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Cholesterol-24-hydroxylase (CYP46), a member of the cytochrome P450 superfamily of enzymes, is selectively expressed in the brain and is mainly responsible for cholesterol turnover in the central nervous system. Although increased cyp46A1 gene expression has been linked to cognitive alterations in aging and observed in neurodegenerative diseases and after traumatic brain injury, a detailed characterization of the brain regions and cell types in which CYP46 is expressed in old individuals has not been performed. Using immunohistochemistry and immunofluorescence, we investigated the specific regions and cell populations in the brain, in which cyp46A1 is expressed in 24-month-old mice. We found that CYP46 is localized in the same neuronal populations in young and old brains, mainly in the hippocampus, in cortical layers, and in Purkinje neurons of the cerebellum. No increase in CYP46 levels was found in astrocytes in old mice brains, in primary astrocyte-neuron cocultures aged in vitro, or in primary cultures of senescent astrocytes. However, interleukin-6 treatment strongly induced cyp46A1 expression in reactive astrocytes characterized by high GFAP levels but had no effect in nonactivated astrocytes. Our data suggest that cholesterol-24-hydroxylase expression is triggered in reactive astrocytes in response to proinflammatory signals, probably as part of a response mechanism to injury.
Assuntos
Astrócitos , Encéfalo , Colesterol 24-Hidroxilase , Animais , Camundongos , Astrócitos/metabolismo , Encéfalo/metabolismo , Colesterol/metabolismo , Colesterol 24-Hidroxilase/metabolismoRESUMO
The amygdaloid complex is a crucial component of the basal forebrain that participates in the modulation of many homeostatic functions, emotional behaviors, and learning. These features require a widespread pattern of connections with several brain structures. In the past, the amygdaloid complex was divided into corticomedial and basolateral groups. The existence of a neuronal continuum linking the central amygdaloid nucleus to the lateral bed nucleus of stria terminalis through the subpallidal area was first revealed by José de Olmos (1932-2008) with the aid of his cupric-silver technique. This observation gave birth to the concept of the extended amygdala, a conceptual framework that is useful for understanding the anatomofunctional organization of the amygdaloid complex, with relevance for basic neuroscience and clinical interventions. Traditional tract-tracing staining methods were complicated and tedious to reproduce. Axonal terminal endings were lost among a myriad of normal fibers. The need to visualize these terminals drove de Olmos to develop cupric-silver methods that revealed disintegrating synaptic terminals, without staining normal fibers. In this article, we describe the historical events leading to the development of the cupric-silver technique that evolved into the amino-cupric-silver technique, which developed hand-in-hand over the years.
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Tonsila do Cerebelo , Prata , Humanos , Tonsila do Cerebelo/fisiologia , NeurôniosRESUMO
Multiple sclerosis (MS), especially in its progressive phase, involves early axonal and neuronal damage resulting from a combination of inflammatory mediators, demyelination, and loss of trophic support. During progressive disease stages, a microenvironment is created within the central nervous system (CNS) favoring the arrival and retention of inflammatory cells. Active demyelination and neurodegeneration have also been linked to microglia (MG) and astrocyte (AST)-activation in early lesions. While reactive MG can damage tissue, exacerbate deleterious effects, and contribute to neurodegeneration, it should be noted that activated MG possess neuroprotective functions as well, including debris phagocytosis and growth factor secretion. The progressive form of MS can be modeled by the prolonged administration to cuprizone (CPZ) in adult mice, as CPZ induces highly reproducible demyelination of different brain regions through oligodendrocyte (OLG) apoptosis, accompanied by MG and AST activation and axonal damage. Therefore, our goal was to evaluate the effects of a reduction in microglial activation through orally administered brain-penetrant colony-stimulating factor-1 receptor (CSF-1R) inhibitor BLZ945 (BLZ) on neurodegeneration and its correlation with demyelination, astroglial activation, and behavior in a chronic CPZ-induced demyelination model. Our results show that BLZ treatment successfully reduced the microglial population and myelin loss. However, no correlation was found between myelin preservation and neurodegeneration, as axonal degeneration was more prominent upon BLZ treatment. Concomitantly, BLZ failed to significantly offset CPZ-induced astroglial activation and behavioral alterations. These results should be taken into account when proposing the modulation of microglial activation in the design of therapies relevant for demyelinating diseases. Cover Image for this issue: https://doi.org/10.1111/jnc.15394.
