RESUMO
Alcohol use disorder (AUD) remains a critical public health issue worldwide, characterized by high relapse rates often triggered by contextual cues. This research investigates the neural mechanisms behind context-induced reinstatement of alcohol-seeking behavior, focusing on the nucleus accumbens and its interactions with the prelimbic cortex, employing Male Long-Evans rats in an ABA renewal model. In our experimental setup, rats were trained to self-administer 10 % ethanol in Context A, followed by extinction of lever pressing in the presence of discrete cues in Context B. The context-induced reinstatement of ethanol-seeking was then assessed by re-exposing rats to Context A or B under extinction conditions, aiming to simulate the environmental cues' influence on relapse behaviors. Three experiments were conducted: Experiment 1 utilized Fos-immunohistochemistry to examine neuronal activation in the nucleus accumbens; Experiment 2 applied the baclofen + muscimol inactivation technique to probe the functional importance of the nucleus accumbens core; Experiment 3 used Fos-immunofluorescence along with Retrobeads injection to investigate activation of neurons projecting from the prelimbic cortex to the nucleus accumbens core. Our findings revealed significant increases in Fos-immunoreactive nuclei within the nucleus accumbens core and shell during the reinstatement phase in Context A, underscoring the environment's potent effect on ethanol-seeking behavior. Additionally, inactivation of the nucleus accumbens core markedly reduced reinstatement, and there was a notable activation of neurons from the prelimbic cortex to the nucleus accumbens core in the ethanol-associated context. These results highlight the critical role of the nucleus accumbens core and its corticostriatal projections in the neural circuitry underlying context-driven ethanol seeking.
Assuntos
Comportamento de Procura de Droga , Etanol , Extinção Psicológica , Núcleo Accumbens , Ratos Long-Evans , Animais , Núcleo Accumbens/efeitos dos fármacos , Masculino , Etanol/administração & dosagem , Etanol/farmacologia , Comportamento de Procura de Droga/fisiologia , Ratos , Extinção Psicológica/fisiologia , Extinção Psicológica/efeitos dos fármacos , Autoadministração , Vias Neurais/fisiologia , Alcoolismo , Sinais (Psicologia) , Córtex Pré-Frontal/fisiologia , Córtex Pré-Frontal/efeitos dos fármacos , Baclofeno/farmacologia , Proteínas Proto-Oncogênicas c-fos/metabolismo , Muscimol/farmacologiaRESUMO
Despite progress in understanding the role of the dorsal hippocampus in the acquisition, consolidation and retrieval of episodic-like memory, plastic changes within the intra- and extrahippocampal circuits for aversive memory formation and anxiety-like behaviours must still be identified since both processes contribute to multiple aspects of flexible decision-making. Here, we investigated the effect of reversible inactivation induced by a muscimol microinfusion into the dorsal CA1 subfield (dCA1) either prior to acquisition or to retrieval testing of a discriminative avoidance task performed in a plus-maze apparatus (PM-DAT). Differential cAMP-response-element-binding protein 1 (CREB-1) expression in the dorsal and ventral CA1 and CA3 of the hippocampus (dCA1, dCA3, vCA1, and vCA3), dorsal dentate gyrus (dDG), and infralimbic (IL) and prelimbic (PrL) regions of the medial prefrontal cortex was also assessed to investigate the molecular changes associated with the consolidation or retrieval of episodic-like memory and anxiety. Adult male Wistar rats were assigned to two control groups, learning (no surgery/no microinfusion, n = 7) and sham-operated (sham surgery/no microinfusion, n = 6) groups, or four experimental groups, in which the vehicle (0.5 µl per side, n = 8/per group) or a GABAA receptor agonist (0.5 µg/0.5 µl muscimol/per side) was bilaterally microinfused in the dCA1 30 min prior to training (n = 9) or prior to testing sessions (n = 6) with a 24 h intertrial interval. Memory was evaluated using the percentage of time spent in the nonaversive enclosed arms, whereas anxiety was measured by calculating the percentages of time spent and entries into open arms and the percentage of time spent self-grooming. Our findings corroborated previous data showing that the dCA1 is required for discriminative avoidance consolidation. Furthermore, additional information indicated that impaired long-term memory was associated with downregulated CREB-1 expression in the dDG and vCA3. Moreover, memory retrieval was not impaired by dCA1 inactivation prior to the testing session, which was associated with the upregulation of CREB-1 in the dCA3 and vCA1 and downregulation in the dCA1 and vCA3. Differential expression of CREB was not identified in the IL or PrL areas. These results improve our understanding of how the hippocampal circuitry mediates the acquisition and retrieval of aversive memory and anxiety.
