Antagonist properties of 1-(2-pyrimidinyl)piperazine at presynaptic alpha 2-adrenoceptors in the rat brain

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.

Effect of the 5-HT(1A) partial agonist buspirone on regional brain electrical activity in man: a functional neuroimaging study using low-resolution electromagnetic tomography (LORETA)

In a double-blind, placebo-controlled study, the effects of 20 mg buspirone - a 5-HT(1A) partial agonist - on regional electrical generators within the human brain were investigated utilizing three-dimensional EEG tomography. Nineteen-channel vigilance-controlled EEG recordings were carried out in 20 healthy subjects before and 1, 2, 4, 6 and 8 h after drug intake. Low-resolution electromagnetic tomography (LORETA; Key Institute for Brain-Mind Research, software: http://www.keyinst.unizh.ch) was computed from spectrally analyzed EEG data, and differences between drug- and placebo-induced changes were displayed as statistical parametric maps. Data were registered to the Talairach-Tournoux human brain atlas available as a digitized MRI (McConnell Brain Imaging Centre: http://www.bic.mni.mcgill.ca). At the pharmacodynamic peak (1st hour), buspirone increased theta and decreased fast alpha and beta sources. Areas of theta increase were mainly the left temporo-occipito-parietal and left prefrontal cortices, which is consistent with PET studies on buspirone-induced decreases in regional cerebral blood flow and fenfluramine-induced serotonin activation demonstrated by changes in regional cerebral glucose metabolism. In later hours (8th hour) with lower buspirone plasma levels, delta, theta, slow alpha and fast beta decreased, predominantly in the prefrontal and anterior limbic lobe. Whereas the results of the 1st hour speak for a slight CNS sedation (more in the sense of relaxation), those obtained in the 8th hour indicate activation. Thus, LORETA may provide useful and direct information on drug-induced changes in central nervous system function in man.

Is the potent 5-HT1A receptor agonist, alnespirone (S-20499), affecting dopaminergic systems in the rat brain?

The effects of the new methoxy-chroman 5-HT1A receptor agonist, alnespirone (S-20499), on the dopamine systems in the rat brain were assessed in vivo by means of electrophysiological and neurochemical techniques. Cumulative doses of alnespirone (0.032-4.1 mg kg(-1), i.v.) did not modify the spontaneous firing rate of dopamine neurons in the substantia nigra as well as in the ventral tegmental area. The local application of alnespirone (0.1-10 microM) by reverse microdialysis into the dorsal striatum did not affect the dopamine output but induced a moderate, although dose-independent, increase of 5-HT (5-hydroxytryptamine, serotonin) concentrations in the dialysate. As expected of a 5-HT1A receptor agonist, intraperitoneal (i.p.) administration of alnespirone at 2-32 mg kg(-1) markedly decreased 5-HT turnover in the striatum. Parallel measurements of dopamine turnover showed that alnespirone exerted no effect except at the highest dose (32 mg kg(-1), i.p.) for which a significant increase was observed. Interestingly, both alnespirone-induced reduction in 5-HT turnover and increase in dopamine turnover could be prevented by pretreatment with the selective 5-HT1A receptor antagonist WAY-100635 (N-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]-N-(2-pyridinyl)cyclohexa ne carboxamide). Altogether, these data indicate that alnespirone does not exert any direct influence on central dopamine systems. The enhanced dopamine turnover due to alnespirone at high dose appeared to result from 5-HT1A receptor stimulation, further supporting the idea that this receptor type may play a key role in 5-HT-dopamine interactions in brain.

Comparative behavioural profiles of buspirone and its metabolite 1-(2-pyrimidinyl)-piperazine (1-PP) in the murine elevated plus-maze

It has been suggested that in vivo formation of the metabolite 1-(2-pyrimidinyl)-piperazine (1-PP) may be a major drawback in the use of buspirone as an anti-anxiety agent. To test this hypothesis, the effects of buspirone, alone or with proadifen (an inhibitor of liver microsomal enzymes) pretreatment, were contrasted with those of 1-PP in the murine elevated plus-maze test of anxiety. At 3.0 mg/kg (but not lower doses), buspirone per se had modest anxiolytic-like effects (increased percentage of open arm entries; reduced stretched-attend postures and flatback approach) that were associated with increased grooming and immobility. However, in proadifen-pretreated mice, buspirone produced behavioural depression only, with marked effects evident both at 1.0 and 3.0 mg/kg. As proadifen blocks the biotransformation of buspirone to 1-PP, these data suggest that any anxiolytic activity of buspirone in the murine plus-maze may be attributable to its principal active metabolite. Consistent with this hypothesis, 1-PP (0.5-13.5 mg/kg) produced dose-dependent anti-anxiety effects on both conventional and ethological measures that were not confounded by motoric impairment. Results are discussed in relation to biochemical and electrophysiological studies suggesting that 1-PP has a direct action at 5-HT1A receptors.

