Acute physical exercise enhances memory persistence in female rats.

Memory is a complex cognitive process with distinct stages, such as acquisition, consolidation, and retrieval. The hippocampus plays a crucial role in memory consolidation and retrieval. Physical exercise (PE) has been shown to enhance memory and cognitive functions, but the available research is mainly developed with males. So, there is limited knowledge about acute PE's effects on females' memory. This study aimed to investigate the impact of acute PE on memory in female rats and explore potential sex differences in PE memory modulation. Forty-two female Wistar rats were subjected to a novel object recognition (NOR) task, with half of them undergoing a single session of 30 min of PE after the learning session (memory acquisition). Behavioral assessments showed that acute PE improved memory persistence in female rats, with increased discrimination of novel objects. Biochemical analysis revealed elevated noradrenaline levels in the hippocampus following acute PE and NOR training. Notably, the positive effects of acute PE on female rats' memory were similar to those previously observed in male rats. These findings suggest that acute PE can enhance memory in female rats and underscore the importance of considering sex differences in cognitive research. PE may offer a non-invasive strategy to promote cognitive health in both males and females.

Evaluation of spontaneous exploratory and anxiety-related behaviors of mice treated with gymnopilins obtained from the mushroom Gymnopilus imperialis (Agaricomycetes, Basidiomycota).

Gymnopilins are long chain oligoisoprenoids produced through the condensation of isoprene units from MEV and MEP biosynthetic pathways. In Gymnopilus, these carotenoid-like molecules are recognized as major compounds in some species. In the present study, oligoisoprenoids derived from gymnopilins were dereplicated from Gymnopilus imperialis, a mushroom-forming basidiomycete, using liquid chromatographic coupled with high-resolution mass spectrometry (tandem LC-HRMS/MS) and GNPS. From the dichloromethane extract (Gym-DCM) of G. imperialis we annotated 3 oligoisoprenoids from the GNPS molecular library spectra and 15 analogs from the curation of the molecular networking. Data from NMR spectroscopic of the extract confirmed the annotation of the metabolites. Based on the literature data suggesting the neurotoxic effect of gymnopilins, we investigated the effects of the administering different doses of gymnopilin extracts (1, 4 or 10 mg/kg) and diazepam (4 mg/kg) on the acquisition of object recognition memory (ORM) in mice. By studying novel object recognition memory (ORM), a type of non-aversive memory. ORM was assessed based on the total time of spontaneous exploration of both objects, the discrimination index (DI), and the frequency of contact with both objects. Our present findings reveal, for the first time, that gymnopilins treatment before training modulates ORM in a dose-dependent manner. It is also suggested that differential effects on memory might be related to differential effects on GABAA receptors but do not exclude its effects in other neurotransmitter systems. Another class of secondary metabolites, alkaloids, might modulate AChR, which is essential for maintaining object recognition memory over time.

The memory impairment by hypothyroidism in mice is dependent on time-of-day and sex.

Hypothyroidism is an endocrine-metabolic disorder, and as such it compromises a wide range of physiological functions. Memory deficits and, the most recently described, circadian rhythm disruption are among the impairments caused by thyroid dysfunctions. However, although highly likely, there is no evidence connecting these two effects of hypothyroidism. Here, we hypothesized the time-of-day interferes with the memory deficit caused by hypothyroidism. C57BL/6 J mice from both sexes were subjected to novel object recognition (NOR) task during the rest and active phases, corresponding to ZT 2-4 and 14-16, respectively (ZT: Zeitgeber time; ZT 0: lights on at 07:00 am). First, we showed that neither sex nor ZT altered object recognition memory (ORM) in euthyroid mice. Next, animals were divided into control (euthyroid) and hypothyroid [induced with methimazole (0.01%) and perchlorate (0.1%) treatment in the drinking water for 21 days] groups. Under euthyroid conditions, male and female mice recognized the novel object regardless of the time-of-day. However, hypothyroidism impaired ORM at rest phase (ZT 2-4) in both sexes. Surprisingly, in the active phase (ZT 14-16), the hypothyroid males performed the NOR, though a longer time to execute the task was required. In contrast, female hypothyroid mice showed a greater impairment in ORM. Our results suggest that hypothyroidism may disrupt the circadian rhythm in brain areas related to mnemonic processes since in euthyroid condition ORM is not affected by the time-of-day. Furthermore, our findings in an animal model indicate a pronounced deleterious effect of hypothyroidism in women.

