Amperozide--a new putatively antipsychotic drug with a limbic mode of action on dopamine mediated behaviour

YKP1447, A Novel Potential Atypical Antipsychotic Agent

(S)-Carbamic acid 2-[4-(4-fluoro-benzoyl)-piperidin-1-yl]-1-phenyl-ethyl ester hydrochloride (YKP1447) is a novel "atypical" antipsychotic drug which selectively binds to serotonin (5-HT(2A), Ki=0.61 nM, 5-HT(2C), Ki=20.7 nM) and dopamine (D(2), Ki=45.9 nM, D(3), Ki=42.1 nM) receptors with over 10~100-fold selectivity over the various receptors which exist in the brain. In the behavioral studies using mice, YKP1447 antagonized the apomorphine-induced cage climbing (ED(50)=0.93 mg/kg) and DOI-induced head twitch (ED(50)=0.18 mg/kg) behavior. In the dextroamphetamine-induced hyperactivity and conditioned avoidance response (CAR) paradigm in rats, YKP1447 inhibited the hyperactivity induced by amphetamine (ED(50)=0.54 mg/kg) and the avoidance response (ED(50)=0.48 mg/kg); however, unlike other antipsychotic drugs, catalepsy was observed only at much higher dose (ED(50)=68.6 mg/kg). Based on the CAR and catalepsy results, the therapeutic index (TI) value for YKP1447 is over 100 (i.p.). These results indicate that YKP1447 has an atypical profile and less undesirable side effects than currently available drugs.

Quetiapine facilitates oligodendrocyte development and prevents mice from myelin breakdown and behavioral changes

Recent neuroimaging and postmortem studies have reported abnormalities in white matter of schizophrenic brains, suggesting the involvement of oligodendrocytes in the etiopathology of schizophrenia. This view is being supported by gene microarray studies showing the downregulation of genes related to oligodendrocyte function and myelination in schizophrenic brain compared to control subjects. However, there is currently little information available on the response of oligodendrocytes to antipsychotic drugs (APDs), which could be invaluable for corroborating the oligodendrocyte hypothesis. In this study we found: (1) quetiapine (QUE, an atypical APD) treatment in conjunction with addition of growth factors increased the proliferation of neural progenitors isolated from the cerebral cortex of embryonic rats; (2) QUE directed the differentiation of neural progenitors to oligodendrocyte lineage through extracellular signal-related kinases; (3) addition of QUE increased the synthesis of myelin basic protein and facilitated myelination in rat embryonic cortical aggregate cultures; (4) chronic administration of QUE to C57BL/6 mice prevented cortical demyelination and concomitant spatial working memory impairment induced by cuprizone, a neurotoxin. These findings suggest a new neural mechanism of antipsychotic action of QUE, and help to establish a role for oligodendrocytes in the etiopathology and treatment of schizophrenia.

KKHA-761, a potent D3 receptor antagonist with high 5-HT1A receptor affinity, exhibits antipsychotic properties in animal models of schizophrenia

KKHA-761, 1-{4-[3-(3,4-dimethoxy-phenyl)-isoxazol-5-yl]-butyl}-4-(2-methoxy-phenyl)-piperazine, has a high affinity (Ki=3.85 nM) for human dopamine D3 receptor with about 70-fold selectivity over the human dopamine D(2L) receptor (Ki=270 nM). KKHA-761 also showed high affinity for cloned human 5-HT1A receptor (Ki=6.4 nM). KKHA-761 exhibited D3 and 5-HT1A receptor antagonist activities in vitro, reversing dopamine- or 5-HT-mediated stimulation of [35S]GTPrS binding. The in vivo pharmacological profile of KKHA-761 was compared with both typical and atypical antipsychotics including clozapine and haloperidol. Apomorphine-induced dopaminergic behavior, cage climbing, in mice was potently blocked by a single administration (i.p.) of KKHA-761 (ID50=4.06 mg/kg) or clozapine (ID50=4.0 mg/kg). Cocaine- or MK-801-induced hyperactivity in animals was markedly inhibited by KKHA-761 or clozapine. In addition, KKHA-761 significantly reversed the disruption of prepulse inhibition (PPI) produced by apomorphine in mice, indicating the antidopaminergic or antipsychotic activity of KKHA-761 in mice. However, KKHA-761 was inactive in the forced swimming behavioral despair model in mice, suggesting lack of antidepressant properties. KKHA-761 attenuated the hypothermia induced by a selective dopamine D3 agonist, 7-OH-DPAT, in mice, whereas clozapine enhanced it. Moderate doses of both KKHA-761 and clozapine did not increase serum prolactin levels in rats. Lower doses of, however, haloperidol significantly increased prolactin secretion. KKHA-761 did not induce cataleptic response up to 20 mg/kg, but significant catalepsy was shown at lower doses of clozapine and haloperidol. Furthermore, KKHA-761 showed a low incidence of rotarod ataxia (TD50=34.4 mg/kg, i.p.) in mice. The present results, therefore, suggest that KKHA-761 is a potent antipsychotic agent with combined dopamine D3 and serotonin 5-HT1A receptors modulation activity, which may further enhance its therapeutic potential for anxiety, psychotic depression, and other related disorders.

Acute effects of amperozide and paroxetine on social cohesion in male conspecifics

The effects of acute administration of the selective 5-hydroxytrypamine (5-HT; serotonin) uptake inhibitor, paroxetine, and the potent 5-HT(2A) receptor antagonist, N-ethyl-4-[4',4'-bis(rho-flourophenyl)butyl]-1-piperazinecarboxamide (amperozide) on social cohesion was determined by using a tether paradigm, in which the movement of one of a pair of rats was restricted to one-half of an observation chamber. Administration of 0.1mg/kg paroxetine, 1.0, 3.0, and 5.0mg/kg amperozide but neither 1.0 nor 10.0mg/kg paroxetine increased time spent in contact with the untreated, tethered rat. Whereas only the lowest dose of paroxetine (0.1mg/kg) promoted social cohesion, all doses of amperozide (1.0, 3.0, and 5.0mg/kg) promoted social cohesion. The amperozide-induced increases in time spent in contact were greater than the paroxetine-induced increases in seconds spent in contact, regardless of dose. Acute administration of amperozide is more effective than acute administration of paroxetine in promoting social cohesion between pairs of male conspecifics. Amperozide may be an effective alternative treatment for patients with social anxiety disorder suffering from adverse side effects of paroxetine. Amperozide may prove to be a more effective treatment for social anxiety disorder than paroxetine, which is supported by our results.