Serotonin1A receptor agonists induce Fos protein expression in the locus coeruleus of the conscious rat

The azapirones, which are partial agonists of the serotonin (5-HT)1A receptor, possess anxiolytic activity. These agents may act at the pre- or postsynaptic 5-HT1A receptors, and involve the noradrenergic system. To determine whether these drugs activate noradrenergic neurons via 5-HT1A receptors, we have evaluated the expression of the immediate early gene c-fos in the locus coeruleus. Tandospirone and ipsapirone each induced expression of Fos protein in the noradrenergic neurons of the locus coeruleus of conscious rats. This effect was reversed by pretreatment with (+)-WAY100135, a specific 5-HT1A antagonist. These results clearly demonstrate that azapirones activate noradrenergic neurons via 5-HT1A receptors.

Increased levels of extracellular noradrenaline in the frontal cortex of rats exposed to naturalistic environmental stimuli: modulation by acute systemic administration of diazepam or buspirone

In vivo microdialysis was used to investigate the effects of an IP injection of diazepam or buspirone (each at 3 mg/kg) on spontaneous efflux of noradrenaline in rat frontal cortex, and on changes in efflux induced by naturalistic stress. After drug administration, rats either remained in their home cages or were transferred individually to a novel cage, 1 h later. The novel cage was brightly lit (1500 lux) and contained another, unfamiliar rat. After transfer to the novel cage, noradrenaline efflux was lower in diazepam-injected rats than in their vehicle-injected counterparts. However, in both cases, stress caused a significant increase in efflux and the net increase was not affected by diazepam. Similarly, buspirone, which increased spontaneous efflux of noradrenaline, did not affect the net increase in efflux during stress. Neither compound modified locomotor activity in the novel cage. This suggests that any changes in noradrenaline efflux are unrelated to drug effects on non-specific arousal. It is concluded that generically unrelated anxiolytic agents can have different effects on spontaneous efflux of noradrenaline but do not modify the noradrenergic response to naturalistic stimuli.

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.

Novel benzodioxan derivative, 5-(3-[((2S)-1,4-benzodioxan-2- ylmethyl)amino]propoxy)-1,3-benzodioxole HCl (MKC-242), with a highly potent and selective agonist activity at rat central serotonin1A receptors

The present study characterizes the neurochemical profile of the newly synthesized compound 5-(3-[((2S)-1,4-benzodioxan-2-ylmethyl)amino]propoxy)-1,3-be nzodioxole HCl (MKC-242). In in vitro experiments, MKC-242 had high affinity for serotonin1A (5-HT1A) receptors (Ki: 0.35 nM) and moderate affinity for alpha 1-adrenoceptors (Ki: 21 nM), whereas it had no appreciable affinity for any other neurotransmitter recognition sites studied and 5-HT transporter. MKC-242 (0.3-3.0 mg/kg, s.c.; 1-10 mg/kg, p.o.) caused presynaptic 5-HT1A-receptor-mediated responses (decreases in 5-HT turnover and 5-HT release) and postsynaptic 5-HT1A-receptor-mediated responses (hypothermia, an increase in serum corticosterone level and 5-HT1A behavioral syndrome). The effects of MKC-242 on decarboxylase inhibitor-induced 5-hydroxytryptophan accumulation and rectal temperature were blocked by the 5-HT1A-receptor antagonist N-tert-butyl-3-(4-(2-methoxyphenyl)piperazin-1-yl)-2-phenylpropana mide. The comparative studies on the in vivo responses induced by MKC-242 and the 5-HT1A-receptor full agonist 8-hydroxy-2-(di-n-propyl-amino)tetralin (8-OH-DPAT) showed that MKC-242 and 8-OH-DPAT had similar efficacy at presynaptic 5-HT1A receptors, whereas the former had less efficacy than the latter at postsynaptic 5-HT1A receptors. Furthermore, MKC-242 partially inhibited forskolin-stimulated adenylate cyclase activity in hippocampal membranes. These findings suggest that MKC-242 acts as a full and partial agonist at pre- and postsynaptic 5-HT1A receptors, respectively, in the central nervous system.

