Selective blockade of neurokinin-2 receptors produces antidepressant-like effects associated with reduced corticotropin-releasing factor function

The present study investigated the effects of the selective neurokinin-2 (NK2) receptor antagonist SR48968 in behavioral, electrophysiological, and biochemical tests sensitive to the action of prototypical antidepressants (fluoxetine, imipramine) or to corticotropin-releasing factor (CRF) receptor antagonists, which have been proposed recently as potential antidepressants. Results showed that SR48968 (0.3-10 mg/kg i.p.) produced antidepressant-like activity because it reduced immobility in the forced swimming test in both mice and rats, and decreased the amount of maternal separation-induced vocalizations in guinea pig pups. This latter effect appears to involve a reduction of stress-induced substance P release because SR48968 reduced the separation-induced increase in the number of neurons displaying neurokinin-1 receptor internalization in the amygdala. Furthermore, SR48968 increased the expression of the cAMP response-element binding protein mRNA in the rat hippocampus after repeated (1 mg/kg i.p., 21 days), but not acute administration. Finally, neuronal firing of the locus coeruleus (LC) and noradrenergic (NE) release in the prefrontal cortex both elicited by an uncontrollable stressor or an intraventricular administration of CRF were reduced by SR48968 (0.3-1 mg/kg i.p.). The finding that SR48968 (1 mg/kg i.p.) blocked the cortical release of NE induced by an intra-LC infusion of the preferential NK2 receptor agonist neurokinin A suggested the presence of NK2 receptors in this latter region. Importantly, SR48965 (1-10 mg/kg i.p.), the optical antipode of SR48968, which is devoid of affinity for the NK2 receptor, was inactive in all the models used. These data suggest that NK2 receptor blockade may constitute a novel mechanism in the treatment of depression and CRF-related disorders.

Effects of neurotensin receptor antagonists on the firing rate of rat ventral pallidum neurons

Using anaesthetized adult rats, we compared the effects of i.v. injections of neurotensin receptor antagonists (SR48692 and SR142948), haloperidol and clozapine on neuronal firing rate in the two ventral pallidal areas. SR48692 (0.5, 1 and 2 mg/kg, i.v.) induced a dose-dependent inhibition of firing rate in two thirds of neurons in the ventromedial part without any effect in the ventrolateral part. These effects are in keeping with the preferential neurotensin immunoreactivity distribution reported in the ventral pallidum. The classical antipsychotic drug haloperidol (0.5 mg/kg, i.v.) induced an inhibition of neuronal firing rate in both ventral pallidal areas whereas the atypical antipsychotic drug clozapine (20 mg/kg, i.v.), like the neurotensin receptor antagonist SR48692, inhibited cell firing only in the ventromedial part.

Blockade of neurokinin3 receptors antagonizes drug-induced population response and depolarization block of midbrain dopamine neurons in guinea pigs

In vivo extracellular recording techniques were used to investigate the effects of neurokinin3 (NK3) receptor blockade on the pharmacological activation of midbrain dopamine (DA) neurons in the guinea pig substantia nigra (A9) and ventral tegmental area (A10). The number of spontaneously active DA cells (population response) was largely increased in A10 and A9 by acute administration of haloperidol (1 and 0.5 mg/kg i.p., respectively) and this effect was dose-dependently prevented in both areas by the selective NK3 receptor antagonist SR142801 (0.3, 1, 3, and 1, 3, 10 mg/kg i.p., respectively). This compound, which was totally inactive by itself, also antagonized the increase of population response induced in A10 cells by the neurotensin receptor antagonist SR142948 (1 mg/kg i.p.) and in A9 cells by the NK2 receptor antagonist SR144190 (1 mg/kg i.p.). None of the effects of SR142801 were reproduced by SR142806, its (R)-enantiomer with 240-fold lower affinity for NK3 receptors. In addition, neither SR144190 (0.3 mg/kg i.p.) nor the NK1 receptor antagonist GR205171 (1 mg/kg i.p.) affected the haloperidol-induced response. The antagonistic effects of SR142801 (3 mg/kg i.p.) were also observed on the depolarization block-related decrease of A10 cell population response evoked by repeated administration (22 days) of haloperidol. Finally, SR142801 (3 mg/kg i.p.) prevented depolarization block induced in A10 cells by acute co-administration of SR142948 and haloperidol, both on population response and on single cell firing. These results on pharmacologically induced activation and depolarization block of dopamine neurons suggest that NK3 receptors play a key role in the midbrain DA function, presumably through activation by neurokinin B.

