Analgesia and pain: Dual effect of dopamine on the peripheral nociceptive system is dependent on D2-or D1-like receptor activation.

In this study, a pharmacological approach, together with the paw pressure test, was used to investigate the role of dopamine and its receptors in the peripheral processing of the nociceptive response in mice. Initially, the administration of dopamine (5, 20, and 80 ng/paw) in the hind paw of male Swiss mice (30-40 g) promoted antinociceptive effects in a dose-dependent manner. This was considered a peripheral effect, as it did not produce changes in the nociceptive threshold of the contralateral paw. The D2, D3, and D4 dopamine receptor antagonists remoxipride (4 µg/paw), U99194 (16 µg/paw), and L-745,870 (16 µg/paw), respectively, reversed the dopamine-mediated antinociception in mice with PGE2-induced hyperalgesia. The D1 and D5 dopamine receptor antagonists SKF 83566 (2 µg/paw) and SCH 23390 (1.6 µg/paw), respectively, did not alter dopamine antinociception. In contrast, dopamine at higher doses (0.1, 1, and 10 µg/paw) caused hyperalgesia in the animals, and the D1 and D5 receptor antagonists reversed this pronociceptive effect (10 µg/paw), whereas the D2 receptor antagonist remoxipride did not. Our data suggest that dopamine has a dual effect that depends on the dose, as it causes peripheral antinociceptive effects at small doses via the activation of D2-like receptors and nociceptive effects at higher doses via the activation of D1-like receptors.

The Expression of Dopamine Receptors Gene and their Potential Role in Targeting Breast Cancer Cells with Selective Agonist and Antagonist Drugs. Could it be the Novel Insight to Therapy?

BACKGROUND: Breast cancer is one of the common causes of mortality for women in Iran and other parts of the world. The substantial increasing rate of breast cancer in both developed and developing countries warns the scientists to provide more preventive steps and therapeutic measures. This study is conducted to investigate the impact of neurotransmitters (e.g., Dopamine) through their receptors and the importance of cancers via damaging immune system. It also evaluates dopamine receptors gene expression in the women with breast cancer at stages II or III and dopamine receptor D2 (DRD2) related agonist and antagonist drug effects on human breast cancer cells, including MCF-7 and SKBR-3. METHODS: The patients were categorized into two groups: 30 native patients who were diagnosed with breast cancer at stages II and III, with the mean age of 44.6 years and they were reported to have the experience of a chronic stress or unpleasant life event. The second group included 30 individuals with the mean age of 39 years as the control group. In order to determine the RNA concentration in all samples, the RNA samples were extracted and cDNA was synthesized. The MCF-7 cells and SKBR-3 cells were treated with dopamine receptors agonists and antagonists. The MTT test was conducted to identify oxidative and reductive enzymes and to specify appropriate dosage at four concentrations of dopamine and Cabergoline on MCF-7 and SKBR-3 cells. Immunofluorescence staining was done by the use of a mixed dye containing acridine orange and ethidiume bromide on account of differentiating between apoptotic and necrotic cells. Flow cytometry assay was an applied method to differentiate necrotic from apoptotic cells. RESULTS: Sixty seven and thirty three percent of the patients were related to stages II and III, respectively. About sixty three percent of the patients expressed ER, while fifty seven percent expressed PR. Thirty seven percent of the patients were identified as HER-2 positive. All types of D2-receptors were expressed in PBMC of patients with breast cancer and healthy individuals. The expression of the whole dopamine receptor subtypes (DRD2-DRD4) was carried out on MCF-7 cell line. The results of RT-PCR confirmed the expression of DRD2 on SKBR-3 cells, whereas the other types of D2- receptors did not have an expression. The remarkable differences in gene expression rates between patients and healthy individuals were revealed in the result of the Real-time PCR analysis. The over expression in DRD2 and DRD4 genes of PBMCs was observed in the patients with breast cancer at stages II and III. The great amount of apoptosis and necrosis occurred after the treatment of MCF-7 cells by Cabergoline from 25 to 100 µmolL-1 concentrations. CONCLUSION: This study revealed the features of dopamine receptors associated with apoptosis induction in breast cancer cells. Moreover, the use of D2-agonist based on dopamine receptors expression in various breast tumoral cells could be promising as a new insight of complementary therapy in breast cancer.

