Gs signaling pathway distinguishes hallucinogenic and nonhallucinogenic 5-HT2AR agonists induced head twitch response in mice.

5- HT2A receptor is a member of the family A G-protein-coupled receptor. It is involved in many psychiatric disorders, such as depression, addiction and Parkinson's disease. 5-HT2AR targeted drugs play an important role in regulating cognition, memory, emotion and other physiological function by coupling G proteins, and their most notable function is stimulating the serotonergic hallucination. However, not all 5-HT2AR agonists exhibit hallucinogenic activity, such as lisuride. Molecular mechanisms of these different effects are not well illustrated. This study suggested that 5-HT2AR coupled both Gs and Gq protein under hallucinogenic agonists DOM and 25CN-NBOH stimulation, but nonhallucinogenic agonist lisuride and TBG only activates Gq signaling. Moreover, in head twitch response (HTR) model, we found that cAMP analogs 8-Bromo-cAMP and PDE4 inhibitor Rolipram could increase HTR, while Gs protein inhibitor Melittin could reduce HTR. Collectively, these results revealed that Gs signaling is a key signaling pathway that may distinguish hallucinogenic agonists and nonhallucinogenic agonists.

5-HT7 receptor antagonism (SB-269970) attenuates bleomycin-induced pulmonary fibrosis in rats via downregulating oxidative burden and inflammatory cascades and ameliorating collagen deposition: Comparison to terguride.

The neurotransmitter 5-hydroxytryptamine (5-HT) is involved in regulation of local tissue inflammation and repair through a set of receptors (5-HT1-7 receptors), which are expressed in the lung. Considering the protective importance of 5-HT receptor antagonists against development of pulmonary fibrosis, we evaluated whether 5-HT7 receptor antagonist (SB-269970) modulates lung inflammatory and fibrogenic processes in comparison with 5-HT2A/B receptor antagonist (terguride), in bleomycin (BLM)-induced idiopathic pulmonary fibrosis (IPF) model. IPF model induced by a single dose of intra-tracheal BLM instillation (5mg/kg), and rats were treated with intraperitoneal injection of SB-269970 (1mg/kg day) or terguride (1.2mg/kg/d). The experiment was carried out on two separate sets of rats that were killed at day 7th and day 21st to evaluate the endpoint of the IPF inflammatory and fibrogenic phases, respectively. During the inflammatory phase 5-HT2A/B and 5-HT7 receptor antagonists attenuated the BLM-induced increase in the lung fluid content, the inflammatory cytokines levels and oxidative stress burden. In the fibrogenic phase, both SB-269970 and terguride reduced the serotonin concentrations in lung homogenates and significantly protected against IPF fibrogenic phase by attenuating collagen deposition and mRNA expression of both transforming growth factor-ß1 (TGF- ß1), and procollagen type Ӏ (PINP). 5-hydroxytryptamine 5-HT7 receptor antagonist showed more benefits than 5-HT2A/B receptor antagonist on the deleterious effects accompanied BLM instillation. The present study showed involvement of 5-HT7 receptor in the pathophysiology of BLM-induced IPF in rats and identified it as a potential therapeutic target in lung fibrotic disorders.

2-Bromoterguride-a potential atypical antipsychotic drug without metabolic effects in rats.

