Modulation of NMDA and dopaminergic neurotransmissions by sigma ligands: possible implications for the treatment of psychiatric disorders

Synthesis and pharmacological evaluation of benzamide derivatives as potent and selective sigma-1 protein ligands

A series of novel benzamide-derived compounds was designed, synthesized and pharmacologically evaluated. Among all 37 synthesized compounds, two series were developed with the modulation of the nature, the position of atoms or groups on the benzamide scaffold, but also the nature of the amine group separated from the benzamide with 2, 3 or 4 methylene groups. In vitro competition binding assays against sigma proteins (sigma-1 S1R and sigma-2 S2R) revealed that most of them conferred S2R/S1R selectivity toward without cytotoxic effects on SY5Y cells, especially with the first series with compounds 7a-z. Some selected compounds were also evaluated for their agonist and antagonist activities on a panel of 40 receptors. Results showed the importance of the nature and the position with halogeno atom on the benzamide scaffold, the length chain but also the contribution of the hydrophobic part on the amine group. Among them, compounds 7i, w, y with Cl, CN or NO₂ groups at the 4-position of the benzamide scaffold showed excellent affinity for S1R (Ki = 1.2-3.6 nM), selectivity for S2R (Ki up to 1400 nM) and high selectivity index (IC_50(SY5Y)/Ki_(S1R) ratio from 28 000 to 83 000). Futhermore, these compounds presented an excellent safety profile over 40 other receptors. These derivatives will be selected for further biological investigations.

Ethanol Stimulates Endoplasmic Reticulum Inositol Triphosphate and Sigma Receptors to Promote Withdrawal-Associated Loss of Neuron-Specific Nuclear Protein/Fox-3

BACKGROUND

Prior studies demonstrate that ethanol (EtOH) exposure induces the release of intracellular calcium (CA(2+) ) in modulation of γ-aminobutyric acid-ergic tone and produces concomitant alterations in sigma (σ)-1 protein expression that may contribute to the development EtOH dependence. However, the influence of CA(2+) released from endoplasmic reticulum (ER)-bound inositol triphosphate (IP3) and σ-1 receptors in regulating hippocampal function has yet to be delineated.

METHODS

Rat hippocampal explants were subjected to chronic intermittent EtOH (CIE) exposure with or without the addition of IP3 inhibitor xestospongin C (0 to 0.5 μM) or σ-1 receptor antagonist BD-1047 (0 to 80 μM). Hippocampal viability was assessed via immunohistochemical labeling of neuron-specific nuclear protein (NeuN)/Fox-3 in CA1, CA3, and dentate gyrus (DG) subregions.

RESULTS

Exposure to CIE produced consistent and significant decreases of NeuN/Fox-3 in each primary cell layer of the hippocampal formation. Co-exposure to xestospongin reversed these effects in the CA1 subregion and significantly attenuated these effects in the CA3 and DG regions. Xestospongin application also significantly increased NeuN/Fox-3 immunofluorescence in EtOH-naïve hippocampi. Co-exposure to 20 μM BD-1047 also reversed the loss of NeuN/Fox-3 during CIE exposure in each hippocampal cell layer, whereas exposure to 80 μM BD-1047 did not alter NeuN/Fox-3 in EtOH-treated hippocampi. By contrast, 80 μM BD-1047 application significantly increased NeuN/Fox-3 immunofluorescence in EtOH-naïve hippocampi in each subregion.

CONCLUSIONS

These data suggest that EtOH stimulates ER IP3 and σ-1 receptors to promote hippocampal loss of NeuN/Fox-3 during CIE.

Dual Therapeutic Effects of C-10068, a Dextromethorphan Derivative, Against Post-Traumatic Nonconvulsive Seizures and Neuroinflammation in a Rat Model of Penetrating Ballistic-Like Brain Injury

Post-traumatic seizures can exacerbate injurious outcomes of severe brain trauma, yet effective treatments are limited owing to the complexity of the pathology underlying the concomitant occurrence of both events. In this study, we tested C-10068, a novel deuterium-containing analog of (+)-N-methyl-3-ethoxymorphinan, in a rat model of penetrating ballistic-like brain injury (PBBI) and evaluated the effects of C-10068 on PBBI-induced nonconvulsive seizures (NCS), acute neuroinflammation, and neurofunctional outcomes. NCS were detected by electroencephalographic monitoring. Neuroinflammation was evaluated by immunohistochemical markers, for example, glial fibrillary acidic protein and major histocompatibility complex class I, for activation of astrocytes and microglia, respectively. Neurofunction was tested using rotarod and Morris water maze tasks. Three infusion doses of C-10068 (1.0, 2.5, and 5.0 mg/kg/h × 72 h) were tested in the antiseizure study. Neuroinflammation and neurofunction were evaluated in animals treated with 5.0 mg/kg/h × 72 h C-10068. Compared to vehicle treatment, C-10068 dose dependently reduced PBBI-induced NCS incidence (40-50%), frequency (20-70%), and duration (30-82%). The most effective antiseizure dose of C-10068 (5.0 mg/kg/h × 72 h) also significantly attenuated hippocampal astrocyte activation and perilesional microglial reactivity post-PBBI. Within C-10068-treated animals, a positive correlation was observed in reduction in NCS frequency and reduction in hippocampal astrocyte activation. Further, C-10068 treatment significantly attenuated astrocyte activation in seizure-free animals. However, C-10068 failed to improve PBBI-induced motor and cognitive functions with the dosing regimen used in this study. Overall, the results indicating that C-10068 exerts both potent antiseizure and antiinflammatory effects are promising and warrant further investigation.

Sigma receptors [σRs]: biology in normal and diseased states

This review compares the biological and physiological function of Sigma receptors [σRs] and their potential therapeutic roles. Sigma receptors are widespread in the central nervous system and across multiple peripheral tissues. σRs consist of sigma receptor one (σ₁R) and sigma receptor two (σ₂R) and are expressed in numerous regions of the brain. The sigma receptor was originally proposed as a subtype of opioid receptors and was suggested to contribute to the delusions and psychoses induced by benzomorphans such as SKF-10047 and pentazocine. Later studies confirmed that σRs are non-opioid receptors (not an µ opioid receptor) and play a more diverse role in intracellular signaling, apoptosis and metabolic regulation. σ₁Rs are intracellular receptors acting as chaperone proteins that modulate Ca²⁺ signaling through the IP₃ receptor. They dynamically translocate inside cells, hence are transmembrane proteins. The σ₁R receptor, at the mitochondrial-associated endoplasmic reticulum membrane, is responsible for mitochondrial metabolic regulation and promotes mitochondrial energy depletion and apoptosis. Studies have demonstrated that they play a role as a modulator of ion channels (K⁺ channels; N-methyl-d-aspartate receptors [NMDAR]; inositol 1,3,5 triphosphate receptors) and regulate lipid transport and metabolism, neuritogenesis, cellular differentiation and myelination in the brain. σ₁R modulation of Ca²⁺ release, modulation of cardiac myocyte contractility and may have links to G-proteins. It has been proposed that σ₁Rs are intracellular signal transduction amplifiers. This review of the literature examines the mechanism of action of the σRs, their interaction with neurotransmitters, pharmacology, location and adverse effects mediated through them.