Modeling of prolactin response following dopamine D2 receptor antagonists in rats: can it be translated to clinical dosing?

Prolactin release is a side effect of antipsychotic therapy with dopamine antagonists, observed in rats as well as humans. We examined whether two semimechanistic models could describe prolactin response in rats and subsequently be translated to predict pituitary dopamine D2 receptor occupancy and plasma prolactin concentrations in humans following administration of paliperidone or remoxipride. Data on male Wistar rats receiving single or multiple doses of risperidone, paliperidone, or remoxipride was described by two semimechanistic models, the precursor pool model and the agonist-antagonist interaction model. Using interspecies scaling approaches, human D2 receptor occupancy and plasma prolactin concentrations were predicted for a range of clinical paliperidone and remoxipride doses. The predictions were compared with corresponding observations described in literature as well as with predictions from published models developed on human data. The pool model could predict D2 receptor occupancy and prolactin response in humans following single doses of paliperidone and remoxipride. Tolerance of prolactin release was predicted following multiple doses. The interaction model underpredicted both D2 receptor occupancy and prolactin response. Prolactin elevation may be deployed as a suitable biomarker for interspecies translation and can inform the clinical safe and effective dose range of antipsychotic drugs. While the pool model was more predictive than the interaction model, it overpredicted tolerance on multiple dosing. Shortcomings of the translations reflect the need for better mechanistic models.

Multivariate pharmacokinetic/pharmacodynamic (PKPD) analysis with metabolomics shows multiple effects of remoxipride in rats.

The study of central nervous system (CNS) pharmacology is limited by a lack of drug effect biomarkers. Pharmacometabolomics is a promising new tool to identify multiple molecular responses upon drug treatment. However, the pharmacodynamics is typically not evaluated in metabolomics studies, although being important properties of biomarkers. In this study we integrated pharmacometabolomics with pharmacokinetic/pharmacodynamic (PKPD) modeling to identify and quantify the multiple endogenous metabolite dose-response relations for the dopamine D2 antagonist remoxipride. Remoxipride (vehicle, 0.7 or 3.5mg/kg) was administered to rats. Endogenous metabolites were analyzed in plasma using a biogenic amine platform and PKPD models were derived for each single metabolite. These models were clustered on basis of proximity between their PKPD parameter estimates, and PKPD models were subsequently fitted for the individual clusters. Finally, the metabolites were evaluated for being significantly affected by remoxipride. In total 44 metabolites were detected in plasma, many of them showing a dose dependent decrease from baseline. We identified 6 different clusters with different time and dose dependent responses and 18 metabolites were revealed as potential biomarker. The glycine, serine and threonine pathway was associated with remoxipride pharmacology, as well as the brain uptake of the dopamine and serotonin precursors. This is the first time that pharmacometabolomics and PKPD modeling were integrated. The resulting PKPD cluster model described diverse pharmacometabolomics responses and provided a further understanding of remoxipride pharmacodynamics. Future research should focus on the simultaneous pharmacometabolomics analysis in brain and plasma to increase the interpretability of these responses.

Revealing the Neuroendocrine Response After Remoxipride Treatment Using Multi-Biomarker Discovery and Quantifying It by PK/PD Modeling.

To reveal unknown and potentially important mechanisms of drug action, multi-biomarker discovery approaches are increasingly used. Time-course relationships between drug action and multi-biomarker profiles, however, are typically missing, while such relationships will provide increased insight in the underlying body processes. The aim of this study was to investigate the effect of the dopamine D2 antagonist remoxipride on the neuroendocrine system. Different doses of remoxipride (0, 0.7, 5.2, or 14 mg/kg) were administered to rats by intravenous infusion. Serial brain extracellular fluid (brainECF) and plasma samples were collected and analyzed for remoxipride pharmacokinetics (PK). Plasma samples were analyzed for concentrations of the eight pituitary-related hormones as a function of time. A Mann-Whitney test was used to identify the responding hormones, which were further analyzed by pharmacokinetic/pharmacodynamic (PK/PD) modeling. A three-compartment PK model adequately described remoxipride PK in plasma and brainECF. Not only plasma PRL, but also adrenocorticotrophic hormone (ACTH) concentrations were increased, the latter especially at higher concentrations of remoxipride. Brain-derived neurotropic factor (BDNF), follicle stimulating hormone (FSH), growth hormone (GH), luteinizing hormone (LH), and thyroid stimulating hormones (TSH) did not respond to remoxipride at the tested doses, while oxytocin (OXT) measurements were below limit of quantification. Precursor pool models were linked to brainECF remoxipride PK by Emax drug effect models, which could accurately describe the PRL and ACTH responses. To conclude, this study shows how a multi-biomarker identification approach combined with PK/PD modeling can reveal and quantify a neuroendocrine multi-biomarker response for single drug action.

