Identification and quantitation of 1-(2-pyrimidinyl)piperazine, an active metabolite of the anxiolytic agent buspirone, in rat plasma and brain

Chronic treatment with tandospirone, a 5-HT(1A) receptor partial agonist, suppresses footshock stress-induced lactate production in the prefrontal cortex of rats

Serotonin 1A receptor (5-HT1A-R) agonists have been demonstrated to elicit antidepressant and anxiolytic effects. Lactate has been considered to play a major role in energy metabolism in the brain. Specifically, extracellular lactate concentrations (eLAC) have been suggested to reflect neural activity. Mild physical (e.g., handling) and non-physical (e.g., psychological) stressors have been shown to increase eLAC in several brain regions, including the medial prefrontal cortex (mPFC) and basolateral amygdala (BLA). Using in vivo microdialysis technique, we measured eLAC in the mPFC and BLA of rats under electric footshock stress to clarify the effect of repeated injection procedure (saline, once daily for 14 days) as a stressor on brain energy metabolism. Then, we examined the effect of chronic treatment with tandospirone, a 5-HT1A-R partial agonist, on eLAC during footshock stress in the mPFC. Footshock stress led to an increase in eLAC both in the mPFC and BLA in rats without injections. Repeated saline injection increased basal eLAC in the BLA, while footshock-induced lactate increment was reduced. In the mPFC, repeated saline injection did not affect basal eLAC and footshock-induced eLAC increments. Chronic treatment with tandospirone, at 0.2 and 1.0 mg/kg/day, but not 2.0 mg/kg/day, attenuated footshock stress-induced eLAC elevation in the mPFC. These observations suggest that eLAC in the BLA is sensitive to repeated exposure to physical stress. Data also indicate chronic treatment with tandospirone diminishes acute energy demands during neural activation in the mPFC. The implications of the present findings in relation to clinical efficacy of 5-HT1A agonists are discussed.

Effect of transient blockade of N-methyl-D-aspartate receptors at neonatal stage on stress-induced lactate metabolism in the medial prefrontal cortex of adult rats: role of 5-HT1A receptor agonism

Decreased activity of the medial prefrontal cortex (mPFC) has been considered a basis for core symptoms of schizophrenia, an illness associated with a neurodevelopmental origin. Evidence from preclinical and clinical studies indicates that serotonin (5-HT)1A receptors play a crucial role in the energy metabolism of the mPFC. This study was undertaken to determine (1) if transient blockade of N-methyl-D-aspartate receptors during the neonatal stage inhibit energy demands in response to stress, as measured by extracellular lactate concentrations, in the mPFC at the young adult stage, and (2) if tandospirone, a 5-HT1A partial agonist, reverses the effect of the neonatal insult on energy metabolism. Male pups received MK-801 (0.20 mg/kg) on postnatal days (PDs) 7-10. On PD 63, footshock stress-induced lactate levels were measured using in vivo microdialysis technique. Tandospirone (0.1, 1.0, and 5.0 mg/kg) was administered once daily for 14 days before the measurement of lactate levels. Neonatal MK-801 treatment suppressed footshock stress-induced lactate production in the mPFC, but not caudate-putamen, whereas basal lactate levels were not significantly changed in either brain region. The MK-801-induced suppression of footshock stress-induced lactate production in the mPFC was attenuated by tandospirone at 1.0mg/kg/day, but not 0.1 or 5.0 mg/kg/day, which is an effect antagonized by coadministration of WAY-100635, a selective 5-HT1A antagonist. These results suggest a role for impaired lactate metabolism in some of the core symptoms of schizophrenia, for example, negative symptoms and cognitive deficits. The implications for the ability of 5-HT1A agonism to ameliorate impaired lactate production in the mPFC of this animal model are discussed.

Effect of tandospirone, a serotonin-1A receptor partial agonist, on information processing and locomotion in dizocilpine-treated rats

RATIONALE

Augmentation therapy with serotonin-1A receptor (5-HT1A) partial agonists has been suggested to ameliorate psychotic symptoms in patients with schizophrenia.

