Behavioral effects of the putative anxiolytic (+/-)-1-(2,5-dimethoxy-4-ethylthiophenyl)-2-aminopropane (ALEPH-2) in rats and mice

Effect of Hallucinogens on Unconditioned Behavior

Because of the ethical and regulatory hurdles associated with human studies, much of what is known about the psychopharmacology of hallucinogens has been derived from animal models. However, developing reliable animal models has proven to be a challenging task due to the complexity and variability of hallucinogen effects in humans. This chapter focuses on three animal models that are frequently used to test the effects of hallucinogens on unconditioned behavior: head twitch response (HTR), prepulse inhibition of startle (PPI), and exploratory behavior. The HTR has demonstrated considerable utility in the neurochemical actions of hallucinogens. However, the latter two models have clearer conceptual bridges to human phenomenology. Consistent with the known mechanism of action of hallucinogens in humans, the behavioral effects of hallucinogens in rodents are mediated primarily by activation of 5-HT2A receptors. There is evidence, however, that other receptors may play secondary roles. The structure-activity relationships (SAR) of hallucinogens are reviewed in relation to each model, with a focus on the HTR in rats and mice.

Psilocybin biases facial recognition, goal-directed behavior, and mood state toward positive relative to negative emotions through different serotonergic subreceptors

BACKGROUND

Serotonin (5-HT) 1A and 2A receptors have been associated with dysfunctional emotional processing biases in mood disorders. These receptors further predominantly mediate the subjective and behavioral effects of psilocybin and might be important for its recently suggested antidepressive effects. However, the effect of psilocybin on emotional processing biases and the specific contribution of 5-HT2A receptors across different emotional domains is unknown.

METHODS

In a randomized, double-blind study, 17 healthy human subjects received on 4 separate days placebo, psilocybin (215 μg/kg), the preferential 5-HT2A antagonist ketanserin (50 mg), or psilocybin plus ketanserin. Mood states were assessed by self-report ratings, and behavioral and event-related potential measurements were used to quantify facial emotional recognition and goal-directed behavior toward emotional cues.

RESULTS

Psilocybin enhanced positive mood and attenuated recognition of negative facial expression. Furthermore, psilocybin increased goal-directed behavior toward positive compared with negative cues, facilitated positive but inhibited negative sequential emotional effects, and valence-dependently attenuated the P300 component. Ketanserin alone had no effects but blocked the psilocybin-induced mood enhancement and decreased recognition of negative facial expression.

CONCLUSIONS

This study shows that psilocybin shifts the emotional bias across various psychological domains and that activation of 5-HT2A receptors is central in mood regulation and emotional face recognition in healthy subjects. These findings may not only have implications for the pathophysiology of dysfunctional emotional biases but may also provide a framework to delineate the mechanisms underlying psylocybin's putative antidepressant effects.

Prefrontal cortex lesions cause only minor effects on the hyperlocomotion induced by MK-801 and its reversal by clozapine

The non-competitive NMDA receptor antagonist MK-801 elicits a behavioural syndrome in rodents characterized by hyperlocomotion and stereotypies, which is antagonized by antipsychotic drugs. NMDA receptor antagonists increase prefrontal cortex (PFC) activity in rodents, as assessed by electrophysiological and neurochemical measures. The increase in glutamate outflow induced by systemic MK-801 administration in the medial PFC (mPFC) is prevented by the local administration of clozapine (Clz). In the present study, we examine whether a PFC lesion alters the behavioural syndrome induced by MK-801 in rats and the Clz-induced antagonism of MK-801 actions. We evaluated the hyperlocomotion, stereotypies and other behavioural changes induced by MK-801 in the open field and the effect of electrolytic lesions of the mPFC, and of cortical transection on the behavioural syndrome induced by MK-801 and its reversal by Clz. MK-801 (0.1-0.2 mg/kg i.p.) reduced rearings but only the higher dose induced hyperlocomotion. At this dose, MK-801 also increased disorganized movements, head weavings, and induced ataxia signs. An electrolytic lesion of the mPFC markedly reduced the number of rearings pre-treatment but caused a very slight attenuation of MK-801-induced hyperlocomotion. Cortical transection did not significantly alter MK-801 effects. Clz administration (1 mg/kg s.c.) significantly attenuated hyperlocomotion, head weavings and ataxia signs induced by MK-801 but did not prevent the decrease in rearings. The effect of Clz was essentially unaffected by electrolytic lesions of the mPFC. These results show that MK-801-induced motor syndrome and its reversal by Clz are mostly independent on PFC integrity.

