Cocaine, norcocaine, ecgonine methylester and benzoylecgonine pharmacokinetics in the rat

Pharmacokinetic and pharmacodynamic analyses of cocaine and its metabolites in behaviorally divergent inbred mouse strains

Cocaine (COC) is a psychostimulant with a high potential for abuse and addiction. Risk for COC use disorder is driven, in part, by genetic factors. Animal models of addiction-relevant behaviors have proven useful for studying both genetic and nongenetic contributions to drug response. In a previous study, we examined initial locomotor sensitivity to COC in genetically diverse inbred mouse strains. That work highlighted the relevance of pharmacokinetics (PK) in initial locomotor response to COC but was limited by a single dose and two sampling points. The objective of the present study was to characterize the PK and pharmacodynamics of COC and its metabolites (norcocaine and benzoylecgonine) in six inbred mouse strains (I/LnJ, C57BL/6J, FVB/NJ, BTBR T+ tf/J, LG/J and LP/J) that exhibit extreme locomotor responses to cocaine. Mice were administered COC at one of four doses and concentrations of cocaine, norcocaine and benzoylecgonine were analyzed in both plasma and brain tissue at 5 different time points. Initial locomotor sensitivity to COC was used as a pharmacodynamic endpoint. We developed an empirical population PK model that simultaneously characterizes cocaine, norcocaine and benzoylecgonine in plasma and brain tissues. We observed interstrain variability occurring in the brain compartment that may contribute to pharmacodynamic differences among select strains. Our current work paves the way for future studies to explore strain-specific pharmacokinetic differences and identify factors other than PK that are responsible for the diverse behavioral response to COC across these inbred mouse strains.

Effects of ecgonine methyl ester on cognition in scopolamine-impaired and aged rats

RATIONALE

Searches for antidotes to cocaine, and for cognition enhancers potentially applicable to Alzheimer's disease, have revealed a novel regulatory site on nicotinic acetylcholine receptors. In the presence of an agonist, inhibitors binding to this site changed the ion channel equilibrium from the open-channel form towards the closed form. Other, related, molecules could bind to the site without changing the equilibrium. These latter compounds were predicted to displace the inhibitors without affecting receptor function per se. These compounds alleviated the inhibition. One of them is ecgonine methyl ester (EME), which is generally described as inactive, but this work suggested a beneficial effect on cognition.

OBJECTIVE

This in vivo study tested for cognitive enhancement by EME in scopolamine-impaired, and aged, rats.

METHODS

Memory was the primary endpoint, but thigmotaxis became an important secondary endpoint in the light of observations made during the study. Impaired cognition was pharmacologically induced by scopolamine in young rats, and spontaneously present in aged rats. Learning ability before and after administration of EME was tested in Morris water maze protocols. Concentrations of EME in the brain and plasma were analyzed by gas chromatography-mass spectrometry.

RESULTS

A single dose of EME reversed scopolamine impairment, indicating involvement of acetylcholine receptors. Longer-term treatment improved cognition in aged rats, with enhanced rates of learning in the absence of an exogenous cognition-impairing compound. Impairment returned with a new challenge; the improvement could be re-established with continued dosing. EME also reversed thigmotaxis seen in aged rats; thigmotaxis is believed to indicate anxiety. The concentrations of EME in the brain proved adequate drug exposure.

CONCLUSIONS

Since other investigators have shown cognition impairment caused by cocaine in aged rats, this work shows that cocaine and EME have opposite effects in Morris water maze models. EME might induce cognitive enhancement and relief of anxiety in cocaine-impaired humans, and in other cognitive disorders.

Emergence of negative affect as motivation for drug taking in rats chronically self-administering cocaine

RATIONALE

The role of negative affect as a motivational factor in animal models of drug addiction has been underexplored in the context of cocaine self-administration.

OBJECTIVES

The present investigation studied the relationship between magnitude of affective response and quantity of cocaine consumed in order to clarify the affective components that drive drug use in a preclinical model.

METHODS

Rats self-administered (SA) cocaine 6 h/day for 14 consecutive days while their ultrasonic vocalizations (USVs) were recorded.

RESULTS

Animals displayed an increase in 50-kHz call rates (indicating positive affect) when their drug levels were rapidly rising and an increase in 22-kHz call rates (indicating negative affect) when forced to abstain. The rate of 50-kHz calls predicted drug consumption during the 1st week of SA, but not week two. Contrarily, there was a strongly predictive positive association between rate of 22-kHz calls and amount of drug consumed during the 2nd week of SA.

CONCLUSIONS

Experimental results indicate that after chronic cocaine self-administration, negative affect emerges when animals are deprived of expected drug during withdrawal. Moreover, the increase in USVs indicating negative affect when deprived of drug was directly related to drug intake, concurrent with a decay in the direct relationship between USVs indicating positive affect and drug intake. The present preclinical support for the widely hypothesized shift from positive to negative affect as a salient motivational factor in human drug abuse adds to growing evidence of the unique value of rat USVs for understanding the role of emotion in drug addiction.

Preconception maternal cocaine self-administration increases the reinforcing efficacy of cocaine in male offspring

RATIONALE

Although the influence of gestational cocaine exposure on offspring has been the focus of a sustained research effort, the effect of preconception cocaine self-administration by dams on progeny has received far less attention.

METHOD

In the current study, adult female rats were allowed to self-administer cocaine 2 h a day for 60 days and then after a 10-day wash out period, bred to naïve males. Maternal behavior was measured in dams until weaning. When male and female progeny reached adulthood, anxiety-like behavior, memory, and cocaine self-administration were assessed in separate cohorts of rats.

