[Narcolepsy in childhood and adolescence: symptoms, diagnosis, and therapy. A case report]

Narcolepsy is a rare, multifactorial disease of the hypothalamus characterized by its leading symptoms of excessive daytime sleepiness and cataplexy. Sleep-EEG and a HLA-DR-genotype serve to secure the diagnosis. We report here on a 14-year-old girl suffering from anxieties, depression, school refusal, social withdrawal as well as very frequent attacks of sleep during the day and cataplexy. Currently, there is no approved drug for children and adolescents suffering from narcolepsy. Our patient benefited significantly and quickly from an off-label treatment with methylphenidate in combination with psychoeducation, cognitive behavioral therapy, and family therapy. Narcolepsy is a very rare but probably underestimated differential diagnosis applied to unclear daytime sleepiness, anxieties, or depression in childhood and adolescence. Both the key symptoms and the comorbid symptoms improve significantly under treatment with stimulants, albeit at a higher dosage.

Individual phenotype predicts nicotine-haloperidol interaction in catalepsy: possible implication for the therapeutic efficacy of nicotine in Tourette's syndrome

In individuals with Tourette's syndrome, the therapeutic efficacy of haloperidol can be augmented by nicotine. In laboratory rats, the dopamine antagonist haloperidol produces catalepsy and nicotine can potentiate it, although this effect is variable and not always observed. Our aim was to understand this variability. In rats, the locomotor response to a novel environment predicts the magnitude of the locomotor response to nicotine. Since the psychostimulant effect of nicotine might counter catalepsy, we hypothesized that rats with a high locomotor response to novelty would show reduced vulnerability to nicotine potentiation of haloperidol catalepsy. First, we administered haloperidol (0, 0.1 or 0.3mg/kg, ip) and found stronger catalepsy in rats with low reactivity to novelty. Second, we administered haloperidol (0.3mg/kg) or haloperidol plus nicotine (0.1mg/kg, ip) and found that nicotine indeed potentiated haloperidol catalepsy but only in rats with low reactivity to novelty. Nicotine did not induce catalepsy on its own. Thus, previously reported inconsistencies in the catalepsy potentiating effect of nicotine may have been due to differential vulnerability to its stimulant actions. As previously observed, the potentiation of haloperidol catalepsy was greatest 4h after injection. Given the short half-life of nicotine, the mechanism(s) underlying the delayed expression of its pro-cataleptic capacity remains obscure.

Anti-psychotic and sedative effect of calcium channel blockers in mice

Calcium channel blockers (CCBs) are widely used as therapeutic agents, for the treatment of cardiovascular disorders. However, the discovery that CCBs bind to various regions of the brain suggest that they might also offer some beneficial effects in the treatment of neuropsychiatry disorders. This study was carried out to evaluate the anti-psychotic and sedative effects of two notable calcium channel blockers, verapamil and nifedipine in mice. The anti-psychotic effects of the CCBs were studied in the animal model of amphetamine-induced stereotyped behavioral disorders. The sedative effect was assessed utilizing the prolongation of the time of sleep, induced by thiopentone. The ability of CCBs to produce catalepsy in mice was also evaluated in the study. Graded doses of verapamil (5.0-20.0 mg/kg, i.p) significantly (p<0.05) suppressed stereotyped behaviour induced by amphetamine (10.0 mg/kg, i.p). In contrast, nifedipine (5.0-20.0 mg/kg, i.p) did not exhibit anti-psychotic effect, as it could not significantly reduce stereotypy caused by amphetamine. In the test for sedation, both verapamil (5.0-20.0 mg/kg, i.p) and nifedipine (10.0-20.0 mg/kg) significantly (p<0.05) prolonged the sleeping time induced by thiopentone (50.0 mg/kg, i.p). However, neither verapamil (5.0-20.0 mg/kg, i.p.) nor nifedipine (5.0-20.0 mg/kg, i.p.) at the tested doses produced any cataleptic behaviour in the animals. The results of the study suggest that verapamil has both anti-psychotic and sedative effects without inducing the side effect of catalepsy and might be relevant in the treatment of psychosis.

[Learning of rats predisposed to catalepsy in Morris water test]

It was shown that GC rats predisposed to catalepsy do not differ from Wistar rats in success rate or latency (time of finding of the hidden escape platform) in the Morris water test. However, unlike Wistar, GC rats are inclined to passive drift and longer floating episodes. Rats of the MD+ strain predisposed to hyperkinesis in the form of horizontal pendulum-like movements of the head and upper limb girdle show longer latency and lower rate of successful trials than Wistar or MD-, rats selected for absence of the pendulum-like movements.

Learning and extinction of a passive avoidance response in mice with high levels of predisposition to catalepsy

This report presents results obtained from comparative analysis of learning and the dynamics of extinction of a conditioned passive avoidance response in ASC mice, which were bred for a high level of predisposition to catalepsy, and in CBA and AKR mice. The following findings were obtained: 1) impairments to the extinction of the memory of fear represent an important symptom of depression in ASC mice; 2) extinction is delayed in CBA mice; and 3) new inhibitory learning occurs quickly in AKR mice. Prolonged retention of the fear memory in ASC mice appears to be related to increased anxiety on prolonged testing without a punishment. The deficit of inhibition of the fear reaction in ASC mice allows this strain to be regarded as a genetic model of depression.

A neurocomputational account of catalepsy sensitization induced by D2 receptor blockade in rats: context dependency, extinction, and renewal

RATIONALE

Repeated haloperidol treatment in rodents results in a day-to-day intensification of catalepsy (i.e., sensitization). Prior experiments suggest that this sensitization is context-dependent and resistant to extinction training.

OBJECTIVES

The aim of this study was to provide a neurobiological mechanistic explanation for these findings.

MATERIALS AND METHODS

We use a neurocomputational model of the basal ganglia and simulate two alternative models based on the reward prediction error and novelty hypotheses of dopamine function. We also conducted a behavioral rat experiment to adjudicate between these models. Twenty male Sprague-Dawley rats were challenged with 0.25 mg/kg haloperidol across multiple days and were subsequently tested in either a familiar or novel context.

RESULTS

Simulation results show that catalepsy sensitization, and its context dependency, can be explained by "NoGo" learning via simulated D2 receptor antagonism in striatopallidal neurons, leading to increasingly slowed response latencies. The model further exhibits a non-extinguishable component of catalepsy sensitization due to latent NoGo representations that are prevented from being expressed, and therefore from being unlearned, during extinction. In the rat experiment, context dependency effects were not dependent on the novelty of the context, ruling out the novelty model's account of context dependency.

CONCLUSIONS

Simulations lend insight into potential complex mechanisms leading to context-dependent catalepsy sensitization, extinction, and renewal.

Chronic administration of imipramine normalizes decreased sexual motivation and increased predisposition to catalepsy induced by propylthiouracil in rats

Thyroxine synthesis inhibitors increase the predisposition to catalepsy and decrease sexual motivation and the amplitude of the acoustic startle reflex in rats. The sensitivity of these behavioral changes to antidepressants remains uncertain. Chronic administration of the classical tricyclic antidepressant imipramine (15 mg/kg, 21 days) prevented the appearance of high sensitivity to catalepsy and the decrease in sexual motivation in Wistar rats given propylthiouracil (50 mg/liter, 28 days), without altering the amplitude of the startle reflex. Normalization of behavior in response to imipramine was not associated with changes in movement activity in the open field test or the animals' body weight. There was also no change in the expression of the 5-HT2A serotonin receptor gene in the frontal cortex. The model of propylthiouracilinduced catalepsy with reduced sexual motivation in rats has potential for studying the role of thyroid abnormalities in the development of depression and the mechanisms of action of antidepressants.

