Open Field Arena Research Articles

Drivers behind co-occurrence patterns between pathogenic bacteria, protozoa, and helminths in populations of the multimammate mouse, Mastomys natalensis

Advances in experimental and theoretical work increasingly suggest that parasite interactions within a single host can affect the spread and severity of wildlife diseases. Yet empirical data to support predicted co-infection patterns are limited due to the practical challenges of gathering convincing data from animal populations and the stochastic nature of parasite transmission. Here, we investigated co-infection patterns between micro- (bacteria and protozoa) and macroparasites (gastro-intestinal helminths) in natural populations of the multimammate mouse (Mastomys natalensis). Fieldwork was performed in Morogoro (Tanzania), where we trapped 211 M. natalensis and tested their behaviour using a modified open-field arena. All animals were checked for the presence of helminths in their gastro-intestinal tract, three bacteria (Anaplasma, Bartonella, and Borrelia) and two protozoan genera (Babesia and Hepatozoon). Besides the presence of eight different helminth genera (reported earlier), we found that 19% of M. natalensis were positive for Anaplasma, 10% for Bartonella, and 2% for Hepatozoon species. Hierarchical modelling of species communities was used to investigate the effect of the different host-related factors on these parasites’ infection probability and community structure. Our results show that the infection probability of Bartonella increased with the host's age, while the infection probability of Anaplasma peaked when individuals reached adulthood. We also observed that less explorative and stress-sensitive individuals had a higher infection probability with Bartonella. Finally, we found limited support for within-host interactions between micro-and macroparasites, as most co-infection patterns could be attributed to host exposure time.

Video-based marker-free tracking and multi-scale analysis of mouse locomotor activity and behavioral aspects in an open field arena: A perspective approach to the quantification of complex gait disturbances associated with Alzheimer's disease.

Complex gait disturbances represent one of the prominent manifestations of various neurophysiological conditions, including widespread neurodegenerative disorders such as Alzheimer's and Parkinson's diseases. Therefore, instrumental measurement techniques and automatic computerized analysis appears essential for the differential diagnostics, as well as for the assessment of treatment effectiveness from experimental animal models to clinical settings. Here we present a marker-free instrumental approach to the analysis of gait disturbances in animal models. Our approach is based on the analysis of video recordings obtained with a camera placed underneath an open field arena with transparent floor using the DeeperCut algorithm capable of online tracking of individual animal body parts, such as the snout, the paws and the tail. The extracted trajectories of animal body parts are next analyzed using an original computerized methodology that relies upon a generalized scalable model based on fractional Brownian motion with parameters identified by detrended partial cross-correlation analysis. We have shown that in a mouse model representative movement patterns are characterized by two asymptotic regimes characterized by integrated 1/f noise at small scales and nearly random displacements at large scales separated by a single crossover. More detailed analysis of gait disturbances revealed that the detrended cross-correlations between the movements of the snout, paws and tail relative to the animal body midpoint exhibit statistically significant discrepancies in the Alzheimer's disease mouse model compared to the control group at scales around the location of the crossover. We expect that the proposed approach, due to its universality, robustness and clear physical interpretation, is a promising direction for the design of applied analysis tools for the diagnostics of various gait disturbances and behavioral aspects in animal models. We further believe that the suggested mathematical models could be relevant as a complementary tool in clinical diagnostics of various neurophysiological conditions associated with movement disorders.

Effect of Sevoflurane and Isoflurane on Post-Anaesthesia Cognitive Dysfunction in Normal and Type II Diabetic Rats.

