Serotonin receptor blocking effect of SCH 23390

D1-like and D2 dopamine receptor antagonists administered into the shell subregion of the rat nucleus accumbens decrease cocaine, but not food, reinforcement

Cocaine self-administration experiments were designed to assess the respective roles of D1-like and D2-like dopamine receptors in the ventral forebrain in cocaine reinforcement. D1-like or D2-like dopamine receptor antagonists were microinjected into the nucleus accumbens core, nucleus accumbens shell, neostriatum or lateral septum prior to sessions in which cocaine was self-administered under a progressive ratio schedule by rats. The results indicated that administration of a D1/5 (SCH-23390) or a D2/D3/D4 (eticlopride), but not a D3 (U99194A) or D4 (L-750,667), dopamine receptor antagonist into the core and shell of the nucleus accumbens decreased the reinforcing efficacy of cocaine. However, in control experiments intra-accumbal core administration of SCH-23390 or eticlopride decreased food self-administration, whereas administration of these drugs into the accumbens shell had no effect on food reinforcement. Neither SCH-23390 nor eticlopride influenced cocaine reinforcement when administered into the neostriatum or lateral septum. Collectively, these results indicate that D1-like and D2 dopamine receptors in the nucleus accumbens shell selectively modulate the reinforcing efficacy of cocaine, whereas D1-like and D2 dopamine receptors in the accumbens core have a more general influence on reinforced behaviors.

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 D(1)-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 D(1)-like dopamine receptor antagonist, SCH-23390 (0.1-1.0 micro g), directly into the medial nucleus accumbens shell dose-dependently attenuated drug seeking induced by 10 mg/kg cocaine. Microinjection of 1.0 micro g 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 D(1)-like dopamine receptors in the medial nucleus accumbens shell contributes to drug-induced reinstatement of cocaine-seeking behavior.

Enhancement of excessive lever-pressing after post-training signal attenuation in rats by repeated administration of the D1 antagonist SCH 23390 or the D2 agonist quinpirole, but not the D1 agonist SKF 38393 or the D2 antagonist haloperidol

The authors have recently shown that attenuation of an external response feedback leads to excessive lever-pressing that is not associated with attempts to collect reward, and they have suggested that this may be an analogue to "unreasonable" excessive behavior characteristic of obsessive-compulsive disorder. The present study shows that repeated administration of SCH 23390 or quinpirole, but not SKF 38393 or haloperidol, enhances this behavioral pattern. On the basis of data regarding the enduring effects of chronic treatment with dopaminergic agents, these results suggest that overstimulation of striatal D1 receptors underlies enhanced response to signal attenuation. These results may link the hypothesis that obsessions and compulsions result from a deficient response feedback mechanism with findings implicating dopaminergic abnormalities in the production of obsessions and compulsions.

Effect of the dopamine D(1/5) antagonist SCH 23390 on the acquisition of conditioned fear

The authors previously reported that typical and atypical antipsychotic drugs inhibited the acquisition but not expression of conditioned fear. The present study examined the effects of the selective dopamine D(1/5) agonist (SKF 38393) and antagonist (SCH 23390) on the acquisition and expression of conditioned fear. Drugs were administered subcutaneously to male Sprague-Dawley rats 30 min before foot shock (2.5 mA for 5 min). Twenty-four hours after foot shock, rats were again placed and observed in the shock chamber without shocks (conditioned fear). Freezing behavior induced by conditioned fear, an index of anxiety or fear, was recorded using a time-sampling procedure. SCH 23390 (0.1-1 mg/kg) inhibited the acquisition of conditioned freezing. The administration of SCH 23390 at a dose of 0.1 mg/kg 30 min after foot shock did not affect conditioned freezing. Taken together, it is concluded that D(1/5) antagonism inhibits the acquisition of conditioned fear. SKF 38393 (3-20 mg/kg) failed to change the acquisition of conditioned fear. SCH 23390 or SKF 38393 administered prior to testing did not reduce the expression of conditioned fear. These results suggest that D(1/5) receptors may play a role in the development of fear or anxiety.

