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The mammalian skull is very malleable and has notably radiated into highly diverse morphologies, fulfilling a broad range of functional needs. Although gnawing is relatively common in mammals, this behavior and its associated morphology are diagnostic features for rodents. These animals possess a very versatile and highly mechanically advantageous masticatory apparatus, which, for instance, allowed caviomorph rodents to colonize South America during the Mid-Eocene and successfully radiate in over 200 extant species throughout most continental niches. Previous work has shown that differences in bite force within caviomorphs could be better explained by changes in muscle development than in mechanical advantages (i.e., in cranial overall morphology). Considering the strong bites they apply, it is interesting to assess how the reaction forces upon the incisors (compression) and the powerful adductor musculature pulling (tension) mechanically affect the cranium, especially between species with different ecologies (e.g., chisel-tooth digging). Thus, we ran finite element analyses upon crania of the subterranean Talas' tuco-tuco Ctenomys talarum, the semi-fossorial common degu Octodon degus, and the saxicolous long-tailed chinchilla Chinchilla lanigera to simulate: (A) in vivo biting in all species, and (B) rescaled muscle forces in non-ctenomyid rodents to match those of the tuco-tuco. Results show that the stress patterns correlate with the mechanical demands of distinctive ecologies, on in vivo-based simulations, with the subterranean tuco-tuco being the most stressed species. In contrast, when standardizing all three species (rescaled models), non-ctenomyid models exhibited a several-fold increase in stress, in both magnitude and affected areas. Detailed observations evidenced that this increase in stress was higher in lateral sections of the snout and, mainly, the zygomatic arch; between approximately 2.5-3.5 times in the common degu and 4.0-5.0 times in the long-tailed chinchilla. Yet, neither species, module, nor simulation condition presented load factor levels that would imply structural failure by strong, incidental biting. Our results let us conclude that caviomorphs have a high baseline for mechanical strength of the cranium because of the inheritance of a very robust "rodent" model, while interspecific differences are associated with particular masticatory habits and the concomitant level of development of the adductor musculature. Especially, the masseteric and zygomaticomandibular muscles contribute to >80% of the bite force, and therefore, their contraction is responsible for the highest strains upon their origin sites, that is, the zygomatic arch and the snout. Thus, the robust crania of the subterranean and highly aggressive tuco-tucos allow them to withstand much stronger forces than degus or chinchillas, such as the ones produced by their hypertrophied jaw adductor muscles or imparted by the soil reaction.
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Força de Mordida , Roedores , Crânio , Animais , Crânio/anatomia & histologia , Crânio/fisiologia , Roedores/fisiologia , Fenômenos Biomecânicos , Mastigação/fisiologia , Comportamento Alimentar/fisiologia , Análise de Elementos FinitosRESUMO
Social interaction can improve animal performance through the prevention of stress-related events, the provision of security, and the enhancement of reproductive output and survival. We investigated the effects of prolonged chronic social isolation stress on behavioral, cognitive, and physiological performance in the social, long-lived rodent Octodon degus. Degu pups were separated into two social stress treatments: control (CTRL) and chronically isolated (CI) individuals from post-natal and post-weaning until adulthood. We quantified anxiety-like behavior and cognitive performance with a battery of behavioral tests. Additionally, we measured their basal metabolic rate (BMR) and analyzed the multifractal properties of the oxygen consumption time series using Multifractal Detrended Fluctuation Analysis, a well-known method for assessing the fractal characteristics of biological signals. Our results showed that CI induced a significant increase in anxiety-like behaviors and led to a reduction in social and working memory in male degus. In addition, CI-treated degus reduced the multifractal complexity of BMR compared to CTRL, which implies a decrease in the ability to respond to environmental stressors and, as a result, an unhealthy state. In contrast, we did not observe significant effects of social stress on BMR. Multivariate analyses showed a clear separation of behavior and physiological variables into two clusters, corresponding to CI and CTRL degus. This study provides novel insights into the effects of prolonged chronic social isolation stress on behavior, cognitive performance, and metabolic complexity in this rodent animal model. To the best of our knowledge, it is the first study to integrate cognitive-behavioral performance and multifractal dynamics of a physiological signal in response to prolonged social isolation. These findings highlight the importance of social interactions for the well-being and overall performance of social animals.
