Novel GPR18 Ligands in Rodent Pharmacological Tests: Effects on Mood, Pain, and Eating Disorders.

The lack of selective pharmacological tools has limited the full unraveling of G protein-coupled receptor 18 (GPR18) functions. The present study was aimed at discovering the activities of three novel preferential or selective GPR18 ligands, one agonist (PSB-KK-1415) and two antagonists (PSB-CB-5 and PSB-CB-27). We investigated these ligands in several screening tests, considering the relationship between GPR18 and the cannabinoid (CB) receptor system, and the control of endoCB signaling over emotions, food intake, pain sensation, and thermoregulation. We also assessed whether the novel compounds could modulate the subjective effects evoked by Δ9-tetrahydrocannabinol (THC). Male mice or rats were pretreated with the GPR18 ligands, and locomotor activity, depression- and anxiety-like symptoms, pain threshold, core temperature, food intake, and THC-vehicle discrimination were measured. Our screening analyses indicated that GPR18 activation partly results in effects that are similar to those of CB receptor activation, considering the impact on emotional behavior, food intake, and pain activity. Thus, the orphan GPR18 may provide a novel therapeutic target for mood, pain, and/or eating disorders, and further investigation is warranted to better discern its function.

A novel JAK/ROCK inhibitor, CPL409116, demonstrates potent efficacy in the mouse model of systemic lupus erythematosus.

Systemic lupus erythematosus is a chronic inflammatory disease, in which treatment is still limited due to suboptimal efficacy and toxicities associated with the available therapies. JAK kinases are well known to play an important role in systemic lupus erythematous. There is growing evidence that ROCK kinases are also important in disease development. In this paper, we present the results of the development of CPL409116, a dual JAK and ROCK inhibitor. The studies we performed demonstrate that this molecule is an effective JAK and ROCK inhibitor which efficiently blocks disease progression in NZBWF1/J mouse models of systemic lupus erythematous.

Correction to: Extinction training following cocaine or MDMA self-administration produces discrete changes in D2-like and mGlu5 receptor density in the rat brain.

In this published article, Fig. 5 contained a mistake-graphs on the right.

Discovery of 4-Phenylpiperidine-2-Carboxamide Analogues as Serotonin 5-HT2C Receptor-Positive Allosteric Modulators with Enhanced Drug-like Properties.

Targeting the serotonin (5-HT) 5-HT2C receptor (5-HT2CR) allosteric site to potentiate endogenous 5-HT tone may provide novel therapeutics to alleviate the impact of costly, chronic diseases such as obesity and substance use disorders. Expanding upon our recently described 5-HT2CR-positive allosteric modulators (PAMs) based on the 4-alkylpiperidine-2-carboxamide scaffold, we optimized the undecyl moiety at the 4-position with variations of cyclohexyl- or phenyl-containing fragments to reduce rotatable bonds and lipophilicity. Compound 12 (CTW0415) was discovered as a 5-HT2CR PAM with improved pharmacokinetics and reduced off-target interactions relative to our previous series of molecules. The in vivo efficacy of compound 12 to potentiate the effects of a selective 5-HT2CR agonist was established in a drug discrimination assay. Thus, 12 is reported as a 5-HT2CR PAM with characteristics suitable for in vivo pharmacological studies to further probe the biological and behavioral mechanisms of allosteric modulation of a receptor important in several chronic diseases.

Extinction training following cocaine or MDMA self-administration produces discrete changes in D2-like and mGlu5 receptor density in the rat brain.

