Endocannabinoid system and aggression across animal species.

This narrative review article summarizes the current state of knowledge regarding the relationship between the endocannabinoid system (ECS) and aggression across multiple vertebrate species. Experimental evidence indicates that acute administration of phytocannabinoids, synthetic cannabinoids, and the pharmacological enhancement of endocannabinoid signaling decreases aggressive behavior in several animal models. However, research on the chronic effects of cannabinoids on animal aggression has yielded inconsistent findings, indicating a need for further investigation. Cannabinoid receptors, particularly cannabinoid receptor type 1, appear to be an important part of the endogenous mechanism involved in the dampening of aggressive behavior. Overall, this review underscores the importance of the ECS in regulating aggressive behavior and provides a foundation for future research in this area.

CB1R chronic intermittent pharmacological activation facilitates amphetamine seeking and self-administration and changes in CB1R/CRFR1 expression in the amygdala and nucleus accumbens in rats.

Patterns of drug ingestion may have a dissimilar impact on the brain, and therefore also the development of drug addiction. One pattern is binge intoxication that refers to the ingestion of a high amount of drug on a single occasion followed by an abstinence period of variable duration. In this study, our goal was to contrast the effect of continuous low amounts with intermittent higher amounts of Arachidonyl-chloro-ethylamide (ACEA), a CB1R agonist, on amphetamine seeking and ingestion, and describe the effects on the expression of CB1R and CRFR1 in the central nucleus of the amygdala (CeA) and in the nucleus accumbens shell (NAcS). Adult male Wistar rats were treated with a daily administration of vehicle or 20 µg of ACEA, or four days of vehicle followed by 100 µg of ACEA on the fifth day, for a total of 30 days. Upon completion of this treatment, the CB1R and CRFR1 expression in the CeA and NAcS was evaluated by immunofluorescence. Additional groups of rats were evaluated for their anxiety levels (elevated plus maze, EPM), amphetamine (AMPH) self-administration (ASA) and breakpoint (A-BP), as well as AMPH-induced conditioned place preference (A-CPP). Results indicated that ACEA induced changes in the CB1R and CRFR1 expression in both the NAcS and CeA. An increase in anxiety-like behavior, ASA, A-BP and A-CPP was also observed. Since the intermittent administration of 100 µg of ACEA induced the most evident changes in most of the parameters studied, we concluded that binge-like ingestion of drugs induces changes in the brain that may make the subject more vulnerable to developing drug addiction.

Amapola, lindísima amapola: de los opiáceos y los opioides, utilidad y riesgos / Poppy, beautiful poppy: opiates and opioids, utility and risks

Resumen El opio y sus derivados, y recientemente los opioides, han acompañado a la humanidad desde las civilizaciones más antiguas hasta la actualidad. Sus efectos analgésicos, hipnóticos y placenteros no pasaron desapercibidos para los antiguos, los consideraron de utilidad médica y beneficiosa para el estado de ánimo. Hoy en día no existe otro tipo de medicamentos que puedan tratar el dolor más intenso tan eficientemente como estos potentes analgésicos. Sin embargo, el uso médico y recreativo de los opiáceos y los opioides conlleva riesgos para la salud, como la tolerancia, la hiperalgesia y la adicción. Actualmente, además de ser indiscutiblemente el tratamiento médico más poderoso para mitigar el sufrimiento ocasionado por el dolor, se ha convertido también en un problema de salud pública debido a la alta cantidad de personas con trastorno por uso de opioides y por las muertes ocasionadas por sobredosis. En esta revisión se hará mención de las bondades de los opiáceos y opioides, y también de los efectos no deseados que estos producen.

Abstract Opium and its derivatives, and recently the opioids have accompanied the humankind since the ancient civilizations to the present day. Its analgesic, hypnotic and pleasant effects did not go unnoticed by ancient people, which considered most of these effects of medical utility and noticed that they had remarkable mood benefits. Currently, there are no other kind of drugs that can palliate intense pain as efficiently as these powerful analgesics. However, the medical and recreational use of opiates and opioids may carry health risks such as tolerance, hyperalgesia, and addiction. Nowadays, in addition to being indisputably the most powerful medical treatment to alleviate the suffering caused by pain, it has also become a public health problem due to the high number of people with opioid use disorder that have facilitated deaths caused by opioids overdose. In this review we will discuss the medical benefits of opiates and opioids, as much as the unwanted effects they produce.

GPR55 activation prevents amphetamine-induced conditioned place preference and decrease the amphetamine-stimulated inflammatory response in the ventral hippocampus in male rats.