Peripheral and intraamygdalar administration of the dopamine D1 receptor antagonist SCH 23390 blocks fear-potentiated startle but not shock reactivity or the shock sensitization of acoustic startle

Central dopamine (DA) activity is thought to play a role in fear motivation. The aim of the present study was to assess the involvement of DA D1 receptors in emotional learning. The authors report that peripheral and intraamygdalar administration of the specific D1 receptor antagonist SCH 23390 blocked the acquisition of fear-potentiated startle. Analysis of shock reactivity during footshock administration revealed that the learning impairment could not be explained by a diminution in the aversive properties of the unconditioned stimulus. Additionally, systemic and intraamygdalar injection of SCH 23390 did not alter fear expression as measured with the shock sensitization of acoustic startle. The potential contribution of mesoamygdaloid DA to the acquisition and retrieval of conditioned fear responses is discussed.

Local application of SCH 39166 reversibly and dose-dependently decreases acetylcholine release in the rat striatum

The effect of local application by reverse dialysis of the dopamine D(1) receptor antagonist (-)-trans-6,7,7a,8,9, 13b-exahydro-3-chloro-2-hydroxy-N-methyl-5H-benzo-[d]-nap hto-[2, 1b]-azepine hydrochloride (SCH 39166) on acetylcholine release was studied in awake, freely moving rats implanted with concentric microdialysis probes in the dorsal striatum. In these experiments, the reversible acetylcholine esterase inhibitor, neostigmine, was added to the perfusion solution at two different concentrations, 0.01 and 0.1 microM. SCH 39166 (1, 5 and 10 microM), in the presence of 0.01 microM neostigmine, reversibly decreased striatal acetylcholine release (1 microM SCH 39166 by 8+/-4%; 5 microM SCH 39166 by 24+/-5%; 10 microM SCH 39166 by 27+/-7%, from basal). Similarly, SCH 39166, applied in the presence of a higher neostigmine concentration (0.1 microM), decreased striatal acetylcholine release by 14+/-4% at 1 microM, by 28+/-8% at 5 microM and by 30+/-5% at 10 microM, in a dose-dependent and time-dependent manner. These results are consistent with the existence of a facilitatory tone of dopamine on striatal acetylcholine transmission mediated by dopamine D(1) receptors located on striatal cholinergic interneurons.

Modification of naloxone-induced withdrawal signs by dextromethorphan in morphine-dependent mice

In the present study the effect of dextromethorphan on naloxone-induced withdrawal signs in morphine-dependent mice was examined. In addition, the modulatory role of dopaminergic mechanisms upon the effect of dextromethorphan was investigated. Mice were rendered dependent on morphine by subcutaneous (s.c.) injections of morphine sulfate three times a day for 3 days, and withdrawal signs were induced by intraperitoneal (i.p.) administration of naloxone 2 h after the 10th injection of morphine sulfate on day 4. Dextromethorphan (20-50 mg/kg, i.p.) caused a significant decrease in withdrawal jumping, paw-shakes, grooming, burrows, writhing and diarrhea in morphine-dependent mice. The mixed dopamine D1/D2 receptor agonist apomorphine (0.5 and 1 mg/kg, s.c.) reduced the response induced by dextromethorphan. The effect of apomorphine was blocked by the dopamine D1 receptor antagonist SCH 23390 (R-(+)-8-chloro-2,3,4,5-tetrahydro-3-methyl-5-phenyl-1H-3-benzazepine-7- ol maleate) (0.5 and 1 mg/kg, i.p.) but not by the dopamine D2 receptor antagonist sulpiride (25 and 50 mg/kg, s.c.) nor the peripheral dopamine receptor antagonist domperidone (5 and 10 mg/kg, s.c.). These results suggest that the dopaminergic system(s) may in part mediate the suppressive action of the NMDA receptor antagonist dextromethorphan on naloxone-induced withdrawal signs in morphine-dependent mice.