Recent Advances in the Development of Sigma-1 Receptor Ligands

The existence of two distinct sigma (σ) receptor subtypes was established in the early 1990s. Sigma-1 and sigma-2 receptors (S1Rs and S2Rs, respectively) were shown to possess distinct molecular size, anatomical distribution, and ligand discrimination. S2R is overexpressed in numerous human cancers, and has therapeutic potential for the imaging and treatment of certain tumours. In contrast, S1R is more broadly involved in a wide variety of central nervous system (CNS) diseases including motor disorders, memory deficits, depression, schizophrenia, anxiety, pain, drug addiction, and many more. Since the human S1R was cloned in 1996, numerous high affinity ligands with excellent selectivity for S1R have been developed. This review focuses on recent developments in the generation of structurally diverse S1R-selective ligands and novel therapeutic candidates targeting S1Rs.

The development of radiotracers for imaging sigma (σ) receptors in the central nervous system (CNS) using positron emission tomography (PET)

Sigma (σ) receptors are unique mammalian proteins, distributed in the central nervous system and elsewhere, which are increasingly implicated in the pathophysiology of virtually all major central nervous system disorders. The heterogeneous but wide distribution of σ1 in the brain has prompted the development of selective radiotracers for imaging these sites using positron emission tomography (PET). To date, some 50 carbon-11-labelled and fluorine-18-labelled candidate PET radioligands targeting σ receptors have been reported. The historical development of selective σ1 receptor ligands as potential PET imaging agents, as well as the radiochemistry and application of the most recently developed examples, is described herein.

Dextromethorphan/quinidine for pseudobulbar affect associated with subarachnoid hemorrhage

ABSTRACT: 

Dextromethorphan/quinidine, sold under the brand name Nuedexta® (Avanir Pharmaceutics, CA, USA), is currently the only US FDA-approved medication for the treatment of pseudobulbar affect (PBA) in the USA. However, the clinical trials for approval of this medication only involved patients diagnosed with amyotrophic lateral sclerosis or multiple sclerosis. This case report describes a 43-year-old woman who developed PBA following an acute subarachnoid hemorrhage with a basilar artery aneurysm. After failing to respond to valproate or haloperidol, she was treated with dextromethorphan/quinidine and showed a reduction in her PBA symptoms. The patient's Center for Neurologic Study-Lability Scale score improved in 1 week and the improvement was maintained at 3 weeks.

The effect of the steroid sulfatase inhibitor (p-O-sulfamoyl)-tetradecanoyl tyramine (DU-14) on learning and memory in rats with selective lesion of septal-hippocampal cholinergic tract

Dehydroepiandrosterone sulfate (DHEAS), is an excitatory neurosteroid synthesized within the CNS that modulates brain function. Effects associated with augmented DHEAS include learning and memory enhancement. Inhibitors of the steroid sulfatase enzyme increase brain DHEAS levels and can also facilitate learning and memory. This study investigated the effect of steroid sulfatase inhibition on learning and memory in rats with selective cholinergic lesion of the septo-hippocampal tract using passive avoidance and delayed matching to position T-maze (DMP) paradigms. The selective cholinergic immunotoxin 192 IgG-saporin (SAP) was infused into the medial septum of animals and then tested using a step-through passive avoidance paradigm or DMP paradigm. Peripheral administration of the steroid sulfatase inhibitor, DU-14, increased step-through latency following footshock in rats with SAP lesion compared to both vehicle treated control and lesioned animals (p<0.05). However, in the DMP task, steroid sulfatase inhibition impaired acquisition in lesioned rats while having no effect on intact animals. These results suggest that steroid sulfatase inhibition facilitates memory associated with contextual fear, but impairs acquisition of spatial memory tasks in rats with selective lesion of the septo-hippocampal tract.

Sigma-1 receptor function is critical for both the discriminative stimulus and aversive effects of the kappa-opioid receptor agonist U-50488H

The present study was undertaken to identify possible similarities between the effects of kappa-opioid receptor agonist, N-methyl-D-aspartate-receptor antagonist, and sigma receptor agonist on the discriminative stimulus effects of U-50488H, and the possible involvement of sigma receptors in the discriminative stimulus and aversive effects of U-50488H. The kappa-opioid receptor agonist U-50488H produced significant place aversion as measured by the conditioned place preference procedure, and this effect was completely abolished by treatment with the putative sigma-1 receptor antagonist NE-100. In addition, phencyclidine (+)-SKF-10047 and (+)-pentazocine, which are sigma receptor agonists, generalized to the discriminative stimulus effects of U-50488H in rats that had been trained to discriminate between U-50488H (3.0 mg/kg) and saline. Furthermore, NE-100 significantly attenuated the discriminative stimulus effects of U-50488H and the U-50488H-like discriminative stimulus effects of phencyclidine. These results suggest that the sigma-1 receptor is responsible for both the discriminative stimulus effects and aversive effects of U-50488H.

Serum levels of brain-derived neurotrophic factor and cortisol to sulfate of dehydroepiandrosterone molar ratio associated with clinical response to L-theanine as augmentation of antipsychotic therapy in schizophrenia and schizoaffective disorder patients

OBJECTIVES

L-Theanine (γ-glutamylethylamide) augmentation to antipsychotic therapy ameliorates positive, activation, and anxiety symptoms in schizophrenia and schizoaffective disorder patients. This study examines the association between circulating levels of neurochemical indicators and the beneficial clinical effects of L-theanine augmentation.

METHODS

Serum levels of neurochemical indicators such as brain-derived neurotrophic factor (BDNF), dehydroepiandrosterone (DHEA), its sulfate (DHEAS), cortisol, cholesterol, and insulin were monitored in 40 schizophrenia and schizoaffective disorder patients during an 8-week, double-blind, randomized, placebo-controlled trial with L-theanine (400 mg/d). Multiple regression analysis was applied for searching association between improvement in symptom scores and changes in circulating levels of neurochemical indicators for an 8-week trial.

RESULTS

Regression models among L-theanine-treated patients indicate that circulating levels of BDNF and cortisol-to-DHEAS*100 molar ratio were significantly associated with the beneficial clinical effects of L-theanine augmentation. Variability of serum BDNF levels accounted for 26.2% of the total variance in reduction of dysphoric mood and 38.2% in anxiety scores. In addition, the changes in cortisol-to-DHEAS*100 molar ratio accounted for 30% to 34% of the variance in activation factor and dysphoric mood scores and for 15.9% in anxiety scores. Regression models among placebo-treated patients did not reach significant level.

CONCLUSIONS

These preliminary results indicate that circulating BDNF and cortisol-to-DHEAS*100 molar ratio may be involved in the beneficial clinical effects of L-theanine as augmentation of antipsychotic therapy in schizophrenia and schizoaffective disorder patients.

N-Arylalkyl-2-azaadamantanes as cage-expanded polycarbocyclic sigma (σ) receptor ligands

A series of racemic N-arylalkyl-2-azaadamantan-1-ols (9-15) and the corresponding deoxygenated, achiral N-arylalkyl-2-azaadamantanes (23-29) were synthesized and screened in competition binding assays against a panel of CNS targets. Adamantyl hemiaminals 9-15 displayed generally low affinity for both σ(1) (K(i) values= 294-1950 nM) and σ(2) receptors (K(i) values=201-1020 nM), and negligible affinity for 42 other CNS proteins. Deoxygenation of 9-15 to give the corresponding achiral azaadamantanes 23-29 greatly improved affinity for σ(1) (K(i) values=8.3-239 nM) and σ(2) receptors (K(i) values=34-312 nM).