RATIONALE: Recently, we showed that 2-bromoterguride acted as a dopamine D2 receptor partial agonist, a serotonin 5-HT2A and α2C-adrenergic receptor antagonist, and exhibited antidopaminergic efficacy in amphetamine-induced locomotion (AIL) in rats without inducing catalepsy. OBJECTIVE: To extend our knowledge on the antipsychotic effects of 2-bromoterguride, we used convergent preclinical animal models and tests; i.e., conditioned avoidance response (CAR), predictive of antipsychotic-like effects; Fos protein expression, a molecular marker for (atypical) antipsychotic activity; wet dog shake behavior, a test for the in vivo effects of drugs acting on central 5-HT2A receptors; and investigated metabolic changes as a common side effect of atypical antipsychotic drugs (APDs). RESULTS: Acute treatment with 2-bromoterguride (0.1 and 0.3 mg/kg) decreased the CAR at 30, 90, and 270 min post-injection in rats without inducing escape failures at any time. Fos protein expression, as shown by Western blotting, was enhanced by 2-bromoterguride in the nucleus accumbens (NAc), the dorsolateral striatum (dStr), and the medial prefrontal cortex (mPFC). (±)-2,5-Dimethoxy-4-iodoamphetamine (DOI)-induced wet dog shakes in rats were reduced by 2-bromoterguride. Chronic treatment with 2-bromoterguride did not affect metabolic parameters such as body weight development and body fat composition as well as behavioral parameters such as food intake and locomotor activity. CONCLUSIONS: Our data suggest that 2-bromoterguride is a promising candidate in the treatment of schizophrenia due to its atypical antipsychotic-like activity and its inability to induce weight gain.

Why drugs fail in clinical trials in pulmonary arterial hypertension, and strategies to succeed in the future.

The past three decades have witnessed a welcome expansion of the therapeutic armamentarium for the management of pulmonary arterial hypertension (PAH). However, against this backdrop, there have been some notable disappointments in drug development. Here we use these as case studies to emphasize the importance of informed drug target selection, the early evaluation of dose-response relationships in human studies, and the value of the deep phenotyping of patients in clinical studies to better understand inter-individual variation in patient response. The integration of "omics" technologies and advanced clinical imaging offer the potential to reduce the risk, and so cost, of drug development in PAH and bring much needed new medicines to those patients most likely to benefit with greater efficiency.

Antiserotonergic properties of terguride in blood vessels, platelets, and valvular interstitial cells.

Serotonin (5-hydroxytryptamine; 5-HT) is involved in heart valve tissue fibrosis, pulmonary arterial fibrosis, and pulmonary hypertension. We aimed at characterizing the antiserotonergic properties of the ergot alkaloid derivative terguride [1,1-diethyl-3-(6-methyl-8α-ergolinyl)urea] by using functional receptor assays and valvular interstitial cell culture. Terguride showed no vasoconstrictor effect in porcine coronary arteries (5-HT(2A) receptor bioassay) and no relaxant effect in porcine pulmonary arteries (5-HT(2B) receptor bioassay). Terguride behaved as a potent antagonist at 5-HT(2A) receptors (noncompetitive antagonist parameter pD'2 9.43) and 5-HT(2B) receptors (apparent pA2 8.87). Metabolites of terguride (N″-monodeethylterguride and 6-norterguride) lacked agonism at both sites. N″-monodeethylterguride and 6-norterguride were surmountable antagonists at 5-HT(2A) receptors (pA2 7.82 and 7.85, respectively) and 5-HT(2B) receptors (pA2 7.30 and 7.11, respectively). Kinetic studies on the effects of terguride in pulmonary arteries showed that the rate to reach drug-receptor equilibrium for terguride was fast. Washout experiments showed that terguride easily disappeared from the receptor biophase. Pretreatment with terguride inhibited 5-HT-induced amplification of ADP-stimulated human platelet aggregation (IC50 16 nM). In porcine valvular interstitial cells, 5-HT-induced activation of extracellular signal-regulated kinase (ERK) 1/2, an initiator of cellular proliferation and activity, was blocked by terguride as shown by Western blotting. In these cells, the stimulatory effect of 5-HT on [³H]proline incorporation (index of extracellular matrix collagen) was blocked by terguride. Because of the inhibition of both 5-HT(2A) and 5-HT(2B) receptors, platelet aggregation, and cellular proliferation and activity (ERK1/2 phosphorylation and collagen production) terguride may have therapeutic potential in the treatment of fibrotic disorders.

