Poly(I:C) source, molecular weight and endotoxin contamination affect dam and prenatal outcomes, implications for models of maternal immune activation.

The viral mimetic polyinosinic:polycytidylic acid (poly(I:C)) is increasingly used to induce maternal immune activation (mIA) to model neurodevelopmental disorders (NDDs). Robust and reproducible phenotypes across studies are essential for the generation of models that will enhance our understanding of NDDs and enable the development of improved therapeutic strategies. However, differences in mIA-induced phenotypes using poly(I:C) have been widely observed, and this has prompted the reporting of useful and much needed methodological guidelines. Here, we perform a detailed investigation of molecular weight and endotoxin variations in poly(I:C) procured from two of the most commonly used suppliers, Sigma and InvivoGen. We demonstrate that endotoxin contamination and molecular weight differences in poly(I:C) composition lead to considerable variability in maternal IL-6 response in rats treated on gestational day (GD)15 and impact on fetal outcomes. Specifically, both endotoxin contamination and molecular weight predicted reductions in litter size on GD21. Further, molecular weight predicted a reduction in placental weight at GD21. While fetal body weight at GD21 was not affected by poly(I:C) treatment, male fetal brain weight was significantly reduced by poly(I:C), dependent on supplier. Our data are in agreement with recent reports of the importance of poly(I:C) molecular weight, and extend this work to demonstrate a key role of endotoxin on relevant phenotypic outcomes. We recommend that the source and batch numbers of poly(I:C) used should always be stated and that molecular weight variability and endotoxin contamination should be minimised for more robust mIA modelling.

Low penetration of oseltamivir and its carboxylate into cerebrospinal fluid in healthy Japanese and Caucasian volunteers.

Oseltamivir is a potent, well-tolerated antiviral for the treatment and prophylaxis of influenza. Although no relationship with treatment could be demonstrated, recent reports of abnormal behavior in young individuals with influenza who were receiving oseltamivir have generated renewed interest in the central nervous system (CNS) tolerability of oseltamivir. This single-center, open-label study explored the pharmacokinetics of oseltamivir and oseltamivir carboxylate (OC) in the plasma and cerebrospinal fluid (CSF) of healthy adult volunteers over a 24-hour interval to determine the CNS penetration of both these compounds. Four Japanese and four Caucasian males were enrolled in the study. Oseltamivir and OC concentrations in CSF were low (mean of observed maximum concentrations [C(max)], 2.4 ng/ml [oseltamivir] and 19.0 ng/ml [OC]) versus those in plasma (mean C(max), 115 ng/ml [oseltamivir] and 544 ng/ml [OC]), with corresponding C(max) CSF/plasma ratios of 2.1% (oseltamivir) and 3.5% (OC). Overall exposure to oseltamivir and OC in CSF was also comparatively low versus that in plasma (mean area under the concentration-time curve CSF/plasma ratio, 2.4% [oseltamivir] and 2.9% [OC]). No gross differences in the pharmacokinetics of oseltamivir or OC were observed between the Japanese and Caucasian subjects. Oseltamivir was well tolerated. This demonstrates that the CNS penetration of oseltamivir and OC is low in Japanese and Caucasian adults. Emerging data support the idea that oseltamivir and OC have limited potential to induce or exacerbate CNS adverse events in individuals with influenza. A disease- rather than drug-related effect appears likely.

Characterization of (R,S)-5,7-di-tert-butyl-3-hydroxy-3-trifluoromethyl-3H-benzofuran-2-one as a positive allosteric modulator of GABAB receptors.

