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RATIONALE: Re-exposing an animal to an environment previously paired with an aversive stimulus evokes large alterations in behavioral and cardiovascular parameters. Dorsal hippocampus (dHC) receives important cholinergic inputs from the basal forebrain, and respective acetylcholine (ACh) levels are described to influence defensive behavior. Activation of muscarinic M1 and M3 receptors facilitates autonomic and behavioral responses along threats. Evidence show activation of cholinergic receptors promoting formation of nitric oxide (NO) and cyclic guanosine monophosphate (cGMP) in dHC. Altogether, the action of ACh and NO on conditioned responses appears to converge within dHC. OBJECTIVES: As answer about how ACh and NO interact to modulate defensive responses has so far been barely addressed, we aimed to shed additional light on this topic. METHODS: Male Wistar rats had guide cannula implanted into the dHC before being submitted to the contextual fear conditioning (3footshocks/085 mA/2 s). A catheter was implanted in the femoral artery the next day for cardiovascular recordings. Drugs were delivered into dHC 10 min before contextual re-exposure, which occurred 48 h after the conditioning procedure. RESULTS: Neostigmine (Neo) amplified the retrieval of conditioned responses. Neo effects (1 nmol) were prevented by the prior infusion of a M1-M3 antagonist (fumarate), a neuronal nitric oxide synthase inhibitor (NPLA), a NO scavenger (cPTIO), a guanylyl cyclase inhibitor (ODQ), and a NMDA antagonist (AP-7). Pretreatment with a selective M1 antagonist (pirenzepine) only prevented the increase in autonomic responses induced by Neo. CONCLUSION: The results show that modulation in the retrieval of contextual fear responses involves coordination of the dHC M1-M3/NO/cGMP/NMDA pathway.
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N-Metilaspartato , Óxido Nítrico , Acetilcolina , Animales , Colinérgicos/farmacología , Miedo/fisiología , Fumaratos/farmacología , Guanosina Monofosfato/farmacología , Guanilato Ciclasa/metabolismo , Guanilato Ciclasa/farmacología , Hipocampo , Masculino , N-Metilaspartato/farmacología , Neostigmina/farmacología , Óxido Nítrico/metabolismo , Óxido Nítrico Sintasa de Tipo I/metabolismo , Pirenzepina/farmacología , Ratas , Ratas Wistar , Receptores Colinérgicos/metabolismo , Receptores de N-Metil-D-Aspartato , Transmisión SinápticaRESUMEN
Growth factors, such as insulin-like growth factor 1 (IGF-1), among others are known for their critical involvement in learning and memory processes. IGF-1 regulates cognitive functions, synapse density, neurotransmission, and adult neurogenesis and induces structural and synaptic plasticity-specific changes. Although IGF-1 has been suggested to participate in different memory processes, its role in memories associated with negative emotional experiences still remains to be elucidated. The principal aim of the present study was to test whether IGF-1 overexpression using adenoviral vectors in basolateral amygdala (BLA) influences both the expression and formation of contextual fear memory, as well as the hippocampal structural plasticity associated with such memory trace. We found that IGF-1 overexpression promotes the formation and expression of a specific contextual fear memory trace, and such effect persisted at least 7 days after recall. Moreover, the overexpression of this growth factor in BLA upregulates the activation of the ERK/MAPK pathway in this brain structure. In addition, intra-BLA IGF-1 overexpression causes dorsal hippocampus (DH) structural plasticity modifications promoting changes in the proportion of mature dendritic spines in the CA1 region, after a weak conditioning protocol. The present findings contribute to the knowledge underlying BLA-DH trace memory of fear and reveal important new insights into the neurobiology and neurochemistry of fear acquisition modulated by IGF-1 overexpression. The understanding of how IGF-1 modulates the formation of a fear contextual trace may pave the way for the development of novel therapeutic strategies focused on fear, anxiety, and trauma-related disorders.
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Complejo Nuclear Basolateral , Complejo Nuclear Basolateral/fisiología , Miedo/fisiología , Hipocampo/fisiología , Factor I del Crecimiento Similar a la Insulina/genética , Factor I del Crecimiento Similar a la Insulina/metabolismo , Memoria/fisiologíaRESUMEN
Despite considerable progress on the study of the effect of standardized extract of Gingko biloba (EGb) on memory processes, our understanding of its role in the persistence of long-term memory (LTM) and the molecular mechanism underlying its effect, particularly episodic-like memory, is limited. We here investigated the effects of EGb on the long-term retention of recognition memory and its persistence and BDNF expression levels in the dorsal hippocampal formation (DHF). Adult male Wistar rats (n = 10/group) were handled for 10 min/5 day. On day 6, the animals were treated with vehicle or 0.4 mg/kg diazepam (control groups) or with EGb (250, 500 or 100 mg/kg) 30 min before the training session (TR1), in which the animals were exposed to two sample objects. On day 7, all rats underwent a second training session (TR2) as described in the TR1 but without drug treatment. Object recognition memory (ORM) was evaluated on day 8 (retention test, T1) and day 9 (persistence test, T2). At the end of T1or T2, animals were decapitated, and DHF samples were frozen at -80 °C for analyses of the differential expression of BDNF by Western blotting. EGb-treated groups spent more time exploring the novel object in T2 and showed the highest recognition index (RI) values during the T1 and T2, which was associated with upregulation of BDNF expression in the DHF in a dose-and session-dependent manner. Our data reveal, for the first time, that EGb treatment before acquisition of ORM promotes persistence of LTM by BDNF differential expression.