Repeated administration of Yokukansan inhibits DOI-induced head-twitch response and decreases expression of 5-hydroxytryptamine (5-HT)2A receptors in the prefrontal cortex

Behavioral and psychological symptoms of dementia (BPSD) are commonly seen in patients with Alzheimer's disease (AD) and other forms of senile dementia. BPSD have a serious impact on the quality of life of dementia patients, as well as their caregivers. However, an effective drug therapy for BPSD has not been established. Recently, the traditional Japanese medicine Yokukansan (YKS, Yi-gan san in Chinese) has been reported to improve BPSD in a randomized, single-blind, placebo-controlled study. Moreover, abnormalities of the serotonin (5-HT) system such as 5-HT2A receptors have been reported to be associated with BPSD of AD patients. In the present study, we investigated the effect of YKS on head-twitch response induced by 2,5-dimethoxy-4-iodoamphetamine (DOI, 5 mg/kg, i.p.) in mice, a behavioral response that is mediated, in part, by 5-HT2A receptors. Acute treatment with YKS (100 and 300 mg/kg, p.o.) had no effect on the DOI-induced head-twitch response, whilst 14 days repeated treatment with YKS (300 mg/kg, p.o.) significantly inhibited this response. Moreover, repeated treatment with YKS (300 mg/kg, p.o.) decreased expression of 5-HT2A receptors in the prefrontal cortex, which is part of the circuitry mediating the head-twitch response. These findings suggest that the inhibition of DOI-induced head-twitch response by YKS may be mediated, in part, by altered expression of 5-HT2A receptors in the prefrontal cortex, which suggests the involvement of the 5-HT system in psychopharmacological effects of YKS.

[Learning and extinction of passive avoidance in mice with high predisposition to catalepsy]

The passive avoidance learning and extinction in mice strain ASC with high predisposition to catalepsy as compared with mice of CBA and AKR strains were analyzed. Impairment of fear extinction as a major symptom of depression was revealed in ASC mice, whereas a delay of extinction in CBA mice and fast formation of new inhibitory learning in AKR mice were found. It is suggested that the long persistence of fear in ASC mice results from increased anxiety during the repeated presentation of a context in the absent of aversive stimulus. Defect of fear inhibition in ASC mice makes it possible to use this strain of mice as genetic model of depression.

[Chronic imipramine treatment normalizes decreased sexual motivation and high predisposition to catalepsy induced by propylthiouracil in rat]

Thyroxine synthesis inhibitors produced augmentation in predisposition to catalepsy and a decrease of sexual motivation and acoustic startle reflex response in rat. Sensitivity of these behavioral alterations to antidepressants was unknown. Chronic treatment with prototypical antidepressant imipramine (15 mg/kg, 21 days) prevented manifestation of catalepsy expression and sexual motivation reduction in Wistar rats given propylthiouracil (50 mg/l, 28 days) but did not influence startle reflex amplitude. Behavioral recovery induced by imipramine did not attribute to alterations in locomotor activity in open-field test or body weight gain. 5-HT(2A)-receptor mRNA level in the frontal cortex was not changed either. Model of sexual motivation disturbance and catalepsy induced by propylthiouracil in rat seems to be prospective to study the role of thyroid dysfunctions in mechanisms of depression and antidepressant treatment.

[High predisposition to catalepsy decreases intermale aggression and increases acoustic startle reflex amplitude]

Reaction of freezing (a pronounced motor inhibition, catalepsy) is suggested to be associated with fear in response to predator appearance or attack of aggressive congener. In order to evaluate association between a kind of behavior such as freezing, aggressiveness and fear, the effects of high predisposition to catalepsy on intermale aggression, acoustic startle response and anxiety-related behavior in the light/dark test were studied. Mice of 14th and 15th generations of selective breeding for high predisposition to catalepsy were characterized by a significant decrease in aggressive behavior. The marked decrease in the percentage of aggressive mice in the catalepsy-prone strain is consistent with the notion that aggression and catalepsy represent two alternative kinds of behavior in intermale conflicts. A positive correlation was found between high predisposition to catalepsy and startle reflex amplitude (but not anxiety-related behavior).

Pharmacological profiles in rats of novel antipsychotics with combined dopamine D2/serotonin 5-HT1A activity: comparison with typical and atypical conventional antipsychotics

Combining antagonist/partial agonist activity at dopamine D2 and agonist activity at serotonin 5-HT1A receptors is one of the approaches that has recently been chosen to develop new generation antipsychotics, including bifeprunox, SSR181507 and SLV313. There have been, however, few comparative data on their pharmacological profiles. Here, we have directly compared a wide array of these novel dopamine D2/5-HT1A and conventional antipsychotics in rat models predictive of antipsychotic activity. Potency of antipsychotics to antagonize conditioned avoidance, methylphenidate-induced behaviour and D-amphetamine-induced hyperlocomotion correlated with their affinity at dopamine D2 receptors. Potency against ketamine-induced hyperlocomotion was independent of affinity at dopamine D2 or 5-HT1A receptors. Propensity to induce catalepsy, predictive of occurrence of extrapyramidal side effects, was inversely related to affinity at 5-HT1A receptors. As a result, preferential D2/5-HT1A antipsychotics displayed a large separation between doses producing 'antipsychotic-like' vs. cataleptogenic actions. These data support the contention that 5-HT1A receptor activation greatly reduces or prevents the cataleptogenic potential of novel antipsychotics. They also emphasize that interactions at 5-HT1A and D2 receptors, and the nature of effects (antagonism or partial agonism) at the latter has a profound influence on pharmacological activities, and is likely to affect therapeutic profiles.

Reversal of haloperidol-induced extrapyramidal symptoms by buspirone: a time-related study

Effects of coadministration of buspirone were investigated on the time course of haloperidol-induced extrapyramidal symptoms in rats. Rats treated with haloperidol at a dose of 1 mg/kg exhibited impaired motor coordination and a decrease in exploratory activity. Coadministration of buspirone at a dose of 1 mg/kg attenuated haloperidol-induced deficits of motor coordination but no effect was produced on the deficits of exploratory activity, possibly because of a 'floor effect'. Long-term administration of haloperidol (1 mg/kg) twice a day for 5 weeks did not produce tolerance to haloperidol-induced deficits of exploratory activity. The deficits of motor coordination were attenuated after 4-5 weeks of drug administration. Coadministration of buspirone for 3-5 weeks attenuated and reversed haloperidol-induced deficits of exploratory activity. Deficits of motor coordination were smaller in rats cotreated with buspirone after 1 week but not after 2-5 weeks. Administration of haloperidol for 2 weeks elicited vacuous chewing movements with twitching of facial musculature that increased in a time-dependent manner as the treatment continued to 5 weeks. Animals cotreated with buspirone exhibited a gradual reversal of the response during 2-5 weeks of treatment. The mechanism involved in the attenuation/reversal of haloperidol-induced extrapyramidal symptoms by buspirone is discussed. Prior administration of buspirone for 2 weeks may be of help in the improvement of extrapyramidal symptoms induced by antipsychotic drugs.

