Cocaine-induced Locomotor Hyperactivity Research Articles

Muscarinic receptor M4 positive allosteric modulators attenuate central effects of cocaine

BackgroundCocaine addiction is a chronic brain disease affecting neurotransmission. Muscarinic cholinergic receptors modulate dopaminergic signaling in the reward system, and muscarinic receptor stimulation can block direct reinforcing effects of cocaine. Here, we tested the hypothesis that specific muscarinic M4 receptor stimulation can attenuate the discriminative stimulus effects and conditioned rewarding effects of cocaine, measures believed to predict the ability of cocaine and cocaine-associated cues to elicit relapse to drug taking. MethodsWe tested the M4-selective positive allosteric modulators VU0152100 and VU0467154 in a drug discrimination assay and a conditioned place preference assay, including extinction and reinstatement of place preference. Specificity of the cocaine discrimination effect was verified using knockout mice lacking either M1 or M4 receptors (M1−/−, M4−/−). We also replicated previous findings in cocaine-induced locomotor hyperactivity and striatal dopamine microdialysis assays. ResultsVU0152100 attenuated the discriminative stimulus effect of cocaine in wild-type mice and M1−/− mice, but not in M4−/− mice, without affecting rates of responding. As previously shown with VU0152100, VU0467154 almost eliminated cocaine-induced hyperactivity and striatal dopamine efflux. VU0467154 failed to attenuate acquisition of cocaine-conditioned place preference, but facilitated extinction and prevented reinstatement of the conditioned place preference. ConclusionsThese findings further support the notion that M4 receptors are promising targets for the treatment of cocaine addiction, by showing that results can be replicated using distinct ligands, and that in addition to blocking reinforcing effects of cocaine relevant to ongoing drug taking, M4 positive allosteric modulators can also attenuate subjective and conditioned effects relevant to relapse.

Cocaine occupancy of sigma1 receptors and dopamine transporters in mice.

Activation of sigma1 (σ1) receptors contributes to the behavioral and toxic effects of (-)-cocaine. We studied a key step, the ability of (-)-cocaine to occupy σ1 receptors in vivo, using CD-1(®) mice and the novel radioligand [(125) I]E-N-1-(3'-iodoallyl)-N'-4-(3",4"-dimethoxyphenethyl)-piperazine ([(125) I]E-IA-DM-PE-PIPZE). (-)-Cocaine displayed an ED50 of 68 μmol/kg for inhibition of specific radioligand binding in whole brain, with values between 73 and 80 μmol/kg for heart, lung, and spleen. For comparison, an ED50 of 26 μmol/kg for (-)-cocaine occupancy of striatal dopamine transporters (DAT) was determined by inhibition of [(125) I]3β-(4-iodophenyl)tropan-2β-carboxylic acid isopropyl ester ([(125) I]RTI-121) binding. A chief finding is the relatively small potency difference between (-)-cocaine occupancy of σ1 receptors and the DAT, although the DAT occupancy is likely underestimated. Interactions of (-)-cocaine with σ1 receptors were assessed further using [(125) I]E-IA-DM-PE-PIPZE for regional cerebral biodistribution studies and quantitative ex vivo autoradiography of brain sections. (-)-Cocaine binding to cerebral σ1 receptors proved directly proportional to the relative site densities known for the brain regions. Nonradioactive E-IA-DM-PE-PIPZE gave an ED50 of 0.23 μmol/kg for occupancy of cerebral σ1 receptors, and a 3.16 μmol/kg (i.p.) dose attenuated (-)-cocaine-induced locomotor hyperactivity by 30%. This effect did not reach statistical significance, but suggests that E-IA-DM-PE-PIPZE is a probable σ1 receptor antagonist. As groundwork for the in vivo studies, we used standard techniques in vitro to determine ligand affinities, site densities, and pharmacological profiles for the σ1 and σ2 receptors expressed in CD-1(®) mouse brain.

Disruption of dopamine D1 receptor phosphorylation at serine 421 attenuates cocaine-induced behaviors in mice.