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Factor Neurotrófico Derivado del Encéfalo/metabolismo , Extractos Vegetales/administración & dosificación , Reconocimiento en Psicología/efectos de los fármacos , Regulación hacia Arriba , Animales , Relación Dosis-Respuesta a Droga , Ginkgo biloba , Hipocampo/metabolismo , Masculino , Extractos Vegetales/química , Extractos Vegetales/farmacología , Ratas , Ratas WistarRESUMEN
Reconsolidation of a contextual fear memory is a protein synthesis-dependent process in which a previously destabilized memory returns to a stable state. This process has become the subject of many studies due to its importance in memory processing, maintenance and updating, and its potential role as a therapeutical target in fear memory disorders such as phobias and post-traumatic stress disorder. In this sense, understanding the underlying mechanisms of memory reconsolidation is paramount in developing potential treatments for such memory dysfunctions. In the present work, we studied the interaction between two key neural structures involved in the reconsolidation process: the basolateral amygdala complex of the amygdala (BLA) and the dorsal hippocampus (DH). Our results show changes in the structural plasticity of the CA1 region of the DH in the form of dendritic spines density changes associated with the destabilization/reconsolidation process. Furthermore, we demonstrate a modulatory role of BLA over such structural plasticity by infusing different drugs such as ifenprodil, a destabilization blocker, and propranolol, a reconsolidation disruptor, in this brain structure. Altogether our work shows a particular temporal dynamic in the CA1 region of DH that accompanies the destabilization/reconsolidation process and aims to provide new information on the underlying mechanisms of this process that potentially contributes for a better understanding of memory storage, maintenance, expression and updating, and its potential medical applications.
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Complejo Nuclear Basolateral , Consolidación de la Memoria , Amígdala del Cerebelo/metabolismo , Miedo , Hipocampo , MemoriaRESUMEN
Chronic stress is related to the acceleration of telomere shortening. Recent work showed a correlation between chronic psychosocial stress and reduced telomere length in certain cells. The exposure of T lymphocytes to cortisol promoted a significant reduction in telomerase activity. Although stress can promote changes in telomere length, whether increased glucocorticoid concentrations alter telomere length in brain tissue cells is unclear. In addition to modulating the activity of the stress system, estrogen also influences telomere length. The objective of this study was to verify whether chronic exposure to glucocorticoids promotes changes in the telomere length of encephalic areas involved in the control of HPA axis activity and whether estrogen affects these changes. Wistar rats were ovariectomized and treated with estradiol cypionate [(50 or 100 µg/kg, subcutaneously)] or oil and 20 mg/kg corticosterone or vehicle (isotonic saline with 2% Tween 80, subcutaneously) for 28 days. On the day after the end of the hormonal treatment, the animals were euthanized for collection of blood, brain and pituitary gland samples. Estrogen modulated the activity of the HPA axis. CRH, AVP and POMC mRNA levels were reduced by estrogen. At least in doses and treatment time used, there was no correlation between effects of exposure to glucocorticoids and estrogen on telomere length in the brain areas of female rats. However, estrogen treatment reduced the telomere length in the central amygdala and dorsal hippocampus, but not in the PVN, indicating a variation of reaction of telomeres for estrogen in different brain areas.
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Corticosterona/farmacología , Estrógenos/farmacología , Homeostasis del Telómero/fisiología , Hormona Adrenocorticotrópica/metabolismo , Amígdala del Cerebelo/efectos de los fármacos , Animales , Encéfalo/efectos de los fármacos , Encéfalo/metabolismo , Corticosterona/metabolismo , Hormona Liberadora de Corticotropina/metabolismo , Estrógenos/metabolismo , Femenino , Hipocampo/efectos de los fármacos , Sistema Hipotálamo-Hipofisario/metabolismo , Núcleo Hipotalámico Paraventricular/efectos de los fármacos , Sistema Hipófiso-Suprarrenal/metabolismo , Ratas , Estrés Fisiológico , Telómero/efectos de los fármacos , Telómero/metabolismo , Telómero/fisiología , Homeostasis del Telómero/efectos de los fármacosRESUMEN
Experiences influence the development of the central nervous system. Cognitive training promotes changes in the structure of the brain, such as in its weight and number of cells, as well as ability to perform dendritic remodeling. The present study was designed to detect possible differences in the neuronal morphology of the dorsal hippocampus between female and male Long-Evans rats after cognitive training (CT). CT was promoted through three learning and memory tests: the Morris water maze, the Barnes circular maze, and Novel object recognition tests. Our data revealed no differences in learning or memory capacities between female and male rats; rats of the two sexes solved the behavioral test with equal efficiency. CT caused an increase in the basilar and apical dendritic arborization of CA1 neurons in male rats, whereas female rats that underwent CT presented only remodeling in the apical arbors of CA1 neurons. The basilar arbors of CA3 neurons of female rats showed an increase in arborization, but their apical arbors were not modified; the arbors of CA3 neurons of male rats submitted to CT were not modified. Total dendritic length was modified by CT in the apical arbors of CA1 neurons of female and male rats and in the basilar CA1 arbors of male rats. There was a significant increase in dendritic spine density in all arbors of CA1 and CA3 neurons of females and males subjected to CT. These results suggest that dendritic remodeling after CT is similar between female and male rats.