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Social interactions have a significant impact on health in humans and animal models. Social isolation initiates a cascade of stress-related physiological disorders and stands as a significant risk factor for a wide spectrum of morbidity and mortality. Indeed, social isolation stress (SIS) is indicative of cognitive decline and risk to neurodegenerative conditions, including Alzheimer's disease (AD). This study aimed to evaluate the impact of chronic, long-term SIS on the propensity to develop hallmarks of AD in young degus (Octodon degus), a long-lived animal model that mimics sporadic AD naturally. We examined inflammatory factors, bioenergetic status, reactive oxygen species (ROS), oxidative stress, antioxidants, abnormal proteins, tau protein, and amyloid-ß (Aß) levels in the hippocampus of female and male degus that were socially isolated from post-natal and post-weaning until adulthood. Additionally, we explored the effect of re-socialization following chronic isolation on these protein profiles. Our results showed that SIS promotes a pro-inflammatory scenario more severe in males, a response that was partially mitigated by a period of re-socialization. In addition, ATP levels, ROS, and markers of oxidative stress are severely affected in female degus, where a period of re-socialization fails to restore them as it does in males. In females, these effects might be linked to antioxidant enzymes like catalase, which experience a decline across all SIS treatments without recovery during re-socialization. Although in males, a previous enzyme in antioxidant pathway diminishes in all treatments, catalase rebounds during re-socialization. Notably, males have less mature neurons after chronic isolation, whereas phosphorylated tau and all detectable forms of Aß increased in both sexes, persisting even post re-socialization. Collectively, these findings suggest that long-term SIS may render males more susceptible to inflammatory states, while females are predisposed to oxidative states. In both scenarios, the accumulation of tau and Aß proteins increase the individual susceptibility to early-onset neurodegenerative conditions such as AD.
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In Octodon degus, the aging process is not equivalent between sexes and worsens for females. To determine the beginning of detrimental features in females and the ways in which to improve them, we compared adult females (36 months old) and aged females (72 months old) treated with Andrographolide (ANDRO), the primary ingredient in Andrographis paniculata. Our behavioral data demonstrated that age does not affect recognition memory and preference for novel experiences, but ANDRO increases these at both ages. Sociability was also not affected by age; however, social recognition and long-term memory were lower in the aged females than adults but were restored with ANDRO. The synaptic physiology data from brain slices showed that adults have more basal synaptic efficiency than aged degus; however, ANDRO reduced basal activity in adults, while it increased long-term potentiation (LTP). Instead, ANDRO increased the basal synaptic activity and LTP in aged females. Age-dependent changes were also observed in synaptic proteins, where aged females have higher synaptotagmin (SYT) and lower postsynaptic density protein-95 (PSD95) levels than adults. ANDRO increased the N-methyl D-aspartate receptor subtype 2B (NR2B) at both ages and the PSD95 and Homer1 only in the aged. Thus, females exposed to long-term ANDRO administration show improved complex behaviors related to age-detrimental effects, modulating mechanisms of synaptic transmission, and proteins.
Assuntos
Diterpenos , Octodon , Animais , Feminino , Octodon/metabolismo , Encéfalo/metabolismo , Diterpenos/farmacologia , Diterpenos/metabolismo , Reconhecimento PsicológicoRESUMO
Octodon degus are a diurnal long-lived social animal widely used to perform longitudinal studies and complex cognitive tasks to test for physiological conditions with similitude in human behavior. They show a complex social organization feasible to be studied under different conditions and ages. Several aspects in degus physiology demonstrated that these animals are susceptible to environmental conditions, such as stress, fear, feeding quality, and isolation. However, the relevance of these factors in life of this animal depends on sex and age. Despite its significance, there are few studies with the intent to characterize neurological parameters that include these two parameters. To determine the basal neurophysiological status, we analyzed basic electrophysiological parameters generated during basal activity or synaptic plasticity in the brain slices of young and aged female and male degus. We studied the hippocampal circuit of animals kept in social ambient in captivity under controlled conditions. The study of basal synaptic activity in young animals (12-24 months old) was similar between sexes, but female degus showed more efficient synaptic transmission than male degus. We found the opposite in aged animals (60-84 months old), where male degus had a more efficient basal transmission and facilitation index than female degus. Furthermore, female and male degus develop significant but not different long-term synaptic plasticity (LTP). However, aged female degus need to recruit twice as many axons to evoke the same postsynaptic activity as male degus and four times more when compared to young female degus. These data suggest that, unlike male degus, the neural status of aged female degus change, showing less number or functional axons available at advanced ages. Our data represent the first approach to incorporate the effect of sex along with age progression in basal neural status.
