Acute Cocaine Administration Research Articles

Characterization of proteins in the rat striatum following acute cocaine administration

Cocaine administration in the brain alters gene expression via dopamine and glutamate receptor-mediated intracellular signaling cascades. The current study was designed to identify alterations in the total proteome in the rat dorsal striatum in response to intraperitoneal injection of cocaine (20 mg/kg). The results demonstrated that alterations of specific proteins at 20, 120, and 360 min following acute cocaine injection decreased over the time course. Proteins that were identified as having changed as a result of exposure to acute cocaine were found to be involved in a variety of functions necessary for maintaining cellular structure, metabolism, and gene expression in the dorsal striatum.

Low or High Cocaine Responding Rats Differ in Striatal Extracellular Dopamine Levels and Dopamine Transporter Number

Both humans and animals exhibit marked individual differences in cocaine responsiveness. By using the median split of cocaine-induced locomotor activity, we have classified outbred male Sprague-Dawley rats as either low or high cocaine responders (LCRs or HCRs, respectively). LCR/HCR classification predicts differences in cocaine inhibition of striatal dopamine (DA) transporters (DATs), cocaine-induced locomotor sensitization, cocaine-conditioned place preference, and motivation to self-administer cocaine. In this study, we used in vivo microdialysis to investigate whether the differential cocaine inhibition of DATs in LCRs and HCRs is translated into differential extracellular DA levels. Paralleling their locomotor profiles, LCRs and HCRS had similar basal extracellular DA levels in dorsal striatum (dSTR) and nucleus accumbens (NAc); after acute cocaine injection (10 mg/kg i.p.), HCRs showed greater cocaine-induced increases in DA than LCRs, with more pronounced differences in NAc. After repeated cocaine injection, LCRs and HCRs no longer differed in cocaine-induced locomotor activity or extracellular DA. To further explore the differential susceptibility of LCR/HCR DATs to cocaine, we used in vitro [(3)H]2-carbomethoxy-3-(4-fluorophenyl)tropane ([(3)H]WIN 35,428) binding and quantitative autoradiography to measure the number of DAT binding sites and cocaine's affinity for them. After acute cocaine administration, HCRs had fewer DAT binding sites in dSTR and NAc shell, compared to LCRs. No LCR/HCR differences were observed in DAT number after repeated cocaine injection or in cocaine's affinity. Our findings suggest that levels of striatal extracellular DA and DATs both make important contributions to initial differences in cocaine activation, which in LCRs/HCRs predict differential cocaine reward and reinforcement.

Cocaine effects on dopamine and NMDA receptors interactions in the striatum of Fischer rats

Numerous studies have shown that biochemical and behavioral effects of cocaine are mediated by dopamine D1 receptor (D1R) and NMDA R1 receptor (NR1)-mediated transmission. In this study, we investigated the physical interactions between D1R and NR1 in response to acute cocaine administration in a time course of 5–60 min. In the caudate-putamen (CPu) of male Fischer rats, a single cocaine injection (30 mg/kg) reduced D1R–NR1 protein–protein interactions 30 min after treatment. In addition, activation or blockade of the NMDA receptor using NMDA (25 mg/kg) or MK-801 (0.25 mg/kg), respectively, also reduced the D1R–NR1 physical interactions. Acute cocaine administration did not alter total D1R or NR1 protein levels in our time course of study. These results indicate that D1R–NR1 physical interaction rather than total protein levels may regulate the intracellular signaling after acute cocaine administration.

The effect of N-nitro-L-arginine methyl ester on cocaine-induced hormonal changes in mice.