Both animal and human studies have documented cognitive and behavioural impairment after exposure to inhalational anaesthetics. Therefore, the current study was designed to demonstrate if the anaesthetics isoflurane and Sevoflurane can result in postoperative cognition dysfunction in normal and diabetic rats. Sixty male Wister rats aged 12 weeks were divided into 6 groups (n=10); group C (standard control), group CD (diabetic control), group S (sevoflurane anaesthesia), group I (isoflurane anaesthesia), group SD (diabetic sevoflurane anaesthesia) group ID (diabetic isoflurane anaesthesia). Animals were anaesthetized with either 2. 5% sevoflurane or 1.5% isoflurane, respectively, for 2h. 1 week later, animals were undergone cognitive tests in (a Morris water maze, T maze and open field arena), the animals were sacrificed, and hippocampus homogenates were studied for caspase 3 activity by western blot assay. Induction of type II diabetes in CD, SD and ID groups was carried out by feeding on a high-fat diet for 8 weeks before the start of the experiment. During the fourth week, Type II diabetes was induced in the experimental group by a single IP injection of 30 mg/kg STZ. Control (normal and diabetic) rats showed no change in long-term/reference memory, non-spatial working memory, exploratory activity or caspase 3 expression in the hippocampus homogenate. Anaesthesia with isoflurane in normoglycemic rats resulted in a significant decline in long-term/reference memory and non-spatial working memory, while exploratory activity and caspase 3 expressions in hippocampus homogenate showed no change to normal control rats. Both isoflurane and Sevoflurane in diabetic rats demonstrated a decline in long-term/reference memory, non-spatial working memory, exploratory activity and caspase 3 expression in hippocampus homogenate compared with normal control rats. Diabetes revealed significant post-anaesthesia cognitive dysfunction after anaesthesia with Sevoflurane or isoflurane in all the studied domains compared to standard control or diabetic control.

Subthalamic neurons interact with nigral dopaminergic neurons to regulate movement in mice.

This study aims to address the role of the interaction between subthalamic (STN) neurons and substantia nigra pars compacta (SNc) dopaminergic (DA) neurons in movement control. Fiber photometry and optogenetic/chemogenetic techniques were utilized to monitor and manipulate neuronal activity, respectively. Locomotion in mice was recorded in an open field arena and on a head-fixed apparatus. A hemiparkinsonian mouse model was established by unilateral injection of 6-OHDA in the medial forebrain bundle. Whole-cell patch-clamp techniques were applied to record electrophysiological signals in STN neurons and SNc DA neurons. c-Fos-immunostaining was used to label activated neurons. A rabies virus-based retrograde tracing system was used to visualize STN neurons projecting to SNc DA neurons. The activity of STN neurons was enhanced upon locomotion in an open field arena and on a head-fixed apparatus, and the enhancement was significantly attenuated in parkinsonian mice. Optogenetic stimulation of STN neurons enhanced locomotion, increased activity of SNc DA neurons, meanwhile, reduced latency to movement initiation. Combining optogenetics with patch-clamp recordings, we confirmed that STN neurons innervated SNc DA neurons through glutamatergic monosynaptic connections. Moreover, STN neurons projecting to SNc DA neurons were evenly distributed in the STN. Either 6-OHDA-lesion or chemogenetic inhibition of SNc DA neurons attenuated the enhancement of locomotion by STN stimulation. SNc DA neurons not only affect the response of STN neurons to movement, but also contribute to the enhancement of movement by STN stimulation. This study demonstrates the role of STN-SNc interaction in movement control.

Marker-less tracking system for multiple mice using Mask R-CNN.

Although the appropriate evaluation of mouse behavior is crucial in pharmacological research, most current methods focus on single mouse behavior under light conditions, owing to the limitations of human observation and experimental tools. In this study, we aimed to develop a novel marker-less tracking method for multiple mice with top-view videos using deep-learning-based techniques. The following stepwise method was introduced: (i) detection of mouse contours, (ii) assignment of identifiers (IDs) to each mouse, and (iii) correction of mis-predictions. The behavior of C57BL/6 mice was recorded in an open-field arena, and the mouse contours were manually annotated for hundreds of frame images. Then, we trained the mask regional convolutional neural network (Mask R-CNN) with all annotated images. The mouse contours predicted by the trained model in each frame were assigned to IDs by calculating the similarities of every mouse pair between frames. After assigning IDs, correction steps were applied to remove the predictive errors semi-automatically. The established method could accurately predict two to four mice for first-look videos recorded under light conditions. The method could also be applied to videos recorded under dark conditions, extending our ability to accurately observe and analyze the sociality of nocturnal mice. This technology would enable a new approach to understand mouse sociality and advance the pharmacological research.

Zebrafish aversion to infrasound in an open field test.

