Similar pharmacological properties of 8-OH-DPAT and alnespirone (S 20499) at dopamine receptors: comparison with buspirone

Effect of psilocybin on marble burying in ICR mice: role of 5-HT1A receptors and implications for the treatment of obsessive-compulsive disorder

Preliminary clinical findings, supported by preclinical studies employing behavioral paradigms such as marble burying, suggest that psilocybin may be effective in treating obsessive-compulsive disorder. However, the receptor mechanisms implicated in the putative anti-obsessional effect are not clear. On this background, we set out to explore (1) the role of serotonin 2A (5-HT2A) and serotonin 1A (5-HT1A) receptors in the effect of psilocybin on marble burying; (2) the effect of staggered versus bolus psilocybin administration and persistence of the effect; (3) the effect of the 5-HT1A partial agonist, buspirone, on marble-burying and the head twitch response (HTR) induced by psilocybin, a rodent correlate of psychedelic effects. Male ICR mice were administered psilocybin 4.4 mg/kg, escitalopram 5 mg/kg, 8-hydroxy-2-(di-n-propylamino) tetralin (8-OH-DPAT) 2 mg/kg, M100907 2 mg/kg, buspirone 5 mg/kg, WAY100635 2 mg/kg or combinations, intraperitoneally, and were tested on the marble burying test. HTR was examined in a magnetometer-based assay. The results show that (1) Psilocybin and escitalopram significantly reduced marble burying. The effect of psilocybin was not attenuated by the 5-HT2A antagonist, M100907. The 5-HT1A agonist, 8-OH-DPAT, reduced marble burying as did the 5-HT1A partial agonist, buspirone. The effect of 8-OH-DPAT was additive to that of psilocybin, but that of buspirone was not. The 5-HT1A antagonist, WAY100635, attenuated the effect of 8-OH-DPAT and buspirone but not the effect of psilocybin. (2) Psilocybin injections over 3.5 h had no effect on marble burying and the effect of bolus injection was not persistent. (3) Co-administration of buspirone with psilocybin blocked its effect on HTR. These data suggest that neither 5-HT2A nor 5-HT1A receptors are pivotally implicated in the effect of psilocybin on marble burying. Co-administration with buspirone may block the psychedelic effects of psilocybin without impeding its anti-obsessional effects.

Modulatory effect of the 5-HT1A agonist buspirone and the mixed non-hallucinogenic 5-HT1A/2A agonist ergotamine on psilocybin-induced psychedelic experience

The mixed serotonin (5-HT) 1A/2A/2B/2C/6/7 receptor agonist psilocybin dose-dependently induces an altered state of consciousness (ASC) that is characterized by changes in sensory perception, mood, thought, and the sense of self. The psychological effects of psilocybin are primarily mediated by 5-HT2A receptor activation. However, accumulating evidence suggests that 5-HT1A or an interaction between 5-HT1A and 5-HT2A receptors may contribute to the overall effects of psilocybin. Therefore, we used a double-blind, counterbalanced, within-subject design to investigate the modulatory effects of the partial 5-HT1A agonist buspirone (20mg p.o.) and the non-hallucinogenic 5-HT2A/1A agonist ergotamine (3mg p.o.) on psilocybin-induced (170 µg/kg p.o.) psychological effects in two groups (n=19, n=17) of healthy human subjects. Psychological effects were assessed using the Altered State of Consciousness (5D-ASC) rating scale. Buspirone significantly reduced the 5D-ASC main scale score for Visionary Restructuralization (VR) (p<0.001), which was mostly driven by a reduction of the VR item cluster scores for elementary and complex visual hallucinations. Further, buspirone also reduced the main scale score for Oceanic Boundlessness (OB) including derealisation and depersonalisation phenomena at a trend level (p=0.062), whereas ergotamine did not show any effects on the psilocybin-induced 5D-ASC main scale scores. The present finding demonstrates that buspirone exerts inhibitory effects on psilocybin-induced effects, presumably via 5-HT1A receptor activation, an interaction between 5-HT1A and 5-HT2A receptors, or both. The data suggest that the modulation of 5-HT1A receptor activity may be a useful target in the treatment of visual hallucinations in different psychiatric and neurological diseases.