Effects of the nitric oxide synthase inhibitor, N-nitroL-arginine methyl ester (L-NAME, 30 mg/kg i.p.), on cocaine-induced changes in corticosterone and testosterone plasma levels were studied in male mice. Acute (30 mg/kg i.p.) and repeated cocaine (30 mg/kg i.p., twice a day for four days) enhanced the corticosterone level after 45 min and 2 hr, respectively. Single administration of L-NAME had no effect on corticosterone level, whereas its repeated injections (30 mg/kg i.p., twice a day for four days) elevated the hormone concentration at 2 hr after the last dose. Pretreatment of mice with L-NAME enhanced the stimulatory effects of both acute and repeated cocaine on corticosterone level. D-NAME (30 mg/kg i.p.), an inactive form of the nitric oxide synthase inhibitor, was without effect on the cocaine-induced changes in corticosterone level. Acute cocaine administration (30 mg/kg) moderately decreased the testosterone plasma level after 45 min and 2 hr; however, that effect disappeared upon repeated cocaine administration. Single and repeated L-NAME administration did not influence the testosterone level in control animals. Single L-NAME injection abolished the decrease in testosterone level evoked by acute cocaine administration. The above results show that inhibition of nitric oxide synthase enhances the stimulatory effect of cocaine on corticosterone secretion, but abolishes the inhibitory effect of this psychostimulant on the plasma testosterone concentration in mice. On the other hand, a weak--if any--effect of L-NAME alone on corticosterone and testosterone levels suggests that nitric oxide plays a minor role in the tonic regulation of these hormones' secretion.

Regulation of dynamin 2 and G protein‐coupled receptor kinase 2 in rat nucleus accumbens during acute and repeated cocaine administration

Exposure to cocaine causes many neuroadaptations including alterations in several neurotransmitter receptors and transporters. This study investigated potential mechanisms of cocaine-induced receptor and transporter regulation by measuring levels of two proteins involved in receptor and transporter trafficking, dynamin 2 and G protein-coupled receptor kinase 2 (GRK2). Male Fischer rats received three daily injections of cocaine, 15 mg/kg, in a binge-pattern (at 1 h intervals) for 1, 3, or 14 days. Brain regions of interest were collected 30 min after the last injection and proteins measured by Western blot. Acute binge-pattern cocaine administration produced a significant increase in both dynamin 2- and GRK2-immunoreactivity (227% and 358% of control) in the nucleus accumbens and GKR2 (150% of control) in the caudate putamen. Tolerance to this effect occurred, as levels of both proteins returned to baseline after 3 days of cocaine. In contrast, dynamin 2 and GRK2 were significantly decreased in the nucleus accumbens after chronic cocaine. This pattern of regulation was unique to the nucleus accumbens and not seen in the frontal cortex or substantia nigra. Pretreatment with either the dopamine (DA) D1 receptor antagonist SCH 23390 or D2 receptor antagonist eticlopride prior to acute cocaine blocked the upregulation of dynamin 2 and GRK2 in the nucleus accumbens. However, only eticlopride was effective in attenuating the decrease in these proteins following chronic cocaine exposure. These results demonstrate that two proteins involved in receptor and transporter trafficking are selectively regulated in the nucleus accumbens following acute versus chronic cocaine exposure, and dopamine receptor activation is required for this regulation.

Cocaine Does Not Alter Microvascular Po2 On-kinetics In Rat Hindlimb Skeletal Muscle

Cocaine abuse in athletes and the associated morbidity and mortality has piqued interest in its mechanisms of action. Acute cocaine intoxication initially enhances muscle performance, but ultimately leads to premature muscle fatigue and may precipitate renal failure, and death. In rats, cocaine administration accelerates muscle glycogen utilization and fatigue during treadmill exercise. Blood flow to rat hindlimb muscles during exercise is not reduced after cocaine administration (Hagen et al., MSSE 29: S218, 1997), suggesting that cocaine may elevate muscle metabolism. PURPOSE: To determine whether acute cocaine administration increases skeletal muscle metabolism and oxygen uptake, thereby accelerating microvascular PO2 (PO2m) on-kinetics. METHODS: PO2m was measured by phosphorescence quenching in the extensor digitorum longus muscle (EDL) of anesthetized female Sprague-Dawley rats at rest and during the rest-to-contraction transition (1 Hz, 6V). In each rat, PO2m was measured during a control stimulation (STIM 1) and after administration of either cocaine (C, n=13; 5 mg/kg i.v.) or an equivalent volume of saline (S; n=10) (STIM 2). EDL twitch tension was measured during each contraction bout using a muscle tension analyzer. RESULTS: During STIM 1, resting PO2m (R-PO2m), the time delay (TD) between the onset of contractions and the fall in PO2m, the time constant (Tau) and the magnitude and of the fall in PO2m at the onset of contractions (D-PO2m) were the same in the S and C groups. Cocaine administration had no effect on R-PO2m during prior to STIM 2 (S, 23 ± 2; C, 26 ± 1 mmHg). Further, cocaine had no effect on D-PO2m (S, -12 ± 2 vs. C, -15 ± 1 mmHg), TD (S, 6 ± 1; C, 6 ± 1 s) or Tau (S, 8 ± 2; C, 9 ± 2 s). Neither twitch tension (S, 31 ± 7; C, 28 ± 7 N) nor any other indices of muscle contractile function were different during STIM 2. CONCLUSION: The results of this study indicate that acute cocaine administration does not alter resting PO2m, PO2m on-kinetics, or contractile function in the rat EDL muscle. Thus, these data do not support the notion that cocaine enhances muscle metabolism in contracting skeletal muscle.