Simultaneous determination of new thioamphetamine designer drugs in plasma by capillary electrophoresis coupled with mass spectrometry

A simple method for the simultaneous identification and quantification of four 2,5-methylenedioxy derivatives of 4-thioamphetamine (ALEPH series) in plasma samples was developed. The method consists of solid-phase extraction (SPE) using a Bond Elut C(18) cartridge and capillary electrophoresis coupled with electrospray ionisation mass spectrometry (CE/ESI-MS). The SPE method used required only simple steps and provided a clean extract from which identification of each drug was feasible, even at low concentrations. The method was validated according to international guidelines. The calibration curves were linear over the concentration range of 50 to 1000 ng/mL for all drugs with correlation coefficients that exceeded 0.998. The lower limits of detection of the drugs were 23-43 ng/mL. The absolute recoveries for the drugs were 64-92% and 75-96% at concentrations of 100 and 500 ng/mL, respectively. The validation data (precision, accuracy, and recovery) show the reproducibility and selectivity of the method. This clean and simple method allows the routine detection of designer drugs such as thioamphetamines which may become a serious problem in the control of illegal drugs.

Effect of noradrenergic system on the anxiolytic-like effect of DOI (5-HT2A/2C agonists) in the four-plate test

RATIONALE

Selective serotonin reuptake inhibitors and serotonin and noradrenaline reuptake inhibitors demonstrated an anxiolytic-like effect in the four-plate test (FPT). (+/-)-1-(2,5-Dimethoxy-4-iodophenyl)-2-aminopropane (DOI; a 5-HT2A receptor agonist) also possessed strong anxiolytic-like effect in the same test. A 5-HT2A mechanism seems to be implicated in the mechanism of action of both antidepressants and DOI in this test. On the other hand, the alpha-adrenergic ligands have also demonstrated an activity in other models of anxiety. A previous study demonstrated that the alpha2-adrenoceptor agonists abolished the anxiolytic-like effect of antidepressants.

OBJECTIVES

The aim of the present study was to evaluate the role of noradrenergic system on the regulation of 5-HT2 receptors implicated in the DOI anxiolytic-like activity in the FPT.

METHODS

First, the effect of noradrenergic and serotonergic lesions on DOI anxiolytic-like activity was studied in the FPT. Second, the effect of co-administration of alpha-adrenoceptor ligands and DOI was evaluated in the same test.

RESULTS

The noradrenergic and serotonergic lesions had no effect on DOI (1 mg/kg) anti-punishment activity in the FPT. Adrafinil 0.25 and 4 mg/kg (an alpha1-adrenoceptor agonist), prazosin 0.5 and 2 mg/kg (an alpha1-adrenoceptor antagonist) and idazoxan 1 and 4 mg/kg (an alpha2-adrenoceptor antagonist) did not modify the activity of DOI. Clonidine 0.06 mg/kg, guanabenz 0.125 and 0.5 mg/kg (two alpha2-adrenoceptor agonists) and guanfacine 0.06 and 0.125 mg/kg (a specific alpha2A-adrenoceptor agonist) completely abolished DOI-induced increase in punished passages.

CONCLUSION

These results indicate that the DOI seems to act on the 5-HT2 receptors post-synaptically located. The effect of DOI is regulated by the alpha2-adrenoceptors.

Serotonin 2C receptors within the basolateral amygdala induce acute fear-like responses in an open-field environment

Several studies indicate a role for the serotonin 2 subfamily (5-HT(2A), 5-HT(2B), 5-HT(2C)) in mediation of fear and anxiety responses. The current study began to examine the effects of stimulating 5-HT(2C) receptors within the basolateral (BLA) or central nucleus of the amygdala (CeA) on acute fear-like responses in rats. Bilateral intra-BLA infusions of mCPP (3-3000 pmol), a mixed 5-HT(2) agonist, produced ultrasonic vocalization and reduced exploratory behavior while increasing the latency to investigate a novel object. These responses were attenuated by SB-242084, a 5-HT(2C)-specific antagonist. Furthermore, a selective 5-HT(2C) agonist, IL-639, produced a similar repertoire of behavioral effects with the exception of effects on time spent in the center of an open-field arena. Finally, infusions of mCPP into the CeA produced no anxiogenic behaviors suggesting that 5-HT(2C) receptors primarily within the BLA are responsible for many of the acute fear-like responses reported here. To characterize further the neural circuits associated with 5-HT(2C)-mediated fear responses, we assessed c-fos mRNA expression after intra-BLA infusions of mCPP, IL-639 or their vehicles. Whereas the overall regional pattern of c-fos mRNA induction for the two compounds was distinct, c-fos activation was confined primarily to limbic nuclei with the medial prefrontal cortex as a common regional target of each drug. These results suggest that activation of 5-HT(2C) receptors within the BLA influences the activity of limbic circuits involved in the expression of acute innate fear responses.

