The sigma-1 receptor behaves as an atypical auxiliary subunit to modulate the functional characteristics of Kv1.2 channels expressed in HEK293 cells.

Expression of Kv1.2 within Kv1.x potassium channel complexes is critical in maintaining appropriate neuronal excitability and determining the threshold for action potential firing. This is attributed to the interaction of Kv1.2 with a hitherto unidentified protein that confers bimodal channel activation gating, allowing neurons to adapt to repetitive trains of stimulation and protecting against hyperexcitability. One potential protein candidate is the sigma-1 receptor (Sig-1R), which regulates other members of the Kv1.x channel family; however, the biophysical nature of the interaction between Sig-1R and Kv1.2 has not been elucidated. We hypothesized that Sig-1R may regulate Kv1.2 and may further act as the unidentified modulator of Kv1.2 activation. In transiently transfected HEK293 cells, we found that ligand activation of the Sig-1R modulates Kv1.2 current amplitude. More importantly, Sig-1R interacts with Kv1.2 in baseline conditions to influence bimodal activation gating. These effects are abolished in the presence of the auxiliary subunit Kvß2 and when the Sig-1R mutation underlying ALS16 (Sig-1R-E102Q), is expressed. These data suggest that Kvß2 occludes the interaction of Sig-1R with Kv1.2, and that E102 may be a residue critical for Sig-1R modulation of Kv1.2. The results of this investigation describe an important new role for Sig-1R in the regulation of neuronal excitability and introduce a novel mechanism of pathophysiology in Sig-1R dysfunction.

Involvement of the sigma receptor in passive-avoidance learning in the day-old chick during the second wave of neuronal activity.

The specific sigma-receptor agonist (+)-SKF 10047 and antagonist BD 1047 were used to investigate whether this receptor was involved in passive-avoidance training in the day-old chick. We found 300 microM (+)-SKF 10047 to be amnesic when injected into the lobus parolfactorius 5 h after training (p < .01). Higher or lower concentrations of (+)-SKF 10047 did not disrupt memory formation. The amnesia produced by the efficacious dose of (+)-SKF 10047 was reversed by the specific antagonist, BD 1047. It is suggested that the sigma-receptor may exert its effect on passive-avoidance memory consolidation during the later stages of long-term memory formation by modulation of memory-related neurotransmission.

[Possible role of sigma-receptors in the regulation of cough reflex, gastrointestinal and retinal function].

This paper provides an overview of our current understanding of the role of sigma-receptors in the regulation of cough, gastrointestinal and retinal function. Systemic administration of N-(+)-allylnormetazocine ((+)SKF-10,047), 1,2-di-(2-toyl)guanidine (DTG) or pentazocine markedly reduced the number of coughs in a dose-dependent manner. The antitussive effect of these sigma-receptor ligands was significantly reduced by pretreatment with haloperidol or rimcazol, a specific antagonist of sigma-receptors. Antitussive effects of dextromethorphan and noscapine were significantly and dose-dependently reduced by pretreatment with rimcazole. However, rimcazole did not have a significant effect on the antitussive effect of morphine. These results suggest that haloperidol-sensitive sigma-receptors may be involved in the antitussive mechanism of non-narcotic antitussive drugs. Selective sigma-receptor ligands such as (+)SKF-10,047, DTG and (+)pentazocine elicit a potent protection against gastric and duodenal ulcers. Ulcerprotective activity of sigma-receptor ligands may be related to their stimulating effect on bicarbonate secretion through interaction with sigma-receptors in the gastrointestinal mucosa. Activation of sigma-receptors in retina protect retinal cells against glutamate-induced neurotoxicity. It is possible that sigma-receptor ligands may be useful as therapeutic drugs against retinal disease with ischemia-induced neuronal cell death such as retinal artery occlusion, diabetes mellitus or glaucoma.

Sigma receptor ligands (+)-SKF10,047 and SA4503 improve dizocilpine-induced spatial memory deficits in rats.