Efficacy of buspirone for attenuating cocaine and methamphetamine reinstatement in rats

BACKGROUND

There are no approved pharmacotherapies for preventing psychomotor stimulant relapse. The operant reinstatement model has been suggested as a screen for identifying candidate medications. The present study examined if the anxiolytic buspirone could attenuate reinstatement of extinguished responding in Long-Evans rats that previously self-administered intravenous cocaine or methamphetamine.

METHODS

Rats were trained in 2-h daily sessions to self-administer 0.5mg/kg cocaine or 0.1mg/kg methamphetamine infusions followed by 12 days of instrumental extinction. Reinstatement was evoked by 17mg/kg i.p. cocaine primes or response-contingent cocaine-paired cues in cocaine-reinforced rats, and by 1mg/kg i.p. methamphetamine primes or response-contingent methamphetamine-paired cues in methamphetamine-reinforced rats.

RESULTS

Buspirone (1 and 3mg/kg) significantly (p<0.05) attenuated cocaine cue but not cocaine prime reinstatement. Buspirone (1 and 3mg/kg) also significantly attenuated methamphetamine cue reinstatement. Buspirone (3mg/kg) significantly attenuated methamphetamine prime reinstatement. During all reinstatement tests, 3mg/kg buspirone reduced levels of inactive lever pressing relative to those of vehicle, significantly so during the cocaine cue-induced reinstatement tests.

CONCLUSIONS

Given the complexity of buspirone's neuropharmacology consisting of serotonin 5-HT1A receptor partial agonist activity, and dopamine D2, D3 and D4 receptor antagonist effects, it is uncertain which of these activities or their combination is responsible for the present results. Overall, these results suggest that buspirone may reduce the likelihood of relapse to cocaine and methamphetamine use under some conditions, although this speculation must be interpreted with caution given buspirone's similar potency to attenuate inactive-lever responding.

Differential Effects of Antipsychotic Drugs on Serotonin-1A Receptor-Mediated Disruption of Prepulse Inhibition

Serotonin-1A (5-HT(1A)) receptors have been implicated in the symptoms of schizophrenia. However, there is limited in vivo evidence for an interaction of antipsychotic drugs with 5-HT(1A) receptor-mediated behavioral effects. We therefore investigated in rats the action of several antipsychotic drugs on prepulse inhibition (PPI), a measure of sensorimotor gating that is deficient in schizophrenia. Disruption of PPI at the 100-ms interstimulus interval (ISI), but not the 30-ms ISI, was induced by treatment with 0.5 mg/kg 8-hydroxy-di-propylaminotetralin (8-OH-DPAT), the 5-HT(1A) receptor agonist. In rats pretreated with 0.25 mg/kg haloperidol (4-[-4-(p-chlorophenyl)-4-hydroxypiperidino]-4'-fluoro butyrophenone) or raclopride [3,5-dichloro-N-(1-ethylpyrrolidin-2-ylmethyl)-2-hydroxy-6-methoxybenzamide tartrate], the disruption of PPI was no longer significant. Of the atypical antipsychotic drugs clozapine (8-chloro-11-(4-methyl-1-piperazinyl)-5H-dibenzo[b,e][1,4]-diazepine), olanzapine (2-methyl-4-(4-methyl-1-piperazinyl)-10H-thieno[2,3-b][1,5]benzodiazepine), risperidone [3-[2-[-4-(6-fluoro-1,2-benzisoxazol-3-yl) piperidino] ethyl-6,7,8,9-tetrahydro-2-methyl-4H-pyrido[1,2-a]pyrimidin-4-one)], amisulpride (4-amino-N-[(1-ethyl-2-pyrrolidinyl)methyl]-5-(ethylsulfonyl)-o-anisamide), and aripiprazole (7-[4-[-4[-(2,3-dichlorophenyl)-1-piperazinyl]butoxy]-3,4-dihydrocarbostyrilor 7-[4-[4-(2,3-dichlorophenyl) piperazin-1-yl]butoxy]-1,2,3,4,-tetrahydroquinolin-2-one), only aripiprazole significantly reduced the effect of 8-OH-DPAT on PPI. This effect was mimicked by pretreatment with the 5-HT(1A) receptor partial agonist, buspirone [N-[4-[4-(2-pyrimidinyl)-1-piperazinyl]butyl]-8-azaspiro[4.5]decane-7,9-dione hydrochloride]. On the other hand, some of the antipsychotic drugs and other pretreatments showed complex, prepulse-dependent effects on their own. These data show little in vivo interaction of several atypical antipsychotic drugs with the disruption of PPI mediated by 5-HT(1A) receptor stimulation. The action of haloperidol and raclopride suggests a major involvement of dopamine D(2) receptors in this effect, possibly downstream from the initial serotonergic stimulation. The action of aripiprazole could be mediated by its partial agonist properties at 5-HT(1A) receptors or its dopamine D(2)-blocking properties.