BACKGROUND AND PURPOSE: As baclofen is active in patients with anxiety disorders, GABAB receptors have been implicated in the modulation of anxiety. To avoid the side effects of baclofen, allosteric enhancers of GABAB receptors have been studied to provide an alternative therapeutic avenue for modulation of GABAB receptors. The aim of this study was to characterize derivatives of (R,S)-5,7-di-tert-butyl-3-hydroxy-3-trifluoromethyl-3H-benzofuran-2-one (rac-BHFF) as enhancers of GABAB receptors. EXPERIMENTAL APPROACH: Enhancing properties of rac-BHFF were assessed in the Chinese hamster ovary (CHO)-Galpha16-hGABA(B1a,2a) cells by Fluorometric Imaging Plate Reader and GTPgamma[35S]-binding assays, and in rat hippocampal slices by population spike (PS) recordings. In vivo activities of rac-BHFF were assessed using the loss of righting reflex (LRR) and stress-induced hyperthermia (SIH) models. KEY RESULTS: In GTPgamma[35S]-binding assays, 0.3 microM rac-BHFF or its pure enantiomer (+)-BHFF shifted the GABA concentration-response curve to the left, an effect that resulted in a large increase in both GABA potency (by 15.3- and 87.3-fold) and efficacy (149% and 181%), respectively. In hippocampal slices, rac-BHFF enhanced baclofen-induced inhibition of PS of CA1 pyramidal cells. In an in vivo mechanism-based model in mice, rac-BHFF increased dose-dependently the LRR induced by baclofen with a minimum effective dose of 3 mg kg(-1) p.o. rac-BHFF (100 mg kg(-1) p.o.) tested alone had no effect on LRR nor on spontaneous locomotor activity, but exhibited anxiolytic-like activity in the SIH model in mice. CONCLUSIONS AND IMPLICATIONS: rac-BHFF derivatives may serve as valuable pharmacological tools to elucidate the pathophysiological roles played by GABAB receptors in the central and peripheral nervous systems.

Peripheral and central adrenoceptor modulation of the behavioural effects of clozapine in the paw test.

1. In rats, the atypical neuroleptic, clozapine, has been found to increase the hindlimb retraction time but not the forelimb retraction time, in the paw test. These parameters have predictive validity for the antipsychotic efficacy and extrapyramidal side-effects of drugs, respectively. The present study analysed to what extent drugs acting on adrenoceptors affect the behavioural effect of clozapine in the paw test. 2. The alpha 1-adrenoceptor agonist, ST 587 but not the peripherally working alpha 1-agonist, methoxamine, decreased the effect of clozapine on the hindlimb retraction time. The alpha 1-antagonist phenoxybenzamine increased this effect of clozapine, and blocked the effect of ST 587 on clozapine at low doses. Only the combination of phenoxybenzamine with clozapine produced an increase in forelimb retraction time. 3. The alpha 2-adrenoceptor agonist, clonidine, decreased the effect of clozapine on the hindlimb retraction time. This effect was neither antagonized by the alpha 2-antagonist rauwolscine nor by the alpha 1-antagonist phenoxybenzamine. Rauwolscine or the peripherally working alpha 2-antagonist L-659,066 did not influence the effect of clozapine on the hindlimb retraction time. The forelimb retraction time was not affected by any of the drug combinations. 4. In contrast to the beta 2-adrenoceptor agonist, clenbuterol, which was ineffective, the peripherally acting beta-agonist, (-)-isoprenaline, increased the effects of clozapine on the hindlimb retraction time. The beta-antagonist, (-)-propranolol as well as the peripherally acting beta-antagonist, nadolol decreased this effect of clozapine. Low doses of the peripherally acting beta 1-antagonist, atenolol, as well as low doses of the beta2-antagonist, ICI-118,551, decreased the effect of clozapine. A low dose of nadolol blocked the effect of (-)-isoprenaline on clozapine. Only the combination of clenbuterol with clozapine produced an increase in forelimb retraction time.5. It is concluded that blockade of central alpha l-adrenoceptors plays an important role in the effect of clozapine on the hindlimb retraction time. Furthermore, the effect of clozapine on the hindlimb retraction time is strongly modulated by peripheral beta 1- and/or beta 2-adrenoceptors. Given the predictive validity of the paw test, the presented data suggest that the alpha 1-adrenoceptor antagonist properties of clozapine are important for its therapeutic effects, but not for its lack of extrapyramidal side-effects.

