Development Of Cocaine-induced Behavioral Sensitization Research Articles

The CaMKII-dependent phosphorylation of GABAB receptors in the nucleus accumbens was involved in cocaine-induced behavioral sensitization in rats.

Previous studies have established that the regulation of prolonged, distal neuronal inhibition by the GABAB heteroreceptor (GABAB R) is determined by its stability, and hence residence time, on the plasma membrane. Here, we show that GABAB R in the nucleus accumbens (NAc) of rats affects the development of cocaine-induced behavioral sensitization by mediating its perinucleus internalization and membrane expression. By immunofluorescent labeling, flow cytometry analysis, Co-immunoprecipitation and open field test, we measured the role of Ca2+ /calmodulin-dependent protein kinase II (CaMKII) to the control of GABAB R membrane anchoring and cocaine induced-behavioral sensitization. Repeated cocaine treatment in rats (15 mg/kg) significantly decreases membrane levels of GABAB1 R and GABAB2 R in the NAc after day 3, 5 and 7. The membrane fluorescence and protein levels of GABAB R was also decreased in NAc GAD67 + neurons post cocaine (1 μM) treatment after 5 min. Moreover, the majority of internalized GABAB1 Rs exhibited perinuclear localization, a decrease in GABAB1 R-pHluroin signals was observed in cocaine-treated NAc neurons. By contrast, membrane expression of phosphorylated CaMKII (pCaMKII) post cocaine treatment was significantly increased after day 1, 3, 5 and 7. Baclofen blocked the cocaine induced behavioral sensitization via inhibition of cocaine enhanced-pCaMKII-GABAB1 R interaction. These findings reveal a new mechanism by which pCaMKII-GABAB R signaling can promote psychostimulant-induced behavioral sensitization.

DNA Methylation Regulates Cocaine-Induced Behavioral Sensitization in Mice

The behavioral sensitization produced by repeated cocaine treatment represents the neural adaptations underlying some of the features of addiction in humans. Cocaine administrations induce neural adaptations through regulation of gene expression. Several studies suggest that epigenetic modifications, including DNA methylation, are the critical regulators of gene expression in the adult central nervous system. DNA methylation is catalyzed by DNA methyltransferases (DNMTs) and consequent promoter region hypermethylation is associated with transcriptional silencing. In this study a potential role for DNA methylation in a cocaine-induced behavioral sensitization model in mice was explored. We report that acute cocaine treatment caused an upregulation of DNMT3A and DNMT3B gene expression in the nucleus accumbens (NAc). Using methylated DNA immunoprecipitation, DNA bisulfite modification, and chromatin immunoprecipitation assays, we observed that cocaine treatment resulted in DNA hypermethylation and increased binding of methyl CpG binding protein 2 (MeCP2) at the protein phosphatase-1 catalytic subunit (PP1c) promoter. These changes are associated with transcriptional downregulation of PP1c in NAc. In contrast, acute and repeated cocaine administrations induced hypomethylation and decreased binding of MeCP2 at the fosB promoter, and these are associated with transcriptional upregulation of fosB in NAc. We also found that pharmacological inhibition of DNMT by zebularine treatment decreased cocaine-induced DNA hypermethylation at the PP1c promoter and attenuated PP1c mRNA downregulation in NAc. Finally, zebularine and cocaine co-treatment delayed the development of cocaine-induced behavioral sensitization. Together, these results suggest that dynamic changes of DNA methylation may be an important gene regulation mechanism underlying cocaine-induced behavioral sensitization.