New perspective therapy of breast cancer based on selective dopamine receptor D2 agonist and antagonist effects on MCF-7 cell line.

Different studies have shown the role of neurotransmitters (e.g., dopamine) in the progression of cancers via their various types of receptors. The aim of this study was to determine the pattern of dopamine receptors gene expression on MCF-7 cells and to evaluate the selective dopamine receptors agonist and antagonist effects on them. In addition, some other discoveries which are patented for the treatment of breast cancer are reviewed in this article. To determine the pattern of dopamine receptors gene expression in human breast cancer cells (MCF-7), RT-PCR was performed. Then, MCF-7 cells were treated by different doses of bromocriptine and remoxipride for 48 hours. Cell viability was evaluated by MTT assay. Thus, nuclear morphology of cells was analyzed by mixed dye florescent staining. Real time PCR technique was performed to determine the decreasing rate of proliferating cell nuclear antigen (PCNA) gene expression in treated MCF-7 cells. Finally, quantification of apoptosis and its difference with necrosis at the single cell level were assessed by Flowcytometery technique. This study revealed that, unlike remoxipride, bromocriptine suppressed proliferation of the MCF-7 cells (54.3% at 12.5µM bromocriptine concentration), but remoxipride could suppress the effect of bromocriptine. Bromocriptine has inhibitory effects on MCF- 7 cells by induction of apoptosis via D2-like receptors. Therefore, in future studies, bromocriptine can be used as a new choice for the treatment of tumoral breast cancer cells.

Mechanism-based PK-PD model for the prolactin biological system response following an acute dopamine inhibition challenge: quantitative extrapolation to humans.

The aim of this investigation was to develop a mechanism-based pharmacokinetic-pharmacodynamic (PK-PD) model for the biological system prolactin response following a dopamine inhibition challenge using remoxipride as a paradigm compound. After assessment of baseline variation in prolactin concentrations, the prolactin response of remoxipride was measured following (1) single intravenous doses of 4, 8 and 16 mg/kg and (2) following double dosing of 3.8 mg/kg with different time intervals. The mechanistic PK-PD model consisted of: (i) a PK model for remoxipride concentrations in brain extracellular fluid; (ii) a pool model incorporating prolactin synthesis, storage in lactotrophs, release into- and elimination from plasma; (iii) a positive feedback component interconnecting prolactin plasma concentrations and prolactin synthesis; and (iv) a dopamine antagonism component interconnecting remoxipride brain extracellular fluid concentrations and stimulation of prolactin release. The most important findings were that the free brain concentration drives the prolactin release into plasma and that the positive feedback on prolactin synthesis in the lactotrophs, in contrast to the negative feedback in the previous models on the PK-PD correlation of remoxipride. An external validation was performed using a dataset obtained in rats following intranasal administration of 4, 8, or 16 mg/kg remoxipride. Following simulation of human remoxipride brain extracellular fluid concentrations, pharmacodynamic extrapolation from rat to humans was performed, using allometric scaling in combination with independent information on the values of biological system specific parameters as prior knowledge. The PK-PD model successfully predicted the system prolactin response in humans, indicating that positive feedback on prolactin synthesis and allometric scaling thereof could be a new feature in describing complex homeostatic mechanisms.

Systemic and direct nose-to-brain transport pharmacokinetic model for remoxipride after intravenous and intranasal administration.