This study examined the effects of the sigma receptor ligands (+)-N-allylnormetazocine ((+)-SKF10,047) and 1-(3,4-dimethoxyphenethyl)-4-(3-phenylpropyl)piperazine dihydrochloride (SA4503) on dizocilpine-induced impairment of working and reference memory in a radial arm maze task in rats. Dizocilpine, a non-competitive NMDA receptor antagonist, significantly impaired both reference and working memory, an effect which was accompanied by ataxia and impairment of food intake. The dizocilpine-induced impairment of reference memory was dose-dependently attenuated by (+)-SKF10,047 and SA4503. SA4503 also attenuated the dizocilpine-induced working memory impairment, although (+)-SKF10,047 had no effect. Neither sigma receptor ligand affected the behavioral symptoms such as ataxia and impairment of food intake induced by dizocilpine. The ameliorating effects of both (+)-SKF10,047 and SA4503 on dizocilpine-induced spatial memory impairment were completely antagonized by a sigma1 receptor antagonist N,N-dipropyl-2-[4-methoxy-3-(2-phenylethoxy)phenyl]-ethylamine-mon ohydrochloride. These results suggest that the interaction of sigma1 receptors with NMDA receptors modulates spatial memory in rats.

SKF-10,047 reverses stress-induced motor suppression: interaction with dopaminergic system.

Mice exhibited a marked suppression of motility (conditioned suppression) when placed in the same environment in which they had previously received an electric footshock. This stress-induced motor suppression was dose dependently attenuated by (+/-)-SKF-10,047, a sigma receptor agonist, but not by its (-)-optical isomer ((-)-SKF-10,047) and the sigma receptor ligands (+)-pentazocine and 1,3-di-(2-tolyl)guanidine. This effect of (+/-)-SKF-10,047 was antagonized by BMY-14802, a sigma receptor antagonist, and by pimozide, a dopamine receptor antagonist. When dopaminergic neurons were destroyed by pretreatment with 6-hydroxydopamine, the effect of (+/-)-SKF-10,047 on the stress response was also attenuated. Furthermore, (+/-)-SKF-10,047 dose dependently reversed the decrease in striatal dopamine turnover in the conditioned suppression group. These results suggest that stress-induced motor suppression is restored by (+/-)-SKF-10,047 acting through sigma receptors, which are closely linked to the dopaminergic neuronal system.

Antagonism of a (+)N-allylnormetazocine stimulus by (-)PPAP and several structurally related analogs.

Employing rats trained to discriminate 5 mg/kg of the benzomorphan opioid (+)N-allylnormetazocine [(+)NANM] from vehicle, tests of stimulus generalization and antagonism were conducted to determine the influence of several potential sigma-receptor ligands. It has been previously suggested that the (+)NANM stimulus may involve concurrent action at sigma- and phencyclidine (PCP) receptors. Although the low-affinity sigma-antagonist rimcazole was without stimulus-attenuating effect, three novel sigma-ligands--(-)PPAP, CNS 3018, and CNS 3093 (ID50 doses = 3.2, 6.7, and 4.5 mg/kg, respectively)--antagonized the (+)NANM stimulus in a dose-related fashion. The nonselective serotonergic agent 1-(3-trifluoromethyl)phenylpiperazine (TFMPP) produced partial generalization in (+)NANM-trained animals whereas buspirone, a 5-hydroxytryptamine1A (5-HT1A) agonist, attenuated (to 27% drug-appropriate responding) the (+)NANM stimulus. Because the prototypic 5-HT1A agonist 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) failed to attenuate the (+)NANM stimulus at pharmacologically relevant doses, it seems unlikely that the (+)NANM stimulus involves a 5-HT1A mechanism. TFMPP and buspirone display modest affinity for sigma-receptors and this may account for the present findings with these agents. The present results neither establish a role for sigma involvement in the stimulus properties of (+)NANM nor eliminate a role for PCP receptors. They do, however, demonstrate that sigma-ligands with little to no affinity for PCP receptors are capable of antagonizing the (+)NANM stimulus.

Discriminative stimulus effects of the PCP/sigma-ligand (+)-N-allylnormetazocine in monkeys.

