RESUMO
Antagonism of nicotinic acetylcholine receptors (nAChRs) in the medial habenula (MHb) or interpeduncular nucleus (IPN) triggers withdrawal-like behaviors in mice chronically exposed to nicotine, implying that nicotine dependence involves the sensitization of nicotinic signaling. Identification of receptor and/or neurophysiological mechanisms underlying this sensitization is important, as it could promote novel therapeutic strategies to reduce tobacco use. Using an approach involving photoactivatable nicotine, we previously demonstrated that chronic nicotine (cNIC) potently enhances nAChR function in dendrites of MHb neurons. However, whether cNIC modulates downstream components of the habenulo-interpeduncular (Hb-IP) circuit is unknown. In this study, cNIC-mediated changes to Hb-IP nAChR function were examined in mouse (male and female) brain slices using molecular, electrophysiological, and optical techniques. cNIC enhanced action potential firing and modified spike waveform characteristics in MHb neurons. Nicotine uncaging revealed nAChR functional enhancement by cNIC on proximal axonal membranes. Similarly, nAChR-driven glutamate release from MHb axons was enhanced by cNIC. In IPN, the target structure of MHb axons, neuronal morphology, and nAChR expression is complex, with stronger nAChR function in the rostral subnucleus [rostral IPN (IPR)]. As in MHb, cNIC induced strong upregulation of nAChR function in IPN neurons. This, coupled with cNIC-enhanced nicotine-stimulated glutamate release, was associated with stronger depolarization responses to brief (1 ms) nicotine uncaging adjacent to IPR neurons. Together, these results indicate that chronic exposure to nicotine dramatically alters nicotinic cholinergic signaling and cell excitability in Hb-IP circuits, a key pathway involved in nicotine dependence.SIGNIFICANCE STATEMENT This study uncovers several neuropharmacological alterations following chronic exposure to nicotine in a key brain circuit involved in nicotine dependence. These results suggest that smokers or regular users of electronic nicotine delivery systems (i.e., "e-cigarettes") likely undergo sensitization of cholinergic circuitry in the Hb-IP system. Reducing the activity of Hb-IP nAChRs, either volitionally during smoking cessation or inadvertently via receptor desensitization during nicotine intake, may be a key trigger of withdrawal in nicotine dependence. Escalation of nicotine intake in smokers, or tolerance, may involve stimulation of these sensitized cholinergic pathways. Smoking cessation therapeutics are only marginally effective, and by identifying cellular/receptor mechanisms of nicotine dependence, our results take a step toward improved therapeutic approaches for this disorder.
Assuntos
Habenula/efeitos dos fármacos , Núcleo Interpeduncular/efeitos dos fármacos , Vias Neurais/efeitos dos fármacos , Nicotina/farmacologia , Animais , Feminino , Habenula/metabolismo , Núcleo Interpeduncular/metabolismo , Masculino , Camundongos , Vias Neurais/metabolismo , Agonistas Nicotínicos/farmacologia , Receptores Nicotínicos/metabolismo , Transmissão Sináptica/efeitos dos fármacos , Tabagismo/metabolismoRESUMO
The basolateral amygdala (BLA) sends excitatory projections to the nucleus accumbens (NAc) and regulates motivated behaviors partially by activating NAc medium spiny neurons (MSNs). Here, we characterized a feedforward inhibition circuit, through which BLA-evoked activation of NAc shell (NAcSh) MSNs was fine-tuned by GABAergic monosynaptic innervation from adjacent fast-spiking interneurons (FSIs). Specifically, BLA-to-NAcSh projections predominantly innervated NAcSh FSIs compared with MSNs and triggered action potentials in FSIs preceding BLA-mediated activation of MSNs. Due to these anatomical and temporal properties, activation of the BLA-to-NAcSh projection resulted in a rapid FSI-mediated inhibition of MSNs, timing-contingently dictating BLA-evoked activation of MSNs. Cocaine self-administration selectively and persistently up-regulated the presynaptic release probability of BLA-to-FSI synapses, entailing enhanced FSI-mediated feedforward inhibition of MSNs upon BLA activation. Experimentally enhancing the BLA-to-FSI transmission in vivo expedited the acquisition of cocaine self-administration. These results reveal a previously unidentified role of an FSI-embedded circuit in regulating NAc-based drug seeking and taking.