Dopamine D1 receptors (D1Rs) play a key role in cocaine addiction, and multiple protein kinases such as GRKs, PKA, and PKC are involved in their phosphorylation. Recently, we reported that protein kinase D1 phosphorylates the D1R at S421 and promotes its membrane localization. Moreover, this phosphorylation of S421 is required for cocaineinduced behaviors in rats. In the present study, we generated transgenic mice over-expressing S421A-D1R in the forebrain. These transgenic mice showed reduced phospho-D1R (S421) and its membrane localization, and reduced downstream ERK1/2 activation in the striatum. Importantly, acute and chronic cocaine-induced locomotor hyperactivity and conditioned place preference were significantly attenuated in these mice. These findings provide in vivo evidence for the critical role of S421 phosphorylation of the D1R in its membrane localization and in cocaine-induced behaviors. Thus, S421 on the D1R represents a potential pharmacotherapeutic target for cocaine addiction and other drug-abuse disorders.

Protein Kinase D1-Dependent Phosphorylation of Dopamine D1 Receptor Regulates Cocaine-Induced Behavioral Responses

The dopamine (DA) D1 receptor (D1R) is critically involved in reward and drug addiction. Phosphorylation-mediated desensitization or internalization of D1R has been extensively investigated. However, the potential for upregulation of D1R function through phosphorylation remains to be determined. Here we report that acute cocaine exposure induces protein kinase D1 (PKD1) activation in the rat striatum, and knockdown of PKD1 in the rat dorsal striatum attenuates cocaine-induced locomotor hyperactivity. Moreover, PKD1-mediated phosphorylation of serine 421 (S421) of D1R promotes surface localization of D1R and enhances downstream extracellular signal-regulated kinase signaling in D1R-transfected HEK 293 cells. Importantly, injection of the peptide Tat-S421, an engineered Tat fusion-peptide targeting S421 (Tat-S421), into the rat dorsal striatum inhibits cocaine-induced locomotor hyperactivity and injection of Tat-S421 into the rat hippocampus or the shell of the nucleus accumbens (NAc) also inhibits cocaine-induced conditioned place preference (CPP). However, injection of Tat-S421 into the rat NAc shell does not establish CPP by itself and injection of Tat-S421 into the hippocampus does not influence spatial learning and memory. Thus, targeting S421 of D1R represents a promising strategy for the development of pharmacotherapeutic treatments for drug addiction and other disorders that result from DA imbalances.

L-Isocorypalmine reduces behavioral sensitization and rewarding effects of cocaine in mice by acting on dopamine receptors

BackgroundWe previously reported isolation of l-isocorypalmine (l-ICP), a mono-demethylated analog of l-tetrahydropalmatine (l-THP), from the plant Corydalis yanhusuo. Here we characterized its in vitro pharmacological properties and examined its effects on cocaine-induced behaviors in mice. MethodsReceptor binding, cAMP and [35S]GTPγS assays were used to examine pharmacological actions of l-ICP in vitro. Effects of l-ICP on cocaine-induced locomotor hyperactivity and sensitization and conditioned place preference (CPP) in mice were investigated. HPLC was employed to analyze metabolites of l-ICP in mouse serum. ResultsAmong more than 40 targets screened, l-ICP and l-THP bound only to dopamine (DA) receptors. l-ICP was a high-affinity partial agonist of D1 and D5 receptors and a moderate-affinity antagonist of D2, D3 and D4 receptors, whereas l-THP bound to only D1 and D5 receptors, with lower affinities than l-ICP. At 10mg/kg (i.p.), l-ICP inhibited spontaneous locomotor activity for a shorter time than l-THP. Pretreatment with l-ICP reduced cocaine-induced locomotor hyperactivities. Administration of l-ICP before cocaine once a day for 5 days reduced cocaine-induced locomotor sensitization on days 5 and 13 after 7 days of withdrawal. Pretreatment with l-ICP before cocaine daily for 6 days blocked cocaine-induced CPP, while l-ICP itself did not cause preference or aversion. HPLC analysis showed that l-ICP was the main compound in mouse serum following i.p. injection of l-ICP. Conclusionsl-ICP likely acts as a D1 partial agonist and a D2 antagonist to produce its in vivo effects and may be a promising agent for treatment of cocaine addiction.