Genome-wide Analysis of Chromatin Regulation by Cocaine Reveals a Role for Sirtuins

Changes in gene expression contribute to the long-lasting regulation of the brain's reward circuitry seen in drug addiction; however, the specific genes regulated and the transcriptional mechanisms underlying such regulation remain poorly understood. Here, we used chromatin immunoprecipitation coupled with promoter microarray analysis to characterize genome-wide chromatin changes in the mouse nucleus accumbens, a crucial brain reward region, after repeated cocaine administration. Our findings reveal several interesting principles of gene regulation by cocaine and of the role of DeltaFosB and CREB, two prominent cocaine-induced transcription factors, in this brain region. The findings also provide comprehensive insight into the molecular pathways regulated by cocaine-including a new role for sirtuins (Sirt1 and Sirt2)-which are induced in the nucleus accumbens by cocaine and, in turn, dramatically enhance the behavioral effects of the drug.

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.

Cocaine challenge enhances release of neuroprotective amino acid taurine in the striatum of chronic cocaine treated rats: A microdialysis study

Drug addiction is a serious public health problem. There is increasing evidence on the involvement of augmented glutamatergic transmission in cocaine-induced addiction and neurotoxicity. We investigated effects of acute or chronic cocaine administration and cocaine challenge following chronic cocaine exposure on the release of excitotoxic glutamate and neuroprotective taurine in the rat striatum by microdialysis. Cocaine challenge, following withdrawal after repeated cocaine exposure markedly increased the release of glutamate, which may cause neurotoxicity. Simultaneously, cocaine challenge after withdrawal also significantly increased the release of taurine, which counteracts glutamate-mediated excitotoxicity and possibly cell death. Thus, the mammalian brain has an endogenous self-protective mechanism against cocaine-mediated neurotoxicity and potentially addiction.

Maturation of coordinated immediate early gene expression by cocaine during adolescence

Adolescence may be a critical period for drug addiction. Young adolescent male rats have greater locomotor responses than adults after acute low dose cocaine administration. Further, repeated cocaine administration produces as much or more conditioned place preference but reduced locomotor sensitization in adolescents compared to adults. Acute activation of neurons by cocaine induces long-term changes in behavior by activating transcriptional complexes. The purpose of the present study was to correlate cocaine-induced locomotor activity with neuronal activation in subregions of the striatum and cortex by acute cocaine in young adolescent (postnatal (PN) 28) and adult (PN 65) male rats by measuring the induction of the plasticity-associated immediate early genes (IEGs) c-fos and zif268 using in situ hybridization. Animals were treated with saline, low (10 mg/kg), or high (40 mg/kg) dose cocaine in locomotor activity chambers and killed 30 min later. Low dose cocaine induced more locomotor activity and striatal c-fos expression in adolescents than adults whereas high dose cocaine induced more locomotor activity, striatal c-fos, and striatal zif268 expression in adults. Locomotor activity correlated with the expression of both genes in adults but correlated with striatal c-fos only in adolescents. Finally, there was a significant correlation between the expression of c-fos and zif268 in the adult striatum but not in adolescents. Our results suggest that the coordinated expression of transcription factors by cocaine continues to develop during adolescence. The immature regulation of transcription factors by cocaine could explain why adolescents show unique sensitivity to specific long-term behavioral alterations following cocaine treatment.