Salience to remember: VTA-IC dopaminergic pathway activity is necessary for object recognition memory formation.

Previous studies have shown that dopaminergic activity modulates the salience of novel stimuli enabling the formation of recognition memories. In this work, we hypothesize that dopamine released into the insular cortex (IC) from the ventral tegmental area (VTA) inputs enables the acquisition to consolidate object recognition memory. It has been reported that short training produces weak recognition memories; on the contrary, longer training produces lasting and robust recognition memories. Using a Cre-recombinase under the tyrosine hydroxylase (TH+) promoter mouse model, we photostimulated the VTA-IC dopaminergic pathway during short training or photoinhibited the same pathway during long training while mice explored objects. Our results showed that the photostimulation of the VTA-IC pathway during a short training enables the acquisition of recognition memory. Conversely, photoinhibition of the same pathway during a long training prevents the acquisition of recognition memory. Interestingly, the exploration time of the objects under photoinhibition or photostimulation of the dopaminergic VTA-IC pathway was not altered. Significantly, this enhancement of acquisition of the object recognition memory through the photostimulation of the VTA dopaminergic neurons could be impaired by the blockage of the D1-like receptors into the IC, either before or after the photostimulation. Altogether, our results suggest that dopamine released by the VTA is required during the acquisition to consolidate the object recognition memory through D1-like receptors into the IC without affecting the activity or the motivation to explore objects.

Assessing episodic memory in rodents using spontaneous object recognition tasks.

Models of episodic memory are successfully established using spontaneous object recognition tasks in rodents. In this review, we present behavioral techniques devised to investigate this type of memory, emphasizing methods based on associations of places and temporal order of items explored by rats and mice. We also provide a review on the areas and circuitry of the medial temporal lobe underlying episodic-like memory, considering that a large number of neurobiology data derived from these protocols. Although spontaneous recognition tasks are commonplace in this field, there is need for careful evaluation of factors affecting animal performance. Such as the ongoing development of tools for investigating the neural basis of memory, efforts should be put in the refinement of experimental designs, in order to provide reliable behavioral evidence of this complex mnemonic system.

Characteristics of the Reminder that Triggers Object Recognition Memory Reconsolidation in Mice.

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). But the features of the reminder that trigger memory destabilization and reconsolidation in this task are poorly characterized. Memory reconsolidation can be evidenced by delivering either an amnesic agent or a memory enhancer after reactivation and testing the resulting long-term memory alteration. Here we trained male mice for 15 min to induce a strong memory formation. Sulfasalazine, a specific inhibitor of the NF-κB pathway, was administered as an amnesic agent in the dorsal hippocampus. NF-κB is a key transcription factor required for consolidation and reconsolidation. We found that reconsolidation was induced when animals were re-exposed for 5 min to a combination of novel and familiar objects, but not to either two familiar or two novel objects. No destabilization was induced by re-exposure to the context without objects. Re-exposure to a combination of novel and familiar objects induced destabilization with a reactivation session as brief as 1 min. 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.

Functional connectivity of anterior retrosplenial cortex in object recognition memory.