(+)-N-Allylnormetazocine [(+)-NANM] binds to both the phencyclidine (PCP) receptor and the sigma-site in brain, with some selectivity for the latter. In rats, the discriminative stimulus effects of (+)-NANM are primarily PCP like. The present study was performed to determine if the discriminative effects of (+)-NANM in a primate species might reflect the actions of this drug at the sigma-site. Six squirrel monkeys were trained to discriminate between IM injections of saline and 1.0 mg/kg (+)-NANM in a two-choice discrete-trial avoidance procedure. In tests of stimulus generalization, dose-dependent increases in trials completed on the (+)-NANM choice lever were produced by (+)- and (-)-NANM, by PCP and the PCP-like drugs MK-801 and thienylcyclohexyl-piperidine, and by the opioids (+)- and (-)-cyclazocine and dextrorphan; order of potency correlated with reported affinities for the PCP receptor. High-affinity sigma-ligands, (+)-pentazocine, 1,3-di-ortho-tolylguanidine (DTG), haloperidol, and BMY 14802, as well as agonists at mu- and kappa-opioid receptors, occasioned selection of the saline-appropriate choice lever. Selection of the (+)-NANM choice lever was reduced by up to 35-50% when 1.0 mg/kg (+)-NANM was given concurrently with haloperidol or BMY 14802, but was not affected substantially by (-)-butaclamol, another sigma-ligand, or by naltrexone, an opioid antagonist. The discriminative effects of (+)-NANM in squirrel monkeys appear to be mediated largely by the PCP receptor and not by the sigma-site or opioid receptors.

Tris inhibits (+)-[3H]SKF-10,047 binding to sigma receptors.

Tris-HCl is the most commonly used buffer in studies of radioligand binding to sigma receptors, with concentrations as high as 50 or 100 mM often used. We report here that these concentrations of Tris substantially inhibit (+)-[3H]SKF-10,047 binding to sigma receptors. The well-established inhibitory effect of Tris-HCl on ligand binding to PCP receptors did not contribute to the presently reported inhibition of (+)-[3H]SKF-10,047 binding. The IC50 of Tris, determined in the presence of 10 mM potassium phosphate buffer, was 15.4 +/- 1.2 mM (n = 3, pH 8.0, 25 degrees C, 1 nM radioligand). Equilibrium saturation studies revealed an apparent competitive inhibition of binding.

The sigma [corrected] ligand rimcazole antagonises (+)SKF 10,047, but not (+)3-PPP, in the mouse isolated vas deferens.

We have characterized the actions of several sigma receptor ligands on the electrically evoked, neurogenic contractions of the mouse isolated vas deferens. (-)SKF 10,047 was significantly more potent than (+)SKF 10,047 in potentiating twitch contractions and was equipotent with (+)3-PPP. Rimcazole (1 and 3 microM) antagonised the potentiation induced by 100 microM (+)SKF 10,047 and, to a lesser extent, that induced by 30 microM (-)SKF 10,047 but increased that elicited by (+)3-PPP (30 microM). This apparent contradiction may arise from sigma agonists acting in this tissue at both sigma and non-sigma sites.

Substitution and antagonism in rats trained to discriminate (+)-N-allylnormetazocine from saline.

(+)-N-Allylnormetazocine (NANM) binds to at least two sites in the mammalian central nervous system, a high-affinity, haloperidol-sensitive site and a lower-affinity site identified as the phencyclidine (PCP) receptor. The relevance of these sites to the discriminative stimulus properties of (+)-NANM was evaluated in rats trained to discriminate (+)-NANM from saline. Drugs with a high affinity for the haloperidol-sensitive site, including haloperidol, (+)-ketocyclazocine, 1,3-di-ortho-tolyl-guanidine and (-)-butaclamol failed to substitute for the (+)-NANM stimulus. In addition, when they were tested in combination with (+)-NANM, only haloperidol evidenced any antagonistic effects. The antagonistic effects of haloperidol were incomplete and only occurred at doses that substantially disrupted responding. Evidence obtained earlier that (+)-3-(3-hydroxyphenyl)-N-(1-propyl) piperidine could antagonize (+)-NANM was not replicated. On the other hand, PCP-like drugs from diverse chemical classes, including PCP, ketamine, MK-801, (-)-2-methyl-3,3-diphenyl-3-propanolamine, etoxadrol and dextrorphan, all substituted fully for the (+)-NANM stimulus with a potency predicted by their relative potency for PCP-like discriminative stimulus effects and relative affinity for the PCP receptor. Taken together, these results fail to provide evidence for an important role for the high-affinity haloperidol-sensitive binding site for (+)-NANM in its discriminative stimulus properties. Instead, activity at the PCP receptor is predictive of (+)-NANM-like effects.

