Antagonism of delta(2)-opioid receptors by naltrindole-5'-isothiocyanate attenuates heroin self-administration but not antinociception in rats

delta-Opioid receptors have been implicated in reinforcement processes and antagonists are available that produce long-lasting and selective antagonism of delta-opioid receptors in vivo. This experiment assessed the contribution of delta-opioid receptors to the antinociceptive and reinforcing properties of heroin. The effects of the irreversible delta-antagonist naltrindole-5'-isothiocyanate (5'-NTII) were evaluated on heroin self-administration and hot-plate antinociception in rats. 5'-NTII (10 nmol i.c.v.) shifted the dose-response curve for heroin self-administration downward, increasing the A(50) values on the ascending and descending limbs by approximately 0.5 log units and decreasing the maximum by 33%. 5'-NTII (40 nmol i.c.v.) shifted both limbs of the heroin self-administration dose-effect curve 1.2 log units to the right and decreased the maximum by 90%. Heroin self-administration gradually returned to baseline levels over 7 or 17 days after administration of 10 or 40 nmol 5'-NTII, respectively. 5'-NTII (40 nmol i.c.v.) decreased the self-administration of 0.17 mg/infusion cocaine by 40% while having no effect on responding maintained by 0.33 or 0.67 mg/infusion. 5'-NTII attenuated the antinociceptive effects of deltorphin (delta(2)) in a dose-dependent manner while having no effect on antinociception elicited after i.c. v. administration of [D-Pen(2),D-Pen(5)]-enkephalin (delta(1)) or [D-Ala(2),N-Me-Phe(4),Gly(5)-ol]-enkephalin (mu). In addition, the antinociceptive effects of heroin were not significantly affected by 5'-NTII (40 nmol i.c.v.). Therefore, 5'-NTII can attenuate the reinforcing effects of heroin at doses that do not affect its antinociceptive effects. Long-acting delta(2)-opioid antagonists may be beneficial in the treatment of heroin dependence or as adjuncts to reduce the abuse liability of opioid analgesics.

Chemical synthesis and pharmacology of 6- and 7-hydroxylated 2-carbomethoxy-3-(p-tolyl)tropanes: antagonism of cocaine's locomotor stimulant effects

In our efforts to identify molecules that might act as cocaine antagonists or cocaine partial agonists, efforts were made to further capitalize on our earlier finding regarding the ability of a 7-methoxylated pseudococaine analogue to act as a weak cocaine functional antagonist. Herein, a series of the 6- and 7-hydroxylated WIN analogues possessing a boat or chair conformation of the tropane ring were prepared and tested for their ability to displace [(3)H]mazindol binding and to inhibit high-affinity monoamine uptake into rat brain nerve endings. These 6- and 7-hydroxylated WIN analogues were readily prepared by use of a classical Willstätter synthesis to construct an appropriately functionalized tropane ring followed by use of a Suzuki coupling reaction to introduce the aryl group at position 3. Reduction of the resulting tropene by use of SmI(2) or by catalytic hydrogenation followed by deprotection delivered the final target compounds. Some of these compounds were found to retain considerable affinity as inhibitors of the dopamine transporter (DAT) and the norepinephrine transporter (NET), but they were less potent inhibitors of the serotonin transporter (SERT). None of the compounds of the present series revealed any substantial potency difference in [(3)H]mazindol binding versus [(3)H]DA uptake, and failed to show "cocaine antagonism" when tested for their ability to prevent cocaine's inhibition of DA transport. However, one of these hydroxylated WIN analogues, namely 12b, which possesses nanomolar potency at the DAT and NET and micromolar potency at the SERT, when tested in vivo, was found capable of attenuating cocaine's locomotor activity (AD(50) = 94 mg/kg). Taken together, this work provides further support for our hypothesis that drugs that lack the ability to inhibit transport by all three monoaminergic transporters may exhibit "partial" cocaine-like properties, but act as cocaine antagonists. Consequently, it may prove valuable to examine the behavioral activity of other 6- and 7-substituted tropanes in animal behavioral paradigms in the search for a cocaine medication.

Application of artificial enzymes to the problem of cocaine

Cocaine mediates its reinforcing and toxic actions through a "loss of function" effect at multiple receptors. The difficulties inherent in blocking a pleiotropic blocker pose a great obstacle for the classical receptor-antagonist approach and have contributed to the failure-to-date to devise specific treatments for cocaine overdose and addiction. As an alternative, we have embarked on an investigation of catalytic antibodies, a programmable class of artificial enzyme, as "peripheral blockers"--agents designed to bind and degrade cocaine in the circulation before it partitions into the central nervous system to exert reinforcing or toxic effects. We synthesized transition-state analogs of cocaine's hydrolysis at its benzoyl ester, immunized mice, prepared hybridomas, and developed the first anti-cocaine catalytic antibodies with the capacity to degrade cocaine to non-reinforcing, non-toxic products. We subsequently identified several families of anti-cocaine catalytic antibodies and found that out most potent antibody, Mab15A10, possessed sufficient activity to block cocaine-induced reinforcement and sudden death in rodent models of addiction and overdose, respectively. With the potential to promote cessation of use, prolong abstinence, and provide a treatment for acute overdose, the artificial enzyme approach comprehensively responds to the problem of cocaine.

Effect of riluzole and gabapentin on cocaine- and methamphetamine-induced behavioral sensitization in mice

RATIONALE

Recent studies have suggested the involvement of excitatory amino acid (EAA) and inhibitory gamma amino butyric acid (GABA) transmission in the effects of psychostimulants such as cocaine and amphetamines.

OBJECTIVES

The present study was undertaken to investigate whether drugs that are considered to inhibit glutamate release (e.g., riluzole) or increase GABAergic transmission (e.g., gabapentin) attenuate the induction and expression of sensitization to cocaine and methamphetamine (METH) in Swiss Webster mice.

METHODS

Sensitization to the psychomotor stimulating effect of cocaine and METH was rendered by five daily injections of cocaine (20 mg/kg) or METH (1.0 mg/kg). Locomotor activity was measured by infrared beam interrupts.

RESULTS

Pretreatment with riluzole (2.5-20.0 mg/kg) affected neither the expression nor the induction of sensitization to cocaine. The pretreatment with riluzole (20 mg/kg) blocked the acute response to METH on day 1 and the expression of the sensitized response on day 5 but not the induction of sensitization to METH. Pretreatment with gabapentin (10 mg/kg and 30 mg/kg) affected neither the expression nor the induction of sensitization to cocaine. The pretreatment with gabapentin attenuated the acute response to METH on day 1 and the expression of the sensitized response on day 5, but it failed to block the induction of sensitization to METH. Psychostimulant-induced conditioned locomotion was affected neither by riluzole nor by gabapentin.

CONCLUSIONS

Riluzole and gabapentin had no effect on the induction of sensitization to cocaine and METH; however, they attenuated the expression of sensitization to METH but not to cocaine. These findings suggest that riluzole- and gabapentin-mediated changes in EAA and GABAergic transmission, respectively, had no effect on mechanisms associated with the induction of sensitization, but they may affect the expression of the sensitized response to METH.

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.

Pharmacological reversal of behavioral and cellular indices of cocaine sensitization in the rat

RATIONALE AND OBJECTIVES

Behavioral sensitization has been proposed as an animal model for the intensification of drug craving in cocaine addiction. Interactions between dopamine and glutamate systems are important for the induction and maintenance of sensitization. The goal of this study was to determine if established cocaine sensitization could be reversed by pharmacological manipulation of these transmitter systems.

METHODS

Rats received 15 mg/kg cocaine (IP) on days 1-10 and were challenged with cocaine (10 mg/kg) on day 13 to verify that sensitization had occurred. On days 14-20, separate groups of sensitized rats received daily injections of dopamine D1- or D2-class agonists, an NMDA receptor antagonist, or a dopamine agonist with an NMDA antagonist. Three days or 2 weeks later, all rats were again tested for their response to cocaine to determine if sensitization had been reversed.