OBJECTIVE AND METHODS

The objective of the present study was to examine the effect of repeated administration of tandospirone (0.05 and 5 mg/kg) on locomotor activity in a novel environment and on sensorimotor gating in rats treated with the N-methyl-D-aspartate receptor antagonist MK-801, which has been used in animal models of schizophrenia. Furthermore, we sought to determine whether the effect of tandospirone on these behavioural measures is blocked by WAY 100635 (0.3 mg/kg), a 5-HT1A receptor antagonist, and whether there is an interaction between haloperidol (0.1 mg/kg; a dopamine-D2 receptor antagonist) and tandospirone.

RESULTS

Tandospirone at 5 mg/kg, but not 0.05 mg/kg, decreased locomotor activity in saline or MK-801-treated rats, which were not affected by co-treatment with WAY 100635. Haloperidol decreased locomotion both in saline and MK-801-treated animals, and this effect was not evident in the latter group receiving the higher dose of tandospirone. Tandospirone (5 mg/kg)-induced disruption of sensorimotor gating in saline or MK-801-treated animals was reversed by WAY-100635, but not by haloperidol.

CONCLUSIONS

These findings suggest that behavioural changes induced by tandospirone are not fully blocked by 5-HT1A antagonists and that tandospirone (5 mg/kg) potentiates the effect of MK-801. Overall, these findings point to an interaction between NMDA and 5-HT(1A) receptors. Part of the effect of tandospirone on locomotor activity may be mediated by the actions of its active metabolites on other neurotransmitter systems.

Development and validation of a high-performance liquid chromatographic method for the determination of buspirone in pharmaceutical preparations

A stability indicating, reversed-phase high-performance liquid chromatographic method was developed and validated for the determination of buspirone (Bsp) in pharmaceutical dosage forms. The use of a semi-micro XTerra MS C18 (150 mm x 3.0 mm i.d., 5 microm particle size) analytical column, results in substantial reduction in solvent consumption and increased sensitivity. The mobile phase consisted of a mixture of 0.010 M ammonium acetate (pH 4.0) and methanol (55:45, v/v), pumped at a flow rate 0.30 ml min-1. The UV detector was operated at 245 nm. The retention times for lidocaine (Ldc), which was used as internal standard, and buspirone were 4.57 and 7.72 min, respectively. The calibration graph was ranged from 1.00 to 5.00 microg ml-1, while detection and quantitation limits were found to be 0.22 and 0.67 microg ml-1, respectively. The intra- and inter-day relative standard deviation (% R.S.D.) values were less than 1.94%, while the relative percentage error (% Er) was less than 4.0% (n = 5). The method was applied to the quality control of commercial tablets and content uniformity test and proved to be suitable for rapid and reliable quality control.

Involvement of 5-hydroxytryptamine(1A) receptors in nicotine-induced tail tremor in rats

Involvement of the serotonergic system in tail tremor induced by repeated administration of nicotine was investigated in rats. Tail tremor induced by nicotine (0.5 mg/kg, s.c.) was suppressed by a 5-HT(1A) receptor antagonist, N-¿2-[4-(2-methoxyphenyl)-1-piperazinyl-]ethyl¿-N-(2-pyridinyl)cycloh exanecarboxamide trihydrochloride (WAY-100635; 0.3-3 mg/kg, i.p.), but not by a 5-HT(2) receptor antagonist, ketanserin (0.1-0.3 mg/kg, i.p). The 5-HT(1A) receptor agonists, buspirone (1-20 mg/kg, i.p.), gepirone (1-10 mg/kg, i.p.), tandospirone (1-10 mg/kg, i.p.) and (+/-)-8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT; 0.01-0.1 mg/kg, s.c.), enhanced the tail tremor. The enhancement of tail tremor by buspirone (10 mg/kg, i.p.) was blocked by WAY-100635 (0.3-3 mg/kg, i.p.). These findings suggest that nicotine-induced tail tremor is mediated by 5-HT(1A) receptors and that 5-HT(1A) receptor antagonists are effective in the treatment of tremor.

