Metaphit prevents locomotor activation induced by various psychostimulants and interferes with the dopaminergic system in mice

Metaphit, an isothiocyanate analog of phencyclidine and a proposed phencyclidine receptor acylator, inactivated the carrier involved in the neuronal uptake of dopamine in in vitro experiments with preparations of the striatum in the mouse. In ex vivo experiments 2 and 24 hr after the intravenous administration of metaphit, no changes were observed either in the binding of [3H]cocaine to striatal membranes or in the uptake of [3H]dopamine into synaptosomes or slices. In in vivo experiments 24 hr after pretreatment with metaphit, selective labelling of uptake sites for dopamine in the striatum of the mouse with [3H]GBR 12935 was unaffected. In these in vivo experiments, however, metaphit antagonized the locomotor stimulation induced by blockers of the uptake of dopamine (methylphenidate, mazindol, cocaine, GBR 12909) but not that induced by drugs that affect locomotion by other mechanisms (amphetamine, phencyclidine). Twenty-four hours after treatment with metaphit there was an increase in homovanillic acid in all regions of the brain studied (striatum, olfactory tubercle, cerebral cortex). There was no effect of metaphit on the disappearance rate of 3,4-dihydroxyphenylacetic acid and homovanillic acid from the striatum during the inhibition of monoamine oxidase with pargyline. If the increase in homovanillic acid reflected a greater rate of dopamine catabolism in metaphit-treated mice, it could explain the lack of locomotor stimulation of blockers uptake of the dopamine in these animals, resulting from a rapid breakdown of extracellularly accumulated dopamine.

Antagonism of cocaine-induced hepatotoxicity by the alpha adrenergic antagonists phentolamine and yohimbine

The ability of the alpha adrenoreceptor antagonists phentolamine and yohimbine to antagonize cocaine-induced hepatotoxicity was determined in phenobarbital-induced B6C3/F1 mice. Hepatotoxicity was assessed by the histologic extent of necrosis, incidence of latent lethality and increases in serum alanine aminotransferase activity. The depression of hepatic glutathione levels also were measured. The administration of a single 5-mg/kg dose of phentolamine antagonized the decrease in glutathione levels and the elevation of aminotransferase activity caused by a 60-mg/kg dose of cocaine. Similar results were obtained in mice pretreated with the alpha-2 antagonist yohimbine. Whereas the duration of antagonism could be extended by administering a 30-mg/kg dose of yohimbine, the magnitude of the antagonism was not increased. In contrast to the experiments with the larger dose, multiple hourly doses of 2.5 mg/kg of yohimbine increased both the duration of antagonism and the magnitude of protection against the hepatotoxicity produced by cocaine. Yohimbine pretreatment reduced cocaine-induced latent lethality by 50%, but did not alter the time to lethality. The results of these experiments indicate that the alpha adrenoreceptor antagonist reduces the toxicity of cocaine rather than merely delaying its time of onset. This effect does not appear to result from an inhibition of the toxic metabolite(s) of cocaine, as a 10-fold molar excess of yohimbine failed to antagonize lipid peroxidation caused by in vitro incubation of cocaine with hepatic microsomes. Additional experiments in mice whose liver metabolism had not been induced by prior pretreatment with phenobarbital revealed that 60 mg/kg of cocaine lowered glutathione but was not hepatotoxic.(ABSTRACT TRUNCATED AT 250 WORDS)

Naloxone attenuation of the effect of cocaine on rewarding brain stimulation

Antagonism of the threshold lowering effect of cocaine for brain stimulation reward by naloxone was investigated. Rats with bipolar electrodes implanted in either the median forebrain bundle (MFB) or the ventral tegmental area (VTA) were trained on a rate-independent threshold procedure. Effective threshold lowering doses of cocaine (10-15 mg/kg i.p.) were determined for each subject. A moderate dose of naloxone (4 mg/kg i.p.) effectively blocked the threshold lowering action of the cocaine. Lower (2 mg/kg) and higher (8 mg/kg) doses of naloxone attenuated but did not completely block the cocaine effect. These results provide further evidence for a catecholamine/endogenous opioid interaction in central reward.