Interactions between neuroleptics and 5-HT(1A) ligands in preclinical behavioral models for antipsychotic and extrapyramidal effects.

RATIONALE: Combining neuroleptics with 5-HT1A ligands is thought to improve the preclinical profile of neuroleptics and may be of interest in the development of new compounds that have greater therapeutic potential and/or are better tolerated. OBJECTIVE: To examine 1) the ability of 5-HT1A ligands to alter the effects of neuroleptics in preclinical models for antipsychotic potential (hindlimb retraction time in the paw test) and extrapyramidal side-effects (forelimb retraction time in the paw test; catalepsy tests), 2) the role of intrinsic activity at 5-HT1A receptors in the modulatory effects of 5-HT1A ligands, and 3) the generality of the interactions across neuroleptics. METHODS: The effects of different doses of 5-HT1A ligands with intrinsic activity ranging from high (e.g., 8-OH-DPAT) to low (e.g., WAY 100135) administered together with a fixed, high dose of the neuroleptics haloperidol, risperidone, and tropapride were examined in the paw test and on catalepsy. RESULTS: Firstly, the 5-HT1A agonists 8-OH-DPAT and ipsapirone attenuated the extrapyramidal-like effects of haloperidol and risperidone more than their therapeutic-like effects; this was not observed for tropapride, where all of its effects were markedly attenuated. Secondly, neither the weak 5-HT1A agonist WAY 100135 nor the silent antagonist WAY 100635 attenuated the effects of neuroleptics. Thirdly, neuroleptics apparently differed in their sensitivity to interactions with 5-HT1A agonists inasmuch as 8-OH-DPAT and ipsapirone attenuated the effects of tropapride on hindlimb retraction times more than those of haloperidol or risperidone. CONCLUSIONS: The present data suggest that 5-HT1A agonists with intermediate or high, but not low, intrinsic activity may abolish the extrapyramidal effects of neuroleptics. Together with results of previous studies, it appears that 5-HT1A agonists alter the antipsychotic-like effects of neuroleptics, although this may depend on the neuroleptic studied.

Repeated administration of cocaethylene induces context-dependent sensitization to its locomotor effects.

The cocaine analog, cocaethylene, has recently been identified as an active metabolite in humans consuming ethanol and cocaine. Since this compound exhibits affinity for the dopamine transporter that is more selective than that of cocaine, it is conceivable that its behavioral properties may be distinguishable from those of cocaine (cf. Elsworth et al. 1993). To investigate further the behavioral effects of cocaethylene, its ability to induce sensitization to locomotor activity in C57BL/6 mice was determined and compared with that of cocaine. In the first part of the study, mice were treated repeatedly with cocaethylene in the test environment and were then challenged with several different doses of the same drug. Repeated administration of 10, 20 or 40 mg/kg cocaethylene (IP) for 3 consecutive days produced leftward and upward shifts of the cocaethylene (2.5-56.6 mg/kg, IP) dose-effect curve on day 4. In the second part of the study, mice were treated with 20 mg/kg cocaethylene for 3 days, but were immediately placed back in their home cage following the injection: repeated administration of cocaethylene for 3 consecutive days did not significantly affect the dose-effect curve of cocaethylene (2.5-40 mg/kg, IP) on day 4. In the same paradigm, repeated administration of 20 mg/kg cocaine for 3 consecutive days produced a significant leftward shift of the cocaine (2.5-56.6 mg/kg, IP) dose-effect curve on day 4. These results confirm that cocaethylene shares a number of properties with cocaine, but also suggest that the drugs are not identical.

Effects of dopamine antagonists in a two-way active avoidance procedure in rats: interactions with 8-OH-DPAT, ritanserin, and prazosin.