SR146131: a new potent, orally active, and selective nonpeptide cholecystokinin subtype 1 receptor agonist. II. In vivo pharmacological characterization

SR146131 is a potent and selective agonist at cholecystokinin subtype 1 (CCK1) receptors in vitro. The present study evaluates the activity of the compound in vivo. SR146131 completely inhibited gastric and gallbladder emptying in mice (ED50 of 66 and 2.7 micrograms/kg p.o., respectively). SR146131 dose dependently reduced food intake in fasted rats (from 0.1 mg/kg p.o.), in nonfasted rats in which food intake had been highly stimulated by the administration of neuropeptide Y (1-36) (from 0.3 mg/kg p.o.), in fasted gerbils (from 0.1 mg/kg p.o.), and in marmosets maintained on a restricted diet (from 3 mg/kg p.o.). SR146131 (10 mg/kg p.o.) also increased the number of Fos-positive cells in the hypothalamic paraventricular nucleus of rats. Locomotor activity of mice was reduced by orally administered SR146131 (from 0.3 mg/kg p.o.). When administered intrastriatally, SR146131 elicited contralateral turning behavior in mice. Furthermore, orally administered SR146131 (0.3-10 mg/kg), also reduced the levels of cerebellar cyclic GMP. Finally, SR146131 (0.1 microgram/kg to 1 mg/kg, p.o.) significantly and dose dependently antagonized fluphenazine-induced mouth movements in rats. The CCK1 antagonist SR27897B prevented all the effects of SR146131. Conversely, SR146131 was unable to elicit any agonist or antagonist effects in a model of CCK2 receptor stimulation in vivo. SR146131 is a very potent and selective nonpeptide CCK1 agonist in vivo. SR146131 is more potent than any other CCK1 agonists reported to date. Because pharmacodynamic studies suggest that SR146131 should have a high absolute bioavailability, it may be a promising drug for the treatment of eating and motor disorders in humans.

Effects of SR140333, a selective non-peptide NK1 receptor antagonist, on trigemino-thalamic nociceptive pathways in the rat

Trigeminal stimulation of C-fibers increased c-fos expression within the trigeminal nucleus caudalis (NtV) and thalamic neuronal activity which both reflect the transmission of a nociceptive message. We examined the effects on both these phenomena of the selective NK1 and NK2 receptor antagonists, SR140333 and SR48968. SR140333 (0.3, 1 and 3 micrograms/kg intravenously [i.v.]) dose-dependently, reversibly and stereoselectively antagonized the increase of contralateral thalamic activity. This compound, when given i.v. (30 micrograms/kg) or orally (10 mg/kg), also reduced the number of Fos-like immunoreactive cells particularly at the medial and caudal level of the NtV. In contrast, SR48968 did not exert any antagonistic effect either on thalamic activity or on Fos-like immunoreactivity. The data strongly suggest a preferential involvement of NK1 vs NK2 receptors in nociceptive transmission following trigeminal ganglion stimulation. Taken together, our results indicate that SR140333 could provide a potent drug for the relief of pain occurring under excessive activity of sensory trigeminal fibers.

