Chronic 3,4-methylenedioxymethamphetamine administration decreases glucocorticoid and mineralocorticoid receptor, but increases 5-hydroxytryptamine1C receptor gene expression in the rat hippocampus

Designer Drugs of Abuse

Designer drugs of abuse represent a major health risk to those who use them. The toxic effects of these agents are very dangerous when they are correctly identified, but they are especially dangerous because they are often misidentified by emergency room personnel. The three groups of designer drugs are the opiates, amphetamine derivatives and phencyclidine derivatives. Amphetamine derivatives such as MDMA and MDA can cause fatal sequelae including hyperthermia, hypertension, and seizures. No specific antidote exists for these agents. Therefore, their widespread use in certain areas is a major concern. The opiate derivatives M PPP, MPTP and the fentanyl analogues produce a wide range of toxic effects. These agents are much more potent than heroin, and are sometimes sold as heroin unknowingly to the user. The results have been catastrophic, with many fatalities. Arylhexylamines such as phencyclidine and ketamine are becoming more popular as agents of abuse. These drugs may result in fatal toxicity resulting from cardiac arrest, hypertensive emergency, or status epilepticus. Familiarity with the signs and symptoms of toxicity from the designer drugs will expedite the care of these patients.

'Ecstasy' enhances noise-induced hearing loss

'Ecstasy' or 3,4-methylenedioxy-N-methamphetamine (MDMA) is an amphetamine abused for its euphoric, empathogenic, hallucinatory, and stimulant effects. It is also used to treat certain psychiatric disorders. Common settings for Ecstasy use are nightclubs and "rave" parties where participants consume MDMA and dance to loud music. One concern with the club setting is that exposure to loud sounds can cause permanent sensorineural hearing loss. Another concern is that consumption of MDMA may enhance such hearing loss. Whereas this latter possibility has not been investigated, this study tested the hypothesis that MDMA enhances noise-induced hearing loss (NIHL) by exposing rats to either MDMA, noise trauma, both MDMA and noise, or neither treatment. MDMA was given in a binge pattern of 5 mg/kg per intraperitoneal injections every 2 h for a total of four injections to animals in the two MDMA-treated groups (MDMA-only and Noise + MDMA). Saline injections were given to the animals in the two non-MDMA groups (Control and Noise-only). Following the final injection, noise trauma was induced by a 10 kHz tone at 120 dB SPL for 1 h to animals in the two noise trauma-treated groups (Noise-only and Noise + MDMA). Hearing loss was assessed by the auditory brainstem response (ABR) and cochlear histology. Results showed that MDMA enhanced NIHL compared to Noise-only and that MDMA alone caused no hearing loss. This implies that "clubbers" and "rave-goers" are exacerbating the amount of NIHL when they consume MDMA and listen to loud sounds. In contrast to earlier reports, the present study found that MDMA by itself caused no changes in the click-evoked ABR's wave latencies or amplitudes.

Cocaine and MDMA Induce Cellular and Molecular Changes in Adult Neurogenic Systems: Functional Implications

The capacity of the brain to generate new adult neurons is a recent discovery that challenges the old theory of an immutable adult brain. A new and fascinating field of research now focuses on this regenerative process. The two brain systems that constantly produce new adult neurons, known as the adult neurogenic systems, are the dentate gyrus (DG) of the hippocampus and the lateral ventricules/olfactory bulb system. Both systems are involved in memory and learning processes. Different drugs of abuse, such as cocaine and MDMA, have been shown to produce cellular and molecular changes that affect adult neurogenesis. This review summarizes the effects that these drugs have on the adult neurogenic systems. The functional relevance of adult neurogenesis is obscured by the functions of the systems that integrate adult neurons. Therefore, we explore the effects that cocaine and MDMA produce not only on adult neurogenesis, but also on the DG and olfactory bulbs. Finally, we discuss the possible role of new adult neurons in cocaine- and MDMA-induced impairments. We conclude that, although harmful drug effects are produced at multiple physiological and anatomical levels, the specific consequences of reduced hippocampus neurogenesis are unclear and require further exploration.

Serotonergic neurotransmission in the ventral hippocampus is enhanced by corticosterone and altered by chronic amphetamine treatment

The ventral hippocampus modulates anxiety-like behavior in rats, and serotonergic transmission within the hippocampus facilitates adaptation to stress. Chronic amphetamine treatment results in anxiety-like behavior in rats and reduced monoamine concentrations in the ventral hippocampus. Since reduced hippocampal serotonergic transmission in response to stress is observed in rats that display high anxiety-like behavior, anxiety states in amphetamine-treated rats may be associated with reduced stress-related serotonergic transmission in the hippocampus. Therefore, using in vivo microdialysis in anesthetized rats, we investigated the effect of corticosterone infused locally into the ventral hippocampus on serotonergic transmission, and the effect of chronic amphetamine pretreatment on corticosteroid receptor protein expression and the corticosterone-induced serotonergic response. Extracellular serotonin in the ventral hippocampus was increased by corticosterone in drug naive rats, and this corticosterone-induced serotonin augmentation was blocked by the glucocorticoid receptor antagonist mifepristone. Furthermore, chronic pretreatment with amphetamine abolished the serotonin response to physiologically relevant corticosterone levels and reduced glucocorticoid receptor protein expression. Together, our results suggest that chronic amphetamine exposure reduces serotonergic neurotransmission, in part via alterations to glucocorticoid receptor-facilitation of serotonin release in the rat ventral hippocampus. Reduced serotonergic activity in the ventral hippocampus may contribute to altered stress responses and adaptive coping following repeated drug exposure.

