(+)-SKF-10,047 and dextromethorphan ameliorate conditioned fear stress via dopaminergic systems linked to phenytoin-regulated sigma 1 sites

Potential effect of ketamine in treatment for dextromethorphan use disorder exploding in Japanese young population

In Japan, the landscape of clinical practice for substance use disorder is changing significantly, primarily due to an increase in patients using over-the-counter drugs. A major concern is the rising number of patients misusing dextromethorphan (DXM). These patients with DXM use disorders often have severe trauma-related and mood symptoms, and therefore try to cope with those symptoms by self-medicating with DXM. In this article, we propose that ketamine, which has similar psychopharmacological effects to DXM, may be a useful alternative pharmacological treatment for these patients.

Dopamine D2-like receptors on conditioned and unconditioned fear: A systematic review of rodent pharmacological studies

Growing evidence supports dopamine's role in aversive states, yet systematic reviews focusing on dopamine receptors in defensive behaviors are lacking. This study presents a systematic review of the literature examining the influence of drugs acting on dopamine D2-like receptors on unconditioned and conditioned fear in rodents. The review reveals a predominant use of adult male rats in the studies, with limited inclusion of female rodents. Commonly employed tests include the elevated plus maze and auditory-cued fear conditioning. The findings indicate that systemic administration of D2-like drugs has a notable impact on both innate and learned aversive states. Generally, antagonists tend to increase unconditioned fear, while agonists decrease it. Moreover, both agonists and antagonists typically reduce conditioned fear. These effects are attributed to the involvement of distinct neural circuits in these states. The observed increase in unconditioned fear induced by D2-like antagonists aligns with dopamine's role in suppressing midbrain-mediated responses. Conversely, the reduction in conditioned fear is likely a result of blocking dopamine activity in the mesolimbic pathway. The study highlights the need for future research to delve into sex differences, explore alternative testing paradigms, and identify specific neural substrates. Such investigations have the potential to advance our understanding of the neurobiology of aversive states and enhance the therapeutic application of dopaminergic agents.

Pharmacological Analysis of GABAA Receptor and Sigma1R Chaperone Interaction: Research Report I-Investigation of the Anxiolytic, Anticonvulsant and Hypnotic Effects of Allosteric GABAA Receptors' Ligands

Two groups of facts have been established in previous drug development studies of the non-benzodiazepine anxiolytic fabomotizole. First, fabomotizole prevents stress-induced decrease in binding ability of the GABAA receptor's benzodiazepine site. Second, fabomotizole is a Sigma1R chaperone agonist, and exposure to Sigma1R antagonists blocks its anxiolytic effect. To prove our main hypothesis of Sigma1R involvement in GABAA receptor-dependent pharmacological effects, we performed a series of experiments on BALB/c and ICR mice using Sigma1R ligands to study anxiolytic effects of benzodiazepine tranquilizers diazepam (1 mg/kg i.p.) and phenazepam (0.1 mg/kg i.p.) in the elevated plus maze test, the anticonvulsant effects of diazepam (1 mg/kg i.p.) in the pentylenetetrazole-induced seizure model, and the hypnotic effects of pentobarbital (50 mg/kg i.p.). Sigma1R antagonists BD-1047 (1, 10, and 20 mg/kg i.p.), NE-100 (1 and 3 mg/kg i.p.), and Sigma1R agonist PRE-084 (1, 5, and 20 mg/kg i.p.) were used in the experiments. Sigma1R antagonists have been found to attenuate while Sigma1R agonists can enhance GABAARs-dependent pharmacological effects.

Emerging Perspectives in the Management of Agitation in Alzheimer's Disease and Patients with Dementia

While Alzheimer's disease, the most common cause of dementia, is perhaps best characterized by cognitive decline, more than 90% of patients exhibit behavioural and psychological symptoms of dementia. Agitation in patients with dementia is often difficult to manage, and is associated with increased morbidity and mortality in patients and a heightened caregiver burden. Thus, effective management of dementia-related agitation (DRA) is vital. Care should first be taken to consider and address causes of agitation and aggression, after which non-pharmacological interventions should be employed. If non-pharmacological measures are unsuccessful in reducing DRA then medications should be considered, although none are approved by the Food and Drug Administration for this indication. Electroconvulsive therapy may be a promising option for patients with treatment-refractory DRA, although more studies are needed. While there are several drugs in the pipeline for DRA treatment, results from robust randomized clinical trials are necessary before they can be administered to patients. Thus, clinicians should employ current strategies to manage DRA to ensure holistic care for patients with Alzheimer's disease.

