Sigma 1 receptor-related neuroactive steroids modulate cocaine-induced reward

Neuroactive steroids and peripheral neuropathy

Peripheral neuropathy, either inherited or acquired, represents a very common disorder for which effective clinical treatments are not available yet. Observations here summarized indicate that neuroactive steroids, such as progesterone, testosterone and their reduced metabolites, might represent a promising therapeutic option. Peripheral nerves are able to synthesize and metabolize neuroactive steroids and are a target for these molecules, since they express classical and non-classical steroid receptors. Neuroactive steroids modulate the expression of key transcription factors for Schwann cell function, regulate Schwann cell proliferation and promote the expression of myelin proteins involved in the maintenance of myelin multilamellar structure, such as myelin protein zero and peripheral myelin protein 22. These actions may result in the protection and regeneration of peripheral nerves affected by different forms of pathological alterations. Indeed, neuroactive steroids are able to counteract biochemical, morphological and functional alterations of peripheral nerves in different experimental models of neuropathy, including the alterations caused by aging, diabetic neuropathy and physical injury. Therefore, neuroactive steroids, pharmacological agents able to increase their local synthesis and synthetic ligands for their receptors have a promising potential for the treatment of different forms of peripheral neuropathy.

Purification and characterization of the guinea pig sigma-1 receptor functionally expressed in Escherichia coli

Sigma receptors once considered as a class of opioid receptors are now regarded as unique orphan receptors, distinguished by the ability to bind various pharmacological agents such as the progesterone (steroid), haloperidol (anti-psychotic), and drugs of abuse such as cocaine and methamphetamine. The sigma-1 receptor is a 223 amino acid protein, proposed to have two transmembrane segments. We have developed a scheme for the purification of the guinea pig sigma-1 receptor following overexpression in Escherichia coli as a maltose binding protein (MBP) fusion and extraction with Triton X-100. Affinity chromatography using an amylose column and Ni2+ affinity column was used to purify the sigma-1 receptor. The sigma-1 receptor purified by this method is a 26 kDa polypeptide as assessed by SDS-PAGE, binds sigma ligands with high affinity and can be specifically photoaffinity labeled with the sigma-1 receptor photoprobe, [125I]-iodoazidococaine. Ligand binding using [3H]-(+)-pentazocine indicated that approximately half of the purified protein in Triton X-100 bound to radioligand. The MBP-sigma-1 receptor and the sigma-1 receptor in 0.5% triton were maximally stable for approximately two weeks at -20 degrees C in buffer containing 30% glycerol.

Immunohistochemical localization and biological activity of the steroidogenic enzyme cytochrome P450 17α-hydroxylase/C17, 20-lyase (P450C17) in the frog brain and pituitary

It is now clearly established that the brain has the capability of synthesizing various biologically active steroids including 17-hydroxypregnenolone (17OH-Delta(5)P), 17-hydroxyprogesterone (17OH-P), dehydroepiandrosterone (DHEA) and androstenedione (Delta(4)). However, the presence, distribution and activity of cytochrome P450 17alpha-hydroxylase/C17, 20-lyase (P450(C17)), a key enzyme required for the conversion of pregnenolone (Delta(5)P) and progesterone (P) into these steroids, are poorly documented. Here, we show that P450(C17)-like immunoreactivity is widely distributed in the frog brain and pituitary. Prominent populations of P450(C17)-containing cells were observed in a number nuclei of the telencephalon, diencephalon, mesencephalon and metencephalon, as well as in the pars distalis and pars intermedia of the pituitary. In the brain, P450(C17)-like immunoreactivity was almost exclusively located in neurons. In several hypothalamic nuclei, P450(C17)-positive cell bodies also contained 3beta-hydroxysteroid dehydrogenase-like immunoreactivity. Incubation of telencephalon, diencephalon, mesencephalon, metencephalon or pituitary explants with [(3)H]Delta(5)P resulted in the formation of several tritiated steroids including 17OH-Delta(5)P, 17OH-P, DHEA and Delta(4). De novo synthesis of C(21) 17-hydroxysteroids and C(19) ketosteroids was reduced in a concentration-dependent manner by ketoconazole, a P450(C17) inhibitor. This is the first detailed immunohistochemical mapping of P450(C17) in the brain and pituitary of any vertebrate. Altogether, the present data provide evidence that CNS neurons and pituitary cells can synthesize androgens.