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Alzheimer's disease is a progressive neurodegenerative disorder and the most common cause of dementia. Although transgenic Alzheimer's disease (AD) animal models have greatly contributed to our understanding of the disease, therapies tested in these animals have resulted in a high rate of failure in preclinical trials for AD. A promising model is Octodon degus (degu), a Chilean rodent that spontaneously develops AD-like neuropathology. Previous studies have reported that, during aging, degus exhibit a progressive decline in cognitive function, reduced neuroinflammation, and concomitant increases in the number and size of amyloid ß (Aß) plaques in several brain regions. Importantly, in humans and several AD models, a correlation has been shown between brain dysfunction and neuronal glucose utilization impairment, a critical aspect considering the high-energy demand of the brain. However, whether degus develop alterations in glucose metabolism remains unknown. In the present work, we measured several markers of glucose metabolism, namely, glucose uptake, ATP production, and glycolysis and pentose phosphate pathway (PPP) flux, in hippocampal slices from degus of different ages. We found a significant decrease in hippocampal glucose metabolism in aged degus, caused mainly by a drop in glucose uptake, which in turn, reduced ATP synthesis. Moreover, we observed a negative correlation between age and PPP flux. Together, our data further support the use of degus as a model for studying the neuropathology involved in sporadic AD-like pathology and as a potentially valuable tool in the search for effective treatments against the disease.
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Aging is a progressive functional decline characterized by a gradual deterioration in physiological function and behavior. The most important age-related change in cognitive function is decline in cognitive performance (i.e., the processing or transformation of information to make decisions that includes speed of processing, working memory, and learning). The purpose of this study is to outline the changes in age-related cognitive performance (i.e., short-term recognition memory and long-term learning and memory) in long-lived Octodon degus. The strong similarity between degus and humans in social, metabolic, biochemical, and cognitive aspects makes it a unique animal model for exploring the mechanisms underlying the behavioral and cognitive deficits related to natural aging. In this study, we examined young adult female degus (12- and 24-months-old) and aged female degus (38-, 56-, and 75-months-old) that were exposed to a battery of cognitive-behavioral tests. Multivariate analyses of data from the Social Interaction test or Novel Object/Local Recognition (to measure short-term recognition memory), and the Barnes maze test (to measure long-term learning and memory) revealed a consistent pattern. Young animals formed a separate group of aged degus for both short- and long-term memories. The association between the first component of the principal component analysis (PCA) from short-term memory with the first component of the PCA from long-term memory showed a significant negative correlation. This suggests age-dependent differences in both memories, with the aged degus having higher values of long-term memory ability but poor short-term recognition memory, whereas in the young degus an opposite pattern was found. Approximately 5% of the young and 80% of the aged degus showed an impaired short-term recognition memory; whereas for long-term memory about 32% of the young degus and 57% of the aged degus showed decreased performance on the Barnes maze test. Throughout this study, we outlined age-dependent cognitive performance decline during natural aging in degus. Moreover, we also demonstrated that the use of a multivariate approach let us explore and visualize complex behavioral variables, and identified specific behavioral patterns that allowed us to make powerful conclusions that will facilitate further the study on the biology of aging. In addition, this study could help predict the onset of the aging process based on behavioral performance.
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Loneliness affects group-living mammals triggering a cascade of stress-dependent physiological disorders. Indeed, social isolation stress is a major risk factor for several neuropsychiatric disorders including anxiety and depression. Furthermore, social isolation has a negative impact on health and fitness. However, the neurobiological consequences of long-term chronic social isolation stress (LTCSIS) manifested during the adulthood of affected individuals are not fully understood. Our study assessed the impact of LTCSIS and social buffering (re-socialization) on the behavioural performance and social-affective brain-related proteins in diurnal, social, and long-lived Octodon degus (degus). Thereby, anxiety-like and social behaviour, and social recognition memory were assessed in male and female animals subjected to a variety of stress-inducing treatments applied from post-natal and post-weaning until their adulthood. Additionally, we evaluated the relationship among LTCSIS, Oxytocin levels (OXT), and OXT-Ca2+-signalling proteins in the hypothalamus, the hippocampus, and the prefrontal cortex. Our findings suggest that LTCSIS induces anxiety like-behaviour and impairs social novelty preference whereas sociability is unaffected. On the other hand, re-socialization can revert both isolation-induced anxiety and social memory impairment. However, OXT and its signalling remained reduced in the abovementioned brain areas, suggesting that the observed changes in OXT-Ca2+ pathway proteins were permanent in male and female degus. Based on these findings, we conclude degus experience social stress differently, suggesting the existence of sex-related mechanisms to cope with specific adaptive challenges.