The dopamine D(2) partial agonist and antagonist terguride decreases heroin self-administration on fixed- and progressive-ratio schedules.

Dopamine partial agonists have been suggested to be potential therapeutic candidates for pharmacological intervention in drug addiction. These drugs bind to dopamine receptors with high affinity and low intrinsic activity and are hypothesized to behave as functional antagonists in conditions of high dopaminergic tone. The aim of the present study was to characterize the effects of terguride, a partial dopamine agonist at the dopamine D(2) receptor, on intravenous heroin self-administration on fixed- and progressive-ratio schedules of reinforcement. The effects of terguride on oral sweet solution (4% sucrose) self-administration on a fixed-ratio schedule were also tested. Terguride dose-dependently decreased heroin self-administration on the fixed-ratio schedule and decreased the maximum number of responses for heroin self-administration on a progressive-ratio schedule. In contrast, terguride did not significantly affect oral sucrose self-administration. These data suggest that terguride may represent a novel pharmacological strategy for the treatment of opiate addiction.

Both mild hypothermia and dopamine D(2) agonist are neuroprotective against hyperthermia-induced injury in PC12 cells.

We exposed rat pheochromocytoma PC12 cells to hyperthermia or high dosage of dopamine and examined the direct effects of mild hypothermia or dopamine D(2) receptor agonist. At a hyperthermia of 42-43 degrees C for 120 min there was approximately 50% loss of cell viability accompanied by dopamine overproduction. The model of cell death due to hyperthermia in PC12 cells belonged to the necrotic and late apoptotic population. At each temperature examined below 37 degrees C, significant decrease in cytotoxicity, the percentage of necrotic and late apoptotic cells, and dopamine overproduction were observed. Cytotoxicity could also be induced by high dosages of dopamine. Both hyperthermia and dopamine induced cytotoxicity in PC12 cells could also be reduced by dopamine D(2) agonists. These results indicate the dopamine is important in hyperthermic situations. The results also indicate that mild hypothermia and dopamine D(2) receptor agonists are neuroprotective against hyperthermia-induced brain injury.

Long-term serotonin effects in the rat are prevented by terguride.

Long-term hyperserotoninemia induces heart valve disease in rats, and cases of cardiac valvulopathies have been reported in patients using ergolines, possibly through activation of the 5-hydroxytryptamine(2B) (5HT(2B)) receptor. The ergoline terguride (transdihydrolisuride) is a 5HT(2B/2C) receptor antagonist. Using a rat model, we have investigated whether terguride could prevent serotonin-induced changes in general and heart disease specifically. During 4 months, twelve Sprague-Dawley rats were given daily subcutaneous serotonin injections; twelve rats received a combination of serotonin injections and terguride by gavage, whereas ten rats were untreated controls. Using echocardiography, rats with aortic insufficiency were found in all 3 groups, while pulmonary insufficiency was only found in two rats injected with serotonin alone. Animals given serotonin alone had significantly higher heart weights compared to the controls (p=0.029) and rats given terguride (p=0.034). Rats injected with serotonin alone developed macroscopic skin changes at the injection sites, histologically identified as orthokeratosis and acanthosis. Terguride completely prevented these changes (p=0.0001, p=0.0003). Liver weights were higher in the animals given serotonin alone compared to controls (p=0.014) and terguride treated animals (p=0.009). Stomach weights were higher in animals given serotonin alone compared to rats given terguride (p=0.012). In the mesenchymal cell-line MC3T3-E1, terguride almost completely inhibited serotonin-induced proliferation (p<0.01). Serotonin increases heart, liver and stomach weights, possibly through enhanced proliferation. Terguride inhibits these effects. We propose that terguride may have beneficial effects in the treatment of diseases such as carcinoid syndrome, where serotonin plays an important pathogenic role.

