Potentiation of the behavioral and convulsant effects of cocaine by chronic administration in the rat

The effect of chronic administration on the behavioral response to cocaine was studied in male Sprague-Dawley rats. In experiment 1 five groups of rats received daily intraperitoneal injections of either saline, 20 mg/kg, or 40 mg/kg cocaine hydrochloride for 10 days, or of higher doses of cocaine until either one or three convulsions occured. Following this initial treatment, all animals were left untreated for seven days, and then sensitivity to cocaine was assessed in all animals by a test injection series (daily injections of increasing doses of cocaine). Animals which had received 40 mg/kg cocaine during the initial treatment exhibited a greater behavioral response (stereotyped behavior) to cocaine during the test injection series than did animals treated with saline; both the 40 mg/kg and one — convulsion treatments during the initial stage of the experiment resulted in greater sensitivity to the convulsant effect of cocaine during the test injection series. In experiment 2 animals were injected intraperitoneally with either saline or 40 mg/kg cocaine for 10 days and then tested with a series of daily cocaine injections of increasing dosage after remaining untreated for 4, 8, 16 or 32 days. The results indicated that the initial treatment with 40 mg/kg cocaine augmented both the behavioral and convulsant effects of cocaine during the subsequent test injection series. The sensitization to the convulsant effect of cocaine was significant at all intervals after initial treatment except 16 days, while the duration of sensitization to the behavioral effects of cocaine could not be determined due to apparent age-related changes in the response of control animals to cocaine. The sensitization which was observed was attributed to the effects of cocaine per se rather than to convulsions produced by the drug.     

8-OH DPAT can restore the locomotor stimulant effects of cocaine blocked by haloperidol

In the first experiment, separate groups of rats (n = 7) were treated with either saline, cocaine (10 mg/kg), haloperidol (0.1 mg/kg), or cocaine (10 mg/kg) plus haloperidol (0.1 mg/kg). Locomotor behavior was measured in an open-field environment, and cocaine induced a reliable locomotor stimulant effect compared to saline-treated animals. Haloperidol produced a progressive decline in locomotion over the 5 test days. Haloperidol also blocked cocaine stimulant effects compared to cocaine-treated animals. In the second experiment, five groups (n = 7) of animals were treated either with saline, cocaine (10 mg/kg), 8-OH DPAT (0.2 mg/kg), 8-OH DPAT (0.2 mg/kg) plus haloperidol (0.1 mg/kg), or 8-OH DPAT (0.2 mg/kg) plus haloperidol 0.1 mg/kg plus cocaine (10 mg/kg). Over the course of 5 days of treatment, cocaine induced a locomotor stimulant effect. Saline and 8-OH DPAT animals did not differ in terms of locomotion. The 0.1 mg/kg haloperidol plus 0.2 mg/kg 8-OH DPAT treatment decreased locomotion compared to the saline group, but the group given 0.2 mg/kg 8-OH DPAT plus 0.1 mg/kg haloperidol plus cocaine (10 mg/kg) exhibited a locomotor stimulant effect equivalent to the cocaine group. In a third experiment, it was found that the 0.2 mg/kg 8-OH DPAT treatment did not enhance the locomotor stimulant effect of cocaine. Thus, the 8-OH DPAT treatment was able to restore a cocaine locomotor stimulant effect in animals treated with haloperidol without directly enhancing the locomotor stimulant effects of cocaine. In Experiments 2 and 3, entries into the central zone of the open field were measured. Cocaine reliably increased central zone entries. The 8-OH DPAT treatment, however, selectively blocked this behavioral effect of cocaine suggesting a qualitative influence of 5-HT(1A) receptors upon cocaine, independent of locomotion activation by cocaine. Ex vivo measurements of dopamine and 5-hydroxytryptamine metabolism in limbic tissue were consistent with the established effects of cocaine, haloperidol, and 8-OH DPAT upon dopamine and 5-hydroxytryptamine neurotransmission. In addition, measurement of cocaine brain concentration indicated that neither haloperidol or 8-OH DPAT affected cocaine concentration in brain.     