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A new argasid (Argasidae) tick is herein described based on morphology and molecular data obtained from larvae parasitizing Octodon degus and from ticks collected inside burrows in northern Chile. Unfed laboratory-reared larvae were mounted in slides for morphometrical and morphological analyses. Larvae of Ornithodoros octodontus n. sp. share morphological traits with Ornithodoros quilinensis and Ornithodoros xerophylus, two species associated with rodents in the Argentinean Chaco. However, a longer hypostome with two rows of 21 and 22 denticles each one, and conspicuous leaf-shaped anal plates separate O. octodontus. While nymphal stages of O. octodontus lack cheeks and possess a micromammillated dorsal integument, adults have cheeks and exhibit markedly irregular mammillae along their dorsal surface. Phylogenetic analyses of neotropical Argasidae based on mitochondrial 16S rDNA sequences point that O. octodontus forms a monophyletic group with O. xerophylus and an unidentified Ornithodoros sp. from Bolivia, all of them associated with burrow-dweller rodents. Ornithodoros aragaoi and Ornithodoros davisi, two rare species collected once only in the Peruvian Andean Plateau during 1955 are morphologically closely related with adults and nymphs of O. octodontus. Biological observations of O. octodontus revealed autogenic females. For the moment, subgeneric classification of this new species depends on further biological studies. The fauna of ticks occurring in Chile is now represented by 22 species, 11 belonging to the Argasidae family.
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Octodon , Ornithodoros/classificação , Doenças dos Roedores/parasitologia , Infestações por Carrapato/veterinária , Animais , Chile , Feminino , Larva/anatomia & histologia , Larva/classificação , Larva/crescimento & desenvolvimento , Larva/ultraestrutura , Masculino , Microscopia Eletrônica de Varredura/veterinária , Ninfa/anatomia & histologia , Ninfa/classificação , Ninfa/crescimento & desenvolvimento , Ninfa/ultraestrutura , Ornithodoros/anatomia & histologia , Ornithodoros/crescimento & desenvolvimento , Ornithodoros/ultraestrutura , Infestações por Carrapato/parasitologiaRESUMO
Alzheimer's disease (AD) is a devastating neurodegenerative disorder in which superior brain functions, such as memory and cognition, are impaired. Currently, no effective treatment is available for AD. Although andrographolide (ANDRO), a compound extracted from the herb Andrographis paniculata, has shown interesting effects in models of several diseases, including AD, its effects on other molecular changes observed in AD, such as neuroinflammation and oxidative stress, have not yet been studied. To evaluate the impact of ANDRO-based intervention on the levels of amyloid-ß (Aß) and neuroinflammatory and oxidative stress markers in the brains of aged Octodon degus, a Chilean rodent, fifty-six-month-old O. degus were treated intraperitoneally with 2 or 4 mg/kg ANDRO. Vehicle-injected and 12-month-old O. degus were used as positive controls. Then, the protein levels of selected markers were assessed via immunohistochemistry and immunoblotting. ANDRO significantly reduced the total Aß burden as well as astrogliosis and interleukin-6 levels. Moreover, ANDRO significantly reduced the levels of 4-hydroxynonenal and N-tyrosine adducts, suggesting a relevant reduction in oxidative stress within aged O. degus brain. Considering that O. degus has been proposed as a potential "natural" model for sporadic AD due to the development of neuropathological markers that resemble this pathology, our results suggest that ANDRO should be further studied to establish its potential as a therapeutic drug for AD.
