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The renin-angiotensin system (RAS) is composed of a series of peptides, receptors, and enzymes that play a pivotal role in maintaining cardiovascular homeostasis. Among the most important players in this system are the angiotensin-II and angiotensin-(1-7) peptides. Our group has recently demonstrated that alamandine (ALA), a peptide with structural and functional similarities to angiotensin-(1-7), interacts with cardiomyocytes, enhancing contractility via the Mas-related G protein-coupled receptor member D (MrgD). It is currently unknown whether this modulation varies along the distinct phases of the day. To address this issue, we assessed the ALA-induced contractility response of cardiomyocytes from mice at four Zeitgeber times (ZTs). At ZT2 (light phase), ALA enhanced cardiomyocyte shortening in an MrgD receptor-dependent manner, which was associated with nitric oxide (NO) production. At ZT14 (dark phase), ALA induced a negative modulation on the cardiomyocyte contraction. ß-Alanine, an MrgD agonist, reproduced the time-of-day effects of ALA on myocyte shortening. NG-nitro-l-arginine methyl ester, an NO synthase inhibitor, blocked the increase in fractional shortening induced by ALA at ZT2. No effect of ALA on myocyte shortening was observed at ZT8 and ZT20. Our results show that ALA/MrgD signaling in cardiomyocytes is subject to temporal modulation. This finding has significant implications for pharmacological approaches that combine chronotherapy for cardiac conditions triggered by disruption of circadian rhythms and hormonal signaling.NEW & NOTEWORTHY Alamandine, a member of the renin-angiotensin system, serves critical roles in cardioprotection, including the modulation of cardiomyocyte contractility. Whether this effect varies along the day is unknown. Our results provide evidence that alamandine via receptor MrgD exerts opposing actions on cardiomyocyte shortening, enhancing, or reducing contraction depending on the time of day. These findings may have significant implications for the development and effectiveness of future cardiac therapies.

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Contracción Miocárdica , Miocitos Cardíacos , Óxido Nítrico , Oligopéptidos , Receptores Acoplados a Proteínas G , Animales , Miocitos Cardíacos/metabolismo , Miocitos Cardíacos/efectos de los fármacos , Contracción Miocárdica/efectos de los fármacos , Contracción Miocárdica/fisiología , Ratones , Receptores Acoplados a Proteínas G/metabolismo , Receptores Acoplados a Proteínas G/agonistas , Óxido Nítrico/metabolismo , Oligopéptidos/farmacología , Ratones Endogámicos C57BL , Ritmo Circadiano/fisiología , Ritmo Circadiano/efectos de los fármacos , Receptores de Neuropéptido/metabolismo , Receptores de Neuropéptido/agonistas , Receptores de Neuropéptido/antagonistas & inhibidores , Masculino , Células Cultivadas , Sistema Renina-Angiotensina/efectos de los fármacos , Sistema Renina-Angiotensina/fisiología

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Resumen El sistema circadiano está sincronizado al ciclo luz-oscuridad que es generado por la rotación de la tierra, asegurando que la vigilia sea durante el día y que el sueño ocurra durante la noche. Sin embargo, el ritmo de sueño-vigilia puede estar desincronizado del ciclo luz-oscuridad o desincronizado de manera endógena, dando como resultado: insomnio, fatiga y bajo rendimiento en las actividades cotidianas. Mientras que los trastornos del sueño están clasificados por la Asociación Americana de Trastornos del Sueño como: disomnias intrínsecas, disomnias extrínsecas, parasomnias o trastornos del sueño médicos/psiquiátricos. Los trastornos circadianos del sueño se han categorizado por separado, en parte para reconocer que en la mayoría de los casos la etiología de los trastornos circadianos es una mezcla de factores internos y ambientales, o por un desajuste temporal entre ambos. Los síntomas generalmente son insomnio o hipersomnia, síntomas comunes en pacientes con trastornos circadianos del sueño, aunque hay otras causas a las que pueden atribuirse y que deben excluirse antes de realizar el diagnóstico de un trastorno circadiano del sueño. En el paciente sin otra patología del sueño, un registro diario de actividades, comidas, ejercicio, siestas y la hora de acostarse es una herramienta esencial para evaluar los trastornos circadianos del sueño. Estos registros deben mantenerse durante 2 semanas o más, ya que una perturbación debida a cambios de trabajo o viajes a través de zonas horarias puede tener efectos sobre el sueño y el estado de alerta durante el día, semanas después del evento.