In vitro characterization of SLV308 (7-[4-methyl-1-piperazinyl]-2(3H)-benzoxazolone, monohydrochloride): a novel partial dopamine D2 and D3 receptor agonist and serotonin 5-HT1A receptor agonist.

Present Parkinson's disease treatment strategies are far from ideal for a variety of reasons; it has therefore been suggested that partial dopamine receptor agonism might be a potential therapeutic approach with potentially fewer side effects. In the present study, we describe the in vitro characterization of the nonergot ligand SLV308 (7-[4-methyl-1-piperazinyl]-2(3H)-benzoxazolonemonohydrochloride). SLV308 binds to dopamine D(2), D(3), and D(4) receptors and 5-HT(1) (A) receptors and is a partial agonist at dopamine D(2) and D(3) receptors and a full agonist at serotonin 5-HT(1) (A) receptors. At cloned human dopamine D(2,L) receptors, SLV308 acted as a potent but partial D(2) receptor agonist (pEC(50) = 8.0 and pA(2) = 8.4) with an efficacy of 50% on forskolin stimulated cAMP accumulation. At human recombinant dopamine D(3) receptors, SLV308 acted as a partial agonist in the induction of [(35)S]GTPgammaS binding (intrinsic activity of 67%; pEC(50) = 9.2) and antagonized the dopamine induction of [(35)S]GTPgammaS binding (pA(2) = 9.0). SLV308 acted as a full 5-HT(1) (A) receptor agonist on forskolin induced cAMP accumulation at cloned human 5-HT(1) (A) receptors but with low potency (pEC(50) = 6.3). In rat striatal slices SLV308 concentration-dependently attenuated forskolin stimulated accumulation of cAMP, as expected for a dopamine D(2) and D(3) receptor agonist. SLV308 antagonized the inhibitory effect of quinpirole on K(+)-stimulated [(3)H]-dopamine release from rat striatal slices (pA(2) = 8.5). In the same paradigm, SLV308 had antagonist properties in the presence of quinpirole (pA(2) = 8.5), but the partial D(2) agonist terguride had much stronger antagonistic properties. In conclusion, SLV308 combines high potency partial agonism at dopamine D(2) and D(3) receptors with full efficacy low potency serotonin 5-HT(1) (A) receptor agonism and is worthy of profiling in in vivo models of Parkinson's disease.

Aripiprazole's low intrinsic activities at human dopamine D2L and D2S receptors render it a unique antipsychotic.

Aripiprazole is the first clinically approved atypical antipsychotic agent having dopamine D2 receptor partial agonist activities. To evaluate aripiprazole's agonist and antagonist properties, we established a Chinese hamster ovary cell line expressing high and low densities of the long and short isoforms of human dopamine D2 receptors, then compared its properties with 7-{3-[4-(2,3-dimethylphenyl)piperazinyl]propoxy}-2(1H)-quinolinone (OPC-4392), S(-)-3-(3-hydroxyphenyl)-N-n-propylpiperidine ((-)-3-PPP), and terguride (other partial agonists) using forskolin-stimulated cAMP accumulation as an index. In cells expressing high receptor densities, all partial agonists predominantly behaved as agonists. However, in cells expressing low receptor densities, the partial agonists showed significantly lower maximal effects than dopamine. Aripiprazole showed the lowest intrinsic activities. In addition, all compounds blocked the action of dopamine with a maximum effect equal to that of each compound alone. Aripiprazole's low intrinsic activities may account for the clinical finding that, unlike the other partial agonists, it is substantially active against both positive and negative symptoms of schizophrenia.

The effects of dopamine receptor agonists and antagonists on the secretory rate of cockroach (Periplaneta americana) salivary glands.