Inflammatory response in the Central Nervous System (CNS) induced by psychostimulants seems to be a crucial factor in the development and maintenance of drug addiction. The ventral hippocampus (vHp) is part of the reward system involved in substance addiction and expresses abundant G protein-coupled receptor 55 (GPR55). This receptor modulates the inflammatory response in vitro and in vivo, but there is no information regarding its anti-inflammatory effects and its impact on psychostimulant consumption. The aim of the present study was to investigate whether vHp GPR55 activation prevents both the inflammatory response induced by amphetamine (AMPH) in the vHp and the AMPH-induced conditioned place preference (A-CPP). Wistar adult male rats with a bilateral cannula into the vHp or intact males were subjected to A-CPP (5 mg/kg). Upon the completion of A-CPP, the vHp was dissected to evaluate IL-1ß and IL-6 expression through RT-PCR, Western blot and immunofluorescence. Our results reveal that AMPH induces both A-CPP and an increase of IL-1ß and IL-6 in the vHp. The GPR55 agonist lysophosphatidylinositol (LPI, 10 µM) infused into the vHp prevented A-CPP and the AMPH-induced IL-1ß increase. CID 16020046 (CID, 10 µM), a selective GPR55 antagonist, abolished LPI effects. To evaluate the effect of the inflammatory response, lipopolysaccharide (LPS, 5 µg/µl) was infused bilaterally into the vHp during A-CPP acquisition. LPS strengthened A-CPP and increased IL-1ß/IL-6 mRNA and protein levels in the vHp. LPS also increased CD68, Iba1, GFAP and vimentin expression. All LPS-induced effects were blocked by LPI. Our results suggest that GPR55 activation in the vHp prevents A-CPP while decreasing the local neuro-inflammatory response. These findings indicate that vHp GPR55 is a crucial factor in preventing the rewarding effects of AMPH due to its capacity to interfere with proinflammatory responses in the vHp.

Dominance status is associated with a variation in cannabinoid receptor 1 expression and amphetamine reward.

The rewarding effects of psychostimulants appear to be distinct between dominant and subordinate individuals. In turn, the endocannabinoid system is an important modulator of drug reward in the nucleus accumbens and medial prefrontal cortex, however the connection with social dominance is yet to be established. Male rats were classified as dominant or subordinate on the basis of their spontaneous agonistic interactions and drug reward was assessed by means of conditioned place preference with amphetamine (AMPH). In addition, the expression of CB1R, CB2R, FAAH1, and DAGLa was quantified from accumbal and cortical tissue samples. Our findings demonstrate that dominant rats required a lesser dose of AMPH to acquire a preference for the drug-associated compartment, thereby suggesting a higher sensitivity to the rewarding effects of AMPH. Furthermore, dominants exhibited a lower expression of CB1R in the medial prefrontal cortex and nucleus accumbens. This study illustrates how CBR1 expression could differentiate the behavioral phenotypes associated to social dominance.

Función de la impulsividad en el trastorno por consumo de sustancias / Impulsivity`s role in substance use disorder

Resumen La proporción de usuarios de una sustancia de abuso que desarrolla problemas con su consumo (abuso o dependencia) representa solo una parte de esta población. En México, el 63.8 % de la población consume alcohol, y de ellos, el 15 % desarrolla algún trastorno por consumo de alcohol (TCA). Se ha observado una relación causal entre el trastorno por consumo de sustancias (TCS) y la falta de autocontrol. Es decir, satisfacer necesidades de manera impulsiva, v. gr., consumir una droga sin evaluar las consecuencias. La corteza prefrontal (CPF) es el principal sustrato neuroanatómico del autocontrol y característicamente la CPF alcanza la madurez alrededor de los 30 años, sugieriendo que el autocontrol se alcanza despues de esta edad. Se ha propuesto que todos los grupos etarios que no han consolidado el uso del autocontrol son vulnerables al TCS. Similarmente ocurre con aquellos sujetos que por algún trastorno psiquiátrico tienen como característica una limitada función prefrontal. La CPF coordina una red subcortical cuya interacción depende de distintos sistemas de neurotransmisión, entre ellos, endocanabinoides. En este trabajo se revisó la función de la CPF y del sistema de endocanabinoides (sECB) y su relación con la vulnerabilidad a la adicción y otros trastornos psiquiátricos.