Intranasal (IN) administration could be an attractive mode of delivery for drugs targeting the central nervous system, potentially providing a high bioavailability because of avoidance of a hepatic first-pass effect and rapid onset of action. However, controversy remains whether a direct transport route from the nasal cavity into the brain exists. Pharmacokinetic modeling is proposed to identify the existence of direct nose-to-brain transport in a quantitative manner. The selective dopamine-D2 receptor antagonist remoxipride was administered at different dosages, in freely moving rats, by the IN and intravenous (IV) route. Plasma and brain extracellular fluid (ECF) concentration-time profiles were obtained and simultaneously analyzed using nonlinear mixed-effects modeling. Brain ECF/plasma area under the curve ratios were 0.28 and 0.19 after IN and IV administration, respectively. A multicompartment pharmacokinetic model with two absorption compartments (nose-to-systemic and nose-to-brain) was found to best describe the observed pharmacokinetic data. Absorption was described in terms of bioavailability and rate. Total bioavailability after IN administration was 89%, of which 75% was attributed to direct nose-to brain transport. Direct nose-to-brain absorption rate was slow, explaining prolonged brain ECF exposure after IN compared with IV administration. These studies explicitly provide separation and quantitation of systemic and direct nose-to-brain transport after IN administration of remoxipride in the rat. Describing remoxipride pharmacokinetics at the target site (brain ECF) in a semiphysiology-based manner would allow for better prediction of pharmacodynamic effects.

Comparison of the agonist-antagonist interaction model and the pool model for the effect of remoxipride on prolactin.

AIMS: The tolerance to the prolactin response following administration of antipsychotic drugs has been modelled as a depletion of a prolactin pool (pool model) and a model where the tolerance is explained by a feedback loop including the dopamine interaction of prolactin release (agonist-antagonist interaction model, (AAI model)). The AAI model was superior to the pool model when analyzing data from clinical trials of risperidone and paliperidone. Here we evaluated the two models using the remoxipride data, designed to challenge the short-term prolactin response, from which the original pool model was built. METHODS: The remoxipride data were collected from a study where eight healthy male subjects received two remoxipride infusions on five occasions. The intervals between the first and second dose on each occasion were 2, 8, 12, 24 and 48 h, respectively. The pool and AAI models were fitted using NONMEM. RESULTS: According to the objective function values the pool model with a circadian rhythm function fitted the data slightly better, while the AAI model was better in describing the circadian rhythm of prolactin. Visual predictive checks revealed that the models predicted the prolactin profiles equally well. CONCLUSIONS: According to the analysis performed here, a previous analysis of several clinical studies and literature reports on prolactin concentrations, it appears that the dopamine feedback mechanism included in the AAI model is better than the storage depletion mechanism in the pool model to estimate the bio-rhythm of prolactin time-course and the tolerance development across different populations, drugs, treatment schedules and time.

Zotepine versus other atypical antipsychotics for schizophrenia.

BACKGROUND: In many parts of the world, particularly in industrialised countries, second generation (atypical) antipsychotic drugs have become first line treatment for people suffering from schizophrenia. The question as to whether the effects of various second generation antipsychotic drugs differ is a matter of debate. OBJECTIVES: To evaluate the effects of zotepine compared with other second generation antipsychotic drugs for people suffering from schizophrenia and schizophrenia-like psychoses. SEARCH STRATEGY: We searched the Cochrane Schizophrenia Group Trials Register (November 2009), inspected references of all identified studies for further trials and contacted authors of trials for additional information. SELECTION CRITERIA: We included only randomised clinical controlled trials that compared zotepine with any forms of amisulpride, aripiprazole, clozapine, olanzapine, risperidone, sertindole or ziprasidone in people suffering from only schizophrenia or schizophrenia-like psychoses. DATA COLLECTION AND ANALYSIS: SS and KK extracted data independently. For dichotomous data we calculated relative risks (RR) and their 95% confidence intervals (CI) on an intention-to-treat basis based on a random-effects model. For continuous data, we calculated weighted mean differences (MD) again based on a random-effects model. MAIN RESULTS: We included three studies (total n=289; 2 RCTs zotepine vs clozapine; 1 RCT zotepine vs clozapine vs risperidone (at 4 mg, 8 mg doses) vs remoxipride. All studies were of limited methodological quality. When zotepine was compared with clozapine, it was clozapine that was found to be more effective in terms of global state (n=59, 1 RCT, RR No clinically significant response 8.23 CI 1.14 to 59.17). Mental state scores also favoured clozapine (n=59, 1 RCT, MD average score (BPRS total, high = poor) 6.00 CI 2.17 to 9.83) and there was less use of antiparkinson medication in the clozapine group (n=116, 2 RCTs, RR 20.96 CI 2.89 to 151.90). In the comparison of zotepine and risperidone, mental state scoring found no significant difference between the groups (vs 4 mg: n=40, 1 RCT, MD average endpoint score (BPRS total, high=poor) 1.40 CI -9.82 to 12.62; vs 8 mg: n=40, 1 RCT, MD -1.30 CI -12.95 to 10.35) and use of antiparkinson medication was equivocal (vs 4 mg: n=40, 1 RCT, MD 1.80 CI -0.64 to 4.24; vs 8 mg: n=40, 1 RCT, MD 2.50 CI -0.05 to 5.05). Finally, when zotepine was compared with remoxipride, again no effect was found for mental state (n=58, 1 RCT, MD average endpoint score (BPRS total, high=poor) 5.70 CI -4.13 to 15.53) and there was no significant difference between the two groups in terms of use of antiparkinson medication (n=49, 1 RCT, RR 0.97 CI 0.41 to 2.29).Data on important other outcomes such as other adverse events, service use or satisfaction with care, quality of life were not available. AUTHORS' CONCLUSIONS: The evidence base around zotepine is insufficient to provide firm conclusions on its absolute or relative effects. This is despite it being in use in Austria, France, Germany, Japan and the UK.