RESULTS

Reversal of sensitization was produced by repeated administration of either a D1-class agonist (SKF 81297) or the combination of an NMDA receptor antagonist and a D2-class agonist. Effective combinations were cocaine+MK-801, quinpirole+MK-801, quinpirole+CGS 19755, and pergolide+memantine. The latter drugs are approved for human use. Reversal of sensitization persisted for at least 2 weeks after cessation of drug treatment. Electrophysiological studies revealed that these drug treatments also reversed dopamine D1 receptor supersensitivity in the nucleus accumbens, a cellular correlate of sensitization.

CONCLUSIONS

These results demonstrate that pharmacotherapy can reverse behavioral and cellular adaptations associated with repeated cocaine administration, and may do so without the need for continued medication.

Tiospirone and the reinforcing effects of cocaine in the conditioned place preference paradigm in rats

Tiospirone (TSP) is an atypical antipsychotic drug. It has 5HT-2 antagonistic properties as well as affinity for D2, 5HT-1a, 5HT-6 and sigma receptors. Behavioural studies in our laboratory, which used a 24h free access to food and fluids paradigm, showed a decreased alcohol and increased food intake after twice-daily administration of TSP; the maximal effect was obtained at a dose of 0.48 mg kg(-1). This study used the conditioned place preference paradigm to determine the effect of TSP on the reinforcing properties of cocaine. Intraperitoneal administration of 5.0 mg kg(-1) cocaine, but not saline, increased the time rats spent in the drug-paired compartment of a three-compartment shuttle box by 104.9%. Two doses of TSP, 0.143 and 0.48 mgkg(-1), were tested subcutaneously 60 min before saline or cocaine administration during the conditioning phase only. A dose-response effect was observed with a significant reduction in the time rats spent in the cocaine-paired compartment on the drug-free test day produced by the dose of 0.48 mg kg(-1) (an increase of only 38.1% when post-conditioned times were compared with preconditioned times). These findings suggest that TSP reduces the reinforcing properties of cocaine exhibited in the conditioned place preference paradigm.

Intra-medial prefrontal cortex injection of quinpirole, but not SKF 38393, blocks the acute motor-stimulant response to cocaine in the rat

RATIONALE

Considerable evidence suggests that the medial prefrontal cortex (mPFC) is an important region in mediating certain behavioral and neurochemical responses to cocaine. However, a role for cortical dopamine (DA) receptor subtypes in modulating these responses has yet to be elucidated.

OBJECTIVES

This study investigated the effects of intra-mPFC administration of DA agonists on the acute motor-stimulant response to cocaine. In addition, in vivo microdialysis techniques were employed to determine the effects of intracortical injection on cocaine-induced extracellular DA concentrations in the nucleus accumbens (NAC).

METHODS

One week following bilateral cannulae implantation over the mPFC and the NAC (for dialysis experiments), male Sprague-Dawley rats received an intra-mPFC injection of saline, the DA D2-like agonist quinpirole (0.015, 0.05, 0.15, 0.5, 1.5, or 5.0 nmol per side) or the partial DA D1-like agonist SKF 38393 (0.5, 1.5, or 5.0 nmol per side) approximately 5 min before peripheral administration of saline or cocaine (15 mg/kg, i.p.). For dialysis experiments, only the highest dose of quinpirole was examined.

RESULTS

Pretreatment with quinpirole produced a dose-dependent decrease in cocaine-induced motor activity, with the highest doses resulting in a complete abolition of the acute motor-stimulant response to cocaine. In contrast, intra-mPFC administration of SKF 38393 was not shown, at the doses tested, to alter cocaine-induced motor activity. In agreement with the behavioral effects, intra-mPFC quinpirole injection (5 nmol per side) significantly blocked cocaine-induced DA overflow in the NAC.

CONCLUSIONS

The results of the present study provide additional support that the mPFC is a neural substrate through which cocaine, in part, produces its motor-stimulant effects. In addition, these data suggest that modulation of cortical DA D2 receptors can block acute cocaine-induced behavioral (locomotor activity) and neurochemical (DA concentrations in the NAC) responses in the rat.

Dopamine uptake by mouse neuroblastoma N1E-115 cells stably expressing human dopamine transporter is differentially inhibited by anti-idiotypic ab2beta antibodies mimicking the configuration of cocaine

We have successfully constructed a mouse neuronal N1E-115 cell line stably expressing a fully functional human dopamine transporter (hDAT). Previous studies in our laboratory have produced several anti-idiotypic Ab2beta antibodies that mimic the configuration of the cocaine molecule at their antigen-combining site. In the present study, we observed that some anti-idiotypic Ab2beta antibodies inhibited dopamine uptake by the hDAT-transfected line. Each antibody showed a different level of inhibition (between 40% and 90%). These findings suggest that the internal images of these antibodies can be used as analog peptides that may compete with cocaine for its binding site on the transporter but not impair dopamine uptake as much as cocaine does.

Carvedilol affects the physiological and behavioral response to smoked cocaine in humans

The noradrenergic system is implicated in mediating some of the physiological effects of cocaine. The purpose of this study was to investigate whether treatment with an adrenergic blocker, carvedilol, which would be expected to attenuate the physiological effects of cocaine, would also attenuate the subjective and behavioral response to cocaine in humans. Twelve crack cocaine users participated in this double-blind, placebo-controlled outpatient study. Acute treatment with 50 mg of oral carvedilol attenuated the smoked cocaine-induced increases in heart rate, systolic and diastolic blood pressure. The number of cocaine self-administrations was lower under 25 mg carvedilol treatment condition compared with 50 mg carvedilol or placebo treatment conditions. The subjective responses to smoked cocaine deliveries were not affected by carvedilol treatment. These results suggest that acute treatment with carvedilol attenuates the physiological effects of smoked cocaine. The effects of carvedilol on cocaine self-administration need to be studied further.

Dissociation of cocaine-antagonist properties and motoric effects of the D1 receptor partial agonists SKF 83959 and SKF 77434

Previous studies suggest that D1 receptor partial agonists may be viable candidates for development as pharmacotherapies for cocaine addiction. This study investigated the ability of the D1 receptor partial agonists SKF 83959 and SKF 77434 to modulate the behavioral effects of cocaine and compared these effects with those of the reference D1 receptor antagonist SCH 39166 and D1 receptor agonists SKF 81297 and 6-Br-APB. Squirrel monkeys were trained either to respond under a fixed-interval schedule of stimulus-shock termination or to discriminate cocaine from vehicle (procedures useful for evaluating the behavioral stimulant and subjective effects of cocaine, respectively). Additional monkeys were studied with quantitative observational techniques to evaluate the effects of the drugs on various forms of motor behavior. Like SCH 39166, but unlike SKF 81297 and 6-Br-APB, the D1 receptor partial agonists attenuated the behavioral stimulant and discriminative stimulus effects of cocaine in a dose-dependent manner, although maximum antagonism produced by SKF 77434 was not always as great as that produced by SKF 83959 or SCH 39166. In observational studies, SKF 83959 and SKF 77434 produced less severe disruptions in motor behavior than did SCH 39166 and, for SKF 83959, showed a greater separation between the dose required to antagonize the behavioral effects of cocaine and the dose that induced catalepsy (>/=33-fold). These results suggest that D1 receptor partial agonists can act as functional cocaine antagonists with less severe behavioral effects than D1 receptor antagonists. The prominent cocaine-antagonist properties and the low incidence of motoric side effects of SKF 83959 may reflect its unique binding profile at D1 as well as nondopaminergic receptors.