BACKGROUND: Several studies strongly support the role of the dopamine D2-like and glutamate mGlu5 receptors in psychostimulant reward and relapse. METHODS: The present study employed cocaine or MDMA self-administration with yoked-triad procedure in rats to explore whether extinction training affects the drug-seeking behavior and the D2-like and mGlu5 receptor Bmax and Kd values in several regions of the animal brain. RESULTS: Both cocaine and MDMA rats developed maintenance of self-administration, but MDMA evoked lower response rates and speed of self-administration acquisition. During reinstatement tests, cocaine or MDMA seeking behavior was produced by either exposure to the drug-associated cues or drug-priming injections. The extinction training after cocaine self-administration did not alter significantly D2-like receptor expression the in the limbic and subcortical brain areas, while MDMA yoked rats showed a decrease of the D2-like binding density in the nucleus accumbens and increase in the hippocampus and a rise of affinity in the striatum and hippocampus. Interestingly, in the prefrontal cortex a reduction in the mGlu5 receptor density in cocaine- or MDMA-abstinent rats was demonstrated, with significant effects being observed after previous MDMA exposure. Moreover, rats self-administered cocaine showed a rise in the density of mGlu5 receptor for the nucleus accumbens. CONCLUSION: This study first time shows that abstinence followed extinction training after cocaine or MDMA self- or passive-injections changes the D2-like and mGlu5 density and affinity. The observed changes in the expression of both receptors are brain-region specific and related to either pharmacological and/or motivational features of cocaine or MDMA.

Alternation in dopamine D2-like and metabotropic glutamate type 5 receptor density caused by differing housing conditions during abstinence from cocaine self-administration in rats.

BACKGROUND: Environmental conditions have an important function in substance use disorder, increasing or decreasing the risks of relapse. Several studies strongly support the role of the dopamine D2-like and metabotropic glutamate type 5 receptors in maladaptive neurobiological responses to cocaine reward and relapse. AIMS: The present study employed cocaine self-administration with yoked-triad procedure in rats to explore whether drug abstinence in different housing conditions affects the drug-seeking behaviour and the dopamine D2-like and metabotropic glutamate type 5 receptor density and affinity in several regions of the animal brain. METHODS: Rats were trained to self-administer cocaine and later they were forced to abstain either in: (a) enriched environment or (b) isolation cage conditions to evaluate the effect of housing conditions on the drug-seeking behaviour and to assess changes concerning receptors in animals brain. RESULTS: Our results show that exposure to enriched environment conditions strongly reduced active lever presses during cue-induced drug-seeking. At the neurochemical level, we demonstrated a significant increase in the dopamine D2-like receptor density in the prefrontal cortex in animals following drug abstinence in isolation cage or enriched environment conditions, and the reduction in their density in the dorsal striatum provoked by isolation cage conditions. The metabotropic glutamate type 5 receptor density decreased only in the prefrontal cortex after isolation cage and enriched environment abstinence. CONCLUSIONS: This study shows the different impacts caused by the type of housing conditions during abstinence from cocaine self-administration on drug-seeking behaviour in rats. The observed changes in the dopamine D2-like and metabotropic glutamate type 5 receptor Bmax and/or Kd values were brain-region specific and related to either pharmacological and/or motivational features of cocaine.

Design, Synthesis, and Characterization of 4-Undecylpiperidine-2-carboxamides as Positive Allosteric Modulators of the Serotonin (5-HT) 5-HT2C Receptor.

An impaired signaling capacity of the serotonin (5-HT) 5-HT2C receptor (5-HT2CR) has been implicated in the neurobehavioral processes that promote relapse vulnerability in cocaine use disorder (CUD). Restoration of the diminished 5-HT2CR signaling through positive allosteric modulation presents a novel therapeutic approach. Several new molecules with the 4-alkylpiperidine-2-carboxamide scaffold were designed, synthesized, and pharmacologically evaluated, leading to the discovery of selective 5-HT2CR positive allosteric modulators (PAMs). Compound 16 (CYD-1-79) potentiated 5-HT-evoked intracellular calcium release in cells stably expressing the human 5-HT2CR but not the 5-HT2AR cells. A topographically distinct allosteric site was identified based on the newly solved 5-HT2CR structure. Compound 16 modulated 5-HT2CR-mediated spontaneous ambulation, partially substituted for the training dose of the 5-HT2CR agonist WAY163909, synergized with a low dose of WAY163909 to substitute fully for the stimulus effects of WAY163909, and attenuated relapse vulnerability as assessed in a rodent self-administration model, indicating its therapeutic promise for CUD.

Amphetamine Self-Administration and Its Extinction Alter the 5-HT1B Receptor Protein Levels in Designated Structures of the Rat Brain.