Circling behavior following unilateral microinjections of cocaine into the medial prefrontal cortex: dopaminergic or local anesthetic effect?

Dopaminergic projections to the medial prefrontal cortex have been implicated in cocaine reinforcement; therefore, it was of interest to examine the locomotor effects of acute administration of cocaine to this area. Circling behavior was assessed following injections of 1.0 microliter of cocaine in doses of 0 (0.9% saline), 25, 50, and 100 micrograms/microliters into the medial prefrontal cortex of rats prepared with chronic unilateral guide cannulae. Animals were scored during four 5 min intervals of a 60 min test session that began with the central injection and placement in a flat circular arena. Cocaine was found to produce dose-dependent contraversive circling, an effect previously seen with the dopamine (DA) agonists LY 14 1865 and (+)-amphetamine, suggesting a unilateral stimulant effect. However, since cocaine has potent local anesthetic properties that have been reported to produce behavioral effects and also to inhibit the reuptake of norepinephrine and 5-HT, it was important to demonstrate that the directional bias was a dopaminergic effect. Intra-frontocortical microinjections of the local anesthetic procaine (10, 100, and 1000 micrograms in 0.5 microliter) did not induce circling. Sulpiride (0.001-10.0 micrograms in 0.5 microliter), a DA antagonist specific for the D-2 receptors, produced ipsiversive circling in a dose-dependent manner in rats treated with (+)-amphetamine (1.5 mg/kg, i.p.). In addition, sulpiride (1.0 micrograms in 0.5 microliter) blocked the circling behavior induced by cocaine (50 micrograms in 0.5 microliter) when administered into the medial prefrontal cortex 15 min prior to the cocaine injection. These results provide further evidence for an excitatory influence of mesocortical DA on motor control.

Cocaine-calcium channel antagonist interactions

Diltiazem, a benzothiazepine calcium channel antagonist, was given to six healthy men as a single 60 mg oral dose 120 min before IV injection of cocaine (0.2 mg/kg) in a double-blind, placebo-controlled, two-session study. Diltiazem alone produced no significant effects. Cocaine increased blood pressure, heart rate, pupil size and subjective "high" ratings, and decreased skin temperature. Diltiazem pretreatment diminished the cocaine effect on skin temperature, but did not otherwise alter the response to cocaine. Calcium channel antagonists diminish the effects of cocaine in vitro and in animals. Dosage considerations may be critical because of the differential sensitivity of various tissues to calcium channel antagonists.

Dopaminergic substrates of cocaine-induced place conditioning

Recently, Spyraki et al. (Brain Research, 253 (1982) 195-203) reported that cocaine-induced place preference conditioning was unaffected by blockade of central dopamine (DA) or norepinephrine function. In addition, systemic injections of the local anesthetic procaine produced place preference conditioning. The present study was undertaken to further evaluate the possible role of DA in cocaine-induced place conditioning. In Expt. 1, a partial replication of Spyraki et al., systemic cocaine (5.0 mg/kg, i.p.) produced significant place conditioning that was not disrupted with the DA antagonist pimozide (1.0 mg/kg, i.p.). In Expt. 2, cocaine was microinjected unilaterally into the lateral ventricles to eliminate peripheral local anesthesia. Cocaine (50.0 micrograms, i.c.v.) produced place conditioning and pretreatment with pimozide (1.0 mg/kg, i.p.) disrupted the effect. In Expt. 3, place conditioning was not observed when cocaine presentations (50.0 micrograms, i.c.v.) were paired with both compartments. The substrates of cocaine-induced place conditioning were further investigated in Expt 4: Procaine (250 micrograms, i.c.v.) did not produce place conditioning whereas the DA agonist bromocriptine (50.0 micrograms, i.c.v.) did. Results suggest the involvement of central DA in cocaine-induced place conditioning.