Involvement of Chaperone Sigma1R in the Anxiolytic Effect of Fabomotizole

Sigma-1 receptor (chaperone Sigma1R) is an intracellular protein with chaperone functions, which is expressed in various organs, including the brain. Sigma1R participates in the regulation of physiological mechanisms of anxiety (Su, T. P. et al., 2016) and reactions to emotional stress (Hayashi, T., 2015). In 2006, fabomotizole (ethoxy-2-[2-(morpholino)-ethylthio]benzimidazole dihydrochloride) was registered in Russia as an anxiolytic (Seredenin S. and Voronin M., 2009). The molecular targets of fabomotizole are Sigma1R, NRH: quinone reductase 2 (NQO2), and monoamine oxidase A (MAO-A) (Seredenin S. and Voronin M., 2009). The current study aimed to clarify the dependence of fabomotizole anxiolytic action on its interaction with Sigma1R and perform a docking analysis of fabomotizole interaction with Sigma1R. An elevated plus maze (EPM) test revealed that the anxiolytic-like effect of fabomotizole (2.5 mg/kg i.p.) administered to male BALB/c mice 30 min prior EPM exposition was blocked by Sigma1R antagonists BD-1047 (1.0 mg/kg i.p.) and NE-100 (1.0 mg/kg i.p.) pretreatment. Results of initial in silico study showed that fabomotizole locates in the active center of Sigma1R, reproducing the interactions with the site's amino acids common for established Sigma1R ligands, with the ΔGbind value closer to that of agonist (+)-pentazocine in the 6DK1 binding site.

Management of Dementia-Related Psychosis, Agitation and Aggression: A Review of the Pharmacology and Clinical Effects of Potential Drug Candidates

Along with cognitive decline, 90% of patients with dementia experience behavioral and psychological symptoms of dementia, such as psychosis, aggression, agitation, and depression. Atypical antipsychotics are commonly prescribed off-label to manage certain symptoms, despite warnings from the regulatory agencies regarding the increased risk of mortality associated with their use in elderly patients. Moreover, these compounds display a limited clinical efficacy, mostly owing to the fact that they were developed to treat schizophrenia, a disease characterized by neurobiological deficits. Thus, to improve clinical efficacy, it has been suggested that patients with dementia should be treated with exclusively designed and developed drugs that interact with pharmacologically relevant targets. Within this context, numerous studies have suggested druggable targets that might achieve therapeutically acceptable pharmacological profiles. Based on this, several different drug candidates have been proposed that are being investigated in clinical trials for behavioral and psychological symptoms of dementia. We highlight the recent advances toward the development of therapeutic agents for dementia-related psychosis and agitation/aggression and discuss the relationship between the relevant biological targets and their etiology. In addition, we review the compounds that are in the early stage of development (discovery or preclinical phase) and those that are currently being investigated in clinical trials for dementia-related psychosis and agitation/aggression. We also discuss the mechanism of action of these compounds and their pharmacological utility in patients with dementia.

AVP-786 for the treatment of agitation in dementia of the Alzheimer's type

INTRODUCTION

Agitation is common and distressing in patients with Alzheimer-type dementia, but safe, effective treatments remain elusive. Psychological treatments are first-line options, but they have limited efficacy. Off-label psychotropic medications are frequently used, but they also have limited effectiveness, and their use may have harmful side effects, including death. Areas covered: This review discusses the history leading to the conception of AVP-786 (deuterated (d6)-dextromethorphan/quinidine), its pharmacokinetic and pharmacodynamic profiles and safety issues, together with an overview of recent clinical trials. Data were found in the medical literature, in US and EU clinical trial registries and in information provided by the manufacturer. Expert opinion: AVP-786 is one of six investigational compounds in recent phase III clinical development for agitation in Alzheimer disease (AD). Quinidine and deuteration appear to prolong dextromethorphan's plasma half-life and facilitate brain penetration. The FDA granted fast-track designation to AVP-786 and allowed use of data generated on dextromethorphan-quinidine (AVP-923, Nuedexta®) for regulatory filings. AVP-923 reduced agitation in AD and was well tolerated in a phase II RCT that included more than 200 patients. A phase III clinical development program of AVP-786 for AD agitation was recently initiated. This program is expected to start generating results in July 2018.