Trishomocubanes: Novel σ ligands modulate cocaine-induced behavioural effects

Trishomocubane analogues TC1 (N-(3'-fluorophenyl)ethyl-4-azahexacyclo [5.4.1.0(2,6).0(3,10).0(5,9).0(8,11)]dodecan-3-ol) and TC4 (N-(3'-fluorophenyl)methyl-4-azahexacyclo [5.4.1.0(2,6).0(3,10).0(5,9).0(8,11)]dodecan-3-ol) were evaluated for their modulatory effects on locomotor activity as well as interactions with cocaine-induced responses. TC1 and TC4 have high affinity and moderate to high selectivity for sigma(1) (Ki=10 nM, sigma1/sigma2=0.03) and sigma2 (Ki=20 nM, sigma1/sigma2=7.6) receptor subtypes respectively. Both compounds have negligible affinity for the dopamine (DAT), serotonin (SERT), and norepinephrine (NET) transporters. In behavioural studies, TC1 produced a dose-related inhibition in spontaneous locomotor activity measured in a Digiscan apparatus. TC1 attenuated the stimulatory locomotor effect of 20 mg/kg cocaine with a half-maximal depressant activity (ID50) of 38.6 mg/kg. TC1 (dose range of 25 to 100 mg/kg) also partially substituted for the effect of cocaine (10 mg/kg) in a discriminative stimulus task, involving the trained discrimination between cocaine and saline using a two-lever choice method. Following a dose of 50 mg/kg TC1, a maximum of 31% substitution was reached. The response rate was reduced to 56% of vehicle control following a TC1 dose of 100 mg/kg. These behavioural effects suggest that TC1 can act as an antagonist via the sigma1 receptor. In contrast to TC1, TC4 produced a stimulant effect in locomotor activity with the ED50 estimated at 0.94 mg/kg. In addition, TC4 failed to inhibit cocaine-induced stimulation; neither did it substitute for the discriminative stimulus effects of cocaine. TC4 thus appears to interact predominantly with the sigma2 receptor subtype (sigma1/sigma2=7.6) which may result in dopamine stimulation independent of the effects of cocaine. The differential effect of TC1 and TC4 warrants further study of the mechanism of these actions. Present data also suggests a potential role for trishomocubane analogues in developing medication or research tools for cocaine addiction.

Protein kinase A activation down-regulates, whereas extracellular signal-regulated kinase activation up-regulates sigma-1 receptors in B-104 cells: Implication for neuroplasticity

The sigma-1 receptor (Sig-1R) can bind psychostimulants and was shown to be up-regulated in the brain of methamphetamine self-administering rats. Up-regulation of Sig-1Rs has been implicated in neuroplasticity. However, the mechanism(s) whereby Sig-1Rs are up-regulated by psychostimulants is unknown. Here, we employed a neuroblastoma cell line B-104, devoid of dopamine receptors and transporter, and examined the effects of psychostimulants as well as cAMP on the expression of Sig-1Rs in this cell line, with a specific goal to identify signal transduction pathway(s) that may regulate Sig-1R expression. Chronic treatments of B-104 cells with physiological concentrations of cocaine or methamphetamine failed to alter the expression of Sig-1Rs. N6,2'-O-Dibutyryl-cAMP (dB-cAMP), when used at 0.5 mM, caused a down-regulation of Sig-1Rs that could be blocked by a protein kinase A (PKA) inhibitor, N-[2-(p-bromocinnamylamino)ethyl]-5-isoquinolinesulfonamide dihydrochloride (H-89). However, dB-cAMP, when used at 2 mM, caused an up-regulation of Sig-1Rs that was insensitive to the H-89 blockade but was partially blocked by an extracellular signal-regulated kinase (ERK)/mitogen-activated protein kinase inhibitor PD98059 (2'-amino-3'-methoxyflavone). Furthermore, 2 mM dB-cAMP induced an ERK phosphorylation lasting at least 90 min, at which time the phosphorylation caused by 0.5 mM dB-cAMP had already diminished. PD98059, applied 90 min after addition of 2 mM dB-cAMP, attenuated the Sig-1R up-regulation. Our results indicate that cAMP is bimodal in regulating Sig-1R expression: a down-regulation via PKA and an up-regulation via ERK. Results also suggest that psychostimulants may manipulate the cAMP-PKA-Sig-1R and/or the cAMP-ERK-Sig-1R pathways to achieve a neuroplasticity that favors addictive behaviors.

