Effects Of SCH23390 Research Articles

Extinction and reinstatement of methamphetamine-induced conditioned place preference in zebrafish.

Conditioned place preference (CPP) paradigm in zebrafish has been used to measure drug reward, but there is limited research on CPP reinstatement to determine relapse vulnerability. The present study aimed to investigate extinction and reinstatement of methamphetamine (MA)-induced CPP in zebrafish and evaluate the model's predictive validity. Zebrafish received different doses of MA (0-60 mg/kg) during CPP training. The preferred dose of MA at 40 mg/kg was used for extinction via either confined or nonconfined procedures. The extinguished CPP was reinstated by administering a priming dose of MA (20 mg/kg) or various stressors. To assess persistent susceptibility to reinstatement, MA CPP and reinstatement were retested following 14 days of abstinence. In addition, the effects of SCH23390, naltrexone, and clonidine on MA CPP during acquisition, expression, or reinstatement phases were monitored. MA induced CPP in a dose-dependent manner. Both nonconfined and confined extinction procedures time-dependently reduced the time spent on the MA-paired side. A priming dose of MA, chasing stress, or yohimbine reinstated the extinguished CPP. After 14 days of abstinence, the MA CPP remained extinguished and was significantly reinstated by MA priming or chasing stress. Similar to the observations in rodents, SCH23390 suppressed the acquisition of MA CPP, naltrexone reduced the expression and MA priming-induced reinstatement, while clonidine prevented stress-induced reinstatement of MA CPP. This work expanded the zebrafish CPP paradigm to include extinction and reinstatement phases, demonstrating predictive validity and highlighting its potential as a valuable tool for exploring drug relapse.

The dopamine D1 receptor antagonist SCH-23390 blocks the acquisition, but not expression of mitragynine-induced conditioned place preference in rats

Mitragynine (MG) is the primary active constituent of Mitragyna speciosa Korth (kratom), a psychoactive Southeast Asian plant with potential therapeutic use. Numerous studies support roles of dopaminergic system in drug reward. However, the involvement of the dopaminergic system in mediating MG reward and drug-seeking is poorly understood. Using conditioned place preference (CPP) paradigm, the present study aims to evaluate the roles of the dopamine (DA) D1 receptor in the acquisition and expression of MG-induced CPP in rats. The effects of SCH-23390, a selective DA D1 receptor antagonist, on the acquisition of MG-induced CPP were first investigated. Rats were pre-treated systemically with SCH-23390 (0, 0.1 and 0.3 mg/kg, i.p.) prior to MG (10 mg/kg) conditioning sessions. Next, we tested the effects of the DA D1 receptor antagonist on the expression of MG-induced CPP. Furthermore, the effects of a MG-priming dose (5 mg/kg) on the reinstatement of extinguished CPP were tested. The results showed that SCH-23390 dose-dependently suppressed the acquisition of a MG-induced CPP. In contrast, SCH-23390 had no effect on the expression of a MG-induced CPP. The findings of this study suggested a crucial role of the DA D1 receptor in the acquisition, but not the expression of the rewarding effects of MG in a CPP test. Furthermore, blockade of the D1-like receptor during conditioning did not prevent MG priming effects on CPP reinstatement test, suggesting no role for the DA D1 receptor in reinstatement sensitivity.

Sex differences and the role of dopamine receptors in the reward-enhancing effects of nicotine and bupropion.

Nicotine and bupropion have been demonstrated to enhance the value of other reinforcers, and this may partially account for nicotine reward and dependence. Evidence suggests that the sexes differ in their sensitivity to the primary and secondary reinforcing effects of nicotine and nicotine-associated stimuli. Whether the sexes also differ in sensitivity to the reward-enhancing effects of nicotine (and bupropion) is yet unclear. The present study evaluated potential sex differences in the enhancement effects of nicotine and bupropion using a reinforcer demand approach. Furthermore, we sought to investigate the role that D1- and D2-type dopamine receptors play in the reward-enhancing effects of nicotine and bupropion. Demand for sensory reinforcement was assessed in male and female rats responding on a progression of fixed ratio schedules. The effects of nicotine and 10 or 20mg/kg bupropion on reinforcer demand were assessed within subjects. Subsequently, the effects of SCH-23390 and eticlopride were assessed on the enhancing effects of nicotine and bupropion on progressive ratio responding. Nicotine and bupropion enhanced demand metrics of reinforcement value in both sexes. Females were more sensitive to the enhancement effects of bupropion assessed by reinforcer demand and progressive ratio performance. D2-like dopamine receptor antagonism by eticlopride attenuated the enhancement effects of bupropion, but not of nicotine. Nicotine and bupropion both enhance reinforcement value in both sexes, though females may be more sensitive to the reward-enhancing effects of bupropion. D2- and possibly D1-type receptors appear to be involved in the reward-enhancing effects of bupropion, but not necessarily nicotine.