Assuntos
Potenciais de Ação/fisiologia , Cocaína/administração & dosagem , Comportamento de Procura de Droga/fisiologia , Inibição Neural , Neurônios/fisiologia , Núcleo Accumbens/fisiologia , Vasoconstritores/administração & dosagem , Animais , Complexo Nuclear Basolateral da Amígdala , Feminino , Técnicas de Introdução de Genes , Depressão Sináptica de Longo Prazo , Masculino , Camundongos Endogâmicos C57BL , Neurônios/citologia , Receptor CB1 de Canabinoide/fisiologia , AutoadministraçãoRESUMO
Nicotinic acetylcholine receptors (nAChRs), prototype members of the cys-loop ligand-gated ion channel family, are key mediators of cholinergic transmission in the central nervous system. Despite their importance, technical gaps exist in our ability to dissect the function of individual subunits in the brain. To overcome these barriers, we designed CRISPR/Cas9 small guide RNA sequences (sgRNAs) for the production of loss-of-function alleles in mouse nAChR genes. These sgRNAs were validated in vitro via deep sequencing. We subsequently targeted candidate nAChR genes in vivo by creating herpes simplex virus (HSV) vectors delivering sgRNAs and Cas9 expression to mouse brain. The production of loss-of-function insertions or deletions (indels) by these 'all-in-one' HSV vectors was confirmed using brain slice patch clamp electrophysiology coupled with pharmacological analysis. Next, we developed a scheme for cell type-specific gene editing in mouse brain. Knockin mice expressing Cas9 in a Cre-dependent manner were validated using viral microinjections and genetic crosses to common Cre-driver mouse lines. We subsequently confirmed functional Cas9 activity by targeting the ubiquitous neuronal protein, NeuN, using adeno-associated virus (AAV) delivery of sgRNAs. Finally, the mouse ß2 nAChR gene was successfully targeted in dopamine transporter (DAT)-positive neurons via CRISPR/Cas9. The sgRNA sequences and viral vectors, including our scheme for Cre-dependent gene editing, should be generally useful to the scientific research community. These tools could lead to new discoveries related to the function of nAChRs in neurotransmission and behavioral processes.
Assuntos
Encéfalo/fisiologia , Neurônios Colinérgicos/fisiologia , Edição de Genes/métodos , Vetores Genéticos/genética , Receptores Nicotínicos/fisiologia , Transmissão Sináptica/fisiologia , Animais , Proteína 9 Associada à CRISPR/biossíntese , Proteína 9 Associada à CRISPR/genética , Sistemas CRISPR-Cas/fisiologia , Feminino , Vetores Genéticos/administração & dosagem , Masculino , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Transgênicos , Técnicas de Cultura de ÓrgãosRESUMO
Methamphetamine (METH) dependence is becoming a serious socioeconomic health problem worldwide. The enhancement of the cholinergic nervous system is expected to greatly alleviate drug dependence. We investigated the effect of galantamine on the reinstatement of cue-induced METH-seeking behavior using a self-administration experiment. Treatment with galantamine (1 mg/kg, p.o.) 30 minutes before exposure to the cues suppressed the reinstatement of METH-seeking behavior. However, galantamine did not affect the cue-induced reinstatement of food-seeking behavior or locomotor activity. These results suggest that galantamine may be a candidate drug for treating relapses of METH-seeking behavior.
Assuntos
Estimulantes do Sistema Nervoso Central/administração & dosagem , Inibidores da Colinesterase/farmacologia , Comportamento de Procura de Droga/efeitos dos fármacos , Galantamina/farmacologia , Metanfetamina/administração & dosagem , Transtornos Relacionados ao Uso de Anfetaminas/prevenção & controle , Análise de Variância , Animais , Comportamento Apetitivo/efeitos dos fármacos , Inibidores da Colinesterase/administração & dosagem , Condicionamento Operante , Sinais (Psicologia) , Relação Dose-Resposta a Droga , Galantamina/administração & dosagem , Humanos , Locomoção/efeitos dos fármacos , Camundongos , Núcleo Accumbens/efeitos dos fármacos , Prevenção Secundária , Autoadministração/estatística & dados numéricosRESUMO
Relapse of drug abuse after abstinence is a major challenge to the treatment of addicts. In our well-established mouse models of methamphetamine (Meth) self-administration and reinstatement, bilateral microinjection of adeno-associated virus vectors expressing GDNF (AAV-Gdnf) into the striatum significantly reduced Meth self-administration, without affecting locomotor activity. Moreover, the intrastriatal AAV-Gdnf attenuated cue-induced reinstatement of Meth-seeking behaviour in a sustainable manner. In addition, this manipulation showed that Meth-primed reinstatement of Meth-seeking behaviour was reduced. These findings suggest that the AAV vector-mediated Gdnf gene transfer into the striatum is an effective and sustainable approach to attenuate Meth self-administration and Meth-associated cue-induced relapsing behaviour and that the AAV-mediated Gdnf gene transfer in the brain may be a valuable gene therapy against drug dependence and protracted relapse in clinical settings.