Metaphit, a receptor acylator, inactivates cocaine binding sites in striatum and antagonizes cocaine-induced locomotor stimulation in rodents

The PCP analog metaphit, a proposed PCP receptor acylator, produced a concentration-dependent loss of the number of high-affinity [3H]cocaine binding sites in rodent striatum. In addition, 24 h after administration of metaphit, a dose of 25 mg/kg of cocaine was not effective in stimulating locomotor behavior of rodents. The results suggest that metaphit antagonizes cocaine-induced locomotor stimulation by acylating cocaine binding sites on dopaminergic nerve terminals.

Antagonism of the behavioral effects of cocaine and d-amphetamine by prazosin

Key pecking by pigeons was maintained under a 30-response fixed-ratio schedule of food delivery; lever pressing by squirrel monkeys was maintained under a 3-min fixed-interval schedule of food delivery. Administered alone, d-amphetamine (0.1-3.0 mg/kg), cocaine (1.0-3.0 mg/kg) and bupropion (1.0-30 mg/kg) either did not affect or decreased fixed-ratio responding of pigeons, whereas d-amphetamine (0.056-0.3 mg/kg) either increased or decreased (0.56 mg/kg) responding of monkeys maintained under the fixed-interval schedule. Prazosin, a selective centrally-active alpha 1 antagonist, produced a dose-dependent reversal of the rate-decreasing effects of d-amphetamine and cocaine but not of bupropion on fixed-ratio responding in pigeons. Prazosin also reversed both the rate-increasing and rate-decreasing effects of d-amphetamine on fixed-interval responding of squirrel monkeys. In contrast, the non-selective alpha-antagonist phentolamine enhanced d-amphetamine-induced decreases in fixed-ratio responding. These findings suggest that the behavioral effects of d-amphetamine and cocaine are produced at least in part by activation of central alpha 1 receptors. Prazosin may be a useful tool for better understanding the mechanisms through which cocaine, amphetamine, and other abused stimulant drugs exert their potent behavioral effects.

Prazosin: effect on psychomotor-stimulant cues and locomotor activity in mice

Mice trained to discriminate 1 mg/kg d-amphetamine from saline, or the selective norepinephrine uptake inhibitor, nisoxetine, from saline, cross-generalized to the alternate drug. They also generalized to 5.6 mg/kg cocaine. The cues produced by amphetamine were antagonized by the selective alpha 1-adrenoceptor antagonist, prazosin, and slightly potentiated by the selective alpha 2-adrenoceptor antagonist, yohimbine. The nisoxetine cue was also antagonized by prazosin. In contrast, the peripherally acting sympathomimetics, p-hydroxyamphetamine and phenylpropranolamine, failed to substitute for, and pimozide and propranolol failed to block, either drug cue. In addition, prazosin, at a dose that did not affect either saline-associated locomotor behavior in mice or the locomotor-activity increase produced by the dopamine uptake inhibitor, bupropion, also antagonized the locomotor stimulation produced by amphetamine and cocaine. Thus, in mice, both the cues and locomotor stimulation produced by amphetamine and cocaine appear to be at least partially mediated by central alpha 1-adrenoceptor activation secondary to increased central synaptic concentrations of norepinephrine.

Prevention of acetaminophen and cocaine hepatotoxicity in mice by cimetidine treatment

Hepatotoxicity occurs in animals after administration of large doses of acetaminophen and cocaine and is thought to result from production of reactive metabolites of these parent drugs by cytochrome P450. Because cimetidine binds to cytochrome P450 and inhibits hepatic drug metabolism in both humans and animals, we determined the effects of cimetidine coadministration on acetaminophen and cocaine hepatotoxicity in mice. Marked elevations of serum glutamic pyruvic transaminase and severe pericentral hepatocellular necrosis occurred in animals receiving intraperitoneal doses of 350 mg/kg acetaminophen or 35 mg/kg cocaine, while minimal serum glutamic pyruvic transaminase elevations and liver necrosis were seen in animals who also received 100 mg/kg cimetidine 1 h before and 1 h after administration of either acetaminophen or cocaine. Consistent with the hypothesis that these in vivo protective effects resulted from interaction with cytochrome P450, cimetidine inhibited in vitro hepatic microsomal metabolism of cocaine. However, despite its protective effect against acetaminophen-induced hepatic injury, concomitant administration of cimetidine did not significantly affect plasma pharmacokinetics of acetaminophen, prevent depletion of hepatic glutathione after acetaminophen administration, or alter in vivo covalent binding of [3H]acetaminophen to hepatic proteins. These studies suggest that current theories regarding production of acetaminophen-induced liver damage require reexamination. The possibility that cimetidine treatment might be useful in preventing hepatic damage due to acetaminophen and other hepatotoxins in humans is intriguing and also warrants consideration.