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Región CA1 Hipocampal/fisiología , Región CA3 Hipocampal/fisiología , Cognición , Espinas Dendríticas/fisiología , Aprendizaje , Animales , Región CA1 Hipocampal/citología , Región CA3 Hipocampal/citología , Femenino , Masculino , Ratas , Ratas Long-Evans , Factores SexualesRESUMEN
Increased nitric oxide (NO) levels have been identified in the hippocampus of animals subjected to social isolation. However, a role of this change in behavioral and physiological changes evoked by isolation has never been evaluated. Thus, this study investigated the involvement of nitrergic neurotransmission acting via the neuronal isoform of nitric oxide synthase (nNOS) within the dorsal hippocampus in behavioral and cardiovascular changes in isolated reared rats. For this, male rats were isolated from weaning at 21 days postnatal for 40 days. We identified that social isolation increased hippocampal NO formation and nNOS expression. Besides, anxiogenic- and depressive-like effect identified in isolated animals were not affected by intra-hippocampal microinjection of either the NO scavenger carboxy-PTIO or the selective nNOS inhibitor Nω-Propyl-l-arginine (NPLA). Isolation also increased basal arterial pressure, impaired the baroreflex function and decreased the tachycardia to restraint stress. The effects in restraint-evoked tachycardia were inhibited by hippocampal treatment with either carboxy-PTIO or NPLA. Intra-hippocampal administration of either carboxy-PTIO or NPLA also enhanced the pressor response to restraint in isolated, but not in control animals. Taken together, these findings indicate that increased NO release within the dorsal hippocampus is involved in impairment of cardiovascular responses to a novel stressor, but not in behavioral effects and baroreflex changes, evoked by social isolation. Furthermore, exposure to this stressor evokes the emergence of an inhibitory role of hippocampal nNOS activation in cardiovascular changes to a novel stressor, which might constitute a prominent adaptive response.
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Conducta Animal , Sistema Cardiovascular/metabolismo , Hipocampo/metabolismo , Óxido Nítrico Sintasa de Tipo I/metabolismo , Óxido Nítrico/metabolismo , Estrés Psicológico , Animales , Sistema Cardiovascular/patología , Enfermedad Crónica , Masculino , Ratas , Ratas Wistar , Transmisión SinápticaRESUMEN
Early life experiences program lifelong responses to stress. In agreement, resilience and vulnerability to psychopathologies, such as posttraumatic stress disorder (PTSD), have been suggested to depend on the early background. New therapies have targeted memory reconsolidation as a strategy to modify the emotional valence of traumatic memories. Here, we used animal models to study the molecular mechanism through which early experiences may later affect aversive memory reconsolidation. Handling (H)-separation of pups from dams for 10 min-or maternal separation (MS) - 3-h separation-were performed from PDN1-10, using non-handled (NH) litters as controls. Adult males were trained in a contextual fear conditioning (CFC) task; 24 h later, a short reactivation session was conducted in the conditioned or in a novel context, followed by administration of midazolam 3 mg/kg i.p. (mdz), known to disturb reconsolidation, or vehicle; a test session was performed 24 h after. The immunocontent of relevant proteins was studied 15 and 60 min after memory reactivation in the dorsal hippocampus (dHc) and basolateral amygdala complex (BLA). Mdz-treated controls (NH) showed decreased freezing to the conditioned context, consistent with reconsolidation impairment, but H and MS were resistant to labilization. Additionally, MS males showed increased freezing to the novel context, suggesting fear generalization; H rats showed lower freezing than the other groups, in accordance with previous suggestions of reduced emotionality facing adversities. Increased levels of Zif268, GluN2B, ß-actin and polyubiquitination found in the BLA of all groups suggest that memory reconsolidation was triggered. In the dHc, only NH showed increased Zif268 levels after memory retrieval; also, a delay in ERK1/2 activation was found in H and MS animals. We showed here that reconsolidation of a contextual fear memory is insensitive to interference by a GABAergic drug in adult male rats exposed to different neonatal experiences; surprisingly, we found no differences in the reconsolidation process in the BLA, but the dHc appears to suffer temporal desynchronization in the engagement of reconsolidation. Our results support a hippocampal-dependent mechanism for reconsolidation resistance in models of early experiences, which aligns with current hypotheses for the etiology of PTSD.