RESULTS

Despite a total of at least 30 days of cocaine abstinence, the quality of maternal behaviors was negatively affected by previous cocaine exposure as reflected by less time spent with pups as well as an excess of other maladaptive maternal behaviors. Measures of anxiety-like behavior and memory were not affected by maternal cocaine intake in either male or female offspring. In contrast, male, but not female, the progeny of dams exposed to cocaine showed increased reinforcing efficacy of cocaine as measured by cocaine self-administration under a progressive ratio schedule. The fact that cocaine self-administration was influenced only in the male offspring of cocaine-exposed dams argues against this phenotype being linked to altered maternal behavior, although this possibility cannot be ruled out completely.

CONCLUSIONS

Collectively, these results indicate that preconception cocaine self-administration by dams results in the relatively selective enhancement of cocaine addiction-like behavior in male offspring.

Revisiting a physiologically based pharmacokinetic model for cocaine with a forensic scope

A whole-body permeability-rate-limited physiologically based pharmacokinetic (PBPK) model for cocaine was developed and adjusted with the pharmacokinetic data from studies with animals and reparametrized scaling to humans with the aim to predict the concentration-time profiles of the drug in blood and different tissues in humans. Estimated time course concentrations could be used as an interpretation tool by forensic toxicologists. The model estimations were compared successfully with pharmacokinetic parameters and time to peak for some effects reported in the literature. Once developed, the PBPK model was employed to predict the time course tissue concentrations reported in previous distribution studies introducing individualizing data. The heart and brain concentrations estimated by the model match adequately with the time and duration of some effects such as chronotropic and psychoactive effects, respectively. This work is the first attempt for employing PBPK modeling as a tool for forensic interpretation. Future modeling of other cocaine metabolite profiles or interaction when co-administered with other substances, such as alcohol, might be developed in the future.

Large-Scale, Ion-Current-Based Proteomic Investigation of the Rat Striatal Proteome in a Model of Short- and Long-Term Cocaine Withdrawal

Given the tremendous detriments of cocaine dependence, effective diagnosis and patient stratification are critical for successful intervention yet difficult to achieve due to the largely unknown molecular mechanisms involved. To obtain new insights into cocaine dependence and withdrawal, we employed a reproducible, reliable, and large-scale proteomics approach to investigate the striatal proteomes of rats (n = 40, 10 per group) subjected to chronic cocaine exposure, followed by either short- (WD1) or long- (WD22) term withdrawal. By implementing a surfactant-aided precipitation/on-pellet digestion procedure, a reproducible and sensitive nanoLC-Orbitrap MS analysis, and an optimized ion-current-based MS1 quantification pipeline, >2000 nonredundant proteins were quantified confidently without missing data in any replicate. Although cocaine was cleared from the body, 129/37 altered proteins were observed in WD1/WD22 that are implicated in several biological processes related closely to drug-induced neuroplasticity. Although many of these changes recapitulate the findings from independent studies reported over the last two decades, some novel insights were obtained and further validated by immunoassays. For example, significantly elevated striatal protein kinase C activity persisted over the 22 day cocaine withdrawal. Cofilin-1 activity was up-regulated in WD1 and down-regulated in WD22. These discoveries suggest potentially distinct structural plasticity after short- and long-term cocaine withdrawal. In addition, this study provides compelling evidence that blood vessel narrowing, a long-known effect of cocaine use, occurred after long-term but not short-term withdrawal. In summary, this work developed a well-optimized paradigm for ion-current-based quantitative proteomics in brain tissues and obtained novel insights into molecular alterations in the striatum following cocaine exposure and withdrawal.

Strain and cocaine-induced differential opioid gene expression may predispose Lewis but not Fischer rats to escalate cocaine self-administration

The aim of the present study was to investigate alterations in gene expression of opioid system components induced by extended access (18 h) cocaine self-administration and to determine the impact of genetic background in the vulnerability to escalate cocaine intake. Comparing two inbred rat strains, we previously reported that Lewis rats progressively escalated cocaine consumption compared to Fischer rats, in a new translational model of intravenous cocaine self-administration, which included 14 sessions of 18-h operant sessions in which rats were allowed to select the cocaine unit dose to self-administer. We compare here Fischer and Lewis rats in the gene expression of endogenous opioid peptides (Pomc, Penk, Pdyn) and cognate receptors (Oprm, Oprk and Oprd) in reward-related brain regions, after exposure to either cocaine self-administration or yoked-saline, in the aforementioned translational paradigm. We performed a correlation analysis between the mRNA level, found in the Dorsal Striatum (DS), Nucleus accumbens (NAcc) shell and core respectively, and individual cocaine intake. Our findings show that the gene expression of all the aforementioned opioid genes exhibit strain-dependent differences in the DS, in absence of cocaine exposure. Also, different strain-specific cocaine-induced mRNA expression of Oprm and Oprk was found in DS. Only few differences were found in the ventral parts of the striatum. Moreover, gene expression level of Pdyn, Penk, Oprk, and Oprm in the DS was significantly correlated with cocaine intake only in Fischer rats. Overall, these data shed light on potential genetic differences which may predispose of subjects to initiate and escalate cocaine consumption.