Involvement of cortical neurotensin in the regulation of rat meso-cortico-limbic dopamine neurons: evidence from changes in the number of spontaneously active A10 cells after neurotensin receptor blockade

In order to further assess the role of endogenous neurotensin on midbrain dopaminergic neuronal function, the effects of the selective neurotensin receptor antagonists SR 48692 and SR 48527 were investigated on the number of spontaneously active A9 and A10 dopaminergic neurons in rats. Single intraperitoneal administration of SR 48692 (0.1-3 mg/kg) dose-dependently increased the number of active A10, but not A9 cells. SR 48527 (1 mg/kg) had a similar profile, but not SR 49711, its low affinity R-enantiomer, indicating that the effects observed were mediated through neurotensin receptor blockade. Five-week treatment with SR 48692 (3 mg/kg/day) produced a significant decrease of the number of active A10, but not A9 cells, which was reversed by apomorphine, suggesting that these cells were under depolarization block. Single co-administration of inactive doses of SR 48692 (0.1 mg/kg) and haloperidol (0.0625 mg/kg) significantly increased the number of active A10 cells. Conversely, co-administered active doses of SR 48692 or SR 48527 and haloperidol (1 and 0.25 mg/kg, respectively) induced an apomorphine-sensitive decrease of the number of A10 active cells. Finally, SR 48692 (10 mg/kg) modified neither accumbal nor cortical basal DA release. Local micro-injection of SR 48692 (10[-11]-10[-9] M), but not that of SR 49711 (10[-9] M), into the prefrontal cortex, increased the number of active A10 cells in a concentration-dependent manner. These results suggest that neurotensin receptor blockade counteracts a tonic inhibitory regulation by endogenous neurotensin of mesolimbic dopaminergic function and indicate that the prefrontal cortex is critically involved in this regulation.

The CB1 cannabinoid receptor antagonist SR 141716A affects A9 dopamine neuronal activity in the rat

CB1 receptors and their putative natural ligand anandamide, have been tentatively involved in the control of midbrain extrapyramidal function. Electrophysiological activity of dopamine neurones was measured after acute and repeated administration of the CB1 receptor antagonist SR 141716A (0.3-3 mg kg-1) in rats. Acute SR 141716A increased A9, but not A10 cell population response without affecting either their spontaneous firing rate or apomorphine-induced rate inhibition and prevented amphetamine-induced inhibition of A9, but not of A10 cell firing. After repeated administration SR 141716A (1 or 5 mg kg-1) decreased population response of A9 cells, which was reversed by apomorphine. These results suggest that CB1 receptor blockade by SR 141716A interrupts a cannabinoid-like endogenous tone controlling extrapyramidal function.

Effects of SR 48692, a selective non-peptide neurotensin receptor antagonist, on two dopamine-dependent behavioural responses in mice and rats

One major mechanism underlying the central action of neurotensin is an interaction with the function of dopamine (DA)-containing neurons. In addition, direct or indirect DA agonists have been reported to promote neurotensin release. We have found that SR 48692, a non-peptide neurotensin receptor antagonist (0.04-0.64 mg/kg orally), antagonizes (50-65%) yawning induced by apomorphine (0.07 mg/kg SC) or bromocriptine (2 mg/kg IP) in rats, and turning behaviour induced by intrastriatal injection of apomorphine (0.25 micrograms), (+) SKF 38393 (0.1 micrograms), bromocriptine (0.01 ng) or (+) amphetamine (10 micrograms) in mice. Other apomorphine-induced effects in mice and rats such as climbing, hypothermia, hypo- and hyper-locomotion, penile erections and stereotypies were not significantly modified by SR 48692. Taken together, these data suggest that neurotensin may play a permissive role in the expression of some but not all behavioural responses to DA receptor stimulation.