Aquatic species are capable of detecting infrasound (sub-20 Hz frequencies) which may be a source of anthropogenic pollution and have a detrimental impact on the environmental fitness of fish. Infrasound is generated by infrastructure, producing acoustic frequency peaks that are not discernible by humans. The presence of these frequencies may therefore impact the environmental wellbeing of aquatic laboratory animals, which are often housed in spaces adjacent to facilities producing infrasound. To investigate the potential impact of infrasound, we used wild-type zebrafish (Danio rerio) and exposed them to short periods of infrasound at either 5, 10, 15, or 20 Hz, or 0 Hz as a control group. A motion-tracking software system was used to monitor fish movement in an open field test and arena location, distance moved, and immobility were quantified. There was a significant effect of 15 Hz which caused the fish to spend more time away from the infrasound source. The 20 Hz group also spent significantly less time in the zone closest to the speaker. There were no differences in distance moved or immobility between infrasound and control groups. These findings demonstrate that 15 Hz infrasound has aversive effects on zebrafish, causing them to move away from the sound source. To enhance environmental enrichment and wellbeing of aquatic laboratory animals, sources of infrasound pollution should be investigated and mitigated.

Infusing zeta inhibitory peptide into the perirhinal cortex of rats abolishes long-term object recognition memory without affecting novel object location recognition.

Infusing the amnesic agent zeta inhibitory peptide (ZIP) into the dorsal hippocampus disrupts established long-term object location recognition memory without affecting object identity recognition, which likely depends on the perirhinal cortex. Here, we tested whether infusing ZIP into the perirhinal cortex can abolish long-term memory supporting object identity recognition, leaving long-term object location recognition memory intact. We infused ZIP into the perirhinal cortex of rats either 1 day or 6 days after exposing them to two identical objects in an open field arena. One day after ZIP infusion, that is, 2 or 7 days after object exposure, we either assessed whether the animals recognized that now one of the two objects was novel or whether they recognized that one of the two familiar objects was at a new location. Our results show for both retention intervals, infusions of ZIP into the perirhinal cortex impaired novel object recognition but spared novel object location recognition. Rats that received a scrambled version of ZIP had no deficit in either test at both retention intervals and expressed stronger novel object recognition compared to rats infused with ZIP. These findings support the view that object recognition depends on dissociable memory representations distributed across different brain areas, with perirhinal cortex maintaining long-term memory for what objects had been encountered, and hippocampus supporting memory for where these objects had been placed.

DJ-1 promotes energy balance by regulating both mitochondrial and autophagic homeostasis

The protein DJ-1 is mutated in rare familial forms of recessive Parkinson's disease and in parkinsonism accompanied by amyotrophic lateral sclerosis symptoms and dementia. DJ-1 is considered a multitasking protein able to confer protection under various conditions of stress. However, the precise cellular function still remains elusive. In the present work, we evaluated fruit flies lacking the expression of the DJ-1 homolog dj-1β as compared to control aged-matched individuals. Behavioral evaluations included lifespan, locomotion in an open field arena, sensitivity to oxidative insults, and resistance to starvation. Molecular analyses were carried out by analyzing the mitochondrial morphology and functionality, and the autophagic response. We demonstrated that dj-1β null mutant flies are hypoactive and display higher sensitivity to oxidative insults and food deprivation. Analysis of mitochondrial homeostasis revealed that loss of dj-1β leads to larger and more circular mitochondria, characterized by impaired complex-I-linked respiration while preserving ATP production capacity. Additionally, dj-1β null mutant flies present an impaired autophagic response, which is suppressed by treatment with the antioxidant molecule N-Acetyl-L-Cysteine. Overall, our data point to a mechanism whereby DJ-1 plays a critical role in the maintenance of energy homeostasis, by sustaining mitochondrial homeostasis and affecting the autophagic flux through the maintenance of the cellular redox state. In light of the involvement of DJ-1 in neurodegenerative diseases and considering that neurons are highly energy-demanding cells, particularly sensitive to redox stress, our study sheds light on a key role of DJ-1 in the maintenance of cellular homeostasis.

Environment Symmetry Drives a Multidirectional Code in Rat Retrosplenial Cortex.