Effects of SCH-23390 and sulpiride on active avoidance in ovariectomized rats treated with a low dose of 17β-estradiol.

We studied the effects of dopamine D1/D2 receptor antagonists on the dynamics of acquisition and extinction of active avoidance responses and open field behavior in ovariectomized female rats. Dopamine D1 receptor antagonist SCH-23390 (0.1 mg/kg intraperitoneally) and dopamine D2 receptor antagonist sulpiride (10.0 mg/kg intraperitoneally) were administered chronically (14 days) either alone or in combination with a low dose of 17β-estradiol (0.5 μg per rat subcutaneously) to females after ovariectomy. It was found that SCH-23390 in combination with a low dose of 17β-estradiol completely restored impaired conditioning and retention of a conditioned avoidance response in ovariectomized animals. Simultaneous correction of behavioral patterns in the open field test was also observed in ovariectomized females receiving SCH-23390. Sulpiride injected alone or in combination with low dose of 17β-estradiol did not correct conditioning and reproduction of active avoidance response in females with estrogen deficiency and did not significantly affect animal behavior. The results indicate positive effect of dopamine D1 receptor blockade on active learning under conditions of estrogen deficiency.

Effects of SCH-23390 in Combination with a Low Dose of 17β-Estradiol on Anxiety-Like Behavior in Ovariectomized Rats

The aim of this study was to explore effects on anxiety-like behavior of D1 dopamine receptor agonist, SKF-38393, and of D1 dopamine receptor antagonist, SCH-23390, given alone or in combination with a low dose of 17β-estradiol (17β-E2) to ovariectomized (OVX) rats. Two weeks after surgery, OVX rats began 14 days of treatment with the vehicle, a low dose of 17β-E2 (5.0 μg/rat, s.c.), SKF-38393 (0.1 mg/kg, i.p.), SCH-23390 (0.1 mg/kg, i.p.), SKF-38393 plus 17β-E2, or SCH-23390 plus 17β-E2. The animals were tested in the black and white model (BWM) and the open field test (OFT). SCH-23390 (0.1 mg/kg, i.p.) alone or in a combination with a low dose of 17β-E2 (5.0 μg/rat, s.c.) resulted in anxiolytic-like effect in OVX rats in the BWM. Repeated treatment with SCH-23390 and 17β-E2 profoundly increased anxiolytic-like effect of single substances exerted per se. Coadministration of SCH-23390 with 17β-E2 increased frequency of rearing and grooming in OVX rats in OFT. SKF-38393 (0.1 mg/kg, i.p.) treatment failed to alter anxiety-like behavior in OVX rats in the BWM. The results of the present study suggest that 17β-E2 and SCH-23390 interact to exert anxiolytic-like action and that each of these drugs can potentiate effects of each other.

Contribution of a Mesocorticolimbic Subcircuit to Drug Context-Induced Reinstatement of Cocaine-Seeking Behavior in Rats