Assuntos
Corpo Estriado/metabolismo , Terapia Genética/métodos , Fator Neurotrófico Derivado de Linhagem de Célula Glial/uso terapêutico , Metanfetamina/toxicidade , Transtornos Relacionados ao Uso de Substâncias/terapia , Análise de Variância , Animais , Estimulantes do Sistema Nervoso Central , Sinais (Psicologia) , Dependovirus/genética , Modelos Animais de Doenças , Comportamento de Procura de Droga/efeitos dos fármacos , Meio Ambiente , Extinção Psicológica/efeitos dos fármacos , Fator Neurotrófico Derivado de Linhagem de Célula Glial/biossíntese , Fator Neurotrófico Derivado de Linhagem de Célula Glial/genética , Proteínas de Fluorescência Verde/genética , Proteínas de Fluorescência Verde/metabolismo , Masculino , Camundongos , Camundongos Endogâmicos C57BL , Microinjeções , Reforço Psicológico , Autoadministração , Transtornos Relacionados ao Uso de Substâncias/mortalidadeRESUMO
Mesolimbic nicotinic acetylcholine receptor (nAChRs) activation is necessary for nicotine reinforcement behavior, but it is unknown whether selective activation of nAChRs in the dopamine (DA) reward pathway is sufficient to support nicotine reinforcement. In this study, we tested the hypothesis that activation of ß2-containing (ß2*) nAChRs on VTA neurons is sufficient for intravenous nicotine self-administration (SA). We expressed ß2 nAChR subunits with enhanced sensitivity to nicotine (referred to as ß2Leu9'Ser) in the VTA of male Sprague Dawley (SD) rats, enabling very low concentrations of nicotine to selectively activate ß2* nAChRs on transduced neurons. Rats expressing ß2Leu9'Ser subunits acquired nicotine SA at 1.5 µg/kg/infusion, a dose too low to support acquisition in control rats. Saline substitution extinguished responding for 1.5 µg/kg/inf, verifying that this dose was reinforcing. ß2Leu9'Ser nAChRs also supported acquisition at the typical training dose in rats (30 µg/kg/inf) and reducing the dose to 1.5 µg/kg/inf caused a significant increase in the rate of nicotine SA. Viral expression of ß2Leu9'Ser subunits only in VTA DA neurons (via TH-Cre rats) also enabled acquisition of nicotine SA at 1.5 µg/kg/inf, and saline substitution significantly attenuated responding. Next, we examined electrically-evoked DA release in slices from ß2Leu9'Ser rats with a history of nicotine SA. Single-pulse evoked DA release and DA uptake rate were reduced in ß2Leu9'Ser NAc slices, but relative increases in DA following a train of stimuli were preserved. These results are the first to report that ß2* nAChR activation on VTA neurons is sufficient for nicotine reinforcement in rats.
Assuntos
Nicotina , Receptores Nicotínicos , Ratos , Masculino , Animais , Nicotina/farmacologia , Nicotina/metabolismo , Agonistas Nicotínicos/farmacologia , Área Tegmentar Ventral/metabolismo , Ratos Sprague-Dawley , Receptores Nicotínicos/metabolismo , Neurônios Dopaminérgicos/metabolismoRESUMO
Effects of varenicline (Champix), a nicotinic partial agonist, were evaluated on subjective effects of nicotine (drug discrimination), motivation for nicotine taking (progressive-ratio schedule of intravenous nicotine self-administration) and reinstatement (cue-induced reinstatement of previously extinguished nicotine-seeking behaviour). Effects on motor performance were assessed in rats trained to discriminate nicotine (0.4 mg/kg) from saline under a fixed-ratio (FR 10) schedule of food delivery and in rats trained to respond for food under a progressive-ratio schedule. At short pretreatment times (5-40 min), varenicline produced full or high levels of partial generalization to nicotine's discriminative-stimulus effects and disrupted responding for food, while there were low levels of partial generalization and no disruption of responding for food at 2- or 4-h pretreatment times. Varenicline (1 and 3 mg/kg, 2-h pretreatment time) enhanced discrimination of low doses of nicotine and to a small extent decreased discrimination of the training dose of nicotine. It also dose-dependently decreased nicotine-taking behaviour, but had no effect on food-taking behaviour under progressive-ratio schedules. Finally, varenicline significantly reduced the ability of a nicotine-associated cue to reinstate extinguished nicotine-seeking behaviour. The ability of varenicline to reduce both nicotine-taking and nicotine-seeking behaviour can contribute to its relatively high efficacy in treating human smokers.