Cocaine-induced hyperactivity and sensitization are dependent on GSK3

Glycogen synthase kinase 3 (GSK3) is a critical mediator of many intracellular signaling systems. The activity of GSK3 is regulated by several kinases, with inactivation occurring via phosphorylation of the inhibitory serine-21 (α-isoform) and serine-9 (β-isoform) residues. Here, we investigated whether acute cocaine administration regulates GSK3 activity and if inhibition of GSK3 by valproate or the selective GSK3 inhibitor SB 216763 would attenuate cocaine-induced behaviors in mice. Mice injected with cocaine (20 mg/kg, i.p.) showed a reduction in the phosphorylation of GSK3β in the caudate putamen, reflecting an increase in the activity of the kinase. To assess the role of GSK3 in cocaine-induced hyperactivity, mice were pretreated with valproate (50–300 mg/kg, i.p.), SB 216763 (0.25–7.5 mg/kg, i.p.), or the appropriate vehicle prior to saline or cocaine (20 mg/kg, i.p.). Valproate or SB 216763 produced significant dose-dependent reductions in cocaine-induced ambulatory and stereotypic activity. Repeated administration of cocaine can result in an augmentation of the locomotor-stimulatory effects of the drug, a phenomenon referred to as sensitization. Mice pretreated with SB 216763 (2.5 mg/kg, i.p.) prior to daily cocaine (20 mg/kg, i.p.) for 5 days showed a significant attenuation of the development of cocaine-induced behavioral sensitization following a cocaine challenge on day 13. These results indicate that cocaine activated GSK3β in the caudate putamen and that pharmacological inhibition of GSK3 reduced both the acute behavioral responses to cocaine and the long-term neuroadaptations produced by repeated cocaine, therefore suggesting a role for GSK3 in the behavioral and neurochemical manifestations associated with cocaine exposure.

Alterations in Fos-Related Antigen 2 and σ1 Receptor Gene and Protein Expression Are Associated with the Development of Cocaine-Induced Behavioral Sensitization: Time Course and Regional Distribution Studies

Repeated exposure to cocaine results in neuroadaptations that can alter the way the brain responds to subsequent stimuli. Earlier studies demonstrated that acute administration of cocaine up-regulates the immediate-early gene fos-related antigen 2 (fra-2) followed by a later up-regulation of sigma(1) receptor gene and protein levels in brain regions involved in addiction and reward. To test whether such alterations could have long-term consequences on behavior, the present study was undertaken. Using a cocaine-induced behavioral sensitization model coupled with gene and protein expression studies in mice, the results show that cocaine induces the expression of fra-2, which leads to a progressive increase in sigma(1) receptor gene and protein expression over a period of days. This progressive increase in sigma(1) expression corresponds to the steady increase in the locomotor response to repeated cocaine administration in mice. The cocaine-induced changes in fra-2 and sigma(1) receptor gene and protein expression occur in brain regions that subserve drug abuse, such as the cortex, striatum, and hippocampus, but not the cerebellum. Moreover, the prototypic sigma(1) receptor antagonist 1-[2-(3,4-dichloropheny)ethyl]-4-methylpiperazine (BD1063) significantly attenuates both the molecular adaptations and behavioral sensitization induced by cocaine. These data suggest that repeated exposure to cocaine elicits alterations in fra-2 and sigma(1) receptor-mediated mechanisms, which ultimately manifest as altered behavioral responses to cocaine.

Intra-accumbal Tat 1–72 alters acute and sensitized responses to cocaine

The effects of Tat, an HIV-1 protein, on intravenous cocaine-induced locomotor activity were examined in ovariectomized rats. Animals were habituated to activity chambers, administered an IV baseline/saline injection, and 24 h later, received bilateral, intra-accumbal microinjections of Tat 1–72 (15 µg/µl) or vehicle. Twenty four hours later, rats received the first of 14 daily IV cocaine injections (3.0 mg/kg/inj, 1 /day) or saline. Locomotor activity was measured in automated chambers for 30 min following baseline and after the 1st and 14th cocaine injections. Observational time sampling following cocaine was also performed. Following acute cocaine/saline, Tat significantly increased cocaine-induced total activity over the 30-min session, with no significant effects for activity in the central compartment. Repeated cocaine injections produced behavioral sensitization with ∼ 2-fold higher levels of total activity, ∼ 3-fold higher levels of centrally directed activity, and increased locomotor scores via direct observations. Following repeated cocaine/saline, Tat altered the development of cocaine-induced behavioral sensitization for total activity with prior Tat exposure attenuating the development of cocaine-induced sensitization. Collectively, these data show that bilateral microinjection of Tat into the N Acc alters IV cocaine-induced behavior, suggesting that Tat produces behavioral changes by disrupting the mesocorticolimbic pathway.