Neuropharmacological characterization of SR 140333, a non peptide antagonist of NK1 receptors

SR 140333 (1-[2-[3-(3,4-dichlorophenyl)-1-(3-isopropoxyphenylacetyl) piperidin-3-yl]ethyl]-4-phenyl-1-azonia-bicyclo[2.2.2]octane , chloride), a potent non peptide ligand of the substance P (SP) NK1 receptor subtype with high affinity for NK1 receptors from both rat cortical membranes and human IM9 cells (Ki = 0.02 nM and 0.01 nM, respectively) was studied in vivo on various effects induced by NK1 agonists in rats and mice. SR 140333 given intraperitoneally (i.p.) in mice antagonized dose-dependently and in a stereoselective manner the scratching responses induced by intracerebroventricular SP and septide (ID50 = 0.73 and 0.08 mg/kg, respectively) and the turning behavior elicited by intrastriatal SP and septide (ID50 = 0.07 and 0.06 mg/kg, respectively). This compound had little effect on the scratching responses and the turning behavior elicited by [Sar9, Met(O2)11]-SP. When SR 140333 was coadministered with the peptide agonist, the compound reduced the scratching responses elicited by SP, [Sar9, Met(O2)11]-SP and septide injected intrathecally (i.t.) in mice (ID50 = 72.0, 64.3 and 52.5 ng i.t., respectively). SR 140333 antagonized the salivation induced by SP, [Sar9, Met(O2)11]-SP and septide in rats (ID50 = 0.13, 0.18 and 0.09 mg/kg i.p., respectively). SR 140333 abolished the facilitation of the tail-flick reflex induced by noxious heat in rats (total reversal at 0.06 mg/kg, i.p.). This compound was also found to inhibit the turning behavior induced by intrastriatal apomorphine in mice (ID50 = 0.1 mg/kg, i.p.). In conclusion, these results indicate that SR 140333 behaves as a potent, selective and centrally active NK1 receptor antagonist.

Turning behavior induced by intrastriatal injection of neurotensin in mice: sensitivity to non-peptide neurotensin antagonists

The intrastriatal injection of neurotensin (10 pg/mouse) elicited vigorous contralateral rotations which were not affected by disruption of dopaminergic transmission using 6-OHDA lesion of the striatum or systemic administration of spiroperidol (0.03 mg/kg). SR 48692, a selective non-peptide antagonist of neurotensin receptor, produced the following pattern of changes: a significant antagonism of rotations was observed at 0.04 and 0.08 mg/kg i.p. followed by a reinstatement of rotations at 0.16-0.64 mg/kg (at higher doses, a second antagonism occurred that lacked stereoselectivity). The reinstatement of rotations observed at 0.16 and 0.32 mg/kg of SR 48692 was abolished by spiroperidol and 6-OHDA lesions, suggesting the role of dopamine regulatory mechanisms.

Neurobehavioural effects of SR 27897, a selective cholecystokinin type A (CCK-A) receptor antagonist

The activity of SR 27897, a potent and selective CCK-A vs CCK-B receptor antagonist (Ki = 0.2 nM on guinea-pig pancreas vs 2000 nM on rat brain) was studied on behavioural, electrophysiological and biochemical effects induced by peripheral or central injection of CCK-8S. For comparative purposes, devazepide, a reference CCK-A receptor antagonist, was investigated in these same models. CCK-induced hypophagia and CCK-induced hypolocomotion in rats, two behavioural changes associated with the stimulation of peripheral CCK-A receptors, were dose-dependently antagonized by SR 27897 (ED50 = 0.003 and 0.002 mg/kg i.p., respectively) and devazepide (ED50 = 0.02 and 0.1 mg/kg i.p., respectively). CCK-induced decrease of cerebellar cGMP levels in mice was also reduced by SR 27897 (ED50 = 0.013 mg/kg) and by devazepide (0.084 mg/kg). The CCK-induced turning behaviour after intrastriatal injection in mice, and the potentiation of the rate suppressant activity of apomorphine on rat DA neurons, were blocked by higher doses of SR 27897 and devazepide, consistent with the probable central origin of these effects. The respective ED50s were 0.2 mg/kg i.p. for SR 27897 and 4.9 mg/kg i.p. for devazepide in the former model, while the respective minimal effective doses were 1.25 and 5 mg/kg i.p. in the latter test. In most tests the i.p./p.o. ratio for SR 27897 was near unity, suggesting a high oral bioavailability of the compound. Taken together, these findings support the notion that SR 27897 behaves as a potent CCK-A antagonist able to cross the blood brain barrier.