DHEA, a neurosteroid, decreases cocaine self-administration and reinstatement of cocaine-seeking behavior in rats

Dehydroepiandrosterone (DHEA), which can act as a potential antidepressant in both animals and humans, appears to lower distress involved with cocaine withdrawal. In fact, a role for neurosteroids in modulation of substance-seeking behavior is becoming increasingly clear. Therefore, we tested the effects of DHEA on the self-administration of cocaine (1 mg/kg/infusion) by rats. At maintenance, a relatively low dose of exogenous DHEA (2 mg/kg; i.p.) attenuated cocaine self-administration after several days of chronic treatment. More than 2 weeks (19 days) of daily DHEA injections were required to decrease the cocaine-seeking behavior of rats to less than 20% of their maintenance levels. DHEA does not seem to decrease cocaine self-administration by increasing the reinforcing properties of the drug, as indicated by a cocaine dose-response determination. After being subjected to extinction conditions in the presence of DHEA, rats demonstrated a minimal response to acute exposure to cocaine (10 mg/kg), which indicated a protective effect of DHEA on relapse to cocaine usage. Our results suggest a potential role for the neurosteroid DHEA in controlling cocaine-seeking behavior, by reducing both the desire for cocaine usage and the incidence of relapse.

Sigma1 receptor ligands and related neuroactive steroids interfere with the cocaine-induced state of memory

The present series of experiments examined the involvement of the sigma(1) receptor and related neuroactive steroids in the memory state induced by a very low dose of cocaine. Using a modified passive avoidance procedure in mice, we examined whether cocaine induces state-dependent (StD) learning. Animals trained and tested with saline or the same dose of cocaine (0.1 or 0.3 mg/kg) showed correct retention, measured using two independent parameters: the retention latency and a ratio between the retention latency and the last training latency. Animals trained with cocaine (0.1 mg/kg) and tested with saline or cocaine (0.03, 0.3 mg/kg), or trained with saline and tested with cocaine, showed altered retention parameters, demonstrating that StD occurred. Therefore, cocaine administered before training produced a chemical state used as an endogenous cue to insure optimal retention. Since sigma(1) receptor activation is an important event during the acquisition of cocaine reward, we tested several sigma(1) ligands and related neurosteroids. The sigma(1) agonist igmesine or antagonist BD1047 failed to produce StD, but modified the cocaine state. Among neuroactive steroids, pregnanolone and allopregnanolone, positive modulators of the gamma-aminobutyric acid type A (GABA(A)) receptor, produced StD. However, steroids also acting as sigma(1) agonists, dehydroepiandrosterone (3beta-hydroxy-5alpha-androsten-17-one (DHEA)), pregnenolone, or antagonist, progesterone, failed to induce StD but modified the cocaine state. Furthermore, optimal retention was observed with mice trained with (igmesine or DHEA)+cocaine and tested with a higher dose of cocaine, or with mice trained with (BD1047 or progesterone)+cocaine and tested with vehicle. This study demonstrated that: (i) low doses of cocaine induce a chemical state/memory trace sustaining StD; (ii) modulation of the sigma(1) receptor activation, although insufficient to provoke StD, modulates the cocaine state; (iii) neuroactive steroids exert a unique role in state-dependent vs state-independent learning, via GABA(A) or sigma(1) receptor modulation, and are able to affect the cocaine-induced mnesic trace at low brain concentrations.

Dehydroepiandrosterone (DHEA) attenuates cocaine-seeking behavior in the self-administration model in rats

The aim of this study was to determine the possible involvement of the neurosteroid dehydroepiandrosterone (DHEA) in cocaine-seeking behavior in a self-administration model in rats. DHEA pretreatment (continued thereafter concomitantly with cocaine self-administration) attenuated cocaine-seeking behavior and elevated the levels of dopamine and serotonin in several brain regions relevant to cocaine addiction. Chronic cocaine self-administration induced elevation in brain DHEA, its sulfate ester, DHEAS, and pregnenolone. The increased brain DHEA following cocaine self-administration may serve as a compensatory protective mechanism geared to attenuate the craving for cocaine. Such anti-craving activity is further enhanced by DHEA treatment before and during cocaine self-administration.