The effect of serotonin(1A) receptor agonism on antipsychotic drug-induced dopamine release in rat striatum and nucleus accumbens

Serotonin (5-HT)(1A) receptor agonism may be of interest in regard to both the antipsychotic action and extrapyramidal symptoms (EPS) of antipsychotic drugs (APD) based, in part, on the effect of 5-HT(1A) receptor stimulation on the release of dopamine (DA) in the nucleus accumbens (NAC) and striatum (STR), respectively. We investigated the effect of R(+)-8-hydroxy-2-(di-n-propylamino)-tetralin (R(+)-8-OH-DPAT) and n-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]-n-(2-pyridinyl)cyclohe xanecarboxamide trihydrochloride (WAY100635), a selective 5-HT(1A) receptor agonist and antagonist, respectively, on basal and APD-induced DA release. In both STR and NAC, R(+)-8-OH-DPAT (0.2 mg/kg) decreased basal DA release; R(+)-8-OH-DPAT (0.05 mg/kg) inhibited DA release produced by the 5-HT(2A)/D(2) receptor antagonists clozapine (20 mg/kg), low dose risperidone (0.01 and 0. 03 mg/kg) and amperozide (10 mg/kg), but not that produced by high dose risperidone (0.1 and 1.0 mg/kg) or haloperidol (0.01-1.0 mg/kg), potent D(2) receptor antagonists. This R(+)-8-OH-DPAT-induced inhibition of the effects of clozapine, risperidone and amperozide was antagonized by WAY100635 (0.05 mg/kg). WAY100635 (0.1-0.5 mg/kg) alone increased DA release in the STR but not NAC. The selective 5-HT(2A) receptor antagonist M100907 (1 mg/kg) did not alter the effect of R(+)-8-OH-DPAT or WAY100635 alone on basal DA release in either region. These results suggest that 5-HT(1A) receptor stimulation inhibits basal and some APD-induced DA release in the STR and NAC, and that this effect is unlikely to be mediated by an interaction with 5-HT(2A) receptors. The significance of these results for EPS and antipsychotic action is discussed.

The effects of amperozide on cocaine-induced social withdrawal in rats

Cocaine decreases social interactions in both humans and animals, but it is not known whether the drugged animal withdraws from an undrugged conspecific, the undrugged conspecific avoids the drugged animal, or a combination of these two factors occurs. In the first experiment, the source of cocaine-induced social withdrawal was determined using a tether paradigm, in which the movement of one of the rats was restricted to one half of the observation chamber, such that the freely moving rat had the option of escaping social interactions. There were decreases in social interactions in the condition in which both rats were freely moving, and in the condition in which the undrugged rat was tethered, but not when the drugged rat was tethered and could not escape social contact. A second experiment was conducted to test the efficacy of the potent serotonin receptor antagonist, amperozide, in attenuating cocaine-induced social withdrawal using the condition in which the drugged rat was freely moving. Either amperozide (1.0, 3.0, and 5.0 mg/kg) or saline vehicle was injected into rats 1 h before receiving a 30.0 mg/kg cocaine dose. Cocaine decreased social interactions. Amperozide restored social interactions to near control levels and elevated social interactions in the animals treated with saline vehicle.

The cardiovascular effects of amperozide: interactions with cocaine

Amperozide is a 5-HT2A receptor antagonist that significantly reduces the acquisition and expression, by rats, of a cocaine conditioned place preference. In order to rule out the possibility that amperozide affects a cocaine conditioned place preference due to effects on blood pressure or heart rate, the cardiovascular effects of amperozide were investigated. Alternating cumulative doses of amperozide (0.5, 1.0, 1.5 and 2.5 mg kg(-1)) or saline and phenylephrine (8 microg kg(-1)) were administered through the femoral vein of awake freely-moving Sprague-Dawley rats and blood pressure and heart rate were recorded from the femoral artery. A single dose of cocaine (5.0 mg kg(-1)) was administered after all the amperozide or saline doses were given. Amperozide (0.5, 1.0, 1.5 and 2.5 mg kg(-1)) did not have any significant effect on blood pressure compared to the saline control treatment to the same animals. However, 0.5 mg kg(-1) amperozide significantly decreased heart rate at 5 and 10 min. after administration. but higher doses did not further depress heart rate. Amperozide did not affect the increased blood pressure and decreased heart rate caused by phenylephrine. an alpha1-adrenoceptor agonist. In addition, amperozide did not affect the cardiovascular response to an intravenous dose of 5.0 mg kg(-1) cocaine. These results suggest that amperozide does not cause direct cardiovascular effects. The mechanism by which the lowest dose of amperozide caused a decrease in heart rate is unknown. Amperozide affects neither alpha-adrenoceptor mediated vasoconstriction nor the increased sympathetic activity caused by the peripheral and central effects of cocaine. The significance of these results, in terms of locomotor activity and the cocaine conditioned place preference paradigm, is discussed.

Serotonin 5-HT2C agonists selectively inhibit morphine-induced dopamine efflux in the nucleus accumbens

In vivo microdialysis was used to compare the effects of serotonergic drugs on morphine- and cocaine-induced increases in extracellular dopamine (DA) concentrations in the rat nucleus accumbens (NAc). Systemic administration of the 5-HT2A/2C agonist, 1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane (DOI) (2.5 mg/kg, s.c. ) prevented the increase in extracellular DA in the NAc produced by morphine (5 mg/kg, i.p.). In contrast, this dose of DOI had no effect on the ability of cocaine (10 mg/kg, i.p.) to increase extracellular DA concentrations in the NAc. A 5-HT2C selective agonist, 6-chloro-2-[1-piperazinyl]-pyrazine (MK-212, 5 mg/kg, s.c.) also inhibited morphine-induced increases in extracellular DA concentrations in the NAc. Pretreatment of rats with the selective 5-HT2A antagonist, amperozide, had no effect on morphine-induced elevation of NAc DA concentrations. In order to determine if inhibition of the firing of 5-HT neurons contributes to the serotonin agonist-mediated inhibition of morphine-induced accumbens DA release, rats were pretreated with the 5-HT1A agonist, 8-OHDPAT. At a dose of 100 microg/kg (sc), 8-OHDPAT did not interfere with morphine's ability to increase DA concentrations in the NAc. These results suggest that the activation of 5-HT2C receptors selectively inhibits morphine-induced DA release in the NAc in a manner which is independent of the inhibition of 5-HT neurons.

