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At least 1,243 records · Page 69Linked to original sources
PubMed1987

On-line low-level radiometric detection of [14C]remoxipride in liquid chromatographic effluents. Application to urine samples.

A method for on-line radiometric detection in liquid chromatography (LC) is described that permits the detection of low levels of radioactivity in LC effluents by using solvent segmentation and storage of the segmented effluent in a capillary storage loop. The object of the method is to make the flow-rate in the on-line radioactivity monitor (and hence the mean residence time in the monitor) independent of the separation process. Therefore, after storage of the complete chromatogram, the segmented effluent is led through the monitor at flow-rates that can be chosen according to the residence time desired for accurate and precise radioactivity determination. In this system, it is possible to use a flow-cell volume small enough to preserve the chromatographic integrity, while maintaining the possibility of increasing the counting time. Tests have been performed on the reproducibility of 14C detection and the influence of the flow-rate through the monitor on the standard deviation in 14C peak area and, thus, on the detection limit, using 14C-labelled remoxipride. As an application, analyses of urine samples for [14C]remoxipride and one of its potential metabolites are reported.

Antipsychotic Agents↗
PubMed2001

Age-related reduction of extrastriatal dopamine D2 receptor measured by PET.

Although the aging effect of dopamine D2 receptor in the striatum is well-documented, the effect of age on the extrastriatal dopamine D2 receptor has not been fully examined. Since the density of extrastriatal dopamine D2 receptor is very low, suitable ligands are limited. In this study, we used [11C]FLB 457 to quantify the extrastriatal dopamine D2 receptor in the living human brain. Twenty-seven healthy male subjects aged from 21 to 82 years participated in the positron emission tomography study. Extrastriatal [11C]FLB 457 binding was quantified with a reference tissue model using cerebellum as a reference region. Binding potentials corresponding to Bmax/Kd were used to evaluate age-related change. We found age-related decreases of D2 receptor binding in all measured extrastriatal regions. The decrease of D2 receptor binding was 13.8% per decade in frontal cortex, 12.0% in temporal cortex, 13.4% in parietal cortex, 12.4% in occipital cortex, 12.2% in hippocampus, and 4.8% in thalamus. These findings suggest that the amounts of D2 receptor declines in all brain regions as part of the normal aging process.

Adult↗
PubMed1999

Effects of chronic treatment with typical and atypical antipsychotic drugs on the rat striatum.

Human MRI studies have demonstrated that treatment with typical antipsychotics may increase the volume of the caudate nucleus while clozapine treatment is associated with either no change or a reversal of the previous volume increase. In this study four groups of seven rats were treated for 8 months with either the typical antipsychotic haloperidol, the atypical antipsychotic clozapine, the D2/D3 receptor antagonist raclopride, or vehicle (plain drinking water). Striatal sections were prepared using D1-like and D2-like receptor ligand autoradiography. Images (4-6 sections per rat, per ligand) were digitized and the area of the striatum was measured on each section. Rats treated with haloperidol did not have a larger mean striatum area than the control group on either D1- or D2-like ligand autoradiograms. Using the D2-like ligand autoradiograms, the clozapine treated animals had a smaller mean striatum area than the control group. Mean left striatum area was larger than mean right striatum area in each treatment group and in the control group. In contrast to the MRI findings reported in schizophrenia, the area of the striatum was not increased in rats treated with typical antipsychotic agents, but the clozapine-associated area reduction may parallel the clinical studies.

Animals↗
PubMed2002

Influence of sildenafil on copulatory behaviour in sluggish or normal ejaculator male rats: a central dopamine mediated effect?

