces antinociception: identification of sex-based divergent analgesic mechanisms

Simulation of the pregnancy blood concentration profile of 17beta-estradiol (E(2)) and progesterone (P) in nonpregnant ovariectomized rats has been shown to result in a significant elevation of nociceptive response thresholds. The present report demonstrates that spinal opioid antinociceptive responsiveness to these ovarian steroids is not sex-specific. Treatment of orchidectomized sexually mature males with an analogous regimen of E(2) and P also elicits an antinociception, the robustness and temporal profile of which is comparable with that previously observed in females. Neither E(2) nor P, alone, is sufficient to produce antinociception in male rats, as was previously demonstrated in females. Neurobiological substrates and antinociceptive mechanisms underlying ovarian sex steroid antinociception do, however, exhibit sex specificity. In males, the analgesia resulting from ovarian steroid treatment derives from the independent contributions of spinal kappa and mu, not delta, opioid receptor pathways that are additive, not synergistic. Spinal alpha(2)-noradrenergic receptor activity and its attendant analgesic synergy with spinal opioid systems do not contribute to ovarian sex steroid analgesia in males. This is in contrast to the previous demonstrations that ovarian sex steroid-induced antinociception in females results from antinociceptive synergy between activated spinal kappa/delta opioid as well as alpha(2)-noradrenergic receptor systems. The current data reveal that ovarian steroid-activated multiplicative spinal antinociceptive pathways that had been demonstrated in female rats are not manifest in their male counterparts.

Effects of tamoxifen on serotonin transporter and 5-hydroxytryptamine(2A) receptor binding sites and mRNA levels in the brain of ovariectomized rats with or without acute estradiol replacement

Estradiol-17beta (E(2)), in its positive feedback mode for gonadotropin release in the female rat, induces expression of the genes for the 5-hydroxytryptamine(2A) receptor (5-HT(2A)R) and the serotonin transporter (SERT) in the dorsal raphe nucleus (DRN) with a concomitant increase in the densities of 5-HT(2A)R and the SERT in rat forebrain. The forebrain regions affected are those which, in humans, are concerned with the control of mood, mental state, cognition and emotion. Here we have used the mixed estradiol agonist/antagonist, tamoxifen, to determine whether this action of estradiol is mediated by cytoplasmic estradiol receptors. Acute treatment ( approximately 32 h) of ovariectomized rats with estradiol benzoate (EB) increased significantly the amount of 5-HT(2A)R mRNA and SERT mRNA in the DRN and the densities of 5-HT(2A)R and SERT binding sites in the forebrain. These effects of EB were completely blocked by tamoxifen. Treatment with tamoxifen alone had no effect on either gene expression or the density of binding sites. Together, these data show that tamoxifen acts as a pure estradiol antagonist with respect to serotonergic mechanisms in brain. Detailed analysis of the effects of estradiol and tamoxifen on the DRN showed that SERT gene expression is constitutive only in the posterior DRN; in the anterior DRN, SERT gene expression appears to depend upon estrogen induction which is blocked by tamoxifen. Our findings strongly suggest that estradiol receptors are involved in mediating estradiol action on central serotonergic mechanisms and are relevant for our understanding of the effects of antiestrogens as well as estradiol on mood, mental state and cognition.

Androgen actions on central serotonin neurotransmission: relevance for mood, mental state and memory

Sex steroids exert potent effects on mood and mental state in the human. Our previous experimental findings in female rats suggest that these effects may be mediated, in part, by the action of estrogen on the 5-hydroxytryptamine2A receptor (5-HT(2A)R) and serotonin transporter (SERT) in brain. Here we review our recent findings on the effect of acute (approximately 32 h) testosterone manipulation on central 5-HT(2A)R and SERT in male rats. Castration decreased while testosterone or estrogen, but not 5alpha-dihydrotestosterone (5alpha-DHT), increased significantly the content of 5-HT(2A)R mRNA and SERT mRNA in the dorsal raphe nucleus (DR) and the density of 5-HT(2A)R and SERT binding sites in higher centers of the brain. The lack of effect of 5alpha-DHT, a potent androgen which cannot be converted to estrogen, suggests that the action of testosterone depends upon its conversion to estrogen by aromatase. This may also explain why estrogen, but not testosterone or 5alpha-DHT, increased the density of 5-HT(2A)R binding sites in the caudate-putamen, a brain region where aromatase is scarce. The estrogen induction of SERT mRNA is most prominent in the rostral DR and this together with the correlation between sensitivity of DR serotonin neurons to estrogen and neurotoxic amphetamine derivatives provides a potential topochemical handle with which to investigate testosterone/estrogen regulation of SERT gene expression. These findings are discussed in relation to the possible role of interactions between sex steroids and serotonin mechanisms in mood disorders, schizophrenia and Alzheimer's disease.