Dopamine transporter transmembrane domain polar mutants: DeltaG and DeltaDeltaG values implicate regions important for transporter functions

Polar residues in dopamine transporter (DAT) transmembrane domains (TMs) are likely to act individually and even interactively in recognizing cocaine and dopamine. We initially evaluated the effects of alanine substitution mutants that remove the polar side chains from residues in each of the 12 putative DAT TMs on the recognition of dopamine and the cocaine analog CFT. Eleven combination mutants with multiple substitutions in DAT TMs 4, 5, 7, or 11 were then selected as candidates for more detailed evaluation based on mutation effects on dopamine and cocaine analog affinities. An evaluation of Gibbs free energy changes displayed by single and combined TM mutants (DeltaG(o) and DeltaDeltaG(o)(int)) reveals three categories of potential interactions among mutants: 1) independent, noncooperative interactions (five influenced CFT and two influenced dopamine affinities), 2) synergistic influences (two for CFT and four for dopamine), and 3) complementation of influences on CFT recognition (four mutants) or on dopamine affinity (five). Combined mutations in TMs 4 and 5 yield the largest DeltaDeltaG(o)(int) values for dopamine uptake. TMs 4 and 11 mutants provide the largest DeltaDeltaG(o)(int) for CFT binding. Interactions between residues lying in DAT TMs 4 and 5 support current DAT structural models that suggest the juxtaposition of these two TMs. These data also support contributions of TM 4 and 11 residues to a polar pocket important for cocaine recognition. These candidate interactive DAT polar domains provide larger target sites for compounds that could modulate specific DAT functions than those provided by single mutations alone.

Relationship between cocaine-induced hepatotoxic neurobehavioral & biochemical changes in mice: the antidotal effects of buprenorphine

Cocaine (COCA)-induced neurobehavioral symptoms, which can be observed simultaneously with exacerbation in biochemical markers, were evaluated in mice, and compared with the changes observed in a representative hepatic failure model induced by thioacetamide (TAA). The effects of pretreatment with buprenorphine (BUP) (0.25, 0.5 or 1 mg/kg i.p.), a mixed opioid agonist-antagonist and an antidote against fatal COCA toxicity, were also examined. At 5 min after the COCA administration (65 mg/kg i.p.), the liver ATP levels were attenuated, and an exacerbation of the CNS-stimulating effects of COCA could be characteristically observed for hepatotoxicity-related neurobehavioral symptoms (changes in alertness, interest, body tension, head movement and walking). At 24 h, the ALT (alanine aminotransferase) activity was elevated, and hepatotoxic attenuation was observed for all of the scores on the neurobehavioral symptoms; this was almost identical to the symptoms observed in the TAA-treated group of mice. Recovery was observed by 72 h for all of the morbid changes. The hepatotoxic biochemical changes and the sum score for all five neurobehavioral symptoms were significantly ameliorated by low doses (0.25 and 0.5 mg/kg) of BUP, both at 5 min and 24 h.

Memantine and ACPC affect conditioned place preference induced by cocaine in rats

The influence of uncompetitive NMDA receptor antagonist, 1-amino-3,5--dimethyl-adamantane (memantine) and partial glycineB site agonist, 1-amino-cyclopropanecarboxylic acid (ACPC) on cocaine-induced conditioned place preference (CPP) were examined in male Wistar rats. After determination of initial preference, animals were conditioned with cocaine (5 mg/kg, ip) for 3 conditioning trials, alone or in combination with memantine (7.5 mg/kg, ip) or ACPC (50.0 mg/kg, ip). Memantine prevented acquisition and expression of the place preference produced by cocaine, while ACPC prevented only acquisition effect. Neither of the NMDA antagonists displayed any reinforcing properties by itself. Our current data suggest that the NMDA receptor complex may be involved in the rewarding effect of cocaine.

Dissociable effects of the kappa-opioid receptor agonists bremazocine, U69593, and U50488H on locomotor activity and long-term behavioral sensitization induced by amphetamine and cocaine

RATIONALE

Mesolimbic dopaminergic neurotransmission plays a critical role in the locomotor effects of psychostimulant drugs, but a general involvement in the induction of long-term psychostimulant sensitization is questionable. By influencing dopaminergic neurotransmission, opioid drugs can alter the behavioral effects of psychostimulants.

OBJECTIVES

The effects of the kappa-opioid receptor agonists bremazocine, U69593, and U50488H on the locomotor stimulant and the long-term sensitizing effects of amphetamine and cocaine were investigated in rats. Unlike U69593 and U50488H, bremazocine is also an antagonist at mu- and delta-opioid receptors, as well as an agonist at a subtype of delta-opioid receptors inhibiting dopamine D1 receptor-stimulated adenylate cyclase.

METHODS

Bremazocine, U69593, and U50488H were administered prior to amphetamine and cocaine, and locomotor activity was measured. In separate studies, the opioids were co-administered with amphetamine and cocaine for 5 days, and locomotor sensitization was assessed 3 weeks post-treatment.

RESULTS

Bremazocine and U69593 attenuated the psychomotor stimulant effects of amphetamine and cocaine. U50488H attenuated the locomotor effect of cocaine and biphasically affected amphetamine-induced locomotion, i.e., suppression followed by stimulation. Bremazocine prevented the development of amphetamine-induced but not cocaine-induced long-term sensitization. Neither U69593 nor U50448H affected the induction of long-term amphetamine or cocaine sensitization.

CONCLUSIONS

In agreement with previous studies, the present data suggest that differential mechanisms underlie the acute stimulant versus the long-term sensitizing effects of psychostimulants, and the induction of long-term sensitization by amphetamine versus cocaine. Stimulation of kappa-opioid receptors does not seem to block the induction of long-term psychostimulant sensitization. Thus, bremazocine is likely to block the induction of amphetamine sensitization through a non-kappa-opioid receptor mechanism. We suggest that this effect of bremazocine is the result of its unique agonist action at a subtype of delta-opioid receptors, thereby acting as a functional dopamine D1 receptor antagonist. This would be consistent with the literature showing that the induction of long-term amphetamine sensitization depends on the activation of dopamine D1 receptors. In addition, the present data are in keeping with studies showing that dopamine neurotransmission is not critical for the induction of long-term cocaine sensitization.

gamma-aminobutyric acid mimetic drugs differentially inhibit the dopaminergic response to cocaine

Dopaminergic activity in the mesocorticolimbic system is associated with reinforcing properties of psychostimulant drugs. We previously demonstrated that increased gamma-aminobutyric acid (GABA)-ergic activity produced by gamma-vinyl GABA [D,L-4-amino-hex-5-enoic acid (Vigabatrin(R))], an irreversible inhibitor of GABA-transaminase, attenuated cocaine, nicotine, heroin, alcohol, and methamphetamine-induced increases in extracellular nucleus accumbens dopamine as well as behaviors associated with these biochemical changes. In the present study, using in vivo microdialysis techniques, we compared three different strategies to increase GABAergic activity in order to modulate cocaine-induced increase in extracellular dopamine. Our data demonstrate that the anticonvulsant 1-(2-(((diphenylmethylene)amino)oxy)ethyl)-1,2,5, 6-tetrahydro-3-pyridinecarboxylic acid hydrochloride (NNC-711), a GABA uptake inhibitor, dose and time dependently diminished increases in extracellular dopamine following acute cocaine challenge. Furthermore, we demonstrated that cyclized analogue of vigabatrin, a competitive reversible GABA-transaminase inhibitor, is a more potent inhibitor of cocaine-induced dopamine increase than vigabatrin. Our data suggest that in addition to irreversible inhibition of GABA transaminase, inhibition of GABA uptake represent another potentially effective, indirect strategy for the treatment of cocaine abuse.

The role of serotonin(2) receptors in mediating cocaine-induced convulsions

Previous research in our laboratory suggests that serotonin (5-HT) neurotransmission mediates the expression of cocaine-induced convulsions. The role of 5-HT in mediating this toxic effect of cocaine appears to be due to activation of 5-HT(2) receptors, because cocaine-induced convulsions are blocked by the 5-HT(2) antagonists cinanserin, ketanserin, and pirenperone. The present study utilized a number of compounds that display a high affinity for 5-HT(2) receptors to further examine the role of these sites in mediating this toxic effect of cocaine. Cocaine-induced convulsions were observed following pretreatment with various doses of the following 5-HT(2) antagonists: mianserin, metergoline, MDL 11939, and methiothepin. In addition, 1-(2-methoxyphenyl)-4-[4-(2-phthalimido)butyl]piperazine (NAN 190) was tested to examine the influence of 5-HT(1) sites and the agonist compound 1-(3-triflurormethylphenyl)piperazine (TFMPP) was examined to further explore the role of 5-HT(1) and 5-HT(2) sites. Each 5-HT(2) antagonist attenuated cocaine-induced convulsions. Conversely, NAN 190 did not alter this toxic effect of cocaine. In addition, TFMPP significantly potentiated cocaine-induced convulsions. The results from this study support the hypothesis that 5-HT neurotransmission, acting primarily at 5-HT(2) receptors, plays an important role in mediating cocaine-induced convulsions.