We investigated how environment symmetry shapes the neural processing of direction by recording directionally tuned retrosplenial neurons in male Lister hooded rats exploring multicompartment environments that had different levels of global rotational symmetry. Our hypothesis built on prior observations of twofold symmetry in the directional tuning curves of rats in a globally twofold-symmetric environment. To test whether environment symmetry was the relevant factor shaping the directional responses, here we deployed the same apparatus (two connected rectangular boxes) plus one with fourfold symmetry (a 2 × 2 array of connected square boxes) and one with onefold symmetry (a circular open-field arena). Consistent with our hypothesis we found many neurons with tuning curve symmetries that mirrored these environment symmetries, having twofold, fourfold, or onefold symmetric tuning, respectively. Some cells expressed this pattern only globally (across the whole environment), maintaining singular tuning curves in each subcompartment. However, others also expressed it locally within each subcompartment. Because multidirectionality has not been reported in naive rats in single environmental compartments, this suggests an experience-dependent effect of global environment symmetry on local firing symmetry. An intermingled population of directional neurons were classic head direction cells with globally referenced directional tuning. These cells were electrophysiologically distinct, with narrower tuning curves and a burstier firing pattern. Thus, retrosplenial directional neurons can simultaneously encode overall head direction and local head direction (relative to compartment layout). Furthermore, they can learn about global environment symmetry and express this locally. This may be important for the encoding of environment structure beyond immediate perceptual reach.SIGNIFICANCE STATEMENT We investigated how environment symmetry shapes the neural code for space by recording directionally tuned neurons from the retrosplenial cortex of rats exploring single- or multicompartment environments having onefold, twofold, or fourfold rotational symmetry. We found that many cells expressed a symmetry in their head direction tuning curves that matched the corresponding global environment symmetry, indicating plasticity of their directional tuning. They were also electrophysiologically distinct from canonical head directional cells. Notably, following exploration of the global space, many multidirectionally tuned neurons encoded global environment symmetry, even in local subcompartments. Our results suggest that multidirectional head direction codes contribute to the cognitive mapping of the complex structure of multicompartmented spaces.

The long-term effects of repeated heroin vapor inhalation during adolescence on measures of nociception and anxiety-like behavior in adult Wistar rats

RationaleAdolescents represent a vulnerable group due to increased experimentation with illicit substances that is often associated with the adolescent period, and because adolescent drug use can result in long-term effects that differ from those caused by drug use initiated during adulthood.ObjectivesThe purpose of the present study was to determine the effects of repeated heroin vapor inhalation during adolescence on measures of nociception, and anxiety-like behavior during adulthood in female and male Wistar rats.MethodsRats were exposed twice daily to 30 min of heroin vapor from post-natal day (PND) 36 to PND 45. At 12 weeks of age, baseline thermal nociception was assessed across a range of temperatures with a warm-water tail-withdrawal assay. Anxiety-like behavior was assessed in an elevated plus-maze (EPM) and activity was measured in an open-field arena. Starting at 23 weeks of age, baseline thermal nociception was re-assessed, nociception was determined after acute heroin or naloxone injection, and anxiety-like behavior was redetermined in the EPM.ResultsAdolescent heroin inhalation altered baseline thermal nociception in female rats at 12 weeks of age and in both female and male rats at ~ 23 weeks. Heroin-treated animals exhibited anxiety-like behavior when tested in the elevated plus-maze, showed blunted heroin-induced analgesia, but exhibited no effect on naloxone-induced hyperalgesia.ConclusionsThe present study demonstrates that heroin vapor inhalation during adolescence produces behavioral and physiological consequences in rats that persist well into adulthood.

Early life environment and adult enrichment: Effects on fearfulness in laying hens

The environmental complexity, both during early and adult life, contributes to shaping individuals’ fearfulness. The present study aimed at testing whether hens reared in an aviary were less fearful than hens reared in cages, and whether provision of additional enrichment during the laying phase could reduce fearfulness. We used White Leghorn laying hens (N = 384) reared in cages (N = 192) or in an aviary (N = 192) and then housed in furnished cages from 18 weeks of age, with or without the provision of additional enrichment. We tested naïve hens at 31 and 60 weeks of age in a novel object test and at 33 and 61 weeks of age in an open field test. Cage-reared hens had a latency to approach the novel object comparable to the one of aviary-reared hens when tested at 31 weeks of age (F1, 17 = 2.71; p = 0.12). At 60 weeks of age, birds housed in additionally enriched furnished cages were significantly faster to approach a novel object than birds housed in standard furnished cages for both rearing conditions (F1, 61 = 19.02; p < 0.01). Hens reared in cages walked distances comparable to aviary-reared hens in the open field arena at 33 and 61 weeks of age (t = −0.33; p = 0.75 and X2 (1, N = 123) = 0.02; p = 0.89, respectively), and the provision of additional enrichment during the laying phase did not increase that distance (X2 (1, N = 123) = 2.01; p = 0.16). We also did not observe any differences in the latency to start moving in the arena (p > 0.05). These results suggest that the environmental complexity during rearing had no medium- and long-term effects on fearfulness measured in the open field and novel object test. However, additional environmental enrichment during the laying phase had a stronger influence, reducing fearfulness towards novelty. This study suggests that environmental enrichment during adulthood can have positive effects on laying hens’ fearfulness.

