RESUMEN
There is considerable interest in NMDAR modulators to enhance memory and treat neuropsychiatric disorders such as addiction, depression, and schizophrenia. D-serine and D-cycloserine, the NMDAR activators at the glycine site, are of particular interest because they have been used in humans without serious adverse effects. Interestingly, D-serine also inhibits some NMDARs active at hyperpolarized potentials (HA-NMDARs), and we previously found that HA-NMDARs within the nucleus accumbens core (NAcore) are critical for promoting compulsion-like alcohol drinking, where rats consume alcohol despite pairing with an aversive stimulus such as quinine, a paradigm considered to model compulsive aspects of human alcohol use disorders (AUDs). Here, we examined the impact of D-serine and D-cycloserine on this aversion-resistant alcohol intake (that persists despite adulteration with quinine) and consumption of quinine-free alcohol. Systemic D-serine reduced aversion-resistant alcohol drinking, without altering consumption of quinine-free alcohol or saccharin with or without quinine. Importantly, D-serine within the NAcore but not the dorsolateral striatum also selectively reduced aversion-resistant alcohol drinking. In addition, D-serine inhibited EPSCs evoked at -70 mV in vitro by optogenetic stimulation of mPFC-NAcore terminals in alcohol-drinking rats, similar to reported effects of the NMDAR blocker AP5. Further, D-serine preexposure occluded AP5 inhibition of mPFC-evoked EPSCs, suggesting that D-serine reduced EPSCs by inhibiting HA-NMDARs. Systemic D-cycloserine also selectively reduced intake of quinine-adulterated alcohol, and D-cycloserine inhibited NAcore HA-NMDARs in vitro. Our results indicate that HA-NMDAR modulators can reduce aversion-resistant alcohol drinking, and support testing of D-serine and D-cycloserine as immediately accessible, FDA-approved drugs to treat AUDs.
Asunto(s)
Consumo de Bebidas Alcohólicas/tratamiento farmacológico , Consumo de Bebidas Alcohólicas/fisiopatología , Conducta Compulsiva/tratamiento farmacológico , Conducta Compulsiva/etiología , Cicloserina/uso terapéutico , Serina/uso terapéutico , Animales , Etanol/efectos adversos , Antagonistas de Aminoácidos Excitadores/farmacología , Potenciales Postsinápticos Excitadores/efectos de los fármacos , Hipocampo/citología , Técnicas In Vitro , Masculino , Corteza Prefrontal/citología , Corteza Prefrontal/efectos de los fármacos , Corteza Prefrontal/metabolismo , Ratas , Ratas Wistar , Sacarina/metabolismo , Valina/análogos & derivados , Valina/farmacologíaRESUMEN
Compulsive drinking despite serious adverse medical, social and economic consequences is a characteristic of alcohol use disorders in humans. Although frontal cortical areas have been implicated in alcohol use disorders, little is known about the molecular mechanisms and pathways that sustain aversion-resistant intake. Here, we show that nucleus accumbens core (NAcore) NMDA-type glutamate receptors and medial prefrontal (mPFC) and insula glutamatergic inputs to the NAcore are necessary for aversion-resistant alcohol consumption in rats. Aversion-resistant intake was associated with a new type of NMDA receptor adaptation, in which hyperpolarization-active NMDA receptors were present at mPFC and insula but not amygdalar inputs in the NAcore. Accordingly, inhibition of Grin2c NMDA receptor subunits in the NAcore reduced aversion-resistant alcohol intake. None of these manipulations altered intake when alcohol was not paired with an aversive consequence. Our results identify a mechanism by which hyperpolarization-active NMDA receptors under mPFC- and insula-to-NAcore inputs sustain aversion-resistant alcohol intake.