Online solid phase extraction with liquid chromatography-tandem mass spectrometry to analyze remoxipride in small plasma-, brain homogenate-, and brain microdialysate samples.

Remoxipride is a selective dopamine D(2) receptor antagonist, and useful as a model compound in mechanism-based pharmacological investigations. To that end, studies in small animals with serial sampling over time are needed. For these small volume samples currently no suitable analytical methods are available. We propose analytical methods for the detection of low concentrations remoxipride in small sample volumes of plasma, brain homogenate, and brain microdialysate, using online solid phase extraction with liquid chromatography-tandem mass spectrometry. Method development, optimization and validation are described in terms of calibration curves, extraction yield, lower limit of quantification (LLOQ), precision, accuracy, inter-day- and intra-day variability. The 20 microl plasma samples showed an extraction yield of 76%, with a LLOQ of 0.5 ng/ml. For 0.6 ml brain homogenate samples the extraction yield was 45%, with a LLOQ of 1.8 ng/ml. The 20 microl brain microdialysate samples, without pre-treatment, had a LLOQ of 0.25 ng/ml. The precision and accuracy were well within the acceptable 15% range. Considering the small sample volumes, the high sensitivity and good reproducibility, the analytical methods are suitable for analyzing small sample volumes with low remoxipride concentrations.

Differences among conventional, atypical and novel putative D(2)/5-HT(1A) antipsychotics on catalepsy-associated behaviour in cynomolgus monkeys.

Typical antipsychotics such as haloperidol exert their therapeutic effects via blockade of dopamine (DA) D(2) receptors, leading to extrapyramidal symptoms (EPS) in humans and catalepsy in rodents. In contrast, atypical antipsychotics and new generation D(2)/5-HT(1A) antipsychotics have low cataleptogenic potential. However, there has been no systematic comparative study on the effects of these different classes of antipsychotics in non-human primates, a species displaying a more sophisticated repertoire of behavioural/motor activity than rats. Once weekly, six young adult female non-haloperidol-sensitised cynomolgus monkeys were treated i.m. with a test compound and videotaped to score catalepsy-associated behaviour (CAB: static postures, unusual positions and crouching). Haloperidol, risperidone, olanzapine, nemonapride and remoxipride induced, to different extents, an increase in unusual positions (a response akin to dystonia), some crouching and static postures. In contrast, clozapine, quetiapine, ziprasidone and aripiprazole produced much lower or no unusual positions; clozapine also produced marked increases in static postures and crouching. Among novel D(2)/5-HT(1A) antipsychotics, SLV313 and F15063 augmented the number of unusual positions, albeit at doses 16-63 times higher than those of haloperidol for approximately the same score. SSR181507 and bifeprunox produced moderate static postures, little crouching and negligible unusual positions. These data provide the first comparative analysis in cynomolgus monkeys of EPS liability of conventional, atypical and novel D(2)/5-HT(1A) antipsychotics. They indicate that the latter are less prone than haloperidol to produce CAB, and provide a basis for comparison with rodent catalepsy studies.