Lack of evidence of a role for the neurosteroid allopregnanolone in ethanol-induced reward and c-fos expression in DBA/2 mice

Previous studies using the 5alpha-reductase inhibitor finasteride suggest that progesterone metabolites, particularly the endogenous neurosteroid allopregnanolone, mediate some of the effects of ethanol. Consequently, we studied the effect of finasteride (2 x 25 mg/kg s.c., 12 h apart) pretreatment on the acquisition and expression of ethanol (2 g/kg i.p.) induced conditioned place preference and c-fos expression in DBA/2 mice; a strain known to be particularly sensitive to ethanol. Ethanol administration induced a clear conditioned place preference and widespread c-fos expression, with elements of the extended amygdala, Edinger-Westphal nucleus and paraventricular nucleus being especially sensitive. However, despite an approximately 99% decrease in whole brain allopregnanolone content, finasteride pretreatment had remarkably little effect on either ethanol-induced conditioned place preference or ethanol-induced c-fos expression. Thus, aside from a general stimulatory effect on c-fos expression in the ventral tegmental area, and generally mild depression of locomotor activity, no other effects of finasteride or interaction with ethanol effects were identifiable. Together, these studies suggest that endogenous allopregnanolone plays little part in mediating acute ethanol-induced reward or neural activation in DBA/2 mice.

Emerging pharmacological strategies in the fight against cocaine addiction

Cocaine addiction continues to be an important public health problem worldwide. At present, there are no proven pharmacotherapies for cocaine addiction. The studies reviewed here revealed a number of emerging targets for cocaine pharmacotherapy. First, disulfiram, a medication with dopaminergic effects, reduced cocaine use in a number of clinical trials. Second, GABA medications, tiagabine and topiramate, were found promising in clinical trials. Third, a beta-adrenergic blocker, propranolol, may be effective especially among cocaine-addicted individuals with high withdrawal severity. Fourth, treatment with a stimulant medication, modafinil, has reduced cocaine use. Last, a cocaine vaccine that slows entry of cocaine into the brain holds promise. These promising findings need to be further tested in controlled clinical trials.

A Medicinal-Chemistry-Guided Approach to Selective and Druglike Sigma 1 Ligands

Based on a medicinal-chemistry-guided approach, three novel series of druglike cycloalkyl-annelated pyrazoles were synthesized and display high affinity (pKi>8) for the sigma1 receptor. Structure-affinity relationships were established, and the different scaffolds were optimized with respect to sigma1 binding and selectivity versus the sigma2 receptor and the hERG channel, resulting in selective compounds that have Ki values (for sigma1) in the subnanomolar range. Selected compounds were screened for cytochrome P450 inhibition (CYP1A2, CYP2A6, CYP2B6, CYP2C8, CYP2C9, CYP2C19, CYP2D6, CYP2E1, CYP3A4), metabolic stability (rat and human liver microsomes), and cell-membrane permeability (Caco-2). They showed favorable in vitro ADME properties as well as favorable calculated druglike and experimental physicochemical properties. Furthermore, compounds 7 f and 17 a, for example, displayed high selectivity (affinity) for the sigma1 receptor against a wide range of other receptors (>60). With these valuable tool compounds in hand, we are further exploring the role of the sigma1 receptor in relevant animal models corresponding to such medicinal indications as drug abuse, pain, depression, anxiety, and psychosis.

The Sigma1 Protein as a Target for the Non-genomic Effects of Neuro(active)steroids: Molecular, Physiological, and Behavioral Aspects

Steroids synthesized in the periphery or de novo in the brain, so called 'neurosteroids', exert both genomic and nongenomic actions on neurotransmission systems. Through rapid modulatory effects on neurotransmitter receptors, they influence inhibitory and excitatory neurotransmission. In particular, progesterone derivatives like 3alpha-hydroxy-5alpha-pregnan-20-one (allopregnanolone) are positive allosteric modulators of the gamma-aminobutyric acid type A (GABA(A)) receptor and therefore act as inhibitory steroids, while pregnenolone sulphate (PREGS) and dehydroepiandrosterone sulphate (DHEAS) are negative modulators of the GABA(A) receptor and positive modulators of the N-methyl-D-aspartate (NMDA) receptor, therefore acting as excitatory neurosteroids. Some steroids also interact with atypical proteins, the sigma (sigma) receptors. Recent studies particularly demonstrated that the sigma1 receptor contributes effectively to their pharmacological actions. The present article will review the data demonstrating that the sigma1 receptor binds neurosteroids in physiological conditions. The physiological relevance of this interaction will be analyzed and the impact on physiopathological outcomes in memory and drug addiction will be illustrated. We will particularly highlight, first, the importance of the sigma1-receptor activation by PREGS and DHEAS which may contribute to their modulatory effect on calcium homeostasis and, second, the importance of the steroid tonus in the pharmacological development of selective sigma1 drugs.