Assuntos
Hipocampo , Memória , Ratos , Animais , Masculino , Ratos Wistar , Muscimol/farmacologia , AprendizagemRESUMO
Anthelmintics are used to treat human and veterinary parasitic diseases and to reduce crop and livestock production loss associated with parasitosis. The free-living nematode Caenorhabditis elegans, a model system for anthelmintic drug discovery, has a serotonin (5-HT)-gated chloride channel, MOD-1, which belongs to the Cys-loop receptor family and modulates locomotory and behavioral functions. Since MOD-1 is unique to nematodes, it is emerging as an attractive anthelmintic drug target, but details of MOD-1 function are unclear. Here, we revealed novel aspects of MOD-1 function from the molecular level to the organism level and identified compounds targeting this receptor, which may provide new directions for anthelmintic drug discovery. We used whole-cell current recordings from heterologously expressed MOD-1 to show that tryptamine (Tryp), a weak partial agonist of vertebrate serotonin type 3 (5-HT3) receptors, efficaciously activates MOD-1. A screen for modulators revealed that GABAergic ligands piperazine (PZE) and muscimol reduce 5-HT-elicited currents, thus identifying novel MOD-1 allosteric inhibitors. Next, we performed locomotor activity assays, and we found 5-HT and Tryp rapidly decrease worm motility, which is reversible only at low 5-HT concentrations. Mutants lacking MOD-1 are partially resistant to both drugs, demonstrating its role in locomotion. Acting as an antagonist of MOD-1, we showed PZE reduces the locomotor effects of exogenous 5-HT. Therefore, Tryp- and PZE-derived compounds, acting at MOD-1 through different molecular mechanisms, emerge as promising anthelmintic agents. This study enhances our knowledge of the function and drug selectivity of Cys-loop receptors and postulates MOD-1 as a potential target for anthelmintic therapy.
Assuntos
Anti-Helmínticos , Receptores de Canais Iônicos de Abertura Ativada por Ligante com Alça de Cisteína , Nematoides , Animais , Anti-Helmínticos/farmacologia , Caenorhabditis elegans/genética , Canais de Cloreto/genética , Humanos , Muscimol/farmacologia , Piperazinas/farmacologia , Serotonina/farmacologiaRESUMO
Recognition memory can rely on three components: "what", "where" and "when". Recently we demonstrated that the anterior retrosplenial cortex (aRSC), like the perirhinal cortex (PRH) and unlike the hippocampus (HP), is required for consolidation of the "what" component. Here, we aimed at studying which brain structures interact with the aRSC to process object recognition (OR) memory in rats. We studied the interaction of six brain structures that are connected to the aRSC during OR memory processing: PRH, medial prefrontal cortex (mPFC), anteromedial thalamic nuclei (AM), medial entorhinal cortex (MEC), anterior cingulate cortex (ACC) and the dorsal HP (dHP). We previously described the role of the PRH and dHP, so we first studied the participation of the mPFC, AM, MEC and ACC in OR memory consolidation by bilateral microinfusions of the GABAA receptor agonist muscimol. We observed an impairment in OR long-term memory (LTM) when inactivating the mPFC, the AM and the MEC, but not the ACC. Then, we studied the functional connections by unilateral inactivation of the aRSC and each one of the six structures in the same (ipsilateral) or the opposite (contralateral) hemisphere. Our results showed an amnesic LTM effect in rats with ipsilateral inactivations of aRSC-PRH, aRSC-mPFC, aRSC-AM, or aRSC-MEC. On the other hand, we observed memory impairment when aRSC-ACC were inactivated in opposite hemispheres, and no effect when the aRSC-dHP connection was inactivated. Thus, our ipsilateral inactivation findings reveal that the aRSC and, at least one brain region required in OR LTM processing are essential to consolidate OR memory. In conclusion, our results show that several cortico-cortical and cortico-thalamic pathways are important for OR memory consolidation.