Sigma receptors: potential targets for a new class of antidepressant drug

Despite the widespread and devastating impact of depression on society, our current understanding of its pathogenesis is limited. Likewise, existing treatments are inadequate, providing relief to only a subset of people suffering from depression. The search for more effective antidepressant drugs includes the investigation of new molecular targets. Among them, current data suggests that sigma receptors are involved in multiple processes effecting antidepressant-like actions in vivo and in vitro. This review summarizes accumulated evidence supporting a role for sigma receptors in antidepressant effects and provides a conceptual framework for delineating their potential roles over the course of antidepressant treatment.

Cognition and depression: the effects of fluvoxamine, a sigma-1 receptor agonist, reconsidered

Cognitive impairment is a primary feature of patients with major depressive disorder (MDD) and is characterised by stress-induced neural atrophy. Via alpha-adrenergic, anti-cholinergic and anti-histaminic activities, several antidepressants can cause significant counter-therapeutic cognitive impairment. Evidence is emerging of the involvement of sigma-1 receptor agonism in the mechanism of action of some antidepressants, notably fluvoxamine. Sigma-1 receptors are abundant in areas affected by depression/stress-induced cerebral atrophy and their ligands have a unique pharmacological profile; they may promote neurogenesis and initiate adaptive neural plasticity as a protection/reaction to stress. Fluvoxamine, as a potent sigma-1 receptor agonist, has shown ameliorating effects in animal models of psychosis, depression, stress, anxiety, obsessive-compulsive disorder (OCD) and aggression and has been shown to improve cognitive impairments. In humans, fluvoxamine may repair central nervous system (CNS) atrophy and restore cognitive function. The current review explores the mechanisms through which sigma-1 receptors can modulate cognitive function and examines how antidepressant therapy with fluvoxamine may help improve cognitive outcomes in patients with depression.

Antidepressant-like effect of PRE-084, a selective sigma1 receptor agonist, in Albino Swiss and C57BL/6J mice

PRE-084, a selective sigma receptor agonist, exhibited an antidepressant-like effect in the forced swim test (FST) in Albino Swiss and C57BL/6J mice. This effect was counteracted by BD 1047 (5 and 10 mg/kg) but not by SM-21 (3 and 10 mg/kg), which are sigma(1)- and sigma(2)-receptor antagonists, respectively. The results indicated that PRE-084 has an antidepressant-like effect in C57BL/6J and, to a lesser extent, in Albino Swiss mice. These results support the idea that sigma(1)-receptors, but not sigma(2)-receptors, contribute to the mechanism of antidepressant activity of sigma agonists in FST.

Effects of dextromethorphan/quinidine on auditory event-related potentials in multiple sclerosis patients with pseudobulbar affect

The purpose of this study was to characterize the brain activity and associated cortical structures involved in pseudobulbar affect (PBA), a condition characterized by uncontrollable episodes of laughing and/or crying in patients with multiple sclerosis before and after treatment with dextromethorphan/quinidine (DM/Q). Behavioral responses and event-related potentials (ERPs) in response to subjectively significant and neutral verbal stimuli were recorded from 2 groups: 6 multiple sclerosis patients with PBA before (PBA-preTx) and after (PBA-DM/Q) treatment with DM/Q and 6 healthy control (HC) subjects. Statistical nonparametric mapping comparisons of ERP source current density distributions between groups were conducted for subjectively significant and neutral stimuli separately before and after treatment with DM/Q. Treatment with DM/Q had a normalizing effect on the behavioral responses of PBA patients. Event-related potential waveform comparisons of PBA-preTx and PBA-DM/Q with HC, for both neutral and subjectively significant stimuli, revealed effects on early ERP components. Comparisons between PBA-preTx and HC, in response to subjectively significant stimuli, revealed both early and late effects. Source analysis comparisons between PBA-preTx and PBA-DM/Q indicated distinct activations in areas involved in emotional processing and high-level and associative visual processing in response to neutral stimuli and in areas involved in emotional, somatosensory, primary, and premotor processing in response to subjectively significant stimuli. In most cases, stimuli evoked higher current density in PBA-DM/Q compared with the other groups. In conclusion, differences in brain activity were observed before and after medication. Also, DM/Q administration resulted in normalization of behavioral and electrophysiological measures.

Synthesis, biological evaluation, and three-dimensional in silico pharmacophore model for sigma(1) receptor ligands based on a series of substituted benzo[d]oxazol-2(3H)-one derivatives

Novel benzo[d]oxazol-2(3H)-one derivatives were designed and synthesized, and their affinities against sigma receptors were evaluated. On the basis of 31 compounds, a three-dimensional pharmacophore model for the sigma(1) receptor binding site was developed using the Catalyst 4.9 software package. The best 3D pharmacophore hypothesis, consisting of one positive ionizable, one hydrogen bond acceptor, two hydrophobic aromatic, and one hydrophobic features provided a 3D-QSAR model with a correlation coefficient of 0.89. The best hypothesis was also validated by three independent methods, i.e., the Fisher randomization test included in the CatScramble functionality of Catalyst, the leave-one-out test, and activity prediction of an additional test set. The achieved results will allow researchers to use this 3D pharmacophore model for the design and synthesis of a second generation of high affinity sigma(1) ligands, as well as to discover other lead compounds for this class of receptors.

Antagonism by haloperidol and its metabolites of mechanical hypersensitivity induced by intraplantar capsaicin in mice: role of sigma-1 receptors

RATIONALE

We evaluated the effects of haloperidol and its metabolites on capsaicin-induced mechanical hypersensitivity (allodynia) and on nociceptive pain induced by punctate mechanical stimuli in mice.

RESULTS

Subcutaneous administration of haloperidol or its metabolites I or II (reduced haloperidol) dose-dependently reversed capsaicin-induced (1 microg, intraplantar) mechanical hypersensitivity of the hind paw (stimulated with a nonpainful, 0.5-g force, punctate stimulus). The order of potency of these drugs to induce antiallodynic effects was the order of their affinity for brain sigma-1 (sigma(1)) receptor ([(3)H](+)-pentazocine-labeled). Antiallodynic activity of haloperidol and its metabolites was dose-dependently prevented by the selective sigma(1) receptor agonist PRE-084, but not by naloxone. These results suggest the involvement of sigma(1) receptors, but discard any role of the endogenous opioid system, on the antiallodynic effects. Dopamine receptor antagonism also appears unlikely to be involved in these effects, since the D(2)/D(3) receptor antagonist (-)-sulpiride, which had no affinity for sigma(1) receptors, showed no antiallodynic effect. None of these drugs modified hind-paw withdrawal after a painful (4 g force) punctate mechanical stimulus in noncapsaicin-sensitized animals. As expected, the control drug gabapentin showed antiallodynic but not antinociceptive activity, whereas clonidine exhibited both activities and rofecoxib, used as negative control, showed neither.