D2-like dopamine receptors mediate the response to amphetamine in a mouse model of ADHD

The mechanisms underlying the effects of psychostimulants in attention deficit hyperactivity disorder (ADHD) are not well understood, but indirect evidence implicates D2 dopamine receptors. Here we dissect the components of dopaminergic neurotransmission in the hyperactive mouse mutant coloboma to identify pre- and postsynaptic elements essential for the effects of amphetamine in these mice. Amphetamine treatment reduced locomotor activity in coloboma mice, but induced a robust increase in dopamine overflow suggesting that abnormal regulation of dopamine efflux does not account for the behavioral effect. However, the D2-like dopamine receptor antagonists haloperidol and raclopride, but not the D1-like dopamine receptor antagonist SCH23390, blocked the amphetamine-induced reduction in locomotor activity in coloboma mice, providing direct evidence that D2-like dopamine receptors mediate the effect of amphetamine in these mice. With the precedent established that it is possible to directly antagonize this response, this strategy should prove useful for identifying novel therapeutics in ADHD.

EFNS guidelines on management of narcolepsy

Management of narcolepsy with or without cataplexy relies on several classes of drugs, namely stimulants for excessive daytime sleepiness and irresistible episodes of sleep, antidepressants for cataplexy and hypnosedative drugs for disturbed nocturnal sleep. In addition, behavioral measures can be of notable value. Guidelines on the management of narcolepsy have already been published. However contemporary guidelines are necessary given the growing use of modafinil to treat excessive daytime sleepiness in Europe within the last 5-10 years, and the decreasing need for amphetamines and amphetamine-like stimulants; the extensive use of new antidepressants in the treatment of cataplexy, apart from consistent randomized placebo-controlled clinical trials; and the present re-emergence of gamma-hydroxybutyrate under the name sodium oxybate, as a treatment of all major symptoms of narcolepsy. A task force composed of the leading specialists of narcolepsy in Europe has been appointed. This task force conducted an extensive review of pharmacological and behavioral trials available in the literature. All trials were analyzed according to their class evidence. Recommendations concerning the treatment of each single symptom of narcolepsy as well as general recommendations were made. Modafinil is the first-line pharmacological treatment of excessive daytime sleepiness and irresistible episodes of sleep in association with behavioral measures. However, based on several large randomized controlled trials showing the activity of sodium oxybate, not only on cataplexy but also on excessive daytime sleepiness and irresistible episodes of sleep, there is a growing practice in the USA to use it for the later indications. Given the availability of modafinil and methylphenidate, and the forseen registration of sodium oxybate for narcolepsy (including excessive daytime sleepiness, cataplexy, disturbed nocturnal sleep) in Europe, the place of other compounds will become fairly limited. Since its recent registration cataplexy sodium oxybate has now become the first-line treatment of cataplexy. Second-line treatments are antidepressants, either tricyclics or newer antidepressants, the later being increasingly used these past years despite few or no randomized placebo-controlled clinical trials. As for disturbed nocturnal sleep the best option is still hypnotics until sodium oxybate is registered for narcolepsy. The treatments used for narcolepsy, either pharmacological or behavioral, are diverse. However the quality of the published clinical evidences supporting them varies widely and studies comparing the efficacy of different substances are lacking. Several treatments are used on an empirical basis, specially antidepressants for cataplexy, due to the fact that these medications are already used widely in depressed patients, leaving little motivation from the manufacturers to investigate efficacy in relatively rare indications. Others, in particular the more recently developed substances, such as modafinil or sodium oxybate, are evaluated in large randomized placebo-controlled trials. Our objective was to reinforce the use of those drugs evaluated in randomized placebo-controlled trials and to reach a consensus, as much as possible, on the use of other available medications.

Dissociation between in vivo occupancy and functional antagonism of dopamine D2 receptors: comparing aripiprazole to other antipsychotics in animal models

The novel antipsychotic aripiprazole requires high (>90%) striatal D2 receptor occupancy (D2RO) to be clinically active, but despite its high D2RO it does not show extrapyramidal symptoms. While most antipsychotics are active at nearly 65% D2RO, they show motor side effects when D2RO exceeds 80%. We investigated this discrepancy between D2RO, 5HT2 receptor occupancy (5-HT2RO) and in vivo functional activity of aripiprazole in comparison to haloperidol (typical) and risperidone (atypical) in animal models. All three drugs showed dose-dependent D2RO. While risperidone clearly showed higher 5-HT2RO than D2RO, aripiprazole and haloperidol showed higher D2RO than 5-HT2RO at all doses. Haloperidol and risperidone induced catalepsy at doses producing >80% D2RO, while aripiprazole despite higher D2RO (>90%) induced no catalepsy. Haloperidol and risperidone's ED50 values for inhibition of conditioned avoidance response (CAR) and amphetamine-induced locomotor activity (AIL) corresponded to approximately 60% D2RO. In contrast, aripiprazole showed a significant dissociation; while it blocked AIL at similar D2RO, a 23-fold higher dose (86% D2RO) was required to inhibit CAR. FOS expression in shell region of the nucleus accumbens was significant for all drugs at D2ROs that were effective in CAR. However, in the core region of the nucleus accumbens and dorsolateral striatum, aripiprazole differed from the others in that despite high D2RO it induced low FOS. Haloperidol and risperidone showed dose/occupancy-dependent prolactin elevations, while aripiprazole did not. Across models, haloperidol and risperidone show similar occupancy-functional antagonism of the D2 system, while aripiprazole shows a clear dissociation. Partial agonism of aripiprazole offers a good explanation for this dissociation and provides a framework for understanding occupancy-functional relationships of partial D2 agonist antipsychotics.

Ketamine-Induced Potentiation of Morphine Analgesia in Rat Tail-Flick Test: Role of Opioid-, .ALPHA.2-Adrenoceptors and ATP-Sensitive Potassium Channels

Ketamine is known to improve opioid efficacy, reduce postoperative opioid requirement and oppose opioid associated pain hypersensitivity and tolerance. However, the mechanisms underlying these beneficial effects are not clear. This study investigated the effects of ketamine at a non-analgesic dose (30 mg/kg, i.p.) on analgesia induced by morphine (2.5, 5.0, 7.5 mg/kg, s.c.), using rat tail-flick test as an animal model of acute pain. Further, the role of opioid-, alpha2-adrenoceptors and ATP-sensitive potassium channels was examined on the potentiating effect of ketamine. Male rats received morphine alone at 5.0 and 7.5 but not at 2.5 mg/kg showed a dose-related increase in tail-flick latencies. The combination of morphine and ketamine resulted in dose-related increase in morphine analgesia, both on the intensity as well as on duration. The ketamine-induced potentiation of morphine (7.5 mg/kg) analgesia was unaffected by glibenclamide (3 mg/kg, s.c.) and only partially blocked by yohimbine (2 mg/kg, i.p.), but more completely abolished by naloxone (2 mg/kg, i.p.). Both morphine (5.0 mg/kg) and ketamine (30 mg/kg) alone did not evoke catalepsy in rats but on combination produced a synergistic effect, which was however, abolished by naloxone pretreatment. In the open-field test, while morphine (5.0 mg/kg) caused a depressant effect, ketamine (30 mg/kg) enhanced the locomotor activity. Nevertheless, in combination potentiated the morphine's depressant effect on locomotion, which was also antagonized by naloxone. These results indicate that ketamine at a non-analgesic dose can potentiate morphine analgesia, induce catalepsy and cause locomotor depression, possibly involving an opioid mechanism. This potentiation, although favorable in acute pain management, may have some adverse clinical implications.

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.