Using a conditioned avoidance procedure in rats, the present study examined the ability of 8-OH-DPAT, ritanserin, and prazosin to alter the effects of the dopamine antagonists, raclopride and haloperidol, on avoidance- and on escape responding. The 5-HT1A agonist 8-OH-DPAT (0.16 mg/kg) significantly enhanced the inhibitory effects of both raclopride and haloperidol on the conditioned avoidance response and produced a small enhancement of the effects of haloperidol on escape failures. the alpha 1-adrenoceptor antagonist prazosin (0.63 mg/kg) significantly enhanced the effects of raclopride on the conditioned avoidance response, but enhanced the effects of only a single dose of haloperidol; prazosin did not alter the effects of either dopamine antagonist on escape failures. The 5-HT2 antagonist ritanserin (0.16 mg/kg) failed significantly to alter the effects of the dopamine antagonists examined here. These findings suggest that blockade of 5-HT2 receptors may not enhance the antipsychotic efficacy of D2-like antagonists. Further, they confirm previous findings with respect to interactions between 5-HT1A agonists and neuroleptics, and support the hypothesis that combined 5-HT1A agonist/D2-like antagonist properties may be of clinical importance.

The olfactory tubercle as a site of action of neuroleptics with an atypical profile in the paw test: effect of risperidone, prothipendyl, ORG 5222, sertindole and olanzapine.

The paw test was used to detect the preclinical profile (classical versus atypical) of five putative, atypical neuroleptics, namely olanzapine, sertindole, risperidone, prothipendyl and ORG 5222. In the paw test classical neuroleptics increase the hindlimb reaction time (HRT), a parameter with predictive validity for antipsychotic efficacy, at doses comparable to those necessary for increasing forelimb reaction time (FRT), a parameter with predictive validity for extrapyramidal side-effects, whereas atypical neuroleptics increase HRT at doses that are much smaller than those increasing FRT. All tested compounds showed the profile of atypical neuroleptics in the paw test. Using the FRT/HRT ratio of minimum effective doses as overall predictor of a favourable ratio of extrapyramidal and therapeutic effects of these drugs, the following order was found: olanzapine (20) > sertindole = risperidone = prothipendyl (10) > ORG 5222 (3). The ability of compounds to attenuate locomotor activity elicited either from the olfactory tubercle (10 micrograms dopamine: OT test) or from the nucleus accumbens (1 microgram ergometrine: ACC test) was used to establish whether the compounds preferentially act in one of these structures. Previous research has shown that classical neuroleptics are far less potent in the OT test than in the ACC test, whereas atypical neuroleptics are far more potent in the OT test than in the ACC test. All five agents preferentially acted in the olfactory tubercle. The order of potency in the olfactory tubercle was as follows: sertindole > ORG 5222 > risperidone > olanzapine > prothipendyl. It is concluded that risperidone, prothipendyl, ORG 5222, sertindole and olanzapine not only show the profile of atypical neuroleptics in the paw test, but also preferentially act in the olfactory tubercle, but not in the nucleus accumbens, viz. two features that they share with the atypical neuroleptics clozapine and thioridazine and with the putative, atypical neuroleptics raclopride and remoxipride.

Does crossing over repeated treatment with the dopamine reuptake inhibitors cocaine and BTCP modify their effects on cocaine-induced locomotion?

Because the dopamine reuptake inhibitors cocaine and BTCP produce different behavioral effects after repeated administration, we studied whether they could alter each other's effects by examining the effects of crossing over repeated treatment with cocaine and BTCP on cocaine-induced locomotion. Male C57BL/6 mice were treated repeatedly with cocaine or BTCP during a first phase (days 1-3) and 3 days later, treated repeatedly with the same or the other compound during a second phase (days 7-9), after which they were administered one of several doses of cocaine on the next day. Locomotor activity was assessed after every daily treatment. The results show that 1) cocaine induced sensitization to its locomotor effects, 2) cocaine-induced sensitization was not altered by subsequent repeated treatment with BTCP, 3) initial repeated treatment with BTCP induced apparent cross-tolerance to cocaine, and 4) the initial effects of repeated BTCP were not markedly altered by subsequent repeated treatment with cocaine. The results indicate that the initial effects produced by repeated cocaine or BTCP are enduring and relatively difficult to alter by crossing over repeated treatment with the other compound. Thus, sensitization to the locomotor effects of cocaine in mice appeared to be attenuated by prior repeated treatment with BTCP but not reversed when followed by repeated treatment with BTCP.