LC/MS/MS evaluation of cocaine and its metabolites in different brain areas, peripheral organs and plasma in cocaine self-administering rats

BACKGROUND

We employed a cocaine intravenous self-administration model based on positive reinforcement of animals' instrumental reactions (i.e., lever pressing) rewarded by a dose of the drug. We also carried out simultaneous characterization of the pharmacokinetics of cocaine and its metabolites in rats during withdrawal; in this part of the experiments, we investigated the cocaine (2 mg/kg, iv)-induced changes in the distribution, rate constant, clearance and t₁/₂ of the parent drug and its metabolites in different structures of the brain and in peripheral tissues.

METHODS

By using liquid chromatography-tandem mass spectrometry (LC/MS/MS) we measured the levels of cocaine and its major metabolites.

RESULTS

Our results demonstrate differences in the levels of cocaine after cocaine self-administration in the rat, with the highest concentration seen in the striatum and the lowest in the cerebellum. Cocaine metabolites determined in the rat brain remained at very low levels (benzoylecgonine), irrespectively of the brain area, whereas the norcocaine concentration varied from 1.56 μg/g (the nucleus accumbens) to 2.73 μg/g (the striatum).

CONCLUSION

A tandem LC/MS/MS is a valid method for evaluation of brain and peripheral levels of cocaine and its metabolites. Our results demonstrate brain area-dependent differences in the levels of cocaine after its self-administration in the rat. There were also differences in pharmacokinetic parameters among the brain areas and peripheral tissues following a bolus iv injection of cocaine to rats withdrawn from cocaine; among brain structures the slowest metabolic rate was detected for the striatum.

Probing cocaine-antibody interactions in buffer and human serum

Background

Despite progress in cocaine immunotherapy, the kinetic and thermodynamic properties of antibodies which bind to cocaine and its metabolites are not well understood. It is also not clear how the interactions between them differ in a complex matrix such as the serum present in the human body. In the present study, we have used microscale thermophoresis (MST), isothermal titration calorimetry (ITC), and surface plasmon resonance (SPR) we have evaluated the affinity properties of a representative mouse monoclonal (mAb08) as well as those of polyclonal antibodies purified from vaccinated mouse and human patient serum.

Results

MST analysis of fluorescently tagged mAb08 binding to cocaine reveals an approximately 15 fold decrease in its equilibrium dissociation constant in 20–50% human serum compared with that in saline buffer. A similar trend was also found using enriched polyclonal antibodies purified from vaccinated mice and patient serum, for which we have used fluorescently tagged bovine serum albumin conjugated to succinyl norcocaine (BSA-SNC). This conjugate closely mimics both cocaine and the hapten used to raise these antibodies. The ITC data also revealed that cocaine has a moderate affinity of about 2 µM to 20% human serum and very little interaction with human serum albumin or nonspecific human IgG at that concentration range. In a SPR inhibition experiment, the binding of mAb08 to immobilized BSA-SNC was inhibited by cocaine and benzoylecgonine in a highly competitive manner, whereas the purified polyclonal antibodies from vaccinated humans and mice, revealed preferential selectivity to pharmacologically active cocaine but not to the inactive metabolite benzoylecgonine. We have also developed a simple binding model to simulate the challenges associated with cocaine immunotherapy using the variable quantitative and kinetic properties of the antibodies.

Conclusions

High sensitivity calorimetric determination of antibody binding to cocaine and its metabolites provide valuable information for characterization of their interactions and thermodynamic properties. In addition MST measurements of antibody affinity in the presence of biological fluids will provide a better opportunity to make reliable decisions and facilitate the design of cocaine vaccines and immunization conditions. The methods should be more widely adopted in characterization of antibody complexes.

Differential effects of cocaine on dopamine neuron firing in awake and anesthetized rats

Cocaine (benzoylmethylecgonine), a natural alkaloid, is a powerful psychostimulant and a highly addictive drug. Unfortunately, the relationships between its behavioral and electrophysiological effects are not clear. We investigated the effects of cocaine on the firing of midbrain dopaminergic (DA) neurons, both in anesthetized and awake rats, using pre-implanted multielectrode arrays and a recently developed telemetric recording system. In anesthetized animals, cocaine (10 mg/kg, intraperitoneally) produced a general decrease of the firing rate and bursting of DA neurons, sometimes preceded by a transient increase in both parameters, as previously reported by others. In awake rats, however, injection of cocaine led to a very different pattern of changes in firing. A decrease in firing rate and bursting was observed in only 14% of DA neurons. Most of the other DA neurons underwent increases in firing rate and bursting: these changes were correlated with locomotor activity in 52% of the neurons, but were uncorrelated in 29% of them. Drug concentration measurements indicated that the observed differences between the two conditions did not have a pharmacokinetic origin. Taken together, our results demonstrate that cocaine injection differentially affects the electrical activity of DA neurons in awake and anesthetized states. The observed increases in neuronal activity may in part reflect the cocaine-induced synaptic potentiation found ex vivo in these neurons. Our observations also show that electrophysiological recordings in awake animals can uncover drug effects, which are masked by general anesthesia.