Cocaine-seeking behavior triggered by drug-paired environmental context exposure is dependent on orbitofrontal cortex (OFC)-basolateral amygdala (BLA) interactions. Here, we present evidence supporting the hypothesis that dopaminergic input from the ventral tegmental area (VTA) to the OFC critically regulates these interactions. In experiment 1, we employed site-specific pharmacological manipulations to show that dopamine D1-like receptor stimulation in the OFC is required for drug context-induced reinstatement of cocaine-seeking behavior following extinction training in an alternate context. Intra-OFC pretreatment with the dopamine D1-like receptor antagonist, SCH23390, dose-dependently attenuated cocaine-seeking behavior in an anatomically selective manner, without altering motor performance. Furthermore, the effects of SCH23390 could be surmounted by co-administration of a sub-threshold dose of the D1-like receptor agonist, SKF81297. In experiment 2, we examined effects of D1-like receptor antagonism in the OFC on OFC-BLA interactions using a functional disconnection manipulation. Unilateral SCH23390 administration into the OFC plus GABA agonist-induced neural inactivation of the contralateral or ipsilateral BLA disrupted drug context-induced cocaine-seeking behavior relative to vehicle, while independent unilateral manipulations of these brain regions were without effect. Finally, in experiment 3, we used fluorescent retrograde tracers to demonstrate that the VTA, but not the substantia nigra, sends dense intra- and interhemispheric projections to the OFC, which in turn has reciprocal bi-hemispheric connections with the BLA. These findings support that dopaminergic input from the VTA, via dopamine D1-like receptor stimulation in the OFC, is required for OFC-BLA functional interactions. Thus, a VTA-OFC-BLA neural circuit promotes drug context-induced motivated behavior.

Lack or inhibition of dopaminergic stimulation induces a development increase of striatal tyrosine hydroxylase-positive interneurons.

We examined the role of endogenous dopamine (DA) in regulating the number of intrinsic tyrosine hydroxylase-positive (TH+) striatal neurons using mice at postnatal day (PND) 4 to 8, a period that corresponds to the developmental peak in the number of these neurons. We adopted the strategy of depleting endogenous DA by a 2-day treatment with α-methyl-p-tyrosine (αMpT, 150 mg/kg, i.p.). This treatment markedly increased the number of striatal TH+ neurons, assessed by stereological counting, and the increase was highly correlated to the extent of DA loss. Interestingly, TH+ neurons were found closer to the clusters of DA fibers after DA depletion, indicating that the concentration gradient of extracellular DA critically regulates the distribution of striatal TH+ neurons. A single i.p. injection of the D1 receptor antagonist, SCH23390 (0.1 mg/kg), the D2/D3 receptor antagonist, raclopride (0.1 mg/kg), or the D4 receptor antagonist, L-745,870 (5 mg/kg) in mice at PND4 also increased the number of TH+ neurons after 4 days. Treatment with the D1-like receptor agonist SKF38393 (10 mg/kg) or with the D2-like receptor agonist, quinpirole (1 mg/kg) did not change the number of TH+ neurons. At least the effects of SCH23390 were prevented by a combined treatment with SKF38393. Immunohistochemical analysis indicated that striatal TH+ neurons expressed D2 and D4 receptors, but not D1 receptors. Moreover, treatment with the α4β2 receptor antagonist dihydro-β-erythroidine (DHβE) (3.2 mg/kg) also increased the number of TH+ neurons. The evidence that DHβE mimicked the action of SCH23390 in increasing the number of TH+ neurons supports the hypothesis that activation of D1 receptors controls the number of striatal TH+ neurons by enhancing the release of acetylcholine. These data demonstrate for the first time that endogenous DA negatively regulates the number of striatal TH+ neurons by direct and indirect mechanisms mediated by multiple DA receptor subtypes.

Antidepressant-like effect of SCH-23390 in combination with low dose of estrogen in rat forced swimming test

Antidepressant-like effect of SCH-23390 in combination with low dose of estrogen in rat forced swimming test

Sodium-Hydrogen Exchanger Regulatory Factor 1 (NHERF-1) Transduces Signals That Mediate Dopamine Inhibition of Sodium-Phosphate Co-transport in Mouse Kidney