CONCLUSION

These results show that haloperidol and its metabolites I and II produce antiallodynic but not antinociceptive effects against punctate mechanical stimuli and suggest that their antiallodynic effect may be due to blockade of sigma(1) receptors but not to dopamine receptor antagonism.

sigma-1 receptors in major depression and anxiety

Major depression and anxiety are two of the major psychiatric disorders that have some overlapping pathophysiologies, the most significant being the dysfunction in the monoaminergic, GABAergic and glutamatergic systems. A large number of drugs that alter these neurotransmitter levels/systems are effective in the treatment of major depression and anxiety. However, full remission of the clinical symptoms has not been achieved, perhaps owing to the complex pathophysiology of the diseases. Thus, the search for newer targets and target-specific drugs continues. Recently, the role of sigma-receptors, particularly the sigma-1 receptor subtype, has been identified as a target for the pathophysiology of neuropsychiatric disorders, and sigma-1 receptor modulators are considered to be the drugs of the future for the treatment of major depression and anxiety. The present review attempts to discuss the role of sigma-1 receptors in the pathophysiology of major depression and anxiety and also tries to position the use of its receptor modulators in the treatment of these two major disorders. The role of sigma-1 receptors in the mechanism of antidepressant action of venlafaxine, bupropion, neurosteroids and one of the herbal antidepressants, berberine, is reviewed. Although, sigma-1 receptor modulators may be future therapeutic options, either as individual agents or adjuvants in the treatment of mental disorders, the topic needs further preclinical and clinical exploration.

An unambiguous assay for the cloned human sigma1 receptor reveals high affinity interactions with dopamine D4 receptor selective compounds and a distinct structure-affinity relationship for butyrophenones

The ability of the sigma(1) receptor to interact with a huge range of drug structural classes coupled with its wide distribution in the body has contributed to it being implicated as a possible therapeutic target for a broad array of disorders ranging from substance abuse to depression to Alzheimer's disease. Surprisingly, the reported affinity values for some sigma(1) receptor ligands vary more than 50-fold. The potential of the sigma(1) receptor as a pharmacotherapeutic target prompted us to develop an unambiguous assay system for measuring the affinity of ligands to the cloned human sigma(1) receptor. In the course of characterizing this system and determining the true affinity values for almost three dozen compounds, it was discovered that some dopamine D(4) receptor selective compounds bind sigma(1) receptors with high affinity. A systematic analysis of haloperidol-like compounds revealed a clear structure-affinity relationship amongst clinically relevant butyrophenones. The antidepressant fluvoxamine, the drug of abuse methamphetamine, and the neurosteroid progesterone were amongst the many ligands whose interactions with the sigma(1) receptor were confirmed with our screening assay.

Substituted benzylaminoalkylindoles with preference for the sigma2 binding site

In the attempt to develop new sigma ligands we synthesized a series of N-benzyl-3-[1-(4-fluorophenyl)-1H-indol-3-yl]-N-methylpropan-1-amines and N-benzyl-4-[1-(4-fluorophenyl)-1H-indol-3-yl]-N-methylbutan-1-amines variously substituted on the phenyl ring. The displacement percentages of [3H]-DTG and [3H]-(+)-pentazocine determined in rat liver homogenates by these compounds at the fixed 100 nM concentration have been determined as a preliminary evaluation of their sigma1 and sigma2 affinity, respectively. The results suggested that the phenyl substituents may positively modulate, in comparison with the unsubstituted compound, the ability to displace [3H]-DTG from sigma2 sites, whereas the same phenyl substituents reduced the displacement percentages of [3H]-(+)-pentazocine from sigma1 sites. Some of these compounds were selected for radioligand binding assays. Compounds with a butylene intermediate chain displayed the greatest binding affinity for sigma2 over sigma1 receptors. The butylene derivative with 2,4-dimethyl substitution on the phenyl ring showed the greatest sigma2 affinity (sigma2Ki=5.9 nM) and an appreciable sigma2 over sigma1 selectivity (sigma1Ki/sigma2Ki=22). The obtained results suggest that a butylene chain separating the indole moiety from variously substituted benzylamino groups may be required to their interaction with a hypothetical secondary sigma2 binding site.

Involuntary emotional expression disorder: treating the untreated

Patients with involuntary emotional expression disorder (IEED) have impaired social and occupational functioning and there is currently no Food an Drug Administration-approved treatment. Treatment options include tricyclic antidepressants (TCAs), selective serotonin reuptake inhibitors (SSRIs), dopaminergic agents, and a combination of dextromethorphan and quinidine. Studies of monaminergic agents have typically been small and executed in single-center settings. Assessment measures generally show significant symptomatic improvements, including a reduction in the number of laughing or crying episodes and improvements in patients' clinical condition. The tolerability profiles of these agents are well defined, and include dizziness, tachycardia and QTc prolongation (TCAs), and sleep and sexual disturbances (SSRIs). The combination of dextromethorphan and quinidine has also been assessed in two large multicenter studies in patients with amyotrophic lateral sclerosis and multiple sclerosis. Compared with placebo and either agent alone, there were significant improvements in symptoms, quality of life, and relationships. The most common side effects were dizziness and nausea, and potential drug interactions with quinidine should also be considered. Choice of treatment should be evidence-based, taking into account both efficacy and tolerability.

Phencyclidine-induced cognitive deficits in mice are improved by subsequent subchronic administration of fluvoxamine: role of sigma-1 receptors

This study was undertaken to examine the effects of the selective serotonin reuptake inhibitors fluvoxamine and paroxetine on cognitive deficits in mice after repeated administration of the N-methyl-D-aspartate receptor antagonist phencyclidine (PCP). In the novel object recognition test, repeated administration of PCP (10 mg/kg/day, 10 days) significantly decreased the exploratory preference in the retention test session, but not in the training test session. PCP-induced cognitive deficits were significantly improved by subsequent subchronic (2-week) administration of fluvoxamine (20 mg/kg/day), but not paroxetine (10 mg/kg/day). Furthermore, the effect of fluvoxamine on PCP-induced cognitive deficits was antagonized by co-administration of the selective sigma-1 receptor antagonist NE-100 (1 mg/kg/day). Moreover, PCP-induced cognitive deficits were also significantly improved by subsequent subchronic (2-week) administration of the selective sigma-1 receptor agonist SA4503 (1 mg/kg/day) or neurosteroid dehydroepiandrosterone 3-sulfate (DHEA-S; 25 mg/kg/day). The effects of SA4503 or DHEA-S were also antagonized by co-administration of NE-100 (1 mg/kg/day), suggesting the role of sigma-1 receptors in the active mechanisms of these drugs. In contrast, acute single administration of these drugs (fluvoxamine, paroxetine, SA4503) alone or combination with NE-100 did not alter PCP-induced cognitive deficits. The present study suggests that agonistic activity of fluvoxamine at sigma-1 receptors plays a role in the active mechanisms of fluvoxamine on PCP-induced cognitive deficits in mice. Therefore, sigma-1 receptor agonists such as fluvoxamine would be potential therapeutic drugs for the treatment of the cognitive deficits of schizophrenia.