The NK2 receptor antagonist SR48968 inhibits thalamic responses evoked by thermal but not mechanical nociception

Extracellular recordings were made in the thalamic posterior nuclear group of anesthetized rats to study the effects of SR48968, a non-peptide NK2 receptor antagonist, on the responses evoked by thermal or mechanical nociceptive cutaneous stimulation. SR48968 (0.125-0.5 mg/kg, i.v. route) inhibited the responses to thermal stimulation while being ineffective on mechanically evoked responses in doses up to 2 mg/kg i.v. This effect was stereoselective since SR48965, the (R) enantiomer of SR48968 with a 2000-fold lower affinity for NK2 receptors, did not modify thermally evoked responses at a dose of 1 mg/kg i.v. These results support the notion that NK2 receptors are involved in thermal nociception.

Neuropharmacological profile of a novel and selective ligand of the sigma site: SR 31742A

The biochemical, electrophysiological and behavioural effects of SR 31742A, a novel and selective ligand of sigma sites in brain, labelled with (+)-[3H]3PPP (Ki = 5.3 +/- 0.3 nM), were investigated in rodents and compared with those of DA antagonists having (haloperidol) or not (spiroperidol) a high affinity for sigma sites. Like haloperidol but unlike spiroperidol, SR 31742A, (ED50 = 0.065 mg/kg, i.p., and 0.21 mg/kg, p.o.) antagonized sigma-dependent turning behaviour in mice and inhibited (0.5 mg/kg, i.v.) the spontaneous firing of hippocampal (CA3) neurones in urethane-anaesthetized rats. In chloral hydrate-anaesthetized rats, like classical antipsychotic compounds, SR 31742A (0.625-5 mg/kg, i.p.) increased the number of spontaneously active A9 and A10 DA cells after single administration and produced an opposite effect after repeated injections. The drug SR 31742A reduced (2.5, 5, 10 mg/kg, i.p.) the hyperactivity elicited by various drugs including that produced by injection of (+)-amphetamine into the nucleus accumbens and impaired avoidance responses at doses (5, 10 mg/kg, i.p.), sparing escape behaviour. SR 31742A lacked affinity for DA receptors and neither did the compound induce catalepsy nor antagonize such effects elicited by apomorphine as climbing, hypothermia, stereotypy or the inhibition of firing of DA neurones. SR 31742A did not affect the basal metabolism of DA but at 10 mg/kg (i.p.) it significantly reduced the amphetamine-induced rise in levels of 3-MT in the striatum of mice. Together, these results indicate a modulatory role for sigma sites upon the activity of hippocampal and DA systems and that sigma ligands exert effects, which suggest antipsychotic potential.

Turning behavior induced in mice by a neurokinin A receptor agonist: stereoselective blockade by SR 48968, a non-peptide receptor antagonist

The intrastriatal injection of [Nle10]-NKA(4-10), a neurokinin A agonist, (0.05-5 ng/mouse) elicited vigorous contralateral rotations. This behavior was dose-dependently antagonized by SR 48968 (ED50: 0.15 mg/kg i.p.: 0.19 mg/kg p.o.), a selective non-peptide antagonist of NK-2 receptors, but it was not affected by spiroperidol. This suggests that NK-2 receptor stimulation may affect the activity of the striatum without necessarily involving dopaminergic systems.