3-Aryl-2-carbomethoxybicyclo[3.2.1]oct-2-enes inhibit WIN 35,428 binding potently and selectively at the dopamine transporter

The search for medications for cocaine abuse has focused upon the design of potential cocaine antagonists or cocaine substitutes which interact at the dopamine transporter of mammalian systems. This manuscript describes the synthesis and biological evaluation of 8-substituted 2-carbomethoxy-3-arylbicyclo[3.2.1]oct-2-enes. These compounds prove potent and selective inhibitors of the dopamine transporter. Their selectivity results primarily from a reduced inhibitory potency toward the serotonin transporter. This work supports the notion that the orientation of the 3-aryl ring in the bicyclo[3.2.1]octane system affects the interaction of these molecules with the serotonin transporter far more markedly than it affects the interaction with the dopamine transporter.

Modification of behavioral effects of drugs in mice by neuroactive steroids

RATIONALE

Neuroactive steroids represent a novel class of potential therapeutic agents (epilepsy, anxiety, migraine, drug dependence) thought to act through positive allosteric modulation of the GABA(A) receptor. A synthetically derived neuroactive steroid, ganaxolone (3alphahydroxy-3beta-methyl-5alpha-pregnan-20-one), is in phase-II clinical trials for epilepsy. Unlike traditional anticonvulsants such as diazepam and phenobarbital, ganaxolone shows equipotent suppression of both the seizure activity and the behavioral effects of pentylenetetrazol (PTZ) administration.

OBJECTIVES

The present study explored possible reversal by ganaxolone and related neuroactive steroids of some behavioral effects of additional pharmacological challenges.

METHODS

Direct behavioral observation and photocell-counted locomotor activity of male, Swiss-Webster mice were made with various compounds alone and in conjunction with ganaxolone.

RESULTS

Ganaxolone both prevented and reversed PTZ-induced locomotor depression in mice. Further, ganaxolone reversed the locomotor depression induced by other convulsant/anxiogenic stimuli: bicuculline, picrotoxin and, to a lesser extent, yohimbine. Ganaxolone failed to reverse the locomotor stimulation induced by cocaine, methamphetamine, dizocilpine, and phencyclidine. In addition to ganaxolone, the endogenous neuroactive steroids allopregnanolone and pregnanolone and the synthetic neuroactive steroid Co 2-1068 also reversed observed behaviors and locomotor depression induced by PTZ.

CONCLUSIONS

The present findings support the unique pharmacological effects of neuroactive steroids as a novel class of positive allosteric modulators of GABA.

Discovery of a novel dopamine transporter inhibitor, 4-hydroxy-1-methyl-4-(4-methylphenyl)-3-piperidyl 4-methylphenyl ketone, as a potential cocaine antagonist through 3D-database pharmacophore searching. Molecular modeling, structure-activity relationships, and behavioral pharmacological studies

A novel, fairly potent dopamine transporter (DAT) inhibitor, 4-hydroxy-1-methyl-4-(4-methylphenyl)-3-piperidyl 4-methylphenyl ketone (3, K(i) values of 492 and 360 nM in binding affinity and inhibition of dopamine reuptake, respectively), with significant functional antagonism against cocaine and a different in vitro pharmacological profile from cocaine at the three transporter sites (dopamine, serotonin, and norepinephrine) was discovered through 3D-database pharmacophore searching. Through structure-activity relationships and molecular modeling studies, we found that hydrophobicity and conformational preference are two additional important parameters that determine affinity at the DAT site. Chemical modifications of the lead compound (3) led to a high affinity analogue (6, K(i) values of 11 and 55 nM in binding affinity and inhibition of dopamine reuptake, respectively). In behavioral pharmacological testing, 6 mimics partially the effect of cocaine in increasing locomotor activity in mice but lacks cocaine-like discriminative stimulus effect in rats. Taken together, these data suggest that 6 represents a promising lead for further evaluations as potential therapy for the treatment of cocaine abuse.

Effects of NMDA receptor blockers on cocaine-stimulated locomotor activity in mice

Effects of MK-801 and ketamine, N-methyl-D-aspartate (NMDA) receptor blockers, on cocaine-stimulated locomotor activity were investigated in male Swiss-Webster mice. MK-801 (0.25, 0.5, 1.0 and 2.5 mg/kg), ketamine (10, 25 and 50 mg/kg) or saline was injected 20 min before cocaine (5, 10 and 20 mg/kg i.p.). Locomotor activity was measured for 30 min immediately following cocaine treatment. All doses of the drugs were also tested for ability to depress or stimulate locomotor activity in the naive (no cocaine-treated) mice. Cocaine produced a dose-dependent increase in locomotor activity that was blocked dose-dependently by MK-801 or ketamine. The blockade by MK-801 was more prominent than by ketamine. Our results may suggest that cocaine-induced locomotor stimulation in mice is modulated via NMDA receptor mediated mechanisms.

Effects of labetalol treatment on the physiological and subjective response to smoked cocaine

Adrenergic receptors mediate some of the physiological and possibly behavioral effects of cocaine. The purpose of this study was to investigate the effect of treatment with a peripherally acting adrenergic blocking drug labetalol on the cardiovascular and subjective response to repeated deliveries of smoked cocaine. In this double-blind, placebo-controlled, crossover study, 12 cocaine users were treated with a single 100 or 200 mg dose of labetalol, or placebo in each of three experimental sessions. Starting 2 h after the medication treatment, subjects received three doses of 0.4 mg/kg smoked cocaine, 30 min apart. Labetalol treatment significantly attenuated the cocaine-induced increases in heart rate and systolic blood pressure. This effect of labetalol on the cardiovascular response did not decrease with repeated cocaine deliveries. The subjective response to smoked cocaine deliveries was not affected by labetalol treatment. These results suggest that labetalol effectively attenuates the systolic blood pressure and heart rate increases induced by repeated doses of smoked cocaine, but does not alter subjective effects.

Isoflurane anesthesia enhances the inhibitory effects of cocaine and GBR12909 on dopamine transporter: PET studies in combination with microdialysis in the monkey brain

The effects of the dopamine transporter (DAT) inhibitors cocaine and GBR12909 on DAT and dopamine D(2) receptors were evaluated in the brains under awake and isoflurane-anesthetized monkeys using high-resolution positron emission tomography (PET) in combination with microdialysis. The striatal DAT availability and dopamine D(2) receptor binding were assayed with [11C]beta-CFT (WIN35,428) and [11C]raclopride, respectively. Cocaine or GBR12909 at a dose of 2 mg/kg was administered intravenously 30 min prior to the injection of labeled compounds. In the awake state, the in vivo binding of [11C]beta-CFT to DAT was significantly decreased by administration of cocaine or GBR12909 at a dose of 2 mg/kg. In contrast, [11C]raclopride binding to dopamine D(2) receptors was decreased only by GBR12909. Under isoflurane anesthesia, dopamine concentration in the striatal extracellular fluid (ECF), as measured by microdialysis, was markedly increased by cocaine or GBR12909 compared to the awake state. Isoflurane anesthesia more markedly enhanced the binding of [11C]beta-CFT in the saline-injected animals, and the degrees of reduction by cocaine and GBR12909 were more marked than those observed in the awake state. Under isoflurane anesthesia, the binding of [11C]raclopride was reduced not only by GBR12909 but also by cocaine which did not affect the binding in the awake state. Taken together, these observations indicated that isoflurane anesthesia enhanced not only the direct inhibitory effects of cocaine and GBR12909 on DAT, but also their indirect effects on dopamine D(2) receptors.