Buspirone attenuates conditioned fear-induced c-Fos expression in the rat hippocampus

The role of hippocampus in the anxiolytic-like effect of buspirone in the conditioned emotional response test (CER, a freezing response), was examined by immunocytochemical detection of the c-Fos protein. It was shown that buspirone at the dose of 0.5 and 1.5 mg/kg i.p. given before test session, which was 24 h after the aversive training, significantly decreased freezing response within a limited dose range of the U-shaped dose-response relationship. Exposure of animals to aversively conditioned context (a contextual fear) induced the production of c-Fos protein in the dentate gyrus, CA-1 and CA-3 layers of the hippocampus. Pretreatment with buspirone (1.5 mg/kg) significantly attenuated the effects of aversive memory on c-Fos protein expression in the CA-1 and CA-3 layers of the hippocampus. These immunocytochemical results support previous data obtained in our laboratory with the help of selective neurotoxic lesions and intrahippocampal drug injections suggesting an important role of hippocampus in the anxiolytic effects of buspirone.

Buspirone Raises Blood Pressure through Activation of Sympathetic Nervous System and by Direct Activation of α1-Adrenergic Receptors after Severe Hemorrhage

5-Hydroxytryptamine 1A (5-HT1A) receptor agonists reverse the hypotensive and sympathoinhibitory responses to severe hemorrhage in rats. To determine whether 5-HT1A receptor-mediated pressor responses in hypovolemic animals are due to sympathoexcitation and/or direct vasoconstriction, blood pressure (BP), heart rate (HR), and renal sympathetic nerve activity (RSNA) responses to the partial 5-HT1A receptor agonist buspirone or the more selective, full 5-HT1A receptor agonist (+)-8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) were compared in intact and ganglionic blocked, hemorrhaged Sprague-Dawley rats. Buspirone produced dose-dependent increases in BP (110 +/- 4(**), 86 +/- 4(**), 65 +/- 7 mm Hg), HR [369 +/- 10(**), 337 +/- 14, 277 +/- 16 beats per minute (bpm)], and RSNA (114 +/- 36(**), 34 +/- 21, -23 +/- 25% baseline for 0.2, 0.1, and 0 mg/kg; (**)p < 0.01 versus 0 mg/kg, 3 min after injection). Ganglionic blockade with hexamethonium chloride blocked the pressor effect of 9.9 microg/kg 8-OH-DPAT and attenuated, but did not block, the pressor response to 0.2 mg/kg buspirone (85 +/- 7 versus 46 +/- 6 mm Hg for buspirone + ganglionic blockade versus saline + ganglionic blockade; p < 0.01). In subsequent tests, rats treated with the selective alpha1-adrenergic receptor antagonist prazosin (25 microg/kg) continued to show extensive tachycardic (+73 +/- 26 bpm) and sympathoexcitatory (128 +/- 55% baseline) responses to 0.2 mg/kg buspirone. Ganglionic blockade combined with prazosin completely blocked all responses to buspirone. Buspirone (0.2 mg/kg) produced significant bradycardic (-89 +/- 12 bpm; p < 0.01) and sympathoinhibitory (-72 +/- 7% baseline; p < 0.01) responses in euvolemic rats 3 min after injection. It is concluded that the pressor effect of buspirone is unique to hypovolemic animals and is mediated by sympathetic activation as well as direct activation of vascular alpha1-adrenergic receptors.