Effects of dopaminergic agents on antinociception in formalin test

Morphine caused a dose-related antinociception in early phase and late phase of formalin test in mice. The D2 dopamine agonist quinpirole, but not the D1 dopamine agonist SKF 38393, increased the antinociceptive effect of morphine in both phases of the test. The antinociceptive effect of quinpirole also was decreased by sulpiride or domperidone pretreatment in the early phase of test. The D1 antagonist SCH23390, the D2 antagonist sulpiride, or the peripheral D2 dopamine antagonist domperidone, increased the morphine effect. Single administration of SKF38393, quinpirole, SCH23390, sulpiride, and domperidone also induce antinociception. The response of SCH23390, but not that of other dopamine agents, was antagonized with naloxone. The effects of the drugs alone and in combination with morphine have been discussed.

Effects of specific dopamine D1 and D2 receptor antagonists and agonists and neuroleptic drugs on emotional defecation in a rat model of akathisia

An increase in emotional defecation in rats in a well-habituated environment induced by neuroleptic drugs (NDef) has been proposed as a model for neuroleptic-induced akathisia. We examined the effects of dopamine receptor antagonists and agonists on this model. A selective dopamine D1 antagonist (SCH 23390) and a selective D2 antagonist (raclopride) induced increased defecation at higher doses, and demonstrated a synergistic effect at lower doses. Selective D1 (SKF 82958) and D2 (quinpirole) agonists did not have a significant effect on defecation, nor did they reverse the effect of haloperidol. In a further pilot study, we explored the effects of typical and atypical neuroleptics on this model. The haloperidol and risperidone treated rats produced more faecal boli than those treated with clozapine, thioridazine and chlorpromazine, with the former being non-significantly greater than the vehicle-treated group. The results of our studies suggest that NDef is most probably an effect of central dopamine antagonism that is not specific to D1 or D2 receptors, but that the two receptor subtypes have a synergistic effect. It is unlikely to be due to actions of neuroleptics on 5HT2 or alpha1 receptors as has sometimes been suggested. The results have implications for our understanding of the pathogenesis of akathisia.

Nicotine attenuates naloxone-induced jumping behaviour in morphine-dependent mice

In the present study the effect of nicotine on naloxone-induced jumping behaviour in morphine-dependent mice was examined. In addition, the modulatory role of dopaminergic, adrenergic and cholinergic mechanisms upon the effect of nicotine were investigated. Animals were rendered dependent on morphine by subcutaneous (s.c.) injections of morphine sulfate 3 times a day for 3 days, and jumping behaviour was induced by intraperitoneal (i.p.) administration of naloxone 2 h after the tenth injection of morphine sulfate on day 4. Nicotine (0.001-2 mg/kg s.c.) caused a significant decrease in withdrawal jumping behaviour in morphine-dependent mice. The effect of nicotine was blocked by the central nicotinic antagonist mecamylamine (0.01-0.1 mg/kg i.p.) but not by the peripheral nicotinic antagonist hexamethonium (0.01 and 0.1 mg/kg i.p.) nor the muscarinic receptor antagonist atropine (2.5-10 mg/kg i.p.). The dopamine receptor antagonist SCH 23390 (R-(+)-8-chloro-2,3,4,5-tetrahydro-3-methyl-5- phenyl-1H-3-benzazepine-7-ol maleate) (0.01-0.5 mg/kg s.c.) reduced the response induced by nicotine. The dopamine receptor antagonist sulpiride (25 and 50 mg/kg s.c.) and the adrenoceptor antagonists phenoxybenzamine (5 and 10 mg/kg i.p.) and propranolol (5 and 10 mg/kg i.p.) were without an effect. The results indicate that the effect of nicotine on naloxone-induced jumping is mediated by central nicotinic receptors.