The influence of buspirone, and its metabolite 1-PP, on the activity of paroxetine in the mouse light/dark paradigm and four plates test

Although numerous animal procedures have been employed in the study of antidepressants (ADs) in anxiety, the results following acute administration remain highly variable. The present study investigated the effect of the SSRI paroxetine (4, 8, and 16 mg/kg, IP) in two tests of anxiety in mice: the light/dark test paradigm, and the four plates test (FPT). In both tests, it was found that paroxetine resulted in an anxiolytic-like effect at doses that did not modify motor performance (at the doses of 4 and 8 mg/kg in the light/dark test and at the doses of 4, 8, and 16 mg/kg in the four plates test). In the light/dark paradigm, both doses of buspirone significantly potentiated paroxetine, while in the four plates only one dose of buspirone (a 5HT(1A) partial agonist) (0.06 mg/kg) increased the anxiolytic-like effect of paroxetine. Prior administration of 1-PP was without effect in the light/dark paradigm but antagonized the effect of paroxetine (at the dose of 0.06 and 0. 5 mg/kg) in the FPT. The results suggested that a balance between pre- and postsynaptic 5-HT(1A) receptor was implicated in the anxiolytic-like effect of paroxetine. Buspirone seemed to emphasize the role of paroxetine in 5-HT(1A) receptor modulation and exerted a biphasic influence in the two tests.

High-performance liquid chromatographic method with coulometric detection for the determination of buspirone in human plasma by means of a column-switching technique

A reversed-phase high-performance liquid chromatographic method with electrochemical detection has been developed for the determination of buspirone from human plasma. The separation was carried out by using a Supelcosil ABZ+ plus C18 reversed-phase column and 0.05 M potassium dihydrogenphosphate (pH 6.5)-acetonitrile (7:3, v/v) as the mobile phase. The compounds were detected by coulometry. Buspirone and the internal standard were extracted from the human plasma using Bond-Elut C18 solid-phase extraction cartridges. Following removal of the the highly lipophilic plasma components we applied a column-switching technique which reduced the duration of HPLC measurement from 60 min to 15 min. The limit of quantitation was found to be 100 pg/ml plasma.

Buspirone enhances immobility in the forced swim test in mice

We studied the effects of buspirone and 8-hydroxy-2-(di-n-propylamino) tetralin (8-OH-DPAT) on duration of immobility in mice in the forced swim test. Buspirone [3-10 mg/kg, intraperitoneally (IP)] potently and dose dependently increased the duration of immobility in mice. In contrast, following a single dose of 8-OH-DPAT (1-3 mg/kg, IP), there was a dose-dependent decrease in the duration of immobility. Pretreatment with the 5-HT synthesis inhibitor p-chlorophenylalanine (200 mg/kg, IP, 3 days before further drug treatment) did not alter the effects of buspirone or 8-OH-DPAT. The increase in the duration of immobility induced by buspirone (3 mg/kg, IP) was blocked by NAN-190 [1-(2-methoxyphenyl)-4-(4-[2-phthalimido]butyl)-piperazine hydrobromide, 1 mg/kg, IP], a postsynaptic 5-HT1A receptor antagonist. However, the effect of 8-OH-DPAT (1 mg/kg, IP) was not blocked by NAN-190 (1 mg/kg, IP). The effect of buspirone (3 mg/kg, IP) was blocked by apomorphine (0.3 mg/kg, IP), a dopamine receptor agonist. Based on the results of this study, it is suggested that the effects of buspirone and of 8-OH-DPAT on immobility in the forced swim test may occur through different mechanisms.

The azapirone metabolite 1-(2-pyrimidinyl)piperazine depresses excitatory synaptic transmission in the hippocampus of the alert rat via 5-HT1A receptors

The effects of acute and repeated treatment with 1-(2-pyrimidinyl)piperazine (1-PP), a metabolite of the 5-HT1A receptor ligand azapirones, were investigated on hippocampal excitatory synaptic transmission. Recordings of the electrically evoked field population excitatory post-synaptic potentials (e.p.s.p.s.) were carried out in the stratum radiatum of the CA1 region of the dorsal hippocampus of alert rats. Acute i.p. administration of 1-PP transiently reduced the e.p.s.p. amplitude in a dose-dependent (0.25-1 mg/kg) manner. This effect was blocked by the 5-HT1A receptor antagonists spiroxatrine (1 mg/kg) and MDL 73005EF (8-[2-(2,3-dihydro-1,4-benzodioxin-2-yl methylaminoethyl]-8-azaspirol[4,5]decane-7,9-dione methyl sulphonate, 2 mg/kg). Intrahippocampal administration of 1-PP (5 microg) evoked a transient reduction of the e.p.s.p. amplitude which was similar to that obtained with 5-HT (10 microg). 1-PP (0.25 mg/kg per day) administered for 9 days produced a gradual reduction in the daily pre-injection baseline e.p.s.p. amplitude coupled with a decrease in the acute response to the drug. The chronic baseline reduction was transiently reversed by spiroxatrine and full recovery to pretreatment levels was observed 4 days after the last 1-PP dose. These findings indicate that the previously reported reduction in the e.p.s.p. produced by the azapirone group of 5-HT1A receptor ligands may be mediated in part by their metabolite 1-PP through activation of 5-HT1A receptors.

