Spatial cognition in mice and rats: similarities and differences in brain and behavior

Effects of estrogen on spatial navigation and memory

RATIONALE

Animal studies suggest that the so-called "female" hormone estrogen enhances spatial navigation and memory. This contradicts the observation that males generally out-perform females in spatial navigation and tasks involving spatial memory. A closer look at the vast number of studies actually reveals that performance differences are not so clear.

OBJECTIVES

To help clarify the unclear performance differences between men and women and the role of estrogen, we attempted to isolate organizational from activational effects of estrogen on spatial navigation and memory.

METHODS

In a double-blind, placebo-controlled study, we tested the effects of orally administered estradiol valerate (E2V) in healthy, young women in their low-hormone menstrual cycle phase, compared to healthy, young men. Participants performed several first-person, environmentally rich, 3-D computer games inspired by spatial navigation and memory paradigms in animal research.

RESULTS

We found navigation behavior suggesting that sex effects dominated any E2 effects with men performing better with allocentric strategies and women with egocentric strategies. Increased E2 levels did not lead to general improvements in spatial ability in either sex but to behavioral changes reflecting navigation flexibility.

CONCLUSION

Estrogen-driven differences in spatial cognition might be better characterized on a spectrum of navigation flexibility rather than by categorical performance measures or skills.

Tonic noradrenergic input to neurons in the dorsal raphe nucleus mediates food intake in male mice

The dorsal raphe nucleus (DRN) is essential for the control of food intake. Efferent projections from the DRN extend to several forebrain regions that are involved in the control of food intake. However, the neurotransmitters released in the DRN related to the control of food intake are not known. We have previously demonstrated that a tonic α1 action on DRN neurons contributes to satiety in the fed rats. In this study we investigated the participation of norepinephrine (NE) signaling in the DRN in the satiety response. Intra-DRN administration of NE causes an increase in the 2-hour food intake of sated mice, an effect that was blocked by previous administration of yohimbine, an α2 antagonist. Similarly, Intra-DRN administration of clonidine, an α2 agonist, increases food intake in sated mice. This result indicates that in the satiated mice exogenous NE acts on α2 receptors to increase food intake. Furthermore, administration of phenylephrine, an α1 agonist, decreases food intake in fasted mice and prazosin, an α1 antagonist, increases food intake in the sated mice. Taken together these results indicate that, in a satiated condition, a tonic α1 adrenergic action on the DRN neurons inhibits food intake and that exogenous NE administered to the DRN acts on α2 adrenergic receptors to increase food intake. These data reinforce the intricate neuronal functioning of the DRN and its effects on feeding.

Spontaneous Dynamics of Hippocampal Place Fields in a Model of Combinatorial Competition among Stable Inputs

We present computer simulations illustrating how the plastic integration of spatially stable inputs could contribute to the dynamic character of hippocampal spatial representations. In novel environments of slightly larger size than typical apparatus, the emergence of well-defined place fields in real place cells seems to rely on inputs from normally functioning grid cells. Theoretically, the grid-to-place transformation is possible if a place cell is able to respond selectively to a combination of suitably aligned grids. We previously identified the functional characteristics that allow a synaptic plasticity rule to accomplish this selection by synaptic competition during rat foraging behavior. Here, we show that the synaptic competition can outlast the formation of place fields, contributing to their spatial reorganization over time, when the model is run in larger environments and the topographical/modular organization of grid inputs is taken into account. Co-simulated cells that differ only by their randomly assigned grid inputs display different degrees and kinds of spatial reorganization-ranging from place-field remapping to more subtle in-field changes or lapses in firing. The model predicts a greater number of place fields and propensity for remapping in place cells recorded from more septal regions of the hippocampus and/or in larger environments, motivating future experimental standardization across studies and animal models. In sum, spontaneous remapping could arise from rapid synaptic learning involving inputs that are functionally homogeneous, spatially stable, and minimally stochastic.

Rodents' visual gamma as a biomarker of pathological neural conditions

Neural gamma oscillations (indicatively 30-100 Hz) are ubiquitous: they are associated with a broad range of functions in multiple cortical areas and across many animal species. Experimental and computational works established gamma rhythms as a global emergent property of neuronal networks generated by the balanced and coordinated interaction of excitation and inhibition. Coherently, gamma activity is strongly influenced by the alterations of synaptic dynamics which are often associated with pathological neural dysfunctions. We argue therefore that these oscillations are an optimal biomarker for probing the mechanism of cortical dysfunctions. Gamma oscillations are also highly sensitive to external stimuli in sensory cortices, especially the primary visual cortex (V1), where the stimulus dependence of gamma oscillations has been thoroughly investigated. Gamma manipulation by visual stimuli tuning is particularly easy in rodents, which have become a standard animal model for investigating the effects of network alterations on gamma oscillations. Overall, gamma in the rodents' visual cortex offers an accessible probe on dysfunctional information processing in pathological conditions. Beyond vision-related dysfunctions, alterations of gamma oscillations in rodents were indeed also reported in neural deficits such as migraine, epilepsy and neurodegenerative or neuropsychiatric conditions such as Alzheimer's, schizophrenia and autism spectrum disorders. Altogether, the connections between visual cortical gamma activity and physio-pathological conditions in rodent models underscore the potential of gamma oscillations as markers of neuronal (dys)functioning.