Assuntos
Córtex Entorrinal/fisiologia , Giro do Cíngulo/fisiologia , Memória de Longo Prazo/fisiologia , Córtex Pré-Frontal/fisiologia , Reconhecimento Psicológico/fisiologia , Animais , Agonistas de Receptores de GABA-A/farmacologia , Hipocampo/fisiologia , Bombas de Infusão , Masculino , Muscimol/farmacologia , RatosRESUMO
Memory extinction has been used in behavioral therapy to treat post-traumatic stress disorders. It was demonstrated that memory reactivation before extinction could facilitate this process. However, the mechanisms involved are still unclear. Here, we investigated the participation of two regions of the ventromedial prefrontal cortex (vmPFC), the infralimbic (IL) and prelimbic (PL), in the memory reactivation modulatory effect of fear extinction. We confirmed that the reactivation facilitates the fear extinction in an inhibitory aversive task; however, when the muscimol (a GABAergic agonist) is infused in IL or PL vmPFC after reactivation, extinction's facilitation was not observed. These findings support the idea that the reactivation can modulate the fear extinction process, facilitating it, and that this effect requires the activation of both IL and PL regions of vmPFC.
Assuntos
Aprendizagem da Esquiva/fisiologia , Extinção Psicológica/fisiologia , Memória/fisiologia , Córtex Pré-Frontal/fisiologia , Animais , Aprendizagem da Esquiva/efeitos dos fármacos , Extinção Psicológica/efeitos dos fármacos , Agonistas de Receptores de GABA-A/farmacologia , Masculino , Memória/efeitos dos fármacos , Muscimol/farmacologia , Córtex Pré-Frontal/efeitos dos fármacos , Ratos , Ratos WistarRESUMO
The insular cortex (IC) is notably implicated in emotional and cognitive processing; however, little is known regarding to what extent its two main subregions play functionally distinct roles on memory consolidation of conditioned fear tasks. Here we verified the effects of temporary functional inactivation of the anterior (aIC) and posterior IC (pIC) on contextual and tone fear memory. Rats received post-training bilateral infusions of the GABAA receptor agonist muscimol into either the aIC or pIC and were tested 48 and 72 h after the delay tone fear conditioning session to assess the background contextual (CFC) and tone (TFC) fear conditioning, respectively. Inactivation of the aIC during memory consolidation did not affect fear memory for CFC or TFC. On the other hand, post-training inactivation of the pIC impaired TFC but not CFC. Our findings indicate that the pIC is a necessary part of the neural circuitry related to the consolidation of cued-fear memories.
Assuntos
Córtex Cerebral/fisiologia , Condicionamento Clássico/fisiologia , Medo , Consolidação da Memória/fisiologia , Estimulação Acústica , Animais , Córtex Cerebral/efeitos dos fármacos , Condicionamento Clássico/efeitos dos fármacos , Agonistas de Receptores de GABA-A/farmacologia , Consolidação da Memória/efeitos dos fármacos , Muscimol/farmacologia , RatosRESUMO
The nucleus reuniens has been shown to support the acquisition, consolidation, maintenance, destabilization upon retrieval, and extinction of aversive memories. However, the direct participation of this thalamic subregion in memory reconsolidation is yet to be examined. The present study addressed this question in contextually fear-conditioned rats. Post-reactivation infusion of the GABAA receptor agonist muscimol, the glutamate N2A-containing NMDA receptor antagonist TCN-201, or the protein synthesis inhibitor anisomycin into the NR induced significant impairments in memory reconsolidation. Administering muscimol or TCN-201 and anisomycin locally, or associating locally infused muscimol or TCN-201 with systemically administered clonidine, an α2-receptor adrenergic agonist that attenuates the noradrenergic tonus associated with memory reconsolidation, produced no further reduction in freezing times when compared with the muscimol-vehicle, TCN-201-vehicle, vehicle-anisomycin, and vehicle-clonidine groups. This pattern of results indicates that such treatment combinations produced no additive/synergistic effects on reconsolidation. It is plausible that NR inactivation and antagonism of glutamate N2A-containing NMDA receptors weakened/prevented the subsequent action of anisomycin and clonidine because they disrupted the early stages of signal transduction pathways involved in memory reconsolidation. It is noteworthy that these pharmacological interventions, either alone or combined, induced no contextual memory specificity changes, as assessed in a later test in a novel and unpaired context. Besides, omitting memory reactivation precluded the impairing effects of muscimol, TCN-201, anisomycin, and clonidine on reconsolidation. Together, the present findings demonstrate interacting mechanisms through which the NR can regulate contextual fear memory restabilization.