RALATIONSHIP BETWEEN THE DEVELOPMENT AND EXPRESSION OF COCAINE‐INDUCED BEHAVIORAL SENSITIZATION AND CHANGES IN FRA‐2 AND SIGMA RECEPTOR GENE AND PROTEIN EXPRESSION: MODULATION BY A SIGMA RECEPTOR ANTAGONIST

Repeated cocaine exposure can cause addiction, which is characterized by altered behavioral responses to the drug (e.g. sensitization). Cocaine also induces the expression of immediate early genes which trigger long-term alterations in brain function. Using a behavioral sensitization model in mice, we measured the ability of a σ receptor antagonist BD1063 to modulate the development and expression of behavioral sensitization to cocaine. In separate studies, BD1063 significantly attenuated both the development and expression of cocaine-induced behavioral sensitization. RT-PCR and Western blots suggested that cocaine administration up regulated the immediate early gene fra-2 which in turn resulted in a progressive up regulation of σ receptor gene and protein expression in brain regions involved in cocaine reward. The progressive up regulation of σ receptors in the striatum and cortex paralleled the development of cocaine-induced behavioral sensitization, and was prevented by administration of BD1063 during the development phase of the study. Together, the data suggest that alterations in fra-2 and σ receptor expression that are induced by cocaine play an important role in the development of behavioral sensitization, and that the functional consequences of these changes can be attenuated by σ receptor antagonism.

Mu-opioid receptors are not involved in acute cocaine-induced locomotor activity nor in development of cocaine-induced behavioral sensitization in mice.

Although mu-opioid receptors have been extensively investigated for their role in drug reinforcement, little is known about the contribution of these receptors to the acute and sensitized locomotor response to cocaine. In this study mu-opioid receptor involvement in acute cocaine-induced locomotor activity and in the development of cocaine-induced behavioral sensitization was evaluated using mu-opioid receptor knockout mice and chronic naltrexone (NTX) pretreatment as models. In addition, co-administration of the specific mu-opioid receptor antagonist CTOP with repeated saline or cocaine injections was used to establish the involvement of mu-opioid receptors in sensitization to the locomotor stimulant effects of cocaine. The acute locomotor response to cocaine (3, 10, 20, or 30 mg/kg i.p.) of mu-opioid receptor knockout or chronic NTX pretreated mice was not different from the cocaine response of their respective controls. With respect to cocaine-induced behavioral sensitization, induced by daily injections of 20 mg/kg cocaine for 11 subsequent days, mu-opioid receptor knockout mice developed behavioral sensitization to the locomotor stimulant effects of cocaine (challenge 10 mg/kg i.p.) comparable to wild-type littermates and the mu-opioid receptor antagonist CTOP did not affect cocaine-induced sensitization either. However, mice that were pretreated with NTX exhibited augmented cocaine-induced behavioral sensitization relative to placebo pretreated controls, which may be ascribed to increased delta-opioid receptor levels as has been described for chronic NTX pretreated mice. The present findings suggest that mu-opioid receptors are not required for the acute locomotor response to cocaine nor are they essential for the development of cocaine-induced behavioral sensitization.

Psychostimulant-Induced Behavioral Sensitization Depends on Nicotinic Receptor Activation

Animal studies have shown that nicotine and psychostimulant drugs (amphetamine and cocaine) share the property of inducing long-lasting behavioral and neurochemical sensitization, which is thought to contribute to their addictive properties. Neuroplasticity subserving learning and memory mechanisms is considered to be involved in psychostimulant-induced sensitization and addiction behavior. Because nicotinic receptors in the brain play a role in the storage of drug-related information underlying reinforcement learning, we evaluated the possibility that activation of central nicotinic receptors may underlie psychostimulant-induced sensitization. Repeated exposure of rats to nicotine profoundly enhanced the psychomotor effects of nicotine and amphetamine 3 weeks after nicotine pretreatment. Moreover, the nicotinic receptor antagonist mecamylamine completely blocked the induction, but not the long-term expression, of behavioral sensitization to amphetamine in amphetamine-pretreated rats. Mecamylamine also prevented the development of cocaine-induced behavioral sensitization. Behavioral sensitization induced by nicotine, amphetamine, or cocaine was associated with an increase in the electrically evoked release of [³H]dopamine from nucleus accumbens slices. Coadministration of mecamylamine during pretreatment with nicotine, amphetamine, or cocaine prevented the development of this long-term hyperreactivity of nucleus accumbens dopamine neurons. Similarly, the high-affinity non-α7 subtype nicotinic receptor antagonist dihydro-β-erythroidine prevented the development of amphetamine-induced behavioral and neurochemical sensitization. These data indicate that nicotinic receptor activation (by endogenously released acetylcholine) is a common denominator initiating neuroplasticity involved in the development of amphetamine, as well as cocaine-induced sensitization.