Analysis of non-benzodiazepinic anxiolytic agents by capillary zone electrophoresis

A simple capillary electrophoretic method was developed for the analysis of a new generation of serotonergic anxiolytics and their related substances: zalospirone, gepirone, ipsapirone and buspirone. All compounds run in a Tris/phosphate buffer at pH 3 as cations and the experimental conditions allowed good resolution of four drugs and their principal impurities. The analyses were made using two different kinds of capillary. The suitability of CZE and HPLC methods for the analysis of these non-benzodiazepinic anxiolytic agents and their impurities was compared.

Buspirone enhances head twitch behavior in mice

We studied the effects of buspirone, a 5-HT1A receptor agonist, on head twitch behavior induced by 5-hydroxy-L-tryptophan (5-HTP) administered together with pargyline in mice. Buspirone dose dependently (0.1-10 mg/kg i.p.) enhanced head twitch behavior. This effect was blocked by (-)-propranolol and NAN-190 (1-(2-methoxyphenyl)-4-[4-(2-phthalimido)butyl]-piperazine hydrobromide). The enhancing effect of buspirone was also observed when mice were pretreated with p-chlorophenylalanine. These findings suggest that the enhancing effect of buspirone on head twitch behavior may be exerted through the activation of post-synaptic 5-HT1A receptors.

Effects of ipsapirone, a 5-HT1A agonist, on sleep/wakefulness cycles: probable post-synaptic action

The effects of ipsapirone, a ligand of the 5-HT1A receptors and a new potential anxiolytic, on sleep/wakefulness regulation were examined in the rat. Injected i.p. at 1, 3 and 5 mg kg-1, this compound induced a dose-dependent reduction of paradoxical sleep for 2 to 4 hours, followed, at a dose of 5 mg kg-1, by a secondary rebound. The other states of vigilance were not modified, except at the latter dose where the amounts of wakefulness were enhanced initially and decreased secondarily, while those of SWS were enhanced from 2 to 4 hours post-treatment. The effects of ipsapirone (3 mg kg-1) persisted after infusion of the neurotoxin 5,7-dihydroxytryptamine into the dorsal raphe nucleus which induced the sub-total destruction of the serotoninergic system. Thus, the action of the 5-HT1A agonist ipsapirone on sleep/wakefulness cycles probably involves the stimulation of the post-synaptic 5-HT1A receptors.

Analysis of new serotonergic anxiolytics by liquid chromatography

A simple isocratic procedure was developed for the analysis of new serotonergic anxiolytics and the related compounds in bulk materials, pharmaceutical formulations and in biological samples. The system may be applied for the assay of other serotonergic anxiolytics of related structure such as buspirone. The liquid chromatographic assay utilizes a reversed-phase C18 column, a mobile phase consisting of a mixture (55:45, v/v) of (A) buffer potassium dihydrogen phosphate (0.05 M) containing sodium lauryl sulphate (0.005 M) and (B) acetonitrile. A fluorescence detection is used with lambda ex 237 nm; lambda cm 374 nm. The accuracy, precision and sensitivity of the proposed method are established. Standard curves are linear with respect to concentration in the range 0.05-7.5 micrograms ml-1. The method also allows the separation and identification of related compounds at concentrations below 0.01%.