The effect of ethanol on oral cocaine pharmacokinetics reveals an unrecognized class of ethanol-mediated drug interactions

Ethanol decreases the clearance of cocaine by inhibiting the hydrolysis of cocaine to benzoylecgonine and ecgonine methyl ester by carboxylesterases, and there is a large body of literature describing this interaction as it relates to the abuse of cocaine. In this study, we describe the effect of intravenous ethanol on the pharmacokinetics of cocaine after intravenous and oral administration in the dog. The intent is to determine the effect ethanol has on metabolic hydrolysis using cocaine metabolism as a surrogate marker of carboxylesterase activity. Five dogs were administered intravenous cocaine alone, intravenous cocaine after ethanol, oral cocaine alone, and oral cocaine after ethanol on separate study days. Cocaine, benzoylecgonine, and cocaethylene concentrations were determined by high-performance liquid chromatography. Cocaine had poor systemic bioavailability with an area under the plasma concentration-time curve that was approximately 4-fold higher after intravenous than after oral administration. The coadministration of ethanol and cocaine resulted in a 23% decrease in the clearance of intravenous cocaine and a 300% increase in the bioavailability of oral cocaine. Cocaine behaves as a high extraction drug, which undergoes first-pass metabolism in the intestines and liver that is profoundly inhibited by ethanol. We infer from these results that ethanol could inhibit the hydrolysis of other drug compounds subject to hydrolysis by carboxylesterases. Indeed, there are numerous commonly prescribed drugs with significant carboxylesterase-mediated metabolism such as enalapril, lovastatin, irinotecan, clopidogrel, prasugrel, methylphenidate, meperidine, and oseltamivir that may interact with ethanol. The clinical significance of the interaction of ethanol with specific drugs subject to carboxylesterase hydrolysis is not well recognized and has not been adequately studied.

Rapid and robust protection against cocaine-induced lethality in rats by the bacterial cocaine esterase

There is no approved means to prevent the toxic actions of cocaine. Cocaine esterase (CocE) is found in a rhodococcal strain of bacteria that grows in the rhizosphere soil around the coca plant and has been found to hydrolyze cocaine in vitro. The esteratic activity of CocE (0.1-1.0 mg, i.v.) was characterized and confirmed in vivo by assessing its ability to prevent cocaine-induced convulsions and lethality in the rat. The therapeutic efficiency of the enzyme was demonstrated by the increasing dose of cocaine (100-1000 mg/kg, i.p.) required to produce toxic effects after a single intravenous injection of CocE. The enzyme demonstrated rapid kinetics for cocaine degradation in rat and human serum. Two catalytically inactive mutants of CocE (S117A or Y44F) failed to protect rats from the toxic effects of cocaine, confirming the protective effects are due to hydrolytic activity. However, butyrylcholinesterase, an endogenous cocaine-hydrolyzing enzyme, was inactive (1.3-13 mg, i.v.) in this rat toxicity procedure. Furthermore, CocE did not block the lethality of WIN-35065-2 (560 mg/kg, i.p.), a cocaine analog that lacks the benzoyl ester moiety targeted by CocE. This characterization of CocE provides preliminary evidence that the enzyme could serve as a suitable antidote to cocaine toxicity in humans.

Maternal Separation and Handling Affects Cocaine Self-Administration in Both the Treated Pups as Adults and the Dams

Repeated maternal separation of pups from dams is often used as an early life stressor that causes profound neurochemical and behavioral changes in the pups that persist into adulthood. The effects of maternal separation on both the dams and the treated pups as adults on cocaine self-administration were examined using four separation conditions: 15- or 180-min separation (MS15 and MS180), brief handling without separation (MS0), and a nonhandled group (NH). The separations and handling occurred daily on postnatal days 2 to 15. The acquisition of cocaine self-administration (0.0625-1.0 mg/kg/infusion) was evaluated in the treated pups as adults. The MS180 group acquired cocaine self-administration at the lowest dose tested (0.0625 mg/kg/infusion), whereas the MS15s did not respond for cocaine at rates greater than that seen with saline administration. The NH group received the greatest number of infusions and intake at the highest doses. After self-administration, no differences were observed between groups in activity of two liver carboxylesterases involved in the inactivation of cocaine, ES10 and ES4. Maternal separation affected cocaine self-administration in the dams as well. Although there was an overall significant affect of treatment on cocaine self-administration, the length of separation (15 or 180 min) did not affect cocaine self-administration on the dams. The MS0 dams averaged a greater number of infusions per session than NH group during the 1st week of acquisition. These data suggest that in addition to the profound changes that occur in pups as result of maternal separation, the dams are also susceptible to alterations in behaviors.

Estrogen and progesterone affect cocaine pharmacokinetics in female rats

Several studies have reported sex differences in behavioral responses to cocaine whereby females display a greater degree of locomotor activity. Fluctuations in estrogen and progesterone during the estrous cycle have been postulated to underlie these behavioral differences. In this study, we tested the hypothesis that hormonal replacement (estrogen or progesterone) in ovariectomized rats affects cocaine pharmacokinetics. We found that estrogen replacement did not affect cocaine-induced locomotor activity, but progesterone attenuated locomotor counts in comparison with control groups receiving only sesame oil. Estrogen, however, decreased brain levels of cocaine and norcocaine 30 min after cocaine administration in comparison to the group-receiving vehicle at that time point. In addition, in progesterone-treated rats, levels of benzoylecgonine and ecgonine methylester were higher at 30 min post-administration than at 15 min. No changes were found in blood levels of the metabolites. These findings suggest that while progesterone has an impact on locomotor behavior, pharmacokinetic effects may have a limited role in mediating behavioral responses to cocaine.

A reliable model of intravenous MDMA self-administration in naïve mice

RATIONALE

MDMA is one of the most widely consumed recreational drugs in Europe. However, the mechanisms involved in the reinforcing properties of MDMA are still unclear. In this sense, the establishment of a reliable model of MDMA self-administration in mice could represent an important approach to study the neuronal substrates associated with MDMA reward by using genetically modified mice.

OBJECTIVES

To develop a reliable model of operant intravenous MDMA self-administration in drug-naïve mice.