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Pro-inflammatory cytokines, particularly Interleukin-1ß (IL-1ß), can affect cognitive processes such as learning and memory. The aim of this study was to establish whether the effect of IL-1ß on contextual fear memory is associated with changes in hippocampal structural plasticity. We also studied the effect of α-melanocyte-stimulating hormone (α-MSH), a potent anti-inflammatory and neuro-protective peptide. Different groups of animals were implanted bilaterally in dorsal hippocampus (DH). After recovery they were conditioned for contextual fear memory and received the different treatments (vehicle, IL-1ß, α-MSH or IL-1ß + α-MSH). Memory was assessed 24 hs after conditioning and immediately after rats were perfused for dendritic spine analysis. Our results show that local hippocampal administration of IL-1ß just after memory encoding induced impairment in contextual memory and a reduction in the total density of CA1 hippocampal dendritic spines, particularly the mature ones. α-MSH administration reversed the IL-1ß induced changes. The results suggest that neuro-inflammation induced by IL-1ß interferes with experience-dependent structural plasticity in DH whereas α-MSH has a beneficial modulatory role in preventing this effect.
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Interleucina-1beta/metabolismo , Consolidación de la Memoria/fisiología , Plasticidad Neuronal/fisiología , Animales , Encéfalo/efectos de los fármacos , Condicionamiento Clásico/efectos de los fármacos , Espinas Dendríticas/efectos de los fármacos , Miedo/efectos de los fármacos , Hipocampo/efectos de los fármacos , Hipocampo/metabolismo , Interleucina-1beta/farmacología , Masculino , Memoria/efectos de los fármacos , Consolidación de la Memoria/efectos de los fármacos , Trastornos de la Memoria/inducido químicamente , Ratas , Ratas Wistar , Lóbulo Temporal/efectos de los fármacos , alfa-MSH/metabolismo , alfa-MSH/farmacologíaRESUMEN
BACKGROUND: The dorsal hippocampus has a central role in modulating cardiovascular responses and behavioral adaptation to stress. The dorsal hippocampus also plays a key role in stress-associated mental disorders. The endocannabinoid system is widely expressed in the dorsal hippocampus and modulates defensive behaviors under stressful conditions. The endocannabinoid anandamide activates cannabinoid type 1 receptors and is metabolized by the fatty acid amide hydrolase enzyme. AIMS: We sought to verify whether cannabinoid type 1 receptors modulate stress-induced cardiovascular changes, and if pharmacological fatty acid amide hydrolase inhibition in the dorsal hippocampus would prevent the cardiovascular responses and the delayed anxiogenic-like behavior evoked by restraint stress in rats via cannabinoid type 1 receptors. METHODS: Independent groups received intra-dorsal-hippocampal injections of N-(piperidin-1yl)-5-(4-iodophenyl)-1-(2,4-dichlorophenyl)-4-methyl-hpyrazole-3-carboxamide (AM251; cannabinoid type 1 receptor antagonist/inverse agonist, 10-300 pmol) and/or cyclohexyl carbamic acid 3'-carbamoyl-biphenyl-3-yl ester (URB597; fatty acid amide hydrolase inhibitor, 10 pmol) before the restraint stress session. Cardiovascular response during restraint stress or later behavioral parameters were evaluated. RESULTS: Acute restraint stress altered the cardiovascular response, characterized by increased heart rate and mean arterial pressure, as well as decreased tail cutaneous temperature. It also induced a delayed anxiogenic-like effect, evidenced by reduced open arm exploration in the elevated plus maze 24 h after stress. AM251 exacerbated the stress-induced cardiovascular responses after injection into the dorsal hippocampus. In contrast, local injection of URB597 prevented the cardiovascular response and the delayed (24 h) behavioral consequences of restraint stress, effects attenuated by pretreatment with AM251. CONCLUSION: Our data corroborate previous results indicating that the hippocampal endocannabinoid system modulates the outcome of stress exposure and suggest that this could involve modulation of the cardiovascular response during stress exposure.