1-(2-Pyrimidinyl)piperazine antagonizes GABA-activated currents in cultured spinal neurones of the rat

Buspirone is an anxiolytic drug with an unknown mechanism of action. We have addressed the proposal that its therapeutic effect is due to a metabolite, 1-(2-pyrimidinyl)-piperazine (1-PP), increasing the open probability of gamma-aminobutyric acid (GABA)-activated channels. By making whole-cell recordings from cultured spinal neurones we demonstrated that 1-PP, in contrast to flurazepam, actually antagonizes GABA- and glycine-activated currents. These observations are inconsistent with this proposed mechanism of action for buspirone.

Determination of a buspirone metabolite in plasma samples

A high-performance liquid chromatographic (HPLC) method is described for the assay of the active metabolite [1-(2-pyrimidinyl)piperazinel of buspirone, an anxiolytic agent, in rat plasma. The method is based on the use of ion-pair HPLC coupled to a liquid-solid extraction scheme. Samples of rat plasma (2 ml) with internal standard (1-phenylpiperazine), adjusted to pH 10.5 with borate buffer, were loaded on to a preactivated C-18 cartridge. The metabolite and the internal standard were eluted with 5 ml of methanol and injected on to a reversed-phase 10-microm Spherisorb ODS-2 column. The column was eluted with a mobile phase of 0.005 M sodium lauryl sulphate in citrate buffer (pH 3.6)-acetonitrile (65:35, v/v) at 2 ml min(-1). Detection was carried out at 248 nm. The recovery of the metabolite was 55%. The method was applied to the determination of the metabolite in rat plasma after oral dosing (25 mg kg(-1)) of the parent compound.

Effects of gepirone, an aryl-piperazine anxiolytic drug, on aggressive behavior and brain monoaminergic neurotransmission

Gepirone (BMY 13805), a buspirone analog, was used to determine the antianxiety mechanism of the arylpiperazine class of drugs. Because of the weak effects of these drugs on conflict behavior, isolation-induced aggressive mice were used as the antianxiety model. Gepirone, like buspirone, potently inhibited attacks against group housed intruder mice (ED50 = 4.5 mg/kg i.p.) without causing sedation or ataxia. Inhibition of aggression was potentiated by co-administration of 0.25 mg/kg methiothepin or 2.5 mg/kg methysergide. Gepirone had variable effects on dopamine metabolism and reduced 5-hydroxytryptamine (5HT) metabolism about one third after a dose of 2.5 mg/kg. In contrast to buspirone, which markedly increased dopaminergic impulse flow, gepirone inhibited the firing of most cells recorded from the substantia nigra zona compacta in doses of 2.3-10 mg/kg i.v. and the effects were reversible by administration of haloperidol. The common metabolite of buspirone and gepirone, 1-(2-pyrimidinyl)-piperazine, caused increased firing rates only. Gepirone potently inhibited serotonergic impulse flow recorded from the dorsal raphe nucleus (88.3% after 0.04 mg/kg) and this effect was partially reversed by serotonergic antagonists. Both buspirone and gepirone displaced [3H]-5HT from the 5HT1a binding site in the hippocampus with IC50 values of 10 and 58 nM, respectively. Non-alkyl substituted aryl-piperazines displaced [3H]-5HT from both 5HT1a and 5HT1b binding sites. Thus, although gepirone may be a weak postsynaptic 5HT agonist, its primary effect is to decrease 5HT neurotransmission. In support of this conclusion was the observed potentiation of antiaggressive effects by blocking 5HT receptors wit small doses of methiothepin or methysergide, which would exacerbate the decreased release of 5HT caused by gepirone. These results are in harmony with reports that decreased serotonergic activity has anxiolytic-like effects in animal models of anxiety.

Buspirone. A preliminary review of its pharmacological properties and therapeutic efficacy as an anxiolytic