Interaction of the novel antipsychotic drug amperozide and its metabolite FG5620 with central nervous system receptors and monoamine uptake sites: relation to behavioral and clinical effects

Behavioral, biochemical, and electrophysiological studies suggest that amperozide affects mesolimbic and mesocortical dopamine neurotransmission. The receptor binding profile of amperozide is discussed and related to behavioral and clinical, i.e., antipsychotic, effects of the drug. As previously reported, amperozide displayed high affinity for serotonin 5-HT2A receptors (Ki = 16 nmol/L), and moderate affinity for striatal dopamine D2 (Ki = 540 nmol/L) and cortical alpha 1-adrenergic receptors (Ki = 172 nmol/L). In the present study amperozide displayed low affinity for several serotonin receptor subtypes as well as for the dopamine D4 receptor transfected in COS7 cells (Ki D4.2 = 769 nmol/L and Ki D4.4 = 384 nmol/L). Amperozide was very weak or did not interact with several other receptor species including adrenergic, histaminergic, muscarinic, benzodiazepine, gamma-aminobutyric acid, amino acid, opiate, and Ca channels; however, amperozide was found to compete for [3H]paroxetine binding for the serotonin transporter in the nanomolar range (Ki = 49 nmol/L). In vitro and in vivo binding potency of amperozide correlates best with behavioral effects, indicating 5-HT2A antagonism, although serotonin uptake inhibition may contribute to the effects of amperozide on dopamine neurotransmission. The metabolite of amperozide, FG5620, displayed 5-10 times lower pharmacologic activity than amperozide. These properties of amperozide may suggest that the antipsychotic effects of amperozide are mediated by 5-HT2A receptors, although 5-HT uptake inhibition and alpha 1-adrenergic receptor-mediated effects may be considered, particularly at higher doses.

Effect of chronic antipsychotic drug treatment on preprosomatostatin and preprotachykinin A mRNA levels in the medial prefrontal cortex, the nucleus accumbens and the caudate putamen of the rat

In situ hybridization histochemistry was used to study the expression of preprosomatostatin (PPSOM) and preprotachykinin A (PPT-A) mRNA in the medial prefrontal cortex (mPFC), the nucleus accumbens (NAC) and the caudate putamen (CP) of the rat after chronic (21 days) treatment with the classical antipsychotic drug haloperidol (1 mg/kg i.p.), the atypical antipsychotic drugs clozapine (15 mg/kg i.p.) and amperozide (5 mg/kg i.p.), and the selective dopamine (DA)-D2/D3 receptor antagonist raclopride (2 mg/kg i.p.). Whereas amperozide markedly elevated the numerical density of PPSOM mRNA expressing neurons in the mPFC (52%), the other drugs did not significantly affect PPSOM mRNA levels in any of the brain regions studied. Amperozide also altered PPT-A mRNA expression in the mPFC, i.e. a decrease (22%) was found. Of the other drugs tested only haloperidol significantly decreased PPT-A mRNA levels in the NAC shell (14%), in the dorso-lateral CP (19%) and in the medial CP (15%). In view of the differences between amperozide and the other drugs studied, as regards both pre-clinical and clinical characteristics, we suggest that the specific effects of amperozide on PPSOM and PPT-A mRNA in the mPFC may be related to its 5-HT releasing action in the frontal cortex, an effect possibly caused by its alpha2-adrenoceptor blocking activity. This effect, in turn, may be related to an antidepressant-like action that this compound exhibits in animal studies. The decrease in PPT-A mRNA levels seen after the haloperidol treatment is probably due to its potent DA-D2 receptor antagonism and may be related to side-effects, rather than therapeutic effects of this drug.

Ritanserin administration potentiates amphetamine-stimulated dopamine release in the rat prefrontal cortex

1. Administration of serotonin 5-HT2 receptor antagonists increases the basal release of dopamine in the mesocorticolimbic pathway. 2. Treatment with dopamine D2 receptor antagonists increases impulse-dependent basal dopamine release in the nigrostriatal pathway. D2 antagonists also potentiate carrier-mediated increases in DA efflux from this pathway. 3. The present study compared the effects of a 5-HT2A/C antagonist (ritanserin) and a D2 antagonist (haloperidol) on carrier-mediated (amphetamine-induced) DA release in the mesocortical system. 4. In vivo microdialysis was used to recover extracellular fluid from the medial prefrontal cortex of conscious rats. Samples were then assayed for dopamine content by HPLC with electrochemical detection. Haloperidol or ritanserin were administered systemically (i.p.) 30 min before d-amphetamine (5.0 mg/kg i.p.). 5. Results demonstrated that 5.0 mg/kg ritanserin, but not 1.0 mg/kg, potentiated amphetamine-induced DA release in the prefrontal cortex. Similar to previous findings in the striatum, haloperidol (1.0 mg/kg) also augmented amphetamine-stimulated DA efflux in the cortex. 6. These results suggest that 5-HT2 and D2 receptor antagonists increase impulse-mediated dopamine release in the rat prefrontal cortex which in turn potentiates carrier-mediated release.

Differential actions of typical and atypical antipsychotic drugs on dopamine release in the core and shell of the nucleus accumbens

The effects of acute administration of typical and atypical antipsychotic drugs on extracellular dopamine (DA) concentrations in brain were examined in two subdivisions of the nucleus accumbens (NAC), the core and the shell, which are largely associated with motor control and limbic functions, respectively, by using in vivo differential normal pulse voltammetry in anesthetized, pargyline pretreated rats. The following drugs were studied: haloperidol (0.1 and 1.0 mg/kg), clozapine (1.0 and 5.0 mg/kg), amperozide (1.0 and 2.0 mg/kg), risperidone (0.1 and 1.0 mg/kg), the selective 5-HT2A/5-HT2C receptor antagonist ritanserin (1 mg/kg) and the selective DA-D2/D3 receptor antagonist raclopride (10 and 320 micrograms/kg). Drugs with predominantly high 5-HT2 receptor antagonistic action, such as amperozide and ritanserin, as well as low doses of either risperidone or clozapine increased DA concentrations to a greater extent in the shell than in the core subdivision of the NAC. In contrast, drugs with a more potent D2 receptor antagonistic action, such as haloperidol and raclopride, as well as high doses of either risperidone or clozapine, elicited a larger DA increase in the core than in the shell. Consequently, atypical antipsychotics characterized by potent 5-HT2 receptor antagonism can be differentiated from typical antipsychotic drugs on the basis of their preferential effect on DA transmission in the shell region of the NAC.