Assuntos
Benzazepinas/farmacologia , Sinais (Psicologia) , Comportamento de Procura de Droga/efeitos dos fármacos , Quinoxalinas/farmacologia , Tabagismo/tratamento farmacológico , Animais , Condicionamento Operante/efeitos dos fármacos , Interpretação Estatística de Dados , Discriminação Psicológica/efeitos dos fármacos , Relação Dose-Resposta a Droga , Comportamento Alimentar/efeitos dos fármacos , Masculino , Motivação/efeitos dos fármacos , Nicotina/farmacologia , Ratos , Ratos Long-Evans , Ratos Sprague-Dawley , Esquema de Reforço , Autoadministração , Tabagismo/psicologia , VareniclinaRESUMO
Ventral tegmental area (VTA) neurons receive glutamatergic and/or GABAergic input from other local neurons within the VTA. Nicotinic acetylcholine receptor (nAChR) activity is capable of modulating such intra-VTA transmission, but the mechanisms are unclear. Here, we isolated monosynaptic glutamate or GABA transmission from mouse medial VTA (mVTA) to lateral VTA (latVTA) using pharmacology and optogenetics, and we studied the ability of nicotine to modulate these modes of transmission. The action of nicotine on mVTA to latVTA glutamate transmission was bidirectional; nicotine enhanced glutamate release in half of the recorded latVTA cells and inhibited release in the other half. Nicotine-mediated reduction in glutamate release was reversed by blockade of GABAA receptors. This, coupled with expression data demonstrating coexpression of vesicular glutamate transporter 2 (VGluT2) and glutamate decarboxylase 2 (Gad2) in mVTA neurons, suggests that nicotine is able to stimulate GABA corelease from mVTA VGluT2+ neurons. Nicotine had an altogether different effect on mVTA to latVTA GABA release from Gad2+ cells; nicotine suppressed GABA release from mVTA Gad2+ terminals in nearly all cells tested. Together, these data uncover a complex system of local circuitry in the VTA that is modulated by nAChR activity. These actions of nicotine, which occurred at concentrations of nicotine found in the artificial CSF of cigarette smokers, may play a role in the adaptive response of the reward system to repeated nicotine exposure.
Assuntos
Neurônios GABAérgicos/metabolismo , Ácido Glutâmico/metabolismo , Nicotina/farmacologia , Agonistas Nicotínicos/farmacologia , Receptores Nicotínicos/metabolismo , Área Tegmentar Ventral/metabolismo , Animais , Potenciais Pós-Sinápticos Excitadores/efeitos dos fármacos , Potenciais Pós-Sinápticos Excitadores/fisiologia , Neurônios GABAérgicos/efeitos dos fármacos , Glutamato Descarboxilase/metabolismo , Masculino , Camundongos , Vias Neurais/efeitos dos fármacos , Vias Neurais/metabolismo , Optogenética , Transmissão Sináptica/efeitos dos fármacos , Transmissão Sináptica/fisiologia , Área Tegmentar Ventral/efeitos dos fármacos , Proteína Vesicular 2 de Transporte de Glutamato/metabolismoRESUMO
Genetic factors are considered to play an important role in drug dependence/addiction including the development of drug dependence and relapse. With the use of a model of drug self-administration in mutant mice, several specific genes and proteins have been identified as potentially important in the development of drug dependence. In contrast, little is known about the role of specific genes in enduring vulnerability to relapse, a clinical hallmark of drug addiction. Using a mouse model of reinstatement, which models relapse of drug-seeking behavior in addicts, we provide evidence that a partial reduction in the expression of the glial cell line-derived neurotrophic factor (GDNF) potentiates methamphetamine (METH) self-administration, enhances motivation to take METH, increases vulnerability to drug-primed reinstatement, and prolongs cue-induced reinstatement of extinguished METH-seeking behavior. In contrast, there was no significant difference in novelty responses, METH-stimulated hyperlocomotion and locomotor sensitization, food-reinforced operant behavior and motivation, or reinstatement of food-seeking behavior between GDNF heterozygous knockout mice and wild-type littermates. These findings suggest that GDNF may be associated with enduring vulnerability to reinstatement of METH-seeking behavior and a potential target in the development of therapies to control relapse.
Assuntos
Transtornos Relacionados ao Uso de Anfetaminas/genética , Fator Neurotrófico Derivado de Linhagem de Célula Glial/fisiologia , Metanfetamina , Transtornos Relacionados ao Uso de Anfetaminas/fisiopatologia , Transtornos Relacionados ao Uso de Anfetaminas/psicologia , Animais , Comportamento Apetitivo/fisiologia , Cateteres de Demora , Condicionamento Operante , Sinais (Psicologia) , Extinção Psicológica/fisiologia , Comportamento Alimentar , Privação de Alimentos , Predisposição Genética para Doença , Fator Neurotrófico Derivado de Linhagem de Célula Glial/deficiência , Fator Neurotrófico Derivado de Linhagem de Célula Glial/genética , Heterozigoto , Bombas de Infusão , Infusões Intravenosas , Masculino , Metanfetamina/administração & dosagem , Camundongos , Camundongos Knockout , Motivação , Recidiva , Reforço Psicológico , AutoadministraçãoRESUMO
Ventral tegmental area (VTA) glutamate neurons are important components of reward circuitry, but whether they are subject to cholinergic modulation is unknown. To study this, we used molecular, physiological, and photostimulation techniques to examine nicotinic acetylcholine receptors (nAChRs) in VTA glutamate neurons. Cells in the medial VTA, where glutamate neurons are enriched, are responsive to acetylcholine (ACh) released from cholinergic axons. VTA VGLUT2+ neurons express mRNA and protein subunits known to comprise heteromeric nAChRs. Electrophysiology, coupled with two-photon microscopy and laser flash photolysis of photoactivatable nicotine, was used to demonstrate nAChR functional activity in the somatodendritic subcellular compartment of VTA VGLUT2+ neurons. Finally, optogenetic isolation of intrinsic VTA glutamatergic microcircuits along with gene-editing techniques demonstrated that nicotine potently modulates excitatory transmission within the VTA via heteromeric nAChRs. These results indicate that VTA glutamate neurons are modulated by cholinergic mechanisms and participate in the cascade of physiological responses to nicotine exposure.