Design, synthesis, and evaluation of the antipsychotic potential of orally bioavailable neurotensin (8-13) analogues containing non-natural arginine and lysine residues

Neurotensin (NT) and its active fragment NT(8-13) elicit behavioral responses typical of clinically used antipsychotic drugs when administered directly to the brain. However, limited peptide stability and oral bioavailability have prevented these compounds from being developed as relevant pharmaceuticals. Recently, our laboratory designed and studied a first-generation NT(8-13) derivative, KK13, that elicited key pharmacokinetic and behavioral responses typical of clinically used antipsychotic drugs when administered to rats parenterally. This compound was the basis for the rational design of a series of second-generation NT(8-13) analogues (KH1-KH30) studied in this paper. Initial screening of these analogues for CNS activity by monitoring hypothermia induction after peripheral administration defined several compounds (KH11, KH24, KH26, and KH28-KH30) that warranted further investigation. Each compound maintained binding affinity for NTR(1), however, only KH24, KH26, and KH28 (as well as KK13) elicited significant hypothermic responses after oral administration. Of these, KH28 demonstrated an oral activity 3-fold greater than any other analogue; hence it was further characterized in a series of rat behavioral assays. KH28 attenuated d-amphetamine induced hyperlocomotion, a hallmark of current clinically effective antipsychotic drugs, after both IP and oral administration. In addition, tolerance to the compound did not develop after repeated daily dosing, as measured by hypothermic induction as well as attenuation of d-amphetamine induced hyperlocomotion. Finally, KH28 did not produce catalepsy, a deleterious side-effect elicited by classical antipsychotic drugs. KH28 is considered to be an ideal compound for further development as a potential novel antipsychotic.

[Does the catalepsy phenomenon reflect the functional dopaminergic activity in pharmacological investigations?]

The dynamics of spontaneous and haloperidol-induced catalepsy in mice has been studied. It is established that the degree of manifestation of the spontaneous catalepsy is directly related to the number of manipulations (mice standings in the "lector position"). At the same time, the intensity of catalepsy (both spontaneous and haloperidol-induced) was not related to the mice response to apomorphine injections. It is concluded that spontaneous catalepsy rather insignificantly influences the results of pharmacological tests, but this factor has to be taken into account in the study of physiological mechanisms. The absence of correlations between catalepsy manifestations and the apomorphine test results is indicative of complexity of the mechanism of this disorder and cannot be attributed entirely to the violation of dopaminergic processes in CNS.

Catalepsy intensifies context-dependently irrespective of whether it is induced by intermittent or chronic dopamine deficiency

It is well known that neuroleptic-induced catalepsy in rats intensifies upon repeated testing. Here, the question is addressed whether intensification of catalepsy results from intermittent drug administration or from intermittent context exposure. In experiment 1, rats were treated with intermittent haloperidol injections (0.25 mg/kg) followed by the catalepsy test (descent latency from the horizontal bar). In experiment 2, rats were lesioned with 6-hydroxydopamine injections into the striatum, resulting in a 45% reduction of dopamine concentration. Catalepsy was tested intermittently for several weeks. In both experiments we found a very stable intensification of catalepsy over 9 (haloperidol rats) and 11 (lesioned rats) days, showing that intensification is not due to intermittent dopamine depletion. In both experiments, intensification of catalepsy was very stable and was observed 18 days later in haloperidol-treated rats and 101 days later in lesioned animals. However, a change of the environmental context abolished the intensified catalepsy in both experiments. It is concluded that intensification of catalepsy is due to intermittent context exposure rather than intermittent drug administration. It is generally accepted that 6-hydroxydopamine lesions represent an animal model of Parkinson's disease. Given the results above, context-dependent intensification of parkinsonian symptoms might also occur in Parkinson's disease, and its prevention should be taken into consideration for future therapy of the disease.

Effects of dopamine receptor blockade on cerebral blood flow response to somatosensory stimulation in the unanesthetized rat

Local cerebral blood flow (CBF) was determined in 30 cerebral structures, including four structures of the whisker-to-barrel cortex sensory pathway, by the quantitative autoradiographic [(14)C]iodoantipyrine method during unilateral vibrissal stimulation in rats administered 0.1 or 1.0 mg/kg haloperidol or its control vehicle intravenously. The low dose of haloperidol had no significant effects on resting CBF or its enhancement by vibrissal stimulation. By standard t tests, the high dose statistically significantly lowered baseline CBF in frontal and visual cortex, hippocampus, dentate gyrus, inferior olive, cerebellar cortex, and the ventral posteromedial (VPM) thalamic nucleus on the unstimulated side, and raised baseline CBF in the lateral habenula; however, these changes lost statistical significance after Bonferroni correction for multiple comparisons. Neither dose had any effects on the increases in CBF evoked by vibrissal stimulation in the principal sensory trigeminal nucleus and barrel cortex, but the higher dose statistically significantly enhanced the percent increases in CBF due to the sensory stimulation in the spinal trigeminal nucleus and VPM thalamic nucleus. These results do not support a role for direct dopaminergic vasoactive mechanisms in the increases in CBF associated with neuronal functional activation.

In vitro and in vivo pharmacological profile of 4-(4-fluorobenzylidene)-1-[2-[5-(4-fluorophenyl)-1H-pyrazol-4-yl] ethyl] piperidine (NRA0161)

Atypical antipsychotic properties of 4-(4-fluorobenzylidene)-1-[2-[5-(4-fluorophenyl)-1H-pyrazol-4-yl]ethyl] piperidine (NRA0161) were investigated by in vitro receptor affinities, in vivo receptor occupancies and findings were compared with those of risperidone and haloperidol in rodent behavioral studies. In in vitro receptor binding studies, NRA0161 has a high affinity for human cloned dopamine D(4) and 5-HT(2A) receptor with Ki values of 1.00 and 2.52 nM, respectively. NRA0161 had a relatively high affinity for the alpha(1) adrenoceptor (Ki; 10.44 nM) and a low affinity for the dopamine D(2) receptor (Ki; 95.80 nM). In in vivo receptor binding studies, NRA0161 highly occupied the 5-HT(2A) receptor in rat frontal cortex. In contrast, NRA0161 did not occupy the striatal D(2) receptor. In behavioral studies, NRA0161, risperidone and haloperidol antagonized the locomotor hyperactivity in mice, as induced by methamphetamine (MAP). At a higher dosage, NRA0161, risperidone and haloperidol dose-dependently antagonized the MAP-induced stereotyped behavior in mice and NRA0161 dose-dependently and significantly induced catalepsy in rats. The ED(50) value in inhibiting the MAP-induced locomotor hyperactivity was 30 times lower than that inhibiting the MAP-induced stereotyped behavior and 50 times lower than that which induced catalepsy. These findings suggest that NRA0161 may have atypical antipsychotic activities yet without producing extrapyramidal side effects.

Rotenone destroys dopaminergic neurons and induces parkinsonian symptoms in rats

Rotenone (an inhibitor of mitochondrial NADH dehydrogenase, a naturally occurring toxin and a commonly used pesticide) appears to reproduce the neurochemical, neuropathological and behavioural feature of Parkinson's disease (PD) in the rat. In this study, rotenone was administrated on a daily basis systemically by intraperitoneal injection of two different doses: 1.5 mg/kg (low dose) and 2.5 mg/kg (moderate dose), over a period of 2 months. This treatment caused depletion of dopamine in the posterior striatum (CPu) and prefrontal cortex and also reduced tyrosine hydroxylase-immunoreactivity in CPu. Behavioural experiments showed dose-dependent catalepsy in the two treatment groups of rats. Data from this study indicate that in rats rotenone is capable of causing degeneration of dopaminergic neurons and induction of parkinsonian symptoms. It is concluded that the causal mechanisms of neuronal degeneration implicate a complex I deficiency in the aetiology of rotenone-induced and perhaps in some cases of sporadic PD.