Synthesis of dopamine and 5-HT in anatomical regions of the rat's brain is unaffected by sustained infusion of amperozide

The 5-HT2A antagonist, amperozide, is considered to be a potentially useful drug for the treatment of substance abuse. The effects of this drug on the Sprague-Dawley rat were examined on the synthesis of dopamine and serotonin (5-HT) as well as on the intakes of food and water and the level of body weight. Amperozide was delivered subcutaneously by osmotic minipump in doses of 2.5 mg/kg or 5.0 mg/kg per day for 7 days. After injection of 100 mg/kg NSD-1015, each brain was dissected post mortem into midbrain, pons, hypothalamus, septum, nucleus accumbens, striatum, frontal cortex and the hippocampus. Neither concentration of amperozide altered the synthesis of dopamine or 5-HT, as measured in terms of the formation of 1-3,4-dihydroxyphenylalanine (L-DOPA) and 5-hydroxytryptophan (5-HTP), respectively, in any of the 8 brain regions analyzed. Both doses of amperozide reduced food intake by 20% within 24 hr after implantation of the pumps, but feeding resumed postoperatively at the control level within 48 hr. Amperozide affected neither the intake of water nor the level of body weight. The lack of effect on the synthesis of dopamine and 5-HT and the absence of side effects on the intakes of food and water suggest that amperozide may be a specific agent for suppressing alcohol drinking.

Systemic administration of amperozide, a new atypical antipsychotic drug, preferentially increases dopamine release in the rat medial prefrontal cortex

The putative atypical antipsychotic drug amperozide (APZ) shows high affinity for serotonin 5-HT2 receptors but only low affinity for dopamine (DA) D2 receptors. By employing microdialysis, we examined the effects of APZ on extracellular concentrations of DA in the nucleus accumbens (NAC), the dorsolateral striatum (STR) and the medial prefrontal cortex (MPC) of awake rats. A 5.0 mg/kg (SC) dose of APZ failed to affect DA concentrations in the NAC, while it increased DA outflow in the STR (by 46%) and the MPC (by 207%). A higher dose of APZ (10 mg/kg, SC) enhanced dialysate DA from the NAC and the STR by 30%, and from the MPC by 326%. Similarly, clozapine (2.5 and 10 mg/kg, SC) produced a greater release of DA in the MPC (+ 127 and + 279%) than in the NAC (+ 52 and + 98%). The selective 5-HT2 receptor antagonist ritanserin (1.5 and 3.0 mg/kg, SC) also produced a slightly higher increase of DA output in the MPC (+ 25 and + 47%) compared with the NAC (+ 19 and + 21%). In contrast, the selective D2 receptor antagonist raclopride (0.5 and 2.0 mg/kg, SC) increased DA release in the NAC (+ 65 and + 119%) to a greater extent than in the MPC (+ 45 and + 67%). These data suggest that the 5-HT2 receptor antagonistic properties of APZ and clozapine may contribute to their preferential effects on DA transmission in the MPC. Infusion of low doses (1, 10 microM, 40 min) of APZ through the probe in the DA terminal areas did not affect significantly DA outflow, while infusion of high doses (100, 1000 microM, 40 min) resulted in a more pronounced elevation of DA levels in the NAC (up to 961%) and the STR (up to 950%) than in the MPC (up to 316%). These findings indicate that the selective action of systemically administered APZ on DA in the MPC is most likely mediated at a level other than the terminal region. Taken together, the present results provide support for the notion that 5-HT2 receptor antagonism may be of considerable significance for the action of atypical antipsychotic drugs on mesolimbocortical dopaminergic neurotransmission.

Effects of amperozide on schedule-induced polydipsia in rats

Schedule-induced polydipsia occurs when food-deprived rats are exposed to a fixed-interval feeding schedule (FI = 60 s) for 1 h every day. Amperozide, a novel antipsychotic drug with a strong affinity for the 5-HT2 receptor, was injected i.p. after completion of the requisite training sessions. The experimental rationale is that although the intensity of licking behavior in schedule-induced polydipsia can be taken as an index for anxiety, the drug-induced motor dysfunction should be assessed. In experiment 1, we tested the effect of amperozide on schedule-induced polydipsia at doses of 2, 4, and 8 mg/kg. The data showed that each dose significantly diminished the amount of licking and water intake. The number of presses decreased only at the dose of 8 mg/kg. During five post-treatment daily sessions for 5 days, these three measures returned to normal levels except that the number of pellets earned during the sessions did not significantly change. In addition, the number of presses showed a rebound after the termination of amperozide administration. In experiment 2, in addition to the total water intake, number of licks, pellets earned and presses, we also analyzed the postpellet temporal variation in the number of licks and presses in each schedule-induced polydipsia session. The drug was stopped for one day after each dose of 0.2, 0.4, 0.8 and 1.6 mg/kg of amperozide. The data showed that doses from 0.2 to 0.8 mg/kg did not alter any measure in drug-treated sessions and that the dose of 1.6 mg/kg decreased the number of licks and water intake.(ABSTRACT TRUNCATED AT 250 WORDS)

Blockade of striatal 5-hydroxytryptamine2 receptors reduces the increase in extracellular concentrations of dopamine produced by the amphetamine analogue 3,4-methylenedioxymethamphetamine

5-Hydroxytryptamine2 (5-HT2) receptor antagonists have been shown to interfere with the stimulation of striatal dopamine synthesis and release produced by the amphetamine analogue 3,4-methylenedioxymethamphetamine (MDMA). To localize the receptors responsible for the attenuation of MDMA-induced release, 5-HT2 receptor antagonists were infused via the microdialysis probe directly into the brains of awake, freely moving rats before the systemic administration of MDMA. Intrastriatal infusions of the selective 5-HT2 antagonist MDL 100,907 produced a concentration-dependent inhibition of MDMA-induced dopamine release. Similar results were observed with intrastriatal infusions of the 5-HT2 antagonist amperozide. In contrast, infusion of MDL 100,907 into the mid-brain region near the dopaminergic cell bodies was without effect on the MDMA-induced elevation of extracellular dopamine in the ipsilateral striatum. Neither antagonist attenuated basal transmitter efflux nor the MDMA-stimulated release of [3H]dopamine from striatal slices in vitro indicating that the in vivo effect of the antagonists was not due to inhibition of the dopamine uptake carrier. Intrastriatal infusion of tetrodotoxin reduced both basal and MDMA-stimulated dopamine efflux and eliminated the effect of intrastriatal MDL 100,907. The results indicate that 5-HT2 receptors located in the striatum augment the release of dopamine produced by high doses of MDMA. Furthermore, these 5-HT2 receptors appear to be located on nondopaminergic elements of the striatum.