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Abstract The circadian system is synchronized to the light-dark cycle generated by the rotation of the earth, ensuring that wakefulness is during the day and sleep occurs at night. However, the sleep-wake rhythm may be out of sync with the light-dark cycle or endogenously out of sync, resulting in insomnia, fatigue, and poor performance in activities of daily living. Sleep disorders are classified by the American Sleep Disorders Association, as intrinsic dyssomnias, extrinsic dyssomnias, parasomnias, or medical/psychiatric sleep disorders. Circadian sleep disorders have been categorized separately to recognize that in most cases the etiology of circadian disturbances is a mix of internal and environmental factors or a temporary mismatch between the two. Symptoms are usually insomnia or hypersomnia, common symptoms in patients with circadian sleep disorders although other causes can be attributed and must be excluded before a diagnosis of a circadian sleep disorder is made. In the patient without other sleep pathology, a daily record of activities, meals, exercise, naps, and bedtime is an essential tool in assessing circadian sleep disorders. These records should be kept for 2 weeks or more, as a disturbance due to job changes or travel across time zones can have effects on sleep and daytime alertness weeks after the event.

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The composition of the gut microbiota oscillates according to the light-dark cycle. However, the existing literature demonstrates these oscillations only by molecular methods. Microbial cultures are an interesting method for studying metabolically active microorganisms. In this work, we aimed to understand the diurnal oscillation of the intestinal microbiota in Wistar male rats through microbial culture analysis. Over a 24 h period, three animals were euthanized every 6 h. Intestinal segments were dissected immediately after euthanasia and diluted in phosphate-buffered saline (PBS) for plating in different culture media. The CFU/mL counts in feces samples cultured in the Brucella medium were significantly higher at ZT0, followed by ZT6, ZT18, and ZT12 (p = 0.0156), which demonstrated the diurnal oscillation of metabolically active anaerobic bacteria every 6 h using microbial culture. In addition, quantitative differences were demonstrated in anaerobic bacteria and fungi in different gastrointestinal tract tissues.

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Puberty onset is tightly regulated by a broad spectrum of neuroendocrine signals and peripheral stimuli which coordinate the hypothalamic-pituitary-gonadal (HPG) axis activation. Numerous studies suggest that light stimulation influences HPG axis function; however, the effect of blindness on puberty timing remains controversial. Given that menarche is a suitable marker for sexual development initiation, the evaluation of the age at which blind girls attain it allows to indirectly assess the effect of light-dark cycle disruption on pubertal development. The present investigation aimed to review the evidence regarding menarcheal age drift in visually impaired girls, as well as to discuss the findings based on the existing hypotheses of the physiological mechanisms linking the light-dark cycle and photic sensitivity loss to the onset of puberty. Eleven studies were retrieved from a literature search conducted in PubMed, Scopus, ScienceDirect, SpringerLink, and Google Scholar databases. Eight studies concluded that light perception impairment is related to a moderately earlier age at menarche. Moreover, the evidence gathered in this review suggests a positive association between the degree of light perception loss and precocious menarcheal onset; yet, no conclusive outcomes were found regarding menarche advancement in acquired versus congenital blindness. We encourage further research aiming to elucidate the physiological mechanism underlying photosensitive regulation and blindness effect on the neuroendocrine pathways involved in human sexual maturation.

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Menarquia , Fotoperiodo , Ceguera , Ritmo Circadiano , Femenino , Humanos , Menarquia/fisiología , Pubertad/fisiología

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OBJECTIVE: to compare daily light exposure, activity-rest rhythm, sleep-wake cycle (SWC) and attention in Brazilian students living in different levels of urbanization. METHODS: 115 adolescents (74 girls), aged 14-18 years (mean 15.5 ± 0.7 years), from the first years of high school have participated. The SWC was evaluated by actimetry and a Sleep Diary for 10 days. Besides, the "Health and Sleep" Questionnaire, the Morningness and Eveningness Scale for adolescents, the Pittsburgh Sleep Quality Index, and the Pediatric Daytime Sleepiness Scale were answered. Attention was assessed by a Continuous Performance Task. RESULTS: In the less urbanized region, there were a greater exposure to light during the day accompanied by a higher proportion of morning-types and less occurrence of excessive daytime sleepiness. Otherwise, in the more urbanized region, adolescents showed a trend to sleep less in weekdays and presented more irregularity in sleep duration between weekdays and weekend, with 83 ± 15% of sleep efficiency, 01:04 ± 1:30 h of WASO and 7 ± 6.7 awakenings per night on the weekdays, suggestive of poor sleep quality. Despite of this, they showed better attentional performance: more correct responses (tonic and phasic alertness, and sustained attention) and less omissions (for all components). Regardless of the degree of urbanization, there was partial sleep deprivation, irregular sleep schedules and poor sleep quality in adolescents. CONCLUSIONS: The daily light exposure and activity-rest profiles, SWC and attention in adolescents varied according to the degree of urbanization. Besides, the negative impacts of early school starting times leading to sleep deprivation, irregular sleep times and poor sleep quality were observed irrespective of the degree of urbanization, reinforcing that the early school starting time at morning is a strong temporal challenge for teenagers, having negative impacts on cognition and academic performance.