Comparative effects of sodium bicarbonate and sodium chloride on reversing cocaine-induced changes in the electrocardiogram

Cocaine abuse is associated with a number of cardiovascular complications that include arrhythmias and sudden cardiac death. Although the mechanism(s) remain unclear, cocaine-induced block of sodium channels resulting in slowed cardiac conduction is thought to play an important role. Several reports suggest that the effects of cocaine effects on cardiac sodium channels can be reversed by administration of sodium bicarbonate. Whether the beneficial effects of sodium bicarbonate are due to sodium ions or an increase in blood pH is unknown. Therefore the purpose of this study was to compare the effects of sodium loading alone (by using sodium chloride) versus sodium loading with an associated increase in arterial pH (by using sodium bicarbonate) on reversing cocaine-induced effects on the electrocardiogram (ECG) in a canine model. Seventeen anesthetized dogs received three i.v. injections of cocaine, 5 mg/kg, with each dose separated by 15 min. Two minutes after the third cocaine dose, each dog was randomly assigned to receive 2 mEq/kg i.v. sodium bicarbonate (1 mEq/ml) or 2 mEq/kg i.v. sodium chloride (1 mEq/ml). ECG, electrophysiologic, and hemodynamic data were recorded at baseline, after each cocaine injection, and after administration of sodium bicarbonate or sodium chloride. In both groups of animals, the first cocaine injection significantly (p < 0.05) prolonged the PR, QTc, AH, and HV intervals, and QRS duration compared with baseline. All intervals continued to lengthen in a dose-dependent manner after the second and third cocaine doses. Sodium bicarbonate significantly (p < 0.05) reduced cocaine-induced prolongation of PR [(147 +/- 5-130 +/- 5 ms), AH (81 +/- 6 - 72 +/- 6 ms), and HV intervals (55 +/- 2 - 39 +/- 1 ms). and QRS duration (96 +/- 6 - 66 +/- 4 ms), peak effect after third cocaine dose versus after sodium bicarbonate, respectively]. Sodium chloride had no effect on reversing cocaine-induced effects on the ECG. Cocaine produces dose-dependent slowing of cardiac conduction that is effectively reversed by sodium bicarbonate. The lack of efficacy of sodium chloride suggests that the increase in arterial pH associated with sodium bicarbonate is responsible for reversal of the effects of cocaine on the ECG. Therefore sodium bicarbonate may be clinically useful in the treatment of cocaine-induced cardiac arrhythmias, primarily as a result of its effects on arterial pH.

Attenuation of the euphoric effects of cocaine by the dopamine D1/D5 antagonist ecopipam (SCH 39166)

BACKGROUND

The subjective and reinforcing effects of cocaine in humans are associated with the enhancement of endogenous dopamine function in the mesolimbic system. This study examined the role of dopamine D1-like receptors in the behavioral and mood effects of cocaine by evaluating the effects of the selective D1/D5 antagonist ecopipam (SCH 39166) on subjective responses to intravenous cocaine in 11 subjects with cocaine dependence as defined by DSM-IV.

METHODS

Subjects were pretreated in a randomized double-blind fashion with either placebo or 10 mg, 25 mg, or 100 mg of ecopipam orally on 4 separate occasions. Two hours later a single intravenous injection of 30 mg of cocaine was administered. Subjective and cardiovascular responses were measured and blood samples for pharmacokinetic evaluation were obtained prior to cocaine dosing and at various times after dosing.

RESULTS

The euphoric (P = .004) and stimulating (P = .03) effects of cocaine were attenuated in a dose-dependent manner by ecopipam, while ratings of desire to take cocaine were diminished (P = .02). Ecopipam in combination with cocaine was safe and well tolerated.

CONCLUSION

These data indicate a potentially important role for D1-like receptors in the acute mood-altering and rewarding effects of cocaine in humans.

Effect of sigma ligands on the cocaine-induced convulsions in mice

It has been hypothesized that some of negative effects exerted by cocaine are mediated via sigma (sigma) receptors. This report demonstrates the effects of selective sigma ligands, panamesine, DTG, rimcazole and SA 4503, on the cocaine-induced convulsions in mice and locomotor hyperactivity in rats. Only panamesine decreased both these effects of cocaine, whereas DTG and rimcazole increased the total time of cocaine-evoked convulsions and locomotor activity. SA 4503 slightly enhanced and prolonged cocaine-induced convulsions but it was ineffective in locomotor hyperactivity test. Moreover, the increase in cocaine-induced locomotor hyperactivity evoked by DTG was antagonized by panamesine. The obtained results indicate that panamesine, a selective sigma ligand with a preference for sigma1 receptor subtype and potential antagonistic activity, decreased the effects of cocaine. DTG and rimcazole (potential sigma1/sigma2 sites agonists) as well as SA 4503 (potential sigma1 site agonist) showed rather opposite effects. These findings support the idea that sigma2 receptor subtype is involved in psychomotor stimulant effects of cocaine while sigma1 receptor subtype participates in the cocaine-induced convulsions. In addition, sigma receptor antagonists (especially sigma1 ones) are able to antagonize toxic effects of cocaine while sigma agonists facilitate them.

Inability of antipsychotics to antagonize the cueing properties of cocaine in rats

In this study the possible antagonistic effects of five different antipsychotics on the discriminative stimulus properties of 10 mg/kg cocaine were evaluated by use of a two-lever food-reinforced drug discrimination procedure in rats. To do so, rats were treated with several doses of haloperidol, risperidone, seroquel, sertindole, and olanzapine, either at 60 or 120 min prior to testing. With all compounds tested, no substantial antagonism of the cocaine cue was observed. Only with haloperidol (maximum 60%), risperidone (maximal 20%), and olanzapine (maximal 20%) a partial antagonism without clearcut dose-response was observed. Clozapine, seroquel, and sertindole did not influence the discriminative stimulus properties of cocaine. These results indicate that antipsychotics with different pharmacological profiles are unable to antagonize more than partially the cueing properties of 10 mg/kg cocaine in rats, pointing to the unique underlying stimulus properties of this stimulant.

Ketoconazole does not block cocaine discrimination or the cocaine-induced reinstatement of cocaine-seeking behavior

Ketoconazole is an FDA-approved antifungal agent that also blocks the synthesis of adrenocorticosteroids and functions as a glucocorticoid receptor antagonist. It has been previously demonstrated that this drug blocks the stress-induced reinstatement of cocaine-seeking behavior and reduces low-dose cocaine self-administration in rats. In the present experiments, the effects of ketoconazole on the cocaine-induced reinstatement of extinguished cocaine-seeking behavior and on cocaine discrimination were investigated in male Wistar rats. In rats trained to self-administer cocaine (0.5 mg/kg/infusion) by pressing a lever under a fixed-ratio 4 schedule of reinforcement, cocaine (5-20 mg/kg, IP) dose dependently reinstated cocaine-seeking behavior following at least 10 days of extinction, during which responding on the cocaine lever resulted in no programmed consequences. Ketoconazole (50 mg/kg, IP) failed to block cocaine-induced reinstatement despite blocking cocaine-induced increases in plasma corticosterone. Ketoconazole (25 or 50 mg/kg) also failed to block cocaine discrimination in rats trained to discriminate 10 mg/kg cocaine from saline. In these rats, generalization to the training dose of cocaine was observed in the absence of increases in plasma corticosterone. The results of these experiments indicate that corticosterone may mediate the effects of stressors on cocaine-seeking behavior but not the direct effects of cocaine itself.