Abstract The proportion of users of a substance of abuse who develop problems with its use (abuse or dependence) represents only a part of this population. In Mexico, 63.8% of the population consumes alcohol and only 15% of them develop an alcohol use disorder (AUD). A causal relation has been observed between substance use disorder (SUD) and the lack of self-control. Which means, satisfying needs in an impulsive way, v.gr. using a drug, without considering the consequences. The prefrontal cortex (PFC) is the main neuroanatomical substrate of self-control and characteristically reaches maturity around the age of 30, suggesting that self-control is reached after this age. We suggest that all age groups that have not consolidated the use of self-control are vulnerable to SUD. The same occurs with those who, due to a psychiatric disorder, have the characteristic of a limited prefrontal function. The PFC coordinates a subcortical network whose interaction depends on different neurotransmission systems among them, the endocannabinoids system (ECBs). In this work we will review the function of the PFC, the ECBs and its relationship with vulnerability to addiction and other psychiatric disorders.

ADHD: Reviewing the Causes and Evaluating Solutions.

Attention deficit hyperactivity disorder (ADHD) is a neurodevelopmental disorder in which patients present inattention, hyperactivity, and impulsivity. The etiology of this condition is diverse, including environmental factors and the presence of variants of some genes. However, a great diversity exists among patients regarding the presence of these ADHD-associated factors. Moreover, there are variations in the reported neurophysiological correlates of ADHD. ADHD is often treated pharmacologically, producing an improvement in symptomatology, albeit there are patients who are refractory to the main pharmacological treatments or present side effects to these drugs, highlighting the importance of developing other therapeutic options. Different non-pharmacological treatments are in this review addressed, finding diverse results regarding efficacy. Altogether, ADHD is associated with different etiologies, all of them producing changes in brain development, leading to the characteristic symptomatology of this condition. Given the heterogeneous etiology of ADHD, discussion is presented about the convenience of personalizing ADHD treatment, whether pharmacological or non-pharmacological, to reach an optimum effect in the majority of patients. Approaches to personalizing both pharmacological therapy and neurofeedback are presented.

Fragility of reward vs antifragility of defense brain systems in drug dependence.

Drug dependence is a debilitating disorder, affecting 30 million people worldwide. In this short review we discuss about the plasticity changes in the reward and defense brain systems induced by early-life psychosocial stressful experiences. Such changes may render persons more vulnerable to illicit drugs use, facilitating behaviors of abuse and development of addiction. We propose that underlying plasticity changes render brain reward system as increasingly fragile because of tolerance and other physiological effects that reduce responsiveness with repeated use. In contrast, we propose that brain defense system makes maintain antifragile mechanisms that generate more robust responses with the prolonged consumption of drugs. Investigating the underlying mechanisms of these brain plasticity changes may advance the development of more efficacious pharmacologic and psychotherapeutic approaches to rehabilitate patients and more efficacious prevention policies to protect children from stressful experiences.

Marihuana: legalización y atención médica / Marihuana: Legalization and Medical Care

Resumen A pesar de que el uso de marihuana se considera ilegal en la mayoría de los países del mundo, es una de las drogas más utilizadas. El 8,6% de la población mexicana, entre 12 y 65 años, ha probado la marihuana alguna vez (2017). Este porcentaje ha aumentado significativamente en los últimos años. Casos fatales asociados con el consumo de cannabis no se documentaron durante mucho tiempo; sin embargo, recientemente se ha informado de muertes causada por un síndrome de hiperémesis de cannabis (CHS) y muerte por automutilación. Si bien se ha documentado que la marihuana sintetiza sustancias activas con potenciales propiedades terapéuticas, en la actualidad, el mayor uso de la marihuana en nuestro país y en el mundo es recreativo. Esta revisión analiza las consecuencias del uso recreativo de marihuana, el contexto social y de salud con respecto a la legalización y los posibles usos terapéuticos de compuestos extraídos de la planta, de acuerdo a estudios reportados en la literatura científica. La contribución que hacemos es alertar sobre el impacto negativo en la salud del uso recreativo de marihuana y la urgencia de favorecer la investigación sobre sus efectos en el cerebro. Asimismo, identificar los principios activos que tengan potencial para el uso terapéutico.

Abstract Despite the fact that the use of marihuana is illegal in most countries of the world, it still is one of the most commonly used drugs worldwide. 8.6% of the Mexican population, between 12-65 years old, has smoked marihuana at least once in their lifetime (2017). There has been a significant increase in the number of consumers in the last few years. Fatal cases associated with cannabis use had not been recognized for a long time, however, lately, deaths due to a cannabis hyperemesis syndrome (CHS) and deaths from self-mutilation have been reported. Although marihuana synthesizes several active substances with potential therapeutic properties, nowadays, the greatest use of marihuana in our country and in the world is recreational. This review discusses the consequences of using marihuana for recreational use, the social and health contexts regarding legalization and potential therapeutic uses of compounds isolated from the plant based on the scientific literature. Our contribution is to warn people about the potential negative impact on the health of recreational use marihuana and the urgency of supporting the research of its effects on the brain. Similarly, we aim to identify the active principles with potential therapeutic use.