The present study investigates the effects induced by sildenafil (1 mg/kg, p.o.) and the dopamine agonist, SND 919 (0.1 mg/kg, i.p.) on copulatory behaviour of male rats, categorized, on the basis of seven consecutive mating pre-tests, as sluggish and normal ejaculators (SE and NE, respectively). The data obtained show that sildenafil modifies both sexual arousal and ejaculatory mechanisms of copulation. It appears that, although it induced a facilitatory effect on ejaculation of all rats, similarly to SND 919, the lowering of ejaculatory threshold was achieved by means of a reduction of mount frequency and intromission frequency in SE and NE groups, respectively. Differently from SND 919, sildenafil increased sexual arousal, diminishing post ejaculatory interval in SE animals and inter-intromission interval in both SE and NE rats. As the dopamine antagonist, (-)eticlopride (0.02 mg/kg, s.c.), significantly inhibited sildenafil-induced enhancement of sexual arousal in SE rats, it is suggested that the drug acts both peripherally and centrally.

Animals↗
PubMed1997

The neurotensin antagonist SR 48692 fails to modify the behavioural responses to a dopamine D1 receptor agonist in the rat.

The effects of the neurotensin antagonist SR 48692 on the behavioural responses to the dopamine D1 receptor agonist SKF 38393 were investigated in the rat. SKF 38393 (5 mg/kg s.c.) elicited vacuous chewing movements (VCMs) and grooming, which were unaffected by SR 48692 (50 micrograms/kg i.p.). The dopamine D2 receptor antagonist raclopride (0.5 mg/kg s.c.) elicited a small increase in VCMs in animals treated with SR 48692 and attenuated grooming induced by SKF 38393. These effects were not otherwise modified by SR 48692. We conclude that VCMs induced by acute administration of a dopamine D1 receptor agonist are unlikely to be dependent upon enhanced release of neurotensin in the striatum or its projections. This is contrast to the vacuous chewing response which emerges following chronic administration of neuroleptics, which is attenuated by neurotensin receptor antagonist. Thus, inasmuch as chronic neuroleptic-induced VCMs in the rat may be analogous to tardive dyskinesia in humans, the responses induced by acute administration of a D1 agonist to the rat cannot be used as a model of this disorder. Furthermore, the behavioural effects of chronic neuroleptic administration reflect more than a simple shift in the balance of D1 versus D2 receptor stimulation.

2,3,4,5-Tetrahydro-7,8-dihydroxy-1-phenyl-1H-3-ben↗
PubMed1997

Involvement of dopamine D2 receptors in the effect of cocaine on sexual behaviour and stretching-yawning of male rats.

The effect of cocaine (7.5, 15 and 30 mg/kg) administered in acute or subchronic mode, on the mating behaviour of sexually active male rats varied in a dose- and mode-dependent manner. Regardless of mode of treatment, 30 mg/kg markedly impaired the rats copulatory ability and impairment continued for a week after suspension of subchronic treatment. An acute dose of 15 mg/kg reduced intromission frequency, while in subchronic mode it also reduced ejaculation latency. Mount frequency was increased by 7.5 and 15 mg/kg, but only on first injection. In the case of sexually-naive male rats, acute administration of cocaine (3-30 mg/kg) stimulated penile erections at 7.5 mg/kg and motor hyperactivity at all doses. (-) Eticlopride (0.025 and 0.05 mg/kg), a DA D2 antagonist, counteracted cocaine-induced motor hyperactivity but not penile erection, which it enhanced. (-) Eticlopride at the same doses also antagonized cocaine potentiation of lisuride (0.2 mg/kg)-induced behavioural effects. When male rats treated with subchronic cocaine (15 mg/kg) were injected with the DA D2 agonist SND 919 (0.1 mg/kg), they displayed a more marked stretching-yawning behaviour than control animals receiving SND 919 at the same dose. The involvement of DA D2 receptors in cocaine-induced effects is suggested.

Animals↗
PubMed1997

[3H]raclopride binding to brain tissue from subjects with schizophrenia: methodological aspects.