Straub tail reaction in mice treated with σ(1) receptor antagonist in combination with methamphetamine

Straub tail reaction (STR) was observed in male ddY mice after simultaneous administration with BMY 14802 (a non-specific σ receptor antagonist) and methamphetamine (METH). The intensity and duration of STR depended on the dose of BMY 14802. The tail reaction was inhibited completely by (+)-SKF 10,047 (a putative σ(1) receptor agonist) and partially by PB 28 (a putative σ(2) receptor agonist). The STR was mimicked in mice treated with BD 1047 (a putative σ(1) receptor antagonist), but not SM-21, a putative σ(2) receptor antagonist, in combination with METH. STR evoked with BD 1047 plus METH was inhibited by (+)-SKF 10,047. STR induced by BMY 14802 and METH was abolished by naloxone (a relatively non-selective opioid receptor antagonist) or U-50,488H (a selective κ-agonist), suggesting that the STR may be mediated by activation of opioid receptor system.

Blockade of CRF1 receptors in the central nucleus of the amygdala attenuates the dysphoria associated with nicotine withdrawal in rats

The majority of smokers relapse during the acute withdrawal phase when withdrawal symptoms are most severe. The goal of the present studies was to investigate the role of corticotropin-releasing factor (CRF) and noradrenergic transmission in the central nucleus of the amygdala (CeA) in the dysphoria associated with smoking cessation. It was investigated if blockade of CRF1 receptors, blockade of α1-adrenergic receptors, or stimulation of α2-adrenergic receptors in the CeA diminishes the deficit in brain reward function associated with nicotine withdrawal in rats. Nicotine dependence was induced by implanting minipumps that delivered a nicotine solution. Withdrawal was precipitated with the nicotinic acetylcholine receptor antagonist mecamylamine. A discrete-trial intracranial self-stimulation procedure was used to assess the negative affective aspects of nicotine withdrawal. Elevations in brain reward thresholds are indicative of a deficit in brain reward function. In all the experiments, mecamylamine elevated the brain reward thresholds of the rats chronically treated with nicotine and did not affect the brain reward thresholds of the saline-treated control rats. Intra-CeA administration of the CRF1 receptor antagonist R278995/CRA0450 completely prevented the mecamylamine-induced elevations in brain reward thresholds in the nicotine-treated rats and did not affect the brain reward thresholds of the saline-treated control rats. R278995/CRA0450 has also been shown to block sigma-1 receptors but there is no evidence that this could affect negative mood states. Intra-CeA administration of the α1-adrenergic receptor antagonist prazosin or the α2-adrenergic receptor agonist clonidine did not affect the brain reward thresholds of the nicotine or saline-treated rats. These studies suggest that CRF1 receptor antagonists may diminish the dysphoria associated with smoking cessation by blocking CRF1 receptors in the CeA.

Sigma-1 receptors amplify dopamine D1 receptor signaling at presynaptic sites in the prelimbic cortex

Sigma-1 receptors are highly expressed in the brain. The downstream signaling mechanisms associated with the sigma-1 receptor activation have been shown to involve the activation of protein kinase C (PKC), the control of Ca(2) homoeostasis and the regulation of voltage- and ligand-gated ion channels. But few studies examined the regulatory effect of sigma-1 receptors on metabotropic receptor signaling. The present paper studied the regulatory effect of sigma-1 receptors on the signaling of dopamine D1 receptors, one of metabotropic receptors, by examining the effect of sigma-1 receptor agonists on the D1 receptor agonist-induced cAMP-dependent protein kinase (PKA) activation at presynaptic sites using the synaptosomes from the prelimbic cortex. The results showed that sigma-1 receptor agonists alone had no effects on the PKA activity, but could amplify the D1 receptor agonist-induced PKA activation. The sigma-1 receptor agonist also amplified the membrane-permeable analog of cAMP- and the adenylyl cyclase (AC) activator-induced PKA activation, but did not on the D1 receptor agonist-induced AC activation. The conventional PKC (cPKC), especially the PKCβI, and the extracellular Ca(2+) influx through L-type Ca(2+) channels might play key roles in the amplifying effect of the sigma-1 receptor agonists. The activation of PKC by sigma-1 receptor agonists was the upstream event of the increase in the intrasynaptosomal Ca(2+) concentration. These results suggest that sigma-1 receptors may amplify the D1 receptor agonist-induced PKA activation by sigma-1 receptors - cPKC (especially the PKCβI) - L-type Ca(2+) channels - Ca(2+) - AC and/or cAMP signaling pathway.