Assuntos
Medo/fisiologia , Consolidação da Memória/fisiologia , Núcleos da Linha Média do Tálamo/fisiologia , Agonistas de Receptores Adrenérgicos alfa 2/farmacologia , Animais , Anisomicina/farmacologia , Clonidina/farmacologia , Medo/psicologia , Agonistas de Receptores de GABA-A/farmacologia , Masculino , Consolidação da Memória/efeitos dos fármacos , Núcleos da Linha Média do Tálamo/efeitos dos fármacos , Núcleos da Linha Média do Tálamo/metabolismo , Muscimol/farmacologia , Ratos , Ratos Wistar , Receptores de N-Metil-D-Aspartato/fisiologia , Sulfonamidas/farmacologiaRESUMO
The neural circuit supporting aversive memory destabilization after retrieval includes the hippocampus, amygdala, and medial prefrontal cortex. The nucleus reuniens (NR) contributes to the functional interaction of these brain regions relevant to cognitive processing. However, the direct participation of this thalamic subregion in memory destabilization is yet to be investigated. The present study addressed this question in contextually fear-conditioned rats. Pre-reactivation infusion of the GABAA receptor agonist muscimol, the protein degradation inhibitor clasto-lactacystin ß-lactone (ß-lac), or the glutamate N2B-containing NMDA receptors antagonist ifenprodil into the NR prevented the post-reactivation amnestic effects of both locally infused anisomycin and systemically administered clonidine. In either case, the results suggest a significant disruption in memory destabilization. It is noteworthy that these pharmacological interventions induced no changes in expression or contextual specificity of the memory. Moreover, omitting memory reactivation precluded the muscimol, ß-lac, and ifenprodil effects on destabilization and the anisomycin and clonidine effects on reconsolidation. We also quantified the Egr1/Zif268-expressing neurons to investigate the effects of muscimol-induced NR inactivation on the activity-related plasticity locally, and in other brain regions supporting fear memory destabilization-reconsolidation. Relative to controls, there were reduced values in the NR, the dorsal CA1 hippocampus, the prelimbic cortex, and the infralimbic cortex. In contrast, increases happened in the ventral CA1 hippocampus and the basolateral amygdala. These results suggest that NR has a circuit-level influence on this process. Together, present findings demonstrate how the NR can regulate contextual fear memory destabilization upon retrieval.