Serotonin transporter (SERT) mRNA and binding site densities in male rat brain affected by sex steroids

Estrogen increases serotonin transporter (SERT) mRNA and binding sites in female rat brain. In order to determine whether changes in SERT are gender- and steroid-specific we have now carried out studies on adult male Wistar rats which were either intact or castrated (under halothane anesthesia) and injected with arachis oil, estradiol benzoate (EB), testosterone propionate (TP) or the non-aromatizable androgen, 5alpha-dihydrotestosterone (5alpha-DHT). The number of SERT mRNA-expressing cells in the dorsal raphe (DR) nucleus was decreased by castration and increased by treatment (for approximately 32 h) with EB or TP, but not 5alpha-DHT. Sex steroids had no effect on the number of SERT mRNA-expressing cells in the median raphe nucleus. The density of SERT sites, assessed by autoradiography of [3H]paroxetine binding, was significantly reduced in arcuate nucleus and median raphe after castration, and increased in arcuate, basolateral amygdala and ventromedial hypothalamic nucleus by treatment with EB or TP, but not 5alpha-DHT. Estradiol, but not testosterone or 5alpha-DHT reduced the density of SERT sites in midbrain central grey. These data show that testosterone as well as estrogen affects SERT expression in male brain, and that the action of testosterone probably depends upon its enzymatic conversion, by aromatase, to estradiol. Our findings may have implications for sex steroid control of mood and behavior, and the action of neurotoxic derivatives of amphetamine, such as 3, 4-methylenedioxymethamphetamine, in the human.

Sex steroid control of mood, mental state and memory

1. Sex steroid hormones exert profound effects on mood and mental state. Thus, in women, oestrogen is thought to protect against depression and delay the onset of schizophrenia and Alzheimer's disease. 2. Our studies in the female rat show that oestradiol, in its positive feedback mode for gonadotrophin release, increases the expression of genes for the 5-hydroxytryptamine 5-HT2A receptor and the serotonin transporter (SERT) in the dorsal raphe nucleus and the density of 5-HT2A receptor and SERT sites in regions of the forebrain that, in the human, are concerned with cognition, mental state, emotion and memory. 3. In the male rat, castration decreases while oestrogen and testosterone, but not 5 alpha-dihydrotestosterone (5 alpha-DHT), increase the density of 5-HT2A receptors in forebrain. The fact that 5 alpha-DHT has no effect suggests that the action of testosterone depends on its conversion to oestradiol by aromatase. 4. In intact rats, the density of 5-HT2A receptors in cerebral cortex is significantly higher in pro-oestrous female than in male and dioestrous female rats, showing that the spontaneous, preovulatory surge of oestradiol that reaches a peak at 12.00 h of pro-oestrus also increases the density of 5-HT2A receptors in cortex. 5. Oestrogen and testosterone (by way of its conversion to oestrogen) also stimulate the expression of the arginine vasopressin gene in the bed nucleus of the stria terminalis of the rodent, a mechanism that plays a key role in olfactory memory. 6. These actions of sex steroid hormones are discussed in the context of genomic versus non-genomic mechanisms, the recent discovery that there are two oestradiol receptors with different distributions in brain, the significance of our findings for our understanding of the control of mood, mental state and memory and the mechanism by which oestrogen stimulation of the 5-HT2A receptor could delay the onset of Alzheimer's disease.