Neuropeptide Y augments cocaine self-administration and cocaine-induced hyperlocomotion in rats

Food restriction and deprivation are known to modulate drug-related behaviors. However, the mechanisms through which metabolic manipulations intercede the rewarding effects of drug reward are unknown. Neuropeptide Y (NPY) is thought to be critically involved in the regulation of energy balance. Central administration of NPY induces feeding in sated animals, and importantly, is reported to increase the rewarding properties of food. NPY has also been shown to be involved in drug-related behavior. We have recently demonstrated that NPY injections augmented on-going heroin self-administration and induced a reinstatement of heroin seeking. The present study sought to support and expand our previous finding on NPY's role in addictive drugs-related behaviors by examining the effects of NPY on cocaine-induced locomotor hyperactivity and cocaine self-administration. In Experiment 1, rats received NPY injections (0.0, 2.5, 5.0 μg/rat, ICV), followed by cocaine administration (0.0, 1.0, 5.0, and 10.0 mg/kg, IP) and their locomotor activity was monitored over 90 min. In Experiment 2, rats were trained to self-administer cocaine (0.50 mg/kg/infusion) during one 3-h session per day for 12 days. Once trained, NPY (0.0, 4.0, 10.0 μg/rat, ICV) was administered 15 min prior to the self-administration session. Results revealed that NPY injections augmented cocaine-induced hyperactivity and moderately increased cocaine self-administration. Together with our previous findings, these results suggest that NPY is involved, albeit to a limited extent, in the augmenting effect of food deprivation on drug-related behaviors.

WIN 55,212-2-induced reduction of cocaine hyperlocomotion: Possible inhibition of 5-HT 3 receptor function

We examined the effect of WIN 55,212-2 (an agonist of cannabinoid receptors) and its enantiomer WIN 55,212-3, as well as of ondansetron (an antagonist of serotonin (5-HT) 3 receptors) on the cocaine-induced locomotor hyperactivity in rats. WIN 55,212-2, but not WIN 55,212-3, in doses of 3 and 6 mg/kg which did not affect the basal locomotor activity, dose-dependently reduced the hyperactivation evoked by cocaine. The inhibitory effect of WIN 55,212-2 was not affected by rimonabant (an antagonist of cannabinoid receptors). Like in the case of WIN 55,212-2, the cocaine-induced hyperlocomotion was reduced in a dose-dependent manner by ondansetron (0.03–0.3 mg/kg). The obtained results indicate that the inhibitory effect of WIN 55,212-2 on cocaine hyperactivation is stereoselective and is not mediated by cannabinoid receptors. Moreover, together with the literature data they may suggest that this effect of WIN 55,212-2 involves inhibition of the 5-HT 3 receptor function.

Effects of 5-HT 1B receptor ligands microinjected into the ventral tegmental area on the locomotor and sensitizating effects of cocaine in rats

The present study was aimed at finding out whether 5-HT 1B receptors located in the ventral tegmental area (VTA) played a role in the locomotor hyperactivity induced by a single dose of cocaine and in the sensitization evoked by repeated exposure to the psychostimulant in rats. Male Wistar rats, implanted bilaterally with cannulae in the VTA, were microinjected with GR 55562 (an antagonist of 5-HT 1B receptors) or CP 93129 (an agonist of 5-HT 1B receptors). GR 55562 (0.3–3 μg/side) did not affect locomotor hyperactivity response to a single dose of cocaine (10 mg/kg). CP 93129 in a dose of 1 μg/side (but not lower), which stimulated basal locomotor activity, enhanced the cocaine-induced locomotor hyperactivity. The rats that were treated repeatedly (for 5 days) with cocaine (10 mg/kg) and then challenged with cocaine (10 mg/kg) after 5-day withdrawal period (day 10 of the experiment) showed significantly higher locomotor hyperactivity compared to the effect observed in saline-pretreated and cocaine-challenged rats. GR 55562 (a dose of 3 μg/side, but not lower), administered for 5 days into the VTA just prior to daily cocaine, attenuated cocaine sensitization. When injected for 5 days into the VTA, CP 93129 (0.03–0.1 μg/side) enhanced the development of cocaine sensitization. The enhancing effect of CP 93129 (0.1 μg/side) was blocked by GR 55562 (1 μg/side). To examine the effects of GR 55562 and CP 93129 on the expression of cocaine sensitization, the 5-HT 1B receptor ligands were given acutely before the challenge dose of cocaine administered on day 10. No change in cocaine sensitization was observed after intra-VTA microinjections of GR 55562 (0.3–3 μg/side) or CP 93129 (0.1–1 μg/side). Our findings suggest that 5-HT 1B receptors located in the VTA play a permissive role in the development of cocaine sensitization, but are not involved in the locomotor hyperactivity induced by a single dose of cocaine or in the expression of the sensitization to the psychostimulant.