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Doenças Desmielinizantes , Esclerose Múltipla , Animais , Fatores Estimuladores de Colônias/efeitos adversos , Fatores Estimuladores de Colônias/metabolismo , Cuprizona/metabolismo , Cuprizona/toxicidade , Doenças Desmielinizantes/induzido quimicamente , Doenças Desmielinizantes/tratamento farmacológico , Doenças Desmielinizantes/metabolismo , Modelos Animais de Doenças , Camundongos , Camundongos Endogâmicos C57BL , Microglia/metabolismo , Esclerose Múltipla/metabolismo , Bainha de Mielina/metabolismoRESUMO
Differences in cytoarchitectural organization and connectivity distinguishes granular (or area 29, A29) and dysgranular (or area 30, A30) subdivisions of the retrosplenial cortex (RSC). Although increasing evidence supports the participation of RSC in contextual fear learning and memory, the contribution of each RSC subdivision remains unknown. Here we used orchiectomized rats and intraperitoneal (i.p.) injections of saline (control) or 5 mg/kg MK801, to trigger selective degeneration of pyramidal neurons in layers IV-Va of A29 (A29MK801 neurons). These treatments were applied 3 days before or two days after contextual fear conditioning, and contextual fear memory was evaluated by scoring freezing in the conditioned context five days after training. Afterwards, brains were fixed and c-Fos and Egr-1 expression were assessed as surrogates of neuronal activity elicited by the recall in A29, A30 and in limbic areas. We found that eliminating A29MK801 neurons after training reduces conditioned freezing to 43.1 ± 9.9% respect to control rats. This was associated with a significant reduction of c-Fos and Egr-1 expression in A30, but not in other limbic areas. On the other hand, eliminating A29MK801 neurons before training caused a mild but significant reduction of conditioned freezing to 79.7 ± 6.8%, which was associated to enhanced expression of c-Fos in A29, A30 and CA1 field of hippocampus, while Egr-1 expression in caudomedial (CEnt) entorhinal cortex was not depressed as in control animals. These observations show that severeness of amnesia differs according to whether A29MK801 neurons were eliminated before or after conditioning, likely because loss of A29MK801 neurons after conditioning disrupt memory engram while their elimination before training allow recruitment of other neurons in A29 for partial compensation of contextual fear learning and memory. These observations add further support for the critical role of A29MK801 neurons in contextual fear learning and memory by connecting limbic structures with A30.