The limbic functional selectivity of amperozide is not mediated by dopamine D2 receptors as assessed by in vitro and in vivo binding

Behavioural, biochemical and electrophysiological studies suggest that amperozide affects mesolimbic dopamine neurotransmission. Amperozide is a potent 5-HT2, receptor antagonist with only a moderate affinity for rat brain dopamine D2 receptors. The brain regional dopamine D2 receptor binding properties of amperozide were investigated by using in vitro and in vivo radioligand binding techniques. Amperozide displaced [3H]spiroperidol binding from rat striatal and limbic dopamine D2 receptors with moderate affinity (Ki = 540 +/- 118 nM and Ki = 403 +/- 84 nM, respectively). The dopamine D2 receptor antagonist l-sulpiride and the agonist dopamine did not show different affinity in the two brain regions. Amperozide potently displaced in vivo [3H]spiroperidol binding in rat frontal cortex (ID50 = 1.4 mg/kg s.c.) but was devoid of effect in striatum, olfactory tubercle and nucleus accumbens (ID50 > 100 mg/kg s.c.). Chronic administration of amperozide (5 mg/kg p.o.) for three weeks did not result in any change of maximal dopamine D2 receptor number in either striatal or limbic tissue. The effects of amperozide on dopamine neurotransmission are thus not likely to occur by a direct interaction with dopamine D2 receptors in either striatal or limbic tissue. The functional limbic selectivity might rather be mediated by serotoninergic pathways.

Amperozide, a 5-HT2 antagonist, attenuates craving for cocaine by rats

Amperozide, a novel 5-HT2 receptor antagonist with little affinity for the dopamine receptor, suppresses the intake of alcohol in rats without affecting food intake or inducing other side effects. Because of these actions, amperozide was examined for its efficacy on the oral preference by the rat for a solution of cocaine. In this study, rats were selected for their voluntary consumption of at least 10 mg/kg of cocaine per day in a two-choice paradigm. A solution of 0.02% to 0.06% cocaine plus 0.03% saccharin in water was offered to each animal simultaneously with a solution of only 0.03% saccharin in water. The consumption of food and both fluids, as well as body weight, was recorded daily for three successive periods: 4 days of pretreatment baseline; 3 days during injections of either amperozide or the saline vehicle solution; and 4 days postinjections. Amperozide was administered SC twice daily in a dose of 0.5, 1.0, or 2.5 mg/kg. The volitional intake of cocaine was significantly reduced not only during the 3-day period of injections of amperozide but also during the 4-day posttreatment period. Amperozide exerted little or no effect on the intake of food or on body weight. Radioligand binding experiments confirmed that amperozide has at least a twentyfold greater affinity for 5-HT2 receptors in the frontal cortex of the rat, as compared to striatal DA1 and DA2 receptors, with the proportion value similar to that of the 5-HT2 receptor antagonist, ritanserin.(ABSTRACT TRUNCATED AT 250 WORDS)

5-HT2 receptor blockade by amperozide suppresses ethanol drinking in genetically preferring rats

Previously, it was shown that the unique diphenylbutylpiperazinecarboxamide derivative, amperozide (FG 5606), inhibits the volitional drinking of ethanol induced in the rat by the inhibitor of aldehyde dehydrogenase, cyanamide. In this study, the efficacy of this long-acting psychotropic agent and potent 5-hydroxytryptamine2 (5-HT2) receptor antagonist was examined in the genetic line of ethanol-preferring (P) and -nonpreferring (NP) rats. In both lines, the pattern of drinking of ethyl alcohol was determined by a standard preference test for 3-30% ethanol vs. water. Then, the maximally preferred concentration of ethanol was determined for each individual, which ranged from 9-15% for P rats and 9-13% for NP animals. After a 4-day predrug test, either the saline control vehicle or amperozide was administered SC b.i.d. at 1600 and 2200 h. The drug was given over a 3-day period in one of three doses: 0.5, 1.0, or 2.5 mg/kg. The intake of ethanol of P rats was reduced significantly in a dose-dependent manner in terms of both absolute g/kg and proportion of ethanol to water during injections of amperozide. The same doses of amperozide had no effect on the low intake of ethanol in NP rats. The saline control vehicle also did not alter the consumption of ethanol of P or NP rats. Further, neither the consumption of food nor level of body weight was affected by amperozide either during or after its administration. These results demonstrate that in the individual predisposed genetically to drink ethanol amperozide exerts a palliative effect on the aberrant preference for ethanol consumed in a pharmacologically significant amount. Presently, dopaminergic and serotonergic synapses in the brain are implicated in the genetic differences in the patterns of ethanol consumption that distinguish the P from the NP line of rats. Because amperozide influences the functional activity of both dopaminergic and serotonergic neurons in the mesolimbic system, it is envisaged that the drug attenuates ethanol drinking by way of its direct action on these neurons.