Dextromethorphan/quinidine: a novel dextromethorphan product for the treatment of emotional lability

Dextromethorphan (DM) is among the most widely used, non-narcotic antitussives, with a predictable safety profile. In 1981, a non-opioid, high-affinity brain recognition site for DM was discovered, and since then a unique neuropharmacological profile has emerged for this 'old' drug , suggesting novel applications. However, an extensive body of research for DM alone in treating various neurological conditions has been inconsistent. This may be largely due to its rapid first-pass metabolism. DM is currently being reintroduced as the active ingredient in a novel combination product in which low-dose quinidine is added to inhibit its breakdown, elevating blood levels of DM and increasing its likelihood of reaching neuronal targets . This has opened new possibilities for therapeutic use; the best evidence at present being for neurological disorders affecting emotional control.

A feasibility study of [11C]SA4503-PET for evaluating sigma1 receptor occupancy by neuroleptics: The binding of haloperidol to sigma1 and dopamine D2-like receptors

We investigated feasibility of positron emission tomography (PET) with [11C]SA4503 for evaluating the sigma1 receptor occupancy rate by neuroleptics. Haloperidol, which is well known to bind dopamine D2-like receptor (D2R) as well as to be a representative non-selective antagonist for sigma1 receptor (sigma1R), was selected as a model drug. Three healthy male subjects underwent 60-min [11C]raclopride-PET and 90-min [11C]SA4503-PET scans successively at a 120-min interval twice in a day for baseline measurement and on another day for haloperidol-loading measurement 16 hours after peroral administration of 3 mg of haloperidol. Binding potential (BP) of [11C]raclopride and [11C]SA4503 was quantitatively evaluated and the sigma1R and D2R occupancy rates were determined. D2R occupancy rates by haloperidol were 64% and 62% in the caudate and putamen, respectively, 16 h after the administration, while sigma1R occupancy rates were approximately 80% in all seven regions investigated including the caudate, putamen and cerebellum 18 h after the administration, suggesting that the sigma1R receptor occupancy rate by haloperidol was slightly larger than the D2R receptor occupancy rate. We concluded that [11C]SA4503-PET can be used for evaluating the sigma1R occupancy rates by neuroleptics or other drugs.

Neuro(active)steroids actions at the neuromodulatory sigma1 (sigma1) receptor: biochemical and physiological evidences, consequences in neuroprotection

Steroids from peripheral sources or synthesized in the brain, i.e. neurosteroids, exert rapid modulations of neurotransmitter responses through specific interactions with membrane receptors, mainly the gamma-aminobutyric acid type A (GABA(A)) receptor and N-methyl-d-aspartate (NMDA) type of glutamate receptor. Progesterone and 3alpha-hydroxy-5alpha-pregnan-20-one (allopregnanolone) act as inhibitory steroids while pregnenolone sulfate or dehydroepiandrosterone sulfate act as excitatory steroids. Some steroids also interact with an atypical protein, the sigma(1) (sigma(1)) receptor. This receptor has been cloned in several species and is centrally expressed in neurons and oligodendrocytes. Activation of the sigma(1) receptor modulates cellular Ca(2+) mobilization, particularly from endoplasmic reticulum pools, and contributes to the formation of lipid droplets, translocating towards the plasma membrane and contributing to the recomposition of lipid microdomains. The present review details the evidences showing that the sigma(1) receptor is a target for neurosteroids in physiological conditions. Analysis of the sigma(1) protein sequence confirmed homologies with the ERG2/emopamil binding protein family but also with the steroidogenic enzymes isopentenyl diphosphate isomerase and 17beta-estradiol dehydrogenase. Biochemical and physiological arguments for an interaction of neuro(active)steroids with the sigma(1) receptor are analyzed and the impact on physiopathological outcomes in neuroprotection is illustrated.

Using the BOLD MR signal to differentiate the stereoisomers of ketamine in the rat

RATIONALE

Ketamine is a chiral molecule that is reported to model aspects of schizophrenia.

OBJECTIVES

To investigate the stereospecificity of the isomers of ketamine using pharmacological magnetic resonance imaging (phMRI) in order to further understand ketamine's pharmacodynamic actions.

METHOD

Responses to 25 mg kg-1S(+) isomer, R(-) isomer and racemic ketamine in independent groups of Sprague-Dawley rats were investigated using a prepulse inhibition paradigm, locomotor observations, MRI and 2-deoxyglucose techniques.

RESULTS

Racemic ketamine and the S(+) isomer were both capable of disrupting sensorimotor gating as measured using prepulse inhibition and produced a longer period of hyperlocomotion comparative to the R(-) isomer. In contrast, large alterations in the BOLD MR signal were observed with R(-) isomer, whereas S(+) isomer and racemate precipitated more localized BOLD signal changes predominantly in cortical, hippocampal and hindbrain regions. Glucose utilization rates in conscious animals are in agreement with previously published data and verify the BOLD responses in the racemic group. However, no significant changes in glucose utilization were observed in the anesthetized cohort.

CONCLUSIONS

Ketamine and its isomers have stereospecific effects on sensorimotor gating and locomotion that correlate with the enantiomer's affinity for the NMDA receptor. It would appear that anesthesia, as required for preclinical MRI procedures, may interact with and potentially attenuate the drug's response. Although analysis of the main effect of isomers in comparison to each other or the racemate offers an alternative analysis method that should be less susceptible to anesthetic interactions, only the R(-) isomer comparative to the racemate offers significant differences of interest.

Interaction with sigma(1) protein, but not N-methyl-D-aspartate receptor, is involved in the pharmacological activity of donepezil

In the present study, we examined the interaction of (+/-)-2,3-dihydro-5,6-dimethoxy-2-[[1-(phenylmethyl)-4-piperidinyl]-methyl]-1H-inden-1-one hydrochloride (donepezil), a potent cholinesterase inhibitor, with two additional therapeutically relevant targets, N-methyl-d-aspartate (NMDA) and sigma(1) receptors. Donepezil blocked the responses of recombinant NMDA receptors expressed in Xenopus oocytes. The blockade was voltage-dependent, suggesting a channel blocker mechanism of action, and was not competitive at either the l-glutamate or glycine binding sites. The low potency of donepezil (IC(50) = 0.7-3 mM) suggests that NMDA receptor blockade does not contribute to the therapeutic actions of donepezil. Of potential therapeutic relevance, donepezil binds to the sigma(1) receptor with high affinity (K(i) = 14.6 nM) in an in vitro preparation (Neurosci Lett 260:5-8, 1999). Thus, we sought to determine whether an interaction with the sigma(1) receptor may occur in vivo under physiologically relevant conditions by evaluating the sigma(1) receptor dependence effects of donepezil in behavioral tasks. Donepezil showed antidepressant-like activity in the mouse-forced swimming test as did the sigma(1) receptor agonist igmesine. This effect was not displayed by the other cholinesterase inhibitors, rivastigmine and tacrine. The donepezil and igmesine effects were blocked by preadministration of the sigma(1) receptor antagonist N-[2-(3,4-dichlorophenyl)ethyl]-N-methyl-2-(dimethylamino) ethylamine (BD1047) and an in vivo antisense probe treatment. The memory-enhancing effect of donepezil was also investigated. All cholinesterase inhibitors attenuated dizocilpine-induced learning impairments. However, only the donepezil and igmesine effects were blocked by BD1047 or the antisense treatment. Therefore, donepezil behaved as an effective sigma(1) receptor agonist on these behavioral responses, and an interaction of the drug with the sigma(1) receptor must be considered in its pharmacological actions.