Differential long-term effects of MDMA on the serotoninergic system and hippocampal cell proliferation in 5-HTT knock-out vs. wild-type mice

Although numerous studies investigated the mechanisms underlying 3,4-methylenedioxymethamphetamine (MDMA)-induced neurotoxicity, little is known about its long-term functional consequences on 5-HT neurotransmission in mice. This led us to evaluate the delayed effects of MDMA exposure on the 5-HT system, using in-vitro and in-vivo approaches in both 5-HTT wild-type and knock-out mice. Acute MDMA in-vitro application on slices of the dorsal raphe nucleus (DRN) induced concentration-dependent 5-HT release and 5-HT cell firing inhibition. Four weeks after MDMA administration (20 mg/kg b.i.d for 4 d), a 2-fold increase in the potency of the 5-HT1A receptor agonist ipsapirone to inhibit the discharge of DRN 5-HT neurons and a larger hypothermic response to 8-OH-DPAT were observed in MDMA- compared to saline-treated mice. This adaptive 5-HT1A autoreceptor supersensitivity was associated with decreases in 5-HT levels but no changes of [3H]citalopram binding in brain. Long-term MDMA treatment also induced a 30% decrease in BrdU labelling of proliferating hippocampal cells and an increased immobility duration in the forced swim test suggesting a depressive-like behaviour induced by MDMA treatment. All these effects were abolished in 5-HTT-/- knock-out mice. These data indicated that, in mice, MDMA administration induced a delayed adaptive supersensitivity of 5-HT1A autoreceptors in the DRN, a deficit in hippocampal cell proliferation and a depressive-like behaviour. These 5-HTT-dependent effects, opposite to those of antidepressants, might contribute to MDMA-induced mood disorders.

Enhanced tau phosphorylation in the hippocampus of mice treated with 3,4-methylenedioxymethamphetamine ("Ecstasy")

3,4-Methylenedioxymethamphetamine (MDMA) ("Ecstasy") produces neurotoxic effects, which result into an impairment of learning and memory and other neurological dysfunctions. We examined whether MDMA induces increases in tau protein phosphorylation, which are typically associated with Alzheimer's disease and other chronic neurodegenerative disorders. We injected mice with MDMA at cumulative doses of 10-50 mg/kg intraperitoneally, which are approximately equivalent to doses generally consumed by humans. MDMA enhanced the formation of reactive oxygen species and induced reactive gliosis in the hippocampus, without histological evidence of neuronal loss. An acute or 6 d treatment with MDMA increased tau protein phosphorylation in the hippocampus, revealed by both anti-phospho(Ser(404))-tau and paired helical filament-1 antibodies. This increase was restricted to the CA2/CA3 subfields and lasted 1 and 7 d after acute and repeated MDMA treatment, respectively. Tau protein was phosphorylated as a result of two nonredundant mechanisms: (1) inhibition of the canonical Wnt (wingless-type MMTV integration site family) pathway, with ensuing activation of glycogen synthase kinase-3beta; and (2) activation of type-5 cyclin-dependent kinase (Cdk5). MDMA induced the expression of the Wnt antagonist, Dickkopf-1, and the expression of the Cdk5-activating protein, p25. In addition, the increase in tau phosphorylation was attenuated by strategies that rescued the Wnt pathway or inhibited Cdk5. Finally, an impairment in hippocampus-dependent spatial learning was induced by doses of MDMA that increased tau phosphorylation, although the impairment outlasted this biochemical event. We conclude that tau hyperphosphorylation in the hippocampus may contribute to the impairment of learning and memory associated with MDMA abuse.

Initial deficit and recovery of function after MDMA preexposure in rats

RATIONALE

3,4-methylenedioxymethamphetamine (MDMA) exposure was reported to result in deficits in serotonergic neurotransmission with concomitant behavioral suppression and tolerance to MDMA. Some data have also suggested that the neurochemical deficits recover over time, raising the question as to whether behavioral suppression would show a similar recovery.

OBJECTIVES

The possibility of recovery of behavioral deficits was examined in the present study. Rats were administered an MDMA pretreatment regimen that was shown to produce numerous serotonergic deficits and behavioral suppression 2 weeks thereafter. The full expression of MDMA-produced hyperactivity was dependent upon serotonergic integrity, therefore, the present study aimed to determine whether MDMA pretreated rats were tolerant to MDMA 2 weeks after exposure. Further, because serotonergic deficits have shown recovery over time, similar behavioral tests were conducted at a later time point to determine whether functional recovery was evident.

METHODS

MDMA-produced hyperactivity was measured at different withdrawal periods (2 and 12 weeks) to determine initial effects and the possibility of recovery of function.

RESULTS

In saline-pretreated control rats, +/-MDMA (0.0-10.0 mg/kg) produced a dose-dependent increase in locomotor activity. Rats that had received prior exposure to MDMA (4 x 10 mg/kg MDMA injections administered at 2 h intervals) demonstrated tolerance when the activity was measured 2 weeks after pretreatment. For these rats, there was a downward shift in the dose-effect curve for MDMA-produced hyperactivity. MDMA-produced hyperactivity in rats that were tested 12 weeks after pretreatment was, however, comparable to controls, suggesting recovery of function.

CONCLUSION

These data are consistent with the idea that high dose MDMA exposure produces neuroadaptations that exhibit recovery with extended abstinence from the drug.

Administration of SCH 23390 into the medial prefrontal cortex blocks the expression of MDMA-induced behavioral sensitization in rats: an effect mediated by 5-HT2C receptor stimulation and not by D1 receptor blockade

Akin to what has been reported for cocaine, systemic administration of the dopamine D1 receptor antagonist, SCH 23390 ((R)-(+)-7-chloro-8-hydroxy-3-methyl-1-phenyl-2,3,4,5-tetrahydro-1H-3-benzazepine hydrochloride), blocks the expression but not the induction of 3,4-methylenedioxymethamphetamine (MDMA)-induced behavioral sensitization. Since the medial prefrontal cortex (mPFC) appears to regulate the expression of sensitization to cocaine, this study examined whether microinjection of SCH 23390 into the mPFC would alter the expression of MDMA sensitization. Saline or MDMA was administered for 5 consecutive days. After 12 days of withdrawal, rats received a bilateral intra-mPFC microinjection of SCH 23390 or saline followed by an intraperitoneal (i.p.) challenge dose of MDMA. While SCH 23390 enhanced locomotion in MDMA-naïve rats, it completely suppressed the expression of sensitization in MDMA-pretreated animals. Since, SCH 23390 has a fairly good affinity for 5-HT(2C) receptors, we went further to study the role of mPFC D1 and 5-HT(2C) receptors in this, apparently, paradoxical effect shown by SCH 23390. Thus, the microinjection of both SKF 81297 (R-(+)-6-chloro-7,8-dihydroxy-1-phenyl-2,3,4,5-tetrahydro-1H-3-benzazepine hydrobromide) and MK 212 (6-chloro-2-(1-piperazinyl)pyrazine hydrochloride), a D1 and 5-HT(2C) receptor agonist, respectively, blocked MDMA sensitization. By contrast, the 5-HT(2C) receptor antagonist, RS 102221 (8-[5-(2,4-dimethoxy-5-(4-trifluoromethylphenylsulfonamido)phenyl-5-oxopentyl]-1,3,8-triazaspiro[4,5]decane-2,4-dione hydrochloride), had no effect in MDMA-naïve or MDMA-sensitized animals, but reversed the effects of SCH 23390 in MDMA-pretreated rats. These results demonstrate that suppression of MDMA-induced sensitization by SCH 23390 is mediated by 5-HT(2C) receptor stimulation in the mPFC and not by the blockade of mPFC D1 receptors. Furthermore, these data indicate that stimulation of 5-HT(2C) receptors by SCH 23390 is not a minor issue and should be considered when interpreting future data.