The acinar salivary glands of the cockroach, Periplaneta americana, are innervated by dopaminergic and serotonergic nerve fibers. Serotonin stimulates the secretion of protein-rich saliva, whereas dopamine causes the production of protein-free saliva. This suggests that dopamine acts selectively on ion-transporting peripheral cells within the acini and the duct cells, and that serotonin acts on the protein-producing central cells of the acini. We have investigated the pharmacology of the dopamine-induced secretory activity of the salivary gland of Periplaneta americana by testing several dopamine receptor agonists and antagonists. The effects of dopamine can be mimicked by the non-selective dopamine receptor agonist 6,7-ADTN and, less effectively, by the vertebrate D1 receptor-selective agonist chloro-APB. The vertebrate D1 receptor-selective agonist SKF 38393 and vertebrate D2 receptor-selective agonist R(-)-TNPA were ineffective. R(+)-Lisuride induces a secretory response with a slower onset and a lower maximal response compared with dopamine-induced secretion. However, lisuride-stimulated glands continue secreting saliva, even after lisuride-washout. Dopamine-induced secretions can be blocked by the vertebrate dopamine receptor antagonists cis(Z)-flupenthixol, chlorpromazine, and S(+)-butaclamol. Our pharmacological data do not unequivocally indicate whether the dopamine receptors on the Periplaneta salivary glands belong to the D1 or D2 subfamily of dopamine receptors, but we can confirm that the pharmacology of invertebrate dopamine receptors is remarkably different from that of their vertebrate counterparts.

The dopamine receptor agonist lisuride attenuates iron-mediated dopaminergic neurodegeneration.

Many dopamine agonists used in the treatment of Parkinson's disease are suggested to be potentially neuroprotective. On the basis of its structure, the dopamine agonist lisuride may share this characteristic. In the current study discrete asymptomatic lesions were produced by the injection of iron-laden neuromelanin into the rat substantia nigra and the animals treated with lisuride to determine the protective potential of this substance. Two treatment regimes were utilised. In the neuroprotective protocol, animals were treated with 0.1 mg.kg(-1) lisuride twice daily 3 days prior to, and 7 days following, the iron lesion. In the neurorescue protocol, the animals received 0.1 mg.kg(-1) lisuride twice daily for 1 week beginning on the fourth day post surgery. Eight weeks post surgery, tyrosine hydroxylase-positive neurons surrounding the injection site (33% of total nigral volume) were counted. Dopamine neuron number in iron-lesioned animals was reduced to 50% of that in vehicle-injected animals. The absence of motoric disturbances or a striatal dopamine deficit in these animals suggests a subclinical dopaminergic lesion. Dopamine neuron number in the quantified area in sham-injected animals receiving lisuride or iron-lesioned animals receiving lisuride in both the neuroprotection and neurorescue groups were not significantly reduced. These results suggest that lisuride can protect neurons against iron-induced cell death and might thus be neuroprotective in Parkinson's disease.

Cortisol as an indicator of dopaminergic effects on nicotine craving.

There is evidence that glucocorticoids mediate the activity of mesencephalic dopaminergic neurons which play an important role in drug-seeking behaviour and that the absence or presence of glucocorticoids determines the intensity of drug self-administration. Moreover, some experiments indicate that corticoids are increased after substance induced dopaminergic stimulation. These findings could imply (a) that differences in basal glucocorticoid levels are associated with differences in craving or (b) that dopamine (DA) induced corticoid release is an indicator of the sensitivity of the dopaminergic system. Therefore, in a sample of 36 male smokers whose DA system was challenged by a DA agonist (lisuride=LIS) and a DA antagonist (fluphenazine=FLU) in a balanced placebo controlled double-blind crossover design, it was investigated if (a) basal cortisol differences and (b) drug induced cortisol responses are related to the amount of nicotine craving after 3.5 h of deprivation from smoking. There were no differences in craving between subjects with high and low basal cortisol levels irrespective of the pharmacological treatment. However, the size of the cortisol change after the DA challenge and deprivation emerged as a good predictor for the amount of craving in that drug condition in which the cortisol response was most pronounced. Findings were interpreted as evidence for the role of cortisol as an indicator of DA sensitivity.