The irreversible gamma-aminobutyric acid (GABA) transaminase inhibitor gamma-vinyl-GABA blocks cocaine self-administration in rats

gamma-Vinyl gamma-aminobutyric acid (GABA) (GVG) is an irreversible inhibitor of GABA transaminase, the primary enzyme involved in GABA metabolism. Acute administration of GVG increases brain GABA levels and blocks cocaine-induced locomotor activity, cocaine-induced lowering of brain stimulation reward thresholds, and cocaine-induced conditioned place preference. To further evaluate the effects of GVG on cocaine-induced reward, we examined its effects on cocaine self-administration in male Wistar rats on fixed ratio 5 and progressive ratio schedules of reinforcement. Additionally, the effects of GVG on operant responding for a food reward were examined on the same two schedules to determine whether the effects of GVG were specific to cocaine reward or generalized to other types of reward. GVG dose dependently decreased responding for cocaine on both schedules of reinforcement, suggesting that GVG attenuated the reward value of the cocaine. Responding for food was also decreased by GVG, suggesting that the effects of increased GABA levels induced by GVG may have a general effect on central reward systems. Data from this and other studies indicate that GVG does not induce motor impairment, decrease spontaneous locomotor activity, or induce catalepsy. Taken together, these data suggest that increases in GABAergic activity induced by GVG have an attenuating effect on centrally mediated reward systems and that the GABA system may be a useful target in the development of new therapeutic strategies for cocaine addiction.

Effects of the NMDA/glycine receptor antagonist, L-701,324, on morphine- and cocaine-induced place preference

Effects of the novel NMDA/glycine receptor antagonist, L-701,324, on morphine- and cocaine-induced conditioned place preference (CPP) were examined in male Wistar rats. After determination of initial preference, animals were conditioned with morphine (5 mg/kg, i.p.) or cocaine (5 mg/kg, i.p.) for 3 conditioning trials, alone or in combination of these drugs with L-701,324 (2.5 mg/kg and 5 mg/kg, p.o.). L-701,324 prevented acquisition of the place preference produced by morphine and cocaine. Administration of L-701,324 on the test day attenuated the expression of morphine-induced CPP, whereas it had no effect on cocaine CPP. When L-701,324 was given alone it did not affect dependent variables (i.e. time spent in non-preferred compartment) suggesting that L-701,324 did not display any reinforcing properties by itself. Our current data suggest that glycine site on the NMDA receptor complex may be involved in the mediation of the rewarding effects of drugs of abuse.

Inhibition by ginsenosides Rb1 and Rg1 of cocaine-induced hyperactivity, conditioned place preference, and postsynaptic dopamine receptor supersensitivity in mice

A single or repeated administration of cocaine (15 mg/kg) in mice produced hyperactivity and conditioned place preference (CPP). Ginsenoside Rb1 (Rb1) and ginsenoside Rg1 (Rg1), prior to and during the cocaine treatment in mice, inhibited cocaine-induced hyperactivity and CPP. The development of enhanced postsynaptic dopamine (DA) receptor sensitivity in mice displaying a cocaine-induced CPP was evidenced by the enhanced response in ambulatory activity to the DA agonist, apomorphine (2 mg/kg). Rb1 and Rg1 inhibited the development of postsynaptic DA receptor supersensitivity. However, Rb1 and Rg1 did not show any antidopaminergic activity at the postsynaptic DA receptors, because the apomorphine-induced climbing behavior was not inhibited by Rb1 and Rg1. Therefore, it is presumed that Rb1 and Rg1 modulate DA activity induced by cocaine at the presynaptic DA receptors, and this modulation results in the inhibition of postsynaptic dopaminergic activation. These results suggest that the cocaine-induced CPP may be associated with enhanced DA receptor sensitivity. The inhibition by Rb1 and Rg1 of cocaine-induced hyperactivity and CPP may be closely related with the inhibition of dopaminergic activation induced by cocaine at the presynaptic DA receptors.

Two novel sigma receptor ligands, BD1047 and LR172, attenuate cocaine-induced toxicity and locomotor activity

The ability of cocaine to interact with sigma receptors indicates that these sites may mediate the negative properties associated with cocaine use, such as toxicity and addiction. Previous studies have shown that the novel sigma receptor ligand, BD1008 (N-[2-(3,4-dicholophenyl)ethyl]-N-methyl-2-(1-pyrrolidinyl)ethylam ine), effectively protects against cocaine-induced convulsions and locomotor activity in mice. Therefore, BD1047 ([2-(3,4-dichlorophenyl)ethyl]-N-methyl-2-(diamino)ethylamine) and LR172 (N-[2-(3,4-dichlorophenyl)ethyl]-N-methyl-2-(1-homopiperidinyl)eth ylamine), two analogs of BD1008, were tested to determine if they also have anti-cocaine properties. Receptor binding assays showed that BD1047 and LR172 both have high affinities for a receptors, but low to negligible affinities for dopamine, opioid, phencyclidine, and 5-HT2 sites. In behavioral studies, pretreatment of mice with BD1047 or LR172 reduced the convulsions, lethality, and locomotor activity produced by cocaine. The data indicates a possible role for sigma receptor ligands in the treatment of cocaine overdose and addiction.

The effects of amperozide on cocaine-induced social withdrawal in rats

Cocaine decreases social interactions in both humans and animals, but it is not known whether the drugged animal withdraws from an undrugged conspecific, the undrugged conspecific avoids the drugged animal, or a combination of these two factors occurs. In the first experiment, the source of cocaine-induced social withdrawal was determined using a tether paradigm, in which the movement of one of the rats was restricted to one half of the observation chamber, such that the freely moving rat had the option of escaping social interactions. There were decreases in social interactions in the condition in which both rats were freely moving, and in the condition in which the undrugged rat was tethered, but not when the drugged rat was tethered and could not escape social contact. A second experiment was conducted to test the efficacy of the potent serotonin receptor antagonist, amperozide, in attenuating cocaine-induced social withdrawal using the condition in which the drugged rat was freely moving. Either amperozide (1.0, 3.0, and 5.0 mg/kg) or saline vehicle was injected into rats 1 h before receiving a 30.0 mg/kg cocaine dose. Cocaine decreased social interactions. Amperozide restored social interactions to near control levels and elevated social interactions in the animals treated with saline vehicle.

Conditioned increase in place preference by access to novel objects: antagonism by MK-801

In three separate place conditioning experiments with rats, repeated access to novel objects in one of two distinct environments conditioned an increase in preference for the novelty-paired environment. A conditioned increase in preference was found whether novel objects were paired with a randomly chosen environment or with the less preferred of two environments (conditioned against a preference). This enhanced preference did not depend on the control group employed. Control groups exposed only to the place conditioning apparatus or to both the apparatus and the novel objects showed no systematic shift in place preference. Intravenous infusions of cocaine also produced an increase in preference using the procedures employed with novel objects. Pretreatment with the N-methyl-D-aspartate (NMDA) receptor antagonist MK-801 (0.03 mg kg(-1)) blocked acquisition of the enhanced place preference conditioned by access to novel objects without decreasing time spent with objects or inducing a place aversion in controls. Combined, these results show that access to novel objects can serve as an appetitive stimulus like drugs of abuse and that this novelty-induced appetitive process involves NMDA receptors. These place-conditioning procedures may provide a good model for determining the behavioral and neural process underlying the appetitive effects of novelty.

Effect of 2,3-dihydroxy-6-nitro-7-sulfamoyl-benzo(f)quinoxaline on methamphetamine- and cocaine-induced behavioral sensitization

The present study investigated the effect of pretreatment with 2,3-dihydroxy-6-nitro-7-sulfamoyl-benzo(f)quinoxaline (NBQX), an alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor antagonist, on behavioral sensitization induced by methamphetamine (METH) and cocaine at doses that are transitional relative to the induction of an acute response of locomotion and interrupting episodes of sniffing and head movement. Male Sprague-Dawley rats were randomly assigned to four groups that received daily either 20 mg/kg NBQX + 3 mg/kg METH, 40 mg/kg NBQX + 3 mg/kg METH, vehicle + 3 mg/kg METH, or vehicle + saline daily for 10 days. In another experiment, rats of four groups received daily either 20 mg/kg NBQX + 15 mg/kg cocaine, 40 mg/kg NBQX + 15 mg/kg cocaine, vehicle + 15 mg/kg cocaine, or vehicle + saline daily for 10 days. NBQX did not attenuate activity/stereotypy induced by acute administration of either psychostimulant. Pretreatment with NBQX did not affect augmentation of activity/stereotypy scores by repeated administration of METH or cocaine. There was no significant difference in the intensity of activity/stereotypy between the NBQX + METH and vehicle + METH groups and between the NBQX + cocaine and vehicle + cocaine groups following a challenge injection with 2 mg/kg METH alone or 15 mg/kg cocaine alone, respectively, given 7 days after the last dose of repeated treatment session. Pretreatment with NBQX alone for 10 days (20 mg/kg for 5 days and 40 mg/kg for subsequent 5 days) did not affect the intensity of activity/stereotypy induced by a challenge injection with 2 mg/kg METH given 7 days after the last dose of repeated injection session. NBQX at 40 mg/kg had no apparent effect on acute METH (3 mg/kg)-induced dopamine release in the striatum. These results suggest tht AMPA receptors are unlikely to be involved in induction of behavioral sensitization that is manifested as augmented activity/stereotypy following repeated administration of METH or cocaine.