Prenatal stress affects 3,4-methylenedioxymethamphetamine pharmacokinetics and drug-induced motor alterations in adolescent female rats

We examined the influence of prenatal stress on 3,4-methylenedioxymethamphetamine (MDMA, 5 mg/kg p.o.) pharmacokinetics in adolescent female SD rats (30 days). Our results indicate that the metabolic rate of MDMA was higher in the prenatal stress group than in the control group. Moreover, MDMA-induced motor alterations were increased in prenatally stressed rats. These findings provide evidence that (i) prenatal stress increases sensitivity to MDMA, (ii) these effects are already detectable at the adolescent stage and (iii) early differences in metabolism may play a role in the behavioural changes associated with this drug of abuse.

Multiple molecular and neuropharmacological effects of MDMA (Ecstasy)

3,4-Methylenedioxymethamphetamine (MDMA), commonly referred to as Ecstasy, is a widely abused, psychoactive recreational drug, which induces short- and long-term neuropsychiatric behaviors. This drug is neurotoxic to serotonergic neurons in vivo, and induces programmed cell death in cultured human serotonergic cells and rat neocortical neurons. Over the years it has been shown that MDMA alters the release of several neurotransmitters in the brain, it induces recompartmentation of intracellular serotonin and c-fos, and modifies the expression of a few genes. Recently, we observed changes in gene expression in mice treated with MDMA, and cloned and sequenced 11 cDNAs thus affected (4 correspond to known and 7 to unknown genes). The effect of MDMA on two of these genes, GABA transporter 1 and synaptotagmin IV was studied in detail. Characterization of the relationship between a given gene and certain physiological or behavioral effects of MDMA could shed light on the mechanism of the drug's action. However, establishing such a connection is difficult for several reasons, including that serotonergic neurons are not the only cells affected by MDMA. In this review, molecular and neurochemical events that occur in the brain following exposure to MDMA, and link between the observed molecular changes with known physiological effects of the drug are discussed. It is indicated that MDMA alters the expression of several proteins involved in GABA neurotransmission, thus having critical effect on thermoregulation and MDMA acute toxicity. This analysis should facilitate development of novel approaches to prevent deleterious effects, especially mortality induced by MDMA and other abused psychostimulants.

Differential regulation of corticosteroid receptors by monoamine neurotransmitters and antidepressant drugs in primary hippocampal culture

Hyperactivity of the hypothalamic-pituitary-adrenal axis is a characteristic feature of depressive illness. The centrally located corticosteroid receptors, the glucocorticoid and mineralocorticoid receptors, are thought to be important modulators of this axis and changes in the levels of these receptors, particularly in the hippocampus, may underlie the hyperactivity observed. Various antidepressant drugs increase hippocampal mineralocorticoid and glucocorticoid receptor levels in vivo. These effects are thought to be mediated via alterations in monoaminergic neurotransmission. We examined whether serotonin (5HT) and noradrenaline (NA) have direct effects on glucocorticoid receptor and mineralocorticoid receptor expression in primary hippocampal neurones, and whether antidepressants also exert direct effects on target neurones. Exposure of hippocampal cells to 5HT for 4 days increased both glucocorticoid and mineralocorticoid receptor mRNA and protein expression. The induction of mineralocorticoid receptor mRNA was completely blocked by the 5HT(7) receptor antagonist SB 269970. In contrast glucocorticoid receptor induction was insensitive to the 5HT(7) receptor, whilst studies with the 5HT(1A) receptor agonist 8-hydroxy-2-(di-n-proplamino) tetralin hydrochloride and the 5HT(1A) receptor antagonist N-[2-[4-2-[O-methoxyphenyl)-1-piperazinyl]ethyl]-N-(2-pyridinyl) cyclohexane carboxamide trihydrochloride (WAY 100635) suggest a partial role for 5HT(1A) receptors in hippocampal glucocorticoid receptor regulation. Treatment with NA for 4 days also increased glucocorticoid receptor expression but had no effect on mineralocorticoid receptor expression. This was blocked by propanolol suggesting action via beta-adrenergic receptors. Similarly to NA, fluoxetine and amitriptyline also selectively increased glucocorticoid receptor mRNA and protein levels over this time course. However, glucocorticoid receptor induction by fluoxetine or amitriptyline was not blocked by WAY 100635 or propanolol. These results show that 5HT, NA and antidepressants act directly but via distinct mechanisms on hippocampal neurones to regulate mineralocorticoid and glucocorticoid receptor expression. Thusly, manipulation of neurotransmitter or antidepressant levels in the brain may aid in reversing hypothalamic-pituitary-adrenal axis hyperactivity by restoring hippocampal corticosteroid receptor balance.