Effects of nicotine on memory retrieval in mice

The effect of nicotine was tested on retrieval 24 h after training on a passive avoidance task. Intraperitoneal (i.p.) injection of nicotine (0.25-1.5 mg/kg) increased the step-down latency in mice dose dependently. Pretreatment with the nicotinic receptor antagonist mecamylamine (0.5-1 mg/kg) decreased, whereas pretreatment with the dopamine D1 receptor antagonist SCH 23390 (R-(+)-8-chloro-2,3,4,5-tetrahydro-3-methyl-5-phenyl-1H-3-benzazepine-7-ol maleate) (0.01, 0.05 and 0.1 mg/kg) and the beta-adrenoreceptor antagonist propranolol (10 mg/kg) increased the nicotine response. The dopamine receptor D2 receptor antagonist sulpiride (5-10 mg/kg), the anti-muscarinic agent atropine (2.5-10 mg/kg), the peripheral nicotinic receptor antagonist hexamethonium (0.01-0.5 mg/kg), the alpha-adrenoceptor antagonist phenoxybenzamine (1 and 10 mg/kg) and the peripheral dopamine D2 receptor antagonist domperidone (5 and 10 mg/kg) did not change the response induced by nicotine. Single administration of the antagonists did not cause response; however, a high dose of domperidone (10 mg/kg) and propranolol alone increased the step-down latencies. It may be concluded that a nicotinic receptor mechanism is involved in the nicotine-induced improvement of memory retrieval.

Prenatal exposure to cocaine selectively disrupts motor responding to D-amphetamine in young and mature rabbits

Acute administration of D-amphetamine probed the functional effects of prenatal exposure to cocaine on the integrity of monoaminergic systems in preweanling (48-56 days old) and adult (> or = 140 days old) Dutch belted rabbits. D-Amphetamine sulfate (0, 0.3, 1.0, 3.3 and 6.0 mg/kg, s.c.) produced equivalent dose-related reductions in food intake in 180 day-old rabbits that had been exposed in utero on gestational days 8-29 to cocaine or saline. Intrauterine exposure to cocaine also did not alter the incidence of exploratory behaviors stimulated by D-amphetamine during the anorexia test. In contrast, however, prenatal cocaine virtually eliminated stereotyped head bobbing elicited by the highest dose of D-amphetamine. When responses to 5.0 mg/kg D-amphetamine were measured during a 90-min open field test, prenatal cocaine prevented head bobbing in preweanling rabbits and reduced this behavior by 92% in 140 day-old adults. Prenatal cocaine also diminished the intensity of other motor responses in the open field in the adults but not in preweanlings. In normal rabbits, the D1 antagonist R(+)-SCH 23390 (0.01 mg/kg, s.c.) blocked D-amphetamine-induced head bobbing. Thus, prenatal exposure to cocaine produces an early and persistent deficit in behavioral responding to a high dose of D-amphetamine. The deficit is especially selective at the time of weaning, broadens to affect more motor behaviors with maturation and may reveal impaired D,-mediated dopaminergic neurotransmission in the brain.

Enhanced oral activity response to A77636 in neonatal 6-hydroxydopamine-lesioned rats