Psychostimulant-induced behavioral sensitization depends on nicotinic receptor activation.

Animal studies have shown that nicotine and psychostimulant drugs (amphetamine and cocaine) share the property of inducing long-lasting behavioral and neurochemical sensitization, which is thought to contribute to their addictive properties. Neuroplasticity subserving learning and memory mechanisms is considered to be involved in psychostimulant-induced sensitization and addiction behavior. Because nicotinic receptors in the brain play a role in the storage of drug-related information underlying reinforcement learning, we evaluated the possibility that activation of central nicotinic receptors may underlie psychostimulant-induced sensitization. Repeated exposure of rats to nicotine profoundly enhanced the psychomotor effects of nicotine and amphetamine 3 weeks after nicotine pretreatment. Moreover, the nicotinic receptor antagonist mecamylamine completely blocked the induction, but not the long-term expression, of behavioral sensitization to amphetamine in amphetamine-pretreated rats. Mecamylamine also prevented the development of cocaine-induced behavioral sensitization. Behavioral sensitization induced by nicotine, amphetamine, or cocaine was associated with an increase in the electrically evoked release of [(3)H]dopamine from nucleus accumbens slices. Coadministration of mecamylamine during pretreatment with nicotine, amphetamine, or cocaine prevented the development of this long-term hyperreactivity of nucleus accumbens dopamine neurons. Similarly, the high-affinity non-alpha7 subtype nicotinic receptor antagonist dihydro-beta-erythroidine prevented the development of amphetamine-induced behavioral and neurochemical sensitization. These data indicate that nicotinic receptor activation (by endogenously released acetylcholine) is a common denominator initiating neuroplasticity involved in the development of amphetamine, as well as cocaine-induced sensitization.

Modulation of pre- and postsynaptic dopamine D2 receptor function by the selective kappa-opioid receptor agonist U69593.

The repeated administration of selective kappa-opioid receptor agonists prevents the locomotor activation produced by acute cocaine administration and the development of cocaine-induced behavioral sensitization. Previous studies have shown that dopamine (DA) D2 autoreceptors modulate the synthesis and release of DA in the striatum. Evidence that kappa agonist treatment downregulates DA D2 receptors in this same brain region has recently been obtained. Accordingly, the present studies were undertaken to examine the influence of repeated kappa-opioid receptor agonist administration on pre- and postsynaptic DA D2 receptor function in the dorsal striatum using pre- and postsynaptic receptor-selective doses of quinpirole. Rats were injected once daily with the selective kappa-opioid receptor agonist U69593 (0.16-0.32 mg/kg s.c.) or vehicle for 3 days. Microdialysis studies assessing basal and quinpirole-evoked (0.05 mg/kg s.c.) DA levels were conducted 2 days later. Basal and quinpirole-stimulated locomotor activity were assessed in a parallel group of animals. The no-net flux method of quantitative microdialysis revealed no effect of U69593 on basal DA dynamics, in that extracellular DA concentration and extraction fraction did not differ in control and U69593-treated animals. Acute administration of quinpirole significantly decreased striatal DA levels in control animals, but in animals treated with U69593, the inhibitory effects of quinpirole were significantly reduced. Quinpirole produced a dose-related increase in locomotor activity in control animals, and this effect was significantly attenuated in U69593-treated animals. These data reveal that prior repeated administration of a selective kappa-opioid receptor agonist attenuates quinpirole-induced alterations in DA neurotransmission and locomotor activity. These results suggest that both pre- and postsynaptic striatal DA D2 receptors may be downregulated following repeated kappa-opioid receptor agonist administration. Synapse 39:343-350, 2001. Published 2001 Wiley-Liss, Inc.