Discriminative stimulus properties of a small dose of cocaine

This study characterized the interoceptive discriminative stimulus (IDS) produced by a small dose of cocaine. Rats were trained to use a dose of cocaine of 1.25 mg/kg vs saline as the basis for choosing one of two levers for food reinforcement on a fixed ratio 10 schedule. The discrimination was acquired over approx. 60 training sessions. d-Amphetamine generalized to cocaine with approximately equal potency (ED50's for cocaine and d-amphetamine were 0.07 and 0.06 mg/kg, respectively); 20 mg/kg cocaine and 10 mg/kg methylphenidate also generalized to the cocaine lever. Pentylenetetrazol, 20 mg/kg, did not generalize to the cocaine lever, and diazepam, 10 mg/kg, did not block the 1.25 mg/kg cocaine discrimination. These data indicate that when a small dose of cocaine is used as the basis of discrimination training, the discriminative stimulus that it produces is qualitatively and quantitatively similar to that produced by small doses of amphetamine, is still discriminated with a large dose of cocaine, and is dissimilar to the discriminative stimulus produced by pentylenetetrazol.

Disruption of primate social behavior by d-amphetamine and cocaine: differential antagonism by antipsychotics

Psychostimulants lead to withdrawal from social interactions and to a decline of affective behavior in squirrel monkeys. These changes, in addition to motor stereotypies, may be related to stimulant-induced psychosis in humans. In the first of two series of experiments, 1 mg/kg d-amphetamine or 10 mg/kg cocaine, administered orally three times over 24 h to one adult male member of an established group (n = 6-9), engendered stereotyped movements of the head and hands, reduced rest postures, and greatly reduced all forms of social initiatives. Chlorpromazine (0.25-1.0 mg/kg), haloperidol (0.25, 0.5 mg/kg), and physostigmine (0.04, 0.08 mg/kg), administered before the third amphetamine or cocaine injection, blocked the motor stereotypies and hyperactivity. Chlorpromazine, haloperidol, and physostigmine did not reliably antagonize the pronounced reduction in social behavior. The second series of experiments focused on agonistic behavior in the context of resident-intruder confrontations and on affiliative behavior toward group members. d-Amphetamine (3 X 0.5 mg/kg) and, to a lesser extent, cocaine (3 X 10 mg/kg) decreased affiliative and agonistic behavior. Chlorpromazine (0.5, 1.0 mg/kg) and haloperidol (0.1, 0.25 mg/kg) did not block the severe disruption of the affiliative and agonistic behavior in amphetamine-treated monkeys; physostigmine (0.06 mg/kg) reversed the decline in time spent close to the familiar monkey in amphetamine-treated monkeys. By contrast, stimulant-induced stereotypies were effectively antagonized by chlorpromazine, haloperidol, and physostigmine. These results suggest that psychostimulant-induced changes in primate social behavior may be mediated by mechanisms other than those underlying motor stereotypies.