Compensatory effect by sigma1 (σ1) receptor stimulation during alcohol withdrawal in mice performing an object recognition task

Chronic alcohol consumption (CAC) provokes intense neurobiological alterations, which lead, notably, to an important abstinence syndrome upon withdrawal with deleterious cognitive consequences. We here examined the effect of activation or inactivation of the sigma(1) receptor during CAC withdrawal on the cognitive abilities of Swiss mice. Animals consumed an alcohol 10%/sucrose 30 g/l solution during 4 months. Control groups consumed only the sucrose vehicle solution. Then, animals experienced a progressive, 16 days long, CAC withdrawal, during which they were administered once daily with saline, igmesine (10 mg/kg i.p.), a sigma(1) receptor agonist, or BD1047 (10 mg/kg i.p.), a sigma(1) antagonist. Mice were then tested using an object exploration task, to evaluate their locomotor and exploratory activities and reactions to object habituation, spatial change or novel object presentation. CAC-treated animals showed augmentation of locomotion, anxiety and object exploration, which impeded correct reaction to object habituation, spatial change or novelty. Treatment with the sigma(1) ligands, ineffective in control groups, resulted in decrease of the hyper-responsiveness and restored habituation. However, correct reactions to spatial change and novelty were only produced by the sigma(1) agonist treatment. Moreover, the sigma(1) receptor hippocampal expression was increased in CAC-treated mice. Treatments with both sigma(1) ligands regulated its expression, but subcellular fractionation experiments revealed that the agonist treatment increased [(3)H](+)-pentazocine binding to sigma(1) sites in the plasma membrane fraction, while the antagonist maintained it only in the microsomal, putatively endoplasmic reticulum, fraction. In conclusion, CAC increased the sigma(1) receptor expression in the hippocampus of mice. Regulation of its expression during withdrawal, notably using a selective agonist, allowed not only to attenuate the CAC-induced hyper-responsiveness, but also to restore correct cognitive abilities.

N-[18F]4'-fluorobenzylpiperidin-4yl-(2-fluorophenyl) acetamide ([18F]FBFPA): a potential fluorine-18 labeled PET radiotracer for imaging sigma-1 receptors in the CNS

A series of brain uptake studies and PET imaging studies were conducted with the sigma(1) selective imaging agent, [(18)F]FBFPA. The results of the study indicate that this radiotracer readily crosses the blood-brain barrier and labels sigma(1) receptors in vivo. In vivo blocking studies with a sigma(1) selective ligand and a nonselective sigma(1)/sigma(2) receptor ligand indicates that [(18)F]FBFPA labels sigma(1) and not sigma(2) receptors in rodent brain. PET imaging studies demonstrated a high uptake in regions of rhesus monkey brain having a high density of sigma(1) receptors. The uptake of [(18)F]FBFPA was displaced by the sigma ligand, haloperidol (1 mg/kg, i.v.). In vivo blocking studies indicate that the progesterone blocked the brain uptake of [(18)F]FBFPA in rat brain. These data indicate that [(18)F]FBFPA is a potential radiotracer for imaging sigma(1) receptors in the CNS in vivo with PET.

Effects of low- and high-nicotine cigarette smoking on mood states and the HPA axis in men