Stimulation of 5-HT2A and 5-HT2C receptors blocks the reward-facilitating effect of cocaine in the rat

Event Abstract Back to Event Stimulation of 5-HT2A and 5-HT2C receptors blocks the reward-facilitating effect of cocaine in the rat Vicky Katsidoni1* and George Panagis1 1 University of Crete, Greece Serotonin (5-HT) appears to play a modulatory role in the behavioral effects of cocaine, although the impact of specific 5-HT receptors in this control has not been fully established. In the present study, the efficacy of selective ligands for the 5-HT2A and 5-HT2C receptors in altering the reward-facilitating effect of cocaine was examined in rats. Male Sprague-Dawley rats were implanted with a monopolar stimulating electrode into the medial forebrain bundle at the level of the lateral hypothalamus. Rate-frequency functions were determined by logarithmically decreasing the number of cathodal pulses in a stimulation train from a value that sustained maximal responding to one that did not sustain responding. After brain reward threshold stabilized rats received systemic injections with the selective 5-HT2A agonist TCB-2 (0.3mg/kg), the selective 5-HT2A antagonist R-96544 (0.3mg/kg), the selective 5-HT2C agonist WAY-161503 (0.3mg/kg) and the selective 5-HT2C antagonist SB-242084 (0.5mg/kg), followed by acute administration of cocaine (5mg/kg). Systemic injections of the 5-HT2A and 5-HT2C agonists blocked the reward-facilitating effect of cocaine. These effects were reversed by pretreatment with selective 5-HT2A and 5-HT2C antagonists, respectively. Interestingly, the 5-HT2C antagonist appeared to act synergistically with cocaine increasing further its reward-facilitating effect. To the contrary, the 5-HT2A antagonist did not have an effect. The present data support the hypothesis that serotonin through 5-HT2A and 5-HT2C receptors exerts an inhibitory influence on the reward-facilitating effect of cocaine. Intracranial microinjections of these drugs into specific brain regions of the mesocorticolimbic dopaminergic system expressing high levels of 5-HT2A and 5-HT2C receptors could reveal the specific neuroanatomical substrate of the present actions. Supported by a grant from the Research Committee of the University of Crete (KA 2581) Conference: 41st European Brain and Behaviour Society Meeting, Rhodes Island, Greece, 13 Sep - 18 Sep, 2009. Presentation Type: Poster Presentation Topic: Poster presentations Citation: Katsidoni V and Panagis G (2009). Stimulation of 5-HT2A and 5-HT2C receptors blocks the reward-facilitating effect of cocaine in the rat. Conference Abstract: 41st European Brain and Behaviour Society Meeting. doi: 10.3389/conf.neuro.08.2009.09.187 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 10 Jun 2009; Published Online: 10 Jun 2009. * Correspondence: Vicky Katsidoni, University of Crete, Crete, Greece, panagis@uoc.gr Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Vicky Katsidoni George Panagis Google Vicky Katsidoni George Panagis Google Scholar Vicky Katsidoni George Panagis PubMed Vicky Katsidoni George Panagis Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

Differential effects of acute cocaine and placebo administration on visual cortical activation in healthy subjects measured using BOLD fMRI

Many blood oxygenation level dependent (BOLD) functional magnetic resonance imaging studies have shown a strong response due to cocaine in brain regions with high concentrations of dopamine receptors. However, cocaine also has non-specific effects, including cardiovascular changes that may cause changes in BOLD signals, raising the possibility that measured changes could be due to these non-specific effects. The following experiment was conducted to address this concern. Subjects were given either cocaine or saline infusions during a long BOLD functional magnetic resonance imaging study. A flashing uniform-field stimulus, periodically alternating between on and off, provided a strong activation of primary visual cortex. There was a significant main effect of drug between cocaine and placebo. Although we did not demonstrate a significant drug × time interaction, BOLD signal changes associated with visual stimulation appeared unchanged after cocaine administration, whereas the signal differences appeared to decrease during placebo. Explanation of the differential response between the two groups may reflect cocaine expectancy instead of a direct effect of cocaine on BOLD signal changes but will require further investigation to fully elucidate.