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Ritmo Circadiano , Sueño , Adolescente , Atención , Brasil , Niño , Femenino , Humanos , Privación de Sueño , Encuestas y Cuestionarios

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The response to a zeitgeber, particularly the light/dark cycle, may vary phenotypically. Phenotypic plasticity can be defined as the ability of one genome to express different phenotypes in response to environmental variation. In this opinion paper, we present some evidence that one of the most prominent effects of the introduction of electric light to the everyday life of humans is a significant increase in phenotypic plasticity and differences in interindividual phases of entrainment. We propose that the healthy limits of phenotypic plasticity have been surpassed in contemporary society.

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From an evolutionary point of view, vitamin D and melatonin appeared very early and share functions related to defense mechanisms. In the current clinical setting, vitamin D is exclusively associated with phosphocalcic metabolism. Meanwhile, melatonin has chronobiological effects and influences the sleep-wake cycle. Scientific evidence, however, has identified new actions of both molecules in different physiological and pathological settings. The biosynthetic pathways of vitamin D and melatonin are inversely related relative to sun exposure. A deficiency of these molecules has been associated with the pathogenesis of cardiovascular diseases, including arterial hypertension, neurodegenerative diseases, sleep disorders, kidney diseases, cancer, psychiatric disorders, bone diseases, metabolic syndrome, and diabetes, among others. During aging, the intake and cutaneous synthesis of vitamin D, as well as the endogenous synthesis of melatonin are remarkably depleted, therefore, producing a state characterized by an increase of oxidative stress, inflammation, and mitochondrial dysfunction. Both molecules are involved in the homeostatic functioning of the mitochondria. Given the presence of specific receptors in the organelle, the antagonism of the renin-angiotensin-aldosterone system (RAAS), the decrease of reactive species of oxygen (ROS), in conjunction with modifications in autophagy and apoptosis, anti-inflammatory properties inter alia, mitochondria emerge as the final common target for melatonin and vitamin D. The primary purpose of this review is to elucidate the common molecular mechanisms by which vitamin D and melatonin might share a synergistic effect in the protection of proper mitochondrial functioning.

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Melatonina/metabolismo , Mitocondrias/metabolismo , Estrés Oxidativo/genética , Vitamina D/metabolismo , Animales , Apoptosis/genética , Humanos , Melatonina/genética , Mitocondrias/genética , Especies Reactivas de Oxígeno/metabolismo , Sistema Renina-Angiotensina/genética , Estaciones del Año , Trastornos del Sueño del Ritmo Circadiano/genética , Trastornos del Sueño del Ritmo Circadiano/metabolismo , Trastornos del Sueño del Ritmo Circadiano/patología , Vitamina D/genética

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The aim of this work was evaluate the role of photoperiods (long-term, frequencies and short) on the growth and lipid content of microalgae Scenedesmus obliquus CPCC05. The results showed that Scenedesmus obliquus can store sufficient energy to sustain cell growth for continuous periods of up to 2h in the dark, without affecting the photosynthetic rate. The values for maximum biomass (9.58mg/Lh) and lipid productivities (2.56mg/Lh) were obtained at photoperiod of 0.91:0.09s (light:dark) and 48 t/d, respectively. Moreover, the best trade-offs between biomass productivity and light energy economy occurred in photoperiods of 0.5:0.5s and 0.91:0.09s (light:dark), and those between lipid productivity and light energy economy occurred in the frequency photoperiod of 24 and 48 t/d. Thus, the use of the photoperiods are an effective strategy for reducing costs of microalgal biomass production.