Antioxidant and anti-apoptotic effects of tocotrienol-rich fraction against streptozotocin-induced diabetic retinopathy in rats

Oxidative stress, a key player in diabetic retinopathy (DR), is associated with retinal cell apoptosis. This study investigated the effect of tocotrienol-rich fraction (TRF), a potent antioxidant, towards visual behaviour, retinal morphology, cells apoptosis and redox status in streptozotocin (STZ)-induced DR rats. Sprague-Dawley rats were divided into 3 groups: non-diabetic (N), was injected with citrate buffer intraperitoneally, diabetic treated with vehicle (DV), and diabetic treated with TRF (DT), were injected with STZ intraperitoneally (55 mg/kg) to induce diabetes. DT received 100 mg of TRF/kg orally for 12-weeks, whereas DV and N received vehicle. The general and visual-behaviour responses were assessed at week 12 in an open field arena. Rats were then sacrificed, and retinae were processed for haematoxylin and eosin (H&E) and terminal transferase-mediated dUTP nick end-labelling (TUNEL) staining. Retinal antioxidant, lipid peroxidation and anti-apoptotic markers were measured. The general and visual-behaviour responses in DT were comparable to N. Retinal thickness and cell counts were lower in DV and DT compared to N. Lower number of TUNEL-positive cells were observed in DT compared to DV (1.48-fold, p < 0.001) which correlated with retinal caspase-3 expression (2.31-fold, p < 0.001). The retinal oxidative stress in DT was lower than DV as indicated by higher reduced glutathione (2.10-fold, p < 0.05), superoxide dismutase (1.12-fold, p < 0.05) and catalase (1.40-fold, p < 0.001), and lower malondialdehyde (2.54-fold, p < 0.001). In conclusion, oral TRF (100 mg/kg) supplementation for 12-weeks reduces retinal oxidative stress in STZ-induced DR rats, which in turn reduces retinal cell apoptosis and protects retinal morphology. These findings were associated with preservation of the visual-behaviour responses.

The Modification of Offspring Stress-Related Behavior and the Expression of Drd1, Drd2, and Nr3c1 by a Western-Pattern Diet in Mus Musculus

The impact of early developmental experience on neurobiological pathways that may contribute to the association between diet and behavior have not yet been elucidated. The focus of the current study was to determine whether the impact of prenatal stress (PS) could be mitigated by a diet that stimulates the same neuroendocrine systems influenced by early stress, using a mouse model. Behavioral and genetic approaches were used to assess how a Western-pattern diet (WPD) interacts with PS and sex to impact the expression of anxiety-like behavior in an open-field arena, as well as the expression of the glucocorticoid receptor in the hippocampus, D1 dopamine receptors in the nucleus accumbens, and D2 dopamine receptors in the ventral tegmental area. Overall, the results demonstrated that a prenatal WPD mitigates the effects of maternal stress in dams and offspring. These results help to elucidate the relationship between pre- and post-natal nutrition, gene expression, and behaviors that lead to long-term health effects.

The rat Lux Actuating Search Task (LAST) and effects of sleep deprivation on task reversal performance

Sleep deprivation (SD) causes significant deficits in multiple aspects of cognition, including sustained attention and working memory. Investigating the neural processes underpinning these cognitive losses has proven challenging due to the confounds of current animal tasks; many employ appetitive or aversive stimuli to motivate behavior, while others lack task complexity that translates to human studies of executive function. We established the Lux Actuating Search Task (LAST) to circumvent these issues. The LAST is performed in a circular, open-field arena that requires rats to find an unmarked, quasi-randomly positioned target. Constant low-level floor vibrations motivate ambulation, while light intensity (determined by the rodent's proximity to the target destination) provides continuous visual feedback. The task has two paradigms that differ based on the relationship between the light intensity and target proximity: the Low Lux Target (LLT) paradigm and the High Lux Target paradigm (HLT). In this study, on days 1–6, the rats completed nine trials per day on one of the two paradigms. On day 7, the rats were either sleep deprived by gentle handling or were left undisturbed before undertaking the opposite (reversal) paradigm on days 7–9. Our results showed that SD significantly impeded the ability of Long Evans rats to learn the reversal paradigm, as indicated by increased times to target and increased failure percentages compared to rats whose sleep was undisturbed. Rats also showed reduced learning with the HLT paradigm, as the initial task or as the reversal task, likely due to the rodents' photophobia limiting their motivation to navigate toward a bright light, which is required to succeed.