Sex differences in basal and cocaine-induced alterations in PKA and CREB proteins in the nucleus accumbens

Alterations in protein kinase (PKA) protein levels have been implicated in the regulation of responses to and development of cocaine addiction. However, the contribution of differences in PKA intracellular cascade to the known sex differences in responses to cocaine is not well understood. This study examined whether there are intrinsic or cocaine-induced alterations in PKA-mediated responses, such as phosphorylation of cyclic AMP response element binding protein, in male and female rats. To this end, protein levels of PKA and phosphorylated CREB (pCREB) in the caudate putamen (CPu) and nucleus accumbens (NAc) of male and female rats were measured basally or after acute (one 30-mg/kg intraperitoneal injection) or chronic (twice-daily 15-mg/kg injections for 14 days) cocaine administration. Behavioral responses to both cocaine administration paradigms were also studied. Similar to previous findings, ambulatory, rearing, and stereotypic activities were higher in female rats after acute cocaine administration. Sex differences in cocaine-induced responses were also observed after chronic cocaine administration: While males developed a robust sensitization in ambulatory activities to cocaine, females developed tolerance in cocaine-induced rearing and stereotypic activities. In the basal group, females had significantly higher PKA protein levels in the NAc. Regardless of the cocaine administration paradigm, PKA protein levels in the NAc were higher overall in females than in males. Furthermore, after cocaine administration, while pCREB protein levels in male rats were induced for a longer amount of time than in female rats, the magnitude of change on pCREB levels were higher in female than male rats. However, in the CPu, no sex differences in PKA or pCREB protein levels were observed either in the basal group or after acute or chronic cocaine administration. Taken together, these findings suggest that sex differences in basal and cocaine-induced alterations in the PKA signaling regulation in the NAc may contribute to sex differences in the psychomotor responses to cocaine.

Proteomic and Behavioral Analysis of Response to Isoliquiritigenin in Brains of Acute Cocaine Treated Rats

Isoliquiritigenin (ISL) is a licorice flavonoid with chalcone structure and is an active component of the root of the plant genus Glycyrrhiza. In addition to anti-inflammatory and antioxidant effects, ISL was previously reported to antagonize increased striatal dopamine release. In the present study, we aimed to investigate whether ISL has an effect on hyperlocomotion in animals subjected to acute cocaine administration and whether ISL modulates acute cocaine-induced molecular changes. To achieve our goals, we analyzed behavior and differential proteomic changes between ISL and vehicle in acute cocaine treated rats. Locomoter activity was reduced in ISL treated animals compared to vehicle in acute cocaine treated rats. Two dimensional electrophoresis (2-DE) revealed that 56 proteins were differentially expressed in response to ISL. Further proteomic analyses using mass spectroscopy, and subsequent validation experiments confirmed that ISL induced changes in proteins related to metabolism, signal transduction, protein folding and transport, oxidative stress, and neural toxicity. Furthermore, cocaine-induced neuronal toxicity was attenuated by ISL treatment, suggesting a neuroprotective role of ISL.

Acute administration of cocaine reduces metabotropic glutamate receptor 8 protein expression in the rat striatum in vivo

Metabotropic glutamate receptors (mGluRs) are densely expressed in the limbic system of the mammalian brain. Increasing evidence suggests a critical role of mGluRs in the pathogenesis of various mental illnesses, including drug abuse and addiction. In this study, we investigated the effect of psychostimulant, cocaine, on protein expression of a specific mGluR subtype, mGluR8, in the rat forebrain in vivo. A rabbit antibody against the extracellular N-terminus of mGluR8 was developed to detect changes in mGluR8 proteins in immunoblot assays. With this antibody, we found that acute systemic injection of cocaine reduced mGluR8 protein levels in the striatum. The reduction of mGluR8 proteins was rapid and transient as it was induced 25min after cocaine injection and returned to the normal level by 6h. No significant change in mGluR8 protein levels in the prefrontal cortex and the hippocampus was observed following cocaine administration. These data demonstrate that protein expression of mGluR8 is subject to the modulation by dopamine stimulation. Acute exposure to cocaine results in a dynamic and region-specific downregulation of mGluR8 expression in the striatum.