FemtoMolar measurements using accelerator mass spectrometry.

Accelerator mass spectrometry (AMS) is an ultra-sensitive analytical method suitable for the detection of sub-nM concentrations of labeled biological substances such as pharmaceutical drugs in body fluids. A limiting factor in extending the concentration measurements to the sub-pM range is the natural (14)C content in living tissues. This was circumvented by separating the labeled drug from the tissue matrix, using standard high-performance liquid chromatography (HPLC) procedures. As the separated total drug amount is in the few fg range, it is not possible to use a standard AMS sample preparation method, where mg sizes are required. We have utilized a sensitive carbon carrier method where a (14)C-deficient compound is added to the HPLC fractions and the composite sample is prepared and analyzed by AMS. Using 50 microL human blood plasma aliquots, we have demonstrated concentration measurements below 20 fM, containing sub-amol amounts of the labeled drug. The method has the immediate potential of operating in the sub-fM region.

Mechanistic model for drug release during the lag phase from pellets coated with a semi-permeable membrane.

A new mechanistic model of drug release during the lag phase from coated pellets undergoing cracking in the coating due to the hydrostatic pressure built up inside the pellet has been developed. The model describes dynamically all the main release processes occurring during the lag phase in pellets coated with a semi-permeable membrane, i.e. the influx of solvent driven by the difference in osmotic pressure across the coating, dissolution of the drug, swelling of the pellet due to solvent accumulation, build-up of hydrostatic pressure inside the pellet, tensile stress acting on the coating, and the efflux of the dissolved drug. The water uptake is described using irreversible thermodynamics theory, while the tensile stress is described using solid mechanics theory. Importantly, the model allows the prediction of the lag time prior to crack formation. The effect of the pellet size, the pellet shape and the coating thickness on the lag time and on the lag phase release profile has been investigated via computer simulations. The model was validated by comparison with dose release data obtained from pellets coated with an ethyl-cellulose-based film. The good agreement found between the predicted release and the experimental data confirmed the validity of the model.

Sigma 1 receptor-mediated increase in hippocampal extracellular dopamine contributes to the mechanism of the anticonvulsant action of neuropeptide Y.

The potent anticonvulsant properties of neuropeptide Y (NPY) are generally attributed to a Y2 receptor-mediated inhibition of glutamatergic synaptic transmission. Independent studies have shown that NPY increases brain dopamine content, possibly via interaction with sigma 1 receptors. Recently, we showed that increased extracellular hippocampal dopamine attenuates pilocarpine-induced limbic seizures via activation of hippocampal D2 receptors. Our aim in this study was to elucidate the role of increased hippocampal dopamine in the mechanism of the anticonvulsant action of NPY and to investigate the involvement of Y2 and sigma 1 receptors in this process. Limbic seizures were evoked in freely moving rats by intrahippocampal administration of pilocarpine via a microdialysis probe. NPY was administered intracerebroventricularly, intrahippocampally via the microdialysis probe, or coadministered intrahippocampally with the D2 receptor antagonist remoxipride, the Y2 receptor antagonist BIIE0246 or the sigma 1 receptor antagonist BD1047. Changes in hippocampal extracellular dopamine were monitored, and behavioural changes indicative of seizure activity were scored. Intracerebroventricular (10 nmol/3 microL) and intrahippocampal (20-50 microm) NPY administration increased hippocampal dopamine and attenuated pilocarpine-induced seizures. Hippocampal D2 receptor blockade (4 microm remoxipride) reversed the anticonvulsant effect of NPY. Y2 receptor blockade (1 microm BIIE0246) reversed the anticonvulsant effect of NPY but did not prevent NPY-induced increases in hippocampal dopamine. Sigma 1 receptor blockade (10 microm BD1047) abolished NPY-induced increases in hippocampal dopamine and reversed the anticonvulsant effect of NPY. Our results indicate that NPY-induced increases in hippocampal dopamine are mediated via sigma 1 receptors and contribute to the anticonvulsant effect of NPY via increased activation of hippocampal D2 receptors. This novel mechanism of anticonvulsant action of NPY is separate from, and may be complementary to, the well established Y2 receptor-mediated inhibition of hippocampal excitability.