Increase of noradrenaline release in the hypothalamus of freely moving rat by postsynaptic 5-hydroxytryptamine1A receptor activation

1. 5-Hydroxytryptamine (5-HT) plays a role in the regulation of noradrenergic neurones in the brain, but the precise mechanism of regulation of noradrenaline (NA) release by 5-HT1A receptors has not been defined. The present study describes the effect of a highly potent and selective 5-HT1A receptor agonist, 5-(3-[[(2S)-1,4-benzodioxan-2-ylmethyl)]amino]propoxy)-1,3-b enzodioxole HC1 (MKC-242), on NA release in the hypothalamus using microdialysis in the freely moving rat. 2. Subcutaneous injection of MKC-242 (0.5 mg kg-1) increased extracellular levels of NA and its metabolite, 3-methoxy-4-hydroxyphenylglycol, in the hypothalamus and hippocampus. 3. The 5-HT1A receptor agonists, 8-hydroxy-2-(di-n-propylamino) tetralin (8-OH-DPAT) (0.2 mg kg-1) and buspirone (3 mg kg-1) mimicked the effect of MKC-242 in increasing NA release in the hypothalamus. 4. The effects of MKC-242 and 8-OH-DPAT in the hypothalamus were antagonized by pretreatment with WAY100135 (10 mg kg-1), a silent 5-HT1A receptor antagonist. 5. Local administration of 8-OH-DPAT (10-100 microM), citalopram (1 microM), a 5-HT reuptake inhibitor, and MDL72222 (10 microM), a 5-HT3 receptor antagonist, into the hypothalamus, had no effect on NA release. 6. Intracerebroventricular injection with 5,7-dihydroxytryptamine caused a marked reduction in brain 5-HT content, but the treatment affected neither basal NA levels nor the MKC-242-induced increase in NA release. 7. The effect of MKC-242 in increasing NA release was not attenuated by repeated treatment with the drug (0.5 mg kg-1, once a day for 2 weeks). 8. The present results suggest that activation of postsynaptic 5-HT1A receptors increases NA release in the hypothalamus.

Buspirone and 1-(2-pyrimidinyl)-piperazine attenuate xylazine-induced antinociception in the mouse

The effects of subcutaneous pretreatment with buspirone and its major metabolite 1-(2-pyrimidinyl)-piperazine (1-PP) on the antinociceptive effect of xylazine were examined using the mouse acetic acid assay. Both buspirone and 1-PP dose-dependently attenuated the antinociceptive action of subcutaneously administered xylazine (0.8 mg kg-1), with ED50 values of 7.3 mg kg-1 for buspirone and 3.4 mg kg-1 for 1-PP. Pretreatment with either buspirone (8 mg kg-1) or 1-PP (4 mg kg-1) increased the antinociceptive ED50 of xylazine 3-4-fold. These data support the involvement of alpha 2-adrenoceptor and 1-PP in the pharmacological activity of buspirone.

Antagonism of clonidine antinociception by buspirone and 1-(2-pyrimidinyl)-piperazine

The effects of pretreatment with buspirone and its major metabolite 1-(2-pyrimidinyl)-piperazine (1-PP) on antinociception produced by clonidine were investigated in mice. Buspirone and 1-PP dose dependently attenuated the antinociceptive action of s.c. administered clonidine in the writhing and tail-flick assays. In both assays, 1-PP was more potent than buspirone in antagonizing clonidine-induced antinociception. After s.c. pretreatment with buspirone (8 mg/kg) and 1-PP (4 mg/kg), the antinociceptive ED50 values of s.c. clonidine were significantly increased. The antagonistic effects of buspirone and 1-PP on clonidine-induced antinociception may be due to their alpha 2-adrenoceptor antagonist activity.

Effects of 5-HT1A receptor ligands on a safety signal withdrawal procedure of conflict in the rat

The present study evaluated in the rat the ability of various 5-HT1A receptor agonists to exert an "anxiolytic-like" release of the suppression of lever pressing for food induced by the withdrawal of a conditioned signal for safety without presentation of a conditioned signal for punishment. During the period associated with the safety signal withdrawal (Saf.CS-/Pun.CS-), control rats exhibited a typical pattern of responding with an initial strong blockade of responding that lessened over the period as presses were rewarded and shocks omitted. The 5-HT1A receptor partial agonists buspirone (0.125-0.5 mg/kg) and 8-(2-[2,3-dihydro-1,4-benzodioxin-2-yl- methylamino]ethyl)-8-azaspiro[4,5]decane-7,9-dione methyl sulfonate (MDL 73005EF; 0.5-2 mg/kg) and the full agonist (+)-4-[N-(5-methoxy-chroman-3-yl)-N-propylamino]-butyl-8- azaspiro[4,5]decane-7,9-dione (S 20499; 0.125-1 mg/kg) produced a robust and dose-related release of pressing during the Saf.CS-/Pun.CS- period. This effect was less marked with ipsapirone (0.125-1 mg/kg). Conversely, 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT; 0.06-0.25 mg/kg), a full agonist, was completely inactive and did not prevent MDL 73005EF (1-2 mg/kg) or diazepam (0.125 mg/kg) from releasing the suppressed behavior. The specific 5-HT1A antagonist (+)-N-tert-butyl-3-4-(2-methoxyphenyl)piperazin-1-yl-2-phenylpr opa namide [(+)-WAY 100135; 0.25-8 mg/kg] and the beta-adrenoceptor/5-HT1A antagonist (-)-tertatolol (2-8 mg/kg) did not modify the behavioral blockade, nor did (+)-WAY 100135 (2-4 mg/kg) reduce the ability of buspirone (0.25 mg/kg) to enhance responding during the Saf.CS-/Pun.CS- period.(ABSTRACT TRUNCATED AT 250 WORDS)