Assuntos
Amnésia/fisiopatologia , Medo/fisiologia , Hipocampo/fisiopatologia , Rememoração Mental/fisiologia , Neurônios/fisiologia , Amnésia/metabolismo , Animais , Maleato de Dizocilpina/toxicidade , Medo/efeitos dos fármacos , Hipocampo/efeitos dos fármacos , Hipocampo/metabolismo , Masculino , Rememoração Mental/efeitos dos fármacos , Atividade Motora/efeitos dos fármacos , Atividade Motora/fisiologia , Neurônios/efeitos dos fármacos , Neurônios/metabolismo , Proteínas Proto-Oncogênicas c-fos/metabolismo , RatosRESUMO
The contribution of the granular (area 29, A29) and dysgranular (area 30, A30) subdivisions of the retrosplenial cortex (RSC) to contextual fear memory (CFM) retrieval remains elusive. Here, intact and orchiectomized (ORC) male rats received an intraperitoneal (I.P.) injection of saline (control) or 5â¯mg/Kg MK801 after training and memory formation. In ORC, but not in intact males, this MK801 treatment selectively induces overt loss of neurons in layers IV-Va of A29 (A29MK801 neurons) (Sigwald et al., 2016). Compared to ORC-saline, ORC-MK801 rats showed impaired CFM retrieval in an A-B-A design for contextual fear conditioning (CFC), however context recognition was not affected. In ORC-MK801 rats, neither novel object recognition nor object-in-context discrimination were impaired, further indicating that A29MK801 neurons are not required for contextual recognition. Elevated plus maze test showed that anxiety-like behavior was not affected in ORC-MK801 animals, suggesting that loss of A29MK801 neurons does not affect the emotional state that could impair freezing during test. Importantly, in a sensory preconditioning test, higher order CFM retrieval was abolished in ORC-MK801, but not in male-MK801. Collectively, these observations indicate that A29MK801 neurons are critically required for retrieving fear-context association. For dissecting the anatomofunctional contribution of A29MK801 neurons to CFM retrieval, expression of c-Fos and Egr-1 was used to map brain-wide neuronal activity. In control male rats CFC and CFM retrieval was associated with significant enhancement of both proteins in limbic structures and A30, but not in A29, suggesting that neurons in A30 and limbic structures encode and store the associative experience. Notably, in ORC but not in intact males, MK801 impairs CFM retrieval and expression of c-Fos and Egr-1 proteins in A30, without affecting their expression in limbic structures. Thus, the loss of A29MK801 neurons after CFM formation precludes activation of associative neurons in A30, impairing CFM recall. FluoroGold retrograde track-tracing confirmed that A29MK801 neurons project to A30. Silver staining provide evidence that MK801 in ORC rats induces axonal deafferentation of A29MK801 neuron in A30. Collectively, our experiments provide the first evidence that A30 neurons participate in encoding and storing CFM while A29 is required for their activation during recall.
Assuntos
Córtex Cerebral/fisiologia , Medo/fisiologia , Rememoração Mental/fisiologia , Animais , Córtex Cerebral/anatomia & histologia , Condicionamento Clássico/fisiologia , Masculino , Aprendizagem em Labirinto/fisiologia , Neurônios/fisiologia , Ratos , Ratos WistarRESUMO
Saint Louis encephalitis virus (SLEV) is a neglected flavivirus that causes severe neurological disorders. The epidemic strain of SLEV, CbaAr-4005, isolated during an outbreak in Córdoba city (Argentina), causes meningitis and encephalitis associated with neurological symptoms in a murine experimental model. Here, we identified the affected brain areas and the damage triggered by this neurotropic arbovirus. We performed a detailed analysis of brain neurodegeneration associated with CbaAr-4005 SLEV infection in mice. The motor cortex, corpus striatum and cerebellum were the most affected structures. Neurodegeneration was also found in the olfactory bulb, thalamus, hypothalamus, hippocampus, and hindbrain. SLEV infection triggered brain cell apoptosis as well as somatodendritic and terminal degeneration. In addition, we observed massive excitotoxic-like degeneration in many cortical structures. Apoptosis was also detected in the neuroblastoma cell line N2a cultured with SLEV. The results evidenced that SLEV CbaAr-4005 infection induced severe degenerative alterations within the central nervous system of infected mice, providing new information about the targets of this flavivirus infection.