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Encéfalo/efeitos dos fármacos , Diterpenos/farmacologia , Inflamação/tratamento farmacológico , Octodon/metabolismo , Estresse Oxidativo/efeitos dos fármacos , Envelhecimento/fisiologia , Doença de Alzheimer/tratamento farmacológico , Doença de Alzheimer/patologia , Peptídeos beta-Amiloides/efeitos dos fármacos , Peptídeos beta-Amiloides/metabolismo , Animais , Encéfalo/metabolismo , Cognição/efeitos dos fármacos , Modelos Animais de Doenças , Proteínas tau/efeitos dos fármacos , Proteínas tau/metabolismoRESUMO
Alzheimer's disease (AD) is the most common cause of dementia worldwide. Despite advances in our understanding of the molecular milieu driving AD pathophysiology, no effective therapy is currently available. Moreover, various clinical trials have continued to fail, suggesting that our approach to AD must be revised. Accordingly, the development and validation of new models are highly desirable. Over the last decade, we have been working with Octodon degus (degu), a Chilean rodent, which spontaneously develops AD-like neuropathology, including increased amyloid-ß (Aß) aggregates, tau hyperphosphorylation, and postsynaptic dysfunction. However, for proper validation of degu as an AD model, the aggregation properties of its Aß peptide must be analyzed. Thus, in this study, we examined the capacity of the degu Aß peptide to aggregate in vitro. Then, we analyzed the age-dependent variation in soluble Aß levels in the hippocampus and cortex of third- to fifth-generation captive-born degu. We also assessed the appearance and spatial distribution of amyloid plaques in O. degus and compared them with the plaques in two AD transgenic mouse models. In agreement with our previous studies, degu Aß was able to aggregate, forming fibrillar species in vitro. Furthermore, amyloid plaques appeared in the anterior brain structures of O. degus at approximately 32 months of age and in the whole brain at 56 months, along with concomitant increases in Aß levels and the Aß42/Aß40 ratio, indicating that O. degus spontaneously develops AD-like pathology earlier than other spontaneous models. Based on these results, we can confirm that O. degus constitutes a valuable model to improve AD research.
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Doença de Alzheimer/patologia , Peptídeos beta-Amiloides/metabolismo , Amiloide/metabolismo , Encéfalo/patologia , Placa Amiloide/patologia , Doença de Alzheimer/metabolismo , Animais , Encéfalo/metabolismo , Modelos Animais de Doenças , Octodon , Placa Amiloide/metabolismo , Agregados Proteicos , Proteínas tau/metabolismoRESUMO
There has been a progressive increase in the incidence of fructose-induced metabolic disorders, such as metabolic syndrome (MetS). Moreover, novel evidence reported negative effects of high-fructose diets in brain function. This study was designed to evaluate for the first time the effects of long-term fructose consumption (LT-FC) on the normal ageing process in a long-lived animal model rodent, Octodon degus or degu. Moreover, we could replicate human sugar consumption behaviour over time, leading us to understand then the possible mechanisms by which this MetS-like condition could affect cognitive abilities. Our results support that 28 months (from pup to adulthood) of a 15% solution of fructose induced clinical conditions similar to MetS which includes an insulin-resistance scenario together with elevated basal metabolic rate and non-alcoholic fatty liver disease. Additionally, we extended our analysis to evaluate the impact of this MetS-like condition on the functional and cognitive brain processes. Behavioural test suggests that fructose-induced MetS-like condition impair hippocampal-dependent and independent memory performance. Moreover, we also reported several neuropathological events as impaired hippocampal redox balance, together with synaptic protein loss. These changes might be responsible for the alterations in synaptic plasticity and transmitter release observed in these cognitively impaired animals. Our results indicate that LT-FC induced several facets of MetS that eventually could trigger brain disorders, in particular, synaptic dysfunction and reduced cognition.