To study the role of dopamine D1 receptors in enhanced oral activity effects of SKF 38393 ((+-)-1-phenyl-2,3,4,5-tetrahydro-1H-3-benzazepine-7,8-diol) in neonatal 6-hydroxydopamine-lesioned rats, SKF 38393 was compared to the full agonist, A77636 ((1R,3S)-3-(1'-adamantyl)-1-aminomethyl-3,4-dihydro-5,6-dihydroxy- 1H-2-benzopyran). At 3 days after birth rats were treated with 6-hydroxydopamine HBr (200 micrograms salt form, i.c.v.; desipramine (20 mg/kg i.p.), 1 h) or vehicle. At 6-8 months a 0.01 mg/kg dose of A77636 HCl increased oral activity in 6-hydroxydopamine vs. control rats (P < 0.01). A77636 and SKF 38393 produced identical maximal responses of 35-36 oral movements at 0.1 and 1.0 mg/kg, respectively. SCH 23390 (R-(+)-7-chloro-8-hydroxy-3-methyl-1-phenyl-2,3,4,5-tetrahydro-1H-3-benz azepine ) HCl (0.3 mg/kg i.p.) attenuated the response to A77636. Neither A77636 HCl (0.01-1.0 mg/kg i.p.) nor SKF 38393 HCl (0.03-3.0 mg/kg i.p.) induced oral activity in intact rats. The findings demonstrate that A77636 is more potent than SKF 38393, and that supersensitized dopamine D1 receptors are involved in the induction of oral behavior in neonatal 6-hydroxydopamine-lesioned rats.

Stimulus effects of d-amphetamine 1: DA mechanisms

As part of a continuing effort to assess the role of monoaminergic neuronal systems in the subjective effects of CNS stimulants, 10 rats trained to discriminate 1.0 mg/kg d-amphetamine from saline were treated with compounds that act through different dopaminergic mechanisms. In substitution (generalization) tests, 20 mg/kg of the dopamine (DA) uptake inhibitor GBR 12909 mimicked the training drug completely; at a dose of 15 mg/kg, GBR 12909 substituted for d-amphetamine incompletely. Neither the D1 agonist SK&F 38393 (1, 10 mg/kg) nor the D2 agonist quinpirole (LY 171555; 0.05-0.2 mg/kg) had amphetamine-like effects. When given in combination with the training drug, the D1 antagonist SCH 23390 blocked the amphetamine cue completely at a dose of 0.05 mg/kg but did not have significant effects at higher or lower doses; the D2 antagonist metoclopramide did not block d-amphetamine at any dose tested (1-5 mg/kg). These data indicate that: a) The discriminable effects of d-amphetamine are due, at least in part, to inhibition of DA uptake; b) direct stimulation of either D1 or D2 receptor sites is not sufficient to evoke d-amphetamine-like responding; and c) blockade of D1 receptors attenuates the subjective effects of d-amphetamine to a greater extent than blockade of D2 receptors.

Dopamine receptor subtypes and formalin test analgesia

The role played by dopamine D1 and D2 receptors in formalin test analgesia was explored by challenging D-amphetamine- and morphine-induced analgesia with mixed and selective D1 and D2 antagonists, and by examining the relative analgesic activity of mixed and selective D1 and D2 agonists. The mixed D1/D2 dopamine antagonist cis-flupenthixol (0.5 mg/kg), the D2 antagonist pimozide (0.5 mg/kg), and the D1 antagonist SCH 23390 (0.1 mg/kg) attenuated both D-amphetamine and morphine analgesia. The mixed D1/D2 agonist apomorphine and the selective D2 agonist quinpirole produced dose-dependent analgesia while the selective D1 agonist SKF 38393 was without effect. These data suggest that D1 receptors play an "enabling" role in D2 receptor-mediated analgesia in the formalin test.

Effects of specific dopaminergic agonists and antagonists in the open-field test

It has been found that dopaminergic transmission could be involved in some aspects of anxiety. The present study aims to explore this hypothesis further, using specific DA1 (SKF 38393) and DA2 (bromocriptine) agonists or DA1 (SCH 23390), and DA2 (zetidoline) antagonists in the open-field test. The results confirm previous studies indicating that DA1 and DA2 agonists predominantly increase locomotor activity, while DA1 and DA2 antagonists predominantly decrease it. However, at low doses, the four drugs increase the peripheral ambulation score significantly and, with the exception of zetidoline, also increase the central ambulation score. The observations made with zetidoline confirm the hypothesis that a specific presynaptic DA2 antagonism could be determinant for the disinhibitory effects of low doses of neuroleptics. A collateral action on 5HT transmission is also suggested to explain an hypothetic anxiolytic action of DA agonists and SCH 23390 at lower doses.