Activation of the A10 mesolimbic system by the sigma-receptor agonist (+)SKF 10,047 can be blocked by rimcazole, a novel putative antipsychotic.

This study evaluated with electrophysiological and behavioral techniques the ability of rimcazole, a novel putative antipsychotic and selective sigma-receptor ligand, to antagonize the stimulation of the mesocorticolimbic dopamine system by the sigma-agonist, (+)SKF 10,047. Rimcazole effectively blocked the (+)SKF 10,047-induced excitation of ventral tegmental dopamine neurons while having no effect on either spontaneous activity or apomorphine-elicited slowing of A10 firing. Rimcazole also antagonized the behavioral hyperactivity produced by (+)SKF 10,047, but not by d-amphetamine which is also mediated through the same mesolimbic dopamine pathway. These data provide further evidence that rimcazole's novel pharmacologic profile may involve a blockade of sigma-receptors on mesocorticolimbic dopamine neurons.

Pharmacologic and reinforcing properties of phencyclidine and the enantiomers of N-allylnormetazocine in the dog.

Experiments were conducted to evaluate the degree of phencyclidine (PCP)-like activity associated with the dextro and levo enantiomers of the sigma agonist N-allylnormetazocine (NANM). In chronic spinal dogs, d- and l-NANM generally produced similar physiologic and gross animal behavior effects which included miosis, tachycardia, hyperthermia, increased secretory activity (lacrimation, rhinorrhea and salivation), nystagmus and stereotyped head movements. For these effects, d- and l-NANM were generally equal in potency and both were about 1/10th as potent as PCP. However, the NANM enantiomers could be differentiated on the basis of their effects on nociceptive reflexes. Comparisons of dose-response curves and efficacies demonstrated that d-NANM was more similar to PCP in its effectiveness in depressing the flexor and skin twitch reflexes than was l-NANM. In addition, naltrexone selectively antagonized or reduced only the effects of l-NANM on reflex activity. In intact dogs, d-NANM and PCP, but not l-NANM maintained self-administration behavior under FR15 or FI900 (FR10:S) schedules of reinforcement. This represented the most stereospecific action of the NANM enantiomers. Additionally, l-NANM failed to maintain self-administration behavior, even following pretreatment with naltrexone, thus suggesting that the opiate activity of l-NANM was not responsible for its lack of reinforcing efficacy. Taken together, the data demonstrate that both d- and l-NANM have PCP-like properties, but d-NANM is pharmacologically more equivalent than l-NANM to PCP and l-NANM has additional activity which is not PCP-like.

Aging and day-night rhythms in feeding in mice: effects of the putative sigma opiate agonist, N-allylnormetazocine (SKF-10,047).

Day-night rhythms in feeding behavior and response to the putative sigma opiate agonist, N-allylnormetazocine (+/- SKF-10,047, 0.10-10 mg/kg), were measured in young (1-2 months), mature (8-12 months) and old (24-30 months) male CF-1 mice. The mice consumed more food at night than in the day-time, though this nocturnal peak was markedly reduced in the mature and old animals. The young mice also displayed a significant nocturnal enhancement in SKF-10,047 (0.10-1.0 mg/kg) stimulated feeding, that could, in part, be suppressed by the opiate antagonist naloxone (1.0 mg/kg). The day-night rhythm in ingestive responses to SKF-10,047 (0.10-1.0 mg/kg) was reduced in the mature animals and absent in the old animals. The old mice failed to show any significant increase in ingestive response following opiate administration. A higher dose of SKF-10,047 (10 mg/kg) had no significant ingestive effects in any of the age groups of mice; the excitatory, psychotomimetic-related effects, being also reduced in the old animals.

Differentiating opioids by their pupillary effects in the rat.