Assuntos
Ácido Glutâmico/metabolismo , Neurônios/metabolismo , Receptores Nicotínicos/metabolismo , Transmissão Sináptica , Área Tegmentar Ventral/metabolismo , Animais , Camundongos , RNA Mensageiro/genética , RNA Mensageiro/metabolismoRESUMO
It is essential to develop animal models to study the role of genetic factors in the relapse of drug-seeking behavior in genetically engineered mutant mice. This paper reports a typical model of drug-primed and cue-induced reinstatement of extinguished methamphetamine (METH)-seeking behavior in mice. C57BL/6J mice were trained to self-administer METH (0.1mg/kg/infusion) by poking their nose into an active hole under a fixed ratio schedule in daily 3-h sessions. After acquiring stable METH self-administration behavior, the mice were subjected to extinction training in the absence of both METH and METH-associated cues. Once the active nose-poking responses were extinguished, drug-primed and cue-induced reinstatement were investigated according to a within-subjects design. A priming injection of METH reliably reinstated the extinguished drug-seeking behavior in the absence of both METH and METH-associated cues. Interestingly, the drug-primed METH-seeking behavior disappeared within 2 months after withdrawal from METH, while cue-induced reinstatement of extinguished METH-seeking behavior lasted for at least 5 months after the withdrawal. A correlation study revealed that drug-primed, but not cue-induced, reinstatement behavior was positively correlated with the total amount of METH taken by individuals during METH self-administration. In conclusion, our findings suggest that the present reinstatement procedure for mouse model of relapse is useful and reliable, and different neural mechanisms may be involved in drug-primed and cue-induced METH-seeking behavior.
Assuntos
Estimulantes do Sistema Nervoso Central/administração & dosagem , Sinais (Psicologia) , Extinção Psicológica/efeitos dos fármacos , Metanfetamina/administração & dosagem , Reforço Psicológico , Transtornos Relacionados ao Uso de Substâncias/psicologia , Análise de Variância , Animais , Comportamento Animal , Relação Dose-Resposta a Droga , Comportamento Exploratório/efeitos dos fármacos , Masculino , Camundongos , Camundongos Endogâmicos C57BL , Esquema de Reforço , AutoadministraçãoRESUMO
Nicotinic acetylcholine receptors containing α4 subunits (α4ß2* nAChRs) are critical for nicotinic cholinergic transmission and the addictive action of nicotine. To identify specific activities of these receptors in the adult mouse brain, we coupled targeted deletion of α4 nAChR subunits with behavioral and and electrophysiological measures of nicotine sensitivity. A viral-mediated Cre/lox approach allowed us to delete α4 from ventral midbrain (vMB) neurons. We used two behavioral assays commonly used to assess the motivational effects of drugs of abuse: home-cage oral self-administration, and place conditioning. Mice lacking α4 subunits in vMB consumed significantly more nicotine at the highest offered nicotine concentration (200 µg/mL) compared to control mice. Deletion of α4 subunits in vMB blocked nicotine-induced conditioned place preference (CPP) without affecting locomotor activity. Acetylcholine-evoked currents as well as nicotine-mediated increases in synaptic potentiation were reduced in mice lacking α4 in vMB. Immunostaining verified that α4 subunits were deleted from both dopamine and non-dopamine neurons in the ventral tegmental area (VTA). These results reveal that attenuation of α4* nAChR function in reward-related brain circuitry of adult animals may increase nicotine intake by enhancing the rewarding effects and/or reducing the aversive effects of nicotine.