The binding of [3H]raclopride to particulate membrane and frozen sections (with quantitative autoradiography) from the caudate-putamen, obtained at autopsy from schizophrenic and non-schizophrenic subjects, was measured. The affinity of [3H]raclopride to particulate membrane was significantly decreased in the schizophrenic compared to non-schizophrenic subjects. The density of [3H]raclopride binding to tissue from subjects with schizophrenia was increased, unchanged or decreased depending on the methodology used. Finally, there was an age-dependent decrease in [3H]raclopride binding in the frozen sections from the caudate-putamen of the non-schizophrenic subjects. This age-dependent decrease was not apparent using particulate membrane from schizophrenic or non-schizophrenic subjects or tissue sections from the schizophrenic subjects. We conclude that the binding of [3H]raclopride is dependent on methodology and therefore data from in vitro and in vivo studies using this drug should be interpreted with caution.

Adult↗
PubMed1997

Caffeine mimics the effect of a dopamine D2/3 receptor agonist on the expression of immediate early genes in globus pallidus.

In order to evaluate the effect of caffeine on striatopallidal neurons we used in situ hybridization to examine the mRNA expression of the immediate early genes (IEGs), c-fos, fos B, c-jun, jun B, NGFI-A and NGFI-B in globus pallidus in rats given single or repeated administration of caffeine. A significant induction of c-fos mRNA, but not of any of the other IEGs, was found 2, 4 and 8 hr after a single injection of 50 mg/kg caffeine. Following repeated injections of caffeine for 2 weeks a single challenge with caffeine did not induce the expression of any of the studied genes. The ability of caffeine to increase pallidal c-fos mRNA expression was mimicked by the dopamine D2/3 receptor agonist quinpirole (1 or 3 mg/kg), whereas the dopamine D2/3 receptor antagonist raclopride (2 mg/kg) was ineffective. Caffeine and quinpirole did not have synergistic effects when given together. The caffeine-induced c-fos mRNA expression was not counteracted by concomitant treatment with raclopride. The present data provide evidence that acute treatment with caffeine reduces the activity of the striatopallidal neuron, and since this neuron is inhibitory the result is an increased activity in globus pallidus. The effect of blocking the striatal A2A receptors with caffeine is essentially identical to that observed after activation of dopamine D2 receptors, but is independent of these receptors. The fact that pallidal c-fos mRNA expression decreased upon repeated administration of caffeine may be related to the development of tolerance to locomotion stimulation that occurs following chronic caffeine ingestion.

Animals↗
PubMed1998

Disruption in prepulse inhibition after alpha-1 adrenoceptor stimulation in rats.

The role of the alpha-1 adrenoceptor in prepulse inhibition (PPI) was evaluated in rats. The alpha-1 adrenergic agonist cirazoline disrupted PPI; this effect was reversed by the alpha-1 adrenergic antagonist prazosin or the atypical antipsychotic quetiapine. Alpha-1 adrenoceptors may thus be involved in the regulation of PPI and in the psychotherapeutic actions of certain antipsychotics.

Adrenergic alpha-Agonists↗
PubMed1999

Adenosine A2A and group I metabotropic glutamate receptors synergistically modulate the binding characteristics of dopamine D2 receptors in the rat striatum.

There is experimental evidence for the existence of interactions between metabotropic glutamate (mGlu), adenosine and dopamine receptors in the striatum. In membrane preparations from rat striatum the group I and II mGlu receptor agonist 1-aminocyclopentane-1S-3R-dicarboxylic acid (1S-3R-ACPD) was found to modulate the binding characteristics of D2 receptors in a similar manner as the A2A receptor agonist 2-[p-(2-carboxyethyl)phenthylamino]-5'-N-ethylcarboxamidoadenosine (CGS 21680), with a significant decrease in the affinity of the high-affinity state of D2 receptors for dopamine. The effect of 1S-3R-ACPD was mimicked by (+/-)-trans-ACPD (t-ACPD; a racemic mixture of 1S-3R-ACPD and its inactive isomer 1R-3S-ACPD) and by the selective group I mGlu receptor agonist 3,5-dihydroxyphenylglycine (DHPG) and it was counteracted by the selective group I mGlu receptor antagonist 1-aminoindan-1,5-dicarboxilic acid (AIDA), but not by the the group II and III mGlu receptor antagonist (RS)-alpha-methyl-4-tetrazolylphenylglycine (MTPG) or the adenosine receptor antagonist 8-phenyltheophylline. Furthermore, a strong synergistic effect was observed when the striatal membranes were exposed to both CGS 21680 and 1S-3R-ACPD. In agreement with the biochemical results, in unilaterally 6-OH-dopamine lesioned rats 1S-3R-ACPD counteracted the turning behaviour induced by the D2 receptor agonist quinpirole, but not by the D1 receptor agonist SKF 38393, and it synergistically potentiated the antagonistic effect of CGS 21680 on quinpirole-induced turning behaviour.