Recognition memory can rely on three components: "what", "where" and "when". Recently we demonstrated that the anterior retrosplenial cortex (aRSC), like the perirhinal cortex (PRH) and unlike the hippocampus (HP), is required for consolidation of the "what" component. Here, we aimed at studying which brain structures interact with the aRSC to process object recognition (OR) memory in rats. We studied the interaction of six brain structures that are connected to the aRSC during OR memory processing: PRH, medial prefrontal cortex (mPFC), anteromedial thalamic nuclei (AM), medial entorhinal cortex (MEC), anterior cingulate cortex (ACC) and the dorsal HP (dHP). We previously described the role of the PRH and dHP, so we first studied the participation of the mPFC, AM, MEC and ACC in OR memory consolidation by bilateral microinfusions of the GABAA receptor agonist muscimol. We observed an impairment in OR long-term memory (LTM) when inactivating the mPFC, the AM and the MEC, but not the ACC. Then, we studied the functional connections by unilateral inactivation of the aRSC and each one of the six structures in the same (ipsilateral) or the opposite (contralateral) hemisphere. Our results showed an amnesic LTM effect in rats with ipsilateral inactivations of aRSC-PRH, aRSC-mPFC, aRSC-AM, or aRSC-MEC. On the other hand, we observed memory impairment when aRSC-ACC were inactivated in opposite hemispheres, and no effect when the aRSC-dHP connection was inactivated. Thus, our ipsilateral inactivation findings reveal that the aRSC and, at least one brain region required in OR LTM processing are essential to consolidate OR memory. In conclusion, our results show that several cortico-cortical and cortico-thalamic pathways are important for OR memory consolidation.

Rats recognize spatial and temporal attributes in a new object recognition memory task with multiple trials.

BACKGROUND: Episodic-like memory tasks based on the spontaneous exploration of objects are commonly applied in one-trial protocols. However, multiple-trial designs are known to reduce animal numbers and data variance, providing faster accumulation of data. NEW METHOD: In this study, we devised a new object recognition memory task for rats that carry out multiple trials per session. We developed three types of continual trial tasks: a longer protocol, a shorter protocol, and a protocol in which the experimental session was divided into two days. RESULTS: In our design, rats expressed temporal and spatial memory, but not what-where-when content integration. We found that shorter protocols were more efficient to evaluate memory capabilities. COMPARISON WITH EXISTING METHODS: To the best of our knowledge, it is the first object recognition task with multiple trials that simultaneously assess the temporal and spatial aspects of episodic-like memory. CONCLUSIONS: We suggest that our task is suitable for the simultaneous measurements of brain functions related to spatial and temporal attributes in rats.

Physical and cognitive training are able to prevent recognition memory deficits related to amyloid beta neurotoxicity.

Alzheimer's disease (AD) is characterized by the presence of amyloid-ß (Aß), oxidative damage and neuronal degeneration, which, together with other pathological events, promote progressive memory loss and cognitive decline. Non-pharmacological strategies have been study to provide some protection against the development of AD. Considering that physical exercise neuroprotective effects on prevention of cognitive deficits are well elucidate, it is important clarify the effects of cognitive training, and verify if they are similar or comparable to those observed for physical exercise. Here we divided male adult Wistar rats in six groups: control, which rats were not submitted to any intervention; Aß, which rats were submitted to hippocampal infusion of Aß; physical exercise (PE), which rats were submitted to 4 weeks of PE training; PE + Aß, which rats were submitted to 4 weeks of PE training followed by hippocampal infusion of Aß; cognitive exercise (CE), which rats were submitted to 4 weeks of CE training; and, CE + Aß, which rats were submitted to 4 weeks of CE training followed by hippocampal infusion of Aß. Ten days after Aß infusion, short (STM) and long-term (LTM) object recognition memory, as well as hippocampal oxidative stress (ROS levels by DCFH test), lipid peroxidation (TBARS), total antioxidant capacity (FRAP) and hippocampal histology were evaluated. Both PE and CE were effective in protect cognitive function against memory deficits related to Aß neurotoxicity, preventing oxidative stress and damage and hippocampal cellular disorganization. So, cognitive training seems to be as good as physical training in the prevention of memory deficits related to Aß and seems to share some mechanisms of actions, as oxidative stress prevention.

Anandamide Effects in a Streptozotocin-Induced Alzheimer's Disease-Like Sporadic Dementia in Rats.

