D1 Dopamine receptor-mediated substance P depletion in the striatonigral neurons of rats subjected to neonatal dopaminergic denervation: implications for self-injurious behavior

The present study examined the influences of dopamine (DA) receptor stimulation on enkephalin (Met5-enkephalin; ME) and tachykinin (substance P; SP) systems of basal ganglia of Sprague-Dawley rats, lesioned as neonates with 6-hydroxydopamine (6-OHDA). It has been proposed that the neonatal 6-OHDA-lesioned rat could serve as a model for the DA deficiency and self-injurious behavior (SIB) observed in the childhood neurological disorder. Lesch-Nyhan syndrome. In agreement with earlier work, the present study found that the neonatal 6-OHDA treatment at 3 days of age, reduced DA and caused an increase in ME and a decrease in SP content in the striatum and substantia nigra, when tested as adults. Administration of the DA precursor, L-dihydroxyphenylalanine (L-DOPA), to lesioned animals, induced SIB; increased DA and DOPAC levels; produced a greater decrease (-64%) in SP levels in the striatum and substantia nigra than was observed with lesion alone (-28%). The L-DOPA-induced decrease in SP levels and the SIB observed in the lesioned animals were blocked by pretreatment with the D1 receptor antagonist, SCH-23390. Moreover, administration of the D1 receptor agonist, SKF-38393, but not the D2 agonist, LY-171555, to lesioned animals mimicked the L-DOPA responses in all respects, except that the agonists did not alter DA or DOPAC levels. None of the DA agonists or antagonists treatments affected lesion-induced increase in ME levels in the striatum. These results indicate for the first time, that SIB precipitated by DA agonists in neonatal dopaminergic denervated animals, is associated with a marked and selective decrease in SP in the striatonigral SP neurons. This process has two components: (a) a retarded development of the SP system due to neonatal dopaminergic denervation: and (b) a depletion of the remaining SP, presumably by enhanced release due to D1 DA receptor-mediated activation of striatonigral SP neurons.     

Two selective 5-HT1A receptor antagonists, WAY-100 635 and NDL-249, stimulate locomotion in rats acclimatised to their environment and alter their behaviour: a behavioural analysis

The aim was to study firstly, the motor effects of a new 5-HT_1A antagonist, NDL-249 [(R)-3-(N-cyclopentyl-N-propylamino)-8-fluoro-3,4-dihydro-2H-1-benzopyran-5-carboxamide hydrochloride] and of the reference 5-HT_1A antagonist WAY-100 635 [N-(2-(1-(4-(2-methoxyphenyl)piperazinyl))ethyl)-N-(2-pyridinyl) cyclohexanecarboxamide trihydrochloride], in comparison to the 5-HT_1A agonist (±)-8-OH-DPAT [(8-hydroxy-2-(di-N-propylamino) tetralin, hereafter 8-OH-DPAT], in rats acclimatised to the automated activity cages; secondly, to study whether the behavioural effects of NDL-249 and 8-OH-DPAT are sensitive to the 5-HT depleting effects of p-chlorophenylalanine (PCPA); thirdly, to characterise the nature of the antagonist-induced activation seen in the automatic activity cages with the aid of a behavioural observation analysis; fourthly, to examine the interaction between the 5-HT_1Areceptors mediating the behavioural effects and dopamine (DA) receptors. NDL-249 was found to bind in vitro to rat hippocampal 5-HT_1A receptors with high affinity and selectivity. In second messenger studies, it was devoid of agonist-like effects. In the locomotor activity studies, each antagonist significantly increased the incidence of horizontal activity, peripheral activity and rearing. 8-OH-DPAT, while significantly increasing peripheral and horizontal activities, decreased the incidence of rearing. PCPA blocked the motor effects of NDL-249 but did not affect those of 8-OH-DPAT. Observational analyses indicated that NDL-249 induced significant increases at one or more doses in sniffing, rearing and locomotion together with a significant reduction in stillness. WAY-100 635 significantly increased the incidence of rearing, intense grooming and vacuous chewing. The significant increases in sniffing, grooming and intense grooming and the significant decrease in stillness induced by the DA D₁ agonist, SK&F 38393 [(±)-1-phenyl-2,3,4,5-tetrahydro-(1H)-3-benzazepine-7,8-diol hydrochloride], were not altered by concomitant pre-treatment with NDL-249. Pre-treatment of rats with either the DA D₁ antagonist SCH-23390 (2,3,4,5-tetrahydro-3-methyl-5-phenyl-1H-3-benzazepin-7-ol) or the DA D₂ antagonist, raclopride, blocked the reduced stillness and increased sniffing and rearing induced by NDL-249. In conclusion, 5-HT_1A antagonists including the new selective antagonist, NDL-249, induce mild behavioural activation in rats, which is mediated probably indirectly via DA systems. Received: 3 April 1997/Final version: 23 February 1998     