Influences of the corticotropic axis and sympathetic activity on neurochemical consequences of 3,4-methylenedioxymethamphetamine (MDMA) administration in Fischer 344 rats

The respective influences of the corticotropic axis and sympathetic activity on 3,4-methylenedioxymethamphetamine (MDMA, ecstasy) immediate effects on body temperature and long-term neurotoxicity, as assessed by decreases in hippocampal and striatal [(3)H]5-hydroxytryptamine ([(3)H]5-HT) reuptake, [(3)H]paroxetine binding at 5-HT transporters (5-HTT), and 5-HT and 5-hydroxyindoleacetic acid (5-HIAA) levels, were examined in Fischer 344 rats. On each of the two injections of MDMA (5 or 10 mg/kg s.c. once a day for 2 consecutive days) body temperature rapidly increased in a dose-dependent manner. Six days after the last injection of 10 mg/kg MDMA, [(3)H]5-HT reuptake, [(3)H]paroxetine binding and 5-HT and 5-HIAA levels were decreased in the hippocampus and, to a lower extent, in striatum. Prior adrenalectomy (1 week beforehand), which weakened the immediate hyperthermic effect of MDMA, prevented the long-term MDMA-elicited reduction in hippocampal and striatal [(3)H]paroxetine binding. Supplementation of adrenalectomised Fischer 344 rats with corticosterone almost reinstated the immediate hyperthermic effect of MDMA and restored MDMA-elicited reduction in hippocampal and striatal [(3)H]paroxetine binding. In a final set of experiments, Fischer 344 rats were pretreated (30 min before each of the two injections of 10 mg/kg MDMA) with the ganglionic blocker chlorisondamine (2.5 mg/kg). This pretreatment markedly reduced the amplitudes of the immediate hyperthermia and long-term declines in hippocampal [(3)H]5-HT reuptake and [(3)H]paroxetine binding at 5-HTT, and in hippocampal and striatal 5-HT and 5-HIAA levels. These results suggest that sympathetic activity (possibly through its control of body temperature), but not corticotropic activity, plays a key role in MDMA-elicited neurotoxicity in Fischer 344 rats.

The effect of chronic fluoxetine treatment on brain corticosteroid receptor mRNA expression and spatial memory in young and aged rats

As rats age, a subgroup will show spatial memory impairments, along with decreased corticosteroid receptors (MR and/or GR) in the hippocampus and a hyperactive hypothalamic-pituitary-adrenal axis. In previous work, we have shown that amitriptyline treatment increases hippocampal MR mRNA and improves spatial memory in young rats but had no effect in aged rats. Here, we examine the effect of 1-month treatment with the selective 5-HT re-uptake inhibitor, fluoxetine (10 mg/kg, p.o.) on hippocampal corticosteroid receptor mRNA and spatial memory in young 4-month-old and aged 24-month-old rats. Aged rats were impaired in spatial memory compared to young controls. MR mRNA expression was reduced with ageing in all hippocampal subfields except CA4 (35% decrease in dentate gyrus (DG) and CA2, P<0.05) and GR mRNA was decreased selectively in CA1 (17% decrease, P<0.05). Fluoxetine treatment increased GR mRNA in the hippocampus of young rats (24 and 46% increase in DG and CA3, respectively, P<0.01) but had no effect on hippocampal MR mRNA expression. In contrast, in aged rats, fluoxetine treatment increased hippocampal MR mRNA selectively in CA2 (43% increase, P<0.05), but had no effect on hippocampal GR mRNA. Fluoxetine treatment did not alter watermaze performance in either young or aged rats. It appears that increased hippocampal MR (at least in the CA2 region) which may underlie the enhancement in memory processing in young rats, is insufficient to improve memory in already cognitively impaired aged rats.

Short-term administration of fluoxetine and venlafaxine decreases corticosteroid receptor mRNA expression in the rat hippocampus

Chronic treatment with antidepressant drugs (2 weeks or longer) increases corticosteroid receptor mRNA expression in the hippocampus and reduces hypothalamic-pituitary-adrenal axis activity in parallel with improving mood and neuroendocrine function. Earlier effects are less well documented. We examined the effects of short term (9 days) treatment with fluoxetine (10 mg/kg) and venlafaxine (10 mg/kg) on hippocampal mineralocorticoid receptor (MR) and glucocorticoid receptor (GR) mRNA expression and spatial memory in adult rats. In situ hybridization histochemistry showed that the antidepressants decreased MR mRNA expression in all hippocampal subregions (e.g. 45% decrease in CA1 with venlafaxine, P<0.001), while GR mRNA expression was selectively reduced in the CA3 subregion. There was a trend for decreased plasma corticosterone levels following fluoxetine (50% fall, P=0.07) and venlafaxine (30% fall, P=0.18) but neither antidepressants affected spatial memory in the watermaze. Thus antidepressants can have complex and opposing actions on hippocampal corticosteroid receptor expression depending on the duration of treatment.

Chronic lithium chloride injection increases glucocorticoid receptor but not mineralocorticoid receptor mRNA expression in rat brain

Lithium has been used clinically for the treatment of bipolar disorders. However, the brain mechanisms, by which lithium acts, are still unclear. An impaired hypothalamic-pituitary-adrenal (HPA) axis has been implicated in the pathogenesis of mood disorders. In this study, we investigated the effects of chronic lithium on the corticosteroid receptors in the brain. Male Wistar rats were injected with LiCl (1.5 mEq/kg) or saline intraperitoneally (i.p.) once a day for 14 days. Twenty-four hours after the last injection, the expressions of mRNA for glucocorticoid receptor (GR) and mineralocorticoid receptor (MR) in the brain were determined by non-radioactive in situ hybridization. Chronic administration of LiCl increased the expression of GR mRNA in the hippocampus and paraventricular nucleus of the hypothalamus (PVN). However, no significant changes were observed in the expression of either MR mRNA in the hippocampus or GR mRNA in the locus ceruleus. Since the hippocampus and PVN mediate negative feedback regulation of the HPA axis, an increased expression of GR mRNA in these regions may normalize HPA axis activity in mood disorders. Thus, the effect of chronic lithium on GR function may be involved in its antimanic and/or prophylactic activity in bipolar disorders.