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Fotobiorreactores , Fotoperiodo , Fotosíntesis/fisiología , Aceites de Plantas/metabolismo , Scenedesmus/fisiología , Biomasa

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Access to electric light might have shifted the ancestral timing and duration of human sleep. To test this hypothesis, we studied two communities of the historically hunter-gatherer indigenous Toba/Qom in the Argentinean Chaco. These communities share the same ethnic and sociocultural background, but one has free access to electricity while the other relies exclusively on natural light. We fitted participants in each community with wrist activity data loggers to assess their sleep-wake cycles during one week in the summer and one week in the winter. During the summer, participants with access to electricity had a tendency to a shorter daily sleep bout (43 ± 21 min) than those living under natural light conditions. This difference was due to a later daily bedtime and sleep onset in the community with electricity, but a similar sleep offset and rise time in both communities. In the winter, participants without access to electricity slept longer (56 ± 17 min) than those with access to electricity, and this was also related to earlier bedtimes and sleep onsets than participants in the community with electricity. In both communities, daily sleep duration was longer during the winter than during the summer. Our field study supports the notion that access to inexpensive sources of artificial light and the ability to create artificially lit environments must have been key factors in reducing sleep in industrialized human societies.

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Ritmo Circadiano/fisiología , Indígenas Sudamericanos , Luz , Iluminación , Sueño/fisiología , Vigilia , Adulto , Argentina , Electricidad , Femenino , Humanos , Masculino , Persona de Mediana Edad , Fotoperiodo , Estaciones del Año , Factores de Tiempo , Adulto Joven

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Prochlorococcus and Synechococcus, which numerically dominate vast oceanic areas, are the two most abundant oxygenic phototrophs on Earth. Although they require solar energy for photosynthesis, excess light and associated high UV radiations can induce high levels of oxidative stress that may have deleterious effects on their growth and productivity. Here, we compared the photophysiologies of the model strains Prochlorococcus marinus PCC 9511 and Synechococcus sp. WH7803 grown under a bell-shaped light/dark cycle of high visible light supplemented or not with UV. Prochlorococcus exhibited a higher sensitivity to photoinactivation than Synechococcus under both conditions, as shown by a larger drop of photosystem II (PSII) quantum yield at noon and different diel patterns of the D1 protein pool. In the presence of UV, the PSII repair rate was significantly depressed at noon in Prochlorococcus compared to Synechococcus. Additionally, Prochlorococcus was more sensitive than Synechococcus to oxidative stress, as shown by the different degrees of PSII photoinactivation after addition of hydrogen peroxide. A transcriptional analysis also revealed dramatic discrepancies between the two organisms in the diel expression patterns of several genes involved notably in the biosynthesis and/or repair of photosystems, light-harvesting complexes, CO(2) fixation as well as protection mechanisms against light, UV, and oxidative stress, which likely translate profound differences in their light-controlled regulation. Altogether our results suggest that while Synechococcus has developed efficient ways to cope with light and UV stress, Prochlorococcus cells seemingly survive stressful hours of the day by launching a minimal set of protection mechanisms and by temporarily bringing down several key metabolic processes. This study provides unprecedented insights into understanding the distinct depth distributions and dynamics of these two picocyanobacteria in the field.

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resumen está disponible en el texto completo