Basal and cocaine-induced sex differences in the DARPP-32-mediated signaling pathway

Behavioral and dopamine responses to cocaine are sexually dimorphic: Female rats exhibit higher levels of locomotor and reward-associated behaviors after cocaine administration and dopamine release than do males. Activation of the dopamine- and cAMP-regulated phosphoprotein of Mr 32 kDa (DARPP-32) intracellular cascade mediates responses to cocaine. To examine the possibility that acute cocaine administration alters the DARPP-32 cascade in a sexually dimorphic pattern. Male and female rats received either saline or cocaine (30 mg/kg). Protein levels of DARPP-32, phosphorylation of DARPP-32 at the Thr34 site (P-Thr34-DARPP-32), protein phosphatase 1 (PP-1), and protein phosphatase 2B (PP-2B) in nucleus accumbens were measured via Western blot analysis. Females had higher protein levels of DARPP-32, P-Thr34-DARPP-32, calcineurin A (CaN-A; catalytic subunit of PP-2B), and calcineurin B (CaN-B; regulatory subunit of PP-2B) than males 5 min after saline treatment. In females, CaN-A protein levels were also higher at 15 min and PP-1 protein levels were higher 30 min after saline administration than males. In male rats, cocaine significantly increased CaN-A protein levels at 30 min and CaN-B protein levels at 15 min. In females, cocaine administration significantly decreased protein levels of DARPP-32, P-Thr34-DARPP-32, and CaN-A at 45 min but increased PP-1 protein levels at 30 min. Overall, males had higher activation of the DARPP-32 pathway after cocaine administration than did females. These novel results show that basal and cocaine-induced sex differences in the DARPP-32/PP-1 cascade may be responsible for the sexual dimorphism in acute cocaine-induced behavioral responses.

Selective D3 Receptor Antagonist SB-277011-A Potentiates the Effect of Cocaine on Extracellular Dopamine in the Nucleus Accumbens: a Dual Core-Shell Voltammetry Study in Anesthetized Rats.

Dopamine (DA) D3 receptors have been associated with drug intake and abuse and selectively distribute in the brain circuits responding to drug administration. Here we examined the effects of an acute systemic administration of cocaine (15 mg/kg) alone or preceded by treatment with the selective D3 receptor antagonist SB-277011-A (10 mg/kg) on DA levels concurrently in the rat nucleus accumbens shell and core sub-regions (NAcshell and NAccore, respectively). It is shown that cocaine increases extracellular DA in both compartments and that blocking D3 receptors with SB-277011-A, although the latter is devoid of dopaminergic effects per se, potentiates these effects. No differences in the amplitude of the response were observed between NAcshell and NAccore compartments, though the dopaminergic response in the NAcshell was transient whereas that in the NAccore rose slowly to reach a plateau. These results demonstrate the feasibility to use multiprobe voltammetry to measure discrete monoaminergic responses in discrete areas of the brain and confirm the effect of D3 receptors antagonist at modifying the neurochemical effects of cocaine.

Cocaine activates Homer1 immediate early gene transcription in the mesocorticolimbic circuit: Differential regulation by dopamine and glutamate signaling