Manipulation of the serotonin (5-HT)1B receptors can modify the behavioral effects of amphetamine including its reinforcing properties. Focus of this study was to examine changes in 5-HT1B receptor protein expression in several brain structures linked to substance drug disorder in different stages of amphetamine addiction-single session of amphetamine self-administration, 20 consecutive days of amphetamine self-administration, and 3 and 14 days of extinction from chronic drug intake. "Yoked" procedure was employed to set apart pharmacological and motivational effects of amphetamine intoxication. Immunohistofluorescence was performed on brain slices containing the following regions: nucleus accumbens (NAc) shell and core, globus pallidum (GP) lateral and ventral, hippocampus (HIP), substantia nigra (SN), and ventral tegmental area (VTA). Single amphetamine session decreased the amount of 5-HT1B receptors in SN, VTA, and HIP in active and yoked rats. On the contrary, 20 days of chronic amphetamine exposure triggered elevation of 5-HT1B receptors exclusively in animals that voluntarily administered the drug in NAc core, GP ventral, and HIP. Furthermore, 14-day (but not 3-day) extinction from amphetamine increased the 5-HT1B receptor expression in ventral and lateral GP, HIP, and SN. This study is the first to demonstrate that exposure to amphetamine and its extinction alter the expression of 5-HT1B receptors in various rat brain regions, and those changes seem to be transient and region specific. Importantly, since increased expression of 5-HT1B receptor after chronic amphetamine self-administration was limited only to active group of animals, we suggest that 5-HT1B receptor is linked to motivational aspect of addiction.

Biophysical validation of serotonin 5-HT2A and 5-HT2C receptor interaction.

The serotonin (5-HT) 5-HT2A receptor (5-HT2AR) and 5-HT2C receptor (5-HT2CR) in the central nervous system are implicated in a range of normal behaviors (e.g., appetite, sleep) and physiological functions (e.g., endocrine secretion) while dysfunctional 5-HT2AR and/or 5-HT2CR are implicated in neuropsychiatric disorders (e.g., addiction, obesity, schizophrenia). Preclinical studies suggest that the 5-HT2AR and 5-HT2CR may act in concert to regulate the neural bases for behavior. Here, we utilize three distinct biophysical and immunocytochemistry-based approaches to identify and study this receptor complex in cultured cells. Employing a split luciferase complementation assay (LCA), we demonstrated that formation of the 5-HT2AR:5-HT2CR complex exists within 50 nm, increases proportionally to the 5-HT2CR:5-HT2AR protein expression ratio, and is specific to the receptor interaction and not due to random complementation of the luciferase fragments. Using a proximity ligation assay (PLA), we found that cells stably expressing both the 5-HT2AR and 5-HT2CR exhibit 5-HT2AR:5-HT2CR heteroreceptor complexes within 40 nm of each other. Lastly, bioluminescence resonance energy transfer (BRET) analyses indicates the formation of a specific and saturable 5-HT2AR:5-HT2CR interaction, suggesting that the 5-HT2AR and 5-HT2CR form a close interaction within 10 nm of each other in intact live cells. The bioengineered receptors generated for the LCA and the BRET exhibit 5-HT-mediated intracellular calcium signaling as seen for the native receptors. Taken together, this study validates a very close 5-HT2AR:5-HT2CR interaction in cultured cells.

Neuroadaptive changes in metabotropic glutamate mGlu2/3R expression during different phases of cocaine addiction in rats.

BACKGROUND: In the cocaine addiction the development from transient into persistent neuroplastic changes strongly involves the glutamatergic system. In this respect, among glutamatergic receptors special attention is paid to the group II of metabotropic glutamatergic receptors (mGlu2/3R) which are involved in the transition from drug use to drug addiction including the relapse mechanisms. METHODS: The present study employed radioligand binding and Western blot assays to study mGlu2/3R density, affinity and protein expression in selected rat brain areas after cocaine self-administration, extinction training and cocaine-induced reinstatement. Rats were randomly assigned in triads to one of three conditions: contingent cocaine intravenous self-administration, non-contingent injections of cocaine (yoked cocaine), or saline yoked to the intake of the self-administering subject. RESULTS: Cocaine self-administration and yoked cocaine delivery resulted in a significant increase in the mGlu2/3R density in the prefrontal cortex and the dorsal striatum, while 10-day extinction training provoked a reduction in the prefrontal cortex and the nucleus accumbens. Cocaine abstinence also enhanced an increase in the [3H]ligand binding to mGlu2/3R in the prefrontal cortex. During reinstatement the cocaine challenge dose (10mg/kg, ip) led to important elevation in the mGlu2/3R density in the prefrontal cortex. CONCLUSIONS: Our study demonstrated the role of mGlu2/3R localized in the prefrontal cortex-striatum pathways to cocaine repeated exposure.