Dopamine inhibited phosphate transport in isolated renal brush border membrane vesicles and in cultured renal proximal tubule cells from wild-type but not from NHERF-1 null mice. Co-immunoprecipitation experiments established that NHERF-1 associated with D1-like receptors. In wild-type mice, dopamine stimulated cAMP accumulation and protein kinase C (PKC) activity in renal proximal tubule cells, an effect that was abolished by SCH-23390, a D1-like receptor antagonist. In NHERF-1 null kidney tissue; however, dopamine failed to stimulate either cAMP accumulation or PKC activity. Infection of proximal tubule cells from NHERF-1 null mice with adenovirus-green fluorescent protein-NHERF-1 restored the ability of dopamine to stimulate cAMP and PKC. Finally, in (32)P-labeled wild-type proximal tubule cells and in opossum kidney cells, dopamine increased NHERF-1 phosphorylation at serine 77 of the PDZ I domain of NHERF-1, a site previously shown to attenuate binding of cellular targets including the Npt2a (sodium-dependent phosphate transporter 2a). Together, these studies establish that NHERF-1 plays a key role in dopamine signaling and is also a downstream target of D1-like receptors in the mouse kidney. These studies suggest a novel role for the PDZ adapter protein NHERF-1 in coordinating dopamine signals that inhibit renal phosphate transport.

Effects of SCH23390 and spiperone administered into medial striatum and intermediate medial mesopallium on rewarding effects of morphine in day-old chicks

In the avian forebrain, the medial striatum and the intermediate medial mesopallium are thought to be important structures for associative learning in chicks, where the role of dopaminergic systems in learning processes has been verified in various behavioral paradigms, such as one-trial passive avoidance learning. However, it is not yet clear whether the dopaminergic system of these regions is responsible for associative learning underlying cue-elicited drug reward. In this study, a 6-day conditioning schedule in day-old chicks with i.p. morphine (2 mg/kg) was used to compare the effects of intracerebrally injected dopamine D 1 receptor antagonist, SCH23390, and D 2 antagonist, spiperone. The antagonists were injected bilaterally (3 µg/site) into either the medial striatum or the intermediate medial mesopallium, and tests were conducted on morphine-induced conditioned place preference or locomotor activity. The acquisition of place preference was significantly inhibited by SCH23390 in either the medial striatum or the intermediate medial mesopallium, but not by spiperone. However, in the medial striatum, but not in the intermediate medial mesopallium, the locomotor activity was blocked by both SCH23390 and spiperone. These data suggest that the medial striatum and the intermediate medial mesopallium in birds are differentially involved in the rewarding effects of morphine, and similarly to mammals, the dopamine D 1 system may play an important role in the development of opiate reward.

Basolateral amygdala D 1- and D 2-dopaminergic system promotes the formation of long-term potentiation in the dentate gyrus of anesthetized rats

We have previously found that the induction of hippocampal long-term potentiation (LTP) is modulated by neuron activities in the basolateral amygdala (BLA). However, little is known about what neurotransmitter system in the BLA contributes to modulation of hippocampal LTP. In the present study, we investigated possible involvement of BLA dopaminergic system in the induction of LTP at the perforant path (PP)–dentate gyrus (DG) granule cell synapses of anesthetized rats. The induction of PP–DG LTP was significantly attenuated by intra-BLA injection of the D 1 receptor antagonist SCH23390 (2 or 6 nmol) or the D 2 receptor antagonists, chlorpromazine (30 or 100 nmol) or haloperidol (4.4 or 13.3 nmol). The effects of SCH23390 and haloperidol were abolished by concomitant intra-BLA injection of the D 1 receptor agonist SKF38393 (17 nmol) and the D 2 receptor agonist quinpirole (3 nmol), respectively. Furthermore, lesioning with 6-hydroxydopamine of the ventral tegmental area, the origin of the dopaminergic system projecting to the BLA, resulted in attenuated PP–DG LTP, which was restored by intra-BLA injection of SKF38393 or quipirole. These results suggest that the induction of PP–DG LTP is promoted by the BLA dopaminergic system via both D 1 and D 2 receptors.