Role of striatal dopamine D2 receptors in the paw test, an animal model for the therapeutic efficacy and extrapyramidal side effects of neuroleptic drugs.

The effect of administration of the D2 antagonist sulpiride in three striatal areas (dorsal striatum, DS; nucleus accumbens, ACC; olfactory tubercle; OT) was studied in the so-called paw test. In the paw test two parameters are measured (the hindlimb retraction time (HRT) and the forelimb retraction time (FRT)) that model the therapeutic efficacy and the extrapyramidal side effects of neuroleptics, respectively. Sulpiride significantly enhanced the HRT in each of the three structures. Identical doses of sulpiride administered in the three structures produced similar effects. The FRT was enhanced after administration of sulpiride in the DS and in the ACC. The minimal effective dose was lower for the DS. Administration of sulpiride in the OT did not affect the FRT. The effects on the FRT were very slow in onset (strong effects 4 h or more following administration of sulpiride), especially in comparison to the rapid effect on FRT following systemic administration of classical neuroleptics. To analyze this slowness of effect, two additional experiments were performed: first, the inter-trial time was changed so that it was identical to that used in systemic studies; second, sulpiride was administered simultaneously in the DS and the ACC. Neither experiment produced an earlier effect on the FRT. The present data provide additional evidence for the theory that regional selectivity of drugs determines their propensity to induce extrapyramidal side effects. However, the data also suggest that the generally held view that the dorsal striatum is solely responsible for the extrapyramidal side effects of neuroleptic drugs is too simple.

The effects of antipsychotics with 5-HT(2C) receptor affinity in behavioral assays selective for 5-HT(2C) receptor antagonist properties of compounds.

Many antipsychotics have marked antagonist effects at 5-hydroxytryptamine (5-HT(2C)) receptors in vitro, which, however, have been difficult to show in behavioral assays. Here, we used two assays - hypolocomotion and hypophagia induced by the 5-HT(2C) receptor agonist 1-(3-chlorophenyl)piperazine (mCPP) - to try to characterize the 5-HT(2C) receptor antagonist properties of antipsychotics in vivo. Clozapine, olanzapine, pipamperone, and trans-5-chloro-2-methyl-2,3,3a,12b-tetrahydro-1H-dibenz-[2,3:6, 7]oxepino[4,5-C] pyrrolidino maleate (ORG 5222), modestly, but significantly, attenuated mCPP (10 mg/kg)-induced hypolocomotion. In contrast, risperidone and loxapine were inactive. The putative antipsychotic ORG 5222 significantly attenuated mCPP (5 mg/kg)-induced hypophagia, whereas the other antipsychotics were inactive. Selective antagonists at dopamine D(2)-like receptors, alpha(1)-adrenoceptors, alpha(2)-adrenoceptors, or muscarinic receptors were not able to antagonize the effects of mCPP in either assay. The results suggest that mCPP-induced hypolocomotion can be used to characterize the 5-HT(2C) receptor antagonist properties of antipsychotics, whereas mCPP-induced hypophagia appeared to be sensitive only to compounds highly selective for 5-HT(2C) receptors. Together, these assays may help to characterize functional, in vivo, 5-HT(2C) receptor antagonist properties of antipsychotics.

Effects of WAY 100635 on antipsychotic-induced catalepsy in 5-HT depleted animals: a role for tonic activation of 5-HT(1A) receptors.