Effects of sigma(1) receptor ligand MS-377 on D(2) antagonists-induced behaviors

(R)-(+)-1-(4-Chlorophenyl)-3-[4-(2-methoxyethyl)piperazin-1-yl]methyl-2-pyrrolidinone L-tartrate (MS-377) is a novel antipsychotic agent with selective and high affinity for sigma(1) receptor. The present study was carried out to clarify the interaction of MS-377 with dopamine D(2) receptor antagonists (D(2) antagonists) in concurrent administration, and then the involvement of sigma receptors in the interaction. The effects of MS-377 on haloperidol- or sultopride-induced inhibition of apomorphine-induced climbing behavior and catalepsy were investigated in mice and rats, respectively. In addition, the effects of (+)-SKF-10,047 and SA4503, both of which are sigma receptor agonists, and WAY-100,635, which is a 5-HT(1A) receptor antagonist, on the interaction due to the concurrent use were also investigated. MS-377 potentiated the inhibitory effects of haloperidol or sultopride on apomorphine-induced climbing behavior in a dose-dependent manner. In contrast, MS-377 did not affect the catalepsy induction by these drugs. The potentiation of the inhibitory effects of haloperidol or sultopride on apomorphine-induced climbing behavior by MS-377 was not inhibited by WAY-100,635, but was inhibited by (+)-SKF-10,047 and SA4503. These findings showed that MS-377 potentiates the efficacy of D(2) antagonists, but it does not deteriorate the adverse effect. Moreover, sigma(1) receptors are involved in this potentiation of the efficacy of D(2) antagonists by MS-377.

Discrimination of morphine- and haloperidol-induced muscular rigidity and akinesia/catalepsy in simple tests in rats

The present study was conducted to establish a simple method for measuring muscular rigidity in rats, which could be used for screening and is able to discriminate between rigidity and akinesia/catalepsy. Therefore, we treated rats with morphine (30 mg/kg i.p.), since large doses of morphine lead to muscular rigidity and akinesia. We measured muscular rigidity with a new method by determining the resistance of the hindlimb to passive flexion in the 'balance test' and also checked haloperidol (3 mg/kg i.p.) treated rats for muscular rigidity. Furthermore, catalepsy was also tested after administration of each of these drugs. Then, the influence of D(1)-like and D(2)-like dopamine receptor stimulation on muscular rigidity and catalepsy was studied. Therefore, the partial D(1) agonist SKF 38393 (3 and 8 mg/kg s.c.), the D(2)/D(1) agonist pergolide (0.25 and 0.5 mg/kg i.p.) and the dopamine precursor L-DOPA (50 and 100 mg/kg i.p.) were administered up to 30 min before muscular rigidity was measured in morphine-treated rats. The results showed that morphine, but not haloperidol led to muscular rigidity, whereas both drugs led to positive scores in the catalepsy test. The dopaminergic drugs partly antagonized the morphine-induced muscular rigidity in the doses applied, but not the catalepsy. Apparently, rigidity, akinesia/catalepsy produced by morphine can be discriminated from that produced by haloperidol in simple and quick tests.

The differential effect of haloperidol and repetitive induction on four immobility responses in mouse and guinea pig

The modification by haloperidol and repetitive induction on four immobility responses -- tonic immobility, cataleptic immobility, immobility by clamping the neck and dorsal immobility -- were compared in mice and guinea pigs. Without drug, three out of four responses (cataleptic, neck clamp and dorsal immobility) were induced in mice; guinea pigs displayed all four responses. Haloperidol (5 mg/kg i.p.) potentiated the three responses shown by mice, but did not potentiate the four responses in guinea pigs. In both undrugged and haloperidol-treated mice, only the cataleptic immobility response was potentiated by repetition. In guinea pigs, none of the four immobility responses was affected due to repetition, haloperidol or a combination of both. These data are discussed, considering that, although these immobility responses could be mediated by the same neurotransmitters (e.g. dopamine), they are possibly expressed in a differential manner as a function of the kind of stimulus used to trigger the response, characteristics of the species and, in some immobility responses such as cataleptic immobility, as a function of their interaction with habituation or another learning-like process.

Effects of the 5-HT(6) receptor antagonist, SB-271046, in animal models for schizophrenia

The 5-HT(6) receptor is targeted by several new antipsychotics such as clozapine, olanzapine, and sertindole. We studied the effect of SB-271046 [5-chloro-N-(4-methoxy-3-piperazin-1-yl-phenyl)-3-methyl-2-benzothiophenesulfonamide], a specific 5-HT(6) receptor antagonist, in three models for the positive symptoms of schizophrenia---D-amphetamine-induced hyperactivity, and D-amphetamine- or phencyclidine (PCP)-disrupted prepulse inhibition (PPI). We also tested this compound in a model for the negative symptoms of schizophrenia, PCP-disrupted social interaction (SIT) in rats. Induction of side effects by this compound was evaluated by testing its potency to reduce spontaneous motility, and to induce catalepsy in rats. The effect of SB-271046 was compared to clozapine in all models tested. This study showed that SB-271046 had no beneficial effect in PCP-disrupted SIT. However, SB-271046 dose-dependently normalised D-amphetamine-disrupted PPI, but did not reverse PCP-disrupted PPI. In addition, SB-271046 did not antagonise D-amphetamine-induced hyperactivity. Thus, this specific 5-HT(6) receptor antagonist was associated with a clear positive outcome in only one model for the positive symptoms of schizophrenia, and had no beneficial effect in the model for negative symptoms. Consequently, it is clear that SB-271046 is not expected to have an antipsychotic efficacy, at least when given as monotherapy.

Central 5-HT(4) receptors and dopamine-dependent motor behaviors: searching for a functional role

In this study, we evaluated the role of central 5-HT(4) receptors in the control of motor behaviors related to change of nigrostriatal dopamine (DA) transmission, namely, stereotyped behavior and catalepsy in rats. Indeed, given that 5-HT(4) receptors indirectly modulate nigrostriatal DA neuron activity, we hypothesized that these receptors would regulate nigrostriatal DA transmission in the basal ganglia, and consequently, associated motor responses. Stereotypy was induced either by an acute administration of apomorphine (0.3 and 1.5 mg/kg sc), or by a single morphine administration (15 mg/kg sc) in chronically morphine-treated (15 mg/kg sc, twice daily for 10 days) rats. Catalepsy was induced by the typical neuroleptic haloperidol (HAL; 1 mg/kg sc). The selective 5-HT(4) antagonist, GR 125487 (1 mg/kg ip), modified neither apomorphine- nor morphine-induced stereotypy. HAL-induced catalepsy, while reduced by the systemic administration of the 5-HT(1A) agonist 8-OH-DPAT (0.1 mg/kg sc), was insensitive to GR 125487, systemically (1, 3, 10 mg/kg ip) or locally (20 and 40 nmol/20 microl) administered into the third ventricle. Also, HAL-induced catalepsy was not affected by the selective 5-HT(4) antagonist GR 113808 (3 mg/kg ip). The obtained results indicate that 5-HT(4) receptor antagonism does not modulate motor behaviors related to change of striatal DA transmission.