Clustered ergot alkaloids modulate cell-mediated cytotoxicity.

Dimers of agroclavine (1) and terguride (2), as well as a series of terguride oligomers, for example trimers (5, 6), tetramer (7), hexamer (8) and functionalized tergurides for further complex clustering were synthesized. Terguride oligomers were screened for their direct cellular toxicity on lymphoma cell lines in vitro and for their immunomodulating activities, represented by the natural killer (NK) cell-mediated cytotoxicity, as the most sensitive screening marker during immune responses. Dimers linked via aromatic spacer showed a high toxicity (1 microM) to lymphoma cells, which was not detected in other derivatives. In vitro and ex vivo experiments performed on mouse spleen lymphocytes in the presence of terguride oligomers demonstrated an immunosuppressive effect of dimers with aromatic spacer (4c-d) and NK cell stimulatory effect of terguride hexamer (8) and trimer with aliphatic spacer (5c). There is a considerable evidence that indolic part of molecule contributes to immunosuppressive action of terguride, which is potentiated in dimers carrying aromatic linker. This effect can be reversed by higher oligomerization of the respective alkaloids.

Nonlinear analysis of partial dopamine agonist effects on cAMP in C6 glioma cells.

Most drugs have some efficacy so that improved methods to determine the relative intrinsic efficacy of partial agonists should be of benefit to preclinical and clinical investigators. We examined the effects of partial D(1) or partial D(2) dopamine agonists using a partial agonist interaction model. The dependent variable was the modulation of the dopamine-receptor-mediated cAMP response in C6 glioma cells selectively and stably expressing either D(1) or D(2) recombinant dopamine receptors. The dissociation constant (K(B)) and relative intrinsic efficacy (E(r)) for each partial agonist were calculated using a partial agonist interaction null model in which the effects of fixed concentrations of each partial agonist on the dopamine dose-response curve were evaluated. This model is an extension of the competitive antagonist null model to drugs with efficacy and assumes only that the log-dose--response curve is monotonic. Generally, the partial agonist interaction model fit the data, as well as fits of the independent logistic curves. Furthermore, the partial agonist K(B) values could be shared across partial agonist concentrations without worsening the model fit (by increasing the residual variance). K(B) values were also similar to drug affinities reported in the literature. The model was validated in three ways. First, we assumed a common tissue stimulus parameter (beta) and calculated the E(r) values. This provided a qualitative check on the interaction model results. Second, we calculated new relative efficacy values, E(r)(beta), using the beta estimate. Third, we calculated relative efficacy using relative maxima times midpoint shift ratios (J. Theor. Biol. 198 (1999) 347.). All three methods indicated that the present model yielded reasonable estimates of affinity and relative efficacy for the set of compounds studied. Our results provide a quick and convenient method of quantification of partial agonist efficacy. Special applications and limitations of the model are discussed. In addition, the present results are the first report of the relative intrinsic efficacy values for this set of D(2) ligands.

Partial agonism at serotonin 5-HT1B and dopamine D2L receptors using a luciferase reporter gene assay.

We have used a luciferase reporter gene assay to study the functional responses of two G-protein-coupled receptors in Chinese hamster ovary (CHO) cells. The rank order of potency of drugs for the endogenous 5-HT1B receptor was 5-Hydroxytryptamine (5-HT) > zolmitriptan > dihydroergocristine > (-)lisuride (with no response to bromocriptine). However, only 5-HT and (-)lisuride produced a full functional response, with zolmitriptan and dihydroergocristine achieving 69+/-2% and 50+/-1% of the maximal response. In the same cells stably transfected with the rat dopamine D2L receptor, dopamine and bromocriptine produced a full agonist functional response, whilst (-)lisuride produced a biphasic response curve, indicating activity at both the endogenous 5-HT1B and exogenous dopamine D2L receptors. Using the receptor specific antagonists, pindolol and (+)butaclamol, (-)lisuride was shown to produce 52% of the maximal response at the dopamine D2 receptor relative to dopamine. In comparison to a cAMP accumulation assay, the rank orders of potency and intrinsic activity were the same for all compounds used. These results demonstrate that this reporter gene assay is capable of discriminating both potency and efficacy of drugs and can be used to characterise partial agonists at endogenously and heterologously expressed receptors in CHO cells.