The acute effects of smoking a low- or high-nicotine cigarette on hypothalamic-pituitary-adrenal (HPA) hormones, subjective responses, and cardiovascular measures were studied in 20 healthy men who met American Psychiatric Association Diagnostic and Statistical Manual IV criteria for nicotine dependence. Within four puffs (or 2 min) after cigarette smoking began, plasma nicotine levels and heart rate increased significantly (P<0.01), and peak ratings of 'high' and 'rush' on a Visual Analogue Scale were reported. Reports of 'high', 'rush', and 'liking' and reduction of 'craving' were significantly greater after smoking a high-nicotine cigarette than a low-nicotine cigarette (P<0.05). Peak plasma nicotine levels after high-nicotine cigarette smoking (23.9+/-2.6 ng/ml) were significantly greater than after low-nicotine cigarette smoking (3.63+/-0.59 ng/ml) (P<0.001). After smoking a low-nicotine cigarette, adrenocorticotropin hormone (ACTH), cortisol, dehydroepiandrosterone (DHEA), and epinephrine did not change significantly from baseline. After high-nicotine cigarette smoking began, plasma ACTH levels increased significantly above baseline within 12 min and reached peak levels of 21.88+/-5.34 pmol/l within 20 min. ACTH increases were significantly correlated with increases in plasma nicotine (r=0.85; P<0.0001), DHEA (r=0.66; P=0.002), and epinephrine (r=0.86; P<0.0001). Cortisol and DHEA increased significantly within 20 min (P<0.05) and reached peak levels of 424+/-48 and 21.13+/-2.55 ng/ml within 60 and 30 min, respectively. Thus cigarette smoking produced nicotine dose-related effects on HPA hormones and subjective and cardiovascular measures. These data suggest that activation of the HPA axis may contribute to the abuse-related effects of cigarette smoking.

Repeated cocaine administration induces gene expression changes through the dopamine D1 receptors

Drug addiction involves compulsive drug-seeking and drug-taking despite known adverse consequences. The enduring nature of drug addiction suggests that repeated exposure to abused drugs leads to stable alterations that likely involve changes in gene expression in the brain. The dopamine D1 receptor has been shown to mediate the long-term behavioral effects of cocaine. To examine how the persistent behavioral effects of cocaine correlate with underlying changes in gene expression, we have used D1 receptor mutant and wild-type mice to identify chronic cocaine-induced gene expression changes mediated via the D1 receptors. We focused on the caudoputamen and nucleus accumbens, two key brain regions that mediate the long-term effects of cocaine. Our analyses demonstrate that repeated cocaine administration induces changes in the expression of 109 genes, including those encoding the stromal cell-derived factor I, insulin-like growth factor binding protein 6, sigma 1 receptor, regulators of G-protein signaling protein 4, Wnt1 responsive Cdc42 homolog, Ca2+/calmodulin-dependent protein kinase II alpha subunit, and cyclin D2, via the D1 receptors. Moreover, the seven genes contain AP-1 binding sites in their promoter regions. These results suggest that genes encoding certain extracellular factors, membrane receptors and modulators, and intracellular signaling molecules, among others, are regulated by cocaine via the D1 receptor, and these AP-1 transcription complex-regulated genes might contribute to persistent cocaine-induced behavioral changes.

Peripheral nerves: a target for the action of neuroactive steroids

Peripheral nervous system possesses both classical and non-classical steroid receptors and consequently may represent a target for the action of neuroactive steroids. The present review summarizes the state of art of this intriguing field of research reporting data which indicate that neuroactive steroids, like for instance progesterone, dihydroprogesterone, tetrahydroprogesterone, dihydrotestosterone and 3alpha-diol, stimulate the expression of two important proteins of the myelin of peripheral nerves, the glycoprotein P0 (P0) and the peripheral myelin protein 22 (PMP22). Interestingly, the mechanisms by which neuroactive steroids exert their effects involve classical steroid receptors, like for instance progesterone and androgen receptors, in case of P0 and non-classical steroid receptors, like GABA(A) receptor, in case of PMP22. Moreover, neuroactive steroids not only control the expression of these specific myelin proteins, but also influence the morphology of myelin sheaths and axons suggesting that these molecules may represent an interesting new therapeutic approach to maintain peripheral nerve integrity during neurodegenerative events.

The sigma1 (sigma1) receptor activation is a key step for the reactivation of cocaine conditioned place preference by drug priming

RATIONALE

Cocaine-seeking behavior can be investigated in rodents using the conditioned place preference (CPP) paradigm, in which the drug-paired environment serves as a conditioned stimulus. Such approach allowed to previously demonstrate the importance of the neuromodulatory sigma1 (sigma1) receptor in acquisition of cocaine-induced CPP. CPP can be extinguished and then reactivated, notably using a cocaine challenge (i.e., priming).

OBJECTIVES AND METHODS

In order to examine the role of the sigma1 receptor in reinstatement of Cocaine-seeking, Swiss mice acquired CPP with cocaine (30 mg/kg, i.p.) and then CPP was extinguished.