MATERIALS AND METHODS

Mice were trained to acquire intravenous self-administration of MDMA at different doses (0, 0.06, 0.125, 0.25, 0.5 and 1.0 mg/kg/infusion) on a FR1 schedule of reinforcement for 15 consecutive days. The motivational value of different doses of MDMA (0.125, 0.25 and 0.5 mg/kg/infusion) was then tested using a progressive ratio paradigm. Finally, [3H]-mazindol autoradiographic studies were carried out in order to quantitatively assess presynaptic dopamine transporter (DAT) binding sites in the striatum of mice trained to self-administer MDMA (0 and 1.0 mg/kg/infusion) during 15 days.

RESULTS

The latency for discrimination between the active and inactive holes, as well as the number of animals acquiring stability criteria, varied as a function of the dose of MDMA. The mice responding for intermediate doses (0.125, 0.25 and 0.5 mg/kg/infusion) discriminated earlier than those responding for low (0.06 mg/kg/infusion) or high (1.0 mg/kg/infusion) doses. The percentage of animals achieving stability criteria increased with days of testing and was inversely proportional to the dose of MDMA. The breaking points achieved for doses of 0.125 and 0.25 mg/kg/infusion were significantly higher than for a dose of 0.5 mg/kg/infusion. No significant DAT neurotoxicity was observed in the striatum of animals self-administering MDMA at a dose of 1 mg/kg/infusion.

CONCLUSIONS

The present results show that MDMA can be reliably self-administered by drug-naïve mice.

Sex differences in cocaine-induced behavioral responses, pharmacokinetics, and monoamine levels

Female rats display a more robust behavioral response to acute cocaine administration than do male rats. However, a clear understanding of the biological mechanisms underlying these differences remains elusive. The present study investigated whether sexual dimorphisms in cocaine-induced motor behavior might be based on monoaminergic levels and/or cocaine pharmacokinetics. An acute injection of cocaine (5, 15, 20 or 30 mg/kg) or saline was administered to male and female rats, and behavioral activity was monitored for 3 h. Following acute cocaine or saline administration motor behavior varied according to dose and sex; overall, female rats displayed greater rearing counts and stereotypic scores, greater total locomotor counts at 15, 20, and 30 mg/kg of cocaine, and greater ambulatory counts at 20 and 30 mg/kg of cocaine than did male rats. Neurochemical determinations in post-mortem tissue showed that both male and female rats had increases in total dopamine (DA) in the caudate putamen (CPu) 15 min following cocaine administration. Additionally, male rats had a decrease in dihydroxyphenylacetic acid (DOPAC)/DA turnover. Female rats showed significant reductions in total levels of DA, DOPAC, HVA, serotonin (5-HT), 5-hydroxyindole acetic acid (5-HIAA), and DOPAC/DA turnover in the nucleus accumbens (NAc). Male rats displayed a reduction only in DOPAC/DA turnover and increases in 5-HT in the NAc following cocaine administration. Furthermore, sex differences in cocaine metabolism were observed where females had greater brain/blood levels of norcocaine and ecgonine methyl ester while male rats had higher blood levels of benzoylecgonine. These results suggest that sex differences in the behavioral responses to cocaine administration could be explained in part by intrinsic differences in both monoaminergic levels and metabolic processes.

Cocaine acts on accumbens monoamines and locomotor behavior via a 5-HT2A/2C receptor mechanism as shown by ketanserin: 24-h follow-up studies

It is well known that cocaine's psychomotor stimulant properties derive from enhanced monoamines via synaptic transporter/reuptake inhibition and release mechanisms. However, to further understand mechanisms of action for cocaine, which may be receptor-related, ketanserin, a selective 5-HT(2A/2C) antagonist was used to ascertain a possible mediation for 5-HT(2A//2C) receptors in the monoamine and behavioral responses to cocaine. The studies were performed in the freely moving and behaving animal with In Vivo Microvoltammetry. Miniature carbon sensors, BRODERICK PROBE microelectrodes detected dopamine (DA) and serotonin (5-HT) concentrations in Nucleus Accumbens (NAcc) of male, Sprague-Dawley laboratory rats in separate signals and within seconds while at the same time, locomotor behavior was monitored with infrared photobeams. Synaptic release of each monoamine was detected because separate studies showed that the depolarization blocker, gamma-butyrolactone (gamma BL), decreased steady-state values [Pharmacol. Biochem. Behav. 40 (1991) 969]. Acute studies (Day 1) were performed; the animals received single injection of drug(s) in the faradaic behavioral chamber after a stable baseline during habituation behavior was achieved. After completion of the study, the animals were returned to their home cages. Subacute studies (Day 2) were also performed; these took place 24 h later in the faradaic behavioral chamber; same animal control was used and no further drug was administered. Day 2 data were compared to baseline (habituation data) on Day 1. Results showed that (1) Acute administration of Cocaine (10 mg/kg, i.p.) (N=5) increased DA and 5-HT release above baseline (p<0.001) while locomotion was also increased above baseline (p<0.001). (2) In Subacute studies in the cocaine group, when no further drug was administered, DA release decreased (p<0.001) and decreases in 5-HT release also occurred throughout the time course (p<0.05). Locomotor behavior increased above baseline and showed a trend toward statistical significance (p<0.07). (3) Acute administration of Ketanserin/Cocaine (3 mg/kg s.c. and 10 mg/kg i.p., respectively) (N=6) showed that ketanserin antagonized DA and 5-HT release (p<0.001), while locomotion was antagonized as well (p<0.001). (4) In Subacute studies, in the ketanserin/cocaine group, when no further drug was administered, DA decreased (p<0.001), but 5-HT increased (p<0.001), while locomotor activity increased above baseline and a trend toward statistical significance was seen (p<0.07). Additional saline controls were without effect (p>0.05). In summary, Acute studies showed that cocaine produced its psychostimulant responses on monoamines and behavior and ketanserin antagonized these responses, likely via a 5-HT(2A/2C) receptor mediation. Presynaptic and postsynaptic responses were not distinguished, suggesting, in addition, a role for 5-HT-ergic modulation of DA, likely DA(2) postsynaptic modulation Subacute cocaine studies showed that on Day 2, deficiencies in monoamines occurred, reflecting cocaine withdrawal mechanisms neurochemically, while locomotor behavior did not show such dramatic deficiencies. Indeed, behavior increased above baseline. Moreover, ketanserin reversed 5-HT-related and not DA-related cocaine monoamine responses, while locomotion continued to be insignificantly increased above baseline as was seen in the Subacute cocaine group. The data suggest that presynaptic 5-HT(2A/2C) receptor mechanisms may be important during withdrawal from single injection of cocaine.