The effects of serotonin on glucocorticoid receptor binding in rat raphe nuclei and hippocampal cells in culture

The raphe-hippocampal serotonin (5-HT) system is involved in the regulation of the hypothalamus-pituitary-adrenal axis. The purpose of this study was to determine and compare the roles of 5-HT in the regulation of glucocorticoid receptor (GR) binding in the raphe nuclei and in the hippocampus. The effects of 5-HT, 5-HT agonists, and the 5-HT reuptake inhibitor citalopram on GR binding sites were studied in primary cultures of the fetal raphe nuclei and the hippocampus. Exposure of hippocampal cells to 5-HT, (+/-)-2,5-dimethoxy-4-iodoamphetamine (DOI; a 5-HT2 agonist), or citalopram resulted in an increase in number of GR binding sites. The effect of DOI was blocked by ketanserin (a 5-HT2 antagonist). Specific and saturable GR binding was found in raphe cells. Exposure of raphe cells to 5-HT, (+/-)-8 hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT; a 5-HT1A agonist), or citalopram induced a significant decrease in number of GR binding sites. The effect of 8-OH-DPAT was reversed by WAY 100135 [N-tert-butyl-3-[1-[1-(2-methoxy)phenyl]piperazinyl]-1-phenylpropiona mide; a 5-HT1A antagonist]. These results show that the regulation of GRs during fetal life is structure-dependent and involves different 5-HT receptor subtypes. Moreover, the regulation of hippocampal GRs by citalopram suggests an action of antidepressants independent of their effects on monoamines.

Effect of serotonin inhibition on glucocorticoid and mineralocorticoid expression in various brain structures

Many studies have shown the existence of functional interactions between central neurotransmitter systems and the hypothalamo-pituitary adrenal axis. Mineralocorticoid receptors (MR) and glucocorticoid receptors (GR) are regulated by multiple factors including glucocorticoids themselves. Neurotransmitters such as serotonin (5-hydroxytryptamine: 5-HT) can regulate brain corticosteroid receptors in a complex way. The present study examined the short-term (48 h) effects of parachlorophenylalanine (PCPA), a drug which specifically inhibits 5-HT synthesis, on corticosteroid receptor levels and on the expression of their respective messenger ribonucleic acids (mRNA) in the rat hippocampus, hypothalamus and brain stem. The study was performed in bilaterally adrenalectomized animals, in order to avoid potential drug-induced changes in plasma corticosterone levels, which could secondarily regulate MR and GR. Short-term inhibition of 5-HT synthesis by PCPA significantly increased the number of hippocampal MR-binding sites. PCPA treatment did not alter the number of GR-binding sites in the hippocampus, hypothalamus and brain stem. We observed no change in the affinities of GR and MR sites in all the structures studied. In PCPA-treated rats, restoration of control 5-HT levels by injection of its immediate precursor, 5-hydroxytryptophan (5-HTP) brings the number of hippocampal MR-binding sites back to control levels. It can therefore be concluded that the increase in number of MR-binding sites induced by acute PCPA treatment is dependent on the decrease in 5-HT levels. The increase in hippocampal MR binding sites was correlated with an induction of their messengers, suggesting that 5-HT modulates the synthesis of MR protein. Although PCPA did not modify the number of hippocampal GR-binding sites, a decrease in hippocampal GR mRNA expression was observed. This study shows that 5-HT inhibits hippocampal mineralocorticoid receptor synthesis and that this effect is not mediated by changes in corticosterone hormone secretion, and illustrates the existence of complex mechanisms for corticosteroid receptor regulation in the hippocampus.

MDMA ('Ecstasy') enhances 5-HT1A receptor density and 8-OH-DPAT-induced hypothermia: blockade by drugs preventing 5-hydroxytryptamine depletion

One week after a single administration of 3,4-methylenedioxymethamphetamine (MDMA HCI, 30 mg/kg i.p.), 5-HT1A receptor density was significantly increased by approximately 25-30% in the frontal cortex and hypothalamus of rats. The increased density correlated with the potentiation of the hypothermic response to the 5-HT1A receptor agonist 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT, 1 mg/kg s.c.). Hypothalamic 5-HT7 receptors, which also bind 8-OH-DPAT, were not changed, however, by MDMA. Fluoxetine (5 mg/kg s.c.), ketanserin (5 mg/kg s.c.) or haloperidol (2 mg/kg i.p.), given 15 min prior to MDMA, prevented the depletion of 5-hydroxytryptamine (5-HT) induced by MDMA and also blocked the effects of this neurotoxin on 5-HT1A receptor density and on 8-OH-DPAT-induced hypothermia. The protection afforded by drugs against 5-HT loss did not correlate, however, with the antagonism of the acute hyperthermic effect of MDMA. The present results indicate that drugs able to prevent or to attenuate MDMA-induced 5-HT loss also prevent the changes in 5-HT1A receptor density as well as the enhanced hypothermic response to the 5-HT1A receptor agonist 8-OH-DPAT in MDMA-treated rats.

Repeated exposure to methylenedioxymethamphetamine (MDMA) alters nucleus accumbens neuronal responses to dopamine and serotonin

The purpose of this experiment was to investigate the effects of repeated exposure to methylenedioxymethamphetamine (MDMA) on responses of neurons in the nucleus accumbens of anesthetized rats to microiontophoretically-applied dopamine and serotonin. In tests conducted 1-4 days or 9-15 days following the last injection of MDMA (20 mg/kg, s.c., twice daily for 4 days), the inhibitory effects of both dopamine and serotonin on glutamate-evoked firing of nucleus accumbens cells were significantly attenuated compared to effects in control rats that were pretreated with saline injections. The inhibitory effect of the D1 receptor agonist SKF38393 was also significantly attenuated in the MDMA-pretreated rats. In contrast, the amount of inhibition of glutamate-evoked firing produced by application of GABA did not significantly differ between the MDMA-pretreated and the saline-pretreated rats. The neurotoxicity of the MDMA treatment regimen was confirmed by demonstrating that 3H-paroxetine binding was significantly decreased in the medial prefrontal cortex and the nucleus accumbens of the MDMA-pretreated rats. The mechanisms that produce the attenuated inhibitory responses to dopamine and serotonin following repeated injections of MDMA are not known. However, the results of these experiments indicate that repeated MDMA administration induces long-lasting changes in dopaminergic as well as serotonergic neurotransmission in the nucleus accumbens.