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Disfunção Cognitiva/complicações , Disfunção Cognitiva/fisiopatologia , Síndrome Metabólica/induzido quimicamente , Síndrome Metabólica/fisiopatologia , Plasticidade Neuronal , Octodon/metabolismo , Animais , Metabolismo Basal , Peso Corporal , Disfunção Cognitiva/sangue , Disfunção Cognitiva/metabolismo , Comportamento Exploratório , Frutose , Hipocampo , Humanos , Relações Interpessoais , Masculino , Aprendizagem em Labirinto , Síndrome Metabólica/sangue , Proteínas do Tecido Nervoso/metabolismo , Hepatopatia Gordurosa não Alcoólica/sangue , Hepatopatia Gordurosa não Alcoólica/complicações , Hepatopatia Gordurosa não Alcoólica/fisiopatologia , Estresse Oxidativo , Fatores de TempoRESUMO
BACKGROUND: Chagas disease caused by Trypanosoma cruzi is considered a major public health problem in America. After an acute phase the disease changes to a chronic phase with very low parasitemia. The parasite presents high genetic variability with seven discrete typing units (DTUs): TcI-TcVI and Tc bat. The aim of this work is to evaluate fluctuation of parasitemia and T. cruzi DTUs in naturally infected Octodon degus. METHODS: After animal capture parasitemia was obtained by qPCR and later the animals were evaluated by three serial xenodiagnoses using two insect vector species, Mepraia spinolai and Triatoma infestans. The parasites amplified over time by insect xenodiagnosis were analyzed by conventional PCR and after that the infective T. cruzi were characterized by means of hybridization tests. RESULTS: The determination of O. degus parasitemia before serial xenodiagnosis by qPCR reveals a great heterogeneity from 1 to 812 parasite equivalents/ml in the blood stream. The T. cruzi DTU composition in 23 analyzed animals by xenodiagnosis oscillated from mixed infections with different DTUs to infections without DTU identification or vice versa, this is equivalent to 50% of the studied animals. Detection of triatomine infection and composition of T. cruzi DTUs was achieved more efficiently 40 days post-infection rather than after 80 or 120 days. CONCLUSION: Trypanosoma cruzi DTUs composition fluctuates over time in naturally infected O. degus. Three replicates of serial xenodiagnosis confirmed that living parasites have been studied. Our results allow us to confirm that M. spinolai and T. infestans are equally competent to maintain T. cruzi DTUs since similar results of infection were obtained after xenodiagnosis procedure.
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Doença de Chagas/parasitologia , Reservatórios de Doenças/parasitologia , Variação Genética , Octodon/parasitologia , Parasitemia , Doença Aguda , Animais , Doença de Chagas/sangue , Doença de Chagas/fisiopatologia , Genótipo , Insetos Vetores/parasitologia , Tipagem Molecular , Reação em Cadeia da Polimerase em Tempo Real/métodos , Sorogrupo , Triatoma/parasitologia , Triatominae/parasitologia , Trypanosoma cruzi/genética , XenodiagnósticoRESUMO
Cognitive ecologist posits that the more efficiently an animal uses information from the biotic and abiotic environment, the more adaptive are its cognitive abilities. Nevertheless, this approach does not test for natural neurodegenerative processes under field or experimental conditions, which may recover animals information processing and decision making and may explain, mechanistically, maladaptive behaviors. Here, we call for integrative approaches to explain the relationship between ultimate and proximate mechanisms behind social behavior. We highlight the importance of using the endemic caviomorph rodent Octodon degus as a valuable natural model for mechanistic studies of social behavior and to explain how physical environments can shape social experiences that might influence impaired cognitive abilities and the onset and progression of neurodegenerative disorders such as Alzheimer disease. We consequently suggest neuroecological approaches to examine how key elements of the environment may affect neural and cognitive mechanisms associated with learning, memory processes and brain structures involved in social behavior. We propose the following three core objectives of a program comprising interdisciplinary research in O. degus, namely: (1) to determine whether diet types provided after weaning can lead to cognitive impairment associated with spatial memory, learning and predisposing to develop Alzheimer disease in younger ages; (2) to examine if early life social experience has long term effects on behavior and cognitive responses and risk for development Alzheimer disease in later life and (3) To determine if an increase of social interactions in adult degu reared in different degree of social stressful conditions alter their behavior and cognitive responses.
