Neuroscience
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Systemic administration of drugs that activate the noradrenergic or glucocorticoid system potentiates aversive memory consolidation and reconsolidation. The opposite happens with the stimulation of endocannabinoid signaling under certain conditions. An unbalance of these interacting neurotransmitters can lead to the formation and maintenance of traumatic memories, whose strength and specificity attributes are often maladaptive. ⋯ Neither the high nor the low dose of adrenaline, corticosterone, or AM251 altered freezing times at test in a novel, neutral context two and ten days later. In contrast, animals receiving the association of their low dose exhibited significantly higher freezing times than controls. Together, the results indicate that newly acquired and destabilized threat memory traces become more intense and generalized after a combined interference acting synergistically and mimicking that reported in patients presenting stress-related psychiatric conditions.
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Social recognition is the ability of animals to identify and recognize a conspecific. The consolidation of social stimuli in long-term memory is crucial for the establishment and maintenance of social groups, reproduction and species survival. Despite its importance, little is known about the circuitry and molecular mechanisms involved in the social recognition memory (SRM). ⋯ The animals that received infusions of 5-HT5A receptor antagonist SB-699551 (10 µg/µL), 5-HT6 receptor agonist WAY-208466 (0.63 µg/µL) or 5-HT7 receptor agonist AS-19 (5 µg/µL) intra-CA1 were unable to recognize the familiar juvenile. This effect was blocked by the coinfusion of WAY-208466 plus 5-HT6 receptor antagonist SB-271046 (10 µg/µL) or AS-19 plus 5-HT7 receptor antagonist SB-269970 (5 µg/µL). The present study helps to clarify the neurobiological functions of the 5-HT receptors more recently described and extends our knowledge about mechanisms underlying the SRM.
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Memories are initially labile and become stable through consolidation. Once consolidated, a memory can be destabilized by a reminder, requiring reconsolidation to become stable again. Memory reconsolidation has been evidenced in several learning tasks, including novel object recognition (NOR). ⋯ One minute of training induced a weak memory that could be enhanced by sodium butyrate, an inhibitor of histone deacetylases (HDACs), after 1 min of re-exposure. Histone acetylation is an epigenetic mechanism involved in gene expression regulation which positively correlates with memory. Thus, in this study we have performed an accurate characterization of the features of the reminder effective in triggering hippocampal NF-κB-dependent reconsolidation.
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Two important themes in Ivan Izquierdo's research each offered both answers and questions about the topic of memory formation and maintenance. The first theme provided evidence supporting the view that short- and long-term memory were distinct processes and could be selectively modulated by several treatments, with some affecting only short-term, others only affecting long-term memory, and still others affecting both. Over many years, Izquierdo's laboratory documented molecular responses across time after training obtaining results that showed differences as well as similarities in the biochemical changes during the first 1-2 h and the next 4-6 h after training, i.e., during the transition from short- to long-term memory. ⋯ Remarkably, these waves of susceptibility to modification were accompanied by biphasic changes in molecular measures at similar times after training. Remarkably, some of the molecular players exhibited persistent changes after training, with increases in levels lasting days following the training experience. These persistent molecular changes may reveal a biological basis for the dynamic nature of memories seen long after the initial memory is consolidated.
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In recent years there has been an increase in the development of new synthetic drugs, among which the "bath salt" 3,4-methylenedioxypyrovalerone (MDPV), a psychostimulant with a mechanism of action similar to those of cocaine and amphetamine, stands out. Drugs of abuse have been consistently shown to affect memory function in male rodents. We have recently shown that amphetamine and MDPV induce generalization of fear memory in an inhibitory avoidance discrimination task in male rats. ⋯ On day 1 of the experimental protocol, all rats were exposed to a safe context and, the day after, to a slightly different chamber where they received an unsignaled footshock. Twenty-four and forty-eight hours later, freezing behavior and emission of 22 kHz-ultrasonic vocalizations (USVs) were measured in the two different contexts to assess fear memory retention and generalization. Our results indicate that MDPV treatment altered freezing in both sexes, USVs were affected by amphetamine in males while by MDPV in females.