Failure of the 5-HT2 receptor antagonist, ritanserin, to alter preference for alcohol in drinking rats

The purpose of this study was to determine whether the 5-HT2 receptor antagonist, ritanserin, possesses the same sort of efficacy as another central 5-HT2 antagonist, amperozide, in reducing the pharmacologically induced preference for ethyl alcohol in the rat. Following the repeated administration of the inhibitor of aldehyde dehydrogenase, cyanamide, the preference for alcohol vs. water was determined in each of 20 Sprague-Dawley rats by a standard test using 3-30% concentrations. Then, each rat was offered water and its maximally preferred concentration of alcohol, which ranged from 9-15% and was consumed at a mean of 5.02 +/- 0.44 g/kg per day. After a 4-day predrug control test, either the saline control solution or 0.1, 0.3, or 1.0 mg/kg ritanserin was administered SC at 1600 h over 3 days. The daily intakes of alcohol of rats both during and after treatment with ritanserin were unchanged in terms of absolute g/kg and proportion of alcohol to total fluid consumed. Similarly, the control saline also was without any effect on alcohol consumption. Neither the consumption of food and total fluids nor the level of body weight was affected by these doses of ritanserin. Because our findings fail to coincide with previous reports on the effect of ritanserin on alcohol preference, it is envisaged that a methodological difference in earlier experimental procedures, such as the use of a weak 3% concentration of alcohol, could explain the discrepancy. Further, the present results contrast with the prolonged reduction in drinking produced by another 5-HT2 receptor antagonist, amperozide, which also acts centrally on dopaminergic neurons in the limbic system.(ABSTRACT TRUNCATED AT 250 WORDS)

Irreversible suppression of alcohol drinking in cyanamide-treated rats after sustained delivery of the 5-HT2 antagonist amperozide

The purpose of this study was to evaluate the long-term effect of sustained treatment with amperozide, which has been shown to attenuate the volitional drinking of ethyl alcohol in the rat without side effects. Preference for alcohol first was induced pharmacologically in Sprague-Dawley rats by the inhibitor of aldehyde dehydrogenase, cyanamide, administered in a dose of 10 mg/kg twice daily for 3 days. Then following a standard preference test, each rat was offered water and its maximally preferred concentration of alcohol which ranged from 7% to 15%. Following a 4-day pre-drug test, saline control vehicle or amperozide was administered for 7 days by an osmotic minipump implanted in the intrascapular space. A single dose of 208 micrograms/kg/h (i.e., 5.0 mg/kg/day) was selected on the basis of a prior dose response study of amperozide. During the interval of sustained release of amperozide, the consumption of alcohol declined significantly in terms of both absolute g/kg intake and proportion of alcohol to water. When the preference of the rats was retested at 4, 30, 70, 110, and 140 day intervals after the pump had exhausted amperozide, the absolute g/kg consumption of alcohol continued to decline significantly. Unlike other drugs, amperozide did not produce any side effects, particularly on the intake of food or water or on body weight, which suggests a pharmacological specificity of its action.(ABSTRACT TRUNCATED AT 250 WORDS)

The role of serotonin in schizophrenia: an overview of the nomenclature, distribution and alterations of serotonin receptors in the central nervous system

Serotonin is a neurotransmitter that is widely distributed throughout the central nervous system. The role of serotonin in schizophrenia is still unclear. Postmortem studies of serotonin receptor subtypes in schizophrenia have been inconclusive for the most part. The most promising findings involve a reduction in 5-HT2 receptors and 5-HT reuptake sites in the prefrontal cortex of schizophrenic patients. In this paper we review the function, distribution and pharmacological characteristics of serotonin receptors. Postmortem studies are also reviewed, focusing upon the role of these receptors in schizophrenia.

Effects of amperozide on psychostimulant-induced hyperlocomotion and dopamine release in the nucleus accumbens

N-Ethyl-4-[4',4'-bis(p-fluorophenyl)-butyl]-1-piperazine carboxamide [amperozide (APZ)] is a novel atypical neuroleptic that appears to selectively act on the limbic system. The present study investigated behavioral and biochemical effects of APZ on either d-amphetamine (AMPH)- or cocaine (COC)-treated rats. Behavior was assessed by locomotor activity measurements. Compared to saline controls, APZ (5 and 10 mg/kg, SC) decreased spontaneous locomotion. AMPH (1.0 mg/kg, SC)- or COC (10 mg/kg, IP)-induced hyperlocomotion was markedly reduced by APZ administered 20 min earlier. Biochemical data were obtained by in vivo microdialysis in freely moving animals. APZ dose dependently increased interstitial concentrations of dopamine (DA, +25%) and its metabolite, homovanillic acid (HVA, +20%), in the nucleus accumbens (NAC). While either AMPH or COC alone increased DA levels (450 and 270%, respectively), pretreatment with APZ had no effect on these increases. In contrast, APZ pretreatment dose dependently attenuated the reduction of DA metabolites induced by both AMPH and COC. Thus, APZ blocked hyperlocomotion induced by psychostimulants without producing correlative changes in DA concentrations in the NAC.

Selective reduction by the 5-HT antagonist amperozide of alcohol preference induced in rats by systemic cyanamide

This investigation was undertaken to determine the effect of a unique psychotropic agent on the volitional drinking of alcohol induced pharmacologically in the rat by an inhibitor of aldehyde dehydrogenase. Following administration of cyanamide in a dose of 10 mg/kg twice daily for 3 days, the pattern of drinking of ethyl alcohol was determined in each of 12 Sprague-Dawley rats by means of a standard preference test for 3-30% alcohol vs. water. Then, each rat was offered water and its maximally preferred concentration of alcohol, which ranged from 7-15%. After a 4-day predrug test, either the saline control vehicle or the diphenylbutylpiperazinecarboxamide derivative, amperozide, was administered subcutaneously. The injections of amperozide were given b.i.d. at 1600 and 2200 h over 3 days in a dose of 0.5, 1.0, or 2.5 mg/kg. The intake of alcohol during the sequence of amperozide injections was significantly reduced in a dose-dependent manner in terms of both absolute g/kg and proportion of alcohol to water intake, whereas the saline control vehicle was without any effect on alcohol consumption. Although the highest dose of amperozide reduced the total intake of fluid due to the sharp decline in alcohol drinking, neither the consumption of food nor level of body weight was affected by any dose of the drug either during or after its administration. Because amperozide acts centrally on the synaptic activity of dopaminergic and serotonergic neurons in limbic system structures, it is envisaged that the drug ameliorates the aberrant drinking of alcohol by virtue of a direct effect on either one or both of these classes of neurons.(ABSTRACT TRUNCATED AT 250 WORDS)

Amperozide, a Novel Antipsychotic Drug, Inhibits the Ability of d-Amphetamine to Increase Dopamine Release In Vivo in Rat Striatum and Nucleus Accumbens