Differential effects of 7-OH-DPAT and apomorphine on hyperactivity induced by MK-801 (dizocilpine) in rats

Recent experiments from this laboratory demonstrated synergistic locomotor depressant effects of AMPA/kainate receptor blockade and D(2/3) dopamine (DA) receptor stimulation. This study explored functional interactions between DA and glutamate (Glu) systems using the NMDA receptor antagonist MK-801 and the DA receptor agonists 7-OH-DPAT and apomorphine. Using photocell locomotor activity boxes, systemic effects of MK-801 in combination with 7-OH-DPAT (0.03 mgkg(-1) SC, n=8) or a pre-synaptically effective dose of apomorphine (0.05 mgkg(-1) SC, n=6) were measured in male Sprague-Dawley rats. Effects of bilateral applications of MK-801 and 7-OH-DPAT into the nucleus accumbens (NAS) shell subregion were also investigated (n=7). When given alone, MK-801 (0.13 mgkg(-1) or 0.66 microg intra-NAS shell) increased horizontal locomotor activity, while 7-OH-DPAT (0.03 mgkg(-1)) or apomorphine (0.05 mgkg(-1)) decreased this measure. Co-administration of 7-OH-DPAT (systemically or into the NAS shell) completely blocked MK-801 induced hyperactivity. In contrast, MK-801 and apomorphine demonstrated additive effects. Stimulation of D(3) DA receptors may therefore block the hyperactivity induced by NMDA receptor antagonism, and the NAS shell is an important site for this interaction. The differential effects of the DA agonists on hyperactivity induced by NMDA receptor blockade support the proposal that 7-OH-DPAT may induce hypoactivity by stimulation of postsynaptic D(3) DA receptors.

Clinical effects of pharmacological variations in selective serotonin reuptake inhibitors: an overview

Although the selective serotonin reuptake inhibitor (SSRI) class of antidepressants shares a common primary pharmacology, namely the inhibition of serotonin reuptake, their secondary pharmacology is remarkably heterogeneous. Inhibition of serotonin reuptake and the consequent increase in serotonin availability are responsible for the relief of depressive symptoms and for some of the adverse effects of this class of drugs. Transsynaptic effects such as modulation of signalling cascades, gene expression processes and neuroplasticity are also important in the mechanism of action of antidepressants. However, this review shows that secondary properties of the SSRIs may contribute to the differences in efficacy and tolerability between members of the class. For example, fluvoxamine has affinity for sigma(1)-receptors -- a property likely to be responsible for its particular efficacy in delusional depression. By understanding the properties of SSRIs and employing careful selection of agents for individual patients, physicians are more able to tailor antidepressant treatments to their patients' particular circumstances.

Antinociceptive effects of haloperidol and its metabolites in the formalin test in mice

RATIONALE

Formalin-induced pain is reduced in sigma-1 (sigma1) receptor knockout mice; therefore, we hypothesized that haloperidol and its metabolites I and II, which have affinity for sigma1 receptors, may modulate formalin-induced pain.

RESULTS

Intraplantar administration of formalin (2.5%) to CD-1 mice produced a biphasic period of pain. Haloperidol (0.03-1 mg/kg, s.c.) and reduced haloperidol (metabolite II, 0.25-8 mg/kg, s.c.) dose-dependently inhibited both phases of formalin-induced pain. Haloperidol metabolite I (4-128 mg/kg, s.c.) also produced dose-dependent antinociception in the second phase of the formalin test, but was less potent and effective against first-phase pain. Haloperidol metabolite III (16 and 128 mg/kg) and (-)sulpiride (200 mg/kg), which have no affinity for sigma1 receptors, did not produce significant antinociception in either phase of the formalin test. The order of potency of the drugs to produce their antinociceptive effect [haloperidol>metabolite II>metabolite I>>metabolite III= (-)sulpiride=inactive] correlated with their affinity for sigma1 receptors, but not with their affinity for sigma2 or dopamine D2 receptors. Naloxone (1 mg/kg, s.c.) did not antagonize the antinociception induced by haloperidol and its metabolites. None of the antinociceptive drugs in the formalin test produced any antinociception in the tail flick test.

CONCLUSION

These results suggest that the antinociceptive effect of haloperidol and its metabolites in the formalin test is not due to unspecific/generalised inhibition of nociception or modulation of opioid receptors, and that it may be related, at least partially, to the ability of these drugs to interact with sigma1 receptors.

Pregnenolone sulfate acts through a G-protein-coupled sigma1-like receptor to enhance short term facilitation in adult hippocampal neurons

Neurosteroids have been linked to cognitive performance, and their levels are altered in neuropsychiatric diseases. These neuromodulators are produced in the brain where they have important effects on synaptic transmission at postsynaptic gamma-amino-butyric acid receptors and N-methyl-D-aspartate receptors and at presynaptic sites. We previously found, in cultured neonatal hippocampal neurons, that the neurosteroid, pregnenolone sulfate, acts presynaptically through a sigma1-like receptor to modulate basal glutamate release. The present study was designed to test whether pregnenolone sulfate acts through a similar presynaptic receptor in adult hippocampal neurons. The sigma1-receptor agonist, 2-(4-morpholino)ethyl-1-phenylcyclohexane-1-carboxylate, enhanced paired-pulse facilitation (PPF) by a similar extent to that which we had previously reported for pregnenolone sulfate. The sigma1-receptor antagonists, 1-(4-Iodophenyl)-3-(2-adamantyl)guanidine and 1[2-(3,4-dichlorophenyl)ethyl]-4-methylpiperazine, blocked the pregnenolone sulfate enhancement of PPF as did pretreatment of slices in pertussis toxin. We conclude that pregnenolone sulfate acts through a Gi/o-coupled sigma1-like receptor to enhance short-term presynaptic facilitation onto adult hippocampal CA1 neurons.

Synthesis and in vivo evaluation of a new PET radioligand for studying sigma-2 receptors

The cyclohexyl piperazine 1 (1-cyclohexyl-4-[3-(5-methoxy-1,2,3,4-tetrahydro-naphthalen-1-yl)-propyl]-piperazine) has been shown to be a potent and selective sigma-2 receptor ligand. In the present study, we prepared [(11)C]1 by O-alkylation of the phenolic precursor 2 with [(11)C]CH(3)I. [(11)C]1 was obtained in a 29% non-decay corrected yield and specific activity of 9299 mCi/micromol calculated at end-of-synthesis. The biodistribution of [(11)C]1 in mouse brain demonstrated rapid and homogenous concentration in all brain structures, which included the cortex, thalamus, cerebellum and striatum. Co-administration of unlabelled 1 (1 mg/kg) or the sigma-2 selective ligand SM-21 (1 mg/kg) failed to show any significant inhibition of [(11)C]1 uptake in the mouse brain. The evaluation of this radioligand in vivo in the mouse clearly indicates that it does not possess the required properties for studying sigma-2 receptors in the brain using PET.