Pharmacological effects of BAM-1120, a novel ergoline derivative, on central dopaminergic functions in rats.

BAM-1120, an ergoline derivative, has been found to display a relatively high affinity for dopamine D2-like receptor subtypes in a preliminary binding study. This study investigated whether BAM-1120 acts as a dopamine receptor agonist on prolactin-secreting and motor functions. BAM-1120 suppressed hyperprolactinemia induced by pretreatment with reserpine or estradiol in female rats. Furthermore, BAM-1120 was able to shrink a prolactin-secreting pituitary tumor (prolactinoma) in the estradiol-treated female rats. BAM-1120 induced rotations contralateral to the lesion side in rats with unilateral 6-hydroxydopamine-induced lesions of nigrostriatal dopamine pathway at a dose that was at least 30-fold higher than that required for the inhibition of prolactin secretion. These findings suggest that BAM-1120 is characterized as a putative dopamine D2-like receptor agonist that possesses a preference of inhibiting prolactin secretion over activating motor behaviors.

Independence of estrogen-induced pituitary proliferation on local IGF-I mRNA and EGF mRNA expression. Modifying effects of tamoxifen and terguride.

Pituitary hyperplasia as well as proliferation of the endometrium are typical responses to estrogen administration in rodents. Both insulin-like growth factor-I (IGF-I) and epidermal growth factor (EGF) have been implicated as paracrine mediators and amplifiers of estrogen action in the rodent uterus. The auto/paracrine role of IGF-I, EGF, their receptors and IGF binding proteins in pituitary proliferation has not yet been solved. Here we have used a semi-quantitative reverse transcription polymerase chain reaction (RT PCR) assay to demonstrate the changes in IGF-I mRNA and EGF mRNA abundance in the proliferating male rat pituitary in response to estradiol benzoate (EB; 1 mg/kg b.w. twice weekly i.m. for 3 weeks) and modifying effect of drugs antagonizing the pituitary enlargement - antiestrogen tamoxifen (TAM, 5 mg/kg b.w. daily) and also the dopaminergic agonist terguride (TER, 0.66 mg/kg b.w. daily, routinely used for the treatment of prolactinomas). In three separate experiments, EB induced a 2.2-2.5 fold increase in pituitary weight. The abundance of IGF-I and EGF mRNAs in pituitaries of EB-treated animals did not differ from the controls in two experiments and in the third series with the most marked pituitary hyperplasia mRNAs of both growth factors were even significantly decreased. Antiestrogen TAM administered with EB partially blocked the EB-induced proliferation and significantly stimulated IGF-I mRNA (p=0.003) and EGF mRNA (p=0.023) expression, while EB or TAM alone did not stimulate mRNAs of the studied growth factors. Significant antiproliferative effect of dopaminergic agonist TER on EB-induced pituitary proliferation (p=0.006) was accompanied with decreased IGF-I mRNA (p=0.025), but not EGF mRNA abundance. Our results suggest that the estrogen-induced pituitary proliferation is independent of the local expression of IGF-I and EGF mRNAs.

Dopamine D2 receptor agonists protect against ischaemia-induced hippocampal neurodegeneration in global cerebral ischaemia.