Blockade or stimulation of D1 dopamine receptors attenuates cue reinstatement of extinguished cocaine-seeking behavior in rats

RATIONALE: D(1) dopamine receptor antagonists and agonists attenuate cocaine reinstatement of cocaine-seeking behavior (i.e., responding in the absence of cocaine reinforcement). OBJECTIVES: The present study investigated the effects of a D(1) antagonist (SCH-23390), partial agonist (SKF-38393), and full agonist (SKF-81297) on reinstatement of cocaine-seeking behavior elicited by presentation of cocaine-paired cues. METHODS: Rats that had been trained to self-administer cocaine with a light/tone stimulus complex paired with each infusion underwent extinction across days. After responding diminished, rats were given response-contingent access to the cocaine-paired stimulus complex. The effects of SCH-23390 (0-10.0 microg/kg), SKF-38393 (0-3.0 mg/kg), and SKF-81297 (0-3.0 mg/kg) on cue reinstatement of cocaine-seeking behavior were examined. The ability of the two D(1) agonists to independently reinstate cocaine-seeking behavior and the effects of SKF-81297 on cocaine reinstatement were also examined. To investigate the possibility of behavioral interference, the effects of SKF-38393 and SKF-81297 on grooming and stereotypy were assessed. RESULTS: SCH-23390 and SKF-81297, but not SKF-38393, attenuated cue reinstatement. However, while SKF-81297 dose-dependently increased response latency, SCH-23390 did not. SKF-81297 also independently reinstated responding at the two lowest doses tested while SKF-38393 had no effect. Furthermore, SKF-81297 decreased cocaine reinstatement and increased response latency only at the highest dose. Finally, stereotypy was observed at all doses of SKF-81297 that also decreased responding, although the patterns of changes in these behaviors did not completely correspond. CONCLUSIONS: While the antagonist and full agonist produced similar effects on cocaine-seeking behavior, only the agonist increased response latency, suggesting that different processes mediate the effects of these drugs.     

Administration of the D1-like dopamine receptor antagonist SCH-23390 into the medial nucleus accumbens shell attenuates cocaine priming-induced reinstatement of drug-seeking behavior in rats

Rationale. A growing literature indicates that increased dopamine transmission in the nucleus accumbens contributes to priming-induced reinstatement of cocaine-seeking behavior. Objectives. The present experiments were designed to assess the role of D₁-like dopamine receptors in the nucleus accumbens core and shell subregions in cocaine priming-induced reinstatement of drug seeking. Methods. Rats were trained to lever press for cocaine using a fixed ratio (FR) 5 schedule of reinforcement. Drug-seeking was measured by active lever presses during daily 2-h sessions. After approximately 30 days of cocaine self-administration, the animals underwent an extinction phase during which cocaine was replaced with saline. Daily extinction sessions were conducted until responding was consistently less than 10% of the response rate maintained by cocaine self-administration. After the extinction phase, priming-induced reinstatement of cocaine-seeking behavior was assessed. Results. Cocaine dose-dependently reinstated cocaine seeking, with robust drug seeking at 10 mg/kg cocaine. Administration of the D₁-like dopamine receptor antagonist, SCH-23390 (0.1–1.0 μg), directly into the medial nucleus accumbens shell dose-dependently attenuated drug seeking induced by 10 mg/kg cocaine. Microinjection of 1.0 μg SCH-23390 into either the nucleus accumbens core or lateral septum had no influence on cocaine-seeking behavior. Conclusions. These results indicate that stimulation of D₁-like dopamine receptors in the medial nucleus accumbens shell contributes to drug-induced reinstatement of cocaine-seeking behavior.     