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Early-onset ethanol consumption predicts later development of alcohol use disorders. Age-related differences in reactivity to ethanol's effects may underlie this effect. Adolescent rats are more sensitive and less sensitive than adults to the appetitive and aversive behavioral effects of ethanol, respectively, and more sensitive to the neurotoxic effects of experimenter-administered binge doses of ethanol. However, less is known about age-related differences in the neural consequences of self-administered ethanol. ΔFosB is a transcription factor that accumulates after chronic drug exposure and serves as a molecular marker of neural plasticity associated with the transition to addiction. We analyzed the impact of chronic (18 two-bottle choice intake sessions spread across 42days, session length: 18h) ethanol [or only vehicle (control group)] self-administration during adolescence or adulthood on the induction of ΔFosB in several brain areas, anxiety-like behavior, and ethanol-induced locomotor activity and conditioned place preference (CPP) in Wistar rats. Adolescent rats exhibited a progressive escalation of ethanol intake and preference, whereas adult rats exhibited a stable pattern of ingestion. Few behavioral differences in the open field or light-dark test were observed after the intake test. Furthermore, ethanol self-administration did not promote the expression of ethanol-induced CPP. There were, however, large age-related differences in the neural consequences of ethanol drinking: a significantly greater number of ethanol-induced ΔFosB-positive cells was found in adolescents vs. adults in the prelimbic cortex, dorsolateral striatum, nucleus accumbens core and shell, and central amygdala nucleus capsular and basolateral amygdala, with sex-related differences found at central amygdala. This greater ethanol-induced ΔFosB induction may represent yet another age-related difference in the sensitivity to ethanol that may put adolescents at higher risk for problematic ethanol use.
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Envelhecimento/efeitos dos fármacos , Encéfalo/efeitos dos fármacos , Depressores do Sistema Nervoso Central/administração & dosagem , Etanol/administração & dosagem , Proteínas Proto-Oncogênicas c-fos/metabolismo , Caracteres Sexuais , Fatores Etários , Consumo de Bebidas Alcoólicas , Análise de Variância , Animais , Encéfalo/metabolismo , Condicionamento Operante/efeitos dos fármacos , Feminino , Locomoção/efeitos dos fármacos , Masculino , Ratos , Ratos Wistar , Autoadministração , Fatores de TempoRESUMO
The retrosplenial cortex (RSC) is one of the largest cortical areas in rodents, and is subdivided in two main regions, A29 and A30, according to their cytoarchitectural organization and connectivities. However, very little is known about the functional activity of each RSC subdivision during the execution of complex cognitive tasks. Here, we used a well-established fear learning protocol that induced long-lasting contextual fear memory and showed that during evocation of the fear memory, the expression of early growth response gene 1 was up-regulated in A30, and in other brain areas implicated in fear and spatial memory, however, was down-regulated in A29, including layers IV and V. To search for the participation of A29 on fear memory, we triggered selective degeneration of neurons within cortical layers IV and V of A29 by using a non-invasive protocol that takes advantage of the vulnerability that these neurons have MK801-toxicity and the modulation of this neurodegeneration by testosterone. Application of 5 mg/kg MK801 in intact males induced negligible neuronal degeneration of A29 neurons and had no impact on fear memory retrieval. However, in orchiectomized rats, 5 mg/kg MK801 induced overt degeneration of layers IV-V neurons of A29, significantly impairing fear memory recall. Degeneration of A29 neurons did not affect exploratory or anxiety-related behavior nor altered unconditioned freezing. Importantly, protecting A29 neurons from MK801-toxicity by testosterone preserved fear memory recall in orchiectomized rats. Thus, neurons within cortical layers IV-V of A29 are critically required for efficient retrieval of contextual fear memory.