Sigma1 receptor antagonists determine the behavioral pattern of the methamphetamine-induced stereotypy in mice

OBJECTIVE

The effects of sigma receptor antagonists on methamphetamine (METH)-induced stereotypy have not been examined. We examined the effects of sigma antagonists on METH-induced stereotypy in mice.

RESULTS

The administration of METH (10 mg/kg) to male ddY mice induced stereotyped behavior consisting of biting (90.1%), sniffing (4.2%), head bobbing (4.1%), and circling (1.7%) during an observation period of 1 h. Pretreatment of the mice with BMY 14802 (alpha-(4-fluorophenyl)-4-(5-fluoro-2-pyrimidinyl)-1-piperazinebutanol; 1, 5, and 10 mg/kg), a non-specific sigma receptor antagonist, significantly increased METH-induced sniffing (19.2%, 30.5%, and 43.8% of total stereotypical behavior) but decreased biting (76.6%, 66.9%, and 49.3% of total stereotypical behavior) in a dose-dependent manner. This response was completely abolished by (+)-SKF 10,047 ([2S-(2alpha,6alpha,11R)]-1,2,3,4,5,6-hexahydro-6,11-dimethyl-3-(2-propenyl)-2,6-methano-3-benzazocin-8-ol; 4 and 10 mg/kg), a putative sigma(1) receptor agonist, and partially by PB 28 (1-cyclohexyl-4-[3-(1,2,3,4-tetrahydro-5-methoxy-1-naphthalen-1-yl)-n-propyl]piperazine; 1 and 10 mg/kg), a putative sigma(2) receptor agonist. The BMY 14802 action on METH-induced stereotypy was mimicked by BD 1047 (N-[2-(3,4-dichlorophenyl)ethyl]-N-methyl-2-(dimethylamino)ethylamine; 10 mg/kg), a putative sigma(1) receptor antagonist, but not by SM-21 ((+/-)-tropanyl 2-(4-chlorophenoxy)butanoate; 1 mg/kg), a putative sigma(2) receptor antagonist. The BD 1047 effect on METH-induced stereotypy was also abolished completely by (+)-SKF 10,047 and partially by PB 28. The overall frequency of METH-induced stereotypical behavior was unchanged with these sigma receptor ligands, despite the alteration in particular behavioral patterns. The BMY 14802 action on METH-induced stereotypy was unaffected by pretreatment with centrally acting histamine H(1) receptor antagonists (pyrilamine or ketotifen, 10 mg/kg), suggesting that these effects are independent of histamine H(1) receptor signaling systems.

CONCLUSION

In summary, modulation of central sigma(1) receptors alters the pattern of METH-induced stereotypy, producing a shift from stereotypical biting to stereotypical sniffing, without affecting the overall frequency of stereotypical behavior.

Anxiolytic- and antidepressant-like profile of a new CRF1 receptor antagonist, R278995/CRA0450