Anxiolytic-like effects of 5-HT2 ligands on three mouse models of anxiety

The behavioural effects of 5-HT(2) receptor agonists, 5-HT(2A) and 5-HT(2C) receptor antagonists were investigated in the mouse four plates test (FPT), light/dark paradigm (L/D) and the elevated plus maze (EPM), in order to elucidate the role of the 5-HT(2) receptor subtypes in these models and to address the inconclusive results previously reported using rat psychopharmacological models. All compounds were administered intraperitoneally 30 min before each test. DOI, a preferential 5-HT(2A) agonist (0.5-8 mg/kg) and BW 723C86, a 5-HT(2B) agonist (8 and 16 mg/kg) provoked an anxiolytic-like response in the FPT. In the EPM, an anxiolytic-like effect was observed for DOI (0.5, 1 and 2 mg/kg), BW 723C86 (0.5, 4, 8 and 16 mg/kg), RO 60-0175 a 5-HT(2C) agonist (4 mg/kg) and the non-selective 5-HT(2) receptor agonist mCPP (0.25 mg/kg.). Ketanserin, a 5-HT(2A/2C) non-selective receptor antagonist (0.015 and 0.03 mg/kg), induced an anxiogenic-like effect in the L/D paradigm. The 5-HT(2C) antagonists (RS 10-2221, SDZ SER082 and SB 206553) were without effect in all three tests. These behavioural results are indicative of an anxiolytic-like action of 5-HT(2) receptor agonists, an anxiogenic-like effect of 5-HT(2A) receptor antagonism, whereas the blockade of 5-HT(2C) receptors are without effect in the mouse models studied.

The elevated T-maze as an experimental model of anxiety

Anxiety disorders are heterogeneous and existing animal models do not discriminate specific types of anxiety. The elevated T-maze is being developed to fulfill this purpose. The apparatus consists of three elevated arms, one enclosed and two open. Inhibitory avoidance--representing learned fear--is measured by recording the time taken to leave the enclosed arm in three consecutive trials. Unconditioned fear is evaluated by recording the time to escape from the open arm. Restraining the animals at the end of the enclosed arm for 30 s did not change the first (baseline) withdrawal latency, indicating that rats are not escaping from the experimenter's hand. In addition, rats trained in a T-maze with the three arms enclosed did not show the usual increase in withdrawal latency over the three consecutive trials. These results indicate that open arm experience, not handling, motivates inhibitory avoidance learning. The same experiment also showed that the latency to leave the open arm did not undergo habituation over five consecutive trials, thereby providing evidence of an aversive motivation for this response. The anxiolytic agents diazepam (benzodiazepine), buspirone and ipsapirone (5-HT1A agonists) as well as ritanserin (5-HT2 antagonist) selectively impaired inhibitory avoidance while leaving one-way escape unchanged. Similar results were obtained with three putative anxiolytics: the 5-HT2B/2C antagonists SB 200646A and SER 082, and the 5-HT2A antagonist SR 46349B. However, RP 62203, another 5-HT2A antagonist, was ineffective on both tasks. In contrast to the above anxiolytics, the anxiogenic agents yohimbine, TFPP and mCPP facilitated inhibitory avoidance. Escape was not affected by yohimbine, but was moderately attenuated by the two 5-HT2C/2B agonists. The 5-HT releaser and uptake inhibitor D-fenfluramine tended to enhance inhibitory avoidance, while impairing one-way escape in a dose-dependent way. The antidepressant clomipramine also had an anxiogenic-like effect on inhibitory avoidance, but did not affect escape from the open arm. Conversely, the phenethylamine hallucinogen ALEPH 2 did not affect inhibitory avoidance while impairing escape. Nevertheless, the similar compound and 5-HT2A agonist DOI was devoid of any effect. Also ineffective were the psychomotor stimulants D,L-amphetamine and caffeine, the reversible monoaminoxidase-A inhibitor moclobemide and the neuroleptic haloperidol. Finally, micro-injection into the dorsal raphe nucleus of two drugs that stimulate 5-HT neurons, the excitatory amino acid kainic acid and the benzodiazepine inverse agonist FG 7142, facilitated inhibitory avoidance. Kainate also significantly impaired escape. In contrast, intra-raphe 8-OH-DPAT, which inhibits 5-HT neurons, selectively impaired inhibitory avoidance in a manner similar to systemically administered anxiolytics. These behavioral and pharmacological results support the view that inhibitory avoidance in the elevated T-maze may be related to generalized anxiety disorder, while one-way escape may be associated with panic disorder.