Cocaine Administration and Its Withdrawal Enhance the Expression of Genes Encoding Histone-Modifying Enzymes and Histone Acetylation in the Rat Prefrontal Cortex.

Chronic exposure to cocaine, craving, and relapse are attributed to long-lasting changes in gene expression arising through epigenetic and transcriptional mechanisms. Although several brain regions are involved in these processes, the prefrontal cortex seems to play a crucial role not only in motivation and decision-making but also in extinction and seeking behavior. In this study, we applied cocaine self-administration and extinction training procedures in rats with a yoked triad to determine differentially expressed genes in prefrontal cortex. Microarray analysis showed significant upregulation of several genes encoding histone modification enzymes during early extinction training. Subsequent real-time PCR testing of these genes following cocaine self-administration or early (third day) and late (tenth day) extinction revealed elevated levels of their transcripts. Interestingly, we found the enrichment of Brd1 messenger RNA in rats self-administering cocaine that lasted until extinction training during cocaine withdrawal with concomitant increased acetylation of H3K9 and H4K8. However, despite elevated levels of methyl- and demethyltransferase-encoded transcripts, no changes in global di- and tri-methylation of histone H3 at lysine 4, 9, 27, and 79 were observed. Surprisingly, at the end of extinction training (10 days of cocaine withdrawal), most of the analyzed genes in the rats actively and passively administering cocaine returned to the control level. Together, the alterations identified in the rat prefrontal cortex may suggest enhanced chromatin remodeling and transcriptional activity induced by early cocaine abstinence; however, to know whether they are beneficial or not for the extinction of drug-seeking behavior, further in vivo evaluation is required.

Increased 5-hydroxymethylation levels in the hippocampus of rat extinguished from cocaine self-administration.

Drug craving and relapse risk during abstinence from cocaine are thought to be caused by persistent changes in transcription and chromatin regulation. Although several brain regions are involved in these processes, the hippocampus seems to play an important role in context-evoked craving and drug-seeking behavior. Only a few studies have examined epigenetic alterations during a period of cocaine abstinence. To investigate the effects of cocaine abstinence on DNA methylation and gene expression, rats that self-administered the drug underwent cocaine abstinence in two time points with extinction training. During the cocaine extinction, we observed elevated global 5-hydroxymethylcytosine(5-hmC) levels with a concurrent increase in Tet3 transcript levels. Moreover, we did not find significant alterations in the levels of Tet3 mRNA and 5-hmC in rats subjected to cocaine abstinence without extinction training. Additionally, our findings demonstrated that the expression of Tet3 target genes was activated. Besides, altered DNA methylation was detected at promoter regions of miRNAs, such as miR-30d and miR-let7i. Further in silico analysis provided evidence that these two molecules targeted the 3' UTR region of the Tet3 gene and thus may contribute to its post-transcriptional regulation. This study has presented novel findings in the hippocampus of rats that underwent extinction training following cocaine self-administration. The alterations in the Tet3 gene expression and the level of 5-hmC may play an important role in extinction learning and the reduction of subsequent cocaine seeking.

Changes in the Brain Endocannabinoid System in Rat Models of Depression.