Alzheimer's disease (AD) is characterized by multiple cognitive deficits including memory and sensorimotor gating impairments as a result of neuronal and synaptic loss. The endocannabinoid system plays an important role in these deficits but little is known about its influence on the molecular mechanism regarding phosphorylated tau (p-tau) protein accumulation - one of the hallmarks of AD -, and on the density of synaptic proteins. Thus, the aim of this study was to investigate the preventive effects of anandamide (N-arachidonoylethanolamine, AEA) on multiple cognitive deficits and on the levels of synaptic proteins (syntaxin 1, synaptophysin and synaptosomal-associated protein, SNAP-25), cannabinoid receptor type 1 (CB1) and molecules related to p-tau degradation machinery (heat shock protein 70, HSP70), and Bcl2-associated athanogene (BAG2) in an AD-like sporadic dementia model in rats using intracerebroventricular (icv) injection of streptozotocin (STZ). Our hypothesis is that AEA could interact with HSP70, modulating the level of p-tau and synaptic proteins, preventing STZ-induced cognitive impairments. Thirty days after receiving bilateral icv injections of AEA or STZ or both, the cognitive performance of adult male Wistar rats was evaluated in the object recognition test, by the escape latency in the elevated plus maze (EPM), by the tone and context fear conditioning as well as in prepulse inhibition tests. Subsequently, the animals were euthanized and their brains were removed for histological analysis or for protein quantification by Western Blotting. The behavioral results showed that STZ impaired recognition, plus maze and tone fear memories but did not affect contextual fear memory and prepulse inhibition. Moreover, AEA prevented recognition and non-associative emotional memory impairments induced by STZ, but did not influence tone fear conditioning. STZ increased the brain ventricular area and this enlargement was prevented by AEA. Additionally, STZ reduced the levels of p-tau (Ser199/202) and increased p-tau (Ser396), although AEA did not affect these alterations. HSP70 was found diminished only by STZ, while BAG2 levels were decreased by STZ and AEA. Synaptophysin, syntaxin and CB1 receptor levels were reduced by STZ, but only syntaxin was recovered by AEA. Altogether, albeit AEA failed to modify some AD-like neurochemical alterations, it partially prevented STZ-induced cognitive impairments, changes in synaptic markers and ventricle enlargement. This study showed, for the first time, that the administration of an endocannabinoid can prevent AD-like effects induced by STZ, boosting further investigations about the modulation of endocannabinoid levels as a therapeutic approach for AD.

Estradiol effect on short-term object memory under hypocholinergic condition.

Estrogens positively affect object recognition memory (ORM). However, whether this effect rely on acetylcholine is unknown. Here we investigated if 17ß-estradiol (E2) would be able to recover ORM deficits in animals with decreased expression of the Vesicular Acetylcholine Transporter (VAChT KDHET). We found that E2 improved short-term ORM (STM) in VAChT KDHET male and in OVX female mutant mice. However, E2 did not recover long-term (LTM) ORM in both sexes. Next, we tested whether hippocampal ERs activation could also rescue STM in mutant mice. Our results showed that ERα seems to be both sufficient and necessary for STM consolidation in female VAChT KDHET. Differently, in male, both ERα and ERß activation recovered STM. In addition, we tested whether mRNA level of estrogen receptors (ER) is also sensitive to VAChT expression. Female mutant mice showed lower levels of ER alpha (ERα) mRNA in the hippocampus, while no differences in male were observed. Together, our results showed that under hypocholinergic function, E2 improve short-term object recognition in both male and female. Furthermore, we showed that changes in VAChT expression might potentially modulate hippocampal ERα expression in a sex-dependent-manner.

Object recognition memory deficit and depressive-like behavior caused by chronic ovariectomy can be transitorialy recovered by the acute activation of hippocampal estrogen receptors.