The in vivo effects of amperozide, a novel atypical antipsychotic drug, on the release of dopamine (DA) and the output of its metabolite, 3,4-dihydroxyphenylacetic acid (DOPAC), were investigated in the striatum and the nucleus accumbens of awake, freely moving rats using microdialysis. Amperozide (2-10 mg/kg, s.c.) significantly increased extracellular levels of DA in both the striatum and nucleus accumbens in a dose-dependent manner. It had a similar but lesser effect on extracellular DOPAC levels in both regions. d-Amphetamine (2 mg/kg, s.c.) alone produced a very large (43-fold) increase in DA release, together with a 70% decrease in DOPAC levels in both the striatum and the nucleus accumbens. Amperozide (1-5 mg/kg, s.c.) 30 min before d-amphetamine (2 mg/kg) dose-dependently attenuated d-amphetamine-induced DA release but had no effect on the d-amphetamine-induced decrease in extracellular DOPAC levels in both regions. The effect of amperozide on d-amphetamine-induced DA release in the nucleus accumbens may explain the inhibitory effect of amperozide on amphetamine-induced locomotor activity. However, the failure of amperozide to block amphetamine-induced stereotypy, despite marked inhibition of striatal DA release, suggests the need to reexamine the importance of striatal DA for amphetamine-induced stereotypy.

Effect of amperozide on rat cortical 5-HT2 and striatal and limbic dopamine D2 receptor occupancy: implications for antipsychotic action

Amperozide (FG 5606, N-ethyl-4-[4',4'-bis(p-fluorophenyl)butyl]-1-piperazine-carboxamide) is an atypical antipsychotic drug which has relatively weak in vitro affinity for striatal dopamine2 (D2) receptors and strong affinity for cortical 5-HT2 receptors. The in vivo affinity for 5-HT2 binding sites in rat cortex was 1.1 mg/kg. In striatum or olfactory tubercle, doses of amperozide up to 40 mg/kg did not displace radioligand binding to D2 receptors. Amperozide, haloperidol and ritanserin had similar in vivo potency in blocking the 5-HT2 binding site, but only haloperidol displaced D2 receptor binding. Based on the clinically effective dose of amperozide (0.14-0.28 mg/kg per day), it is suggested that the antipsychotic effect of amperozide is related, in part, to its in vivo interaction with the 5-HT2 receptor and that amperozide cannot be expected to exert its antipsychotic action by blockade of D2 receptors in the striatum or limbic regions.

The effect of chronic atypical antipsychotic drugs and haloperidol on amphetamine-induced dopamine release in vivo

The effect of chronic administration of antipsychotic drugs (21 days in drinking water followed by 3 days drug washout) on the D-amphetamine (1.0 mg/kg, s.c.)-induced increase in dopamine (DA) release in the striatum and the nucleus accumbens of awake, freely-moving rats was investigated with microdialysis. Chronic administration of haloperidol, a typical antipsychotic, (0.5 mg/kg/day), decreased basal extracellular DA release in the striatum and the nucleus accumbens but did not affect D-amphetamine-induced DA release in either region. In marked contrast, chronic administration of three atypical antipsychotic drugs: amperozide (2 mg/kg/day), clozapine (10 mg/kg/day) and melperone (2 mg/kg/day) increased basal extracellular DA and enhanced D-amphetamine-induced DA release in the striatum. In the nucleus accumbens, basal extracellular DA was decreased by chronic amperozide, unchanged by chronic clozapine and increased by chronic melperone. Most significantly, D-amphetamine-induced DA release was inhibited by chronic amperozide or clozapine, but unaffected by chronic melperone in this region. These results suggest that atypical antipsychotic drugs can alter DA release in a region specific manner. In particular, attenuation of amphetamine-like stimulation of DA release with reduced basal DA release in the nucleus accumbens could contribute to the antipsychotic action of amperozide which has a very weak affinity for D2 DA receptors.

Amperozide and clozapine but not haloperidol or raclopride increase the secretion of oxytocin in rats

The aim of the present study was to investigate whether amperozide, an antipsychotic drug which possesses anti-aggressive and anxiolytic-like properties, stimulates the secretion of oxytocin and if so, by which receptor mechanism. For this purpose, female or male Sprague Dawley rats were given amperozide (0.5, 2.5 and 5.0 mg/kg IP), ritanserin (5.0 mg/kg), raclopride (2.0 mg/kg) and prazosin (1.0 mg/kg) and were subsequently decapitated for collection of blood (30 and 120 min) after injection. Oxytocin levels were measured with radioimmunoassay. Amperozide 2.5 and 5 mg/kg increased plasma levels of oxytocin significantly (P < 0.05 and < 0.001). The effect appeared maximal about 30 min after injection of the drug and oxytocin levels were almost back to basal within 120 min. Similar effects were obtained in female and male rats as well as in animals that were freely fed or food deprived for 24 h. CSF levels of oxytocin were also increased. Ritanserin, a 5-HT2-receptor antagonist but not the D2 receptor antagonist raclopride or the alpha 1-adrenoceptor antagonist prazosin stimulated oxytocin release. In addition, clozapine, a neuroleptic with potent HT2-antagonistic properties, was a potent releaser of oxytocin, whereas haloperidol was without effect. A possible role for oxytocin in the behavioural effects of amperozide and clozapine remains to be explored.

The effect of amperozide, a new antipsychotic drug, on plasma corticosterone concentration in the rat

Amperozide is an atypical antipsychotic drug with high affinity for the serotonin 5-HT2 receptor but with low affinity for the dopamine D1 and D2 receptors. Amperozide dose-dependently increased the level of plasma corticocorticosterone in the rat. The effect of amperozide on plasma corticosterone was not inhibited by pretreatment with the 5-HT1A receptor antagonist pindolol or the 5-HT2 receptor antagonist ritanserin. Nor was it inhibited by the dopamine D2 receptor antagonist haloperidol. In contrast to ritanserin, amperozide did not antagonize plasma corticosterone elevation elicited by the serotonin receptor agonist MK-212. Similar to the serotonin uptake inhibitor fluoxetine, amperozide (0.5 mg/kg) significantly (p < 0.05) blocked p-chloroamphetamine (PCA) induced corticosterone release 4 and 16 hrs after amperozide administration. However, amperozide significantly increased the plasma corticosterone concentration also in rats pretreated with parachlorophenylalanine (PCPA). These data suggest that other mechanisms than a 5-HT uptake inhibitory effect are involved in the acute stimulation of corticosterone by amperozide.