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Animais , Comportamento Social , Cognição/fisiologia , Octodon , Modelos Animais de Doenças , Meio Ambiente , Doença de Alzheimer/etiologia , Doença de Alzheimer/psicologia , Estresse Psicológico , Envelhecimento , Fatores de Risco , Pesquisa Biomédica/métodos , Doença de Alzheimer/fisiopatologia , Transtornos da Memória/fisiopatologiaRESUMO
The retina is sensitive to age-dependent degeneration. To find suitable animal models to understand and map this process has particular importance. The degu (Octodon degus) is a diurnal rodent with dichromatic color vision. Its retinal structure is similar to that in humans in many respects, therefore, it is well suited to study retinal aging. Histological, cell type-specific and ultrastructural alterations were examined in 6-, 12- and 36-months old degus. The characteristic layers of the retina were present at all ages, but slightly loosened tissue structure could be observed in 36-month-old animals both at light and electron microscopic levels. Elevated Glial fibrillary acidic protein (GFAP) expression was observed in Müller glial cells in aging retinas. The number of rod bipolar cells and the ganglion cells was reduced in the aging specimens, while that of cone bipolar cells remained unchanged. Other age-related differences were detected at ultrastructural level: alteration of the retinal pigment epithelium and degenerated photoreceptor cells were evident. Ribbon synapses were sparse and often differed in morphology from those in the young animals. These results support our hypothesis that (i) the rod pathway seems to be more sensitive than the cone pathway to age-related cell loss; (ii) structural changes in the basement membrane of pigment epithelial cells can be one of the early signs of degenerative processes; (iii) the loss of synaptic proteins especially from those of the ribbon synapses are characteristic; and (iv) the degu retina may be a suitable model for studying retinal aging.
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Several reports have described host species diversity and identity as the most important factors influencing disease risk, producing either dilution or amplification of the pathogen in a host community. Triatomine vectors, mammals and the protozoan Trypanosoma cruzi (Trypanosomatida: Trypanosomatidae) Chagas are involved in the wild cycle of Chagas disease, in which infection of mammals occurs by contamination of mucous membranes or skin abrasions with insect-infected faeces. We examined the extent to which host diversity and identity determine the infection level observed in vector populations (i.e. disease risk in humans). We recorded infection in triatomine colonies and on the coexisting host mammalian species in semi-arid Chile. Host diversity, and total and infected host species densities are used as predictor variables for disease risk. Disease risk did not correlate with host diversity changes. However, the densities of each infected rodent species were positively associated with disease risk. We suggest that the infected host density surrounding the vector colonies is a relevant variable for disease risk and should be considered to understand disease dynamics. It is crucial to pay attention on the spatial scale of analysis, considering the pattern of vector dispersal, when the relationship between host diversity and disease risk is studied.
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Roedores/parasitologia , Triatominae/parasitologia , Trypanosoma cruzi/fisiologia , Animais , Chile , Fezes/parasitologia , Insetos Vetores , Densidade Demográfica , Fatores de Risco , Roedores/classificaçãoRESUMO
Mammals exposed to low temperatures increase their metabolic rate to maintain constant body temperature and thus compensate for heat loss. This high and costly energetic demand can be mitigated through thermoregulatory behavior such as social grouping or huddling, which helps to decrease metabolic rate as function of the numbers of individuals grouped. Sustained low temperatures in endothermic animals produce changes over time in rates of energy expenditure, by means of phenotypic plasticity. However, the putative modulating effect that huddling exerts on the flexibility of the basal metabolic rate (BMR) due to thermal acclimation remains unknown. We determined BMR values in Octodon degus, an endemic Chilean rodent, after being acclimated to either 15 or 30°C during 60 days, both alone and in groups of three and five individuals. At 15°C, BMR of huddling individuals was 40% lower than that of animals housed alone. Moreover, infrared thermography revealed a significant increase in local surface temperatures in huddled animals. Furthermore, individual thermal conductance was lower in individuals acclimated to 15°C than to 30°C, but no differences were observed between single and grouped animals. Our results indicate that huddling prevents an increase in BMR when animals are acclimated to cold conditions and that this effect is proportional to the number of animals grouped.