Elevated Expression of 5-HT1BReceptors in Nucleus Accumbens Efferents Sensitizes Animals to Cocaine

Although the effects of psychostimulants on brain dopamine systems are well recognized, the direct actions of cocaine on serotonin systems also appear to be important to its addictive properties. For example, serotonin actions at 5-HT1B receptors in the ventral tegmental area (VTA) modulate cocaine-induced dopamine release in the nucleus accumbens (NAcc) and alter the rewarding and stimulant properties of cocaine. However, the mechanisms of these effects have been unclear, because several neuron types in VTA express 5-HT1B receptors. One possibility is that 5-HT1B receptors on the terminals of GABAergic projections from NAcc to VTA inhibit local GABA release, thereby disinhibiting VTA neurons. We tested this hypothesis directly by using viral-mediated gene transfer to overexpress 5-HT1B receptors in NAcc projections to VTA. A viral vector containing either epitope hemagglutinin-tagged 5-HT1B and green fluorescent protein (HA1B-GFP) cassettes or green fluorescent protein cassette alone (GFP-only) was injected into the NAcc shell, which sends projections to the VTA. HA1B-GFP injection induced elevated expression of 5-HT1B receptors in neuronal fibers in VTA and increased cocaine-induced locomotor hyperactivity without affecting baseline locomotion. Overexpression of 5-HT1B receptors also shifted the dose-response curve for cocaine-conditioned place preference to the left, indicating alterations in the rewarding effects of cocaine. Thus, increased expression of 5-HT1B receptors in NAcc efferents, probably in the terminals of medium spiny neurons projecting to the VTA, may contribute to psychomotor sensitization and offer an important target for regulating the addictive effects of cocaine.

Effect of serotonin (5-HT)1B receptor ligands on cocaine sensitization in rats.

Recent studies have shown that antagonists of serotonin (5-HT)1B receptors attenuate cocaine-induced locomotor hyperactivity, whereas agonists enhance reinforcing and discriminative stimulus effects of the psychostimulant. The present study was designed to determine how 5-HT1B receptor ligands affected the development or the expression phase of sensitization to the cocaine-induced locomotor response in rats. In Experiment 1, rats were treated repeatedly (for 5 days) with cocaine (10 mg/kg) in combination with either saline, GR 127935 (5-HT1B antagonist), CP 94,253 (5-HT1B agonist) or GR 127935 + CP 94,253. On day 10, they received a challenge dose of cocaine (10 mg/kg). In Experiment 2, animals received either saline or cocaine (10 mg/kg) for 5 days, and were then challenged with cocaine (10 mg/kg) in combination with saline, GR 127935, CP 94,253 or GR 127935 + CP 94,253, on day 10. In Experiment 3, rats received either saline, cocaine or CP 94,253 for 5 days; on day 10 they received challenge doses of CP 94,253 or cocaine. In rats treated repeatedly with cocaine, the locomotor hyperactivity induced by a challenge dose of the psychostimulant was about twice as high as that observed after its first administration. The effect evoked by cocaine challenge was further increased in animals treated repeatedly with CP 94,253 + cocaine, but not with GR 127935 + CP 94,253 + cocaine. No difference was observed in the response to cocaine challenge in rats treated repeatedly with cocaine or GR 127935 + cocaine (Experiment 1). In animals treated repeatedly with the psychostimulant, the behavioral response to a challenge dose of cocaine was dose-dependently increased when that drug was combined with CP 94,253, but not with GR 127935 + CP 94,253. No difference was observed in the locomotor response of rats challenged with cocaine or GR 127935 + cocaine (Experiment 2). When rats were treated repeatedly with cocaine, a challenge dose of CP 94,253 produced an about threefold increase in the locomotor effect compared to the animals treated likewise with saline (Experiment 3). Our results indicate that 5-HT1B receptors are involved in neither the development nor the expression of sensitization to cocaine-induced locomotor hyperactivity. On the other hand, they also show that pharmacological activation of 5-HT1B receptors enhances both phases of this phenomenon, and that repeated administration of cocaine leads to an increased functional reactivity of these receptors.