Anxiolytic-like effects of 4-phenyl-2-trichloromethyl-3H-1, 5-benzodiazepine hydrogen sulfate in mice

The pharmacological effects of 4-phenyl-2-trichloromethyl-3H-1, 5-benzodiazepine hydrogen sulfate (PTMB), a novel synthetic benzodiazepine, were examined in mice. In the elevated plus-maze test of anxiety, 0.3-1 mg/kg diazepam ip (F(3,53) = 3.78; P<0.05) and 1-10 mg/kg PTMB ip increased (F(5,98) = 3.26; P<0.01), whereas 2 mg/kg picrotoxin ip decreased (F(3,59) = 8.32; P<0.001) the proportion of time spent in the open arms, consistent with an anxiolytic action of both benzodiazepines, and an anxiogenic role for picrotoxin. In the holeboard, 1.0 mg/kg diazepam ip increased (F(3,54) = 2.78; P<0.05) and 2 mg/kg picrotoxin ip decreased (F(3, 59) = 4.69; P<0.01) locomotor activity. Rotarod assessment revealed that 1 mg/kg diazepam ip and 3, 10 and 30 mg/kg PTMB ip produced significant motor incoordination compared to vehicle control (F(4, 70) = 7.6; P<0.001). These data suggest that the recently synthesized PTMB compound possesses anxiolytic activity and produces motor incoordination similar to those observed with diazepam.

U-69,593 microinjection in the infralimbic cortex reduces anxiety and enhances spontaneous alternation memory in mice

The present report investigated the contributions of the ventromedial prefrontal cortex to the control of spontaneous alternation/working memory and anxiety-related behaviour. In Experiment 1, we examined the effects of microinjections of the selective kappa(1) receptor agonist, U-69,593, in the infralimbic cortex (IL) of CD-1 mice on several ethologically-derived anxiety indices in the elevated plus-maze (EPM) and defensive/withdrawal (D/W) anxiety in the open field, as well as on memory in the EPM transfer-latency (T-L) test and implicit spontaneous alternation memory (SAP) in the Y-maze. In week 1, pretreatment with one injection of vehicle, 1, 10 or 25 nmol/1.0 microliter U-69,593 in the IL dose-dependently prolonged T-L and produced a dose-dependent anxiolytic behavioural profile in the first EPM trial. Following a 24-h delay, the same mice were given a drug-free second trial in the EPM tests of T-L memory and anxiety. Whereas T-L memory was not disturbed, small but detectable carry-over effects were observed in trial-2 EPM behaviour relative to vehicle-treated animals. In week 2, the same groups of mice were again pretreated with one injection of the same doses of U-69,593 in the IL and given a D/W test in an open field, followed immediately by an 8-min SAP trial in the Y-maze. The smallest U-69,593 dose was anxiolytic in the D/W test, and SAP/working memory was dose-dependently enhanced in the Y-maze. In Experiment 2, we evaluated whether 0.5 microliter volume microinjections would produce comparable behavioural and carry-over effects in the IL of three new groups of CD-1 mice, in the event that the 1.0 microl volume injections used in Experiment 1 diffused beyond the IL and therefore may have confounded some effects. Experiment 2 procedures were carried out in the same manner as in Experiment 1, except the animals were tested in reverse order. Thus in week 1, SAP memory was tested in the Y-maze followed by D/W anxiety in the open field for half of the animals in each group, and the other half was tested in reverse order. In week 2, T/L memory and anxiety were tested in the EPM in 2 trials as described in Experiment 1. Pretreatment with one injection of vehicle, 10 or 25 nmol/0.5 microliter U-69,593 in the IL reduced D/W anxiety and enhanced SAP memory regardless of testing order in week 1. In week 2, the same groups of mice were again pretreated with one injection of the same doses of U-69,593 in 0.5 microliter volumes in the IL and tested in the EPM. In a similar fashion to Experiment 1, U-69,593 dose-dependently prolonged T/L and produced an anxiolytic behavioural profile in the first EPM trial. Following a 24-h delay, T/L recall memory was again not significantly influenced, but a robust anxiolytic behavioural profile was observed in the second drug-free anxiety trial in the EPM relative to vehicle-treated animals. Results are discussed relative to a) injection volumes and testing order, b) the possible influence kappa receptors may exert on neurochemical responsivity to anxiety-provoking environments in the IL area of the mPFC, c) the possibility that kappa-mediated anxiolysis from the IL in CD-1 mice results from interactions with neurochemical systems involved in the blunting of incoming anxiety-provoking information, d) evidence that SAP memory may be an implicit subtype of working memory, and e) the possibility that IL implicit working memory processes may modulate the induction and expression of anxiety-related behaviour.