1-[8-(2,4-dichlorophenyl)-2-methylquinolin-4-yl]-1,2,3,6-tetrahydropyridine-4-carboxamide benzenesulfonate (R278995/CRA0450) is a newly synthesized corticotropin-releasing factor subtype 1 (CRF(1)) receptor antagonist. In the present study, in vitro and in vivo pharmacological profiles of R278995/CRA0450 were investigated. R278995/CRA0450 showed high affinity for recombinant and native CRF(1) receptors without having affinity for the CRF(2) receptor. R278995/CRA0450 attenuated CRF-induced cyclic AMP formation in AtT-20 cells and CRF-induced forepaw treading in gerbils, indicating that R278995/CRA0450 is an antagonist of the CRF(1) receptor. In addition to CRF(1) receptor antagonism, R278995/CRA0450 showed high affinity for the sigma(1) receptor, and attenuated (+)-SKF10,047-induced head-weaving behavior, suggesting sigma(1) receptor antagonism. R278995/CRA0450 showed dose-dependent in vivo occupancy when assessed by ex vivo receptor binding, indicating good brain penetration. R278995/CRA0450 did not alter spontaneous anxiety when tested in the rat elevated plus maze (up to 3 mg/kg, p.o.) or lick suppression test (up to 10 mg/kg, i.p.). However, potent anxiolytic-like properties were observed in rats subjected to swim stress prior to testing on the elevated plus-maze, indicating activity primarily in tests taxing stress-induced anxiety. R278995/CRA0450 was inactive in mouse tail suspension, rat forced swim and rat differential-reinforcement-of-low-rate 72-s (DRL72), while it showed dose-dependent antidepressant-like effects in the rat learned helplessness paradigm and the olfactory bulbectomy model, demonstrating activity in a subset of animal models of depression associated with subchronic stress exposure. No or only mild effects were seen in tests of locomotor activity, motor coordination and sedation. These results indicate that R278995/CRA0450 is an orally active CRF(1) and sigma(1) receptor antagonist with potent anxiolytic-like and antidepressant-like activities.

NMDA-receptor antagonism via dextromethorphan and ifenprodil modulates graded anxiety test performance of C57BL/6 mice

The majority of N-methyl-D-aspartate receptors (NMDA-R) in the adult forebrain are di- or triheteromers composed of NR1, NR2A and NR2B subunits. Subunit non-selective NMDA-R antagonists produce anxiolytic-like effects together with motor and sensory side-effects. The graded anxiety test (GAT), permits the within-task distinction of drug effects on anxiety from those on activity and perception. By testing NMDA-R subunit selective agents in the GAT it might be possible to determine whether their effects on anxiety, activity and perception are interrelated, and whether separate NMDA-R subtypes are involved. Dextromethorphan (weakly NR2A-selective) (10 and 30 mg/kg, i.p.) and ifenprodil (highly NR2B-selective) (1, 3 and 5 mg/kg, i.p.) were tested in the GAT. Both drugs failed to induce anxiolysis devoid of side-effects. However, the 10 mg/kg dose of dextromethorpan showed an anxiolytic, whereas the 30 mg/kg dose showed an anxiogenic, behavioral profile. Since the selective blockade of the NR2B subunit by ifenprodil had no clear anxiolytic effect, the anxiolytic potential of NMDA subunit non-selective agents might involve NR2A-containing receptors.

Synthesis and structure-activity relationships of N-(1-benzylpiperidin-4-yl)arylacetamide analogues as potent sigma1 receptor ligands

A series of N-(1-benzylpiperidin-4-yl)arylacetamides were synthesized and evaluated for their binding properties for sigma1 and sigma2 receptors. In agreement with previously reported sigma1/sigma2 receptor binding data for N-(1-benzylpiperidin-4-yl)phenylacetamide, all of the N-(1-benzylpiperidin-4-yl)arylacetamide compounds reported below displayed higher affinity for sigma1 vs sigma2 receptors. Replacement of the phenyl ring of the phenylacetamide moiety with a thiophene, naphthyl, or indole aromatic ring had no significant effect on the sigma1 receptor affinity. Replacement of the phenyl ring with an imidazole or pyridyl aromatic ring resulted in a >60-fold loss in affinity for sigma1 receptors and no significant binding affinity for sigma2 receptors. Substitution on the aromatic ring of the benzyl group showed a similar or slightly decreased affinity for sigma1 receptors. Substitution on the aromatic rings of both the phenylacetamide moiety and the benzyl group with a halogen resulted in a similar affinity for sigma(1) receptors and a significantly increased affinity for sigma2 receptors. Comparative molecular field analysis revealed that electrostatic properties of the substituents in the phenylacetamide aromatic ring strongly influenced binding to sigma1 receptors. Compounds 1, 10, 18, 22, 37, and 40 showed the highest selectivity for sigma1 receptors with K(i) (sigma2) to K(i) (sigma(1)) ratios of 100, >92, >122, 77, 74, and 80, respectively. In agreement with previously reported results, the phenylacetamide analogues had no binding affinity for dopamine receptors (D2/D3).