We recently observed that the 5-hydroxytryptamine (5-HT)(1A) receptor antagonist N-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]-N-(2-pyridinyl)-cycloh exanecarboxamide (WAY 100635) enhanced antipsychotic-induced catalepsy, which we hypothesized to be due to a blockade of tonic 5-HT(1A) receptor activation. Here, we examined this hypothesis by studying the effects of WAY 100635 in animals that were depleted of 5-HT by repeated treatment with the 5-HT synthesis inhibitor p-chlorophenylalanine methyl ester. Depletion of 5-HT abolished the enhancement by WAY 100635 of catalepsy induced by low doses of the antipsychotics nemonapride and raclopride, in agreement with the hypothesis that WAY 100635 enhances catalepsy by blocking tonic 5-HT(1A) receptor activation. Given the predictive validity of catalepsy, these findings indicate that 5-HT(1A) receptor blockade may enhance the extrapyramidal side-effects of antipsychotics in humans.

Role of 5-HT1A receptors in the ability of mixed 5-HT1A receptor agonist/dopamine D2 receptor antagonists to inhibit methylphenidate-induced behaviors in rats.

Behavioral effects produced by the indirect-acting dopamine receptor agonist, methylphenidate (40 mg/kg i.p.) were examined in rats after administration of the 5-HT1A receptor agonists (+/-)-8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) and flesinoxan, the mixed 5-HT1A receptor agonist/dopamine D2 receptor antagonists buspirone and 1-[-4-fluorobenzoylamino)ethyl]-ethyl]-4-(7-methoxynaphthyl) piperazine (S 14506), the neuroleptics haloperidol and clozapine, and the sigma receptor ligand/partial 5-HT1A receptor agonist alpha-(4-fluorophenyl)-4-(5-fluoro-2-pyrimidinyl)-1-piperazine-butanol (BMY 14802). All of the compounds produced dose-related decreases in methylphenidate-induced stereotyped gnawing, and, as gnawing was inhibited, other methylphenidate-induced responses (i.e. sniffing, rearing and locomotion) appeared. Higher doses of haloperidol and buspirone, but none of the remaining compounds, inhibited these other responses, so that the behavior of the methyphenidate-treated animals became similar to that of normal controls. Pretreatment with the 5-HT1A receptor antagonist N-[2-4-(2-methoxyphenyl)-1-piperazinyl]-ethyl]-N-(2-pyridinyl)- cyclohexanecarboxamide (WAY-100635; 0.63 mg/kg s.c.) blocked the ability of 8-OH-DPAT, S 14506 and flesinoxan to inhibit methylphenidate-induced gnawing, demonstrating the involvement of 5-HT1A receptors in their ability to inhibit methylphenidate-induced behaviors. In contrast, pretreatment with WAY-100635 did not alter the ability of haloperidol, clozapine, buspirone, or BMY 14802 to inhibit methylphenidate-induced gnawing, or in the case of haloperidol and buspirone, to normalize behavior. The results indicate that mixed compounds with 5-HT1A receptor agonist and dopamine receptor antagonist properties can be differentiated on the basis of the ability of WAY-100635 to reverse their effects on methylphenidate-induced behaviors.

Involvement of the nucleus accumbens in oral behaviour in the freely moving rat.

The role of the nucleus accumbens in oral behaviour was examined by intra-accumbens injections of a single dose of a selective dopamine D1 receptor agonist (SKF 38393: 5 micrograms/side), a selective dopamine D2 receptor agonist (quinpirole: 10 micrograms/side), and their combination in freely moving rats. Principal factor analysis revealed four factors to be involved in the scored behaviours, two of which concerned oral behaviour: a chew factor, comprising the behaviours chew, tongue protrusion, yawn and lick, and a groom factor, with high factor loadings of tremor and groom. The two remaining factors were the circle factor comprising circle, walk and rear, and the sniff factor comprising sniff, yawn and rear. Two-way ANOVA (independent variable D1 with H2O and SKF 38393 level; independent variable D2 with H2O and quinpirole level) of the factor scores revealed that SKF 38393 and quinpirole had similar or opposite effects which were additive or antagonistic, depending on which behaviour was studied. This study demonstrates that (a) the nucleus accumbens plays a major role in the oral behaviour of freely moving rats, and (b) an integrated study of all oral behavioural elements is necessary to describe the effects of drugs on oral behaviour.