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Metabolismo Basal , Regulação da Temperatura Corporal , Octodon/fisiologia , Comportamento Social , Aclimatação , Animais , Temperatura Baixa , Feminino , Masculino , Condutividade Térmica , Termografia , Perda Insensível de ÁguaRESUMO
STUDY OBJECTIVES: To determine rapid eye movement (REM) sleep phase preference in a crepuscular mammal (Octodon degus) by challenging the specific REM sleep homeostatic response during the diurnal and nocturnal anticrepuscular rest phases. DESIGN: We have investigated REM sleep rebound, recovery, and documented REM sleep propensity measures during and after diurnal and nocturnal selective REM sleep deprivations. SUBJECTS: Nine male wild-captured O. degus prepared for polysomnographic recordings. INTERVENTIONS: Animals were recorded during four consecutive baseline and two separate diurnal or nocturnal deprivation days, under a 12:12 light-dark schedule. Three-h selective REM sleep deprivations were performed, starting at midday (zeitgeber time 6) or midnight (zeitgeber time 18). MEASUREMENTS AND RESULTS: Diurnal and nocturnal REM sleep deprivations provoked equivalent amounts of REM sleep debt, but a consistent REM sleep rebound was found only after nocturnal deprivation. The nocturnal rebound was characterized by a complete recovery of REM sleep associated with an augment in REM/total sleep time ratio and enhancement in REM sleep episode consolidation. CONCLUSIONS: Our results support the notion that the circadian system actively promotes REM sleep. We propose that the sleep-wake cycle of O. degus is modulated by a chorus of circadian oscillators with a bimodal crepuscular modulation of arousal and a unimodal promotion of nocturnal REM sleep
Assuntos
Octodon/fisiologia , Privação do Sono/fisiopatologia , Sono REM/fisiologia , Animais , Ritmo Circadiano/fisiologia , Masculino , Polissonografia , Fatores de TempoRESUMO
Estudios experimentales demuestran que modificaciones medioambientales pueden producir alteraciones en el desarrollo normal de la corteza cerebral visual y sus conexiones. Por otra parte, es posible que en condiciones naturales, las especies animales hayan desarrollado adaptaciones genéticas a las distintas condiciones de luminosidad en que realizan su actividad. Recientemente, se han observado variaciones significativas en la densidad neuronal cortical del área 17 (área visual primaria), en roedores silvestres con diferentes períodos diarios de actividad y relación filogenética distante (Abrothrix olivaceus y Phyllotis darwini), pero aún no se ha determinado la naturaleza genética o plástica de dichas diferencias. En este trabajo se compararon especies con una mayor cercanía filogenética, para disminuir al máximo la variable taxonómica. Se estudió la corteza visual primaria (área 17), de roedores silvestres nativos, de las especies Octodon degus (n=5) y Octodon bridgesi (n=3), pertenecientes a la Familia Octodontidae, con el propósito de evidenciar cambios a través de la medición de la densidad neuronal, mediante la técnica del disector óptico, en cortes de 40 µm, incluidos en celoidina y teñidos con Nissl. Complementariamente, se realizó una cuantificación de la densidad neuronal de la corteza motora de las especies en estudio. O. degus, que presenta un período de actividad diurna, evidenció una densidad neuronal menor en la corteza visual (34,32 +/- 2,51 x 104 neuronas/mm3), que la observada en O. bridgesi (39,55 +/- 0,64 x 104 neuronas/mm3), especie de período de actividad nocturna; lo cual fue estadísticamente significativo (t=3,44; p<0,05). Las diferencias encontradas se podrían relacionar con el tipo de condiciones de luminosidad en que se desenvuelven dichas especies, aunque no se puede descartar la influencia de otros factores.
Studies show that environmental modifications can produce profound alterations in the normal development of the visual cortex and its connectivity. For the other hand it is possible that in natural conditions, animal species have developed genetic adaptations to the different conditions of luminance in which they normally behave. Recently have observed significant changes in cortical neuronal density of area 17 (primary visual area), in two sympatric Chilean rodents with different daily activity (Phyllotis darwini and Abrothrix olivaceus), but have not yet determined the genetic nature or plastic such differences. In this paper we compared species with a closer phylogenetic relation so as to minimize the taxonomic variable. We studied the primary visual cortex (area 17) of wild rodents native of the species Octodon degus (n=5) and Octodon bridgesi (n=3), belonging to the Octodontidae family, in order to show changes in the neuronal density, using celloidin-embedded, 40µm-thickness Nissl sections, with the aid of an optical dissector. In addition, we performed a quantification of the neuronal density of the motor cortex of the species under study. O. degus, bearing a crepuscular-diurnal activity pattern, showed a lower neuronal density in the visual cortex (34.32 +/- 2.51 x10(4) neuron/mm³) than that observed in O. bridgesi (39.55 +/- 0.64 x10(4) neuron/mm³), a species that exhibits a nocturnal phase preference, which was statistically significant (t=3.44; p<0.05). These differences might be related to differences in daily activity in two species, but we cannot discount the influence of other factors.