Plasma dehydroepiandrosterone levels are strongly increased in schizophrenia

Dehydroepiandrosterone has been recently recognized as neuroactive steroid with several vital neurophysiological activities on membrane receptors, such as N-methyl-d-aspartate, and gamma-aminobutyric acid receptors and on genomic androgen receptors. DHEA does also have an antiglucocorticoid effect. So far, the relevance of this neuroactive steroid to psychiatric disorders is not well known. In this study, plasma levels of DHEA were determined with a highly sensitive and specific gas-chromatography/mass-spectrometry method in 23 outpatients suffering from Diagnostic and Statistical Manual of Mental Disorders-IV schizophrenia compared with 23 healthy control subjects matched for age and sex. Plasma levels of DHEA were found to be strongly elevated in the group of schizophrenic patients (mean+/-SD=90.9+/-61.4 nmol/l) compared to that of control subjects (mean+/-SD=24.0+/-17.9 nmol/l) and the difference was highly significant (t=5.018, df=44, p<0.0001). This statistically significant difference was also found when we divided the groups of schizophrenics and controls in subgroups of males (t=4.536, df=24, p=0.0001) and females (t=2.777, df=18, p=0.0124). These results suggest that DHEA may have some role in the pathophysiology of schizophrenia due to its complex mechanism of action in the brain involving genomic and non-genomic components. Therefore, its study may provide further understanding of the pathophysiology of psychoses and open new avenues for their treatment.

Antidepressant treatment of psychotic major depression: potential role of the sigma receptor

Psychotic major depression is a severe condition that frequently proves difficult-to-treat. The most effective traditional treatments (electroconvulsive therapy and combinations of antipsychotics with tricyclic antidepressants) are associated with significant side effects, and the use of tricyclic antidepressants alone is largely ineffective. Recent evidence has indicated that the selective serotonin reuptake inhibitors, either alone or in combination with antipsychotics, may provide a desirable alternative to traditional treatments. Among selective serotonin reuptake inhibitors, fluvoxamine has been the best studied and, somewhat surprisingly, has proven effective in several studies as a monotherapy without the need to combine with an antipsychotic. It is proposed that the apparent efficacy of fluvoxamine in psychotic major depression may be related to its unique property of high affinity for the sigma 1 receptor, which is thought to play a role in psychosis and in the action of some antipsychotic drugs.

Pharmacology and structure-activity relationships of bioactive polycyclic cage compounds: a focus on pentacycloundecane derivatives

The chemistry of organic polycyclic cage compounds has intrigued medicinal chemists for over 50 years, yet little is published about their pharmacological profiles. Polycyclic cage compounds have important pharmaceutical applications, ranging from the symptomatic and proposed curative treatment of neurodegenerative diseases such as Parkinson's and Alzheimer's disease (e.g., amantadine and memantine), to use as anti-viral agents against influenza and the immunodeficiency virus (HIV). The polycyclic cage appears to be a useful scaffold to yield drugs with a wide scope of applications, and can be used also to modify and improve the pharmacokinetic and pharmacodynamic properties of drugs in current use. This review attempts to summarize the pharmacological profiles of polycyclic cage compounds with an emphasis on the lesser known pentacycloundecanes, homocubanes, and trishomocubanes.

Formalin-induced pain is reduced in sigma(1) receptor knockout mice

The role of sigma1 receptors in non-acute pain has not been explored. In this study we show that both phases of formalin-induced pain were reduced by approximately 55% in sigma1 receptor knockout mice in comparison to wild-type animals. These results suggest that the tonic pain induced by formalin is altered in mice lacking sigma1 receptors, and highlight the potential usefulness of further studies of the role of sigma1 receptors in models of non-acute pain.

No association found between the type 1 sigma receptor gene polymorphisms and methamphetamine abuse in the Japanese population: a collaborative study by the Japanese Genetics Initiative for Drug Abuse

It has been suggested that individual genetic factors are involved in susceptibility to drug dependence and the manifestation of drug-induced psychosis. The aim of this study was to examine the relation between methamphetamine abusers/psychosis and the type 1 sigma receptor gene polymorphisms. Subjects comprised 143 MAP abusers and 181 healthy controls. Two polymorphisms in the type 1 sigma receptor gene, GC-241-240TT and A61C (Gln2Pro), were examined in the present study. No significant differences were observed in either polymorphism between healthy controls and MAP abusers/psychosis. In the subgroup analyses, the rate of CC genotype of A61C tended to be higher in MAP patients who had experienced spontaneous relapse without MAP use than in those who had not (P = .06, OR = 3.02 95%CI = 0.92-9.92). However, the level of this significant trend did not remain after the Bonferroni's multiple correction. This study suggests that type 1 sigma receptor gene is unlikely to play a major role in substance abuse liability and/or the development of MAP psychosis.

Thioxanthene-derived analogs as sigma(1) receptor ligands

An investigation of the structure-affinity relationships for the binding of thioxanthene-related structures indicates that an intact thioxanthene ring is not required for binding at sigma(1) receptors, and that with the appropriate structural modifications, affinity can be enhanced to the subnanomolar level. Certain of the analogs displayed sigma(1)-fold selectivity for sigma(1) versus sigma(2) receptors.

Beneficial effects of the sigma1 receptor agonists igmesine and dehydroepiandrosterone against learning impairments in rats prenatally exposed to cocaine

In utero cocaine (IUC) exposure results in offspring rats in complex neurochemical and behavioral alterations, particularly affecting learning and memory processes. We examined here the impact of IUC exposure on memory functions in male and female offspring rats and report that selective sigma(1) (sigma(1)) receptor agonists are effective in reversing the deficits. Dams received a daily cocaine, 20 mg/kg ip, injection between gestational days E17 to E20. Learning was examined in offspring between day P30 and P41 using delayed alternation in the T-maze, water-maze learning and passive avoidance. Both male and female rats prenatally exposed to cocaine showed delayed alternation deficits and impairments of acquisition of a fixed platform position in the water maze, as shown by higher acquisition latencies and diminutions of time spent in the training quadrant during the probe test. The acquisition of a daily changing platform position also demonstrated impaired working memory. Finally, passive avoidance deficits were observed. Pretreatment with the synthetic sigma(1) agonist igmesine (0.1-1 mg/kg ip) or the neuroactive steroid dehydroepiandrosterone (DHEA 10-40 mg/kg ip) reversed the prenatal cocaine-induced learning deficits in offspring rats for each test. The sigma(1) antagonist BD1063 (1 mg/kg ip) failed to affect performances alone but blocked the igmesine and DHEA effects, confirming the involvement of the sigma(1) receptor. IUC exposure thus results in marked memory deficits, affecting spatial and nonspatial short- and long-term memories in juvenile male and female offspring rats. The activation of the sigma(1) neuromodulatory receptor allows a complete behavioral recovery of the memory functions in prenatally cocaine-exposed rats.