Clozapine and cocaine effects on dopamine and serotonin release in nucleus accumbens during psychostimulant behavior and withdrawal

There is an increasing awareness that a psychosis, similar to that of schizophrenic psychosis, can be derived from cocaine addiction. Thus, the prototypical atypical antipsychotic medication, clozapine, a 5-HT(2)/DA(2) antagonist, was studied for its effects on cocaine-induced dopamine (DA) and serotonin (5-HT) release in nucleus accumbens (NAcc) of behaving male Sprague-Dawley laboratory rats with In Vivo Microvoltammetry, while animals' locomotor (forward ambulations), an A(10) behavior, was monitored at the same time with infrared photobeams. Release mechanisms for monoamines were determined by using a depolarization blocker, gamma-butyrolactone (gammaBL). BRODERICK PROBE microelectrodes selectively detected release of DA and 5-HT within seconds and sequentially in A(10) nerve terminals, NAcc. Acute and subacute studies were performed for each treatment group. Acute studies are defined as single injection of drug(s) after a stable baseline of each monoamine and locomotor behavior has been achieved. Subacute studies are defined as 24-h follow-up studies on each monoamine and locomotor behavior, in the same animal at which time, no further drug was administered. Results showed that (1) acute administration of cocaine (10 mg/kg ip) (n=5) significantly increased both DA and 5-HT release above baseline (P<.001) while locomotion was also significantly increased above baseline (P<.001). In subacute studies, DA release decreased significantly below baseline (P<.001) and significant decreases in 5-HT release occurred at the 15-min mark and at each time point during the second part of the hour (P<.05); the maximum decrease in 5-HT was 40% below baseline. Locomotor behavior, on the other hand, increased significantly above baseline (P<.05). (2) Acute administration of clozapine/cocaine (20 and 10 mg/kg ip, respectively; n=6) produced a significant block of the cocaine-induced increase in DA (P<.001) and 5-HT release (P<.001). Cocaine-induced locomotion was blocked simultaneously with each monoamine by clozapine as well (P<.001). In subacute studies, DA release continued to be blocked presumably via clozapine by exhibiting a statistically significant decrease (P<.001), but 5-HT release increased significantly (P<.001), while cocaine-induced locomotor activity also continued to be antagonized by clozapine, i.e., locomotor activity exhibited no difference from baseline (P>.05). In summary, acute studies (a) support previous data from this laboratory and others that cocaine acts as a stimulant on the monoamines, DA and 5-HT and on locomotor behavior as well and (b) show that clozapine, 5-HT(2)/DA(2) antagonist, blocked enhanced DA, 5-HT and psychomotor stimulant behavior induced by cocaine. Subacute studies (a) suggest that withdrawal responses occurred in the cocaine group, based on recorded deficiencies in monoamine neurotransmitters (b) show that withdrawal effects in the cocaine group likely presynaptic, were distinguished from locomotor behavior, classically known to be mediated postsynaptically, and finally, (c) suggest that clozapine, with longer lived pharmacokinetic properties, reversed 5-HT cocaine-related withdrawal effects, but was unable to reverse DA cocaine-related withdrawal responses. Taken together with data from this laboratory, in which the 5-HT(2A/2C) antagonist, ketanserin, affected cocaine neurochemistry in much the same way as did clozapine, a mediation by either separate or combined 5-HT(2A/2C) receptors for these clozapine/cocaine interactions, is suggested. Further studies, designed to tease out the responses of selective 5-HT(2A) and 5-HT(2C) receptor compounds to cocaine and clozapine/cocaine, are underway.

Evaluation of the blood-brain barrier transport, population pharmacokinetics, and brain distribution of benztropine analogs and cocaine using in vitro and in vivo techniques