Homer proteins are intracellular scaffolding proteins that, among glutamate receptors, selectively bind to group1 metabotropic glutamate receptors and regulate their trafficking and intracellular signaling. Homer proteins have been implicated in synaptic and behavioral plasticity, including drug-seeking behavior after cocaine treatment. Homer1 gene activation leads to transcription of a variant mRNA (Homer1a), which functions as an immediate early gene. Homer1a competes with the constitutive Homer proteins (Homer1b/c/d, Homer2a/b, Homer3) for binding to group1 metabotropic glutamate and IP3 receptors. Binding of Homer1a to these proteins disrupts their association with the intracellular signaling scaffold and modulates receptor function. In this study, using RT-PCR, activation of Homer1a mRNA transcription in response to acute and repeated administration of cocaine was characterized in prefrontal cortex, nucleus accumbens, and ventral tegmental area, three mesocorticolimbic nuclei of the rat brain. Moreover, the dopaminergic and glutamatergic regulation of Homer1 gene activation by cocaine was investigated. Acute cocaine rapidly and transiently activated transcription of Homer1a mRNA in all three nuclei. However, repeated administration of cocaine was not effective in inducing the Homer1a mRNA transcription after various withdrawal times ranging from 2 h to 3 weeks. The acute cocaine-mediated activation of Homer1 gene was regulated by D1 but not D2 dopamine receptors. The blockade of AMPA or NMDA glutamate receptors did not prevent cocaine-mediated activation of Homer1 gene in the three mesocorticolimbic nuclei. These data indicate that acute administration of cocaine transiently activates Homer1 gene producing the immediate early gene Homer1a mRNA in the three mesocorticolimbic nuclei of the rat brain. Activation of Homer1 gene may contribute to the cocaine-mediated synaptic and behavioral plasticity.

Effects of dopamine and NMDA receptors on cocaine-induced Fos expression in the striatum of Fischer rats

Cocaine is an addictive psychostimulant that induces immediate early gene (IEG) expression by activating dopamine (DA) D1 and glutamate NMDA receptors in the striatum. In this study, we show that a single cocaine administration (30 mg/kg) time-dependently increases ERK phosphorylation, c-Fos and FosB protein expression, and MKP-1 phosphorylation (p-MKP-1), in the caudate–putamen (CPu) and nucleus accumbens (NAc) of Fischer rats. In the CPu, 1 h after cocaine injection, the increase in c-Fos and FosB protein expressions is totally abolished by pre-administration of DA-D1 receptor antagonist, SCH23390. In the NAc, SCH23390 also inhibits cocaine-induced c-Fos protein expression. The pre-treatment of NMDA receptor antagonist, MK801, partially reduces cocaine-activated c-Fos protein expression in the CPu. Furthermore, the escalation of p-MKP-1 after acute cocaine administration is dependent on both DA-D1 and NMDA receptor activation in both brain regions examined. Our data suggest that cocaine may modulate ERK pathway signaling through the activation of DA-D1 and NMDA receptors, subsequently influencing the IEG protein expression.

TOLERANCE TO EFFECTS OF COCAINE ON BEHAVIOR UNDER A RESPONSE‐INITIATED FIXED‐INTERVAL SCHEDULE

Tolerance to effects of cocaine can be modulated by schedules of reinforcement. With multiple ratio schedules, research has shown an inverse relationship between ratio requirement and amount of tolerance that resulted from daily administration of the drug. In contrast, tolerance to the effects of cocaine on behavior under multiple interval schedules generally has developed regardless of interval value. Under interval schedules reinforcement depends on the animal making one response following a time interval. Thus, as time to respond increases, the time to reinforcement decreases. On the other hand, fixed ratio schedules require a specified number of responses to be made prior to reinforcement. Therefore, delaying the initiation of responding does not coincide with a significant decrease in the time to reinforcement. In the current experiment, 6 pigeons were trained to respond under a three-component multiple schedule, with a different tandem fixed-ratio 1 fixed-interval schedule in each component. The multiple schedule required one response, which was followed by one of three fixed-interval values (5, 15, or 60 s). Thus, the multiple schedule was interval-like because after the fixed-ratio 1, only one more response was required for reinforcement, but it was also ratio-like because the length of the pause at the beginning of each interreinforcer interval affected the time until the next reinforcer. Acute administration of cocaine generally resulted in dose-dependent decreases in responding. Chronic (i.e., daily) administration of a rate-decreasing dose resulted in tolerance patterns similar to those usually obtained with multiple ratio schedules. That is, the magnitude of tolerance was related inversely to schedule size. These results suggest that delay to reinforcement from the initial response may play a role in the development of schedule-parameter-related tolerance.