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Ansiedad , Presión Arterial/fisiología , Conducta Animal/fisiología , Agonistas de Receptores de Cannabinoides/farmacología , Antagonistas de Receptores de Cannabinoides/farmacología , Endocannabinoides/fisiología , Frecuencia Cardíaca/fisiología , Hipocampo/metabolismo , Receptor Cannabinoide CB1/fisiología , Estrés Psicológico , Amidohidrolasas/farmacología , Animales , Ansiedad/inducido químicamente , Ansiedad/etiología , Ansiedad/metabolismo , Ácidos Araquidónicos/farmacología , Presión Arterial/efectos de los fármacos , Conducta Animal/efectos de los fármacos , Benzamidas/farmacología , Agonistas de Receptores de Cannabinoides/administración & dosificación , Antagonistas de Receptores de Cannabinoides/administración & dosificación , Carbamatos/farmacología , Modelos Animales de Enfermedad , Endocannabinoides/farmacología , Frecuencia Cardíaca/efectos de los fármacos , Hipocampo/efectos de los fármacos , Masculino , Piperidinas/farmacología , Alcamidas Poliinsaturadas/farmacología , Pirazoles/farmacología , Ratas , Ratas Wistar , Receptor Cannabinoide CB1/agonistas , Receptor Cannabinoide CB1/antagonistas & inhibidores , Restricción Física/efectos adversos , Temperatura Cutánea/efectos de los fármacos , Temperatura Cutánea/fisiología , Estrés Psicológico/complicaciones , Estrés Psicológico/metabolismo , Estrés Psicológico/fisiopatologíaRESUMEN
The role of 5-HT2C receptors (5-HT2CRs) in the regulation of anxiety has been widely acknowledged. However, conflicting results have been reported on whether stimulation of these receptors increases or decreases anxiety. We here investigated the role of 5-HT2CRs of the dorsal hippocampus (DH) in the mediation of anxiety- or panic-associated defensive behaviors and in the anxiolytic effect of the tricyclic antidepressant imipramine. In the Vogel conflict test, administration of the mixed 5-HT2CR agonist mCPP into the DH of male Wistar rats was anxiogenic, whereas infusions of the more selective agonists MK-212 and RO-600175 were anxiolytic. The 5-HT2CR antagonist SB-242084, on the other hand, was anxiogenic. A sub-effective dose of this antagonist blocked the anxiolytic effect of RO-600175, but not the increase in anxiety observed with mCPP, indicating that the latter effect was not due to 5-HT2CR activation. In full agreement with these findings, MK-212 and RO-600175 in the DH also inhibited inhibitory avoidance acquisition in the elevated T-maze, whereas SB-242084 caused the opposite effect. None of these drugs interfered with escape expression in this test, which has been associated with panic. Chronic administration of imipramine (15â¯mg/kg, ip, 21 days) caused an anxiolytic effect in the elevated T-maze and light-dark transition tests, which was not blocked by previous infusion of SB-242084 into the DH. Therefore, facilitation of 5-HT2CR-mediated neurotransmission in the DH decreases the expression of anxiety-, but not panic-related defensive behaviors. This mechanism, however, is not involved in the anxiolytic effect caused by imipramine.
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Ansiedad/fisiopatología , Hipocampo/fisiología , Pánico/fisiología , Receptor de Serotonina 5-HT2C/fisiología , Aminopiridinas/farmacología , Animales , Ansiolíticos/farmacología , Ansiedad/inducido químicamente , Reacción de Prevención/efectos de los fármacos , Etilaminas/antagonistas & inhibidores , Etilaminas/farmacología , Hipocampo/efectos de los fármacos , Imipramina/farmacología , Indoles/antagonistas & inhibidores , Indoles/farmacología , Masculino , Aprendizaje por Laberinto/efectos de los fármacos , Microinyecciones , Pánico/efectos de los fármacos , Piperazinas/antagonistas & inhibidores , Piperazinas/farmacología , Castigo , Pirazinas/farmacología , Ratas , Agonistas del Receptor de Serotonina 5-HT2RESUMEN
To uncover the factors that dictate the persistence of a memory, it is critical to determine the molecular basis of consolidation. Here, we submitted male adult C57/BL6 mice to contextual fear conditioning using 1US (US: foot-shock, 0.7 mA, 2 s) or 5US, to generate recent (24 to 48 h) and remote (30 days) memories, respectively. To access the functional role of de novo transcription, we injected actinomycin D (ActD: 2.5 ng/side) directly into the dorsal hippocampus (HIP) or dorsomedial prefrontal cortex (dmPFC), 0 (early consolidation) or 12 h (late consolidation) after training. Our results showed that de novo transcription at 0 h was required for recent and remote memories. However, 12 h was a critical time point to memory persistence. In the dHIP, de novo transcription at 12 h post-training differentiated the recent memory from the remote. In the dmPFC, ActD affected memory formation depending on the training intensity (1 or 5US). Specifically, freezing was amplified after 5US conditioning. Furthermore, inhibiting de novo transcription at 12 h post-training in the dmPFC rapidly increased c-Fos expression in the amygdala. Altogether, our results indicate that contextual fear memory duration is particularly sensitive to de novo transcription in the dHIP and dmPFC, at a specific time point of late consolidation.