Inhibition of behavioral effects of cocaine by actinomycin D in rats

Interactions of actinomycin D (AD, 25 micrograms--50 micrograms/kg intraperitoneally, i.p., or 1 microgram intracerebroventricularly, i.c.v.) with repeated cocaine administration (15 mg/kg i.p. twice daily at 8-hr intervals) were investigated on the spontaneous motor activity (SMA) and stereotypy (ST) in rats. Following repeated injections of cocaine in combination with saline (i.p. or i.c.v.), both SMA and ST were gradually increased to their peaks on day 9, then decreased up to the day 19 and thereafter maintained at higher than normal levels. Given along with cocaine or saline, AD (i.p. or i.c.v.) caused gradual and significant decreases of SMA and ST. On stopping AD (i.p. on day 5 and i.c.v. on day 9) injection, both SMA and ST increased again. After stopping its i.c.v. injection both behaviors were increased to their peaks on day 10, then gradually decreased to and maintained at slightly higher than normal levels on day 18 onwards. The possible mechanisms of actions of AD as an inhibitor of cocaine-induced behavioral effects have been discussed.

Metabolism correlates of cocaine-induced stereotypy in rats

An increase in stereotyped behavior was observed in rats injected daily with cocaine (40 mg/kg, IP), as compared with the first day. This increase persisted 14 days after discontinuation of the drug treatment, and corresponded to increased levels of 3H-cocaine norcocaine and benzoylecgonine in brain. Pretreatment of the animals with SKF-522A, an inhibitor of cocaine demethylation, produced a decrease in stereotypy rating and concomitantly a lower level of 3H-norcocaine in the brain. The role of this metabolite in the production of cocaine-induced stereotyped behavior is discussed.

Antagonism of behavioral effects of cocaine by lithium

Ten rats, serving as their own controls, were tested for hyperactivity (HyA) (by number of turns of an activity wheel cage) and stereotyped behavior (SB). The animals were given one week each of acclimation to the cages, saline, cocaine (19 mg/kg in 1 cc/kg saline), rest, two weeks on LiCl, and a week on LiCl plus the same dose of cocaine. LiCl produced a nonsignificant decrease of HyA and significantly decreased cocaine SB. The same procedure was duplicated using two different doses of cocaine in five animals each with identical results. The author concludes that Li seems to inhibit cocaine effects in animals and suggests a potential area of research for the use of Li in humans.

A second conponent of atropine mydriasis

A patient with Waardenburg syndrome had, in addition to the classical findings, a semidilated fixed pupil which did not react to changes of illumination, to convergence, or to pilocarpine of phospholine iodide. However, it responded normally to locally applied drugs acting on the sympathetic system. The pupil dilated after application of atropine, homatropine, or cocaine. The effect of cocaine, but not of atropine and homatropine, was prevented by pretreatment with guanethidine. It is concluded that the mydriasis caused by atropine and homatropine is partly dependent upon a direct action on the radial smooth muscle.

[Pharmacokinetics and general pharmacological actions of lithium salts administered singly or repeatedly]

Absorption, distribution and excretion after oral administration of lithium carbonate (Li2CO3) and/or lithium chloride (LiCl) were studied in Wistar rats and beagle dogs. The maximum level of concentration in the blood was seen within 4 hr after administration of Li2CO3, and a greater part of the orally dosed Li2CO3 was excreted into the urine. The blood and urine Li levels after the administration of LiCl were similar to those seen with Li2CO3. In dogs, Li2CO3 was more slowly excreted into the urine than it was in rats. Li was selectively incorporated into the thyroid and pituitary a short time after administration, and was not detected in any organ 7 days after cessation of repeated dosing for 19 days. The movement of Li into the brain was slow and relatively low levels were achieved after a single administration, but high and constant levels were shown after repeated administration. Effects of Li salts on behavior of ddy mice with repeated administration were investigated. The spontaneous motor activity was suppressed with Li2CO3 more strongly than with LiCl. The high dose of Li2CO3 suppressed not only the stimulating actions of methamphetamine and cocaine, but the ptotic and hypothermic action of reserpine. From these results, it is concluded that the repeated administration of Li salts reveals higher levels of Li ion in the brain than does a single administration, and also more responsive action on the central nervous system.