Assuntos
Nicotina/metabolismo , Receptores Nicotínicos/metabolismo , Recompensa , Área Tegmentar Ventral/metabolismo , Animais , Neurônios Dopaminérgicos/metabolismo , Neurônios Dopaminérgicos/fisiologia , Comportamento de Procura de Droga , Feminino , Deleção de Genes , Potenciação de Longa Duração , Masculino , Camundongos , Camundongos Endogâmicos C57BL , Receptores Nicotínicos/genética , Potenciais Sinápticos , Área Tegmentar Ventral/fisiologiaRESUMO
There is an urgent need to develop a reliable mouse model of relapse to address the genetic factors involved in susceptibility to relapse of drug-seeking behavior by using mutant mice. This paper presents a feasible way to reinstate extinguished methamphetamine (METH)-seeking behavior. Male C57BL/6J mice acquired stable nose-poking responses for taking METH after approximately 10 daily 3-h sessions of METH (0.1mg/kg/infusion) self-administration under a fixed ratio 1 or 2 (FR1/2) schedule. During the self-administration, cue- and hole-lamps indicated the availability of METH and were inactivated simultaneously with each infusion for 5s. The mice were exposed to extinction training in the absence of METH-paired stimuli (cue- and hole-lamps) and METH infusion, until they met the extinction criterion (less than 25 active responses or 30% of active responses in the stable self-administration phase on 2 consecutive days). METH-paired stimuli (cue- and hole-lamps) during METH self-administration reliably triggered a relapse of METH-seeking behavior in the absence of METH infusion. A combination of non-contingent intravenous (i.v.) priming and self-injected METH also increased the reinstatement of METH-seeking behavior in the absence of METH-paired stimuli (cue- and hole-lamps) and without METH infusion posterior to the self-injection. These results suggest that the mouse model of relapse in our study might provide a new stage for the exploration of genetic factors involved in relapse of drug dependence and of the underlying mechanisms of drugs of abuse.
Assuntos
Transtornos Relacionados ao Uso de Anfetaminas/psicologia , Estimulantes do Sistema Nervoso Central/farmacologia , Metanfetamina/farmacologia , Abuso de Substâncias por Via Intravenosa/psicologia , Animais , Cateterismo Periférico , Sinais (Psicologia) , Extinção Psicológica/efeitos dos fármacos , Masculino , Camundongos , Camundongos Endogâmicos C57BL , AutoadministraçãoRESUMO
Animal models of drug discrimination have been used to examine the subjective effects of addictive substances. The cAMP system is a crucial downstream signaling pathway implicated in the long-lasting neuroadaptations induced by addictive drugs. We examined effects of rolipram, nefiracetam, and dopamine D2-like receptor antagonists, all of which have been reported to modulate cAMP level in vivo, on the discriminative-stimulus effects of methamphetamine (METH) and morphine in rats. All these compounds inhibited the discriminative-stimulus effects of METH, while only rolipram and nefiracetam attenuated the discriminative-stimulus effects of morphine. In addition, neither nifedipine nor neomycin, two voltage-sensitive calcium channel blockers, was found to modulate the effect of nefiracetam on METH-associated discriminative stimuli, suggesting that the inhibitory effect of nefiracetam may not involve the activation of calcium channels. These findings suggest that the cAMP signaling cascade may play a key role in the discriminative-stimulus effects of METH and morphine and may be a potential target for the development of therapeutics to counter drugs of abuse.
Assuntos
Estimulantes do Sistema Nervoso Central/farmacologia , AMP Cíclico/análogos & derivados , Aprendizagem por Discriminação/efeitos dos fármacos , Metanfetamina/farmacologia , Morfina/farmacologia , Entorpecentes/farmacologia , Transdução de Sinais/efeitos dos fármacos , Análise de Variância , Animais , Bloqueadores dos Canais de Cálcio/farmacologia , Fármacos do Sistema Nervoso Central/farmacologia , AMP Cíclico/metabolismo , Antagonistas de Dopamina/farmacologia , Antagonistas dos Receptores de Dopamina D2 , Masculino , Pirrolidinonas/farmacologia , Ratos , Ratos Sprague-Dawley , Rolipram/farmacologia , Sistemas do Segundo Mensageiro/efeitos dos fármacos , Transdução de Sinais/fisiologiaRESUMO
Exposure to cocaine induces addiction-associated behaviors partially through remodeling neurocircuits in the nucleus accumbens (NAc). The paraventricular nucleus of thalamus (PVT), which projects to the NAc monosynaptically, is activated by cocaine exposure and has been implicated in several cocaine-induced emotional and motivational states. Here we show that disrupting synaptic transmission of select PVT neurons with tetanus toxin activated via retrograde trans-synaptic transport of cre from NAc efferents decreased cocaine self-administration in rats. This projection underwent complex adaptations after self-administration of cocaine (0.75 mg/kg/infusion; 2 h/d × 5 d, 1d overnight training). Specifically, 1d after cocaine self-administration, we observed increased levels of AMPA receptor (AMPAR)-silent glutamatergic synapses in this projection, accompanied by a decreased ratio of AMPAR-to-NMDA receptor (NMDAR)-mediated EPSCs. Furthermore, the decay kinetics of NMDAR EPSCs was significantly prolonged, suggesting insertion of new GluN2B-containing NMDARs to PVT-to-NAc synapses. After 45-d withdrawal, silent synapses within this projection returned to the basal levels, accompanied by a return of the AMPAR/NMDAR ratio and NMDAR decay kinetics to the basal levels. In amygdala and infralimbic prefrontal cortical projections to the NAc, a portion of cocaine-generated silent synapses becomes unsilenced by recruiting calcium-permeable AMPARs (CP-AMPARs) after drug withdrawal. However, the sensitivity of PVT-to-NAc synapses to CP-AMPAR-selective antagonists was not changed after withdrawal, suggesting that CP-AMPAR trafficking is not involved in the evolution of cocaine-generated silent synapses within this projection. Meanwhile, the release probability of PVT-to-NAc synapses was increased after short- and long-term cocaine withdrawal. These results reveal complex and profound alterations at PVT-to-NAc synapses after cocaine exposure and withdrawal.