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Abstract: In the first part of this work we reviewed the hippocampus and striatum anatomy and function in the context of the memory systems. In this second part we describe the anatomic and physiologic basis of the memory systems represented by the amygdala and prefrontal cortex (PFC) and their participation in the expression of strategies for the solution of specific problems. Amygdaloid formation is divided in three principal regions, the baso-lateral nucleus, the superficial nucleus, and the centromedial nucleus. Amygdala is highly connected with several regions of the brain including hippocampus, striatum and PFC. Amygdala has been implicated in the processing, storing and retrieval of emotional information. Another function proposed for the amygdala is to modulate the activity of structures such as the hippocampus, the striatum and the cerebral cortex. The participation of the amygdala has been shown in different tasks such as the Morris water maze, the radial maze, the passive avoidance task, and the freezing behavior among others. In some of these studies it has been shown that the activation of the amygdala enhances the acquisition of the task. When the amygdala is activated pharmacologically it is able to enhance the acquisition of hippocampus or striatum related tasks. In these context, the efficiency of the amygdala activation depends on the synchrony, the precise time, at which it occurs in relation to the event the subject is learning. This is, either immediately before, during or immediately after learning. In support of this enhancing role of the amygdala, some electrophysiological studies have shown that the activation of the amygdala facilitates the development of LTP in the hippocampus while its lesion decreases it. On the other hand, it has also been shown that the amygdala activation increases c-Fos expression in both, the hippocampus and the striatum. In summary, the amygdaloid formation has been proposed as an enhancer of learning, representing the emotional component of the response to the environment. PFC is the other structure involved in the generation of strategies. It has been related with the correct functioning of higher functions such as memory, attention, emotion, anticipation and planning. It has been called the central executor for its fundamental role as a coordinator of past, present information and future performance. It is been proposed as responsible for the so called working memory, that allows to put together different kinds of information at the same time, giving the chance of comparing, selecting and generating a goaloriented behavior. Working memory has been studied with many different techniques, however electrophysiological experiments have shown interesting aspects of its functioning. Recording cells from the PFC of monkeys, Goldman-Rakic showed that these cells remain firing in a short period of time when visual information should be retained to be used in ulterior comparison task. This cell activity suggests that these neurons would be responsible for the maintenance of information in our "mind" a short period of time. These results have been replicated in humans by using real time imaging techniques as fMRI and PET. Again, during the periods of retention of the information, the activity on prefrontal areas increase until such information is used. Besides working memory, anticipation is another important function regulated by the PFC. Several studies have shown that the activity of prefrontal cortex increases before the performance, it seems like the prefrontal cortex predicts the actions in the environment and readily generates a strategy to efficiently act in response. PFC is connected reciprocally with the hippocampus, the striatum and the amygdala, the relation between these structures is under heavy investigation. Regarding the hippocampus, some interaction has been observed, and it has been proposed an interaction between these structures for the long term consolidation of memory. As for the striatum, the relationship with PFC has been studied preferentially with the ventral striatum or nucleus accumbens with respect to reinforcement of behavior. We understand poorly the relationship with the dorsal striatum. The relation between amygdala and PFC, on the other hand, has been studied in relation to the expectancy of the reinforcement. This is defined as the representation in the mind of the reinforcement and the association of that representation with the conditions under which it was delivered. In simple words, this is a way to explain how is that a subject prefers a specific reinforcer over another. It has been shown that lesions of the basolateral amygdala as well as PFC interfere with the expectancy of reinforcement. The function of the amygdala in this case is to provide the emotional component related to the presence of the reinforcement. An extensive literature has addressed the question of circadian variations in the release of neurotransmitters. For example, the diurnal variations in the release of acetylcholine in the hippocampus and PFC. The binding for acetylcholine, serotonin and norepinephrine to glutamatergic hippocampal cells is different depending on the light-dark cycle, suggesting that the modulation of the hippocampus by these neurotransmitters is different depending on the presence or absence of light. In this review, we have devoted special interest to the influence of the light dark cycle on these mnemonic systems and on goaloriented behaviors. We analyze selected papers from the available literature on circadian rhythms and memory, emphasizing the hippocampus role. We believe that the study of this relationship (brain/light-dark cycle) could be a useful tool to understand how the environment influences behavior. On this topic, there's evidence that the learning of a task may be different depending on the part of the day when it was learned. For example, it has been shown in humans that when subjects are submitted to explicit or implicit task the performance is different depending on the hour of the day, being better during the light for the explicit memory and better during the dark for the implicit memory. Studies in rats trained in fear conditioning tasks, showed that subjects learn the task easily when they are trained during the light phase of the cycle and the learned behavior showed a higher resistance to extinction. Conclusión. When a subject is confronted with a specific problem, he/she can find the solution by using different strategies. The expression of one of those strategies depends on the interaction of the different memory systems, these systems process and storage different kinds of information, and this information is useful to generate and exhibit a given strategy. The memory systems are constantly under the influence of the environment, one critical component of this environment is the lightdark cycle, which apparently is modulating the activity of these structures. As a result of the influence of the light-dark cycle on these structures, the behavior of the subject would be modulated as well. All these interaction just for the sake of adaptation, survival, and reproduction in this rotating and translating world.