Biochemical and pharmacological profile of a potent and selective nonpeptide antagonist of the neurotensin receptor

We describe the characteristics of SR 48692, a selective, nonpeptide antagonist of the neurotensin receptor. In vitro, this compound competitively inhibits 125I-labeled neurotensin binding to the high-affinity binding site present in brain tissue from various species with IC50 values of 0.99 +/- 0.14 nM (guinea pig), 4.0 +/- 0.4 nM (rat mesencephalic cells), 7.6 +/- 0.6 nM (COS-7 cells transfected with the cloned high-affinity rat brain receptor), 13.7 +/- 0.3 nM (newborn mouse brain), 17.8 +/- 0.9 nM (newborn human brain), 8.7 +/- 0.7 nM (adult human brain), and 30.3 +/- 1.5 nM (HT-29 cells). It also displaces 125I-labeled neurotensin from the low-affinity levocabastine-sensitive binding sites but at higher concentrations (34.8 +/- 8.3 nM for adult mouse brain and 82.0 +/- 7.4 nM for adult rat brain). In guinea pig striatal slices, SR 48692 blocks K(+)-evoked release of [3H]dopamine stimulated by neurotensin with a potency (IC50 = 0.46 +/- 0.02 nM) that correlates with its binding affinity. In a cell line derived from a human colon carcinoma (HT-29), SR 48692 competitively antagonizes neurotensin-induced intracellular Ca2+ mobilization with a pA2 (-log Kapp) values of 8.13 +/- 0.03, which is consistent with results obtained in binding studies. Moreover, SR 48692 is devoid of any intrinsic agonist activity. This compound is also active in vivo, since it reverses at low dose (80 micrograms/kg) the turning behavior induced by intrastriatal injection of neurotensin in mice with similar potency whatever the route of administration (i.p. or orally) and with a long duration of action (6 hr). Thus, being a potent and selective neurotensin receptor antagonist, SR 48692 may be considered as a powerful tool for investigating the role of neurotensin in physiological and pathological processes.

SR 46559A: a novel and potent muscarinic compound with no cholinergic syndrome

The cholinergic activities of SR 46559A, 3-[N-(2 diethyl-amino-2-methylpropyl)-6-phenyl-5-propyl] pyridazinamine sesquifumarate, have been investigated in vitro and in vivo, in rodents. Using rat brain cortical membranes, SR 46559A was a competitive ligand (Ki = 112 nM) at muscarinic M1 receptors, its affinity for muscarinic M2 (cardiac) and M3 (glandular) receptors being 6-7 times lower. SR 46559A did not interact with brain nicotinic receptors and high affinity choline uptake sites nor did it inhibit brain acetylcholinesterase activity. In contrast to reference muscarinic agonists, SR 46559A (1 mM) did not inhibit the forskolin-induced activation of cAMP synthesis nor did it stimulate phosphoinositides breakdown in various brain preparations. However, this compound enhanced (+67% at 1 mM) diacylglycerol formation in rat striatal miniprisms, an effect fully reversed by atropine. As shown with reference agonists, SR 46559A inhibited (IC50 = 10 microM) the K(+)-evoked release of [3H]GABA from rat striatal slices and reduced at 0.5 and 1 microM, the population spike amplitude of the CA1 pyramidal cells induced by stimulation of the Schaffer's collateral commissural pathway in rat hippocampal slices. In mice, SR 46559A at a near lethal dose (200 mg/kg PO) did not induce the typical cholinergic syndrome nor did it modify at 30 mg/kg PO the oxotremorine-induced hypothermia. Like muscarinic agonists, SR 46559A (1 mg/kg PO) potentiated haloperidol-induced catalepsy in rats and inhibited (ED50 = 0.12 mg/kg PO) rotations induced in mice by intrastriatal injection of pirenzepine.(ABSTRACT TRUNCATED AT 250 WORDS)

Pharmacological activity of cholecystokinin analogues modified in the Met28-Gly29 region