Regulation of affect by the lateral septum: implications for neuropsychiatry

Substantial evidence indicates that the lateral septum (LS) plays a critical role in regulating processes related to mood and motivation. This review presents findings from the basic neuroscience literature and from some clinically oriented research, drawing from behavioral, neuroanatomical, electrophysiological, and molecular studies in support of such a role, and articulates models and hypotheses intended to advance our understanding of these functions. Neuroanatomically, the LS is connected with numerous regions known to regulate affect, such as the hippocampus, amygdala, and hypothalamus. Through its connections with the mesocorticolimbic dopamine system, the LS regulates motivation, both by stimulating the activity of midbrain dopamine neurons and regulating the consequences of this activity on the ventral striatum. Evidence that LS function could impact processes related to schizophrenia and other psychotic spectrum disorders, such as alterations in LS function following administration of antipsychotics and psychotomimetics in animals, will also be presented. The LS can also diminish or enable fear responding when its neural activity is stimulated or inhibited, respectively, perhaps through its projections to the hypothalamus. It also regulates behavioral manifestations of depression, with antidepressants stimulating the activity of LS neurons, and depression-like phenotypes corresponding to blunted activity of LS neurons; serotonin likely plays a key role in modulating these functions by influencing the responsiveness of the LS to hippocampal input. In conclusion, a better understanding of the LS may provide important and useful information in the pursuit of better treatments for a wide range of psychiatric conditions typified by disregulation of affective functions.

Blocking the anoxic depolarization protects without functional compromise following simulated stroke in cortical brain slices

Within 2 min of stroke onset, neurons and glia in brain regions most deprived of blood (the ischemic core) undergo a sudden and profound loss of membrane potential caused by failure of the Na+/K+ ATPase pump. This anoxic depolarization (AD) represents a collapse in membrane ion selectivity that causes acute neuronal injury because neurons simply cannot survive the energy demands of repolarization while deprived of oxygen and glucose. In vivo and in live brain slices, the AD resists blockade by antagonists of neurotransmitter receptors (including glutamate) or by ion channel blockers. Our neuroprotective strategy is to identify AD blockers that minimally affect neuronal function. If the conductance underlying AD is not normally active, its selective blockade should not alter neuronal excitability. Imaging changes in light transmittance in live neocortical and hippocampal slices reveal AD onset, propagation, and subsequent dendritic damage. Here we identify several sigma-1 receptor ligands that block the AD in slices that are pretreated with 10-30 microM of ligand. Blockade prevents subsequent cell swelling, dendritic damage, and loss of evoked field potentials recorded in layers II/III of neocortex and in the CA1 region of hippocampus. Even when AD onset is merely delayed, electrophysiological recovery is markedly improved. With ligand treatment, evoked axonal conduction and synaptic transmission remain intact. The large nonselective conductance that drives AD is still unidentified but represents a prime upstream target for suppressing acute neuronal damage arising during the first critical minutes of stroke. Sigma receptor ligands provide insight to better define the properties of the channel responsible for anoxic depolarization. Video clips of anoxic depolarization and spreading depression can be viewed at http://anatomy.queensu.ca/faculty/andrew.cfm.

4-(Tetralin-1-yl)- and 4-(Naphthalen-1-yl)alkyl Derivatives of 1-Cyclohexylpiperazine as σ Receptor Ligands with Agonist σ2 Activity

Several 1-cyclohexylpiperazine derivatives related to sigma(2) receptor ligand 1-cyclohexyl-4-[3-(5-methoxy-1,2,3,4-tetrahydronaphthalen-1-yl)propyl]piperazine (33, K(i) = 0.34 nM) were synthesized and tested in radioligand binding assays, to attempt a structure-affinity relationship study. Intermediate alkyl chain length and methoxyl group position on the tetralin nucleus were varied. A few naphthalene analogues were also prepared. High affinities were found in sigma(2) receptor binding for almost all compounds, some of which displayed K(i) values in subnanomolar range, but low sigma(2)/sigma(1) selectivities were found. The highest sigma(2) affinities were displayed by compounds with an intermediate alkyl chain of three (32 and 43) or five methylenes (39 and 46). Quite high sigma(1) receptor affinity was found for compounds with a four-methylene chain; 36 (K(i) = 0.036 nM) and 45 (K(i) = 0.22 nM) displaying good sigma(1)/sigma(2) selectivity (406- and 139-fold, respectively). Moreover, homologues of compound 33 displayed also satisfactory selectivities over dopamine D(2)-like, serotonin 5-HT(3), and adrenergic alpha(1) receptors. These compounds and a few others were tested in the inhibition of the electrically evoked contractions in guinea pig bladder and were demonstrated to be full sigma(2) agonists. The activity values correlated well to the affinity scale (EC(50) in microM range). 33 and related compounds are proposed as a class of potential antineoplastic and PET diagnosis agents.

Functional polymorphisms in the sigma1 receptor gene associated with alcoholism

BACKGROUND

Sigma1 receptors are involved in the pathogenesis of drug abuse. Two polymorphisms (GC-241-240TT and Gln2Pro) in the sigma1 receptor gene (SIGMAR1) have been identified. To investigate the role of SIGMAR1 in conveying susceptibility to alcoholism, we performed a functional analysis of polymorphisms in the SIGMAR1 and a case-control study.

METHODS

We initially screened for polymorphisms in the 5'-upstream region. The effects of the polymorphisms on transcriptional activity were determined using a gene reporter assay. The distribution of SIGMAR1 polymorphisms was analyzed in 307 alcoholic and 302 control subjects.

RESULTS

A novel T-485A polymorphism was identified. The transcriptional activity of the A-485 allele and the TT-241-240 allele was significantly reduced compared with that of the T-485 allele and the GC-241-240 allele. The frequencies of the A-485 allele (chi2=5.575, df=1, p=.0205) and the TT-241-240/Pro2 haplotype (chi2=21.464, df=1, p<.0001) were significantly higher in control subjects compared with alcoholic subjects. The T-485A and the GC-241-240TT may be functional polymorphisms, and the A-485 allele and TT-241-240/Pro2 haplotype are possible protective factors for the development of alcoholism.

Preclinical acute toxicity studies and rodent-based dosimetry estimates of the novel sigma-1 receptor radiotracer [(18)F]FPS

[(18)F]1-(Fluoropropyl)-4-[(4-cyanophenoxy)methyl]piperidine ([(18)F]FPS) is a novel high affinity (KD = 0.5 nM) sigma receptor radioligand that exhibits saturable and selective in vivo binding to sigma receptors in rats, mice and non-human primates. In order to support an IND application for the characterization of [(18)F]FPS through PET imaging studies in humans, single organ and whole body radiation adsorbed doses associated with [(18)F]FPS injection were estimated from distribution data obtained in rats. In addition, acute toxicity studies were conducted in rats and rabbits and limited toxicity analyses were performed in dogs. Radiation dosimetry estimates obtained using rat biodistribution analysis of [(18)F]FPS suggest that most organs would receive around 0.012-0.015 mGy/MBq. The adrenal glands, brain, kidneys, lungs, and spleen would receive slightly higher doses (0.02-0.03 mGy/MBq). The adrenal glands were identified as the organs receiving the greatest adsorbed radiation dose. The total exposure resulting from a 5 mCi administration of [(18)F]FPS is well below the FDA defined limits for yearly cumulative and per study exposures to research participants. Extended acute toxicity studies in rats and rabbits, and limited acute toxicity studies in beagle dogs suggest at least a 175-fold safety margin in humans at a mass dose limit of 2.8 microg per intravenous injection. This estimate is based on the measured no observable effect doses (in mg/m(2)) in these species. These data support the expectation that [(18)F]FPS will be safe for use in human PET imaging studies at a maximum administration of 5 mCi and a mass dose equal to or less than 2.8 microg FPS per injection.