Serotonin-4 receptor antagonists reverse cocaine-induced cardiac arrhythmia

The effect of the 5-HT4 antagonists GR113808A and GR125487D on cocaine-induced cardiac arrhythmia was examined in the rat. Cocaine alone, given i.v. at a rate of 2 mg/kg every 5 min, produced an initial increase in blood pressure followed by a severe drop in pressure and bradycardia. Sustained ventricular fibrillation was noted after 6-12 mg/kg cocaine and quickly progressed to asystole. Pretreatment with both GR113808A and GR125487D antagonized these effects in a dose-dependent manner. When given after the onset of arrhythmia, both drugs reversed the cocaine-induced arrhythmia's. Thus, the 5-HT4 antagonists may be useful in the treatment of cocaine toxicity.

Imidazenil, a positive allosteric GABAA receptor modulator, inhibits the effects of cocaine on locomotor activity and extracellular dopamine in the nucleus accumbens shell without tolerance liability

Imidazenil, a benzodiazepine recognition site ligand that acts as partial positive allosteric modulator of gamma-aminobutyric acid (GABA) action at GABAA receptors, inhibits in a dose-dependent manner (0.56-2.5 micromol/kg i.p. to rats) the cocaine-induced increase in dopamine (DA) content in the dialysates of the nucleus accumbens shell and striatum and also inhibits cocaine-induced locomotor activity. Diazepam, a full allosteric modulator of GABA action at GABAA receptors, in a dose of 4.4 micromol/kg i.p. also attenuates the cocaine-induced increase in DA content in the dialysates of nucleus accumbens shell, and striatum and the cocaine-induced locomotor activity. However, imidazenil (2.5 micromol/kg i.p.) fails to reduce spontaneous locomotor activity, whereas diazepam (4.4 micromol/kg i.p.) elicits sedation and ataxia and clearly impairs spontaneous locomotor activity. When added in vitro, both imidazenil and diazepam potentiate the GABA-mediated reduction of the ventral tegmental area DA neuron firing rate. After protracted treatment (14 days/three times a day with an increasing-dose schedule), the inhibitory actions of imidazenil fail to develop tolerance, whereas the actions of diazepam exhibit high tolerance liability. We conclude that imidazenil is devoid of tolerance liability and that, via a GABAA-mediated reduction in the extracellular DA in nucleus accumbens shell, it might reduce the psychomotor activity and reinforcing properties of cocaine.

A catalytic antibody against cocaine prevents cocaine's reinforcing and toxic effects in rats

Cocaine addiction and overdose have long defied specific treatment. To provide a new approach, the high-activity catalytic antibody mAb 15A10 was elicited using a transition-state analog for the hydrolysis of cocaine to nontoxic, nonaddictive products. In a model of cocaine overdose, mAb 15A10 protected rats from cocaine-induced seizures and sudden death in a dose-dependent fashion; a noncatalytic anticocaine antibody did not reduce toxicity. Consistent with accelerated catalysis, the hydrolysis product ecgonine methyl ester was increased >10-fold in plasma of rats receiving mAb 15A10 and lethal amounts of cocaine. In a model of cocaine addiction, mAb 15A10 blocked completely the reinforcing effect of cocaine in rats. mAb 15A10 blocked cocaine specifically and did not affect behavior maintained by milk or by the dopamine reuptake inhibitor bupropion. This artificial cocaine esterase is a rationally designed cocaine antagonist and a catalytic antibody with potential for medicinal use.

Vasopressin opposes locomotor stimulation by ethanol, cocaine and amphetamine in mice

The effects of arginine8-vasopressin on the stimulation of locomotor activity induced by ethanol, cocaine and amphetamine were examined in DBA/2N mice. Locomotor activity was measured by photocell beam interruption for a period of 45 min following ethanol, cocaine or amphetamine administration. Pretreatment with vasopressin alone in a dose of 2 (but not 1) microg/mouse s.c. reduced locomotor activity. The low dose of vasopressin did not modify the stimulation of locomotor activity induced by i.p. administration of ethanol in doses of either 1.5 or 2 g/kg. The high dose of vasopressin reduced locomotor activity induced by both doses of ethanol, in an apparently additive manner. Cocaine in doses of 15 and 20 mg/kg strongly stimulated locomotor activity, but this stimulation was completely antagonized by pretreatment with 1 microg of vasopressin. Similarly, the stimulation of locomotor activity induced by amphetamine (5 mg/kg) was also blocked by pretreatment with vasopressin. These findings raise the possibility that the effect of vasopressin varies with the extent and nature of dopaminergic involvement in the drug-induced stimulation of activity. For drugs like cocaine or amphetamine which stimulate locomotor activity primarily through the mesolimbic dopaminergic system, vasopressin can completely antagonize the stimulation. For ethanol, which stimulates locomotor activity through action on a number of other neurotransmitters as well as dopamine, vasopressin treatment only reduces its stimulation of locomotor activity in an additive manner. These results suggest a close interaction between vasopressin and dopamine action.

A combination of isradipine and naltrexone blocks cocaine's enhancement of a cocaine place preference

Rats were conditioned by pairing cocaine with one side of an alley and placebo with the other. After conditioning, compared to Baseline and a placebo-control group, rats spent more time in the place of cocaine experience. Subsequently, there were further tests except now cocaine was given just before the test session in addition to one of two other kinds of injections. One of these additional injections was a placebo and the other was a combination of a small dose of isradipine (1 mg/kg) and a dose of naltrexone (3 mg/kg) (ISR + NTX). Measures of gross activity (movement from one side of the alley to the other) were taken during testing. ISR + NTX blocked cocaine's ability to sustain a place preference. ISR + NTX also blocked sensitization of cocaine's ability to enhance locomotor activity. This blockade of cocaine's usual effects indicates that ISR + NTX may have a role in treating cocaine use disorders.

Fourphit, an acylating phencyclidine derivative, attenuates cocaine-induced hyperactivity in rats

Fourphit (4-isothiocyanato-1-[1-phenylcyclohexyl]piperidine), an acylating phencyclidine derivative that irreversibly inhibits stimulant binding to the dopamine transporter in vitro (Schweri et al., J. Pharmacol. Exp. Ther. 261:936-942, 1992), was tested in rats for its ability to block the increased locomotor activity caused by cocaine. Administration of Fourphit (20 mg/kg, i.v.) significantly reduced the hyperactivity caused by challenge with either 15 or 40 mg/kg (-)cocaine x HCl (i.p.) 24 h later. It also increased the amount of thigmotaxis and decreased the rearing frequency of rats given the higher dose of cocaine. Only negligible effects on behavior were found upon acute administration of the compound by itself, or in response to a saline challenge 24 h later. Activity during the dark cycle immediately following Fourphit administration, however, was moderately depressed. Contrary to the results predicted from its activity in vitro, Fourphit did not inhibit the ex vivo binding of [3H]methylphenidate to stimulant receptors in the striatal tissue of treated rats. These results show that Fourphit can antagonize some behavioral actions of cocaine, but these effects are not likely due to covalent modification of the site on the dopamine transporter recognized by cocaine.