Asunto(s)
Disuasivos de Alcohol/farmacología , Consumo de Bebidas Alcohólicas/fisiopatología , Reacción de Prevención/fisiología , Corteza Cerebral/fisiopatología , Resistencia a Medicamentos/fisiología , Proteínas del Tejido Nervioso/fisiología , Núcleo Accumbens/fisiopatología , Corteza Prefrontal/fisiopatología , Quinina/farmacología , Receptores de N-Metil-D-Aspartato/fisiología , Consumo de Bebidas Alcohólicas/sangre , Consumo de Bebidas Alcohólicas/tratamiento farmacológico , Amígdala del Cerebelo/química , Animales , Proteínas Bacterianas/análisis , Corteza Cerebral/química , Condicionamiento Operante , Etanol/sangre , Antagonistas de Aminoácidos Excitadores/farmacología , Halorrodopsinas/análisis , Proteínas Luminiscentes/análisis , Masculino , Optogenética , Técnicas de Placa-Clamp , Piperidinas/farmacología , Corteza Prefrontal/química , Interferencia de ARN , ARN Interferente Pequeño/farmacología , Distribución Aleatoria , Ratas , Ratas Wistar , Receptores de N-Metil-D-Aspartato/antagonistas & inhibidores , Receptores de N-Metil-D-Aspartato/genética , Valina/análogos & derivados , Valina/farmacologíaRESUMEN
The MCH and dopamine receptor systems have been shown to modulate a number of behaviors related to reward processing, addiction, and neuropsychiatric conditions such as schizophrenia and depression. In addition, MCH and dopamine receptors can interact in a positive manner, for example in the expression of cocaine self-administration. A recent report (Chung et al., 2011a) showed that the DA1/DA2 dopamine receptor activator apomorphine suppresses pre-pulse inhibition, a preclinical model for some aspects of schizophrenia. Importantly, MCH can enhance the effects of lower doses of apomorphine, suggesting that co-modulation of dopamine and MCH receptors might alleviate some symptoms of schizophrenia with a lower dose of dopamine receptor modulator and thus fewer potential side effects. Here, we investigated whether MCH and apomorphine could enhance action potential firing in vitro in the nucleus accumbens shell (NAshell), a region which has previously been shown to mediate some behavioral effects of MCH. Using whole-cell patch-clamp electrophysiology, we found that MCH, which has no effect on firing on its own, was able to increase NAshell firing when combined with a subthreshold dose of apomorphine. Further, this MCH/apomorphine increase in firing was prevented by an antagonist of either a DA1 or a DA2 receptor, suggesting that apomorphine acts through both receptor types to enhance NAshell firing. The MCH/apomorphine-mediated firing increase was also prevented by an MCH receptor antagonist or a PKA inhibitor. Taken together, our results suggest that MCH can interact with lower doses of apomorphine to enhance NAshell firing, and thus that MCH and apomorphine might interact in vivo within the NAshell to suppress pre-pulse inhibition.
RESUMEN
D(1) dopamine receptors are primary mediators of dopaminergic signaling in the CNS. These receptors internalize rapidly following agonist-induced activation, but the functional significance of this process is unknown. We investigated D(1) receptor endocytosis and signaling in HEK293 cells and cultured striatal neurons using real-time fluorescence imaging and cAMP biosensor technology. Agonist-induced activation of D(1) receptors promoted endocytosis of receptors with a time course overlapping that of acute cAMP accumulation. Inhibiting receptor endocytosis blunted acute D(1) receptor-mediated signaling in both dissociated cells and striatal slice preparations. Although endocytic inhibition markedly attenuated acute cAMP accumulation, inhibiting the subsequent recycling of receptors had no effect. Further, D(1) receptors localized in close proximity to endomembrane-associated trimeric G protein and adenylyl cyclase immediately after endocytosis. Together, these results suggest a previously unanticipated role of endocytosis, and the early endocytic pathway, in supporting rapid dopaminergic neurotransmission.
Asunto(s)
Dopamina/metabolismo , Endocitosis/fisiología , Neuronas/fisiología , Transducción de Señal/fisiología , Potenciales de Acción/efectos de los fármacos , Potenciales de Acción/genética , Adenilil Ciclasas/farmacología , Animales , Benzazepinas/farmacología , Proteínas Portadoras/antagonistas & inhibidores , Proteínas Portadoras/genética , Células Cultivadas , Cuerpo Estriado/citología , AMP Cíclico/farmacología , Dopamina/farmacología , Agonistas de Dopamina/farmacología , Relación Dosis-Respuesta a Droga , Embrión de Mamíferos , Endocitosis/efectos de los fármacos , Citometría de Flujo/métodos , Factores de Intercambio de Guanina Nucleótido/metabolismo , Humanos , Hidrazonas/farmacología , Microscopía Fluorescente/métodos , Neuronas/efectos de los fármacos , Transporte de Proteínas/efectos de los fármacos , ARN Interferente Pequeño/farmacología , Ratas , Receptores de Dopamina D1/genética , Factores de Tiempo , Transfección/métodosRESUMEN
We recently described the SK-type potassium channel as a novel target for treatment of excessive alcohol intake.1 SK channel function is reduced in the nucleus accumbens (NAcb) core in rats consuming alcohol under intermittent (IAA) but not continuous (CAA) access, and the FDA-approved SK activator chlorzoxazone reduces the excessive alcohol intake in IAA rats but not the more moderate intake in CAA rats. Here, we discuss the implications of these and related findings for SK as a treatment for alcohol use disorders. In addition, we report that many NAcb core electrophysiological parameters related to action potential waveform or basal parameters were not altered in alcohol-drinking rats. These results are in strong contrast to those reported for cocaine, where several NAcb ion channels show adaptations after cocaine exposure. These results suggest that alcohol intake is associated with only limited ion channel neuro-adaptations in the NAcb relative to cocaine, and support the hypothesis that SK represents a selective and potent intervention to reduce excessive alcohol intake.