2,3,4,5-Tetrahydro-7,8-dihydroxy-1-phenyl-1H-3-ben↗
PubMed1999

Effects of the substituted (S)-3-phenylpiperidine (-)-OSU6162 on PET measurements of [11C]SCH23390 and [11C]raclopride binding in primate brains.

The substituted (S)-3-phenylpiperidine (-)-OSU6162 belongs to a novel class of functional modulators of dopaminergic systems. In vivo, (-)-OSU6162 has a unique stabilising profile on dopaminergic functions. In vitro this compound exhibits low affinity for the dopamine D2 receptor, but due to its similarity to neuroleptics on brain dopaminergic neurochemistry and different postsynaptic effects it has been characterised as a preferential dopamine autoreceptor antagonist. To further clarify the effects of (-)-OSU6162 on the postjunctional nigrostriatal dopaminergic system, dopamine receptor binding was measured in rhesus monkeys (Macaca mulatta) by positron emission tomography (PET) using the D1 and D2 dopamine receptor radioligands [11C]SCH23390 and [11C]raclopride respectively, before and during continuous intravenous infusions of(-)-OSU6162. Additionally, the test-retest variability of sequential [11C]SCH23390 scans was estimated. Following the administration of (-)-OSU6162, [11C]raclopride binding in striatum was dose-dependently decreased with a 76% reduction occurring after 3.0 mg/kg per h continuous infusion. Whereas (-)-OSU6162 in the lower doses had no effect on [11C]SCH23390 binding, the highest dose, 3.0 mg/kg per h, increased [11C]SCH23390 binding, which may indicate a potentiating effect on D1 dopamine receptor mediated functions. Thus, in contrast to the conditions in vitro, (-)-OSU6162 produces a high displacement of raclopride from D2 receptors in vivo.

Animals↗
PubMed1972

Antipyretics.

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Acetaminophen↗
PubMed1997

Involvement of dopamine receptors in the antipsychotic profile of (-) eticlopride.

The present study was performed to assess the effects exerted by the dopamine (DA) D2/D3 antagonist (-) eticlopride on rodent behavioral models considered to be predictive of antipsychotic activity, namely, antagonism toward DA agonist-induced stereotyped behavior (SB), and ketamine-and cocaine-induced hypermotility. (-) Eticlopride (10-50 micrograms/kg) dose-dependently inhibited SB elicited by SND 919 (10 mg/kg), CQP 201-403 (0.5 mg/kg), and 7-OH-DPAT (5 mg/kg); moreover, it significantly counteracted the hypermotility induced in rats and mice by ketamine (5 and 10 mg/kg). When (-) eticlopride was injected before cocaine (15 mg/kg) either acutely or subchronically administered in male rats, it also potently antagonized the hypermotility typically induced by the drug. These results are discussed in the light of putative D2/D3 receptor involvement, and are considered as predictive of antipsychotic potential.

Animals↗
PubMed2002

Accumulation of arachidonic acid-rich triacylglycerols in the microalga Parietochloris incisa (Trebuxiophyceae, Chlorophyta).