The selective sigma2 ligand Lu 28-179 has an antidepressant-like profile in the rat chronic mild stress model of depression

The selective sigma2 (sigma2) ligand Lu 28-179, or 1'-[4[1-(4-fluorophenyl)-1H-indol-3-yl]-l-butyl]spiro[isobenzofuran++ +-1(3H),4'-piperidine], was studied in the chronic mild stress (CMS) model of depression. The CMS test procedure consists of sequential exposures to a variety of mild stressors for a prolonged period of time and results in behavioural hedonic deficits, which can be measured as decreased consumption of a palatable sucrose solution. In rats, exposure to CMS treatment with citalopram or imipramine for 2 or 4 weeks, respectively, normalized the sucrose intake. Similarly, Lu 28-179 (1.0 mg/kg subcutaneously per day) normalized sucrose intake in rats exposed to CMS. This effect was found in two separate experiments and was achieved after 3 and 4 weeks of treatment, respectively. This suggests an antidepressant potential for Lu 28-179. Doses of 0.01 and 0.1 mg/kg were inactive. Groups exposed to CMS and treated with 0.5, 2.0 or 3.0 mg/kg showed a significantly increased sucrose intake compared with vehicle-treated stressed animals at week 5. However, this effect was confounded by decreased intake in the vehicle controls. Lu 28-179 did not affect sucrose intake in non-stressed rats at any of the doses tested.

Neuroactive neurosteroids as endogenous effectors for the sigma1 (sigma1) receptor: pharmacological evidence and therapeutic opportunities

Neuroactive neurosteroids, including progesterone, allopregnanolone, pregnenolone and dehydroepiandrosterone, represent steroid hormones synthesized de novo in the brain and acting locally on nervous cells. Neurosteroids modulate several neurotransmitter systems such as gamma-aminobutyric acid type A (GABA(A)), N-methyl-D-aspartate (NMDA) and acetylcholine receptors. As physiologic consequences, they are involved in neuronal plasticity, learning and memory processes, aggression and epilepsy, and they modulate the responses to stress, anxiety and depression. The sigma1-receptor protein was recently purified and its cDNA was cloned in several species. The amino-acid sequences are structurally unrelated to known mammalian proteins, but shared homology with a fungal sterol C8-C7 isomerase. The sigma1-receptor ligands exert a potent neuromodulation on excitatory neurotransmitter systems, including the glutamate and cholinergic systems. Consequently, selective sigma1 agonists show neuroprotective properties and beneficial effects in memory processes, stress and depression. The evidence of a direct interaction between neurosteroids and sigma1 receptors was first suggested by the ability of several steroids to inhibit the binding of sigma1-receptor radioligands in vitro and in vivo. A crossed pharmacology between neurosteroids and sigma1-receptor ligands was described in several physiological tests and behavioral responses. This review will detail the recent evidence for a common mechanism of action between neurosteroids and sigma1-receptor ligands and focus on the potential therapeutic interests of such interaction in the physiopathology of learning and memory impairments, stress, depression and neuroprotection.

Modulation of steroidal levels by adrenalectomy/castration and inhibition of neurosteroid synthesis enzymes affect sigma1 receptor-mediated behaviour in mice

The interaction between neurosteroids and sigma1 (sigma1) receptors may be of therapeutic interest during physiological or pathological ageing, particularly concerning their neuromodulatory role on cognitive functions. Neurosteroids modulate memory processes through a mechanism involving interactions with GABAA, N-methyl-D-aspartate and/or sigma1 receptors. To measure the contribution of endogenous neurosteroid levels to the antiamnesic effects of sigma1 agonists, we investigated the effects of inhibitors of key enzymes involved in neurosteroid synthesis, in adrenalectomized/castrated (AdX/CX) mice to avoid the effect of circulating steroids. Trilostane, a 3beta-hydroxysteroid-deshydrogenase inhibitor, blocks the pregnenolone to progesterone conversion and leads to a decrease of progesterone. Finasteride, a 5alpha-reductase inhibitor, blocks the progesterone to 5alpha-pregnane-3,20-dione conversion and leads to an accumulation of progesterone. The in vivo binding of (+)-[3H]SKF-10 047 to sigma1 sites was measured in the mouse hippocampus and cortex. The attenuating effect of the selective sigma1 agonist PRE-084 (0.1-3 mg/kg) against dizocilpine (0.15 mg/kg)-induced learning impairment was examined using spontaneous alternation behaviour, step-down passive avoidance and place learning in the elevated plus-maze. The in vivo (+)-[3H]SKF-10 047 binding appeared significantly increased in AdX/CX mice and after trilostane treatment (10 mg/kg twice a day, 7 days), compared with sham-operated animals. The finasteride treatment (25 mg/kg, 7 days) significantly decreased binding levels. The learning deficits induced by dizocilpine were not affected by the treatments. The antiamnesic effect of PRE-084 was facilitated in AdX/CX mice and even more after trilostane treatment, as several parameters for animals treated with both PRE-084 and dizocilpine returned to control values. The PRE-084 effect was blocked after finasteride. These results confirmed that endogenous neurosteroidal levels modulate sigma1 receptor-mediated behaviour directly, and revealed that, among neurosteroids, progesterone may be the main modulator of sigma1 receptors.