A growing body of evidence implicates the endocannabinoid (eCB) system in the pathophysiology of depression. The aim of this study was to investigate the influence of changes in the eCB system, such as levels of neuromodulators, eCB synthesizing and degrading enzymes, and cannabinoid (CB) receptors, in different brain structures in animal models of depression using behavioral and biochemical analyses. Both models used, i.e., bulbectomized (OBX) and Wistar Kyoto (WKY) rats, were characterized at the behavioral level by increased immobility time. In the OBX rats, anandamide (AEA) levels were decreased in the prefrontal cortex, hippocampus, and striatum and increased in the nucleus accumbens, while 2-arachidonoylglycerol (2-AG) levels were increased in the prefrontal cortex and decreased in the nucleus accumbens with parallel changes in the expression of eCB metabolizing enzymes in several structures. It was also observed that CB1 receptor expression decreased in the hippocampus, dorsal striatum, and nucleus accumbens, and CB2 receptor expression decreased in the prefrontal cortex and hippocampus. In WKY rats, the levels of eCBs were reduced in the prefrontal cortex (2-AG) and dorsal striatum (AEA) and increased in the prefrontal cortex (AEA) with different changes in the expression of eCB metabolizing enzymes, while the CB1 receptor density was increased in several brain regions. These findings suggest that dysregulation in the eCB system is implicated in the pathogenesis of depression, although neurochemical changes were linked to the particular brain structure and the factor inducing depression (surgical removal of the olfactory bulbs vs. genetic modulation).

Prolonged Induction of miR-212/132 and REST Expression in Rat Striatum Following Cocaine Self-Administration.

Chronic exposure to cocaine in vivo induces long-term synaptic plasticity associated with the brain's circuitry that underlies development of repetitive and automatic behaviors called habits. In fact, prolonged drug consumption results in aberrant expression of protein-coding genes and small regulatory RNAs, including miRNAs that are involved in synaptic plasticity and neuroadaptations. However, the mechanisms mediating cocaine use disorder are still not fully understood. The present study is designed to examine the expression of miR-124, miR-132, miR-134, and miR-212, as well as the levels of the Ago2, Pum2, and REST mRNAs and proteins implicated in their regulation. We applied rat cocaine self-administration (SA) and extinction training procedures with a yoked triad to assess the changes in the levels of four miRNAs and three protein-coding genes and corresponding proteins in the dorsal striatum. We demonstrated that elevated expression of mature miR-212 and miR-132 is long-lasting and persists in the drug-free period (till 10-day abstinence). Moreover, mRNA and protein of REST, a regulator of neuronal transcription, was raised selectively in cocaine self-administering rats and Ago2 transcript decreased after cocaine treatment. Unexpectedly, the expression level of Ago2 and Pum2 proteins changed only in the active cocaine-receiving animals. These results point out the important aspects of long-lasting alterations in microRNAs, genes, and protein expressions involved in the control of synaptic plasticity associated with reward and motivation learning related to cocaine addiction.

The Alterations in Mitochondrial DNA Copy Number and Nuclear-Encoded Mitochondrial Genes in Rat Brain Structures after Cocaine Self-Administration.

The repeated intake of cocaine evokes oxidative stress that is present even during drug withdrawal. Recent studies demonstrate that cocaine-induced oxidative and/or endoplasmic reticulum stress can affect mitochondrial function and dynamics as well as the expression of mitochondrial and nuclear genes. These alterations in mitochondrial function may determine synaptic and behavioral plasticity. Mitochondria and mitochondrial DNA (mtDNA) seem to play an important role in the initiation of drug addiction. We used a microarray approach to investigate the expression patterns of nuclear-encoded genes relevant for mitochondrial functions and quantitative real-time PCR assays to determine the numbers of copies of mtDNA and of mRNAs corresponding to two mitochondrial proteins in the prefrontal cortex and hippocampus of rats during early cocaine abstinence. We found a significant elevation in the copy number of mtDNA and concomitant increased expression of mitochondrial genes. Moreover, microarray analysis revealed changes in the transcription of nuclear genes engaged in mtDNA replication, nucleoid formation, the oxidative phosphorylation pathway, and mitochondrial fission and fusion. Finally, we observed the upregulation of endoplasmic reticulum stress-induced genes. Cocaine self-administration influences the expression of both nuclear and mitochondrial genes as well as mtDNA replication. To determine whether these alterations serve as compensatory mechanisms to help maintain normal level of ATP production, further studies are necessary.

Cocaine self-administration, extinction training and drug-induced relapse change metabotropic glutamate mGlu5 receptors expression: Evidence from radioligand binding and immunohistochemistry assays.