Dysregulation of diurnal rhythms of serotonin 5-HT2C and corticosteroid receptor gene expression in the hippocampus with food restriction and glucocorticoids

Both serotonergic dysfunction and glucocorticoid hypersecretion are implicated in affective and eating disorders. The adverse effects of serotonergic (5-HT)2C receptor activation on mood and food intake, the antidepressant efficacy of 5-HT2 receptor antagonists, and the hyperphagia observed in 5-HT2C receptor knockout mice all suggest a key role for increased 5-HT2C receptor-mediated neurotransmission. Glucocorticoids, however, downregulate 5-HT2C receptor mRNA in the hippocampus, and it is unclear how increased 5-HT2C receptor sensitivity is achieved in the presence of elevated glucocorticoid levels in depression. Here we show a monophasic diurnal rhythm of 5-HT2C receptor mRNA expression in the rat hippocampus that parallels time-dependent variations in 5-HT2C receptor agonist-induced behaviors in open field tests. Rats entrained to chronic food restriction show marked but intermittent corticosterone hypersecretion and maintain an unaltered 5-HT2C receptor mRNA rhythm. The 5-HT2C receptor mRNA rhythm, however, is suppressed by even modest constant elevations of corticosterone (adrenalectomy + pellet) or with elevated corticosterone during the daytime (8 A.M.), whereas a normal rhythm exists in animals that have the same dose of corticosterone in the evening (6 P.M.). Thus, animals showing even a transient daytime corticosterone nadir exhibit normal hippocampal 5-HT2C receptor mRNA rhythms, even in the presence of overt corticosterone hypersecretion. Chronic food restriction also abolishes the normal diurnal variation in hippocampal glucocorticoid receptor (GR) and mineralocorticoid receptor mRNAs and produces, unusually, both elevated corticosterone and increased GR. The mismatch between elevated glucocorticoids and maintained 5-HT2C receptor and increased GR gene expression in the hippocampus provides a new model to dissect mechanisms that may underlie affective and eating disorders.

Site-specific regulation of corticosteroid and serotonin receptor subtype gene expression in the rat hippocampus following 3,4-methylenedioxymethamphetamine: role of corticosterone and serotonin

Abnormal interactions between serotonin (5-hydroxytryptamine) and glucocorticoids, notably in the hippocampus, may underpin neuroendocrine, affective and cognitive dysfunction in depression and ageing. Glucocorticoids act via intracellular glucocorticoid and mineralocorticoid receptors, whereas 5-hydroxytryptamine binds to a family of transmembrane sites; both cross- and auto-regulation have been proposed. To determine the roles of 5-hydroxytryptamine and corticosterone in the short-term control of hippocampal receptor gene expression, we used 3,4-methylenedioxymethamphetamine (20 mg/kg), which causes acute release of both 5-hydroxytryptamine and corticosterone. 3,4-methylenedioxymethamphetamine increased mineralocorticoid receptor messenger RNA expression throughout the hippocampus after 16 h. In rats with fixed glucocorticoid levels (adrenalectomy plus corticosterone pellets) this effect was lost in CA1-4, suggesting corticosterone-mediation, but maintained in the dentate gyrus, indicating 5-hydroxytryptamine involvement. In contrast, 3,4-methylenedioxymethamphetamine decreased glucocorticoid receptor messenger RNA expression in the dentate gyrus and CA1 within 4 h, but only in adrenal-intact rats, suggesting corticosterone control. 5-Hydroxytryptamine1A receptor messenger RNA expression was decreased in CA1 in both groups of rats, but increased in the dentate gyrus only in corticosterone-fixed rats, suggesting 5-hydroxytryptamine differentially regulates expression of this gene within hippocampal subfields. 5-hydroxytryptamine2C receptor messenger RNA was decreased in ventral CA1 only in adrenal-intact rats, suggesting a corticosterone effect, and decreased in the subiculum in both groups, indicating 5-hydroxytryptamine mediation. These results show the complexity and intricate subregional-specificity of 5-hydroxytryptamine and corticosterone interactions upon hippocampal corticosteroid and 5-hydroxytryptamine receptor gene expression. 3,4-Methylenedioxymethamphetamine-induced alterations in hippocampal receptor gene expression may play a role in the mood and behavioural changes associated with this drug of abuse.

Impact of adrenalectomy on 5-HT6 and 5-HT7 receptor gene expression in the rat hippocampus

Both glucocorticoid excess and decreased serotonergic (5-HT) transmission may cause depression. The recently cloned 5-HT6 and 5-HT7 receptors have high affinity for antidepressants. Here, we show that pharmacological adrenalectomy increases 5-HT6 and 5-HT7 receptor mRNA expression in specific hippocampal subfields, effects partly reversed by corticosterone replacement. Increased 5-HT6 and 5-HT7 receptor expression may provide a basis, in part, for the therapeutic actions of adrenal steroid synthesis inhibitors in resistant depression.

Ketanserin selectively blocks acute stress-induced changes in NGFI-A and mineralocorticoid receptor gene expression in hippocampal neurons

Serotonin and glucocorticoids interact at the hippocampus to alter neuronal function. Serotonin and antidepressant drugs increase glucocorticoid receptor and mineralocorticoid receptor gene expression in hippocampal neurons over a few days. The effects of serotonin are mediated via ketanserin-sensitive "serotonin-2 type" receptors and induction of cyclic AMP, although the subsequent molecular mechanisms are unclear. Recently, we have shown that chronic environmental manipulations which induce glucocorticoid receptor gene expression in specific hippocampal subfields of the rat are associated with congruent induction of the transcription factor NGFI-A (zif268, krox24, egr-1) and repression of AP-2; both factors may bind to the glucocorticoid receptor gene promoter. However, any relationship between serotonin and these transcription factors is unknown. Here, we show that acute restraint stress, which causes serotonin release at the hippocampus, induces hipppocampal NGFI-A, but represses activator protein-2 and mineralocorticoid receptor gene expression within 90 min. These changes are sustained for 4 h, but not 12 h. Ketanserin attenuates the stress-induced rise in NGFI-A and fall in mineralocorticoid receptor gene expression, and partly also the fall in AP-2 messenger RNA expression. These data suggest that restraint stress, acting via serotonin release and ketanserin-sensitive serotonin receptors, produces rapid, transient and specific changes in transcription factor gene expression in hippocampal neurons. Any link between these effects and the control of glucocorticoid and mineralocorticoid receptor expression with chronic serotonin or antidepressant treatment remains to be elucidated.