The attenuation of learning impairments induced after exposure to CO or trimethyltin in mice by sigma (sigma) receptor ligands involves both sigma1 and sigma2 sites

1. Sigma (sigma) receptor ligands were previously reported to alleviate learning and memory impairments on several pharmacological and pathological rodent models of amnesia. Such effect was demonstrated as involving the sigma1 subtype of sigma receptor. 2. In this study, we characterized the pharmacological effect mediated by sigma ligands on two lesional models of amnesia in mice: (1) the hypoxia-related learning and memory impairment model induced by repeated exposure to carbon monoxide (CO) gas; and (2) the intoxication with trimethyltin (1 mg kg(-1)). 3. The selective sigma1 ligand PRE-084 (1 mg kg(-1)) or the non-selective sigma1/sigma2 compounds DTG (0.1 mg kg(-1)), BD1008 (3 mg kg(-1)), and haloperidol (0.1 mg kg(-1)) reversed significantly the spontaneous alternation deficits observed 7 days after exposure to CO or 14 days after intoxication with trimethyltin. 4. The selective sigma1 receptor antagonist NE-100 (1 mg kg(-1)) was ineffective by itself, but blocked completely the PRE-084 effects, partially the DTG effects, and did not affect the effects induced by BD1008 or haloperidol. 5. A similar pharmacological profile was observed in the step-down type passive avoidance test performed 8 days after exposure to CO. 6. These results show that, in contrast to the previously reported amnesia models, the impairments induced after exposure to CO or intoxication with trimethyltin could be alleviated not only by sigma1 receptor agonists but also by sigma2 agonists. The particular pattern of neurodegeneration observed in these lesional models may explain these differences.

Role of (+)-SKF-10,047-sensitive sub-population of sigma 1 receptors in amelioration of conditioned fear stress in rats: association with mesolimbic dopaminergic systems

Rats exhibited a marked suppression of motility when they were re-placed in the same environment as that in which they had previously received an electric footshock. We examined the behavioral and neurochemical effects of (+)-N-allylnormetazocine hydrochloride ((+)-SKF-10,047) and (+)-pentazocine, putative sigma 1 receptor ligands, on this psychological-stress-induced motor suppression, defined as a conditioned fear stress. (+)-SKF-10,047 (3 and 6 mg/kg) dose-dependently attenuated the conditioned fear stress, whereas (+)-pentazocine failed to do so even at a higher dose (32 mg/kg). In rats showing the conditioned fear stress, dopamine turnover (i.e., the ratio of dopamine metabolites/dopamine contents) was decreased in the nucleus accumbens and was increased in the medial prefrontal cortex, but remained unchanged in the striatum. (+)-SKF-10,047 (3 and 6 mg/kg) dose-dependently reversed the decreased dopamine turnover in the nucleus accumbens without changing the increased dopamine turnover in the medial prefrontal cortex. (+)-Pentazocine (32 mg/kg) did not affect the stress-induced changes in dopamine turnover in these brain regions. Thus, the decreased dopamine turnover in the nucleus accumbens appears to be involved in the conditioned fear stress. These results suggest that (+)-SKF-10,047 ameliorates the conditioned fear stress by reversing the psychological stress-induced dysfunction in the mesolimbic dopaminergic systems, and that the (+)-SKF-10,047-sensitive sub-population of sigma 1 receptors may play in important role in this stress response.