Asunto(s)
Consumo de Bebidas Alcohólicas/tratamiento farmacológico , Alcoholes/administración & dosificación , Agonistas de los Canales de Calcio/farmacología , Canales de Potasio de Pequeña Conductancia Activados por el Calcio/metabolismo , Animales , MasculinoRESUMEN
BACKGROUND: Alcoholism imposes a tremendous social and economic burden. There are relatively few pharmacological treatments for alcoholism, with only moderate efficacy, and there is considerable interest in identifying additional therapeutic options. Alcohol exposure alters SK-type potassium channel (SK) function in limbic brain regions. Thus, positive SK modulators such as chlorzoxazone (CZX), a US Food and Drug Administration-approved centrally acting myorelaxant, might enhance SK function and decrease neuronal activity, resulting in reduced alcohol intake. METHODS: We examined whether CZX reduced alcohol consumption under two-bottle choice (20% alcohol and water) in rats with intermittent access to alcohol (IAA) or continuous access to alcohol (CAA). In addition, we used ex vivo electrophysiology to determine whether SK inhibition and activation can alter firing of nucleus accumbens (NAcb) core medium spiny neurons. RESULTS: Chlorzoxazone significantly and dose-dependently decreased alcohol but not water intake in IAA rats, with no effects in CAA rats. Chlorzoxazone also reduced alcohol preference in IAA but not CAA rats and reduced the tendency for rapid initial alcohol consumption in IAA rats. Chlorzoxazone reduction of IAA drinking was not explained by locomotor effects. Finally, NAcb core neurons ex vivo showed enhanced firing, reduced SK regulation of firing, and greater CZX inhibition of firing in IAA versus CAA rats. CONCLUSIONS: The potent CZX-induced reduction of excessive IAA alcohol intake, with no effect on the more moderate intake in CAA rats, might reflect the greater CZX reduction in IAA NAcb core firing observed ex vivo. Thus, CZX could represent a novel and immediately accessible pharmacotherapeutic intervention for human alcoholism.
Asunto(s)
Consumo de Bebidas Alcohólicas/tratamiento farmacológico , Alcoholes/administración & dosificación , Agonistas de los Canales de Calcio/farmacología , Canales de Potasio de Pequeña Conductancia Activados por el Calcio/metabolismo , Potenciales de Acción/efectos de los fármacos , Consumo de Bebidas Alcohólicas/psicología , Animales , Apamina/farmacología , Conducta Animal/efectos de los fármacos , Agonistas de los Canales de Calcio/uso terapéutico , Clorzoxazona/farmacología , Clorzoxazona/uso terapéutico , Modelos Animales de Enfermedad , Relación Dosis-Respuesta a Droga , Masculino , Neuronas/efectos de los fármacos , Núcleo Accumbens/patología , Técnicas de Placa-Clamp , Ratas , Ratas Wistar , AutoadministraciónRESUMEN
There is considerable interest in the regulation of sensorimotor gating, since deficits in this process could play a critical role in the symptoms of schizophrenia and other psychiatric disorders. Sensorimotor gating is often studied in humans and rodents using the prepulse inhibition of the acoustic startle response (PPI) model, in which an acoustic prepulse suppresses behavioral output to a startle-inducing stimulus. However, the molecular and neural mechanisms underlying PPI are poorly understood. Here, we show that a regulatory pathway involving protein phosphatase 2A (PP2A), glycogen synthase kinase 3 beta (GSK3beta), and their downstream target, the M-type potassium channel, regulates PPI. Mice (Mus musculus) carrying a hypomorphic allele of Ppp2r5delta, encoding a regulatory subunit of PP2A, show attenuated PPI. This PPP2R5delta reduction increases the phosphorylation of GSK3beta at serine 9, which inactivates GSK3beta, indicating that PPP2R5delta positively regulates GSK3beta activity in the brain. Consistently, genetic and pharmacological manipulations that reduce GSK3beta function attenuate PPI. The M-type potassium channel subunit, KCNQ2, is a putative GSK3beta substrate. Genetic reduction of Kcnq2 also reduces PPI, as does systemic inhibition of M-channels with linopirdine. Importantly, both the GSK3 inhibitor 3-(2,4-dichlorophenyl)-4-(1-methyl-1H-indol-3-yl)1H-pyrrole-2,5-dione (SB216763) and linopirdine reduce PPI when directly infused into the medial prefrontal cortex (mPFC). Whole-cell electrophysiological recordings of mPFC neurons show that SB216763 and linopirdine have similar effects on firing, and GSK3 inhibition occludes the effects of M-channel inhibition. These data support a previously uncharacterized mechanism by which PP2A/GSK3beta signaling regulates M-type potassium channel activity in the mPFC to modulate sensorimotor gating.