Several behavioral findings highlight the importance of glutamatergic transmission and its metabotropic receptor type 5 (mGlu5) in the controlling of cocaine reward and seeking behaviors. The molecular or neurochemical nature of such interactions is not well recognized, so in the present paper we determine if cocaine self-administration and extinction/reinstatement models with the yoked triad control procedure alter mGlu5 receptor density in rats. [³H]MPEP was used to evaluate mGlu5 receptors density and affinity in selected brain structures, while immunofluorescence analysis was used to detect changes in mGlu5 receptors' brain location. Cocaine self-administration and yoked cocaine delivery evoked a significant elevation in mGlu5 receptors' density in the dorsal striatum, while receptor protein expression was importantly elevated in the substantia nigra and reduced in the nucleus accumbens shell. Cocaine administration followed by 10 extinction training sessions resulted in biphasic mGlu5 receptor density changes in the prefrontal cortex-nucleus accumbens pathway. mGlu5 receptors' up-regulation was noted for cocaine self-administration and extinction training in the hippocampus and in yoked cocaine controls following drug abstinence in the dorsal striatum. A cocaine priming dose (but not a saline priming) resulted in a significant decrease of mGlu5 receptors' density in the nucleus accumbens of rats previously treated with the drug and in the hippocampus of rats previously self-administered cocaine. The latter decrease in mGlu5 receptors' density and protein expression in the hippocampus was parallel to an increase in [³H]MPEP affinity and opposite to a rise observed after single cocaine administration (ip) to drug-naïve yoked saline controls. Additionally, we also observed a significant elevation in the protein expression of the tested receptors in the limbic cortex in both cocaine groups. The present results shown modality dependent and brain-region specific changes in mGlu5 receptors' localization and membrane specific binding.

Withdrawal from cocaine self-administration and yoked cocaine delivery dysregulates glutamatergic mGlu5 and NMDA receptors in the rat brain.

In human addicts and in animal models, chronic cocaine use leads to numerous alterations in glutamatergic transmission, including its receptors. The present study focused on metabotropic glutamatergic receptors type 5 (mGluR(5)) and N-methyl-D-aspartate receptor subunits (NMDAR: GluN1, GluN2A, GluN2B) proteins during cocaine self-administration and after 10-day of extinction training in rats. To discriminate the contingent from the non-contingent cocaine delivery, we employed the "yoked"-triad control procedure. Protein expression in rat prefrontal cortex, nucleus accumbens, hippocampus, and dorsal striatum was determined. We also examined the Homer1b/c protein, a member of the postsynaptic density protein family that links NMDAR to mGluR(5). Our results revealed that cocaine self-administration selectively increased GluN1 and GluN2A subunit in the rat hippocampus and dorsal striatum, respectively, while mGluR(5) protein expression was similarly increased in the dorsal striatum of both experimental groups. Withdrawal from both contingent and non-contingent cocaine delivery induced parallel increases in prefrontal cortical GluN2A protein expression, hippocampal mGluR(5), and GluN1 protein expression as well as in accumbal GluN1 subunit expression, while the mGluR(5) expression was reduced in the prefrontal cortex. Extinction training in animals with a history of cocaine self-administration resulted in an elevation of the hippocampal GluN2A/GluN2B subunits and accumbal mGluR(5), and in a 50 % decrease of mGluR(5) protein expression in the dorsal striatum. The latter reduction was associated with Homer1b/1c protein level decrease. Our results showed that both contingent and non-contingent cocaine administration produces numerous, brain region specific, alterations in the mGluR(5), NMDA, and Homer1b/1c protein expression which are dependent on the modality of cocaine administration.

Cocaine-induced glutamate receptor trafficking is abrogated by extinction training in the rat hippocampus.