Sexual Behavior and Synaptic Plasticity.

Although sex drive is present in many animal species, sexual behavior is not static and, like many other behaviors, can be modified by experience. This modification relies on synaptic plasticity, a sophisticated mechanism through which neurons change how they process a given stimulus, and the neurophysiological basis of learning. This review addresses the main plastic effects of steroid sex hormones in the central nervous system (CNS) and the effects of sexual experience on the CNS, including effects on neurogenesis, intracellular signaling, gene expression, and changes in dendritic spines, as well as behavioral changes.

Endocannabinoids as Therapeutic Targets.

Most of the drugs of abuse affect the brain by interacting with naturally expressed molecular receptors. Marihuana affects a series of receptors including cannabinoid receptor 1 (CB1R) and CB2R, among others. Endogenous molecules with cannabinoid activity interact with these receptors naturally. Receptors, ligands, synthesizing and degrading enzymes, as well as transporters, have been described. This endocannabinoid system modulates behaviors and physiological processes, i.e. food intake, the sleep-waking cycle, learning and memory, motivation, and pain perception, among others. The rather broad distribution of endocannabinoids in the brain explains the different effects marihuana induces in its users. However, this very same anatomical and physiological distribution makes this system a useful target for therapeutic endeavors. In this review, we briefly discuss the potential of small molecules that target the endocannabinoids as therapeutic tools to improve behaviors and treat illnesses. We believe that under medical supervision, endocannabinoid targets offer new advantages for patients for controlling multiple medical disorders.

Dopaminergic Modulation of Sleep-Wake States.

The role of dopamine in sleep-wake regulation is considered as a wakefulness-promoting agent. For the clinical treatment of excessive daytime sleepiness, drugs have been commonly used to increase dopamine release. However, sleep disorders or lack of sleep are related to several dopaminerelated disorders. The effects of dopaminergic agents, nevertheless, are mediated by two families of dopamine receptors, D1 and D2-like receptors; the first family increases adenylyl cyclase activity and the second inhibits adenylyl cyclase. For this reason, the dopaminergic agonist effects on sleep-wake cycle are complex. Here, we review the state-of-the-art and discuss the different effects of dopaminergic agonists in sleep-wake states, and propose that these receptors account for the affinity, although not the specificity, of several effects on the sleep-wake cycle.

Role of ß4* Nicotinic Acetylcholine Receptors in the Habenulo-Interpeduncular Pathway in Nicotine Reinforcement in Mice.

Nicotine exerts its psychopharmacological effects by activating the nicotinic acetylcholine receptor (nAChR), composed of alpha and/or beta subunits, giving rise to a diverse population of receptors with a distinct pharmacology. ß4-containing (ß4*) nAChRs are located almost exclusively in the habenulo-interpeduncular pathway. We examined the role of ß4* nAChRs in the medial habenula (MHb) and the interpeduncular nucleus (IPN) in nicotine reinforcement using behavioral, electrophysiological, and molecular techniques in transgenic mice. Nicotine intravenous self-administration (IVSA) was lower in constitutive ß4 knockout (KO) mice at all doses tested (7.5, 15, 30, and 60 µg/kg/infusion) compared with wild-type (WT) mice. In vivo microdialysis showed that ß4KO mice have higher extracellular dopamine (DA) levels in the nucleus accumbens than in WT mice, and exhibit a differential sensitivity to nicotine-induced DA outflow. Furthermore, electrophysiological recordings in the ventral tegmental area (VTA) demonstrated that DA neurons of ß4KO mice are more sensitive to lower doses of nicotine than that of WT mice. Re-expression of ß4* nAChRs in IPN neurons fully restored nicotine IVSA, and attenuated the increased sensitivity of VTA DA neurons to nicotine. These findings suggest that ß4* nAChRs in the IPN have a role in maintaining nicotine IVSA.

Detrimental role of prolonged sleep deprivation on adult neurogenesis.

Adult mammalian brains continuously generate new neurons, a phenomenon called adult neurogenesis. Both environmental stimuli and endogenous factors are important regulators of adult neurogenesis. Sleep has an important role in normal brain physiology and its disturbance causes very stressful conditions, which disrupt normal brain physiology. Recently, an influence of sleep in adult neurogenesis has been established, mainly based on sleep deprivation studies. This review provides an overview on how rhythms and sleep cycles regulate hippocampal and subventricular zone neurogenesis, discussing some potential underlying mechanisms. In addition, our review highlights some interacting points between sleep and adult neurogenesis in brain function, such as learning, memory, and mood states, and provides some insights on the effects of antidepressants and hypnotic drugs on adult neurogenesis.