Neuropharmacological profile of a novel potential atypical antipsychotic drug Y-931 (8-fluoro-12-(4-methylpiperazin-1-yl)- 6H-[1]benzothieno[2,3-b][1,5] benzodiazepine maleate)

The neuropharmacological profile of Y-931, 8-fluoro-12- (4-methylpiperazin-1-yl)- 6H-[1]benzothieno [2,3-b][1,5]benzodiazepine maleate, was investigated in comparison with those of typical and claimed atypical antipsychotic drugs. Similar to clozapine and olanzapine, Y-931 interacted with multiple neurotransmitter receptors such as dopaminergic, serotonergic, alpha-adrenergic, muscarinic and histaminergic receptors. Y-931, as well as the other antipsychotics, was active in a dose-dependent manner in established tests which are indicative of potential antipsychotic activity such as inhibition of apomorphine-induced hyperactivity and suppression of conditioned avoidance responses, however, only Y-931 and clozapine were devoid of cataleptogenic potential. In models of N-methyl-D-aspartate (NMDA) receptor hypofunction, Y-931 demonstrated the most potent protective action against the dizocilpine-induced neurotoxicity (neuronal vacuolization) in the rat retrosplenial cortex ([Y-931 (ED(50); 0.20 mg/kg, p.o.), olanzapine (1.1), clozapine (5.7), risperidone (6.9), haloperidol (19)). Furthermore, Y-931 and clozapine, unlike the other antipsychotics used, reversed the dizocilpine-induced social deficits at the same doses at which their neuroprotective action was exhibited. The present results suggest that Y-931 may be a novel potential atypical antipsychotic drug with a low risk of extrapyramidal syndrome (EPS) and the property to ameliorate NMDA receptor hypofunction.

Effects of the 5-HT(7) receptor antagonist SB-258741 in animal models for schizophrenia

The 5-HT(7) receptor is targeted by several new antipsychotics such as clozapine and risperidone. We studied the effect of R-(+)-1-(toluene-3-sulfonyl)-2-[2-(4-methylpiperidin-1-yl)ethyl]-pyrrolidine (SB-258741), a specific 5-HT(7) receptor antagonist, in three models for positive symptoms, D-amphetamine-induced hyperactivity and D-amphetamine- and phencyclidine (PCP)-disrupted prepulse inhibition (PPI) in rats, with the aim of investigating the role of this receptor in the clinical effect of antipsychotics. We also tested this compound in a model for negative symptoms, PCP-disrupted social interaction (SIT) in rats. Induction of side effects by this compound was evaluated by testing its potency to reduce spontaneous motility and to induce catalepsy in rats. The effect of SB-258741 was compared to risperidone in all models. This study showed that SB-258741 had no beneficial effect on PCP-disrupted SIT. SB-258741 did not reverse D-amphetamine-disrupted PPI; however, it dose-dependently normalised PCP-disrupted PPI. SB-258741 antagonised D-amphetamine-induced hyperactivity but reduced motility of rats at similar doses. Thus, this specific 5-HT(7) receptor antagonist brought a clear positive outcome in only one model for positive symptoms of schizophrenia and had no beneficial effect in the model for negative symptoms. Consequently, it is clear that SB-258741 affects the PPI phenomenon but is not expected to have an antipsychotic effect on its own in clinic.

Behavioral characteristics of mice with genetic knockout of monoamine oxidase type A

Transgenic mice of line Tg8 were used to study the effects of deletion of the monoamine oxidase type A gene and the absence of the corresponding enzyme on behavior. These experiments showed that Tg8 mice with genetic knockout of monoamine oxidase type A differed from mice of the parental line C3H/HeJ by lower levels of the startle reflex in response to an acoustic signal, while there was no difference in the prestimulus inhibition of the startle response. Tg8 mice showed decreased investigative activity and decreases in the number of sector crossings in the light-dark anxiety test. There were significant increases in aggression as a motivation in male Tg8 mice, which was manifest as an increase in the number of mice demonstrating aggression and a decrease in the latent period of attack. The intensity of aggression changed to a lesser extent - the number of fights even decreased, though longer periods of keeping mice together resulted in increased numbers of deaths among intruder mice. At the same time, there were no significant differences between mice with genetic knockout of monoamine oxidase type A and control mice in terms of the expression of sexual activation: the behavioral responses of Tg8 males to presentation of females was marked and was no different from that of male C3H/HeJ mice. Knockout of the gene had no effect on movement activity on behavior in an elevated cross-shaped maze or in the test for predisposition to catalepsy.

[Effect of cross-fostering on catalepsy and the brain monoamine level in rat offspring prone to catalepsy and in the control strain]

Duration of cataleptic reactions in male rats of Wistar and GC strains depended both on the genotype and on the type of rearing: it was longer in the GC rats than in the Wistar ones. In the GC males reared by Wistar foster mothers this parameter was smaller than in the control GC but higher than in Wistar rats. The NA content was significantly lower in the GC cortex, hypothalamus and striatum, and the level of serotonin and 5-HIAA was lower in cortex of the GC as compared with Wistar rats. The cross-fostering affected monoamine content in some brain structures. On the whole, serotonin, DA and NA systems of the GC rats proved to be more susceptible to stress caused by cross-fostering than those of the Wistar rats. The cross-fostering diminished interstrain differences in the NA level in cortex, striatum, and hypothalamus.

Some physiological manifestations of the activity of the gene controlling the predisposition to pendulum-like movements in rats

The physiological actions of the gene controlling the predisposition to stereotypic hyperkinesia in the form of pendulum-like movements (PM) and, probably, a form of spontaneous nystagmus in rats with albinism are manifest as a number of behavioral characteristics (total motor activity, emotionality, startle reflex intensity, sensitivity to serotonin 5-HT2 receptors as assessed in terms of the intensity of head twitching, and predisposition to cataleptic responses). A number of parameters showed differences between hybrids of gray handling-tolerant rats and carriers of the PM gene on the one hand, and between gray rats and animals not carrying the PM gene on the other. Some behavioral characteristics of rats with PM were closer to those of Wistar rats than to those of rats without PM. This, as well as the high frequency of PM in Wistar rats, indicates that the gene responsible for the manifestations of PM is not pathological, but controls a variety of adaptive features of the nervous system. The interaction between PM and the predisposition to catalepsy is biphasic in nature and is described by a curve in the form of an inverted U.

[Effect of cross-fostering on various physiological and behavioral features in Wistar and genetically cataleptic rats]

In the GC rats reared by their natural mothers the plasma corticosterone concentration and open field locomotion were lower than in Wistar rats whereas the startle-reflex amplitude was higher. Cross-fostering did not affect the plasma corticosterone concentration or the startle-reflex amplitude. A negative correlation between these parameters was found. An open field test yielded lower results in Wistar rats reared by foster mothers belonging to the GC strain whereas the reverse cross-fostering did not affect the locomotion in GC rats. The data suggest that fostering affects the open field behaviour whereas cross-fostering effects depend on the genotype of fostered litter.

[Characteristics of behavior of knockout mice with genetic monoamine oxidase A deficiency]

The effect of deletion of monoamine oxidase A (MAO A) in the gene encoding on behavior of transgenic Tg8 mice was studied. A decrease in the amplitude of acoustic startle reflex rather than the prepulse inhibition was found in lacking MAO A Tg8 mice, as compared with the control C3H strain. The exploratory activity in the hole-board test in Tg8 was decreased as well as the number of crossed lines in the light-dark test. Tg8 mice showed decreased latency and increased intensity of intermale aggression. At the same time, no difference was found between Tg8 and C3H mice in locomotor activity, in the expression of sexual motivation, and in the behavior in the elevated plus-maze test. No predisposition to catalepsy was shown.