Buspirone hydrochloride (HCl)1 is a new anxiolytic with a unique chemical structure. Its mechanism of action remains to be elucidated. Unlike the benzodiazepines, buspirone lacks hypnotic, anticonvulsant and muscle relaxant properties, and hence has been termed 'anxioselective'. As evidenced by a few double-blind clinical trials, buspirone 15 to 30 mg/day improves symptoms of anxiety assessed by standard rating scales similarly to diazepam, clorazepate, alprazolam and lorazepam. Like diazepam, buspirone is effective in patients with mixed anxiety/depression, although the number of patients studied to date is small. In several studies, a 'lagtime' of 1 to 2 weeks to the onset of anxiolytic effect has been noted; hence motivation of patient compliance may be necessary. Sedation occurs much less often after buspirone than after the benzodiazepines; other side effects are minor and infrequent. In healthy volunteers, buspirone does not impair psychomotor or cognitive function, and appears to have no additive effect with alcohol. Early evidence suggests that buspirone has limited potential for abuse and dependence. Thus, although only wider clinical use for longer periods of time will more clearly define some elements of its pharmacological profile, with its low incidence of sedation buspirone is a useful addition to the treatments available for generalised anxiety. It may well become the preferred therapy in patients in whom daytime alertness is particularly important.

Recent developments in 5HT-related pharmacology of animal models of anxiety

The proposed anxioselective drug, buspirone, interacts with 5HT1 receptors. An analogue, MJ 13805, produces a 5HT behavioural syndrome blocked by central 5HT pathway lesion. Both compounds inhibit 5HT neurone firing. An association of any such action with models of anxiety is not yet possible. Several compounds selective for 5HT receptor sub-types have been tested in models of anxiety. Ritanserin, a selective 5HT2 antagonist, shows activity in an emergence test but not conflict models. Preliminary clinical reports indicate qualitatively different anxiolytic activity from that of benzodiazepines. TVXQ 7821 is selective for 5HT1 receptors and has shown activity in several models of anxiety. 8OHDPAT and RU 24969 are 5HT1 agonists, selective for 5HT1A and 5HT1B sites respectively. 8OHDPAT released punished drinking but reversed a similar effect of PCPA. Its mode of action remains unclear. RU 24969 has shown no marked anxiolytic-like activity in food or water-motivated conflicts. Further studies are necessary before associating modulation of central 5HT systems with anxiolytic activity, either in animal models or patients.

Quantitative analysis of 1-(2-pyrimidinyl)piperazine in plasma by capillary gas chromatography-mass spectrometry

A sensitive method for detecting and quantifying 1-(2-pyrimidinyl)piperazine, an important metabolite of buspirone, in human plasma was developed and validated. The range of the method is 0.2-15 ng/ml. The analyte was removed from buffered, sodium chloride-saturated plasma with benzene, extracted into aqueous acid, washed with diethyl ether and reextracted into benzene. The processed extract was derivatized with pentafluorobenzoyl chloride. Instrumental analysis involved on-column injection into a fused-silica capillary gas chromatography column and detection by selected-ion monitoring mass spectrometry.

Disposition of the psychotropic drugs buspirone, MJ-13805 and piribedil, and of their common active metabolite 1-(2-pyrimidinyl)-piperazine in the rat

1-(2-Pyrimidinyl)-piperazine (PmP) is a common metabolite of the structurally related drugs buspirone, MJ-13805 and piribedil. After i.v. injection (25 mumol/kg) to rats, all three parent drugs are rapidly cleared with a t 1/2 (beta) of about 30 min. The metabolite t 1/2 is about four times that of its parent drugs. About 25, 23 and 2% of buspirone, MJ-13805 and piribedil, respectively, reaches the systemic circulation as PmP. The metabolite concentrates in the brain where its A.U.C. is about twice those of buspirone and MJ-13805. Results indicate that PmP formation is a pharmacologically significant process for both buspirone and MJ-13805 but it is probably less important for piribedil.

Buspirone: a new type of anxiolytic

Buspirone is a member of a new class of agents known as azaspirodecanediones, and represents the first nonbenzodiazepine anxiolytic to be introduced in the U.S. in recent years. It does not resemble the benzodiazepines or older anxiolytics such as meprobamate and the barbiturates in pharmacologic profile. Buspirone lacks anticonvulsant activity, interacts minimally with central nervous system depressants such as alcohol, and does not cause muscle relaxation. The drug is reported to have minimal sedating effect, to cause no impairment of driving-related skills, and to have no euphoriant effect or addictive potential. With this low side-effect profile, buspirone should not require Drug Enforcement Agency scheduling controls. Clinical trials indicate buspirone is efficacious in the treatment of mild to moderate anxiety disorders. Answers to questions of possible side effects related to dopaminergic intractions must await post-marketing experience. Buspirone is a suitable addition to drug formularies as its pre-marketing data suggest several advantages compared with anxiolytics currently available.