Attenuation of the rate-altering effects of cocaine by magnesium chloride in squirrel monkeys

Three adult male squirrel monkeys that were trained to respond on a 3-min fixed-interval schedule of food reinforcement were injected with various doses of magnesium chloride (MgCl(2), 30 and 100mg/kg), cocaine (0.03-3.0mg/kg), and their combination. The purpose of the study was to determine if MgCl(2) could alter the rate of responding and if it could alter the rate-increasing and rate-decreasing effects of cocaine. MgCl(2) had little effect on responding during the 2h sessions. Low doses of cocaine (0.03-0.1mg/kg) were ineffective, intermediate doses (0.1-1.0mg/kg) increased responding, and high doses (1.0-3.0mg/kg) decreased responding. When MgCl(2) was combined with intermediate doses of cocaine, the rate-increasing effects of cocaine were attenuated. Less reliably, increased rates of responding were sometimes observed when MgCl(2) was combined with low (ineffective) or high (rate-decreasing) doses of cocaine. These interactions depended both on the time following injection and the dose of MgCl(2) and showed marked individual differences. These effects observed in monkeys are similar to some of the interactions previously reported in rodents.     

Psychomotor stimulant effects of cocaine in rats and 15 mouse strains

Relative to intravenous drug self-administration, locomotor activity is easier to measure with high throughput, particularly in mice. Therefore its potential to predict differences in self-administration between genotypes (e.g., targeted mutations, recombinant inbred strains) is appealing, but such predictive value is unverified. The main goal of this study was to evaluate the utility of the locomotor assay for accurately predicting differences in cocaine self-administration. A second goal was to evaluate any correlation between activity in a novel environment, and cocaine-induced hyperactivity, between strains. We evaluated locomotor activity in male and female Sprague-Dawley rats and 15 mouse strains (129S1/SvImJ, 129S6/SvEvTac, 129X1/SvJ, A/J, BALB/cByJ, BALB/cJ, C3H/HeJ, C57BL/6J, CAST/EiJ, DBA/2J, FVB/NJ, SJL/J, SPRET/EiJ, and outbred Swiss Webster and CD-1/ICR), as well as cocaine self-administration in BALB substrains. All but BALB/cJ mice showed locomotor habituation and significant cocaine-induced hyperactivity. BALB/cJ mice also failed to self-administer cocaine. BALB/cByJ mice showed modest locomotor habituation, cocaine-induced locomotion, and cocaine self-administration. As previously reported, female rats showed greater cocaine-induced locomotion than males, but this was only observed in one of 15 mouse strains (FVB/NJ), and the reverse was observed in two strains (129X1/SvJ, BALB/cByJ). The intriguing phenotype of the BALB/cJ strain may indicate some correlation between all-or-none locomotion in a novel environment, and stimulant and reinforcing effects of cocaine. However, neither novelty- nor cocaine-induced activity offered a clear prediction of relative reinforcing effects among strains. Additionally, these results should aid in selecting mouse strains for future studies in which relative locomotor responsiveness to psychostimulants is a necessary consideration.     

Tyrosine depletion attenuates the behavioural stimulant effects of amphetamine and cocaine in rats

The effects of intracerebroventricular administration of endomorphin-1 and endomorphin-2, endogenous mu-opioid receptor agonists, on passive avoidance learning associated with long-term memory were investigated in mice. Endomorphin-1 (10 and 17.5 microg) and endomorphin-2 (17.5 microg) produced a significant decrease in step-down latency in a passive avoidance learning task. beta-Funaltrexamine (5 microg) almost completely reversed the endomorphin-1 (17.5 microg)- and endomorphin-2 (17.5 microg)-induced shortening of step-down latency, although neither naltrindole (4 ng) nor nor-binaltorphimine (4 microg) produced any significant effects on the effects of endomorphins 1 and 2. These results suggest that endomorphins 1 and 2 impair long-term memory through the mediation of mu-opioid receptors in the brain.     

Effects of ifenprodil on stimulatory, discriminative stimulus, and convulsant effects of cocaine

Ifenprodil, like cocaine, binds to the dopamine transporter and blocks uptake of dopamine. In this study, the ability of ifenprodil to mimic, enhance or block behavioral and toxic effects of cocaine was evaluated. Fixed-interval responding maintained by food presentation in rats was increased by cocaine but decreased by ifenprodil. Low rates of responding during timeout periods were also increased by cocaine but not ifenprodil. Ifenprodil neither increased locomotor activity nor augmented the stimulatory effect of cocaine; however, ifenprodil attenuated the stimulant effects of cocaine at doses 0.5 log unit lower than those required to reduce spontaneous activity when given alone. Ifenprodil neither substituted for nor augmented the discriminative stimulus effects of cocaine in rats discriminating 10mg/kg cocaine from saline. In contrast to cocaine, ifenprodil did not produce convulsions or signs of proconvulsant activity, and ifenprodil reduced the percentage of mice convulsing in the presence of cocaine. These results suggest that pharmacological actions in addition to blockade of dopamine uptake or novel interactions with the dopamine transporter may contribute to the non-stimulant behavioral profile and cocaine-blocking actions of ifenprodil.     