The cataleptogenic effects of the neuroleptic nemonapride are attenuated by its 5-HT1A receptor agonist properties.

The effects of the 5-HT1A receptor antagonist N-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]-N-(2-pyridinyl)-cycloh exanecarboxamide (WAY 100635) on catalepsy induced by the dopamine D2-like receptor antagonist/5-HT1A receptor agonist nemonapride were examined and compared to its effects on catalepsy induced by neuroleptics that have low affinity for 5-HT1A receptors. Nemonapride induced catalepsy in both cross-legged position and bar tests at low, but not at high doses. Pretreatment with WAY 100635 (0.63 mg/kg) reinstated catalepsy at higher doses of nemonapride, indicating that the 5-HT1A receptor agonist properties of nemonapride are responsible for its inability to produce catalepsy at high doses. Additionally, WAY 100635 enhanced significantly the effects of low doses of nemonapride, and of the dopamine D2-like receptor antagonists raclopride and haloperidol. The present data indicate that the 5-HT1A receptor agonist properties of nemonapride attenuate its ability to induce catalepsy at higher doses, and suggest further that tonic 5-HT1A receptor activation may modulate neuroleptic-induced catalepsy.

Cocaine sensitization prevents the hypolocomotor effects of high but not low doses of PD 128,907.

In this study we examined the effects of the preferential dopamine D3 receptor agonist S(+)-(4aR,10bR)-3,4,4a,10b-tetrahydro-4-propyl-2H,5H-[1]b enzopyrano-[4,3-b]-1,4-oxazin-9-ol (PD 128,907) on locomotion in mice sensitized to cocaine. In mice repeatedly treated with saline, PD 128,907 induced hypoactivity over a wide dose range (0.01-40 mg/kg); however, after repeated treatment with 40 mg/kg cocaine, higher doses of PD 128,907 (2.5-40 mg/kg) no longer induced hypoactivity whereas the effects of lower doses (0.01-0.16 mg/kg) were not altered. Because lower doses of PD 128,907 are thought to induce hypoactivity via activation of dopamine D3 receptors, the present data suggest that, under conditions where cocaine induces marked sensitization to its locomotor effects, the sensitivity of these receptors is not altered. In contrast, because higher doses of PD 128,907 can activate dopamine D2 receptors, it is conceivable that apparent cross-sensitization to its dopamine D2 receptor agonist properties is responsible for the lack of hypolocomotor effects at high doses. Overall, the results indicate that altered dopamine D3 receptor sensitivity does not play an important role in the expression of cocaine-induced sensitization.

Combined antagonism of adrenoceptors and dopamine and 5-HT receptors underlies the atypical profile of clozapine.

Previous studies have shown that alpha 1-adrenoceptors, dopamine D1-like and 5-HT2A receptors play an important role in the effects of the atypical neuroleptic, clozapine, on the parameter modelling antipsychotic efficacy in the paw test. Therefore, it became of interest to investigate whether antagonism of all these receptors together would give rise to effects characteristic of clozapine. The effects of the combined administration of the alpha 1-adrenoceptor antagonist phenoxybenzamine, the dopamine D1 receptor antagonist, SCH 39166 (4-(4-chloro-3-methoxyphenyl)-1,2- dihydronaphthalene), and the 5-HT2A receptor antagonist, ketanserin, were therefore measured in the paw test. The present data show that all three drugs together, but not simply combinations of two out of three, produced a profile similar to that of clozapine: a significant increase in the parameter modelling antipsychotic efficacy and no change in the parameter modelling extrapyramidal side-effects.

The effects of haloperidol and raclopride in the paw test are influenced similarly by SCH 39166.