N-benzylpiperazine has characteristics of a drug of abuse

The ability of benzylpiperazine (BZP) to substitute for cocaine and to initiate self-administration in drug-naive subjects was assessed to determine whether BZP has abuse liability. Further, the effects of a pretreatment with dopamine D1-like receptor antagonist (SCH23390) were examined to elucidate the mechanisms associated with BZP reward. First, the ability for BZP (0.125, 0.25 and 0.5 mg/kg/infusion) to substitute for cocaine self-administration was assessed, and the acquisition of BZP (0.5 mg/kg/infusion) self-administration by drug-naive and untrained rats was determined during a 15-day period. Subsequently, dose-effect curves for cocaine (0.06, 0.125, 0.25 or 0.5 mg/kg/infusion) and BZP self-administration (0.125, 0.25, 0.5 or 1.0 mg/kg/infusion) and the effect of SCH23390 (0.00 or 0.02 mg/kg) on BZP and cocaine self-administration were examined. BZP substituted for cocaine, and drug-naive rats rapidly acquired BZP self-administration. BZP self-administration was maintained by a more restricted range of doses than was cocaine self-administration, and responding maintained by BZP was sensitive to dopamine antagonism. The present findings indicate that BZP self-administration, like cocaine self-administration, is readily acquired and mediated by dopaminergic mechanisms.

Drugs of Abuse Specifically Sensitize Noradrenergic and Serotonergic Neurons Via a Non-Dopaminergic Mechanism

A challenge in drug dependence is to delineate long-term neurochemical modifications induced by drugs of abuse. Repeated d-amphetamine was recently shown to disrupt a mutual regulatory link between noradrenergic and serotonergic neurons, thus inducing long-term increased responses to d-amphetamine and para-chloroamphetamine, respectively. We show here that such a sensitization of noradrenergic and serotonergic neurons also occurs following repeated treatment with cocaine, morphine, or alcohol, three compounds belonging to main groups of addictive substances. In all cases, this sensitization is prevented by alpha 1b-adrenergic and 5-HT2A receptors blockade, indicating the critical role of these receptors on long-term effects of drugs of abuse. However, repeated treatments with two non-addictive antidepressants, venlafaxine, and clorimipramine, which nevertheless inhibit noradrenergic and serotonergic reuptake, do not induce noradrenergic and serotonergic neurons sensitization. Similarly, this sensitization does not occur following repeated treatments with a specific inhibitor of dopamine (DA) reuptake, GBR12783. Moreover, we show that the effects of SCH23390, a D1 receptor antagonist known to inhibit development of d-amphetamine behavioral sensitization, are due to its 5-HT2C receptor agonist property. SCH23390 blocks amphetamine-induced release of norepinephrine and RS102221, a 5-HT2C antagonist, can reverse this inhibition as well as inhibition of noradrenergic sensitization and development of behavioral sensitization induced by repeated d-amphetamine. We propose that noradrenergic/serotonergic uncoupling is a common neurochemical consequence of repeated consumption of drugs of abuse, unrelated with DA release. Our data also suggest that compounds able to restore the link between noradrenergic and serotonergic modulatory systems could represent important therapeutic targets for investigation.

AMPA receptor antagonists reverse effects of extended habit training on signaled food approach responding in rats

Dopamine D1 receptor stimulation is critically involved in early appetitive phases of learning in various behavioral paradigms. However, extended habit training was previously shown to reduce the ability of dopamine D1 receptor antagonists such as R(+)-7-chloro-8-hydroxy-3-methyl-1-phenyl-2,3,4,5-tetrahydro-1H-3-benzazepine hydrochloride (SCH-23390) to disrupt behavioral performance. The present study aimed to evaluate whether coadministration of glutamate alpha-amino-3-hydroxy-5-methyl-isoxazole-4-propionic acid (AMPA) receptor antagonists restores sensitivity to acute blockade of D1 receptors. Adult male Wistar rats were presented with 45-mg food pellets delivered to the food tray, which was immediately preceded by a 400-ms tone (2.8 kHz, 78 dB). During each training and test session, there were 28 food-tone presentations with an average intertrial interval of 70 s, and each head entry into the food tray was recorded. Drug tests were conducted on either day 3 or 9 of the training using independent groups of animals. The main dependent variable was the number of trials during which no head-entry response was made during the 10-s period immediately after the food delivery. Longer training duration enhanced the resistance of the signaled food approach behavior to extinction and to disrupting effects of supplementary food ration. Similarly, acute administration of SCH-23390 (0.04-0.16 mg/kg) dose-dependently reduced the number of omitted trials when given before the test session on day 3 but much less so when injected on day 9. AMPA receptor antagonists, NBQX (10 mg/kg) or GYKI-52466 (3-10 mg/kg), had no effects on their own but significantly enhanced the disrupting effects of SCH-23390 (0.08 and 0.16 mg/kg) when given on day 9 but not on day 3 of the training. These results indicate that AMPA receptor blockade restores sensitivity to appetitive behavior-disrupting effects of SCH-23390 in subjects exposed to extended training protocol.