Evidence that dopamine in the nucleus accumbens is involved in the ability of rats to switch to cue-directed behaviours

Recently we have reported that injections of d-amphetamine into the nucleus accumbens enhanced the number of switches to cue-directed behaviours without an effect on the number of switches to non-cue-directed behaviours in a swimming test. In the present study we investigated to what extent this effect is mediated via the dopaminergic system in the nucleus accumbens. For that purpose drugs selective for D1- and D2-receptors were studied in this swimming test. It was found that the selective D2-agonist LY 171 555 (50 ng/0.5 microliters) enhanced the number of different cue-directed behaviours. The selective D2-antagonist raclopride (50 ng/0.5 microliters) decreased it. Furthermore an ineffective dose of raclopride attenuated the effect of LY 171 555. Both the selective D1-antagonist SCH 23390 (400 ng/0.5 microliters) and the selective D1-agonist SKF 38393 (50-400 ng/0.5 microliters) decreased the number of different cue-directed behaviours. The effect induced by SCH 23390 could not be blocked by SKF 38393. Similarly the effect induced by SKF could not be attenuated by SCH 23390. These data point to a role for dopamine D2-receptors in the ability to switch to cue-directed behaviours. The present findings do not yet allow the conclusion that D1-receptors are involved.

Neuroanatomical substrates mediating the aversive effects of D-1 dopamine receptor antagonists

An unbiased place preference conditioning procedure was used to examine the secondary reinforcing effects of selective D-1 dopamine (DA) receptor antagonists and the neuroanatomical substrates mediating these effects. Systemic administration of SCH-23390 or the non-benzazepine D-1 receptor antagonist A-69024 produced dose-related conditioned aversions for the drug-associated place. In contrast, the D-2 antagonists spiperone and (-)sulpiride were without effect. SCH-23390-induced place aversions were also observed after intracerebroventricular administration. The minimum dose producing this effect was significantly lower than that after systemic injection. Aversive effects were also observed after microinjection of SCH-23390 into the n. accumbens. In contrast, microinjections of this antagonist into the ventral tegmental area, caudate putamen or medial prefrontal cortex were without effect. These data confirm that the blockade of D-1 but not D-2 DA receptors induces aversive states. Furthermore, they suggest that D-1 receptors in the n. accumbens may play an important role in the regulation of non-drug induced affective states.

SCH 23390: D-1 modulation of oral dyskinesias induced in snakes by Xenopus skin mucus

The granular gland skin secretion of Xenopus laevis induces seven involuntary oral dyskinesias and climbing behavior in the water snake Nerodia sipedon. In a previous study the D-2 receptor antagonist, haloperidol (HAL), selectively potentiated mucus-induced yawning and chewing but attenuated fixed gaping; other oral behaviors were unaffected; HAL alone induced no dyskinesias and failed to modify mucus-induced decreases in tongue flicking, cage climbing and activity. As skin compounds have neuroleptic properties known to induce human and animal dyskinesias, we hypothesized that D-1 receptor antagonism may modulate the four of seven mucus-induced dyskinesias and the climbing not altered by HAL. We found that, like HAL, SCH 23390 (SCH) potentiated mucus-induced yawning, attenuated fixed gaping and had no effect on climbing. Unlike HAL's potentiation of chewing, SCH attenuated chewing and potentiated writhing tongue movements. SCH alone, like skin mucus, attenuated tongue flicking and activity but, given with mucus, SCH increased tongue flicking and activity to control levels. Compared to the HAL study, results suggest that mucus-induced yawning and fixed gaping are similarly modulated by both HAL and SCH, while these drugs have opposite effects on writhing tongue and chewing. SCH given alone or with frog mucus had unique effects on activity and normal tongue flicking.