To characterise the role played by dopamine receptors in ischaemic brain damage, we have evaluated the effects of pergolide, bromocriptine and lisuride (dopamine D2 receptor agonists), haloperidol (a dopamine D2 receptor antagonist), 2,3,4,5-tetrahydro-7,8,dihydroxy-1-phenyl-1H-3-benzazepine (SKF 38393; a dopamine D1 receptor agonist) and (R)-(+)-8-chloro 2,3,4,5-tetra-hydro-3-methyl-5-phenyl-1H-3-benzazepin-7-ol (SCH 23390; a dopamine D1 receptor antagonist) in the gerbil model of global cerebral ischaemia. Ischaemia was induced by 5 min of bilateral carotid artery occlusion under halothane anaesthesia. Sham operated animals were used as controls. Pergolide (0.5 or 1.0 mg/kg i.p), bromocriptine (0.5 or 1.0 mg/kg i.p.), lisuride (0.5 or 1.0 mg/kg i.p.), SCH 23390 (0.1 or 1.0 mg/kg i.p.), haloperidol (0.5, 1.0 or 2 mg/kg i.p.) and SKF 38393 (1.0 or 2 mg/kg i.p.) were administered 1 h before occlusion. Five-minute-occluded animals had extensive damage in the CA1 region of the hippocampus 5 days after surgery. Pergolide 0.5 and 1.0 mg/kg i.p. provided significant (P < 0.05 and P < 0.01, respectively) neuroprotection against the ischaemia-induced hippocampal damage. Bromocriptine and lisuride also provided significant (P < 0.05) neuroprotection, but only at the higher 1.0 mg/kg dose. In contrast, the dopamine D2 receptor antagonist (haloperidol), the dopamine D1 receptor agonist (SKF 38393) and the dopamine D1 receptor antagonist (SCH 23390) failed to provide any neuroprotection in the model. These results support studies indicating that dopamine is important in ischaemic situations. The results also indicate that dopamine D2 receptor agonists are neuroprotective against ischaemia-induced brain injury and may play a role in neurodegenerative disorders.

5-HT1A receptor agonist properties of the antipsychotic, nemonapride: comparison with bromerguride and clozapine.

5-HT1A receptor agonists are thought to enhance the antipsychotic-like effects of dopamine D2 receptor antagonists while reducing their potential to produce extrapyramidal side effects. Thus, 5-HT1A receptor agonist properties of mixed 5-HT1A receptor agonists/D2 receptor antagonists might be of clinical importance. The antipsychotics, clozapine and nemonapride, and the putative antipsychotic, bromerguride, have intermediate to high affinity for 5-HT1A receptors. The present study examined the 5-HT1A receptor agonist activity of nemonapride and bromerguride, in comparison with clozapine, which has partial 5-HT1A receptor agonist properties in vitro. Here, 5-HT1A receptor activation was examined in vitro, by measuring forskolin-stimulated cAMP accumulation in HeLa cells expressing human 5-HT1A receptors, and in vivo, by using microdialysis to measure the extracellular concentration of hippocampal 5-hydroxytryptamine (5-HT) in rats. Nemonapride markedly decreased both forskolin-stimulated cAMP accumulation and the extracellular concentration of 5-HT; both effects were antagonized by the 5-HT1A receptor antagonist, N-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]-N-(2-pyridinyl) cyclohexanecarboxamide (WAY100635). In contrast, clozapine only partially decreased forskolin-stimulated cAMP accumulation and extracellular 5-HT, and only its effects on cAMP accumulation were attenuated by WAY100635. Bromerguride decreased neither forskolin-stimulated cAMP accumulation nor extracellular 5-HT; instead, it antagonized the decrease of cAMP accumulation produced by 5-HT and the decrease of extracellular 5-HT produced by the 5-HT1A agonist (+/-)-8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT). The selective D2 receptor antagonist, raclopride, affected neither forskolin-stimulated cAMP in vitro nor extracellular 5-HT in vivo. Thus, in contrast with clozapine and bromerguride, only the novel antipsychotic, nemonapride, exhibited marked 5-HT1A receptor agonist properties both in vitro and in vivo; conceivably, these properties may play a role in its preclinical and clinical effects.