Assuntos
Medo/fisiologia , Giro do Cíngulo/fisiologia , Rememoração Mental/fisiologia , Neurônios/fisiologia , Animais , Condicionamento Clássico/efeitos dos fármacos , Condicionamento Clássico/fisiologia , Maleato de Dizocilpina/administração & dosagem , Proteína 1 de Resposta de Crescimento Precoce/metabolismo , Antagonistas de Aminoácidos Excitatórios/administração & dosagem , Medo/efeitos dos fármacos , Giro do Cíngulo/efeitos dos fármacos , Masculino , Rememoração Mental/efeitos dos fármacos , Neurônios/efeitos dos fármacos , Neurônios/patologia , Ratos , Ratos Wistar , Testosterona/administração & dosagemRESUMO
Non-competitive NMDA-receptor-antagonist drugs such as dizocilpine (MK801) induce behavioral changes and neurotoxicity that have made an impact in different fields of neuroscience. New approaches in research use transgenic mice to elucidate cellular mechanisms and circuits involved in the effects of these drugs. However, the neurodegeneration induced by these drugs has been extensively studied in rats, but the data in mice is limited. Therefore it is important to characterize if the neurotoxic pattern in mice corresponds to that of rats. A comparative analysis of the neurodegeneration induced by MK801 (10mg/kg) between Wistar rats, and CD-1, CF-1, and C57BL/6-129/Sv mice of both sexes, at different survival times (15, 24, 32, 48, 56 and 72 h) was analysed with the amino-cupric-silver and fluoro-jade B techniques. To compare different administration patterns, groups of mice received subchronic treatments with different doses (final doses of 20 and 40 mg/kg). Results showed that mice treated with MK801 presented different neurotoxic profiles, such as excitotoxic-like cell death in the retrosplenial cortex, terminal degeneration in CA1 and apoptotic-like degeneration in the olfactory bulb. Unlike rats, mice subjected to the same treatment failed to show neurodegeneration in corticolimbic areas such as piriform cortex and dentate gyrus. The amount of degeneration was lower in mice, and the subchronic administration of MK801 did not change the neurotoxic pattern. Additionally, mice lacked the sexually dimorphic response to MK801 toxicity observed in rats. Altogether these results indicate important species dissimilarities. Neurotoxicological studies aimed to explore pathways and mechanisms of MK801 toxicity should consider these differences when using mice as rodent models.
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Maleato de Dizocilpina/toxicidade , Antagonistas de Aminoácidos Excitatórios/toxicidade , Doenças Neurodegenerativas/induzido quimicamente , Análise de Variância , Animais , Comportamento Animal , Modelos Animais de Doenças , Feminino , Masculino , Camundongos , Camundongos Endogâmicos C57BL , Doenças Neurodegenerativas/patologia , Doenças Neurodegenerativas/fisiopatologia , Neurônios/patologia , Ratos , Ratos Wistar , Fatores Sexuais , Fatores de TempoRESUMO
MK801, PCP, and ketamine are non-competitive NMDA receptor-antagonists drugs that in humans produce psychomimetic effects and neurocognitive disturbances reminiscent to those of schizophrenia. The administration of these drugs in animals has been used as a pharmacological model to study the NMDA receptor hypofunction-hypothesis of schizophrenia. In animals, the biological effect of MK801 is dose-dependent. Low doses induce behavioral disturbances and higher doses, in addition, promote neurotoxicity in many brain regions, particularly the granular retrosplenial cortex (RSG). The neurotoxic effect of MK801 is sexually dimorphic, being females markedly more sensitive than males; however, the involvement of gonadal hormones is elusive. Here we show that a single intraperitoneal injection of 5 mg/kg of MK801 induced overt neurodegeneration in RSG of female rats, including abundant somatic degeneration in layer 4, and somatodendritic and terminal degeneration in layers 1, 4, and 5. MK801-degeneration in males was scarce and mainly evidenced by the presence of few argirophilic somas in layer 4. Ovariectomized rats were not significantly different than intact females, while orchiectomized rats showed robust MK801-toxicity. Testosterone and dihydrotestosterone (DHT) inhibit MK801-toxicity in orchiectomized rats. In ovariectomized rats only DHT, but not testosterone, prevented MK801-induced degeneration, while in intact females, DHT was only partially protective. Treatment of intact males with estradiol benzoate significantly enhanced MK801-toxicity. Altogether, our experiments indicate that non-aromatizable androgens protect RSG from MK801-toxicity, while estrogens counteract this protection. Thus, the balance of androgens and estrogens delineate the sexual dimorphism of the RSG to the toxic effect of MK801.