Design and synthesis of trans-N-[4-[2-(6-cyano-1,2,3, 4-tetrahydroisoquinolin-2-yl)ethyl]cyclohexyl]-4-quinolinecarboxamide (SB-277011): A potent and selective dopamine D(3) receptor antagonist with high oral bioavailability and CNS penetration in the rat

A selective dopamine D(3) receptor antagonist offers the potential for an effective antipsychotic therapy, free of the serious side effects of currently available drugs. Using clearance and brain penetration studies as a screen, a series of 1,2,3, 4-tetrahydroisoquinolines, exemplified by 13, was identified with high D(3) affinity and selectivity against the D(2) receptor. Following examination of molecular models, the flexible butyl linker present in 13 was replaced by a more conformationally constrained cyclohexylethyl linker, leading to compounds with improved oral bioavailability and selectivity over other receptors. Subsequent optimization of this new series to improve the cytochrome P450 inhibitory profile and CNS penetration gave trans-N-[4-[2-(6-cyano-1, 2,3, 4-tetrahydroisoquinolin-2-yl)ethyl]cyclohexyl]-4-quinolinecarbo xamide (24, SB-277011). This compound is a potent and selective dopamine D(3) receptor antagonist with high oral bioavailability and brain penetration in the rat and represents an excellent new chemical tool for the investigation of the role of the dopamine D(3) receptor in the CNS.

Dopamine receptor blockade in the nucleus accumbens inhibits maternal retrieval and licking, but enhances nursing behavior in lactating rats

Maternal behaviors were recorded in rats after a 4-h dam-litter separation and intracranial microinfusion of saline on Day 6 postpartum or cis-flupenthixol (FLU), a dopamine (DA) receptor antagonist, on Days 7-9, within the nucleus accumbens (NA) or dorsomedial striatum (DMS) bilaterally (5, 10, or 20 micro/microL/side), or the lateral ventricle (LV) unilaterally (20 or 40 micro/microL). The number of pups retrieved was inhibited in a dosage-dependent manner by FLU within the NA, but not in other sites. Pup retrieval did not occur within 5 min after 20 microg FLU in five out of nine NA dams; only in these dams did infusions include the shell region of the NA. Duration of pup licking was dose dependently decreased by FLU, the most within the NA, and to a lesser extent within the DMS. Nursing behavior in the kyphotic (upright, dorsally arched) posture, initiated in the absence of pup retrieval by placing the dam over the gathered pups, was not inhibited by intracranial FLU in any site assessed, but rather lasted longer after FLU in NA dams. These various effects of FLU, especially in NA, may be related to modest increases in catalepsy.

Acoustic startle, prepulse inhibition, locomotion, and latent inhibition in the neuroleptic-responsive (NR) and neuroleptic-nonresponsive (NNR) lines of mice

The acoustic startle reflex (ASR) is inhibited by low intensity acoustic stimuli (prepulse inhibition; PPI) delivered prior to the startle stimulus. PPI may reflect underlying sensorimotor processes involved in the filtering of exteroceptive stimuli for their cognitive or physiological relevance. Latent inhibition (LI) is a cognitive process in which pre-exposure to the conditioned stimulus (CS) produces pro-active interference with the acquisition of an associative learning task. LI is thought to reflect a selective attention mechanism that contributes to an organism's ability to adjust its behavior to changing contingencies of reinforcement. In the present series of experiments, the ASR, PPI at three prepulse intensities (56, 68, and 80 dB), locomotor activity, and LI using an active avoidance paradigm were assessed in mice bidirectionally selected from a heterogeneous stock for response (NR line) or nonresponse (NNR line) to neuroleptic-induced catalepsy. A randomly selected line was used as the control. Mice from the NNR line displayed weak startle responses and a complete absence of PPI. In contrast, the NR line displayed the largest ASR and the greatest PPI. The control line displayed ASRs and PPI values intermediate to the selected lines. Locomotor activity which is known to affect LI was lowest in the NR line but was similar in the NNR and control lines. In the LI paradigm, acquisition of the avoidance response was impaired in mice from the NR and control lines that were pre-exposed to the auditory CS (normal response). In contrast, the acquisition of the avoidance response in the NNR line was similar in CS pre-exposed and CS non-pre-exposed animals. Overall, the results demonstrate that some of the same genetic factors which regulate neuroleptic response also play a significant role in PPI and LI.

Central action of glucagon

The central action of the peptide of intestinal tract, glucagon, was studied in Albino Swiss mice (20-25 g) and Wistar rats (200-220 g). Glucagon was injected intracerebroventricularly (icv) at the dose of 0.25, 0.5 and 1 microgram in 1 microliter of distilled water per mouse or 5 micrograms in 5 microliters per rat. It was found that glucagon administered icv increased glucose content in the peripheral blood serum. Behavioral studies have shown that glucagon diminished spontaneous locomotor activity in rats and mice, impaired exploratory activity and reduced amphetamine-induced hyperactivity. The results were not dependent on hyperglycaemia because the administration of 20% glucose solution po did not cause above effects. In addition, glucagon potentiated cataleptogenic effects of haloperidol. Icv injection of glucagon did not change the pain sensitivity or seizure susceptibility. The substance did not show the anxiolytic properties and did not affect the duration of hexobarbital-induced sleep. In biochemical studies it was found that glucagon injected icv induced the decrease in GABA content while the DA content was increased. The utilization of DA was not changed. The obtained results indicated, that glucagon injected icv exerted the central action, which was manifested by the central regulation of glucose level in the periphery. Moreover, glucagon inhibited the locomotor and exploratory activity as well as the amphetamine-induced hyperactivity and enhanced haloperidol-induced catalepsy. These effect could be connected with the inhibition of the central dopaminergic structures by glucagon.

Mirtazapine enhances the effect of haloperidol on apomorphine-induced climbing behaviour in mice and attenuates haloperidol-induced catalepsy in rats

Activation of 5-HT1A receptors has been shown to attenuate catalepsy induced by typical antipsychotic compounds. Since mirtazapine (Remeron; Org 3770) has indirect 5-HT1A receptor stimulating properties as well as antagonist properties at alpha2-adrenoceptors and 5-HT2 receptors, it was of interest to investigate how the compound could modulate the effect of haloperidol on apomorphine-induced climbing behaviour in mice and haloperidol-induced catalepsy in rats. In the apomorphine climbing test, it was found that mirtazapine (2.2-22 mg/kg) did not change the climbing behaviour of mice induced by 1 mg/kg of apomorphine. However, when given as a co-treatment with haloperidol, mirtazapine (1 and 10 mg/kg) dose-dependently augmented the inhibiting effect of haloperidol on this climbing behaviour. Co-treatment with the 5-HT1A receptor agonist 8-OH-DPAT (0.1 mg/kg) also augmented the effect of haloperidol. Catalepsy induced by haloperidol (4.6 mg/kg) was attenuated by mirtazapine (2.2-22 mg/kg). The strongest effect was seen at 90 min after haloperidol treatment. The results obtained in these experiments suggest that co-treatment with mirtazapine may enhance the antipsychotic effect of haloperidol and reduce its extrapyramidal side effects, thereby widening its therapeutic window.

Behavioral and neurochemical effects of the preferential dopamine D3 receptor agonist cis-8-OH-PBZI

In the present study we investigated the in vivo pharmacological profile of the benz[e]indole cis-8-hydroxy-3-(n-propyl)],2,3a,4,5,9b-hexahydro-1H-benz[e]indole (cis-8-OH-PBZI), which has been described as a preferential dopamine D3 receptor agonist in vitro. The compound inhibited spontaneous locomotor activity in mice, an effect which was antagonized by the dopamine D3 receptor antagonist 5,6-dimethoxy-2-(di-u-propylamino) indan (U99194A). Moreover, cis-8-OH-PBZI inhibited conditioned avoidance responding in rats, a preclinical test indicative of antipsychotic efficacy, at doses which did not induce catalepsy. Doses of cis-8-OH-PBZI (6 and 12 mg/kg) that inhibited spontaneous locomotor activity in rats did not affect interstitial levels of dopamine and dihydroxyphenylacetic acid (DOPAC) in the nucleus accumbens or dorsolateral striatum. In contrast to the effect of the dopamine receptor agonist (+/-)-2-dipropylamino-7-hydroxy-1,2,3,4-tetrahydronaphythalene (7-OH-DPAT), cis-8-OH-PBZI did not induce locomotor activity in reserpinized mice. In conclusion, cis-8-OH-PBZI exhibits a pharmacological profile that suggests it has antipsychotic activity but lacks the motoric side effects often associated with antipsychotic medication. The data suggest a mechanism requiring the activation of postsynaptic dopamine D3 receptors and support the hypothesis that these receptors mediate inhibitory behavioral effects.