Influence of SCH23390 and spiperone on the expression of conditioned place preference induced by d-amphetamine or cocaine in the rat

The present study investigated the effects of selective dopamine D1 and D2 receptor antagonists, SCH23390 and spiperone, on the expression of conditioned place preference (CPP) induced by either d-amphetamine or cocaine. The CPP protocol consisted of three phases: pre-conditioning exploration, conditioning, and a post-conditioning test. The data indicated that CPP was significantly induced by intraperitoneal injection of either d-amphetamine (2 mg/kg) or cocaine (10 mg/kg). The expression of d-amphetamine CPP was significantly inhibited by SCH23390 (0.08, 0.16 mg/kg) and spiperone (0.15 mg/kg) when given alone before the post-conditioning test session. In contrast, such pretreatment to produce antagonistic effects was not observed for cocaine CPP. However, the expression of cocaine CPP was significantly attenuated by a combination of SCH23390 and spiperone administered prior to the test session. These data indicate that the rewarding properties of d-amphetamine and cocaine as expressed under the CPP task may depend upon different neural substrates. The degrees of D1 and D2 receptors involved in mediating the expression of CPP induced by d-amphetamine and cocaine are different.

Effects of heroin/cocaine combinations in rats trained to discriminate heroin or cocaine from saline

The effects of heroin and cocaine administered alone or in combination were examined in rats trained to discriminate either heroin (0.56 mg/kg i.p.; n = 6) or cocaine (5.6 mg/kg i.p.; n = 6) from saline. Heroin (0.032-1.8 mg/kg) substituted completely for the heroin training stimulus in all six heroin-trained rats, but failed to substitute for cocaine in any of the cocaine-trained rats. Cocaine (0.1-32 mg/kg) substituted completely for the cocaine training stimulus in all six cocaine-trained rats, and substituted for heroin in two of six heroin-trained rats. The opioid antagonist naltrexone (0.01-1.0 mg/kg) antagonized the discriminative stimulus effects of heroin, but naltrexone at doses up to 10 mg/kg had no effect on the discriminative stimulus effects of cocaine. The dopamine receptor antagonist flupenthixol (0.032-0.56 mg/kg) attenuated the discriminative stimulus effects of heroin and completely blocked the discriminative stimulus effects of cocaine. When heroin-cocaine combinations were administered to the heroin-trained rats, cocaine (1-5.6 mg/kg) did not significantly alter the mean heroin dose-effect curve. Similarly, in the cocaine-trained rats, heroin (0.1-0.56 mg/kg) did not significantly alter the mean cocaine dose-effect curve. These results suggest that combinations of heroin and cocaine usually produce discriminative stimulus effects similar to either heroin or cocaine alone.

In vivo ibogaine blockade and in vitro PKC action of cocaine

Ibogaine may have antiaddiction potential against alcohol, psychostimulant and opiate abuse, but its mechanism of action is unclear. Ibogaine, however, has been demonstrated in numerous studies to have effects in multiple central nervous system (CNS) neurotransmitters systems. We are using in vitro and in vivo systems to study the effects of cocaine and whether these effects can be blocked by ibogaine. For the in vivo studies, we first determined the acute and subacute effects of ibogaine (1-5.0 mg/kg) in mice using the plus-maze test. Acutely increasing doses of ibogaine produced a reduced aversion to the open arms. The subacute administration provoked a variable response which was characterized by fluctuations in aversive and antiaversive behavior of the animals to the open arms of the plus-maze during the 14-day treatment period. A separate group of mice received 1.0 mg/kg cocaine for 14 days, and upon abrupt cessation from cocaine treatment, ibogaine 2.5 mg/kg was administered to a subgroup of these mice. Ibogaine reversed the withdrawal aversions produced by the abrupt cessation from cocaine administration. For the in vitro studies, the expression and activity of protein kinase C (PKC) isoforms and Ca2+ levels were examined following the incubation of PC 12 cells with cocaine. This is because PKC plays a key role in a number of cellular and neuronal functions. We report that cocaine disrupts signal transduction in PC 12 cells by altering the expression and activity of PKC isoforms and Ca2+ levels. The data obtained suggest (1) that the PC 12 cells may be useful in studying the neurobiology of abused drugs, like cocaine in vitro, (2) that if anxiety is a factor in drug dependency, then the antiaddictive property of ibogaine in vivo may be associated with modifying the CNS neurotransmission that may be involved in anxiety. It remains to be determined whether the signaling involving PKC is important in the antiaddictive properties of ibogaine.

Isradipine prevents global and regional cocaine-induced changes in brain blood flow: a preliminary study

The L-type calcium channel antagonist, isradipine, reduces brain ischemia in animal models of ischemic stroke. These effects of isradipine appear more pronounced in dopamine (DA) rich brain regions. These same DA-rich brain regions have also been shown to be the areas most affected by cocaine-induced ischemic changes. Using a novel quantified approach to single photon emission computerized tomography, we demonstrated that isradipine pre-treatment prevented cocaine-induced ischemic changes, especially in these DA-rich brain regions. This is the first demonstration that any medication, including isradipine, can prevent the ischemic effects of cocaine on brain blood flow. Isradipine may, therefore, be a useful therapeutic agent for the prevention of brain ischemia in cocaine addicts.

Effects of buprenorphine and Ro 15-4513 on delayed death and brain beta-endorphin levels in rats treated with cocaine or cocaine-ethanol

The present study was aimed at elucidating the relationship between brain beta-endorphin, which was estimated by the immunofluorescence method, and fatal drug toxicities due to cocaine and combined cocaine-ethanol administration, including the late fatal toxicities clinically noted. beta-endorphin is an endogenous opioid peptide, and its secretion has been suggested to be influenced by physiological stresses. Furthermore, since protection against these fatal toxicities has been previously reported to be provided by buprenorphine (a ligand for opioid receptors) and Ro 15-4513 (a ligand for benzodiazepine receptors), this study also focused on the relationship between the effects of these two ligands and the changes in brain beta-endorphin immunoreactivity. In the fatal toxicity study, a toxic dose (75 mg/kg, i.p.) of cocaine combined with and without ethanol (3 g/kg, i.p.) was administered to the rats, with and without buprenorphine (0.25, 0.5, 1 mg/kg, i.p.) or Ro 15-4513 (5, 10, 15 mg/kg, i.p.). All of the deaths that occurred in these animals were divided into two groups: early deaths with early toxic symptoms in which the drugs were detected in the tissue samples, and late deaths with late toxic symptoms in which no drugs were detected in the samples. Without the administration of buprenorphine or Ro 15-4513, the frequency of late deaths was higher in the cocaine group as compared to the cocaine-ethanol group. The total mortality rate was effectively attenuated by treatment with 0.25 mg/kg buprenorphine or 10 mg/kg Ro 15-4513. Following treatment with 1 mg/kg buprenorphine or 15 mg/kg Ro 15-4513, the frequency of late deaths was significantly enhanced in the cocaine group. The brain and liver cocaethylene concentrations were also attenuated in those groups in which the total mortality rates were attenuated. In the brain beta-endorphin immunoreactivity study, the number of beta-endorphin immunoreactive nerve cells at the arcuate nucleus was counted at 3 minutes or 24 hours after the drug treatment. At 3 minutes after the drug treatment, the number of weakly immunoreactive cells with photographic light absorption values greater than 50% was enhanced in the groups in which the frequency of late deaths had been increased. In the cocaine-ethanol groups treated with buprenorphine or Ro 15-4513, this enhancement of weakly immunoreactive cells was observed when the total mortality rate was increased, regardless of the type of death. At 24 hours after the drug treatment (50 mg/kg cocaine), an enhancement of the weakly immunoreactive cells only was observed in all of the groups in which the occurrence of toxicities had been enhanced, regardless of the type of toxicity. Therefore, it can be concluded that the enhancement of total brain beta-endorphin immunoreactivity was closely correlated with the increase in the frequency of total fatal toxicities, and that the enhancement of weakly immunoreactive cells was closely correlated with the increase in the frequency of delayed fatal toxicities.