In vivo effects of aripiprazole on cortical and striatal dopaminergic and serotonergic function

In vivo microdialysis was used to monitor the effects of oral aripiprazole and olanzapine on basal extracellular concentrations of dopamine, 3,4-dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA) and 5-hydroxyindole acetic acid (5-HIAA) in the medial prefrontal cortex and striatum of conscious, freely moving rats. Acute aripiprazole administration did not affect dopamine output, but produced moderate increases in DOPAC and HVA concentrations, in medial prefrontal cortex or striatum of drug-naïve rats. Similarly, aripiprazole did not affect dopamine output but produced moderate elevations in DOPAC and HVA concentrations in the striatum of chronic aripiprazole-pretreated rats. Olanzapine produced comparatively larger elevations in dopamine, DOPAC, and HVA in both regions, which, in the striatum, were diminished after chronic olanzapine exposure. Aripiprazole reduced extracellular 5-HIAA concentrations in the medial prefrontal cortex and striatum of drug-nai;ve rats, but not in chronic aripiprazole-pretreated rats. Together, these data provide in vivo evidence of aripiprazole-induced changes in forebrain dopaminergic and serotonergic function that may reflect its partial agonist activity at presynaptic dopamine D(2) and 5-HT(1A) receptors and antagonist activity at 5-HT(2A) receptors.

Buspirone-induced antinociception is mediated by L-type calcium channels and calcium/caffeine-sensitive pools in mice

RATIONALE

Previous studies have shown that buspirone, a partial 5-HT(1A) receptor agonist, produces antinociceptive effects in rats and mice; Ca(2+) plays a critical role as a second messenger in mediating nociceptive transmission. 5-HT(1A) receptors have been proven to be coupled functionally with various types of Ca(2+) channels in neurons, including N-, P/Q-, T-, or L-type. It was of interest to investigate the involvement of extracellular/intracellular Ca(2+) in buspirone-induced antinociception.

OBJECTIVES

To determine whether central serotonergic pathways participate in the antinociceptive processes of buspirone, and investigate the involvement of Ca(2+) mechanisms, particularly L-voltage-gated Ca(2+) channels and Ca(2+)/caffeine-sensitive pools, in buspirone-induced antinociception.

METHODS

Antinociception was assessed using the hot-plate test (55 degrees C, hind-paw licking latency) in mice treated with either buspirone (1.25-20 mg/kg i.p.) alone or the combination of buspirone and fluoxetine (2.5-10 mg/kg i.p.), 5-HTP (25 mg/kg i.p.), nimodipine (2.5-10 mg/kg i.p.), nifedipine (2.5-10 mg/kg i.p.), CaCl(2) (25-200 nmol per mouse i.c.v.), EGTA (5-30 nmol per mouse i.c.v.), or ryanodine (0.25-2 nmol per mouse i.c.v.).

RESULTS

Buspirone dose dependently increased the licking latency in the hot-plate test in mice. This effect of buspirone was enhanced by fluoxetine, 5-HTP, nimodipine, and nifedipine. Interestingly, central administration of Ca(2+) reversed the antinociceptive effects of buspirone. In contrast to these, ryanodine or EGTA administered centrally potentiated buspirone-induced antinociception.

CONCLUSIONS

Decreasing neuronal Ca(2+) levels potentiated buspirone-induced antinociception; conversely, increasing intracellular Ca(2+) abolished the antinociceptive effects of buspirone. These results suggest that Ca(2+) influx from extracellular fluid and release of Ca(2+) from Ca(2+)/caffeine-sensitive microsomal pools may be involved in buspirone-induced antinociception.

Effects of some antioxidative aporphine derivatives on striatal dopaminergic transmission and on MPTP-induced striatal dopamine depletion in B6CBA mice