Kappa-opioid receptor activation prevents alterations in mesocortical dopamine neurotransmission that occur during abstinence from cocaine

In vivo microdialysis was used to characterize basal dopamine dynamics and cocaine-evoked dopamine levels in the medial prefrontal cortex of male Sprague–Dawley rats that had previously received once daily injections of cocaine (days 1–5; 20 mg/kg, i.p.) in combination with the selective kappa-opioid receptor agonist U-69593 (days 3–5; 0.32 mg/kg, s.c.) or its vehicle. The influence of these treatments on [ 3H]dopamine uptake in medial prefrontal cortex synaptosomes was also determined. Three days following the cessation of drug treatment, animals with prior history of cocaine administration exhibited enhanced psychomotor stimulation in response to a subsequent cocaine challenge. This effect was not apparent in animals that had previously received the cocaine treatment regimen in combination with the kappa-opioid receptor agonist U-69593. Cocaine challenge increased prefrontal dopamine levels in all pretreatment groups, but cocaine-pre-exposed animals had lower cocaine-evoked dopamine levels and higher basal in vivo extraction fraction, indicative of an increase in basal dopamine uptake relative to controls. Pretreatment with U-69593 prevented these effects of cocaine. Measurement of [ 3H]dopamine uptake in synaptosomes revealed a significant increase in uptake three days after the cessation of cocaine treatment. No increase in uptake was observed in animals that had received the cocaine treatment regimen in combination with U-69593. These results demonstrate that the early phase of abstinence from cocaine is associated with marked alterations in medial prefrontal cortex dopamine neurotransmission and that these neuroadaptations are prevented by the activation of kappa-opioid receptors. Furthermore, they raise the possibility that mesocortical dopamine neurons may be an important neural substrate upon which kappa-opioid agonists act to prevent the development of cocaine-induced behavioral sensitization.

The development of cocaine-induced behavioral sensitization is affected by discrete quinolinic acid lesions of the prelimbic medial prefrontal cortex

The brain circuitry thought to be involved in the development of behavioral sensitization to psychostimulants consists of the mesocorticolimbic dopaminergic system and its afferent and efferent structures, including the medial prefrontal cortex (mPFC). The mPFC can be further subdivided into several regions, one of which being the prelimbic area (PL). This study sought to examine the role that the PL mPFC plays in the development of cocaine-induced behavioral sensitization. Intact and lesioned animals were treated with cocaine (10 mg/kg) or saline once daily for 14 days and tested in an open field and in a `sniffing box' on day 1, and then again on day 16, 48 h after the last drug injection. Behavioral parameters analyzed included locomotion, rearing, sniffing and grooming. It was found that the lesion affected the development of sensitization to cocaine. In the open field, lesioned animals showed a smaller increase in locomotion and rearing, but a larger increase in grooming as compared to the intact animals. While total sniffing scores in the sniffing box remained unchanged with repeated cocaine in the non-lesioned group, the lesioned group showed a decrease in sniffing. Finally, similar to what was seen in the open field, lesioned rats showed a strong tendency towards increased grooming. These results show that small discrete lesions of the PL mPFC can affect the development of behavioral sensitization to cocaine in a characteristic way. It is suggested that this effect might be mediated by the destruction of descending glutamatergic projections from the mPFC to the ventral tegmental area and/or nucleus accumbens.

Intra-Ventral Tegmental Area Administration of H7 Delays, But Does Not Prevent the Development of Cocaine-Induced Sensitization

Previous studies have suggested that increased protein kinase C activity in the ventral tegmental area (VTA) may play a role in the acute and development of the sensitized behavioral responses to cocaine. The present study was conducted to further characterize the role of protein kinases in the development of sensitization. Animals received injections of saline or the nonspecific protein kinase inhibitor H7 into the VTA before each of their four daily systemic injections of saline or cocaine. Animals were tested for sensitization with a challenge injection of systemic cocaine after a withdrawal period of 24 h or 1 week. Tests for sensitization included monitoring cocaine-induced motor activity and/or dopamine concentrations in the nucleus accumbens, as measured by in vivo microdialysis. Pretreatment with H7 in the VTA attenuated the acute motor stimulant response to cocaine as well as the cocaine-induced increase in extracellular dopamine in the nucleus accumbens. In addition, the augmented increase in dopamine in the nucleus accumbens of cocaine-sensitized animals was prevented in animals pretreated with H7 before each of their daily cocaine injections, when tested after a 24 h withdrawal. However, when tested after a 1 week withdrawal, animals demonstrated sensitization to both the cocaine-induced increase in motor activity and the cocaine-induced increase in dopamine in the nucleus accumbens regardless of whether they received intra-VTA saline or H7 before each of their daily cocaine injections. These data suggest that injection of a protein kinase inhibitor into the VTA delays, but does not prevent the development of cocaine-induced behavioral sensitization.