Effects of Information Load on Schema and Episodic Memory Formation.

The formation of semantic memories is assumed to result from the abstraction of general, schema-like knowledge across multiple experiences, while at the same time, episodic details from individual experiences are forgotten. Against this backdrop, our study examined the effects of information load (high vs. low) during encoding on the formation of episodic and schema memory using an elaborated version of an object-place recognition (OPR) task in rats. The task allowed for the abstraction of a spatial rule across four (low information load) or eight (high information load) encoding episodes (spaced apart by a 20 min interval) in which the rats could freely explore two objects in an open field arena. After this encoding phase, animals were left undisturbed for 24 h and then tested either for the expression of schema memory, i.e., for the spatial rule, or memory for an individual encoding episode. Rats in the high information load condition exhibited a more robust schema memory for the spatial rule than in the low information load condition. In contrast, rats in the low load condition showed more robust memory for individual learning episodes than in the high information load condition. Our findings of opposing effects might point to an information-load-dependent competitive relationship between processes of schema and episodic memory formation, although other explanations are possible.

Differential Effects of a Novel Opioid Ligand UTA1003 on Antinociceptive Tolerance and Motor Behaviour.

Analgesic tolerance is a major problem in the clinic for the maintenance of opioid-induced long-term pain relief. Opioids with mixed activity on multiple opioid receptors promise reduced antinociceptive tolerance in preclinical studies, but these compounds typically show poor bioavailability upon oral, subcutaneous, intraperitoneal, or intravenous administration. We designed UTA1003 as a novel opioid that acts as a mu (MOP) and kappa (KOP) opioid receptor agonist and a partial agonist for delta (DOP) opioid receptor. In the present study, its antinociceptive effects, as well as its effects on antinociceptive tolerance and motor behaviour, were investigated in male rats. Acute antinociception was measured before (basal) and at different time points after subcutaneous injection of UTA1003 or morphine using the tail flick and hot plate assays. Various motor behavioural activities, including horizontal locomotion, rearing, and turning, were automatically measured in an open-field arena. The antinociceptive and behavioural effects of repeated administration of UTA1003 and morphine were determined over eight days. UTA1003 induced mild antinociceptive effects after acute administration but induced no tolerance after repeated treatment. Importantly, UTA1003 co-treatment with morphine prevented antinociceptive tolerance compared to morphine alone. UTA1003 showed less motor suppression than morphine in both acute and sub-chronic treatment regimens, while it did not affect morphine-induced motor suppression or hyper-excitation. Based on these activities, we speculate that UTA1003 crosses the blood-brain barrier after subcutaneous administration and, therefore, could be developed as a lead molecule to avoid opioid-induced antinociceptive tolerance and motor suppression. Further structural modifications to improve its antinociceptive effects, toxicity profile, and ADME parameters are nevertheless required.

Locomotor Activity of Ixodes ricinus Females in 900 MHz Electromagnetic Field.

Mobile telecommunications technologies have become an indispensable part of people’s lives of all ages around the world. They affect personal life and social interactions and are a work tool in the work routine. Network availability requirements and the quality of the Internet connection are constantly increasing, to which telecommunications providers are responding. Humans and wildlife live in the permanent presence of electromagnetic radiation with just a minor knowledge of the impact this radiation has. The aim of our study was to investigate the effect of a 900 MHz electromagnetic field (EMF) on the locomotor behavior of female Ixodes ricinus ticks under laboratory conditions. Experiments were performed in the radiation-shielded tube (RST) test and radiation-shielded circular open-field arena placed in an anechoic chamber. Altogether, 480 female I. ricinus ticks were tested. In the RST arena, no differences in preference for irradiated and shielded parts of experimental modules were observed; in the open-field arena, the time spent and the trajectory passed was significantly longer in the part exposed to the EMF.