Acute amphetamine down‐regulates RGS4 mRNA and protein expression in rat forebrain: distinct roles of D1 and D2 dopamine receptors

Administration of psychostimulants modulates mRNA of several regulators of guanine nucleotide-binding protein signaling (RGSs) proteins in the brain. In the present study, the regulation of amphetamine-induced decrease of RGS4 expression in the rat forebrain was evaluated. RGS4 mRNA was reduced by amphetamine in an inverse, dose-dependent manner. The lowest dose (2.5 mg/kg) decreased RGS4 mRNA in caudate putamen for up to 6 h after injection whereas the decrease in several frontal cortical areas was detected at 3 h only. Analysis of RGS4 immunoreactivity by western blotting revealed a decrease 3 h after amphetamine solely in the caudate putamen. Systemic administration of D(1) (SCH23390) or D(2) (eticlopride) receptor antagonists blocked amphetamine-induced locomotion but amphetamine augmented both the SCH23390-induced increase and the eticlopride-induced decrease in RGS4 mRNA in the caudate putamen. Further, the down-regulation of RGS4 immunoreactivity by eticlopride was robust whereas the effect of SCH23390 was blunted as compared with its effect on mRNA. These data suggest that, by decreasing RGS4 expression in the caudate putamen via D(1) receptors, acute amphetamine could disinhibit RGS4-sensitive guanine nucleotide-binding protein alpha-subunit i- and/or q-coupled signaling pathways and favor mechanisms that counterbalance D(1) receptor stimulation.

Characterization of the distribution of the cocaine priming threshold and the effect of SCH23390

The cocaine-induced reinstatement (priming) of cocaine self-administration occurs when the cumulative concentration of cocaine reaches a threshold level that we have previously termed the cocaine priming threshold. The present studies used a modified procedure to measure the cocaine priming threshold over 4–8-month periods in individual rats. The values for the priming threshold varied between days but there was no evidence of a systematic change in the priming threshold over time, indicating that neither tolerance nor sensitization occurred. The frequency distribution of the priming threshold was significantly different from a normal distribution but was not significantly different from a log-normal distribution. Therefore, the geometric mean with its associated variance estimates, but not the arithmetic mean, appropriately describe the distribution of the cocaine priming threshold. The estimate of the geometric mean value of the priming threshold for this group of Sprague–Dawley rats was 284 (CI 95: 234–344) μg/kg of cocaine. The log-normal distribution of equieffective doses of cocaine is typical of agonist-induced pharmacological responses. In the presence of the D 1 dopamine receptor-selective antagonist SCH23390, the geometric means of the cocaine priming threshold were significantly increased in a dose-dependent manner, implying a role for D 1 dopamine receptors in the priming response. This technique provides a quantitative method for the measurement of antagonist-induced increases in the cocaine priming threshold.

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

D(1) dopamine receptor antagonists and agonists attenuate cocaine reinstatement of cocaine-seeking behavior (i.e., responding in the absence of cocaine reinforcement). 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. 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. 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. 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.

Stoichiometry of Tyrosine Hydroxylase Phosphorylation in the Nigrostriatal and Mesolimbic Systems In Vivo