Attenuation of the effects of cocaine on milk consumption in rats by dopamine antagonists.

Recent research suggest the both D1 and D2 dopamine (DA) receptors play an important role in the behavioral effects of psychomotor stimulants. The present study utilized selective DA antagonists to examine the role of DA receptors in the effects of cocaine on milk intake in rats. Male Sprague-Dawley rats were given access to a milk solution (2:1 tap water:Bordens sweetened condensed milk) for 15 min each day. When milk intake was stable, dose-response functions were determined for cocaine (4.0-32 mg/kg, IP, 10 min presession) administered alone or in combination with the D1 antagonist SCH 23390 (0.12-0.5 mg/kg, IP, 30 min presession) or the D2 antagonist raclopride (0.25-1.0 mg/kg, IP, 30 min presession). As a control for the serotonin (5-HT2) antagonist effects of SCH 23390, the 5-HT2 antagonist ketanserin (4.0-16 mg/kg) was evaluated as well. To control for nonspecific drug effects on fluid consumption, the effects of cocaine alone on water intake were determined in a separate group of rats. All drugs decreased milk intake when given alone. Both SCH 23390 and raclopride attenuated the effects of at least one dose of cocaine. Ketanserin did not alter the effects of cocaine. These results suggest that stimulation of both D1 and D2, but not 5-HT2, receptors is involved in the effects of cocaine on milk intake in rats.     

Escalation of food-maintained responding and sensitivity to the locomotor stimulant effects of cocaine in mice

Escalation of drug self-administration is a consequence of extended drug access and is thought to be specifically related to addiction, but few studies have investigated whether intake of non-drug reinforcers may also escalate with extended-access. The goal of these studies was to determine the effects of limited and extended-access to food reinforcers on behavioral and pharmacological endpoints in mice. In distinct groups, responding on a lever was maintained by liquid reinforcement, or nose-poke responses were maintained by sucrose pellets or liquid food in sessions lasting 1 h (limited-access) or 10 h (extended-access). The reinforcing strength of each food, as well as reinforcer-associated cues, was tested before and after extended-access using a progressive ratio (PR) schedule, and locomotor activity in response to novelty and increasing doses of cocaine was assessed in an open field setting in all animals after access to food reinforcers. Escalation of lever-pressing behavior reinforced by liquid food, but not nose-poke behavior reinforced by liquid food or sucrose pellets, was observed across successive extended-access sessions. A concomitant increase in the reinforcing strength of liquid food and its associated cues was apparent in mice that escalated their responding, but not in mice that did not escalate. Finally, extended reinforcer access leading to behavioral escalation was accompanied by an increased sensitivity to the psychostimulant effects of cocaine compared to limited-access. These findings indicate that behavioral escalation can develop as a consequence of extended-access to a non-drug reinforcer, although both the nature of the reinforcer (liquid versus solid food) and the topography of the operant response (lever versus nose-poke) modulate its development. These data also suggest that some of the behavioral and pharmacological corrolaries of behavioral escalation observed following extended-access to drug self-administration may not be due to drug exposure, but rather, may result from basic behavioral processes which underlie operant responding maintained by appetitive stimuli.     

Chromosomal mapping of the psychomotor stimulant effects of cocaine in BXD recombinant inbred mice

To elucidate genes associated with cocaine's locomotor stimulant effects, we used recombinant inbred-quantitative trait loci (RI-QTL) analyses to identify chromosomal loci associated with locomotor activity before (baseline) and after cocaine treatment. RI-QTL analyses seek to identify associations between a quantitative measure of a phenotype and one or more previously mapped marker loci across a panel of RI strains. In the present study, 11 BXD RI strains were used to identify several putative QTLs for each phenotype. Both baseline locomotor activity and cocaine's locomotor stimulant effects are polygenic, with both unique and overlapping genetic influences. The largest associations for baseline activity were observed on chromosomes 5 and 9 and the largest associations for cocaine's psychomotor stimulant effects on chromosomes 3 and 17.     