It is well known that estradiol (E2) replacement therapy is effective on restoring memory deficits and mood disorders that may occur during natural menopause or after surgical ovarian removal (ovariectomy, OVX). However, it is still unknown the effectiveness of acute and localized E2 administration on the effects of chronic OVX. Here we tested the hypothesis that the intra-hippocampal E2 infusion, as well as specific agonists of estrogen receptors (ERs) alpha (ERα) and beta (ERß), are able to mend novel object recognition (NOR) memory deficit and depressive-like behavior caused by 12 weeks of OVX. We found that both ERα and ERß activation, at earlier stages of consolidation, recovered the NOR memory deficit caused by 12 w of OVX. Conversely, only the ERß activation was effective in decreasing the depressive-like behavior caused by 12 w of OVX. Furthermore, we investigated the effect of OVX on hippocampal volume and ERs expression. The structural MRI showed no alteration in the hippocampus volume of 12 w OVX animals. Interestingly, ERα expression in the hippocampus decreased after one week of OVX, but increased in 12 w OVX animals. Overall, we may conclude that the chronic estrogen deprivation, induced by 12 weeks of OVX, modulates the hippocampal ERα expression and induces NOR memory deficit and depressive-like behaviors. Nonetheless, it is noteworthy that the acute effects of E2 on NOR memory and depressive-like behavior are still apparent even after 12 weeks of OVX.

State-dependent effect of dopamine D1/D5 receptors inactivation on memory destabilization and reconsolidation.

Object recognition memories (ORM) can incorporate new information upon reactivation. This update initially involves destabilization of the original memory, which is followed by restabilization of the upgraded engram through a reconsolidation process that requires gene expression and protein synthesis in the hippocampus. We found that when given in dorsal CA1 either immediately after training or 15 min before ORM reactivation in the presence of a novel object, the dopamine D1/D5 receptor antagonist SCH23390 did not affect ORM consolidation, expression or retention but impeded the amnesia caused by the post-retrieval administration of the mRNA synthesis inhibitor α-amanitin or the protein synthesis blocker anisomycin. This anti-amnesic effect was not observed when SCH23390 was given immediately after training and again 15 min before memory reactivation. Our results demonstrate that hippocampal D1/D5 receptors are not needed for formation, retrieval or post-retrieval restabilization of the ORM trace but are essential for its destabilization when reactivation occurs together with the incorporation of new information into the original memory. Importantly, they also suggest that reenactment of the animal's post-learning neurochemical milieu at the moment of memory reactivation can be a boundary condition for reconsolidation.

The intrahippocampal infusion of crotamine from Crotalus durissus terrificus venom enhances memory persistence in rats.

Previous research has shown that crotamine, a toxin isolated from the venom of Crotalus durissus terrificus, induces the release of acetylcholine and dopamine in the central nervous system of rats. Particularly, these neurotransmitters are important modulators of memory processes. Therefore, in this study we investigated the effects of crotamine infusion on persistence of memory in rats. We verified that the intrahippocampal infusion of crotamine (1 µg/µl; 1 µl/side) improved the persistence of object recognition and aversive memory. By other side, the intrahippocampal infusion of the toxin did not alter locomotor and exploratory activities, anxiety or pain threshold. These results demonstrate a future prospect of using crotamine as potential pharmacological tool to treat diseases involving memory impairment, although it is still necessary more researches to better elucidate the crotamine effects on hippocampus and memory.

Decrease of ERK/MAPK overactivation in prefrontal cortex reverses early memory deficit in a mouse model of Alzheimer's disease.

Alzheimer's disease (AD) can be considered as a disease of memory in its initial clinical stages. Amyloid-ß (Aß) peptide accumulation is central to the disease initiation leading later to intracellular neurofibrillary tangles (NFTs) of cytoskeletal tau protein formation. It is under discussion whether different Aß levels of aggregation, concentration, brain area, and/or time of exposure might be critical to the disease progression, as well as which intracellular pathways it activates. The aim of the present work was to study memory-related early molecular and behavioral alterations in a mouse model of AD, in which a subtle deregulation of the physiologic function of Aß can be inferred. For this purpose we used triple-transgenic (3xTg) mice, which develop Aß and tau pathology resembling the disease progression in humans. Memory impairment in novel object recognition task was evident by 5 months of age in 3xTg mice. Hippocampus and prefrontal cortex extra-nuclear protein extracts developed differential patterns of Aß aggregation. ERK1/MAPK showed higher levels of cytosolic activity at 3 months and higher levels of nuclear activity at 6 months in the prefrontal cortex. No significant differences were found in JNK and NF-κB activity and in calcineurin protein levels. Finally, intra-PFC administration of a MEK inhibitor in 6-month-old 3xTg mice was able to reverse memory impairment, suggesting that ERK pathway alterations might at least partially explain memory deficits observed in this model, likely as a consequence of memory trace disruption.