Immunocytochemical detection of the serotonin transporter in rat brain

The regional distribution of the serotonin uptake system was studied in rat brain using a specific polyclonal antibody raised against the putative extracellular loop between transmembrane domains 7 and 8 of the cloned rat serotonin transporter. Light microscope analysis with fluorescence and avidin-biotin-peroxidase techniques revealed a punctate staining as well as numerous labelled thin fibres, which exhibited accumulation of reaction end-product deposit over varicosities. These immunopositive processes were widely and heterogeneously distributed in the rat brain. High densities of immunoreactivity were seen within the caudate-putamen, amygdaloid complex, cortical areas, substantia nigra, ventral pallidum, Islands of Calleja, septal nuclei, interpeduncular nucleus, trigeminal motor nucleus and olfactory nuclei. We also found strong expression of serotonin transporter in the stratum oriens of area CA3 and, to a lesser extent, in the stratum oriens of CA1 and the stratum lacunosum molecular of CA1-CA3 regions of the hippocampus. Within the raphe nuclei, a moderate to high incidence of stained processes was observed, and immunopositive cell bodies were detected in the dorsal raphe nucleus. In addition, some immunoreactive fibres were present in the molecular and granular layers of the cerebellum as well as in the cochlear and olivary nuclei. In none of the regions analysed was evidence for glial staining obtained. The present immunocytochemical data reveal a widespread and heterogeneous distribution of the serotonin transporter in rat brain and suggest that serotoni transporter is preferentially sorted into axons, where it appears concentrated at varicosities and terminal boutons.

Cloning and production of antisera to human placental 11 beta-hydroxysteroid dehydrogenase type 2

By inactivating potent glucocorticoid hormones (cortisol and corticosterone), 11 beta-hydroxysteroid dehydrogenase type 2 (11 beta-HSD2) plays an important role in the placenta by controlling fetal exposure to maternal glucocorticoids, and in aldosterone target tissues by controlling ligand access to co-localized glucocorticoid and mineralocorticoid receptors. Amino acid sequence from homogeneous human placental 11 beta-HSD2 was used to isolate a 1897 bp cDNA encoding this enzyme (predicted M(r) 44126; predicted pI 9.9). Transfection into mammalian (CHO) cells produces 11 beta-HSD2 activity which is NAD(+)-dependent, is without reductase activity, avidly metabolizes glucocorticoids (Km values for corticosterone, cortisol and dexamethasone of 12.4 +/- 1.5, 43.9 +/- 8.5 and 119 +/- 15 nM respectively) and is inhibited by glycyrrhetinic acid and carbenoxolone (IC50 values 10-20 nM). Rabbit antisera recognizing 11 beta-HSD2 have been raised to an 11 beta-HSD2-(370--383)-peptide-carrier conjugate. Recombinant 11 beta-HSD2, like native human placental 11 beta-HSD2, is detectable with affinity labelling and anti-11 beta-HSD2 antisera, and appears to require little post-translational processing for activity. 11 beta-HSD2 mRNA (approximately 1.9 kb transcript) is expressed in placenta, aldosterone target tissues (kidney, parotid, colon and skin) and pancreas. In situ hybridization and immunohistochemistry localize abundant 11 beta-HSD2 expression to the distal nephron in human adult kidney and to the trophoblast in the placenta. 11 beta-HSD2 transcripts are expressed in fetal kidney (but not lung, liver or brain) at 21-26 weeks, suggesting that an 11 beta-HSD2 distribution resembling that in the adult is established by this stage in human development.

Distribution of hippocampal mineralocorticoid and glucocorticoid receptor mRNA in a glucocorticoid resistant nonhuman primate

Glucocorticoids regulate the activity of the hypothalamic-pituitary-adrenal axis through both mineralocorticoid (MR) and glucocorticoid (GR) receptors in the hippocampus. In addition, glucocorticoids down-regulate hippocampal expression of MR and GR mRNA and protein, presumably decreasing their own effect. Marmosets are a New World primate characterized by extraordinarily high levels of circulating ACTH and cortisol. The relative glucocorticoid insensitivity of these animals to their massive levels of glucocorticoids was attributed to a decreased affinity of their GR for glucocorticoids, as well as a compromised ability of this receptor to transactivate glucocorticoid-responsive genes. The lack of mineralocorticoid excess, on the other hand, was attributed to a renal MR which responded poorly to cortisol, but normally to aldosterone. The purpose of this study was to examine MR and GR mRNA expression in the marmoset (Callithrix jacchus jacchus) hippocampus. Overall, steady state levels of both MR and GR mRNA were elevated in all of the hippocampal subfields of the marmoset, and this was obvious in rough comparisons with those of a typical glucocorticoid-sensitive Old World primate, the rhesus monkey (Macaca mulata). Notable were the extremely high levels of GR mRNA in the dentate gyrus and field CA3 of the marmoset. The GR mRNA density distribution of the marmoset also appeared to differ from that in the rhesus and from those previously reported in rats and humans. These findings suggest that there is a compensatory elevation of MR and GR mRNAs in the marmoset hippocampus, which appears to be the result of target tissue resistance to glucocorticoids and inappropriate down-regulation by the elevated, but ineffective, circulating cortisol.

Glucocorticoids, hippocampal corticosteroid receptor gene expression and antidepressant treatment: relationship with spatial learning in young and aged rats