Abuse liability and stimulant properties of dextromethorphan and diphenhydramine combinations in rats

Rationale The abuse of over-the-counter (OTC) medications has been widely reported. However, there are few preclinical studies examining the behavioral effects of OTC medications at higher, abused doses.Objectives The objectives of the current study were to determine whether the anti-histamine diphenhydramine (DIP) and the antitussive dextromethorphan (DEX), either alone or in combination, would have stimulant properties and be self-administered in animals.Methods For drug self-administration, naive rats with no history of exposure to other drugs were trained to self-administer IV DEX+DIP (0.5+0.5, 1+1 or 2+2 mg/kg per injection), DEX alone (1 mg/kg) or DIP (1 mg/kg) alone under five-response fixed-ratio (FR) schedule with a 30-s time-out after each injection in 2-h sessions 3–5 days a week. Separate groups of rats were tested on locomotor activity. After 8 consecutive days of habituation, naive rats were injected with 3, 10, or 30 mg/kg DEX or DIP alone IP, or in combination of 3+3 mg/kg, 10+10 mg/kg, or 30+30 mg/kg DEX+DIP IP. Saline was injected IP during the intervening days. Locomotor activity was measured for each session.Results DEX+DIP combinations were self-administered, but the drugs alone were not. The acquisition of DEX+DIP self-administration was rapid with a majority of rats reaching the final FR5 schedule in 22–23 sessions. The total IV combination dose for each final scheduled session ranged from 40 mg/kg to 160 mg/kg DEX+DIP. Significant increases in locomotor activity were observed for DIP, an effect that was significantly enhanced when DIP was given in combination with DEX. Significant mortality was also observed for the drug combination at each dose tested when given IV, with the highest mortality following the highest dose (2+2 mg/kg). When given IP, no mortality was observed.Conclusions These results show that combinations of DEX and DIP have stimulant properties and are self-administered by animals. Abuse of this combination in humans would be expected.     

Synthesis and antinociceptive activity of 6-substituted-3-pyridazinone derivatives.

A series of 3-pyridazinones carrying morpholino, arylpiperidino and arylpiperazino moiety in the position 6 IIa-g were synthesized and evaluated for antinociceptive activity. In the modified Koster test in mice 4-(4-fluorophenyl) piperazine, IIf, was found the most active compound. All the compounds except IId were more active than aspirin in the antinociceptive activity test.     

2-取代-3-氧代羊毛甾烷-24-酰胺类化合物的合成及抗肿瘤活性研究

目的设计合成一系列2-取代-3-氧代羊毛甾烷-24-酰胺类化合物,并考察其体外抗肿瘤活性。方法以羊毛甾醇为起始化合物,对其A环和侧链24位双键进行结构改造,经多步反应合成目标化合物。以阿霉素为阳性对照药,采用MTT法测试目标化合物对PC-3和As PC-1细胞的生长抑制活性。结果与结论设计并合成了18个羊毛甾醇衍生物,结构均经1H-NMR、MS、IR谱确证。药理试验结果表明,目标化合物的抗肿瘤活性较羊毛甾醇均有所提高,其中化合物9b、9g、9h、10d、10f、10g对PC-3细胞表现出显著的生长抑制活性,IC50值小于3μmol·L-1;化合物9d、9e、9f、10d对As PC-1细胞表现出显著的生长抑制活性,IC50值小于3μmol·L-1;化合物10d对PC-3和As PC-1细胞的生长抑制活性与阳性对照药阿霉素相当。初步构效关系研究表明,A环2位氰基取代优于碘代,侧链24位引入哌啶基哌啶、N-甲基哌嗪、3,5-二甲基哌啶活性较好。     

Differential effects of trihexyphenidyl on place preference conditioning and locomotor stimulant activity of cocaine and methamphetamine

Cocaine produces rewarding and locomotor stimulant effects by increasing extracellular dopamine (DA) levels in the terminal areas of the mesolimbic DA system. Our recent in vitro studies have shown that a muscarinic receptor antagonist, trihexyphenidyl (THP) inhibits the binding of a cocaine analogue to the DA transporter at concentrations that are ineffective in inhibiting 3H-DA uptake, suggesting that THP may attenuate the actions of cocaine selectively. The present study examined whether THP could affect conditioned place preference (CPP) for and locomotor stimulant activity of cocaine and methamphetamine (MAP) in mice. Mice were injected with cocaine (10 mg/kg) or MAP (1 mg/kg) in one compartment of the CPP chamber 4 times every second day. On alternate days the animals received saline in the other compartment of the CPP chamber. Pretreatment with THP was made 10 min before cocaine or MAP injection. The CPP score and locomotor activity were assessed using a novel activity monitor, SCANET. Cocaine and MAP produced CPP for the drug-paired compartment. Pretreatment with THP (0.05-5 mg/kg) had no influence on cocaine-induced CPP at any dose tested. In contrast, MAP-induced CPP was completely antagonized by THP at 5 mg/kg, which produced no CPP by itself. Another muscarinic receptor antagonist, scopolamine (SCP, 3 mg/kg) neither caused CPP by itself nor affected the development of cocaine- or MAP-induced CPP. Both THP and SCP enhanced spontaneous, cocaine- or MAP-induced locomotor activity. Though the present conditioning treatments failed to develop locomotor sensitization to cocaine, THP, but not SCP, acted cooperatively with cocaine to develop locomotor sensitization. The development of locomotor sensitization to MAP was retarded by SCP but was not affected by THP. These results suggest that, contrary to our anticipation, THP has a unique characteristic of specifically counter-acting the rewarding properties of MAP via a non-cholinergic (muscarinic) mechanism.     