Assuntos
Cocaína/administração & dosagem , Núcleos da Linha Média do Tálamo/efeitos dos fármacos , Núcleos da Linha Média do Tálamo/fisiologia , Núcleo Accumbens/efeitos dos fármacos , Núcleo Accumbens/fisiologia , Sinapses/efeitos dos fármacos , Transmissão Sináptica/efeitos dos fármacos , Animais , Condicionamento Operante , Masculino , Vias Neurais , Ratos Sprague-Dawley , Autoadministração , Sinapses/fisiologiaRESUMO
Oxidative stress plays an important role in neuronal cell death associated with many different neurodegenerative conditions, and it is reported that 4-hydroxynonenal (HNE), an aldehydic product of membrane lipid peroxidation, is a key mediator of neuronal cell death induced by oxidative stress. Previously, we have demonstrated that interleukin-6 (IL-6) protects PC12 cells from serum deprivation and 6-hydroxydopamine-induced toxicity. Therefore, in the present study, we examined the effects of interleukins on HNE toxicity in PC12 cells. Exposure of PC12 cells to HNE resulted in a decrease in levels of 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) reduction, which was due to necrotic and apoptotic cell death. Addition of IL-6 24 h before HNE treatment provided a concentration-dependent protection against HNE toxicity, whereas neither IL-1beta nor IL-2 had any effect. Addition of glutathione (GSH)-ethyl ester, but not superoxide dismutase or catalase, before HNE treatment to the culture medium protected PC12 cells from HNE toxicity. We found that IL-6 increases intracellular GSH levels and the activity of gamma-glutamylcysteine synthetase (gamma-GCS) in PC12 cells. Buthionine sulfoximine (BSO), an inhibitor of gamma-GCS, reversed the protective effect of IL-6 against HNE toxicity. These results suggest that IL-6 protects PC12 cells from HNE-induced cytotoxicity by increasing intracellular levels of GSH.
Assuntos
Aldeídos/toxicidade , Glutationa/metabolismo , Inibidores do Crescimento/toxicidade , Interleucina-6/farmacologia , Fármacos Neuroprotetores/farmacologia , Células PC12/efeitos dos fármacos , Animais , Butionina Sulfoximina/farmacologia , Sobrevivência Celular/efeitos dos fármacos , Primers do DNA/química , Inibidores Enzimáticos/farmacologia , Glutamato-Cisteína Ligase/metabolismo , Humanos , Concentração de Íons de Hidrogênio , Interleucina-1/farmacologia , Interleucina-2/farmacologia , Estresse Oxidativo , Células PC12/metabolismo , Ratos , Reação em Cadeia da Polimerase Via Transcriptase ReversaRESUMO
Nefiracetam has been reported to increase intracellular cyclic AMP levels and enhance calcium channel current. Since the cAMP cascade is involved in the development of drug dependence, we investigated whether nefiracetam attenuates the methamphetamine (MAP)-induced discriminative responses in rats. Nefiracetam (50 mg/kg) inhibited MAP-induced discriminative responses. Furthermore, rolipram, raclopride, and L-745870, all of which can enhance cAMP activity, disrupted MAP-paired lever press of rats. Nifedipine and neomycin, which are blockers of voltage-sensitive calcium channels (VSCCs), decreased MAP-induced discriminative responses. However, pretreatment of these VSCC blockers failed to affect the inhibitory effects of nefiracetam on MAP-induced discriminative responses. Our findings suggested that nefiracetam inhibits MAP-induced discriminative responses, which may be at least partly associated with the changes in intracellular cAMP levels.