The N-substituted 3alpha-[bis(4'-fluorophenyl)methoxy]tropanes (AHN 2-003, AHN 1-055, AHN 2-005, and JHW 007) bind with high affinity to the dopamine transporter and inhibit dopamine uptake more potently than cocaine, but they demonstrate behavioral profiles in animal models of psychostimulant abuse that are unlike that of cocaine. The objective of this study was to characterize the in vitro permeability, brain distribution, and pharmacokinetics of the benztropine (BZT) analogs. Transport studies of cocaine and the BZT analogs (10-4 M) were conducted across bovine brain microvessel endothelial cells. Male Sprague-Dawley rats (approximately 300 g) were administered BZT analogs (10 mg/kg) or cocaine (5 mg/kg) via the tail vein. Blood and brain samples were collected over 36 h and assayed using UV-high-performance liquid chromatography. Transport of both AHN 1-055 (2.15 x 10-4 cm/s) and JHW 007 (2.83 x 10-4 cm/s) was higher (p < 0.05) than that of cocaine (1.63 x 10-4 cm/s). The volume of distribution (12.3-30.5 l/kg) of the analogs was significantly higher than cocaine (0.9 l/kg). The BZT analogs displayed a > or =8-fold higher elimination half-life (4.12-16.49 h) compared with cocaine (0.49 h). The brain-to-plasma partition coefficients were at least two-fold higher for the BZTs versus cocaine, except for AHN 2-003. The BZT analogs are highly permeable across the blood-brain barrier and possess a pharmacokinetic profile different from that of cocaine. These characteristics, in addition to their distinctive behavioral profiles, suggest that the BZT analogs may be promising candidates for the treatment of cocaine abuse.

Acute and subacute effects of risperidone and cocaine on accumbens dopamine and serotonin release using in vivo microvoltammetry on line with open-field behavior

In vivo microvoltammetry was used to detect dopamine (DA) and serotonin (5-HT) release from nucleus accumbens (NAcc) of freely moving, male, Sprague-Dawley laboratory rats, while animals' locomotor (forward ambulations) and stereotypic behavior (fine movements of sniffing and grooming) were monitored at the same time with infrared photobeams. Monoamine release mechanisms were determined by using a depolarization blocker (gamma-butyrolactone, gamma BL). Miniature carbon sensors (BRODERICK PROBES microelectrodes) smaller than a human hair were used in conjunction with a semidifferential electrochemical circuit to detect release of each monoamine in separate signals and within seconds. The purpose was to evaluate the neuropharmacology of the 5-HT(2)/DA(2) antagonist risperidone in its current therapeutic role as an atypical antipsychotic medication as well as in its potential role as pharmacotherapy for cocaine psychosis and withdrawal symptoms. Acute (single drug dose) and subacute (24-h follow-up studies in the same animal, no drug administration) studies were performed for each treatment group. The hypothesis for the present studies is derived from a growing body of evidence that cocaine-induced psychosis and schizophrenic psychosis share similar neurochemical and behavioral manifestations. Results showed that (1) Acute administration of risperidone (2 mg/kg sc) significantly increased DA and 5-HT release in NAcc above baseline (habituation) values (P<.001) while locomotion and stereotypy were virtually unaffected. In subacute studies, DA release did not differ from baseline (P>.05), whereas 5-HT release was significantly increased above baseline (P<.001). Locomotion increased over baseline but not to a significant degree, while stereotypy was significantly increased above baseline (P<.05). (2) Acute administration of cocaine (10 mg/kg ip) significantly increased both DA and 5-HT release above baseline (P<.001), while locomotion and stereotypy were significantly increased over baseline (P<.001). In subacute studies, DA decreased significantly below baseline (P<.001) and significant decreases in 5-HT release occurred at 15, 20, 50 and 55 min (P<.05). Behavior increased above baseline but did not reach a statistically significant degree. (3) Acute administration of risperidone/cocaine (2 mg/kg sc and 10 mg/kg ip, respectively) showed a significant block of the cocaine-induced increase in DA release in the first hour (P<.001) and 5-HT release in both hours of study (P<.001). Cocaine-induced locomotion and stereotypy were blocked simultaneously with the monoamines (P<.001). In subacute studies, DA and 5-HT release returned to baseline while locomotion and stereotypy increased insignificantly above baseline. Thus, (a) these studies were able to tease out pharmacologically the critical differences between presynaptic and postsynaptic responses to drug treatment(s) and these differences may lead to more effective therapies for schizophrenic and/or cocaine psychosis. (b) Taken together with other data, these acute studies suggest that risperidone may possibly act via inhibition of presynaptic autoreceptors to produce the observed increases in accumbens DA and 5-HT release, whereas cocaine may be acting at least in part via serotoninergic modulation of DA postsynaptically. The subacute data suggest that pharmacokinetics may play a role in risperidone's action and that neuroadaptation may play a role in the mechanism of action of cocaine. Finally, the ability of risperidone to block cocaine-induced psychostimulant neurochemistry and behavior during acute studies while diminishing the withdrawal symptoms of cocaine during subacute studies suggests that risperidone may be a viable pharmacotherapy for cocaine psychosis and withdrawal.

Toxic cocaine- and convulsant-induced modification of forced swimming behaviors and their interaction with ethanol: comparison with immobilization stress

BACKGROUND

Swimming behaviors in the forced swimming test have been reported to be depressed by stressors. Since toxic convulsion-inducing drugs related to dopamine [cocaine (COC)], benzodiazepine [methyl 6,7-dimethoxy-4-ethyl-beta-carboline-carboxylate (DMCM)], gamma-aminobutyric acid (GABA) [bicuculline (BIC)], and glutamate [N-methyl-D-aspartate (NMDA)] receptors can function as stressors, the present study compared their effects on the forced swimming behaviors with the effects of immobilization stress (IM) in rats. Their interactions with ethanol (EtOH), the most frequently coabused drug with COC which also induces convulsions as withdrawal symptoms but interferes with the convulsions caused by other drugs, were also investigated.