Mechanisms of action of atypical antipsychotic drugs. Implications for novel therapeutic strategies for schizophrenia

The mechanisms which contribute to the actions of atypical antipsychotic drugs, such as clozapine and the putative atypical agents remoxipride and raclopride, are reviewed. Examination of available preclinical and clinical data leads to two hypotheses concerning the mode of action of atypical antipsychotic drugs. The first hypothesis is that antagonism of the dopamine D2 receptor is both necessary and sufficient for the atypical profile, but that interaction with subtypes of the D2 receptor differentiates typical from atypical antipsychotic drugs. The second hypothesis has been previously advanced, and suggests that a relatively high ratio of serotonin 5-HT2:dopamine D2 receptor antagonism may subserve the atypical profile. It seems likely that the atypical antipsychotic drug profile may be achieved in more than one way.

Amperozide, a putative anti-psychotic drug: uptake inhibition and release of dopamine in vitro in the rat brain

The effects of amperozide (a diphenylbutylpiperazinecarboxamide derivative) on the uptake and release of 3H-dopamine in vitro were investigated. Amperozide inhibited the amphetamine-stimulated release of dopamine from perfused rat striatal tissue in a dose-dependent manner. With 1 and 10 microM amperozide there was significant inhibition of the amphetamine-stimulated release of dopamine, to 44 and 36% of control. In contrast, 10 microM amperozide significantly strengthened the electrically stimulated release of dopamine from perfused striatal slices. Amperozide 1-10 microM had no significant effect on the potassium-stimulated release of dopamine. 10 microM amperozide also slightly increased the basal release of 3H-dopamine from perfused striatal tissue. These effects on various types of release are similar to those reported for uptake inhibitors (Bowyer et al, 1984). The uptake of dopamine in striatal tissue was inhibited by amperozide with IC50 values of 18 microM for uptake in chopped tissue and 1.0 microM for uptake in synaptosomes. Amperozide also inhibited the uptake of serotonin in synaptosomes from frontal cortex, IC50 = 0.32 microM and the uptake of noradrenaline in cortical synaptosomes, IC50 = 0.78 microM. In conclusion, amperozide shows uptake-inhibiting properties in both release and uptake studies done in vitro on the rat. In the in vivo studies, however, amperozide differs from dopamine uptake inhibitors.

Effect of amperozide on the synthesis and turnover of monoamines in rat brain

The effects of amperozide on the synthesis and the turnover of monoamines in different brain regions of the rat were determined using both ex vivo and in vivo biochemical techniques (i.e. post-mortem measurements of the tissue levels by HPLC-EC, and direct measurements with the in vivo voltammetry technique). It was found that amperozide slightly increased the DOPA accumulation and the DOPAC content in limbic brain areas but not in the striatum. The DOPA accumulation was also slightly increased in the noradrenaline rich cortical region indicating increased synthesis of noradrenaline. Furthermore, amperozide increased the utilization of noradrenaline after tyrosine hydroxylase inhibition by alpha-methyl-p-tyrosine. The synthesis of 5-HT was not significantly altered by amperozide. In conclusion, the biochemical data obtained in this study suggest that amperozide produces preferential effects on the mesolimbic dopaminergic system. In addition, amperozide also interacts with the noradrenergic system.

The effect of amperozide on uptake and release of [3H]-dopamine in vitro from perfused rat striatal and limbic brain areas

Amperozide, a putatively antipsychotic drug, was studied for its effects on uptake and release of [3H]-dopamine in rat brain in vitro. Amperozide inhibited uptake of [3H]-dopamine in striatal chopped tissue in vitro with an IC50 of 18 microM. It also increased basal release of [3H]-dopamine from perfused rat striatal and limbic tissue in vitro at concentrations above 5 microM. Release of [3H]-dopamine from perfused rat striatal and limbic tissue stimulated with 5 microM amphetamine, was inhibited by 1 microM amperozide to 46%. No significant difference was found for the effect of amperozide on in vitro release of [3H]-dopamine from corpus striatum compared to tissue from limbic brain regions; neither on basal release nor an amphetamine-stimulated release of dopamine.

Amperozide and emotional behaviour

The new putatively antipsychotic drug amperozide is characterized pharmacologically by a specific limbic mode of action. Thus amperozide is a potent antagonist of muricidal behaviour (ED50 = 0.16 mg/kg) as well as aggression between isolated male mice. Although amperozide displays anxiolytic properties in Vogel's conflict test as well as an antidepressive effect in the despair test, the drug does not interfere with motor coordination or cause sedation (ED50 greater than 50 mg/kg). These results could make amperozide very interesting as an antipsychotic drug in the clinic, with effect on both positive and negative symptoms.

Amperozide and conditioned behaviour in rats: potentiation by classical neuroleptics and alpha-methylparatyrosine

Amperozide, a new putatively antipsychotic compound, has been evaluated for its effect on conditioned avoidance response and food-reinforced lever-pressing. Given alone, amperozide was almost equipotent to clozapine, but less potent than haloperidol in both test models. It was found that there was a statistically significant synergism, in these two models, between amperozide and classical neuroleptics. Since amperozide is inactive in behavioural tests reflecting striatal dopaminergic mechanisms, the synergistic effect could be of great therapeutic value in the treatment of psychotic disorders.

Effects of amperozide on induced turning behaviour in 6-OHDA lesioned rats

The effect of amperozide on DA synapses was studied in 6-OHDA lesioned rats exhibiting a specific turning behaviour in response to the DA agonists apomorphine and pergolide or indirectly acting stimulating agents like amphetamine. Amperozide, unlike classical neuroleptics, failed to antagonize apomorphine induced turning behaviour in a regular fashion, but showed pergolide antagonism within the D2 receptor selective dose range, suggesting a type of selective interference with dopaminergic nerve transmission which differs from that caused by classical neuroleptics. Furthermore, amperozide antagonized the turning behaviour induced by amphetamine, presumably by interfering with the availability of newly synthesized DA and NA suggesting a similar influence also on other DA releasing agents. Although amperozide potentiated the effects of alpha-MPT, the drug seemed not to influence the reserpine sensitive pool of DA.