Further studies on alpha 2-adrenoceptor subtypes involved in the modulation of [3H]noradrenaline and [3H]5-hydroxytryptamine release from rat brain cortex synaptosomes

Three selective alpha 2A- or alpha 2B-adrenergic antagonists (BRL-44408, BRL-41992 and imiloxan) were used in the present study designed to classify the presynaptic alpha 2-auto- and heteroreceptors in the rat brain cortex. The rank order of potency in antagonizing the inhibitory effect of (-)-noradrenaline or clonidine on the K(+)-induced [3H]noradrenaline and [3H]5-hydroxytryptamine (5-HT) release from superfused synaptosomes was BRL-44408 > or = BRL-41992 >> imiloxan. The same rank order was found for the affinities of these compounds for [3H]yohimbine binding in human platelet membranes, containing only alpha 2A-adrenoceptors, but does not correlate with the known affinities for alpha 2B-adrenoceptors (BRL-41992 > or = imiloxan > BRL-44408). These data support the conclusion that presynaptic alpha 2-auto- and heteroreceptors in rat brain cortex do not belong to the alpha 2B-subtype and suggest that the modulation of noradrenaline and 5-HT release may be mediated by the alpha 2A-subtype.

Comparison of the effect of buspirone and 1-(2-pyrimidinyl)-piperazine on cerebral glucose utilization in the rat

The novel anxiolytic and antidepressant, buspirone, and its main metabolite 1-(2-pyrimidinyl)-piperazine (1-PP), which is pharmacologically active, were examined for their effect on regional cerebral glucose utilization in awake rats using quantitative 2-deoxyglucose autoradiography. At a dose of 1 mg/kg, buspirone reduced glucose utilization in the hippocampus by approximately 15%, whilst 1-PP at the same dose had no effect. In comparison, at a higher dose, 10 mg/kg of both buspirone and 1-PP decreased glucose utilization in the hippocampus by 20% and 27%, respectively. In addition, widespread reductions in local cerebral glucose utilization were noted with this higher dose of 1-PP; such generalized effects are compatible with those reported for alpha 2 adrenoceptor antagonists. Buspirone at 1 and 10 mg/kg increased glucose utilization by 40% and 65%, respectively, in the lateral habenular nucleus, whilst 1-PP at 1 and 10 mg/kg had no effect. The findings suggest that buspirone's effects on glucose utilization cannot be attributed to 1-PP, unless high doses of buspirone are administered.

Effect of the 5-HT1A partial agonist buspirone on regional cerebral blood flow in man

Repeated measurements of regional cerebral blood flow (rCBF) were made in normal volunteers before, and after, the administration of the 5-HT1A partial agonist, buspirone, or placebo. The difference in rCBF, before and after drug, (buspirone versus placebo) was used to identify brain areas affected by buspirone. Buspirone-induced changes in rCBF were studied under two behavioural conditions (5 word-list learning and 15 word-list learning). Compared to placebo, buspirone increased blood flow in the cuneus during both behavioural states. However, decreases in blood flow, centred in the left dorso-lateral prefrontal cortex and posterior cingulate cortex, were only observed under one of the two behavioural conditions. It is concluded that buspirone-induced alterations in regional cerebral blood flow are better understood, not in relation to the known distribution of monoamine neurotransmitter systems (particularly ascending 5-HT projections), but rather in relation to putative neuronal circuits possibly many synapses "downstream" of buspirone's pharmacological site of action.

Effects of the 5-HT1A partial agonists gepirone, ipsapirone and buspirone on local cerebral glucose utilization in the conscious rat

The azospirones gepirone (10 mg/kg), ipsapirone (10 mg/kg) and buspirone (10 mg/kg) were examined for their effect on regional cerebral glucose utilization in conscious rats using quantitative 2-deoxy-glucose autoradiography. All three 5-HT1A partial agonists reduced glucose utilization in the hippocampus and dentate gyrus by 20-25% and increased glucose utilization by 38-65% in the lateral habenular nucleus; an important relay between striatal/limbic areas and the mid-brain raphe nuclei. The findings emphasize the potential importance of the hippocampus as a site of action for 5-HT1A receptor active drugs in vivo and also suggest that functional activity in the striatal/limbic-habenular-raphe pathway may be influenced by gepirone, ipsapirone and buspirone.