Differences in the cellular mechanism underlying the effects of amphetamine on prepulse inhibition in apomorphine-susceptible and apomorphine-unsusceptible rats.

BACKGROUND: Amphetamine is often used to mimic certain aspects of schizophrenia in laboratory animals, such as a decreased prepulse inhibition. MATERIALS AND METHODS: Apomorphine-susceptible and apomorphine-unsusceptible rats represent a well-characterized animal model for individual differences in the sensitivity to dopaminergic drugs. Moreover, apomorphine-susceptible rats show a wide variety of schizophrenia-like abnormalities. The differential response to administration of amphetamine (1-4 mg/kg, i.p.) was investigated in these two rat lines using the prepulse inhibition paradigm. Because amphetamine promotes dopamine release, the cellular mechanism underlying the line-specific effects of amphetamine was investigated by administration of alpha-methyl-para-tyrosine (aMpT) and reserpine, substances that are known to deplete the cytosolic dopamine pool and the vesicular dopamine pool, respectively, the former being primarily implicated in mediating the effects of amphetamine. RESULTS: All doses of amphetamine decreased prepulse inhibition in apomorphine-susceptible rats, whereas only the highest doses (2 and 4 mg/kg, i.p.) of amphetamine decreased prepulse inhibition in apomorphine-unsusceptible rats. Alpha-methyl-para-tyrosine, but not reserpine, blocked the amphetamine-induced disruption in prepulse inhibition in apomorphine-unsusceptible rats, whereas both substances alone had no effect in apomorphine-susceptible rats. However, the combination of alpha-methyl-para-tyrosine and reserpine did block the amphetamine-induced effects in the latter rat line. DISCUSSION: The present study suggests that apomorphine-susceptible rats are more sensitive to systemic administration of amphetamine than apomorphine-unsusceptible rats. In addition, the data show that the cellular mechanism underlying the effects of amphetamine differs between apomorphine-susceptible and apomorphine-unsusceptible rats. Whereas the effects of amphetamine on prepulse inhibition in apomorphine-unsusceptible rats just require the alpha-methyl-para-tyrosine sensitive dopamine pool, the effects in apomorphine-susceptible rats require both the alpha-methyl-para-tyrosine sensitive and the reserpine sensitive dopamine pool. Because apomorphine-susceptible rats share many features with schizophrenic patients, these data open the perspective that in these patients amphetamine may induce dopamine release from both types of dopamine pool. This might provide an explanation for the increased dopamine release after this psychostimulant drug in patients vs controls.

Evaluation of osmotic effects on coated pellets using a mechanistic model.

The aim of this study was to develop a simple experimental methodology and to develop a mechanistic model to characterize the release mechanism from pellets developing cracks during the release process with special focus on osmotic effects. The release of remoxipride from pellets coated with an ethyl cellulose film was chosen as a case study. Dose release experiments at different bulk osmotic pressures revealed that the release process was mainly osmotically driven. The model was used to calculate the solvent permeability of the coating, 1.1 x 10(-10)m(2)h(-1)MPa(-1). The model was validated by release experiments using similar pellets having different coating thicknesses. The effective diffusion coefficient of remoxipride in the coating was also calculated and found to be 1.7 x 10(-10)m(2)h(-1). A series of experiments was performed in which the osmotic pressure of the receiving solution was changed during the experiment. From the results of these experiments, the area of the cracks in the film, formed by the hydrostatic pressure built up inside the pellets, was estimated to be 3.5 x 10(-5)m(2)/m(2) coating. It could also be deduced that the solvent permeability of the coating film was affected by swelling in the same way at different osmotic pressures.

Dopamine D2 and D3 receptors in human putamen, caudate nucleus, and globus pallidus.