Oxytocin and neuroadaptation to cocaine

Oxytocin (OT) has been implicated in neuroadaptive processes such as learning, memory, and social-affiliative behavior as well as in the regulation of physiological responses leading to adaptation to the changing external and internal environment. Drugs of abuse constitute a major challenge to the homeostasis of the body and behavior. Drug tolerance, dependence and addiction may involve neuroadaptive mechanisms related to learning and memory at cellular and systems levels. Considerable effort has been made toward the understanding the neurobiological mechanisms of addictive behavior. Neuropeptides OT and vasopressin (VP) might be involved in these processes based on their effects on neuroadaptation and on their neuroanatomical localization and pharmacological actions. It has been demonstrated that both OT and VP have modulatory effects on opiate and alcohol tolerance and dependence. This chapter summarize the effects of OT, and in lesser extent VP, on neuroadaptation to cocaine, a psychostimulant drug of abuse. We have shown that OT inhibits acute cocaine-induced locomotor hyperactivity, exploratory activity and stereotyped behavior in rodents. Furthermore, OT facilitated, whereas VP inhibited the development of behavioral sensitization to cocaine. In a different model, OT inhibited the development of tolerance to the stereotyped behavior-inducing effects of cocaine as well as cocaine intravenous self-administration in rats. We demonstrated that OT acts through its specific receptors in the basal forebrain and in the hippocampus. OT and VP contents in the hypothalamus and limbic structures were altered by acute and chronic cocaine administration in a dose-dependent and region-selective manner. The differential plasticity of the brain OT-ergic and VP-ergic neurotransmissions in response to cocaine may underlie the differences in the involvement of these neuropeptides in cocaine addiction. Interaction of OT with dopaminergic neurotransmission in the nucleus accumbens, a key brain structure in drug addiction, as well as OT-ergic regulation of hippocampal processes may be among the mechanisms of action through which OT modulates neuroadaptation to cocaine. A better understanding of the role of OT in neuroadaptation to cocaine may provide an insight into both the mechanisms of neuropeptide actions in the brain as well as into the neurobiology of drug addiction.

Neurobiology of stress and cocaine addiction. Studies on corticotropin-releasing factor in rats, monkeys, and humans.

Stress may contribute to the increased vulnerability to and the development of cocaine addiction. Corticotropin-releasing factor (CRF) activates the hypothalamic-pituitary-adrenal (HPA) axis as well as behavioral and immune processes in response to different environmental and pharmacologic stressors. We hypothesized that CRF might mediate some of the effects of cocaine and as such it may be a link between stressful events and increased vulnerability to cocaine addiction. We demonstrated that blockade of endogenous CRF by a CRF antiserum or a receptor antagonist prevented the cocaine-induced corticosterone response in rats. In male rhesus monkeys and in humans, cocaine selectively increased the amplitude-related, CRF-dependent, elements of pulsatile ACTH release. Cocaine-induced locomotor hyperactivity was antagonized by intracerebroventricular (i.c.v.) administration of a CRF antiserum and a CRF receptor antagonist in rats. In rhesus monkeys, strong correlations were found between behavioral hyperactivity and CRF-dependent elements of pulsatile activity of the HPA axis. Acute cocaine administration induced dose- and time-dependent alterations in hypothalamic and extrahypothalamic/limbic CRF concentrations in rats. Cocaine withdrawal elicited anxiety-like behavior and alterations of CRF concentration in the hypothalamus, amygdala, and basal forebrain. CRF antiserum (i.c.v.) antagonized anxiety-like behavior related to cocaine withdrawal. These data strongly suggest that the HPA axis, brain CRF in particular, may mediate some of the neuroendocrine and behavioral effects of cocaine. The potential involvement of CRF and HPA axis in cocaine-induced psychopathology is hypothesized.