Electrical stimulation of the medial forebrain bundle increases (32)P incorporation into striatal tyrosine hydroxylase (TH) at Ser (19), Ser(31), and Ser(40). In the present studies, the effects of acute haloperidol and related drugs on sitespecific TH phosphorylation stoichiometry (PS) in the nigrostriatal and mesolimbic systems were determined by quantitative blot immunolabeling using phosphorylation statespecific antibodies. The striatum (Str), substantia nigra (SN), nucleus accumbens (NAc), and ventral tegmental area (VTA) from Sprague-Dawley rats were harvested 30-40 min after a single injection of either vehicle, haloperidol (2 mg/kg), raclopride (2 mg/kg), clozapine (30 mg/kg), or SCH23390 (0.5 mg/kg). In vehicle-injected control rats, Ser(19) PS was 1.5- to 2. 5-fold lower in Str and NAc than in SN and VTA, Ser(31) PS was two-to fourfold higher in Str and NAc than in SN and VTA, and Ser(40) PS was similar between the terminal field and cell body regions. After haloperidol, Ser(40) PS increased twofold in Str and NAc, whereas a smaller increase in SN and VTA was observed. The effects of haloperidol on Ser(19) PS were similar to those on Ser(40) in each region; however, haloperidol treatment increased Ser(31) PS at least 1.6-fold in all regions. The effects of raclopride on TH PS were comparable to those of haloperidol, whereas clozapine treatment increased TH PS at all sites in all regions. By contrast, the effects of SCH23390 on TH PS were relatively small and restricted to the NAc. The stoichiometries of site-specific TH phosphorylation in vivo are presented for the first time. The nigrostriatal and mesolimbic systems have common features of TH PS, distinguished by differences in TH PS between the terminal field and cell body regions and by dissimilar increases in TH PS in the terminal field and cell body regions after acute haloperidol.

Effects of SCH-23390 and Raclopride on Cocaine Discrimination in Male and Female Wistar Rats

Male and female rats were trained to discriminate 10.0 mg/kg cocaine from saline in a two-lever discrimination task. Injection-appropriate responding was reinforced by food pellet presentation on a tandem random-interval 30-s fixed-ratio 10 schedule. Generalization testing was conducted in extinction 10 min following an injection of saline, 1.0, 3.0, 5.6, or 10.0 mg/kg cocaine. No differences in the generalization gradients and ED 50s were observed between male and female rats. Following the determination of the cocaine generalization gradient, the dopamine D 1 antagonist SCH-23390 (0.01–0.10 mg/kg) and the dopamine D 2 antagonist raclopride (0.1–1.6 mg/kg) were administered (independently) prior to the injection of the training dose of cocaine (10.0 mg/kg). Cocaine-antagonism tests were conducted in extinction. It was found, for each dopamine antagonist, that as the dose increased, the percentage of cocaine-appropriate responding decreased. No sex differences were observed between these generalization gradients.

Effects of SCH23390 and Raclopride on Anxiety-Like Behavior in Rats Tested in the Black-White Box

TIMOTHY C., B. COSTALL AND J. W. SMYTHE. Effects of SCH23390 and raclopride on anxiety-like behavior in rats tested in the black-white box. PHARMACOL BIOCHEM BEHAV 62(2) 323–327, 1999.—Dopamine (DA) systems are activated by stress, and this response has as a corollary the induction of stress-related behaviors such as anxiety. In mice, D 2 receptor blockade produces an apparent anxiogenic effect, although locomotor impairments might have been present. We investigated the effects of D 1 and D 2 antagonists on a variety of anxiety-like behaviors induced by the black-white box in rats and carefully screened for any locomotor deficits. Adult male Lister hooded rats were injected with either the D 1 antagonist SCH23390 (0, 0.1, or 0.25 mg/kg IP) or the D 2 antagonist raclopride (0, 0.05, or 0.10 mg/kg IP) 20 min prior to being placed into the white chamber of the black-white box ( n = 8–10/group). Rats were videotaped and the tapes were scored for latency to exit the white chamber, latency to reenter the white chamber, time spent in the white chamber, intercompartmental crossing, and locomotor activity. ANOVA revealed no effect of the D 1 antagonist SCH23390 on any behavioral measure. However, the raclopride-treated rats left the white area sooner than control rats ( p < 0.01). Raclopride-treated rats also exhibited delayed reentry times to the white chamber compared to control rats ( p < 0.01) and spent significantly less time in the white chamber ( p < 0.05). Neither SCH23390 nor raclopride affected locomotor activity in a manner that confounded these behaviors. These results confirm that D 2 receptor blockade enhances anxiety in rats tested in the black-white box.