Interactions between atropine, chlorpromazine and cocaine on food reinforced behavior

Previous investigations have demonstrated the ability of atropine and chlorpromazine pretreatment to increase intravenous cocaine self-administration in rhesus monkeys. These results were interpreted as resulting from either an antagonism of cocaine's reinforcing effect or an effect of cocaine which may interfere with its self-administration. The generality of the postulated drug antagonism was tested in monkeys exhibiting stable FR10 food-reinforced behavior. Intramuscular pretreatment with 0.25-4.0 mg/kg of chlorpromazine significantly depressed this behavior as did pretreatment with 0.25-2.0 mg/kg of atropine. These same dosages had been shown to increase cocaine self-administration. Fifteen-minute influsions of cocaine (1.0-10 mg/kg), which began 15 min after session onset, also resulted in a depression of food reinforced behavior. When chlorpromazine pretreatment and cocaine infusion were combined, the decrement in food reinforced responding was lessened. However, when cocaine infusion and atropine pretreatment occurred concurrently, the depression in responding was increased. These data indicate that chlorpromazine may nonspecifically antagonize the behavioral effects of cocaine; whereas, atropine may enhance these effects.

Inhibition of post-ganglionic motor transmission in vas deferens by indirectly acting sympathomimetic drugs

1. Using field stimulation with short trains of pulses (< 10 per train), the post-ganglionic motor transmission in the mammalian vas deferens has been further analysed pharmacologically.2. In preparations taken from guinea-pigs, rats and rabbits the effects of the indirectly sympathomimetic drugs, tyramine and cocaine, could be explained entirely on the basis of the actions of released, endogenous noradrenaline.3. Tyramine produced a contraction in vasa taken from normal rats but not from normal guinea-pigs. The tyramine contraction was due to release of endogenous noradrenaline because it was not seen in preparations taken from reserpinized rats and because it was abolished in normal vasa by phenoxybenzamine or phentolamine, thus denying the supposed inaccessibility, to alpha-blockers, of the motor alpha-adrenoceptors activated by endogenous noradrenaline.4. Phenoxybenzamine or phentolamine failed to block post-ganglionic motor transmission in rat and in guinea-pig vasa.5. Tyramine strongly inhibited motor transmission in vasa taken from normal but not from reserpinized guinea-pigs.6. Tyramine produced inhibition of motor transmission in phenoxybenzamine-treated preparations taken from normal but not from reserpinized rats.7. Cocaine inhibited motor transmission in guinea-pig and in rat vasa. This effect was not due to a local anaesthetic or to a smooth-muscle depressant action because it did not occur in preparations taken from reserpinized animals.8. The inhibitory effect of tyramine or cocaine was not abolished by beta-adrenoceptor blockade with propranolol.9. Whereas reserpinization abolished the tyramine- and cocaine-inhibitions, it did not affect the inhibitory actions of noradrenaline or of PGE(2).10. Indomethacin and sodium meclofenamate, which suppress prostaglandin synthesis, did not affect the twitch-inhibiting actions of noradrenaline, tyramine or cocaine.11. These results provide further support for the conclusion that post-ganglionic motor transmission to the vas deferens is non-adrenergic in these species and assign to endogenously released noradrenaline an inhibitory role upon motor transmission.

The responses of rat and guinea pig vas deferens to cocaine

Cocaine caused contractions and potentiation of motor responses to transmural stimulation of vas deferens of the rat but not of the guinea pig. Tachyphylaxis was not observed after repeated doses of cocaine to vasa deferentia from both normal and reserpine-treated rats. Pretreatment with reserpine reduced significantly (p < 0.05) the responses to cocaine but abolished completely the responses to tyramine. No catecholamines could be detected spectrophotofluorometrically in reserpine-treated preparations. Contractions following the application of cocaine to vasa deferentia from both normal and reserpine-treated rats were completely abolished by phenoxybenzamine, phentolamine, and tolazoline. Cocaine failed to protect alpha-adrenergic receptors against phenoxybenzamine blockade in reserpine-treated preparations; however, cocaine could still evoke contractions of reserpine-treated preparations protected with noradrenaline against phenoxybenzamine blockade. The evidence presented indicates that cocaine acts as a mixed sympathomimetic on the rat vas deferens preparation. The possibility that cocaine is an indirect-acting sympathomimetic amine could not be ruled out in the present study.