Analogues of the C-terminal octapeptide of cholecystokinin (CCK) modified in the Met28-Gly29 region, were tested for their ability to interact with peripheral cholecystokinin receptors on rat pancreatic acini and to stimulate amylase secretion. These analogues were further evaluated for their ability to recognize central CCK receptors on guinea pig brain membranes. The behavioral effect of these analogues was also tested after intrastriatal injection into mice. It appeared that these analogues were full CCK agonists in the peripheral system. Although some induced dopaminomimetic effects after intrastriatal injection into mice, being as potent as the C-terminal octapeptide of cholecystokinin (CCK-8), others did not have any effect and were able to antagonize CCK-8 actions in the striatum. The results of this study confirm that one can obtain very potent CCK analogues by modifying the peptide bond between Met28 and Gly29, and that this modification can produce either CCK agonists or antagonists of CCK-induced dopamine transmission in the striatum.

Systemic injection of pirenzepine induces a deficit in passive avoidance learning in rats

When injected IP, the M1 muscarinic receptor antagonist pirenzepine dose-dependently induced a deficit in passive avoidance learning in rats. This activity was optimal at 75 mg/kg injected 1 h before the acquisition session. The deficit induced by pirenzepine was antagonized by oxotremorine (0.03-0.3 mg/kg SC) and physostigmine (0.1 mg/kg SC), but not neostigmine. By comparison, under the same experimental conditions, physostigmine and oxotremorine also antagonized the deficit induced by an equipotent dose of scopolamine (0.5 mg/kg IP), although the activity of physostigmine appeared stronger against scopolamine than against pirenzepine. These results suggest that pirenzepine could produce a centrally-mediated behavioural disruption when injected systemically.

A pseudopeptide that is a potent cholecystokinin agonist in the peripheral system is able to inhibit the dopamine-like effects of cholecystokinin in the striatum

There are no known specific effective cholecystokinin (CCK) receptor antagonists of both peripheral and central nervous systems. Here, we describe experiments which demonstrate that a synthetic pseudopeptide analogue of CCK-7 is a potent agonist in the peripheral system and behaves as a selective and highly potent inhibitor of the dopamine-like effects of CCK in the striatum. This compound, t-butyloxycarbonyl-Tyr (SO3H)-Nle psi (COCH2)Gly-Trp-Nle-Asp-Phe-NH2, is able to stimulate enzyme secretion from rat pancreatic acini, with high efficacy and potency. It is also very potent in inhibiting the binding of labeled CCK-8 to rat pancreatic acini (IC50 = 5 nM) and to guinea pig and mouse brain membranes (IC50 = 0.7 nM). However, this compound is able to antagonize the effects of intrastriatally injected t-butyloxycarbonyl-[Nle28,31] CCK-8 in mice, with high potency.

Induction of turning by direct intrastriatal injection of dopaminomimetic drugs in mice: pharmacological analysis of a simple screening model

A new simple model designed for the screening of dopaminomimetic drugs in mice is presented. When injected directly into the right striatum of conscious mice, the dopamine (DA) receptor agonists apomorphine, SKF 38393 and bromocryptine, the indirect DAmimetic drugs (+)-amphetamine and nomifensine, the atypical DAergic antidepressant drug minaprine, induced contralateral rotations. Rotations induced by DA mimetics were antagonized by i.p. injected haloperidol. A pretreatment with the D1 antagonist SCH 23390 (s.c.) antagonized the turning induced by apomorphine or by the D1 agonist SKF 38393, and, to a lesser extent, that induced by the D2 agonist bromocryptine. In contrast, the D2 antagonist (-)-sulpiride (i.p.) blocked the effects of the 3 agonists to the same extent. A pretreatment with alpha-methylparatyrosine (i.p.) antagonized rotations induced by bromocryptine, (+)-amphetamine and minaprine, but not those induced by nomifensine or apomorphine. The results suggest that this model could represent a useful screening tool for the search of new DAmimetic drugs, and for the assessment of DA receptor blockade.