BACKGROUND: It has been demonstrated that long-term exposure to cocaine leads to plastic changes in the brain that contribute to the manifestation of addictive behaviors. While attention has mostly focused on the meso-cortico-limbic pathway, the hippocampus seems to play a role in the craving induced by cues in drug addicts, in particular in cue- and drug-induced reinstatement of cocaine seeking. Since glutamate appears to be critical for context-induced drug seeking behaviors, the major aim of our work was to investigate the expression of hippocampal AMPA and NMDA glutamate receptors following repeated cocaine exposure and during extinction training. METHODS: We thus employed the yoked control operant paradigm and exposed the animals to contingent or non-contingent cocaine exposure for 2 weeks and sacrificed the animals after the last self-administration (SA) session and following 1 or 10 days of extinction. Protein levels of glutamate receptors were analyzed by Western blotting. RESULTS: We found increased levels of the main subunits of both NMDA and AMPA receptors in the post-synaptic density (PSD) fraction, but not in the whole homogenate, of the hippocampus of animals repeatedly exposed to cocaine indicating increased trafficking toward the membrane of these receptors. Also, we found that extinction abolished such effect, suggesting that the trafficking was tightly linked to the presence of the psychostimulant. CONCLUSIONS: These data reveal a novel, previously unappreciated role of glutamate receptors in the action of cocaine and cocaine-extinction behavior in rat hippocampus.

The effect of active and passive intravenous cocaine administration on the extracellular signal-regulated kinase (ERK) activity in the rat brain.

According to a current hypothesis of learning processes, recent papers pointed out to an important role of the extracellular signal-regulated kinase (ERK), in drug addiction. We employed the Western blotting techniques to examine the ERK activity immediately after cocaine iv self-administration and in different drug-free withdrawal periods in rats. To distinguish motivational vs. pharmacological effects of the psychostimulant intake, a "yoked" procedure was used. Animals were decapitated after 14 daily cocaine self-administration sessions or on the 1st, 3rd or 10th extinction days. At each time point the activity of the ERK was assessed in several brain structures, including the prefrontal cortex, hippocampus, dorsal striatum and nucleus accumbens. Passive, repeated iv cocaine administration resulted in a 45% increase in ERK phosphorylation in the hippocampus while cocaine self-administration did not change brain ERK activity. On the 1st day of extinction, the activity of the ERK in the prefrontal cortex was decreased in rats with a history of cocaine chronic intake: by 66% for "active" cocaine group and by 35% for "yoked" cocaine group. On the 3rd day the reduction in the ERK activity (25-34%) was observed in the hippocampus for both cocaine-treated groups, and also in the nucleus accumbens for "yoked" cocaine group (40%). On the 10th day of extinction there was no significant alteration in ERK activity in any group of rats. Our findings suggest that cortical ERK is involved in cocaine seeking behavior in rats. They also indicate the time and regional adaptations in this enzyme activity after cocaine withdrawal.

Effects of serotonin (5-HT)1B receptor ligands on amphetamine-seeking behavior in rats.

BACKGROUND: Numerous studies have indicated that serotonin (5-HT)1B receptor ligands affect the behavioral effects of psychostimulants (cocaine, amphetamine), including the reinforcing activities of these drugs. METHODS: To substantiate a role for those receptors in incentive motivation for amphetamine, we used the extinction/reinstatement model to examine the effects of the 5-HT1B receptor ligands on the reinstatement of extinguished amphetamine-seeking behavior. Rats trained to self-administer amphetamine (0.06 mg/kg/infusion) subsequently underwent the extinction procedure. These rats were then tested for the amphetamine-primed or amphetamine-associated cue-induced reinstatement of extinguished amphetamine-seeking behavior. RESULTS: The 5-HT1B receptor antagonist SB 216641 (5-7.5 mg/kg) attenuated the amphetamine (1.5 mg/kg)- and the amphetamine-associated cue combined with the threshold dose of amphetamine (0.5 mg/kg)-induced reinstatement of amphetamine-seeking behavior. The 5-HT1B receptor agonist CP 94253 (1.25-5 mg/kg) also inhibited the amphetamine-seeking behavior induced by amphetamine (1.5 mg/kg) but not by the cue combined with the threshold dose of amphetamine. The inhibitory effect of CP94253 on amphetamine-seeking behavior remained unaffected by the 5-HT1B receptor antagonist. CONCLUSION: Our results indicate that tonic activation of 5-HT1B receptors is involved in amphetamine- and cue-induced reinstatement of amphetamine-seeking behavior and that the inhibitory effects of 5-HT1B receptor antagonists on these phenomena are directly related to the motivational aspects of amphetamine abuse. The inhibitory effect of CP 94253 on amphetamine-seeking behavior seems to be unrelated to 5-HT1B receptor activation and may result from a general reduction of motivation.