Assuntos
Discriminação Psicológica/efeitos dos fármacos , Metanfetamina/farmacologia , Pirrolidinonas/farmacologia , Animais , Bloqueadores dos Canais de Cálcio/farmacologia , Canais de Cálcio/fisiologia , Discriminação Psicológica/fisiologia , Masculino , Metanfetamina/antagonistas & inibidores , Ratos , Ratos Sprague-DawleyRESUMO
RATIONALE: During the development of addiction, addictive drugs induce transient and long-lasting changes in the brain including expression of endogenous molecules and alteration of morphological structure. Of the altered endogenous molecules, some facilitate but others slow the development of drug addiction. Previously, we have reported that tumor necrosis factor alpha (TNF-α) is a critical molecule among endogenous anti-addictive modulators using animal models of drug-conditioned place preference and drug discrimination. OBJECTIVES: Does targeted deletion of the TNF-α gene in mice affect methamphetamine (METH) self-administration, motivation to self-administer METH, cue-induced reinstatement of METH-seeking behavior, and food reinforcement or seeking behavior? METHODS: Both METH self-administration and reinstatement of drug-seeking behavior and food self-delivery and food-seeking behavior were measured in TNF-α (-/-) and wild-type mice. RESULTS: There were an upward shift of dose responses to METH self-administration under a fixed ratio schedule of reinforcement and higher breaking points under a progressive ratio schedule of reinforcement in TNF-α knockout (TNF-α (-/-)) mice as compared with wild-type mice. There was no significant difference in cue-induced reinstatement of METH-seeking behavior, food-maintained operant behavior, motivation to natural food, and cue-induced food-seeking behavior between TNF-α (-/-) and wild-type mice. CONCLUSION: TNF-α affects METH self-administration and motivation to self-administer METH but contributes to neither METH-associated cue-induced relapsing behavior nor food reward and food-seeking behavior. TNF-α may be explored for use as a diagnostic biomarker for the early stage of drug addiction.
Assuntos
Comportamento Animal/efeitos dos fármacos , Estimulantes do Sistema Nervoso Central/administração & dosagem , Metanfetamina/administração & dosagem , Fator de Necrose Tumoral alfa/genética , Animais , Condicionamento Operante , Sinais (Psicologia) , Relação Dose-Resposta a Droga , Comportamento Alimentar , Deleção de Genes , Masculino , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Knockout , Motivação , Esquema de Reforço , AutoadministraçãoRESUMO
Extinction bursts are characterized by a temporary increase in responding when drug access is withheld from rats trained to self-administer drugs of abuse. Thus far, one study has examined extinction bursts for nicotine self-administration using a 23-h access paradigm [1]. Here we examined extinction bursts using previously published and unpublished data in which rats were trained to self-administer nicotine (0.03mg/kg/infusion) or food pellets (as a comparator) in 1-h sessions under an FR5 schedule of reinforcement followed by 1-h extinction sessions. Analysis of response rates during nicotine self-administration (NSA) was indicative of a loading phase, as response rates were significantly higher at the beginning of the session, which was not observed for food self-administration. At the start of extinction for both food and nicotine, although sessional response rates did not increase, there was an increase in response rate during the first 5-min of the first extinction session relative to self-administration. This transient extinction burst following nicotine was observed in a minority of subjects and correlated with the number of nicotine infusions obtained during self-administration. This transient extinction burst following food was observed in all subjects. Nicotine and food produce more transient extinction bursts compared to other drugs of abuse and only for a minority of animals in the case of nicotine. This study supports the presence of a loading phase in rats trained to self-administer nicotine in 1-r daily sessions and the presence of a transient extinction burst.
RESUMO
Since cloning of the dopamine receptor D4 (DRD4), its role in the brain has remained unclear. It has been reported that polymorphism of the DRD4 gene in humans is associated with reactivity to cues related to tobacco smoking. However, the role of DRD4 in animal models of nicotine addiction has seldom been explored. In our study, male Long-Evans rats learned to intravenously self-administer nicotine under a fixed-ratio (FR) schedule of reinforcement. Effects of the selective DRD4 antagonist L-745,870 were evaluated on nicotine self-administration behavior and on reinstatement of extinguished nicotine-seeking behavior induced by nicotine-associated cues or by priming injections of nicotine. L-745,870 was also tested on reinstatement of extinguished food-seeking behavior as a control. In addition, the selective DRD4 agonist PD 168,077 was tested for its ability to reinstate extinguished nicotine-seeking behavior. Finally, L-745,870 was tested in Sprague Dawley rats trained to discriminate administration of 0.4 mg/kg nicotine from vehicle under an FR schedule of food delivery. L-745,870 significantly attenuated reinstatement of nicotine-seeking induced by both nicotine-associated cues and nicotine priming. In contrast, L-745,870 did not affect established nicotine self-administration behavior or reinstatement of food-seeking behavior induced by food cues or food priming. L-745,870 did not produce nicotine-like discriminative-stimulus effects and did not alter discriminative-stimulus effects of nicotine. PD 168,077 did not reinstate extinguished nicotine-seeking behavior. As DRD4 blockade by L-745,870 selectively attenuated both cue- and nicotine-induced reinstatement of nicotine-seeking behavior, without affecting cue- or food-induced reinstatement of food-seeking behavior, DRD4 antagonists are potential therapeutic agents against tobacco smoking relapse.