Effects of dopamine receptor antagonists on sucrose consumption and preference

Effects of the dopamine D2 receptor antagonist sulpiride and the D1 antagonist SCH-23390 were examined, in rats, in two-bottle preference tests (sucrose versus water) and in single-bottle tests, at different sucrose concentrations. Both drugs decreased sucrose intake in single bottle tests, at low sucrose concentrations, but had no effect at high concentrations; reducing drive level had exactly the opposite pattern of effects. In two-bottle tests, both drugs reduced preference for the weakest sucrose concetration (0.7%) but increased preference for the strongest concentration (34%). The effects of antagonizing either subtype of DA receptor appear to be similar to those of reducing the concentration of sucrose.     

Determination of a novel thrombin receptor antagonist (SCH 530348) in human plasma: evaluation of Ultra Performance Liquid Chromatography™-tandem mass spectrometry for routine bioanalytical analysis

SCH 530348 is a safe and effective oral anti-platelet agent for patients with acute coronary syndrome. Clinical study results suggest that SCH 530348 dosage at 20 mg or 40 mg is feasible to achieve rapid maximum platelet inhibition following an acute coronary event or intervention procedure. To permit accurate determinations of circulating SCH 530348 in plasma following dosing, a method for measuring SCH 530348 concentrations in human plasma was validated using liquid chromatography–tandem mass spectrometry (LC–MS/MS). The method utilized semi-automated 96-well protein precipitation with gradient chromatography using an ACQUITY™ UPLC BEH C₁₈ (2.1 mm × 50 mm, 1.7 μm) column. The retention time of SCH 530348 was approximately 1.5 min. This method was validated for routine quantitation of SCH 530348 over the concentration range of 1.00–1000 ng/mL. Inter-run accuracy based on mean percent theoretical for replicate quality control samples was better than 95.2%. Inter-run precision based on percent relative deviation for replicate quality control samples was ≤3.3%. SCH 530348 quality control samples were stable in human plasma for up to three freeze/thaw cycles, for at least 467 days when frozen at −20 °C and for at least 7 h when stored at room temperature. The lower limit of quantitation was 1.00 ng/mL for a 100 μL plasma aliquot.     

Stimulation of forward locomotion by SCH-23390 and raclopride in d-amphetamine-treated rats

In d-amphetamine-treated (4.0 mg kg^–1 s.c.) rats the selective dopamine D₁ and D_2/3 receptor antagonists SCH-23390 (2.5–20.0 μg kg^–1 s.c.) and raclopride (12.5–100.0 μg kg^–1 s.c.), respectively, produced a biphasic pattern of effects on forward locomotion, as observed in an open-field arena (≈0.5 m²). Thus, at the low doses of SCH-23390 (2.5–10.0 μg kg^–1) or raclopride (12.5–50.0 μg kg^–1), there was a statistically significant increase in forward locomotion, followed by suppression of the behavior at the higher doses. The SCH-23390-induced (5.0 μg kg^–1) stimulation of forward locomotion was partially antagonized by concomitant raclopride treatment (12.5–25.0 μg kg^–1) and the corresponding raclopride-induced (12.5 μg kg^–1) stimulation was fully antagonized by treatment with SCH-23390 (2.5–5.0 μg kg^–1). Furthermore, the SCH-23390- or raclopride-induced stimulation of forward locomotion was also antagonized by treatment with the α₁-adrenoceptor antagonist prazosin (1.0 mg kg^–1 s.c.). These observations suggest that under conditions of an increased general tone at brain dopamine receptors, there is a mutual inhibitory synergy between dopamine D₁ and D_2/3 receptors. Received: 21 July 1997 / Accepted: 6 March 1998     