Neuropharmacological profile of EMD 57445, a σ receptor ligand with potential antipsychotic activity

EMD 57445 (( S)-(−)-[4-hydroxy-4-(3,4-benzodioxol-5-yl)-piperidin-1-ylmethyl]-3-(4-methoxyphenyl)-oxazolidin-2-one) is a new σ receptor ligand with only marginal affinity for many other (including dopamine) receptors. In the present study, central, particularly neuroleptic-like, effects of this compound were evaluated and compared with those of another σ receptor ligand, rimcazole. EMD 57445 decreased locomotor activity in rats and mice. The amphetamine-induced locomotor hyperactivity and stereotypy were reduced by EMD 57445. The drug was able to inhibit the behavioural effects induced by apomorphine, i.e., the locomotor hyperactivity, stereotypy and aggression in rats, as well as climbing in mice. The hyperlocomotion induced by quinpirole (a dopamine D 2 3 receptor agonist) and the grooming induced by SKF 38393 (a dopamine D 1 receptor agonist) were decreased by EMD 57445. The behavioural stimulation evoked in rats by non-competitive (MK-801, (+)-5-methyl-10,11-dihydroxy-5 H-dibenzo( a,b)-cyclohepten-5,10-imine hydrogen maleate) or competitive (CGP 37849, d,l-E-amino-4-methyl-5-phosphono-3-pentenoic acid) NMDA receptor antagonists was also inhibited. EMD 57445 decreased the cocaine-, morphine- or caffeine-induced locomotor hyperactivity in rats or mice. It neither induced catalepsy nor increased muscle tone in rats. Rimcazole had somewhat different effects: it increased the amphetamine stereotypy as well as the amphetamine-, quinpirole- and cocaine-induced locomotor hyperactivity in rats. The results indicate that EMD 57445 shows functional antidopaminergic activity and may be useful as an antipsychotic drug devoid of extrapyramidal side-effects.

D1 and D2 receptor antagonists differently affect cocaine-induced locomotor hyperactivity in the mouse

Pretreatment with small, per se ineffective doses of the selective D1 antagonist SCH 23390 inhibited hyperactivity induced by cocaine. On the other hand, the classic neuroleptic haloperidol and the selective D2 antagonist metoclopramide prevented the stimulatory effects of cocaine on locomotion only at hypokinetic doses, while the atypical neuroleptic (-)-sulpiride, a selective D2 antagonist, did not produce significant effects when administered at the hypokinetic dose of 12 mg/kg. Finally, at low doses (-)-sulpiride dose-dependently potentiated the locomotor-stimulating effects of cocaine, an effect that is not shared either with haloperidol or with metoclopramide. These results are discussed in terms of different roles of DA receptor subtypes in the modulation of the stimulant effects of cocaine on locomotion.

The role of oxytocin-dopamine interactions in cocaine-induced locomotor hyperactivity

Cocaine is a widely used drug of abuse. One of the characteristic effects of this stimulant drug in the CNS of mice is the induction of motor hyperactivity. It was demonstrated that cocaine-induced motor hyperactivity could be blocked by pimozide, a dopamine receptor blocker, suggesting that dopamine was involved in cocaine-induced hyperactivity. Oxytocin, a neurohypophyseal neuropeptide, also partially antagonized cocaine-induced motor hyperactivity. Moreover, oxytocin antagonized the increased utilization of dopamine, elicited by cocaine in the nucleus accumbens. The data suggest that oxytocin may influence the behavioural effects of cocaine by affecting dopaminergic neurotransmission in some regions of the brain.