We investigated the role of dopamine D1 and D2 receptors in the paw test, an animal model used to assess both the antipsychotic potential and extrapyramidal side effects of drugs. The dopamine D1 receptor antagonist, SCH 39166, as well as the dopamine D2 receptor antagonist raclopride, increased the hindlimb retraction time (HRT), viz. a parameter that models antipsychotic potential, at doses that were lower than those that increased the forelimb retraction time (FRT), viz. a parameter that models extrapyramidal side effects. In contrast, the same dose of haloperidol enhanced both parameters. SCH 39166 enhanced the haloperidol- and raclopride-induced effects on FRT, whereas neither haloperidol nor raclopride enhanced the SCH 39166-induced effects upon this parameter. Except at very high doses, SCH 39166 did not alter the haloperidol- and raclopride-induced effects on HRT, and vice versa. No difference between haloperidol and raclopride was found in the interaction experiments. The clinical impact of these findings is discussed.

Jaw muscle activity, the nucleus accumbens, and dopaminergic agonists: a new approach.

A method was developed to analyze electromyographic (EMG) signals in terms of power, viz., a measure for overall muscle activity, and number of seconds marked by distinct frequency ranges. With the help of this method, the effects of intraaccumbens administration of distilled water, the D1 receptor agonist SK&F 38393 (SKF; 5 micrograms), the D2 receptor agonist LY 171555 (LY; 10 micrograms), and their combination upon the EMG signals of the masseter and the digastric muscle were analysed in freely moving rats. Only the combined treatment affected the power: The noted increase was limited to the digastric muscle. The time/frequency analysis was limited to frequency ranges 3-4 Hz (class A), 4-5 and 5-6 Hz (class B), and 6-7, 7-8, ..., 12-13, and 13-14 Hz (class C). Apart from a small effect of SKF alone and of SKF in combination with LY on class B of the masseter muscle, neither SKF nor LY affected class A or B. SKF and LY increased and decreased, respectively, class C in both muscles. The data suggest that SKF and LY elicited both opposite and synergistic effects. The method is a new tool to analyze EMG signals in freely moving rats.

d-Sulpiride inhibits oral behaviour elicited from the nucleus accumbens of freely moving rats.

The present study analyzed the effect of intra-accumbens administration of the stereoisomers of sulpiride upon (3,4-dihydroxyphenylimino)-2-imidazoline (DPI)-induced changes in oral behaviours and electromyographic patterns of jaw muscles. In line with earlier findings, DPI (5 micrograms) administered into the nucleus accumbens increased chewing and tremor. l-Sulpiride (2-50 ng) had no effect on DPI-induced oro-facial behaviours. d-Sulpiride (10-50 ng) significantly antagonized the DPI-induced increase in chewing and had a biphasic effect on tremor with potentiation (10 ng) followed by attenuation (50 ng). When administered alone, l- or d-sulpiride did not affect oro-facial behaviours. The electromyographic signals, which were analyzed according to a previously described method, were described with the help of three classes: A (the seconds marked by frequency 3 Hz), B (the seconds marked by the frequencies 4-6 Hz); C (the seconds marked by the frequencies 7-15 Hz). DPI enhanced Class B and C of the masseter muscle but did not significantly affect any frequency class of the digastric muscle. l-Sulpiride (2-50 ng) had no effect on DPI-induced (5 micrograms) changes in electromyographic signals. d-Sulpiride (50 ng) antagonized the effects of DPI on Class B of the masseter muscle. Furthermore, d-sulpiride had a biphasic effect on Class C with potentiation (10 ng) followed by attenuation (50 ng). When administered alone, l- or d-sulpiride did not affect the frequency classes of the jaw muscles. It is concluded that d-sulpiride inhibits DPI-induced changes in oral behaviour and electromyographic patterns. It is suggested that d-sulpiride may be effective in the pharmacotherapy of oro-facial dyskinesias in man.