The non-benzodiazepine anxiolytic buspirone inhibits stress-induced renin secretion and lowers heart rate

The non benzodiazepine drug, buspirone, produces a dose-dependent biphasic effect on plasma renin activity in non-stressed rats. Low doses (0.1 - 2.0 mg/kg i.p.) decrease while high doses (10.0 - 50.0 mg/kg i.p.) increase plasma renin activity. The maximal decrease in plasma renin activity produced by buspirone (1.0 mg/kg i.p.) was observed 30 minutes post-injection. In addition, buspirone (0.5 and 2.0 mg/kg i.p.) blocked the stress-induced rise in plasma renin activity. This effect of buspirone is in contrast to the previously observed failure of the benzodiazepine anxiolytics to alter the effect of stress on plasma renin activity. Administration of buspirone (0.5 mg/kg i.p.) produced a sustained reduction (15%) in heart rate but did not affect mean arterial pressure. The present data support the view that the mechanism of the anxiolytic action of buspirone is different from that of the benzodiazepines.

Comparative chronic effects of buspirone or neuroleptics on rat brain dopaminergic neurotransmission

Buspirone is a novel anti-anxiety drug which has neither a benzodiazepine structure nor any other benzodiazepine-like properties. Since buspirone is known to block dopamine autoreceptors and increase dopamine metabolism, it was compared to classical antipsychotic drugs for subchronic and chronic effects on dopaminergic function. When continuously infused into rats at 1.0 mg/kg/day s.c. for 2 weeks there was a small diminution of striatal dopamine metabolism response to acute injection of buspirone, but haloperidol produced a normal increase in DOPAC concentrations. In contrast, infusion of 0.3 mg/kg/day of haloperidol caused a marked subsensitivity to both acute buspirone and haloperidol challenge. The data from 3 months of treatment with buspirone or trifluoperazine (3.0 or 1.0 mg/kg/day, respectively) added to the rats' drinking water yielded similar results. Also, there was no alteration of dopamine autoreceptor sensitivity or postsynaptic D2 receptor sensitivity in 3 month buspirone treated rats. Three months of trifluoperazine produced a 45% increase in striatal binding of 3H-spiperone, which was reversed by simultaneous administration of buspirone during the final 2 weeks of trifluoperazine treatment. These data indicate that buspirone in moderate doses, such as used for treating anxiety, should be free of extrapyramidal side-effects. The modulation of neuroleptic-induced increased D2 receptor binding reinforces the hypothesis that buspirone has a modulatory effect at an unknown site within the extrapyramidal system.

Toxic effects of chemicals: difficulties in extrapolating data from animals to man

This review attempts an analysis of the major components which make it extremely difficult to extrapolate toxicological data obtained with chemicals from animals to man. A first problem concerns the use of doses to express the unit of comparison across animal species; the dose is a parameter exogenous to the body and when a chemical enters the body concentrations should be utilized. There is in fact evidence that for several chemicals equal doses in different animal species do not mean equal concentrations in blood or tissues. Concentrations of chemicals should be measured for extrapolation purposes as close as possible to the site of the toxic effect. A second problem regards the fact that several chemical are transformed in the body into other chemical species--sometimes few and sometimes many--and some of these species (active metabolites) display biological activity in some cases higher than different from or antagonistic to those of the parent compounds. Some of these metabolites are highly reactive and therefore bind to body components, particularly macromolecules such as proteins and nucleic acids. There is evidence that metabolism is quantitatively and/or qualitatively different in various animal species. A third problem concerns the difference in various animal species in the biological substrates on which chemicals exert their toxic effects. Equal concentrations of chemicals and their metabolites do not mean equal toxic effects across animal species because endogenous metabolic processes, cell permeability, enzymes, and receptors are not necessarily the same in animals and man. To overcome these difficulties there is a need for closer integration of different disciplines in the toxicological evaluation of chemicals. A scientific rather than a routine approach in toxicology is emphasized.