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Miedo/fisiología , Hipocampo/fisiología , Consolidación de la Memoria/fisiología , Corteza Prefrontal/fisiología , Transcripción Genética , Amígdala del Cerebelo/fisiología , Animales , Biomarcadores/metabolismo , Factor Neurotrófico Derivado del Encéfalo/genética , Factor Neurotrófico Derivado del Encéfalo/metabolismo , Proteínas del Citoesqueleto/genética , Proteínas del Citoesqueleto/metabolismo , Electrochoque , Regulación de la Expresión Génica , Masculino , Ratones Endogámicos C57BL , Proteínas del Tejido Nervioso/genética , Proteínas del Tejido Nervioso/metabolismo , ARN/biosíntesis , ARN Mensajero/genética , ARN Mensajero/metabolismoRESUMEN
Fear extinction is defined as a decline in fear-conditioned responses following non-reinforced exposure to a fear conditioned stimulus, therefore the conditioned stimulus gains new predictive properties. Patients with anxiety related disorders (e.g.: PTSD) subjected to extinction-like exposure treatments often experience a relapse of symptoms. Stress is a risk factor for those psychiatric disorders and a critical modulator of fear learning that turns the memory resistant to the extinction process. Dendritic spines are the anatomical sites where neuronal activity reshapes brain networks during learning and memory processes. Thus, we planned to characterize the dynamics of synaptic remodeling before and after contextual fear extinction in the dorsal hippocampus (DH), and how this process is affected by a previous stress experience. Animals with or without previous stress were contextually fear conditioned and one day later trained in an extinction paradigm. Rats were sacrificed one day after conditioning (pre-extinction) or one day after extinction for spine density analysis in the DH. We confirmed that stress exposure induced a deficit in extinction learning. Further, a higher density of dendritic spines, particularly mature ones, was observed in the DH of non-stressed conditioned animals at pre-extinction. Interestingly, after extinction, the spine levels returned to the control values. Conversely, stressed animals did not show such spines boost (pre-extinction) or any other change (post-extinction). In contrast, such standard dynamics of dendritic changes as well as the behavioral extinction was recovered when stressed animals received an intra-basolateral amygdala infusion of midazolam prior to stress. Altogether, these findings suggest that stress hinders the normal dynamic of dendritic remodeling after fear extinction and this could be part of the neurobiological substrate that makes those memories resistant to be extinguished.
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Espinas Dendríticas/fisiología , Extinción Psicológica/fisiología , Miedo/fisiología , Hipocampo/fisiología , Memoria/fisiología , Plasticidad Neuronal , Estrés Psicológico/psicología , Animales , Complejo Nuclear Basolateral/fisiología , Condicionamiento Clásico , Masculino , Recuerdo Mental/fisiología , Ratas WistarRESUMEN
Studies conducted in rodents subjected to chronic stress and some observations in humans after psychosocial stress, have allowed to establish a link between stress and the susceptibility to many complex diseases, including mood disorders. The studies in rodents have revealed that chronic exposure to stress negatively affects synaptic plasticity by triggering changes in the production of trophic factors, subunit levels of glutamate ionotropic receptors, neuron morphology, and neurogenesis in the adult hippocampus. These modifications may account for the impairment in learning and memory processes observed in chronically stressed animals. It is plausible then, that stress modifies the interplay between signal transduction cascades and gene expression regulation in the hippocampus, therefore leading to altered neuroplasticity and functioning of neural circuits. Considering that miRNAs play an important role in post-transcriptional-regulation of gene expression and participate in several hippocampus-dependent functions; we evaluated the consequences of chronic stress on the expression of miRNAs in dorsal (anterior) portion of the hippocampus, which participates in memory formation in rodents. Here, we show that male rats exposed to daily restraint stress (2.5 h/day) during 7 and 14 days display a differential profile of miRNA levels in dorsal hippocampus and remarkably, we found that some of these miRNAs belong to the miR-379-410 cluster. We confirmed a rise in miR-92a and miR-485 levels after 14 days of stress by qPCR, an effect that was not mimicked by chronic administration of corticosterone (14 days). Our in silico study identified the top-10 biological functions influenced by miR-92a, nine of which were shared with miR-485: Nervous system development and function, Tissue development, Behavior, Embryonic development, Organ development, Organismal development, Organismal survival, Tissue morphology, and Organ morphology. Furthermore, our in silico study provided a landscape of potential miRNA-92a and miR-485 targets, along with relevant canonical pathways related to axonal guidance signaling and cAMP signaling, which may influence the functioning of several neuroplastic substrates in dorsal hippocampus. Additionally, the combined effect of miR-92a and miR-485 on transcription factors, along with histone-modifying enzymes, may have a functional relevance by producing changes in gene regulatory networks that modify the neuroplastic capacity of the adult dorsal hippocampus under stress.
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Galanin, a peptide expressed in mammalian brain regions, has been implicated in anxiety and depression. Galanin signalling occurs through three G protein-linked receptors (GAL1, GAL2 and GAL3). Galanin regulates the release of neurotransmitters in some brain regions related to anxiety, including the hippocampus. GAL2 is the most abundant galanin receptor in the dorsal hippocampus. In this study, we evaluated whether galanin administered in the dorsal hippocampus affected anxiety-like behaviours of rats. We also investigated if GAL2 receptors are involved in the anxiogenic-like effect of galanin using a GAL2 antagonist, M871. To achieve these objectives, male adult Wistar rats received intra-dorsal hippocampal delivery of galanin (0.3 and 1.0â¯nmol/0.5⯵l) or vehicle in experiment 1 and GAL2 antagonist M871 (1.0 and 3.0â¯nmol/0.5⯵l) or vehicle in experiment 2. Twenty min after administration of drugs, the animals were tested in the elevated plus-maze (EPM). Galanin (1.0â¯nmol) induced anxiogenic-like behaviours, while the GAL2 receptor antagonist M871 (3.0â¯nmol) induced anxiolytic-like behaviours in rats exposed to the EPM, indicating a tonic effect of galanin. In experiment 3, we evaluated whether previous infusion of the GAL2 antagonist M871 (1 or 2â¯nmol) in the dorsal hippocampus would block the anxiogenic-like effect of galanin in rats tested in the EPM. We showed that M871 (2.0â¯nmol) counteracted the anxiogenic-like effect of galanin infused in the dorsal hippocampus of rats. Altogether, our results provide evidence that galanin promotes pharmacological and tonic anxiogenic-like effects in the dorsal hippocampus, possibly mediated by GAL2 receptors.