Selective interaction of homophtalazine derivatives with morphine

Homophtalazines show specific binding sites in the nigrostriatal system and to find their target of action the interactions between these derivatives, nerisopam and girisopam, and chlorpromazine, chlordiazepoxide and morphine were assessed. The compounds did not influence the chlorpromazine induced decrease in motility and catalepsy, nor did they alter the antiaggressive and anticonvulsive action of chlordiazepoxide. However, nerisopam and girisopam augmented the agonist potency of morphine to induce catalepsy or analgesia; they also altered the opioid antagonist potency of naloxone. The naloxone-induced decrease in sucrose consumption in drinking water was augmented by nerisopam and girisopam. It is suggested that a possible target of action of homophtalazines is the opioid signal transduction.

SA4503, a novel cognitive enhancer, with sigma 1 receptor agonistic properties

We found a potent and selective sigma 1 (sigma 1) receptor ligand, SA4503 (1-(3,4-dimethoxyphenethyl)-4-(3-phenylpropyl)piperazine dihydrochloride). This compound had a high affinity for sigma 1 receptor subtype (IC50 = 17 +/- 1.9 nM), but a low affinity for sigma 2 receptor subtype (IC50 = 1800 +/- 310 nM). The present study examines the effect of this compound on the central cholinergic functions, since sigma receptor has been reported to interact with the central cholinergic neurons. SA4503 elicited the increase in extracellular acetylcholine level in rat frontal cortex, while it did not affect the striatal acetylcholine level. On the other hand, tetrahydroaminoacridine (THA), an acetylcholinesterase (AChE) inhibitor, increased the extracellular acetylcholine level in both regions. Although both compounds had anti-amnesic effect against scopolamine-induced memory impairment, THA also induced catalepsy in rats. These results suggest that SA4503 may be a novel cognitive enhancer, with sigma 1 receptor agonistic properties. In addition, SA4503 does not cause striatal cholinomimetic side-effects, which is different from THA.

Neuropsychopharmacological profile of remoxipride in comparison with clozapine

Central effects of remoxipride /(-)-(S)-3-bromo-N-[(1-ethyl-2-pyrrolidinyl)methyl]-2-6-dimethoxybenz amide hydrochloride, RPD/, one of newer antipsychotic drugs with high affinity to sigma sites was studied in comparison with clozapine (CLOZ), another atypical antipsychotic agent, devoid of such an activity. It has been found that RPD decreased the locomotor activity of naive rats, as well as hyperactivity induced by D-amphetamine and apomorphine. The drug antagonized stereotypy induced by both dopamine agonists as well as apomorphine-induced climbing in mice. RPD shortened the time of SKF 38393 (dopamine D1 receptor agonist)-induced grooming in rats. Moreover, it markedly decreased quinpirole (dopamine D2/3 receptor agonist)-induced hyperactivity of rats, and less potently inhibited stimulatory activity induced by cocaine and MK-801 (non-competitive NMDA receptor antagonist). The drug impaired retention of conditioned avoidance responses and induced catalepsy in rats, at relatively high doses though. The effects of CLOZ differed to some extent from those of RPD. The former did not antagonize the apomorphine-induced stereotypy and decreased that caused by D-amphetamine less potently than RPD did. Besides, it did not induce catalepsy, even at relatively high doses while its inhibitory activity towards apomorphine- and quinpirole-induced hyperactivity, as well as locomotor activity of naive rats were much less potent. The effects of RPD and CLOZ in other experimental models were comparable. The obtained results indicating many similarities between psychopharmacological profiles of RPD and CLOZ with some essential differences as well as an equivalence of RPD central effects and the activity of EMD 57445 (selective sigma ligand devoid of any effects at other receptors) permit a supposition that, beside dopamine receptors, the sigma receptors may also be of importance to the mechanism of action of RPD.

Nitric oxide synthase inhibitors produce phencyclidine-like behavioral effects in pigeons

The present study assessed the ability of nitric oxide synthase (NOS) inhibitors to produce PCP-like behavioral effects in pigeons. Food-restricted pigeons were trained to discriminate between PCP (1.0 mg/kg, i.m.) from saline in a two-key operant procedure. NOS inhibitors 7-nitroindazole (7-NI) and N omega-nitro-L-arginine methyl ester (L-NAME) produced PCP-like discriminative stimulus effects. 7-NI (17.8 mg/kg, i.m.) completely generalized to PCP. L-NAME (320-1000 mg/kg) produced partial generalization to PCP. D-NAME, the enantiomer of L-NAME, did not produce PCP-appropriate behavior. L-NAME was approximately 200-times more potent i.c.v., but did not fully generalize to PCP. Both NOS inhibitors were effective in producing catalepsy, which is an effect commonly produced by competitive and uncompetitive NMDA antagonists. 7-NI (32 mg/kg) produced catalepsy in all subjects, whereas L-NAME (3200 mg/kg) produced catalepsy in 50% of the subjects, D-NAME did not produce catalepsy. Pretreatment with L-arginine (32-3200 mg/kg) prevented the PCP-like discriminative stimulus and cataleptic effects of 7-NI (17.8-32 mg/kg), demonstrating that 7-NI produced PCP-like effects through blockade of NO synthesis. The current studies reveal that NOS inhibitors induced two behavioral actions, discriminative stimulus effects and catalepsy, that are very selective for NMDA antagonists in pigeons.

Effect of pre-treatment of some calcium channel blockers on catalepsy and stereotypic behaviour in rats

Effect of pretreatment of intraperitoneally administered Ca-channel blockers Nifedipine (5, 10, 20 mg/kg). Verapamil (5, 10, 20 mg/kg) and Diltiazem (5, 10, 20 mg/kg) was studied on Haloperidol-induced catalepsy and Methamphetamine-induced stereotypy in albino rats. All these drugs reduced the onset of catalepsy, significantly increased the cataleptic score and delayed the onset and inhibited the Methamphetamine-induced stereotypy. The possible involvement of dopaminergic and adrenergic mechanisms and modification by Ca-channel blockers are discussed.

SDZ PSD 958, a novel D1 receptor antagonist with potential limbic selectivity

SDZ PSD 958, a novel benzo[g]quinoxaline derivative exhibits the properties of a potent orally active selective D1 receptor antagonist. It has high affinity for D1-like receptors (D1, D5; pKi = 9.7-9.8) labelled by [3H]SCH23390 and is at least 400 fold less active at D2-like receptors (i.e. D2, D4) labelled by [3H]spiperone. Effects in functional tests are consistent with D1 receptor antagonist properties. SDZ PSD 958 inhibited apomorphine-induced rearing in mice and prevented prolongation of novelty-induced locomotion in rats elicited by the selective D1 receptor agonist CY 208-243. By contrast, SDZ PSD 958 did not induce catalepsy and only weakly inhibited apomorphine-induced stereotyped gnawing in rats. This suggests that SDZ PSD 958 preferentially inhibits responses mediated by dopamine systems innervating the limbic system.