Assuntos
Tonsila do Cerebelo/fisiologia , Região CA1 Hipocampal/fisiologia , Medo , Memória/fisiologia , Núcleos da Linha Média do Tálamo/fisiologia , Neurônios/fisiologia , Córtex Pré-Frontal/fisiologia , Tonsila do Cerebelo/efeitos dos fármacos , Tonsila do Cerebelo/metabolismo , Animais , Anisomicina/farmacologia , Região CA1 Hipocampal/efeitos dos fármacos , Região CA1 Hipocampal/metabolismo , Clonidina/farmacologia , Cognição , Inibidores de Cisteína Proteinase/farmacologia , Proteína 1 de Resposta de Crescimento Precoce/metabolismo , Antagonistas de Aminoácidos Excitatórios/farmacologia , Agonistas de Receptores de GABA-A/farmacologia , Lactonas/farmacologia , Memória/efeitos dos fármacos , Núcleos da Linha Média do Tálamo/efeitos dos fármacos , Núcleos da Linha Média do Tálamo/metabolismo , Muscimol/farmacologia , Neurônios/efeitos dos fármacos , Neurônios/metabolismo , Piperidinas/farmacologia , Córtex Pré-Frontal/efeitos dos fármacos , Córtex Pré-Frontal/metabolismo , Ratos , Receptores de N-Metil-D-Aspartato/antagonistas & inibidoresRESUMO
Active expiration represents an important mechanism to improve ventilation in conditions of augmented ventilatory demand, such as hypercapnia. While a rostral ventromedullary region, the parafacial respiratory group (pFRG), has been identified as a conditional expiratory oscillator, little is known about how central chemosensitive sites contribute to modulate active expiration under hypercapnia. In this study, we investigated the influence of the medullary raphe in the emergence of phasic expiratory abdominal activity during hypercapnia in unanesthetized adult male rats, in a state-dependent manner. To do so, reverse microdialysis of muscimol (GABAA receptor agonist, 1 mM) or 8-OH-DPAT (5-HT1A agonist, 1 mM) was applied in the MR during sleep and wakefulness periods, both in normocapnic (room air) and hypercapnic conditions (7% CO2). Electromyography (EMG) of diaphragm and abdominal muscles was performed to measure inspiratory and expiratory motor outputs. We found that active expiration did not occur in room air exposure during wakefulness or sleep. However, hypercapnia did recruit active expiration, and differential effects were observed with the drug dialyses in the medullary raphe. Muscimol increased the diaphragm inspiratory motor output and also increased the amplitude and frequency of abdominal expiratory rhythmic activity during hypercapnia in wakefulness periods. On the other hand, the microdialysis of 8-OH-DPAT attenuated hypercapnia-induced active expiration in a state-dependent manner. Our data suggest that the medullary raphe can either inhibit or potentiate respiratory motor activity during hypercapnia, and the balance of these inhibitory or excitatory outputs may determine the expression of active expiration.
Assuntos
Diafragma/fisiopatologia , Expiração , Hipercapnia/fisiopatologia , Núcleos da Rafe/fisiopatologia , 8-Hidroxi-2-(di-n-propilamino)tetralina/farmacologia , Músculos Abdominais/inervação , Músculos Abdominais/fisiopatologia , Animais , Diafragma/inervação , Agonistas de Receptores de GABA-A/farmacologia , Masculino , Muscimol/farmacologia , Contração Muscular , Núcleos da Rafe/efeitos dos fármacos , Ratos , Ratos Wistar , Agonistas do Receptor de Serotonina/farmacologia , Sono , VigíliaRESUMO
Lesioning or inactivating the infralimbic (IL) subregion of the medial prefrontal cortex before acquisition produces more generalized and extinction-resistant fear memories. However, whether and how it modulates memory specificity and extinction susceptibility while consolidation takes place is still unknown. The present study aims to investigate these questions using muscimol-induced temporary inactivation and anisomycin-induced protein synthesis inhibition in the rat IL following contextual fear conditioning. Results indicate that the IL activity immediately after acquisition, but not six hours later, controls memory generalization over a week, regardless of its strength. Such IL function depends on the context-shock pairing since muscimol induced no changes in animals exposed to immediate shocks or the conditioning context only. Animals in which the IL was inactivated during consolidation extinguished similarly to controls within the session but were unable to recall the extinction memory the following day. Noteworthy, these post-acquisition IL inactivation-induced effects were not associated with changes in anxiety, as assessed in the elevated plus-maze test. Anisomycin results indicate that the IL protein synthesis during consolidation contributes more to producing extinction-sensitive fear memories than memory specificity. Collectively, present results provide evidence for the IL's role in controlling generalization and susceptibility to extinction during fear memory consolidation.