RESULTS

A challenge cocaine priming (15 mg/kg) reactivated CPP up to 140% of the post-conditioning response. Pre-administration of the sigma1 receptor antagonist BD1047 (330 mg/kg, i.p.) or repeated treatment with an antisense probe targeting the sigma1 receptor prevented CPP reactivation. The sigma1 agonist igmesine (1-10 mg/kg, i.p.) or the steroid dehydroepiandrosterone (DHEA, 10-40 mg/kg, s.c.) reactivated CPP, in a BD1047-sensitive manner. Moreover, the in vivo [3H](+)-SKF-10,047 binding levels to the sigma1 receptor were increased after cocaine conditioning in numerous brain structures and these increases subsisted after extinction. Finally, cross-reactivation of cocaine-induced CPP was observed after phencyclidine (PCP), morphine, nicotine and ethanol administration. However, BD1047 blocked reactivation of CPP induced by PCP, morphine and nicotine but not ethanol.

CONCLUSIONS

Since activation of the sigma1 receptor is not sufficient to sustain CPP in naive animals [Neuropsychopharmacology 26 (2002) 444], it is concluded that sigma1 receptor activation is a key event for relapse to drug seeking. Activation may occur via sensitization due to enhanced in vivo available of receptors.

Effects of progesterone treatment on cocaine responses in male and female cocaine users

We recently reported that progesterone treatment attenuated some of the subjective effects of smoked cocaine in female cocaine users. In this study, we further examined the interaction between progesterone and cocaine in both male and female cocaine users using subjective, physiological and behavioral outcomes. A total of 10 subjects, 6 male and 4 female cocaine users, had two experimental sessions. Before each session, participants received either two oral doses of 200 mg of progesterone or placebo. Two hours after the second dose of medication treatment, the participants received a 0.3 mg/kg dose of cocaine intravenously and started the self-administration period, in which five optional doses of cocaine were available. Progesterone treatment attenuated the cocaine-induced diastolic blood pressure increases without affecting the systolic blood pressure and heart rate increases. Progesterone treatment also attenuated the subjective ratings of high and feel the effect of last dose in response to cocaine but did not affect cocaine self-administration behavior. These results suggest that progesterone attenuates some of the physiological and subjective effects of cocaine in both male and female participants. The effects of progesterone treatment on cocaine dependence need to be further studied in controlled trials.

Enhanced antidepressant efficacy of sigma1 receptor agonists in rats after chronic intracerebroventricular infusion of beta-amyloid-(1-40) protein

Treatment of depressive symptoms in patients suffering from neurodegenerative disorders remains a challenging issue, since few available antidepressants present an adequate efficacy during pathological aging. Previous reports suggested that selective sigma(1) receptor agonists might constitute putative candidates. We here examined the pharmacological efficacy of igmesine and (+)-SKF-10,047 and the sigma(1) receptor-related neuroactive steroid dehydroepiandrosterone sulfate, in rats infused intracerebroventricularly during 14 days with the beta-amyloid-(1-40) protein and then submitted to the conditioned fear stress test. Igmesine and (+)-SKF-10,047 significantly reduced the stress-induced motor suppression at 30 and 6 mg/kg, respectively, in beta-amyloid-(40-1)-treated control rats. Active doses were decreased, to 10 and 3 mg/kg, respectively, in beta-amyloid-(1-40)-treated animals. The dehydroepiandrosterone sulfate effect was also facilitated, both in dose (10 vs. 30 mg/kg) and intensity, in beta-amyloid-(1-40)-treated rats. Neurosteroid levels were measured in several brain structures after beta-amyloid infusion, in basal and stress conditions. Progesterone levels, both under basal and stress-induced conditions, were decreased in the hippocampus and cortex of beta-amyloid-(1-40)-treated rats. The levels in pregnenolone, dehydroepiandrosterone and their sulfate esters appeared less affected by the beta-amyloid infusion. The sigma(1) receptor agonist efficacy is known to be inversely correlated to brain progesterone levels, synthesized mainly by neurons that are mainly affected by the beta-amyloid toxicity. The present study suggests that sigma(1) receptor agonists, due to their enhanced efficacy in a nontransgenic animal model, may alleviate Alzheimer's disease-associated depressive symptoms.