Identification and quantitation of 1-arylpiperazines, metabolites resulting from side-chain cleavage of (4-substituted aryl-1-piperazinyl)alkyl heterocyclic derivatives in rat plasma and brain

Many drugs contain the arylpiperazine moiety in the side-chain of their molecules. A common metabolic pathway of such drugs is cleavage of the side-chain with the formation of 1-arylpiperazines. This has been verified by combined gas chromatography-mass spectrometry of biological samples from rats given orally a series of heterocyclic derivatives bearing a 4-aryl(phenyl, pyrimidinyl, pyridyl or thiazolyl)-1-piperazinylalkyl moiety (oxypertine, zolertine, millipertine, empiprazole, dapiprazole, antrafenine, piribedil, azaperone). A sensitive and selective electron-capture gas-liquid chromatographic procedure for 1-arylpiperazines in rat plasma and brain is described. The overall recovery from plasma and brain was 70-90%. The limit of detection for substituted (halogenated) phenylpiperazines was 10-25 ng/ml or ng/g and 25-100 ng/ml or ng/g for other derivatives. Preliminary data are reported on the time course of the production and elimination of 1-arylpiperazines after oral administration of representative compounds with the arylpiperazine moiety (oxypertine, azaperone and S-3608).

The effects of benzodiazepine and non-benzodiazepine anxiolytics on locus coeruleus unit activity

Two theories have been put forth concerning the anxiolytic actions of the anti-anxiety drugs. One theory maintains that these drugs decrease locus coeruleus output, and the other maintains that they facilitate gamma-aminobutyric acid (GABA) neurotransmission at benzodiazepine (BZ)-linked GABA receptors. The BZ-anxiolytic diazepam does decrease locus coeruleus neuronal impulse flow. However, this decrease is not due to effects on BZ-linked GABA receptors in the locus coeruleus. Furthermore, the non-BZ anxiolytic buspirone, its metabolite and its analog all slightly increase locus coeruleus neuronal impulse flow. This increase, in the case of the metabolite, appears to be due, in part, to blockade of alpha 2-adrenoceptors. Finally, buspirone, unlike diazepam, did not potentiate GABA inhibition at BZ-linked GABA receptor sites (i.e. cerebellar Purkinje cells). These data suggest that the non-BZ anxiolytic buspirone produces its anti-anxiety effects by unconventional mechanisms.

Dopaminergic effects of buspirone, a novel anxiolytic agent

The novel anxiolytic drug buspirone raised striatal levels of the dopamine metabolites homovanillic acid (HVA) and dihydroxyphenylacetic acid (DOPAC) 1 hr after oral administration. This effect was dose-dependent with a peak at 60 min. No changes were observed in the levels of 3-methoxytyramine (3MT), the extraneuronal metabolite of dopamine. Noradrenaline, serotonin and its metabolite 5-hydroxyindoleacetic acid (5HIAA) were not affected. Buspirone displaced [3H]spiroperidol from striatal binding sites, with an IC50 (1.8 x 10(-7) M), comparable to that of clozapine (IC50 = 1.4 x 10(-7) M) but considerably lower than that of haloperidol (4.7 x 10(-9) M). Buspirone was only a weak inhibitor of dopamine-stimulated adenyl cyclase. Buspirone was not active on the binding of trifluoperazine to calmodulin and did not modify calmodulin-induced activation of phosphodiesterase (PDE). Repeated administration of buspirone did not increase the number of DA receptors. These data show that, although buspirone has antidopaminergic activity, it can hardly be classified as a classic neuroleptic agent.

Disposition and metabolism of buspirone and its metabolite 1-(2-pyrimidinyl)-piperazine in the rat

After i.v. injection (10 mg/kg) to rats, buspirone is rapidly cleared from blood with a t1/2 (beta) or 30 min. After the same dose is given orally, the drug is not detectable in blood or brain within the limits of sensitivity of the method. The metabolite 1-(2-pyrimidinyl)-piperazine (1-PP) has a longer t1/2 than buspirone. It is present to about the same extent in rat plasma and brain after either i.v. or p.o. buspirone. Unlike buspirone, 1-PP accumulates in the brain reaching concentrations between four-and five times those in plasma. Its brain AUC is higher than that of buspirone even when buspirone is given i.v. The results suggest that 1-PP may contribute to the pharmacological effect of the parent drug.