Pupillary effects of several opioids were examined as part of a broader in vivo study of multiple opioid receptors in the rat. Agonist activity, stereospecificity, and naloxone sensitivity were determined by methadone (Me), ethylketocyclazocine (EK), and N-allylnormetazocine (SKF 10,047), selected for their purportedly predominant actions at mu, kappa, and sigma receptors, respectively. After an acute, subcutaneous injection of each drug, pupil area and fluctuations in pupil size were measured by means of an infrared video pupillometer on line with a microcomputer data processing and storage system. Despite differences in the magnitude of the response, each opioid tested produced an increase in pupil size which was stereospecific, independent of behavioral responses to the drugs and, for 1-Me and 1-SKF 10,047, dose-related. Other differences among the opioids were found in their ability to induce fluctuations (1-Me and 1-EK) and a pendular nystagmus (1-SKF 10,047 only), and in their sensitivity to naloxone. Although 1.0 mg/kg naloxone completely reversed 1-Me-induced mydriasis, 10 mg/kg was needed to reverse 1-EK, and this dose only partially antagonized 1-SKF 10,047. These characteristic patterns of pupillary responses to opioids in terms of agonist activities and naloxone sensitivities indicate that the different opioid receptor types subserve different functions with respect to pupillary control.

Sigma opioid receptors; SKF-10,047 update.

We found that (-)-SKF-10,047 blocks EEG and behavioral effects of morphine in the naive rat, precipitates withdrawal in morphine-dependent rats, produces physical dependence as evidenced by naloxone-induced withdrawal, and displaces [3H] dihydromorphine from brain homogenates. (+)-SKF-10,047 did not produce dependence upon chronic treatment, and it did not displace [3H] dihydromorphine from brain homogenates. Such pharmacodynamic dissociation of SKF-10,047 effects suggests an association of sigma receptors with psychotogenic, but not opioid characteristics. The latter are most likely mediated by mu or kappa receptors.

Naltrexone fails to antagonize the sigma effects of PCP and SKF 10,047 in the dog.

SKF 10,047, N-allylnormetazocine, a benzomorphan narcotic antagonist, and the arylcyclohexylamine anesthetic phencyclidine produced similar reflex, autonomic and behavioral effects in the chronic spinal dog which were not antagonized by naltrexone pretreatment. Naltrexone did effectively prevent the effects of morphine. These data provide further evidence that the acute effects of phencyclidine and SKF 10,047 are alike and that their principal mechanism of action does not involve opiate activity of the morphine type.

Non-opioid psychotomimetic-like discriminative stimulus properties of N-allylnormetazocine (SKF 10,047) in the rat.

The purpose of this study was to characterize the discriminative stimulus property of dl-SKF 10,047 in the rat and to investigate if this property is the result of an interaction with opiate receptors or dopaminergic mechanisms. Male Sprague Dawley rats were trained in a two-lever food-reinforced procedure to discriminate between the effect of saline and of dl-SKF 10,047 (5 mg/kg). The trained rats dose dependently generalized the effect of dl-, d- and l-SKF 10,047, as well as cyclazocine, phencyclidine and ketamine but did not generalize the effect of either fentanyl, morphine, bremazocine, ethylketocyclazocine, pentazocine, nalorphine, naloxone, MR 2266, d-lysergic acid diethylamide, apomorphine or d-amphetamine. Neither naloxone, MR 2266, fentanyl, ethylketocyclazocine nor haloperidol antagonized the discriminative stimulus produced by dl-SKF 10,047. These data suggest that the discriminative stimulus property of dl-SKF 10,047 in the rat is not due to its interaction with either opiate receptors or dopaminergic mechanisms but may be related to its psychotomimetic effect in man.

Synthesis and narcotic agonist-antagonist evaluation of some 2,6-methano-3-benzazocine-11 propanols. Analogues of the ring C bridged oripavine-7-mehtanols.

A general synthesis of variously substituted 2,6-methano-3-benzazocine-11-propanols is described. Nine N-CH3 derivatives and their corresponding N-cyclopropylmethyl counterparts were prepared and studied in the mouse acetylcholine induced writhing and rat phenazocine antagonism tests. The results are compared with literature information on the bridged oripavine methanols. It is concluded that the synthetic analogues have a different structure-activity profile, in general being weak agonists but potent antagonists.

Effect of 9-hydroxylation on benzomorphan antagonist activity.

In a benzomorphan bearing an antagonist side chain, introduction on the methano bridge of a hydroxyl oriented away from nitrogen has little effect on antagonist activity whereas a hydroxyl oriented toward nitrogen enhances this activity. Hydroxylation tends to decrease analgesic activity.