Because radioactive raclopride and radioactive (+)-4-propyl-9-hydroxynaphthoxazine ((+)-PHNO) are used to image dopamine (DA) D2 and D3 receptors in the striatum and globus pallidus in humans, the present study examined the proportions of D2 and D3 receptors in postmortem tissues from these regions. Conflicting results were obtained when using a single concentration of remoxipride to occlude D2 receptors or using a single concentration of U99194A or FAUC 365 to occlude D3 receptors. However, using a range of concentrations of FAUC 365, a D3-selective antagonist, to inhibit the binding [(3)H]raclopride or [(3)H]-(+)-PHNO to D3 receptors at low concentrations (1-10 nM) and to inhibit ligand binding to D2 receptors at higher concentrations (100-2000 nM), it was possible to measure the proportion of D2 and D3 receptors in the tissues. This method revealed that these two radioligands detected only D2 receptors in the dorsal putamen and the dorsal caudate nucleus, but detected a mixed population of two-thirds D2 and one-third D3 DA receptors in the ventral putamen, the ventral caudate, and the globus pallidus. The present findings are in good agreement with the known gene expression data for D2 and D3 receptors in these human brain regions.

D2 dopamine receptor blockade prevents cognitive effects of Ang IV and des-Phe6 Ang IV.

Angiotensins, especially angiotensin IV (Ang IV), have recently been found to be potent cognitive enhancers in rodents. However, the precise mechanisms of their memory improving effects remain unknown. In this study we tested the hypothesis that D2 dopamine receptors at least partially mediate cognitive effects of Ang IV and its derivative des-Phe6 Ang IV. Namely, the well known cognitive effects of both peptides [facilitation of a conditioned avoidance responses (CARs) acquisition, increase of a passive avoidance behavior (PAB) retrieval, and improvement of object recognition] were evaluated in rats either pretreated or not with a selective D2 dopamine receptor antagonist remoxipride {(S)-(-)-3-Bromo-N-[(1-ethyl-2-pyrrolidinylOmethyl]2,6-dimethoxybenzamide hydrochloride}. To control for the unspecific motor and emotional effects of our treatments that could confound results of the memory tests we used respectively, 'open' field and elevated 'plus' maze tests. Ang IV as well as des-Phe6 Ang IV remarkably improved learning of CARs, recall of PAB and recognition of the previously seen objects. D2 receptors blockade by remoxipride abolished all these effects of both peptides. In the elevated 'plus' maze remoxipride abolished anxiogenic effects of both Ang IV and des-Phe6 Ang IV. Also, the drug followed by Ang IV decreased number of crossings and by des-Phe6 Ang IV number of crossings and rearings. The results point to importance of the functional D2 dopamine receptors in cognitive effects of Ang IV and its naturally occurring product devoid of C-terminal Phe6.

Dopaminergic mechanisms controlling urethral function in rats.

AIMS: To investigate the role of dopamine receptor subtypes in the control of urethral activity. METHODS: Simultaneous recordings of intravesical and urethral perfusion pressure (UPP) were performed in rats under urethane anesthesia. Changes in coordinated activity of the bladder and urethral sphincter were examined following intravenous (i.v.), intrathecal (i.t.), or intracerebroventricular (i.c.v.) administration of dopamine D1- and D2-like receptor agonists (SKF38393 and quinpirole, respectively) and antagonists (SCH23390 and remoxipride, respectively). RESULTS: Quinpirole (0.03, 0.1, and 0.3 mg/kg i.v.) dose-dependently decreased baseline urethral pressure to 45.33 +/- 5.8, 33.7 +/- 3.3 (P < 0.05, n = 6), and 27.7 +/- 3.3 cm H(2)O (P < 0.05, n = 5) from the control value (46.0 +/- 4.0 cm H(2)O), respectively. i.c.v. injection of quinpirole (1 microg) decreased baseline urethral pressure to 33.6 +/- 5.0 cm H(2)O (P < 0.05, n = 4) from the control value (51.4 +/- 4.9 cm H(2)O) in contrast to the insignificant effects of i.t. administration of the drug (3 microg). The decrement of baseline pressure induced by quinpirole (0.1 mg/kg i.v.) was suppressed by alpha-bungarotoxin (BGT), a neuromuscular blocking agent. SCH23390 (1 and 3 mg/kg, i.v.) dose-dependently decreased the frequency of high frequency oscillation (HFO) of the urethral sphincter. SKF38393 or remoxipride did not have significant effects on any parameters of bladder and urethral activity. CONCLUSIONS: These results indicate that activation of D2-like dopamine receptors at a supraspinal site can suppress activity of the striated muscle urethral sphincter. Thus, decreased urethral resistance induced by D2 dopamine receptor activation might aggravate urge incontinence symptoms often seen in patients with Parkinson's disease (PD).