The freshwater green microalga Parietochloris incisa is the richest known plant source of the polyunsaturated fatty acid (PUFA), arachidonic acid (20:4omega6, AA). While many microalgae accumulate triacylglycerols (TAG) in the stationary phase or under certain stress conditions, these TAG are generally made of saturated and monounsaturated fatty acids. In contrast, most cellular AA of P. incisa resides in TAG. Using various inhibitors, we have attempted to find out if the induction of the biosynthesis of AA and the accumulation of TAG are codependent. Salicylhydroxamic acid (SHAM) affected a growth reduction that was accompanied with an increase in the content of TAG from 3.0 to 6.2% of dry weight. The proportion of 18:1 increased sharply in all lipids while that of 18:2 and its down stream products, 18:3omega6, 20:3omega6 and AA, decreased, indicating an inhibition of the Delta12 desaturation of 18:1. Treatment with the herbicide SAN 9785 significantly reduced the proportion of TAG. However, the proportion of AA in TAG, as well as in the polar lipids, increased. These findings indicate that while there is a preference for AA as a building block of TAG, the latter can be produced using other fatty acids, when the production of AA is inhibited. On the other hand, inhibiting TAG construction did not affect the production of AA. In order to elucidate the possible role of AA in TAG we have labeled exponential cultures of P. incisa kept at 25 degrees C with [1-14C]arachidonic acid and cultivated the cultures for another 12 h at 25, 12 or 4 degrees C. At the lower temperatures, labeled AA was transferred from TAG to polar lipids, indicating that TAG of P. incisa may have a role as a depot of AA that can be incorporated into the membranes, enabling the organism to quickly respond to low temperature-induced stress.

Arachidonic Acid↗
PubMed2001

Cocaine induces conditioned place preference and increases locomotor activity in male Japanese quail.

The conditioned place preference (CPP) procedure is a popular method used for testing the rewarding properties of human drugs of abuse. Most CPP studies utilize mammalian models. However, avian species have better visual systems than rodent species, and because the cues that become associated with human drug-taking behavior are often visual, Aves might serve as an alternative animal model for investigating drugs of abuse. In three experiments, we examined the locomotor stimulant and rewarding effects of cocaine in adult male Japanese quail. In Experiment 1, cocaine increased locomotor activity relative to saline. In addition, behavioral sensitization was evident across repeated injections. In Experiment 2, CPP was established after six pairings of cocaine. Finally, the dopamine D(2) receptor subtype antagonist eticlopride did not attenuate acquisition of cocaine CPP in Experiment 3. Rather, subjects receiving pretreatment of eticlopride demonstrated a place preference for the cocaine-paired context. In contrast, pretreatment of eticlopride reduced cocaine-induced locomotor activity. The findings suggest that drug-reward processes may be highly conserved across species and that birds may serve as a viable model for investigating drug-reward processes especially with regard to the ability of cocaine to become associated with visual cues.

Animals↗
PubMed2001

Nicotine-conditioned locomotor activity in rats: dopaminergic and GABAergic influences on conditioned expression.

Little is known about the processes that mediate acquisition and expression of conditioned associations between contextual cues and psychomotor effects of nicotine. In four separate experiments using rats, an environment repeatedly paired with nicotine acquired the ability to elicit increases in activity even in the absence of drug. This conditioned effect was sensitive to nicotine dose. Rats that had 0.6 or 1.2 mg/kg nicotine, but not 0.3 mg/kg, paired with the environment were more active than an unpaired control group (Experiment 1). In Experiment 2, control groups eliminated accounts based on nonspecific effects of nicotine and inhibitory conditioning decreasing activity in the unpaired controls of Experiment 1. Pretreatment on the test day with 100 mg/kg of gamma vinyl-GABA (GVG), a compound that inhibits the enzyme required to breakdown GABA, partially blocked the expression of locomotor conditioning without impairing activity in controls (Experiment 3). In Experiment 4, pretreatment on the test day with the dopamine D(1) receptor antagonist SCH-23390 (0.03 mg/kg) blocked expression of nicotine-conditioned locomotor activity; the D(2)/D(3) receptor antagonist eticlopride did not. Thus, the dopamine D(1) receptor subtype appears to play a role in context-elicited increases in activity conditioned by nicotine; GABA may also modulate the expression of this conditioned effect.

4-Aminobutyrate Transaminase↗