Disposition of cocaine in blood and brain after a single pretreatment

In vivo microdialysis studies reveal that repeated cocaine administration will enhance the extracellular level of dopamine that occurs following subsequent challenge injections of cocaine. Not only are dopamine levels enhanced, but the in vivo concentration of cocaine in the brain and blood is also increased as a result of repeated cocaine exposure. Increases in cocaine levels can, in part, account for the behavioral sensitization that occurs as a result of repeated cocaine treatment. The present study reveals that enhanced cocaine concentrations can be observed after a single exposure to cocaine and that enhanced levels are not observed when the challenge injection of cocaine is given by an intravenous as opposed to an intraperitoneal injection. Enhanced cocaine levels were also not due to a decrease in the rate of cocaine metabolism that leads to the formation of benzoylecgonine. Repeated cocaine exposure produces effects that enhance in vivo levels of cocaine and these effects occur outside of blood and brain environments. Pharmacokinetic effects play a major role in the development of cocaine-induced behavioral sensitization.

Opposite actions of oxytocin and vasopressin in the development of cocaine-induced behavioral sensitization in mice

Subchronic administration of cocaine induces behavioral sensitization (increasing hypermotility) to a challenge dose of the drug administered 72 h after the cessation of treatment. The effects of repeated administration of the neurohypophyseal hormones oxytocin (OXT) and arginine8-vasopressin (AVP) on the development of behavioral sensitization induced by subchronic treatment with cocaine were investigated in mice. Repeated treatment of OXT and AVP did not modify the locomotor stimulatory effect of the challenge dose of cocaine in cocaine-naive control animals. OXT in a dose of 0.5 μg (sc) augmented the cocaine-induced behavioral sensitization. In contrast, AVP (0.005–0.5 μg/mouse, sc) dose dependently attenuated the development of sensitization to the hypermotility-inducing effect of cocaine. The results suggest that the behavioral sensitization induced by cocaine can be modulated in opposite directions by neurohypophyseal hormones.

Differential effects of carbamazepine and lithium on sensitization and kindling

Abstracto1.Lithium carbonate appears to inhibit the development of cocaine-induced behavioral sensitization while it does not inhibit the development of amygdala kindling. Lithium chloride did not inhibit kindled seizures.2.Carbamazepine does not inhibit cocaine-induced motor activity or the development of behavioral sensitization in the rat.3.Carbamazepine is highly effective in blocking completed amygdala-kindled seizures, but does not block their development in the rat.4.Lithium carbonate and carbamazepine, two drugs of use in the prophylactic treatment of affective illness, appear to have differential effects on sensitization and kindling. Lithium carbonate appears to inhibit the development of cocaine-induced behavioral sensitization while it does not inhibit the development of amygdala kindling. Lithium chloride did not inhibit kindled seizures. Carbamazepine does not inhibit cocaine-induced motor activity or the development of behavioral sensitization in the rat. Carbamazepine is highly effective in blocking completed amygdala-kindled seizures, but does not block their development in the rat. Lithium carbonate and carbamazepine, two drugs of use in the prophylactic treatment of affective illness, appear to have differential effects on sensitization and kindling.

Differential effects of carbamazepine and lithium on sensitization and kindling

Lithium carbonate appears to inhibit the development of cocaine-induced behavioral sensitization while it does not inhibit the development of amygdala kindling. Lithium chloride did not inhibit kindled seizures. Carbamazepine does not inhibit cocaine-induced motor activity or the development of behavioral sensitization in the rat. Carbamazepine is highly effective in blocking completed amygdala-kindled seizures, but does not block their development in the rat. Lithium carbonate and carbamazepine, two drugs of use in the prophylactic treatment of affective illness, appear to have differential effects on sensitization and kindling.