Responses of peritubular macrophages and the testis transcriptome profiles of peripubertal and adult rodents exposed to an acute dose of MEHP

Exposure of rodents to mono-(2-ethylhexyl) phthalate (MEHP) is known to disrupt the blood-testis barrier and cause testicular germ cell apoptosis. Peritubular macrophages (PTMφ) are a newly identified type of testicular macrophage that aggregates near the spermatogonial stem cell niche. We have previously reported that MEHP exposure increased the numbers of PTMφs by 6-fold within the testis of peripubertal rats. The underlying mechanism(s) accounting for this change in PTMφs and its biological significance is unknown. This study investigates if MEHP-induced alterations in PTMφs occur in rodents (PND 75 adult rats and PND 26 peripubertal mice) that are known to be less sensitive to MEHP-induced testicular toxicity. Results show that adult rats have a 2-fold higher basal level of PTMφ numbers than species-matched peripubertal animals, but there was no significant increase in PTMφ numbers after MEHP exposure. Peripubertal mice have a 5-fold higher basal level of PTMφ compared with peripubertal rats but did not exhibit increases in number after MEHP exposure. Further, the interrogation of the testis transcriptome was profiled from both the MEHP-responsive peripubertal rats and the less sensitive rodents via 3' Tag sequencing. Significant changes in gene expression were observed in peripubertal rats after MEHP exposure. However, adult rats showed lesser changes in gene expression, and peripubertal mice showed only minor changes. Collectively, the data show that PTMφ numbers are associated with the sensitivity of rodents to MEHP in an age- and species-dependent manner.

Spatial navigation: A touch in the dark

New work reveals whisker landmark coding in the retrosplenial cortex of mice, broadening our understanding of multisensory spatial cognition, contextual processing, and spatial predictive coding.

Spontaneous dynamics of hippocampal place fields in a model of combinatorial competition among stable inputs

We present computer simulations illustrating how the plastic integration of spatially stable inputs could contribute to the dynamic character of hippocampal spatial representations. In novel environments of slightly larger size than typical apparatus, the emergence of well-defined place fields in real place cells seems to rely on inputs from normally functioning grid cells. Theoretically, the grid-to-place transformation is possible if a place cell is able to respond selectively to a combination of suitably aligned grids. We previously identified the functional characteristics that allow a synaptic plasticity rule to accomplish this selection by synaptic competition during rat foraging behavior. Here, we show that the synaptic competition can outlast the formation of place fields, contributing to their spatial reorganization over time, when the model is run in larger environments and the topographical/modular organization of grid inputs is taken into account. Co-simulated cells that differ only by their randomly assigned grid inputs display different degrees and kinds of spatial reorganization-ranging from place-field remapping to more subtle in-field changes or lapses in firing. The model predicts a greater number of place fields and propensity for remapping in place cells recorded from more septal regions of the hippocampus and/or in larger environments, motivating future experimental standardization across studies and animal models. In sum, spontaneous remapping could arise from rapid synaptic learning involving inputs that are functionally homogeneous, spatially stable, and minimally stochastic.

Significance Statement

In both AI and theoretical neuroscience, learning systems often rely on the asymptotic convergence of slow-acting learning rules applied to input spaces that are presumed to be sampled repeatedly, for example over developmental timescales. Place cells of the hippocampus testify to a neural system capable of rapidly encoding cognitive variables-such as the animal's position in space-from limited experience. These internal representations undergo "spontaneous" changes over time, spurring much interest in their cognitive significance and underlying mechanisms. We investigate a model suggesting that some of these changes could be a tradeoff of rapid learning.

Neuronal signature of spatial decision-making during navigation by freely moving rats by using calcium imaging

This manuscript addresses a longstanding problem about how place cell firing contributes to navigation in spatial environments, and data derived from on-line calcium imaging offer a new solution. These data support the view that prior to entering an arena where an animal will navigate to only one of several possible places on each day, a population of spatially responsive cells, including place cells, fire during the last 5 s. This population is shown to be predictive of the destination and trajectory that the animal is about to take.