Effects of the D3 preferring dopamine agonist pramipexole on sleep and waking, locomotor activity and striatal dopamine release in rats

Quantitation of 2 h sessions after administration of the D3 preferring dopamine (DA) agonist pramipexole (10-500 microg/kg) showed dose-related effects on wakefulness (W), slow wave sleep (SWS) and REM sleep in rats. The 30 microg/kg dose of the DA agonist increased SWS and REM sleep and reduced W during the first recording hour, while the 500 microg/kg dose augmented W. On the other hand, W was increased while SWS and REMS were decreased after the 500 microg/kg dose during the second recording hour. The mixed D2- and D3 receptor antagonist YM-09151-2 (30-500 microg/kg), which per se affected sleep variables prevented the increase of REMS induced by pramipexole. Furthermore, the highest doses (500-1000 microg/kg) of the DA antagonist effectively antagonized the increase of W and reduction of SWS induced by the 500 microg/kg dose of the DA agonist. Pramipexole (30-100 microg/kg) induced a decrease of locomotor activity during the 2 h recording period. In addition, the 500 microg/kg dose gave rise to an initial reduction of motor behavior which was reverted 2 h later. Pramipexole (30 and 500 microg/kg) did not significantly affect striatal DA release during the first two hours following drug administration, as measured by microdialysis. It is tentatively suggested that D3 receptor could be involved in the pramipexole-induced increase of sleep and reduction of locomotor activity. On the other hand, the increase of W and of motor behavior after relatively high doses could be related to activation of postsynaptic D2 receptor.

Monoamine oxidase inhibitory properties of some methoxylated and alkylthio amphetamine derivatives: structure-activity relationships

The monoamine oxidase (MAO) inhibitory properties of a series of amphetamine derivatives with different substituents at or around the para position of the aromatic ring were evaluated. In in vitro studies in which a crude rat brain mitochondrial suspension was used as the source of MAO, several compounds showed a strong (IC50 in the submicromolar range), selective, reversible, time-independent, and concentration-related inhibition of MAO-A. After i.p. injection, the compounds induced an increase of serotonin and a decrease of 5-hydroxyindoleacetic acid in the raphe nuclei and hippocampus, confirming the in vitro results. The analysis of structure-activity relationships indicates that: molecules with amphetamine-like structure and different substitutions on the aromatic ring are potentially MAO-A inhibitors; substituents at different positions of the aromatic ring modify the potency but have little influence on the selectivity; substituents at the para position such as amino, alkoxyl, halogens, or alkylthio produce a significant increase in the activity; the para-substituent must be an electron donor; bulky groups next to the para substituent lead to a decrease in the activity; substituents located at positions more distant on the aromatic ring have less influence and, even when the substituent is a halogen (Cl, Br), an increase in the activity of the compound is obtained. Finally, the MAO-A inhibitory properties of some of the compounds evaluated are discussed in relation to: (a) potential antidepressant activity, and (b) their reported hallucinogenic, neurotoxic, or anxiolytic effects.

(+/-)-1-(2,5-Dimethoxy-4-ethylthiophenyl)-2-aminopropane (ALEPH-2), a novel putative anxiolytic agent lacking affinity for benzodiazepine sites and serotonin-1A receptors

Serotonergic behavioral responses, effects on motor activity and core temperature, and binding properties of the novel putative anxiolytic amphetamine derivative (+/-)1-(2,5-dimethoxy-4-ethylthio-phenyl)-2-aminopropane (ALEPH-2), were examined in rodents in order to elucidate the mechanism underlying its anxiolytic-like effect. After peripheral administration in rats, ALEPH-2 induced some symptoms of the serotonergic syndrome, e.g. forepaw treading and flat body posture. Additionally, a decrease in motor activity was observed. No significant effects on the number of head shakes were observed after injection, although high inter-subject variability was noted. Higher doses of ALEPH-2, in the range exhibiting anxiolytic properties (4mg/kg), elicited significant hypothermia in mice. The affinity of the drug for 5-HT2A/2C receptors ([3H]ketanserin sites) was in the nanomolar range (Ki = 173 nM), whereas for 5-HT1A, benzodiazepine sites, and GABAA receptors, the affinity was micromolar of lower. Based on these results the mechanism of action and the anxiolytic-like properties of ALEPH-2 are discussed.