(S)-(+)-boldine, an aporphine alkaloid displaying antioxidative and dopaminergic properties, and six of its derivatives (glaucine, 3-bromoboldine, 3-iodoboldine, 8-aminoboldine, 8-nitrosoboldine and 2,9-O,O'-dipivaloylboldine) were tested for these properties in comparison with their parent compound. All the tested compounds displayed in vitro antioxidative properties equal to or slightly weaker than those of boldine, and equal to or stronger than (+/-)-6-hydroxy-2,5,7,8,-tetramethylchromane-2-carboxylic acid (Trolox), a water-soluble vitamin E analogue, used as a reference compound. All the aporphine compounds tested displaced [3H]SCH 23390 and [3H]raclopride from their specific binding sites in rat striatum. When tested on dopamine (DA) metabolism in the striatum of B6CBA mice, all the compounds, except 8-aminoboldine, increased striatal levels of DOPAC and HVA, and the HVA/DA ratio, indicating that they cross the blood-brain barrier and that they seem to act as dopamine antagonists in vivo. B6CBA mice were sensitive to the neurotoxic action of MPTP on dopaminergic neurons as indicated by the strongly decreased striatal levels of DA, DOPAC and HVA following administration of MPTP (20 mg/kg, i.p.). Among these aporphine derivatives, only 3-bromoboldine was able to reduce the MPTP-induced decrease of striatal levels of DA and DOPAC, whereas (R)-apomorphine (5 mg/kg, s.c.) and acetylsalicylic acid (100 mg/kg, i.p.), used as reference compounds, were very active. These data suggest that potent in vitro antioxidative properties and the ability to cross the blood-brain barrier are not sufficient criteria to predict the inhibition of neuronal degeneration induced by MPTP.

In vivo comparison of two 5-HT1A receptors agonists alnespirone (S-20499) and buspirone on locus coeruleus neuronal activity

The aim of the present study was to compare, in chloral-hydrate anaesthetized rats, the alpha(2)-adrenergic properties of the selective 5-HT(1A) receptor agonist, alnespirone (S-20499), with those of buspirone, a 5-HT(1A) receptor agonist exhibiting potent alpha(2)-adrenoceptor antagonist properties via its principal metabolite, 1-(2-pyrimidinyl)-piperazine. Both locus coeruleus spontaneous firing activity and noradrenaline release in the medial prefrontal cortex were potently inhibited by the alpha(2)-adrenoceptor agonist clonidine, at a dose of 40 microg/kg (i.p.). Such an inhibition was neither prevented nor reversed by alnespirone (10 mg/kg, i.p.), while buspirone, at the same dose, potently antagonized the locus coeruleus inhibitory effects of clonidine. These data demonstrate that, in contrast with some aryl-piperazine compounds (such as buspirone), alnespirone, either on its own or via a possible metabolite such as buspirone, is devoid in vivo of significant alpha(2)-adrenoceptor antagonist properties.

[Buspirone increases D2-like dopaminergic receptor density in rat corpus striatum]

Buspirone (busp) a piperazinyl derivative with anxiolytic properties is a partial agonist on 5-HT1A with affinity for D2-like dopaminergic receptors (RD2). The objective of this study was to verify the effects of busp on RD2. Female Wistar rats 150-200 g were treated with busp (5 and 10 mg/kg, p.o.) 1 or 2 times daily for 7 days. Controls (C) received saline. The density of RD2 (fmol/mg protein) was determined through binding assays in striatum (ST) using [3H]-spiroperidol as radioligand. No alteration in Bmax or Kd values were seen after busp administration once a day. However, a RD2 upregulation of 55 % increase was observed after busp 2 times a day with no change in Kd values. The results showed that busp interact not only with serotonergic, but also with dopaminergic system.

Serotonergic agonists behave as partial agonists at the dopamine D2 receptor

RAT dopamine D2short receptors expressed in CHO cells were characterized by activation of [35S]GTPgammaS binding. There were no significant differences between the maximal effects seen in activation of [35S]GTPgammaS binding caused by dopaminergic agonists, but the effects of 5-HT, 8OH-DPAT and 5-methoxytryptamine amounted to 47 +/- 7%, 43 +/- 5% and 70 +/- 7% of the dopamine effect, respectively. The dopaminergic antagonist (+)butaclamol inhibited activations of both types of ligands with equal potency (pA2 = 8.9 +/- 0.1), indicating that only one type of receptor is involved. In competition with [3H]raclopride binding, dopaminergic agonists showed 53 +/- 2% of the binding sites in the GTP-dependent high-affinity state, whereas 5-HT showed only 20 +/- 3%. Taken together, the results indicate that serotonergic agonists behave as typical partial agonists for D2 receptors with potential antiparkinsonian activity.