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resumen está disponible en el texto completo

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Abstract: The ability to abstract, store and recover information from the environment in order to generate new strategies to solve problems is one of the most important qualities of the human brain. We mean by strategy, the sophisticated way to solve a problem. A strategy represents in essence the refinement of a given behavior to solve a problem. A strategy could be generalized to solve different problems. The generation of strategies is subjected to the correct functioning of the brain, meaning, alertness, attention, memory among others brain processes in good stand. In this work we focus on the role of memory in the generation of strategies. In this context, we focus on the literature concerning to memory systems, to show that different memory systems process and store different kinds of information. Therefore, the generation of a given strategy would require the participation of one system instead of other, or at least, one system would be commanding over the others. A memory system is defined as neural network consisting on a central structure communicated through afferences and efferences with others. The ones conveying information to this central structure would provide information from the internal or external environment to be interpreted and stored; while the ones that receive information from the central structure would execute its commands. Curiously, the role of central structure can be played by one structure "A" that in other conditions was under the control of a structure "B". In this condition, "B" is under the control of "A". In this review we sought to describe the anatomic and physiologic basis of the memory systems and their participation in the expression of strategies for the solution of specific problems. In this first part, we review the literature concerning to the hippocampus and striatum. Our endeavor was to make a synthesis of the main components of the functional neuroanatomy of memory and of its specific participation in the generation and expression of strategies, and also of the influence of the light-dark cycle on the strategies resulting from the interaction of these structures. In this review we focus mainly on the basic description of memory systems and on the data obtained from intact rats and of others with lesions and subject to electrophysiological experiments. Many studies reviewed on this first part confront subjects to situations where different solutions can be performed; basically this studies are conducted on mazes were the subject can use different kinds of information for spatial orientation. Depending on the nature of the information available or selected by the subject, investigators may infer the kind of strategy the subject is using to solve the problem. From this background, concepts such as stimulus-stimulus strategy and stimulus-response strategy have been generated. The first one consists of making associations between neutral stimuli, to make a conceptual map that guides the subject toward his/her objective. It has been related with the hippocampus function and it has been classically related to the processing, interpretation, and storage of contexts and events as well as to spatial navigation. We center our attention on studies carried out in mazes, showing that lesions or temporal inactivation of the hippocampus disturb the capacity of orientation by using spatial cues. We also review studies where the expression of spatial strategies is correlated with preferential activation of hippocampus detected with different techniques such as immuno-histochemistry and mycrodialisis in vivo. The stimulus-response strategy, on the other hand, consists on making associations between a particular stimulus and the immediate consequence of its presence. This kind of strategy has been related with the striatum, particularly with its dorsolateral region. For this section we discuss studies where lesions or inactivation of the dorsolateral striatum were performed, on rats submitted to tasks where the solution could be achieved by using stimu-lus-stimulus or stimulus-response strategy. In subjects with striatal dysfunction the ability to perform using a stimulus-response strategy was disrupted but not the ability to use a stimulus-stimu-lus strategy. In addition, we revise studies where the expression of the stimulus-response strategy is correlated with a preferential activation of the striatum over hippocampus. We additionally discuss the interaction hippocampus-striatum to solve a spatial task. We make special emphasis in describing the hippocampal and the striatal systems as independent systems that process and store different kinds of information; therefore, they seem to alternate their activity depending on the demand of the environment. This means that if a stimulus-stimulus strategy is required, the hippocampus will govern the response of the subject, increasing its activity that will be over the activity of the striatum. The opposite will occur if a stimulus-response strategy is required. Studies in humans and rats have been performed to understand the interaction between hippocampus and striatum with similar results. Apparently hippocampus appears more active during the first stages of learning, leading behavior and being expressed as stimulus-stimulus strategy. Later, in learning, the hippocampus decreases in activity and the striatum increases, thus becoming the leader structure. This later activation of stria-tum has been related with the phase of learning when the task is mastered and is starting to become a habit. Finally, we devoted special interest to describe the influence of the light dark cycle over these systems and over the goal-oriented behavior. And as we will see on the second part of this review, the functioning of these structures may be regulated by the light-dark cycle. We will review the influence of the presence or absence of light on neurotransmitters release. We will give evidence indicating that the neurochemical modulation depends greatly on the influence of the light-dark cycle and that it results obviously in a different activity of these structures and hence the behavior. In conclusion, when a subject is confronted with a specific problem, he/she can find the solution by using different strategies. At present, we can not say which are the mechanisms responsible for the selection of a particular strategy at a given mo-ment, but we can say that the expression of any strategy depends on the activity of structures such as the hippocampus and the striatum. In theory each structure represents a memory system or a fundamental part of a memory system. The interaction of the different memory systems, produce a scenario were each system provides, processes, and stores different information about the environment, and this information is useful to generate and exhibit a given strategy. On the second part of this review we will focus on the func-tioning and participation of the amygdala and prefrontal cortex, and the influence of the environment on the memory systems.