Asunto(s)
Ansiolíticos/uso terapéutico , Ansiedad/tratamiento farmacológico , Galanina/uso terapéutico , Hipocampo/efectos de los fármacos , Análisis de Varianza , Animales , Modelos Animales de Enfermedad , Relación Dosis-Respuesta a Droga , Masculino , Aprendizaje por Laberinto/efectos de los fármacos , Microinyecciones , Péptidos/uso terapéutico , Ratas , Ratas WistarRESUMEN
The main κ opioid receptors (κORs) subtypes already described (κ1ORs and κ2ORs) are expressed in brain regions involved in aversive memory consolidation, including the dorsal hippocampus (DH). However, the role of DH κORs in consolidation of aversive memories with varied intensity and specificity is still uncertain. The present study aimed to investigate this question using pharmacological agents in rats subjected to a weak, moderate or strong contextual aversive conditioning (CAC) protocol. Antagonizing DH κORs with nor-binaltorphimine (nor-BNI), immediately after, but not 6â¯h later, a moderate CAC leads to intensified freezing behavior in the re-exposure to the paired context. Thus, indicating that DH κORs have an inhibitory role in the consolidation of an aversive memory. Increased DH κORs expression 1â¯h and 3â¯h after the moderate CAC was also observed. This up-regulation was absent in animals only exposed to the shock or to the context, indicating that this phenomenon requires a shock-context pairing to occur. Intra-DH nor-BNI infusion induced no changes following a weak CAC, but it was able to potentiate the expression of freezing behavior in novel and unpaired context after a strong CAC, indicating that DH κORs also modulate the consolidation of a more intense and generalized memory. Moreover, infusing the κ2ORs agonist GR 89696, but not the κ1ORs agonist U-69593, into the DH reduced the conditioned freezing expression. Nor-BNI pretreatment in a sub-effective dose prevented the κ2ORs agonist effects. Altogether, the present findings provide convergent evidence that κORs activation negatively modulates contextual aversive memory consolidation in rat dorsal hippocampus.
Asunto(s)
Reacción de Prevención/fisiología , Hipocampo/metabolismo , Consolidación de la Memoria/fisiología , Receptores Opioides kappa/metabolismo , Analgésicos Opioides/farmacología , Animales , Asociación , Reacción de Prevención/efectos de los fármacos , Bencenoacetamidas/farmacología , Condicionamiento Psicológico/efectos de los fármacos , Condicionamiento Psicológico/fisiología , Electrochoque , Reacción Cataléptica de Congelación/efectos de los fármacos , Reacción Cataléptica de Congelación/fisiología , Hipocampo/efectos de los fármacos , Masculino , Consolidación de la Memoria/efectos de los fármacos , Naltrexona/análogos & derivados , Naltrexona/farmacología , Antagonistas de Narcóticos/farmacología , Piperazinas/farmacología , Psicotrópicos/farmacología , Pirrolidinas/farmacología , Distribución Aleatoria , Ratas Wistar , Receptores Opioides kappa/agonistas , Receptores Opioides kappa/antagonistas & inhibidoresRESUMEN
Long-lasting changes in dendritic spines provide a physical correlate for memory formation and persistence. LIM kinase (LIMK) plays a critical role in orchestrating dendritic actin dynamics during memory processing, since it is the convergent downstream target of both the Rac1/PAK and RhoA/ROCK pathways that in turn induce cofilin phosphorylation and prevent depolymerization of actin filaments. Here, using a potent LIMK inhibitor (BMS-5), we investigated the role of LIMK activity in the dorsal hippocampus during contextual fear memory in rats. We first found that post-training administration of BMS-5 impaired memory consolidation in a dose-dependent manner. Inhibiting LIMK before training also disrupted memory acquisition. We then demonstrated that hippocampal LIMK activity seems to be critical for memory retrieval and reconsolidation, since both processes were impaired by BMS-5 treatment. Contextual fear memory extinction, however, was not sensitive to the same treatment. In conclusion, our findings demonstrate that hippocampal LIMK activity plays an important role in memory acquisition, consolidation, retrieval, and reconsolidation during contextual fear conditioning.