Retrieval and reconsolidation of object recognition memory are independent processes in the perirhinal cortex.

Reconsolidation refers to the destabilization/re-stabilization process upon memory reactivation. However, the parameters needed to induce reconsolidation remain unclear. Here we evaluated the capacity of memory retrieval to induce reconsolidation of object recognition memory in rats. To assess whether retrieval is indispensable to trigger reconsolidation, we injected muscimol in the perirhinal cortex to block retrieval, and anisomycin (ani) to impede reconsolidation. We observed that ani impaired reconsolidation in the absence of retrieval. Therefore, stored memory underwent reconsolidation even though it was not recalled. These results indicate that retrieval and reconsolidation of object recognition memory are independent processes.

Divergent short- and long-term effects of acute stress in object recognition memory are mediated by endogenous opioid system activation.

Acute stress induces short-term object recognition memory impairment and elicits endogenous opioid system activation. The aim of this study was thus to evaluate whether opiate system activation mediates the acute stress-induced object recognition memory changes. Adult male Wistar rats were trained in an object recognition task designed to test both short- and long-term memory. Subjects were randomly assigned to receive an intraperitoneal injection of saline, 1 mg/kg naltrexone or 3 mg/kg naltrexone, four and a half hours before the sample trial. Five minutes after the injection, half the subjects were submitted to movement restraint during four hours while the other half remained in their home cages. Non-stressed subjects receiving saline (control) performed adequately during the short-term memory test, while stressed subjects receiving saline displayed impaired performance. Naltrexone prevented such deleterious effect, in spite of the fact that it had no intrinsic effect on short-term object recognition memory. Stressed subjects receiving saline and non-stressed subjects receiving naltrexone performed adequately during the long-term memory test; however, control subjects as well as stressed subjects receiving a high dose of naltrexone performed poorly. Control subjects' dissociated performance during both memory tests suggests that the short-term memory test induced a retroactive interference effect mediated through light opioid system activation; such effect was prevented either by low dose naltrexone administration or by strongly activating the opioid system through acute stress. Both short-term memory retrieval impairment and long-term memory improvement observed in stressed subjects may have been mediated through strong opioid system activation, since they were prevented by high dose naltrexone administration. Therefore, the activation of the opioid system plays a dual modulating role in object recognition memory.

Consolidation of object recognition memory requires simultaneous activation of dopamine D1/D5 receptors in the amygdala and medial prefrontal cortex but not in the hippocampus.

The mesocorticolimbic dopaminergic system includes the ventral tegmental area (VTA) and its projections to the amygdala (AMY), the hippocampus (HIP) and the medial prefrontal cortex (mPFC), among others. Object recognition (OR) long-term memory (LTM) processing requires dopaminergic activity but, although some of the brain regions mentioned above are necessary for OR LTM consolidation, their possible dopamine-mediated interplay remains to be analyzed. Using adult male Wistar rats, we found that posttraining microinjection of the dopamine D1/D5 receptor antagonist SCH23390 in mPFC or AMY, but not in HIP, impaired OR LTM. The dopamine D2 receptor agonist quinpirole had no effect on retention. VTA inactivation also hindered OR LTM, and even though this effect was unaffected by co-infusion of the dopamine D1/D5 receptor agonist SKF38393 in HIP, mPFC or AMY alone, it was reversed by simultaneous activation of D1/D5 receptors in the last two regions. Our results demonstrate that the mesocorticolimbic dopaminergic system is indeed essential for OR LTM consolidation and suggest that the role played by some of its components during this process is much more complex than previously thought.