Separation of the locomotor stimulant and discriminative stimulus effects of cocaine by its C-2 phenyl ester analog,RTI-15

During a routine evaluation of several analogs of cocaine, we observed that the C-2 phenyl ester, RTI-15, appeared to suppress motor activity in rats. We subsequently examined RTI-15 for its cocaine-like stimulus effects as well as for its locomotor activity effects. RTI-15 dose-dependently generalized from the cocaine stimulus in rats trained to discriminate 10 mg/kg cocaine from saline with complete substitution (⩾80% cocaine-lever responding) occurring at 24 mg/kg. During automated locomotor activity tests in mice, cocaine (3–60 mg/kg) dose-dependently increased activity counts and movement time across the entire 1 h test session. RTI-15, however, had little affect on activity counts and movement time from 10–30 mg/kg, and decreased these measures at 60 mg/kg, the highest dose tested. These results indicate that while changing the C-2 methyl ester of cocaine to a C-2 phenyl ester increases dopamine-transporter selectivity, it dissociates its locomotor activity effects from its discriminative stimulus effects suggesting that the underlying mechanisms mediating these effects are not identical.     

Inbred rat strain comparisons indicate different sites of action for cocaine and amphetamine locomotor stimulant effects

Cocaine and amphetamine produce several behavioral effects, most notably locomotor stimulation. Biochemically, evidence suggests specific involvement of dopaminergic systems, although not necessarily identical sites, in mediating cocaine- and amphetamine-induced locomotor stimulation. This study examined the effects of cocaine or amphetamine on locomotor activity in rats from the ACI, F344, LEW and NBR inbred strains. Dose-dependent increases in locomotor activity were found for both drugs in all strains. However, large potency and efficacy differences were found. Further, significant strain by drug interactions were found, in that the strain rank order for stimulant response to the two drugs was not identical. Since striatal dopaminergic neurons influence locomotor activity, we also assessed ligand affinity and receptor density of dopamine transporters and dopaminergic D₁ and D₂ receptors in striatal tissue from these same strains of rats. No differences in these receptor binding parameters were found. These findings support the conclusion that these two drugs produce their locomotor stimulant effects through different sites of action, and that genetic differences in response to these drugs at the behavioral level do not appear to be mediated significantly by differences in structure or number of striatal dopaminergic sites. The further use of genetic methods, however, may aid in determining the specific sites of action of these widely used stimulant drugs.     

The role of D2-like dopamine receptors in the locomotor stimulant effects of cocaine in mice

RATIONALE: Previous studies indicate antagonism of cocaine-stimulated locomotor activity by dopamine D2-like receptor antagonists, but only at doses of the antagonists, that by themselves attenuate locomotor activity, raising questions of the specificity of the interaction and whether it might be due solely to a summation of opposing effects. OBJECTIVES: The interactions of cocaine and several D2-like dopamine antagonists and non-dopamine "physiological antagonists" were compared across a full range of doses in order to fully characterize the interaction and assess the specificity of the effects of dopamine antagonists and cocaine. METHODS: Swiss-Webster mice were treated with either vehicle, a D2-like antagonist (haloperidol, spiperone, raclopride, spiperone, (+) or (-) eticlopride), or a "physiological" antagonist (chlordiazepoxide, clonidine, or R(-) N6-(2-phenylisopropyl)adenosine) and cocaine (5-80 mg/kg) prior to a 30-min locomotor activity test. RESULTS: All test drugs decreased locomotor activity when given alone. All test drugs attenuated cocaine-induced locomotion and decreased peak responding to cocaine. In general, the D2-like antagonists also decreased maximal responding to cocaine and decreased the slope of the ascending limb of the cocaine dose-effect curve, effects not obtained with physiological antagonists. CONCLUSIONS: Blockade of D2-like receptors resulted in an interaction with cocaine that was fundamentally different from that produced through non-dopaminergic mechanisms and appears to be more than a summation of opposing effects. The present data suggest that D2-like receptors are involved in the mechanisms underlying the induction of locomotor activity by cocaine.