Asunto(s)
Inhibidores Enzimáticos/farmacología , Extinción Psicológica/efectos de los fármacos , Hipocampo/efectos de los fármacos , Quinasas Lim/antagonistas & inhibidores , Consolidación de la Memoria/efectos de los fármacos , Memoria/efectos de los fármacos , Animales , Condicionamiento Psicológico/efectos de los fármacos , Miedo/efectos de los fármacos , Masculino , Umbral del Dolor/efectos de los fármacos , Ratas , Ratas WistarRESUMEN
Previous studies in rats have demonstrated that chronic restraint stress triggers anhedonia, depressive-like behaviors, anxiety and a reduction in dendritic spine density in hippocampal neurons. In this study, we compared the effect of repeated stress on the expression of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) and N-methyl-D-aspartate (NMDA) receptor subunits in dorsal and ventral hippocampus (VH). Adult male Sprague-Dawley rats were randomly divided into control and stressed groups, and were daily restrained in their motion (2.5 h/day) during 14 days. We found that chronic stress promotes an increase in c-Fos mRNA levels in both hippocampal areas, although it was observed a reduction in the immunoreactivity at pyramidal cell layer. Furthermore, Arc mRNAs levels were increased in both dorsal and VH, accompanied by an increase in Arc immunoreactivity in dendritic hippocampal layers. Furthermore, stress triggered a reduction in PSD-95 and NR1 protein levels in whole extract of dorsal and VH. Moreover, a reduction in NR2A/NR2B ratio was observed only in dorsal pole. In synaptosomal fractions, we detected a rise in NR1 in dorsal hippocampus (DH). By indirect immunofluorescence we found that NR1 subunits rise, especially in neuropil areas of dorsal, but not VH. In relation to AMPA receptor (AMPAR) subunits, chronic stress did not trigger any change, either in dorsal or ventral hippocampal areas. These data suggest that DH is more sensitive than VH to chronic stress exposure, mainly altering the expression of NMDA receptor (NMDAR) subunits, and probably favors changes in the configuration of this receptor that may influence the function of this area.
RESUMEN
GABAergic signaling in the basolateral amygdala complex (BLA) plays a crucial role on the modulation of the stress influence on fear memory. Moreover, accumulating evidence suggests that the dorsal hippocampus (DH) is a downstream target of BLA neurons in contextual fear. Given that hippocampal structural plasticity is proposed to provide a substrate for the storage of long-term memories, the main aim of this study is to evaluate the modulation of GABA neurotransmission in the BLA on spine density in the DH following stress on contextual fear learning. The present findings show that prior stressful experience promoted contextual fear memory and enhanced spine density in the DH. Intra-BLA infusion of midazolam, a positive modulator of GABAa sites, prevented the facilitating influence of stress on both fear retention and hippocampal dendritic spine remodeling. Similarly to the stress-induced effects, the blockade of GABAa sites within the BLA ameliorated fear memory emergence and induced structural remodeling in the DH. These findings suggest that GABAergic transmission in BLA modulates the structural changes in DH associated to the influence of stress on fear memory.
Asunto(s)
Complejo Nuclear Basolateral/fisiología , Espinas Dendríticas/fisiología , Miedo/fisiología , Hipocampo/fisiología , Memoria/fisiología , Ácido gamma-Aminobutírico/metabolismo , Animales , Complejo Nuclear Basolateral/efectos de los fármacos , Condicionamiento Psicológico/fisiología , Moduladores del GABA/farmacología , Masculino , Midazolam/farmacología , Plasticidad Neuronal/fisiología , Distribución Aleatoria , Ratas Wistar , Restricción Física , Estrés Psicológico/fisiopatología , Transmisión Sináptica/fisiologíaRESUMEN
To identify an individual as familiar, rodents form a specific type of memory named social recognition memory. The olfactory bulb (OB) is an important structure for social recognition memory, while the hippocampus recruitment is still controversial. The present study was designed to elucidate the OB and the dorsal hippocampus contribution to the consolidation of social memory. For that purpose, we tested the effect of anisomycin (ANI), which one of the effects is the inhibition of protein synthesis, on the consolidation of social recognition memory. Swiss adult mice with cannulae implanted into the CA1 region of the dorsal hippocampus or into the OB were exposed to a juvenile during 5 min (training session; TR), and once again 1.5 h or 24 h later to test social short-term memory (S-STM) or social long-term memory (S-LTM), respectively. To study S-LTM consolidation, mice received intra-OB or intra-CA1 infusion of saline or ANI immediately, 3, 6 or 18 h after TR. ANI impaired S-LTM consolidation in the OB, when administered immediately or 6h after TR. In the dorsal hippocampus, ANI was amnesic only if administered 3 h after TR. Furthermore, the infusion of ANI in either OB or CA1, immediately after training, did not affect S-STM. Moreover, ANI administered into the OB did not alter the animal's performance in the buried food-finding task. Altogether, our results suggest the consolidation of S-LTM requires both OB and hippocampus participation, although in different time points. This study may help shedding light on the specific roles of the OB and dorsal hippocampus in social recognition memory.