RESULTS

Similar to the IM (10 min) group, depressed swimming behaviors (attenuated time until immobility and activity counts) were observed in the BIC (5 mg/kg IP) and DMCM (10 mg/kg IP) groups at the 5 h time point, after which no toxic behavioral symptoms were observed. However, they were normalized to the control levels at the 12 h point, with or without EtOH (1.5 g/kg IP). In the COC (60 mg/kg IP) and NMDA (200 mg/kg IP) groups, the depression occurred late (12 h point), and was normalized by the EtOH cotreatment. At the 5 h point, the COC treatment enhanced the swimming behaviors above the control level.

CONCLUSIONS

Although the physiological stress (IM), BIC, and DMCM also depressed the swimming behaviors, a delayed occurrence and EtOH-induced recovery of depressed swimming were observed only in the COC and NMDA groups. This might be correlated with the previously-reported delayed responses of DA and NMDA neurons rather than direct effects of the drugs, which could be suppressed by EtOH. Furthermore, the characteristic psychostimulant effects of COC seemed to be correlated with an early enhancement of swimming behaviors.

The pharmacokinetic determinants of the frequency and pattern of intravenous cocaine self-administration in rats by pharmacokinetic modeling

We investigated the pharmacokinetic determinants of the frequency of intravenous cocaine self-administration in 2.5-h sessions. Two groups of rats were implanted with dual catheters that permitted cocaine infusion and blood sampling via the femoral and jugular vein catheters, respectively. Half of the animals in each group self-administered one of the two cocaine unit doses (0.5 and 1 mg/kg/infusion) by pressing a lever under a continuous schedule of reinforcement. To monitor serum cocaine concentrations, the remaining animals received concurrent, response-independent infusions whenever the matched animals self-administered cocaine infusions. Multiple concentration-time data in two successive self-administrations were determined to monitor the extent of fluctuation in concentrations by pharmacokinetic modeling. Behavioral analyses revealed the higher unit dose (1 mg/kg) resulted in less frequent cocaine self-administration, and a longer interinfusion interval, whereas the total doses were similar for the two groups (24.5-27.0 mg/kg/2.5 h). Cocaine decayed biexponentially. Both the values of clearance and terminal elimination rate constant for the self-administration paradigm were significantly greater than those after the bolus cocaine dosing series (0.5 and 1 mg/kg, separated by 3 days). The regularity in cocaine self-administration produced relatively stable serum cocaine concentrations that oscillated between maximum (C(max)) and minimum (C(min)) values regardless of dose size and interinfusion interval. Although the C(max) for the 1-mg/kg unit dose (1.47 microg/ml) was significantly higher than that for the 0.5-mg/kg dose (0.82 microg/ml), the C(min) values between the groups approximated each other (0.28, and 0.34 microg/ml, respectively). Hence, the C(min) is the determinant of the initiation of the next drug-taking behavior.

Arteriovenous serum cocaine concentration difference after intravenous bolus injection and constant-rate infusions: relation to pharmacodynamic estimates in rats

We characterized the pharmacokinetics of cocaine using both arterial and venous serum data after a bolus dose (2 mg/kg) and two constant-rate infusions (12.24 and 24.48 microg/min) for 2 h in rats. A published behavioral effect was used to investigate the effects of arteriovenous serum concentration differences on pharmacodynamic estimates for the 2 mg/kg dose. Significant temporal arteriovenous serum cocaine and benzoylecgonine (the major metabolite) concentration differences existed after cocaine administrations. The AUCs for arterial serum data were greater than the AUCs for venous data, indicating that cocaine was metabolized more extensively in the venous sampling site. Cocaine's behavioral effect could be directly related to serum concentrations with no hysteresis observed between the effects and arterial or venous serum concentrations. The pharmacodynamic estimates derived from arterial serum data approximated those from the venous data due to the most decline of cocaine's effect occurred in the elimination phase during which serum cocaine concentrations were not significantly different between the two sampling sites.

The disposition of benzoylecgonine in maternal and fetal rats

We tested our hypothesis that pregnancy alters the pharmacokinetic profile of benzoylecgonine, and that this metabolite accumulates in the fetus longer than in the mother. Chronically catheterized near-term pregnant and nonpregnant female Sprague-Dawley rats received an intravenous infusion of benzoylecgonine over a period of 30 min. Adult or fetal blood and tissue samples were obtained either at the end of the infusion or 6 h postinfusion for analysis of benzoylecgonine and other cocaine metabolite concentrations via gas chromatography/mass spectrometry (GC/MS). Pregnancy altered benzoylecgonine pharmacokinetics. At the end of the infusion, benzoylecgonine concentration in the fetal plasma was markedly lower than in the maternal plasma with a fetal/maternal ratio of 0.14+/-0.01. A significantly lower concentration of benzoylecgonine was found in both maternal and fetal brain at 0 h postinfusion, with tissue/plasma concentration ratios of 0.04 and 0.24, respectively, suggesting that benzoylecgonine does not readily penetrate into the brain. At 6 h, the fetal concentration of benzoylecgonine was significantly higher than in the corresponding maternal blood and tissues. Ecgonine methyl ester, a metabolite of benzoylecgonine was found in the maternal liver, but not in the fetus. In addition, the amniotic fluid concentration of benzoylecgonine became significantly higher in the 6-h postinfusion samples as compared to the end of infusion value, suggesting that repeated intrauterine exposure to cocaine may cause an accumulation of benzoylecgonine in the fetus.

The binding of cocaine to cyclodextrins

Cocaine binds into beta-cyclodextrin, but not detectably into alpha- or gamma-cyclodextrin, in water solution. NMR studies indicate the geometry of the complex, which is confirmed by molecular mechanics calculations and binding studies on cocaine analogues and cyclodextrin dimers.