Cooperative activation of D1-like and D2-like dopamine receptors in the nucleus accumbens shell is required for the reinstatement of cocaine-seeking behavior in the rat

Activation of D1-like (D1, D5) or D2-like (D1, D3, D4) dopamine receptors in the nucleus accumbens shell is sufficient to reinstate cocaine-seeking behavior in rats. The goal of these experiments was to assess whether cooperative activation of D1-like and D2-like dopamine receptors in the accumbens shell is required to promote cocaine reinstatement. Rats were initially trained to self-administer cocaine (0.25 mg, i.v.) using a fixed-ratio schedule of reinforcement for approximately 21 days. Animals subsequently underwent an extinction phase during which saline was substituted for cocaine. Once cocaine self-administration behavior was extinguished (defined as <15% of the total responses maintained during self-administration), dopamine receptor agonist-induced reinstatement of cocaine seeking was assessed. Administration of the selective D1/5 agonist R-(+)-6-chloro-7,8-dihydroxy-1-phenyl-2,3,4,5-tetrahydro-1H-3-benzazepine hydrobromide (SKF-81297) (1.0 microg) or the D2/3 receptor agonist trans-(-)-(4aR)-4,4a,5,6,7,8,8a,9-octahydro-5-propyl-1H-pyrazolo[3,4-g]quinoline hydrochloride (quinpirole) (3.0 microg) directly into the nucleus accumbens shell promoted reinstatement of cocaine seeking. In order to determine if endogenous dopamine tone in the accumbens shell is required for dopamine receptor agonist-induced reinstatement of cocaine seeking, D1/5 or D2/3 dopamine receptor antagonists were administered into the nucleus accumbens shell prior to a selective dopamine receptor agonist. Microinfusion of the D2/3 dopamine receptor antagonist sulpiride ((S)-5-aminosulfonyl-N-[(1-ethyl-2-pyrrolidinyl)methyl]-2-methoxybenzamide) (1.0 microg) into the nucleus accumbens shell 10 minutes prior to SKF-81297 (1.0 microg) blocked the ability of this D1-like dopamine receptor agonist to reinstate cocaine seeking. Similarly, administration of the selective D1/5 dopamine receptor antagonist R(+)-7-chloro-8-hydroxy-3-methyl-1-phenyl-2,3,4,5-tetrahydro-1H-3-benzazepine hydrochloride (SCH-23390) (1.0 microg) into the nucleus accumbens shell prior to quinpirole (3.0 microg) blocked reinstatement of drug-seeking behavior elicited by this D2/3 dopamine receptor agonist. Moreover, intra-accumbal shell co-administration of subthreshold doses of quinpirole (1.5 microg) and SKF-81297 (0.1 microg) promoted cocaine-seeking behavior. Collectively, these results indicate that cooperative activation of D1-like and D2-like dopamine receptors in the nucleus accumbens shell is necessary to reinstate cocaine seeking in rats.     

Recent developments in reversing glycopeptide-resistant pathogens

Recent studies addressing vancomycin-resistance phenomena are surveyed. Besides leading semi-synthetic glycopeptides: BI-397 and LY 333328, other new synthetic derivatives are also presented. Rational design based on the known mode of action is seen in recent research from both industrial and academic groups. Thus, Biosearch Italia SpA worked on new synthetic glycopeptides with a modified binding pocket in order to find drugs active against both vancomycin-sensitive and -resistant strains. Eli Lilly & Co. and research groups at Stanford, Cambridge and Harvard synthesised covalently linked dimers in order to copy the dimerisation and membrane anchoring effects. Both directions proved to be rewarding and some interesting compounds with potent in vitro activity against vancomycin-resistant enterococci (VRE) were found from these investigations. A new mechanistic proposal that can account for the bioactivity of LY 333328 against VRE was summarised. Research on new agents with modes of action different to that of glycopeptide antibiotics have also been successful and recent investigations related to RP-59500, SCH-27899 and U-100766 are presented.