Selective re-expression of ß2 nicotinic acetylcholine receptor subunits in the ventral tegmental area of the mouse restores intravenous nicotine self-administration.

Beta-2 (ß2) nicotinic acetylcholine receptor subunits have been particularly related with nicotine reinforcement. However, the importance of these subunits in the chronic aspects of nicotine addiction has not been established. In this study we evaluated the role of ventral tegmental area (VTA) ß2 receptor subunits in the acquisition and maintenance of nicotine self-administration. We used an operant mouse model of intravenous self-administration of different doses of nicotine (15, 30, and 60 µg/kg/infusion) during 10 days in constitutive knockout mice lacking ß2 receptor subunits (ß2KO), wild-type (WT) controls, mice with ß2 receptor subunits re-expressed in the VTA using a lentiviral vector (ß2-VEC), and control knockout mice with a sham injection (KO-GFP). The results showed that ß2KO mice did not reliably acquire nicotine self-administration at any of the doses tested, while WT controls showed dose-dependent acquisition of this behaviour. ß2-VEC mice readily acquired and maintained nicotine self-administration at the effective dose of 15 µg/kg/infusion, while sham KO-GFP mice did not. The recovery of the WT phenotype by the re-expression of ß2 receptor subunits within the VTA supports the role of this specific population in nicotine reinforcement, and reveals that they are sufficient for the acquisition and maintenance of systemic nicotine self-administration.

Chemoenzymatic synthesis and cannabinoid activity of a new diazabicyclic amide of phenylacetylricinoleic acid.

Endocannabinoids (eCBs) are endogenous neuromodulators of synaptic transmission. Their dysfunction may cause debilitating disorders of diverse clinical manifestation. For example, drug addiction, lack of sex desire, eating disorders, such as anorexia or bulimia and dyssomnias. eCBs also participate in the regulation of core temperature and pain perception. In this context, it is important to recognize the utility of cannabinoid receptor 1 (CB1R) agonists, natural as Delta(9)-tetrahydrocannabinol (THC) or synthetic as Nabilone as useful drugs to alleviate this kind of patients' suffering. Therefore, we have developed a new drug, (R,Z)-18-((1S,4S)-5-methyl-2,5-diazabicyclo[2.2.1]heptan-2-yl)-18-oxooctadec-9-en-7-yl phenylacetate (PhAR-DBH-Me), that appears to bind and activate the CB1R. This diazabicyclic amide was synthesized from phenylacetylricinoleic acid and (1S,4S)-2,5-diazabicyclo[2.2.1]heptane. To test its cannabinergic properties we evaluated its effects on core temperature, pain perception, and the sleep-waking cycle of rats. Results indicate that 20 and 40mg/kg of PhAR-DBH-Me readily reduced core temperature and increased pain perception threshold. In addition, 20mg/kg increased REM sleep in otherwise normal rats. All these effects were prevented or attenuated by AM251, a CB1R antagonist. Place preference conditioning studies indicated that this molecule does not produce rewarding effects. These results strongly support that PhAR-DBH-Me possesses cannabinoid activity without the reinforcement effects.

Acute and subchronic administration of anandamide or oleamide increases REM sleep in rats.

Anandamide and oleamide, induce sleep when administered acutely, via the CB1 receptor. Their subchronic administration must be tested to demonstrate the absence of tolerance to this effect, and that the sudden withdrawal of these endocannabinoids (eCBs) does not affect sleep negatively. The sleep-waking cycle of rats was evaluated for 24h, under the effect of an acute or subchronic administration of eCBs, and during sudden eCBs withdrawal. AM251, a CB1 receptor antagonist (CB1Ra) was utilized to block eCBs effects. Our results indicated that both acute and subchronic administration of eCBs increase REMS. During eCBs withdrawal, rats lack the expression of an abstinence-like syndrome. AM251 was efficacious to prevent REMS increase caused by both acute and subchronic administration of these eCBs, suggesting that this effect is mediated by the CB1 receptor. Our data further support a role of the eCBs in REMS regulation.

Dependencia de los sistemas de memoria al ciclo luz-oscuridad en la expresión de estrategias adaptativas. Segunda parte

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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.

Dependencia de los sistemas de memoria al ciclo luz-oscuridad en la expresión de estrategias adaptativas. Primera parte

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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.