Asunto(s)
Percepción Auditiva/fisiología , Encéfalo/fisiología , Glucógeno Sintasa Quinasa 3/metabolismo , Inhibición Psicológica , Canales de Potasio/metabolismo , Proteína Fosfatasa 2/metabolismo , Secuencia de Aminoácidos , Animales , Percepción Auditiva/efectos de los fármacos , Encéfalo/efectos de los fármacos , Glucógeno Sintasa Quinasa 3/antagonistas & inhibidores , Glucógeno Sintasa Quinasa 3 beta , Canal de Potasio KCNQ2/genética , Canal de Potasio KCNQ2/metabolismo , Ratones , Ratones Endogámicos C57BL , Ratones Transgénicos , Modelos Neurológicos , Neuronas/efectos de los fármacos , Neuronas/fisiología , Fosforilación , Corteza Prefrontal/efectos de los fármacos , Corteza Prefrontal/fisiología , Proteína Fosfatasa 2/genética , Reflejo de Sobresalto/efectos de los fármacos , Reflejo de Sobresalto/fisiología , Transducción de SeñalRESUMEN
The striatum is considered to be critical for the control of goal-directed action, with the lateral dorsal striatum (latDS) being implicated in modulation of habits and the nucleus accumbens thought to represent a limbic-motor interface. Although medium spiny neurons from different striatal subregions exhibit many similar properties, differential firing and synaptic plasticity could contribute to the varied behavioral roles across subregions. Here, we examined the contribution of small-conductance calcium-activated potassium channels (SKs) to action potential generation and synaptic plasticity in adult rat latDS and nucleus accumbens shell (NAS) projection neurons in vitro. The SK-selective antagonist apamin exerted a prominent effect on latDS firing, significantly decreasing the interspike interval. Furthermore, prolonged latDS depolarization increased the interspike interval and reduced firing, and this enhancement was reversed by apamin. In contrast, NAS neurons exhibited greater basal firing rates and less regulation of firing by SK inhibition and prolonged depolarization. LatDS neurons also had greater SK currents than NAS neurons under voltage-clamp. Importantly, SK inhibition with apamin facilitated long-term depression (LTD) induction in the latDS but not the NAS, without alterations in glutamate release. In addition, SK activation in the latDS prevented LTD induction. Greater SK function in the latDS than in the NAS was not secondary to differences in sodium or inwardly rectifying potassium channel function, and apamin enhancement of firing did not reflect indirect action through cholinergic interneurons. Thus, these data demonstrate that SKs are potent modulators of action potential generation and LTD in the dorsal striatum, and could represent a fundamental cellular mechanism through which habits are regulated.
Asunto(s)
Potenciales de Acción/fisiología , Cuerpo Estriado/metabolismo , Depresión Sináptica a Largo Plazo/fisiología , Canales de Potasio de Pequeña Conductancia Activados por el Calcio/metabolismo , Potenciales de Acción/efectos de los fármacos , Animales , Apamina/farmacología , Cuerpo Estriado/citología , Depresión Sináptica a Largo Plazo/efectos de los fármacos , Masculino , Plasticidad Neuronal/efectos de los fármacos , Plasticidad Neuronal/fisiología , Neuronas/efectos de los fármacos , Neuronas/fisiología , Técnicas de Placa-Clamp , Ratas , Ratas Long-EvansRESUMEN
The cellular mechanisms underlying pathological alcohol seeking remain poorly understood. Here, we show an enhancement of nucleus accumbens (NAcb) core action potential firing ex vivo after protracted abstinence from alcohol but not sucrose self-administration. Increased firing is associated with reduced small-conductance calcium-activated potassium channel (SK) currents and decreased SK3 but not SK2 subunit protein expression. Furthermore, SK activation ex vivo produces greater firing suppression in NAcb core neurons from alcohol- versus sucrose-abstinent rats. Accordingly, SK activation in the NAcb core significantly reduces alcohol but not sucrose seeking after abstinence. In contrast, NAcb shell and lateral dorsal striatal firing ex vivo are not altered after abstinence from alcohol, and SK activation in these regions has little effect on alcohol seeking. Thus, decreased NAcb core SK currents and increased excitability represents a critical mechanism that facilitates motivation to seek alcohol after abstinence.