Hyperphosphorylated Tau Relates to Improved Cognitive Performance and Reduced Hippocampal Excitability in the Young rTg4510 Mouse Model of Tauopathy.

Tau hyperphosphorylation at several sites, including those close to its microtubule domain (MD), is considered a key pathogenic event in the development of tauopathies. Nevertheless, we recently demonstrated that at the very early disease stage, tau phosphorylation (pTau) at MD sites promotes neuroprotection by preventing seizure-like activity. To further support the notion that very early pTau is not detrimental, the present work evaluated the young rTg4510 mouse model of tauopathy as a case study. Thus, in mice at one month of age (PN30-35), we studied the increase of pTau within the hippocampal area as well as hippocampal and locomotor function. We used immunohistochemistry, T-maze, nesting test, novel object recognition test, open field arena, and electrophysiology. Our results showed that the very young rTg4510 mouse model has no detectable changes in hippocampal dependent tasks, such as spontaneous alternation and nesting, or in locomotor activity. However, at this very early stage the hippocampal neurons from PN30-35 rTg4510 mice accumulate pTau protein and exhibit changes in hippocampal oscillatory activity. Moreover, we found a significant reduction in the somatic area of pTau positive pyramidal and granule neurons in the young rTg4510 mice. Despite this, improved memory and increased number of dendrites per cell in granule neurons was found. Altogether, this study provides new insights into the early pathogenesis of tauopathies and provides further evidence that pTau remodels hippocampal function and morphology.

Sex differences in the acute ethanol effects on object recognition memory: influence of estrous cycle.

Effects of acute ethanol (EtOH) on memory depend on several factors, including type of behavioral task. Sex differences in EtOH effects have been reported in humans and animals, and recognition memory can be influenced by circulating sex hormones. The aim of this study was to investigate the influence of sex and estrous cycle in the acute effects of EtOH on novel object recognition memory in rats. Male and female Wistar rats were part of one of the groups: control, 0.6-g/kg EtOH and 1.8-g/kg EtOH (administered intraperitoneally before the training session). The estrous cycle was evaluated by vaginal smear. The task was conducted in an open field arena. During training, animals were exposed to two identical objects, and test sessions were performed 1 h (short-term) and 24 h (long-term) later. One of the objects was changed in each test. Increased novel object exploration was shown by male and female controls in the short- and long-term tests, respectively. In the short-term test, females did not show preference for the novel object, and EtOH 1.8 g/kg impaired performance in males. In the long-term test, both sexes showed object discrimination, and 1.8-g/kg EtOH reduced preference for the new object in male rats. The phase of the cycle, the performance on proestrus was worse compared with other phases, and EtOH failed to impair performance mainly on estrous. In conclusion, while male rats displayed ethanol-induced recognition memory deficit, female rats were unaffected by EtOH impairing effects. In addition, the performance of female rats was influenced by the estrous cycle phases.

Impaired Experience-Dependent Refinement of Place Cells in a Rat Model of Alzheimer's Disease.

Hippocampal place cells play an integral role in generating spatial maps. Impaired spatial memory is a characteristic pathology of Alzheimer's disease (AD), yet it remains unclear how AD influences the properties of hippocampal place cells. To record electrophysiological activity in hippocampal CA1 neurons in freely-moving 18-month-old male TgF344-AD and age-matched wild-type (WT) littermates to examine place cell properties. We implanted 32-channel electrode arrays into the CA1 subfield of 18-month-old male WT and TgF344-AD (n = 6/group) rats. Ten days after implantation, single unit activity in an open field arena was recorded across days. The spatial information content, in-field firing rate, and stability of each place cell was compared across groups. Pathology was assessed by immunohistochemical staining, and a deep neural network approach was used to count cell profiles. Aged TgF344-AD rats exhibited hippocampal amyloid-β deposition, and a significant increase in Iba1 immunoreactivity and microglia cell counts. Place cells from WT and TgF344-AD rat showed equivalent spatial information, in-field firing rates, and place field stability when initially exposed to the arena. However, by day 3, the place cells in aged WT rats showed characteristic spatial tuning as evidenced by higher spatial information content, stability, and in-field firing rates, an effect not seen in TgF344-AD rats. These findings support the notion that altered electrophysiological properties of place cells may contribute to the learning and memory deficits observed in AD.