The emergence of cognitive deficits in a subgroup of aged rats is associated with increased hypothalamic-pituitary-adrenal axis activity, decreased hippocampal mineralocorticoid and/or glucocorticoid receptor gene expression and neuronal loss. Short-term treatment with antidepressant drugs in young rats increases hippocampal corticosteroid receptor gene expression. In this study, the effects of chronic antidepressant administration on hippocampal mineralocorticoid and glucocorticoid receptor gene expression and spatial memory in young and aged rats were investigated. Young (eight months) and old (22 +/- 1 months) Lister-hooded rats were ranked according to watermaze performance. Matched pairs of rats were treated with amitriptyline (10 mg/kg) or saline daily for nine weeks, then reassessed in the watermaze. Amitriptyline significantly improved spatial memory in the young rats (33% increase in transfer test time) and increased hippocampal mineralocorticoid, but not glucocorticoid receptor messenger RNA expression. By contrast, in aged rats, amitriptyline had no effect on spatial memory or hippocampal corticosteroid receptor gene expression, either in cognitively unimpaired or cognitively-impaired animals. In aged rats, basal plasma corticosterone levels, which were significantly higher than in young animals, correlated negatively with spatial memory, while hippocampal glucocorticoid receptor mRNA expression correlated negatively with plasma corticosterone levels and positively with spatial memory. Amitriptyline had no significant effect on basal morning plasma corticosterone levels in either young or aged rats, but significantly decreased evening corticosterone levels in aged rats. Our data support the notion that corticosterone exerts a concentration-dependent biphasic influence, via selective activation of hippocampal mineralocorticoid and glucocorticoid receptor, on spatial memory. Amitriptyline improves spatial memory in young rats and increases hippocampal mineralocorticoid receptor gene expression. The lack of amitriptyline effect on spatial memory in aged rats may reflect decreased plasticity of both the synaptic processes underlying spatial memory and the regulation of hippocampal mineralocorticoid/glucocorticoid receptor expression, with mineralocorticoid receptors fully occupied due to elevated basal plasma corticosterone levels (in part a consequence of inadequate glucocorticoid receptor function).

Modulation of serotonin and corticosteroid receptor gene expression in the rat hippocampus with circadian rhythm and stress

Glucocorticoids and serotonin (5-HT) modulate behaviour and hypothalamic-pituitary-adrenal (HPA) axis responses. The two systems interact prominently in the hippocampus, where these effects may occur. We have previously shown that hippocampal 5-HT2C receptor mRNA expression is increased by adrenalectomy or central 5-HT lesions. We have now determined expression of corticosteroid and 5-HT receptor subtype genes in the hippocampus across the diurnal cycle, when there are changes both in plasma corticosterone and hippocampal 5-HT levels, as well as the responses of these transcripts to acute and chronic stress, using in situ hybridisation histochemistry. Expression of both glucocorticoid (GR) and mineralocorticoid (MR) receptor mRNAs was significantly higher (131-153%) in the hippocampus at 08.00 h (corticosterone nadir) than at 20.00 h (corticosterone peak). 5-HT2C receptor mRNA expression also showed circadian variation (106-184% higher in CA1-CA3 in the morning). Hippocampal 5-HT1A and 5-HT2A receptor mRNA expression had no diurnal variation. Chronic (15 day) adjuvant arthritis stress, abolished the circadian corticosterone nadir, maintaining plasma corticosterone around diurnal peak values. Chronic arthritis stress suppressed hippocampal 5-HT2C receptor mRNA expression at 08.00 h to levels comparable to 20.00 h controls. By contrast to chronic stress, 6 h after acute laparotomy stress, plasma corticosterone was elevated above control (20.00 h) and 5-HT2C receptor mRNA expression was increased (CA2). Neither acute nor chronic stress altered MR, GR, 5-HT1A or 5-HT2A receptor mRNA expression in any hippocampal subfield. These results show that hippocampal expression of the 5-HT2C receptor gene, but not other subtypes, is sensitive to a variety of manipulations.(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of adrenalectomy on 5-hydroxytryptamine and corticosteroid receptor subtype messenger RNA expression in rat hippocampus

Both central serotonergic dysfunction and glucocorticoid hypersecretion have been separately implicated in the aetiology of affective disorders. The hippocampus highly expresses receptors for 5-hydroxytryptamine and glucocorticoids, and adrenalectomy alters the responsivity of hippocampal neurons to 5-hydroxytryptamine. The hippocampus thus represents a prime locus for interactions between the two systems. In this study we examined the effects of glucocorticoid manipulations on neuronal expression of messenger RNA encoding corticosteroid receptor and 5-hydroxytryptamine receptor subtypes in the hippocampus and 5-hydroxytryptamine1A messenger RNA expression in the dorsal raphe, in the rat. Interestingly, there was no effect of adrenalectomy on 5-hydroxytryptamine1A or 5-hydroxytryptamine2A receptor messenger RNA expression in the dorsal or ventral hippocampus at any time point measured. Furthermore, no changes in 5-hydroxytryptamine1A receptor gene expression were seen in the dorsal raphe (encoding autoreceptors) after adrenalectomy. However, 5-hydroxytryptamine2C (5-hydroxytryptamine1C) receptor messenger RNA expression was increased specifically in posterior CA1 and CA3 neurons following adrenalectomy, an effect that was reversed by glucocorticoid replacement. Following adrenalectomy, glucocorticoid and mineralocorticoid receptor messenger RNA expression increased in the dentate gyrus, CA1 and CA3 subfields of the hippocampus. These increases were apparent 6 h after adrenalectomy, were maintained at two days, but 14 days after adrenalectomy hippocampal glucocorticoid receptor and mineralocorticoid receptor gene expression had returned to control levels. These effects of adrenalectomy were abolished by dexamethasone, but not aldosterone administration, suggesting mediation by autoregulatory glucocorticoid receptors. Our results show that adrenalectomy only transiently increases corticosteroid receptor gene expression in the hippocampus, and selectively increases hippocampal 5-hydroxytryptamine2C receptor messenger RNA expression. The resulting change in 5-hydroxytryptamine2C receptor-mediated responses may produce the alterations in hippocampal neuronal activity in response to 5-hydroxytryptamine observed after adrenalectomy.

Increased glucocorticoid receptor gene expression in the rat hippocampus following combined serotonergic and medial septal cholinergic lesions

Glucocorticoid excess is associated with hippocampal neuronal dysfunction and loss, mainly affecting CA1. Degeneration of both cholinergic and serotonergic (5-HT) hippocampal afferents is prominent in aged rats and Alzheimer's disease. Lesions of these individual pathways alter hippocampal expression of mineralocorticoid (MR) and glucocorticoid (GR) receptor mRNAs; both transcripts are increased by cholinergic lesions, but markedly decreased by serotonergic denervation. In the present study we found that combined medial septal cholinergic and central 5-HT lesions increase hippocampal GR mRNA expression, specifically in CA1 and CA2 subfields, whereas MR mRNA expression was similar to controls. Thus the effects of the cholinergic lesion, at least upon GR gene expression, appear to predominate while the effects of the lesions upon MR gene expression were additive. Increased hippocampal GR gene expression per neuron may increase hippocampal neuronal vulnerability with age or disease.