A challenge in spatial memory is understanding how place cell firing contributes to decision-making in navigation. A spatial recency task was created in which freely moving rats first became familiar with a spatial context over several days and thereafter were required to encode and then selectively recall one of three specific locations within it that was chosen to be rewarded that day. Calcium imaging was used to record from more than 1,000 cells in area CA1 of the hippocampus of five rats during the exploration, sample, and choice phases of the daily task. The key finding was that neural activity in the startbox rose steadily in the short period prior to entry to the arena and that this selective population cell firing was predictive of the daily changing goal on correct trials but not on trials in which the animals made errors. Single-cell and population activity measures converged on the idea that prospective coding of neural activity can be involved in navigational decision-making.

Interleukin 15 modulates the effects of poly I:C maternal immune activation on offspring behaviour

Maternal infections during pregnancy are linked with an increased risk for disorders like Autism Spectrum Disorder and schizophrenia in the offspring. Although precise mechanisms are still unclear, clinical and preclinical evidence suggest a strong role for maternal immune activation (MIA) in the neurodevelopmental disruptions caused by maternal infection. Previously, studies using the Polyinosinic:Polycytidylic (Poly I:C) MIA preclinical model showed that cytokines like Interleukin 6 (Il6) are important mediators of MIA's effects. In this study, we hypothesized that Il15 may similarly act as a mediator of Poly I:C MIA, given its role in the antiviral immune response. To test this hypothesis, we induced Poly I:C MIA at gestational day 9.5 in wildtype (WT) and Il15^−/− rat dams and tested their offspring in adolescence and adulthood. Poly I:C MIA and Il15 knockout produced both independent and synergistic effects on offspring behaviour. Poly I:C MIA decreased startle reactivity in adult WT offspring but resulted in increased adolescent anxiety and decreased adult locomotor activity in Il15^−/− offspring. In addition, Poly I:C MIA led to genotype-independent effects on locomotor activity and prepulse inhibition. Finally, we showed that Il15^−/− offspring exhibit distinct phenotypes that were unrelated to Poly I:C MIA including altered startle reactivity, locomotion and signal transduction in the auditory brainstem. Overall, our findings indicate that the lack of Il15 can leave offspring either more or less susceptible to Poly I:C MIA, depending on the phenotype in question. Future studies should examine the contribution of fetal versus maternal Il15 in MIA to determine the precise developmental mechanisms underlying these changes.

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Poly I:C MIA decreases startle reactivity in adult WT but not Il15^−/− offspring.

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Il15^−/− offspring exposed to Poly I:C MIA show altered PPI and open field exploration.

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Il15^−/− rats exhibit distinct behavioural phenotypes independent from MIA.

In Vivo Multi-Day Calcium Imaging of CA1 Hippocampus in Freely Moving Rats Reveals a High Preponderance of Place Cells with Consistent Place Fields

Calcium imaging using GCaMP indicators and miniature microscopes has been used to image cellular populations during long timescales and in different task phases, as well as to determine neuronal circuit topology and organization. Because the hippocampus (HPC) is essential for tasks of memory, spatial navigation, and learning, calcium imaging of large populations of HPC neurons can provide new insight on cell changes over time during these tasks. All reported HPC in vivo calcium imaging experiments have been done in mouse. However, rats have many behavioral and physiological experimental advantages over mice. In this paper, we present the first (to our knowledge) in vivo calcium imaging from CA1 HPC in freely moving male rats. Using the UCLA Miniscope, we demonstrate that, in rat, hundreds of cells can be visualized and held across weeks. We show that calcium events in these cells are highly correlated with periods of movement, with few calcium events occurring during periods without movement. We additionally show that an extremely large percent of cells recorded during a navigational task are place cells (77.3 ± 5.0%, surpassing the percent seen during mouse calcium imaging), and that these cells enable accurate decoding of animal position and can be held over days with consistent place fields in a consistent spatial map. A detailed protocol is included, and implications of these advancements on in vivo imaging and place field literature are discussed.SIGNIFICANCE STATEMENT In vivo calcium imaging in freely moving animals allows the visualization of cellular activity across days. In this paper, we present the first in vivo Ca2+ recording from CA1 hippocampus (HPC) in freely moving rats. We demonstrate that hundreds of cells can be visualized and held across weeks, and that calcium activity corresponds to periods of movement. We show that a high percentage (77.3 ± 5.0%) of imaged cells are place cells, and that these place cells enable accurate decoding and can be held stably over days with little change in field location. Because the HPC is essential for many tasks involving memory, navigation, and learning, imaging of large populations of HPC neurons can shed new insight on cellular activity changes and organization.

Functional neuroanatomy of allocentric remote spatial memory in rodents

Successful spatial cognition involves learning, consolidation, storage, and later retrieval of a spatial memory trace. The functional contributions of specific brain areas and their interactions during retrieval of past spatial events are unclear. This systematic review collects studies about allocentric remote spatial retrieval assessed at least two weeks post-acquisition in rodents. Results including non-invasive interventions, brain lesion and inactivation experiments, pharmacological treatments, chemical agent administration, and genetic manipulations revealed that there is a normal forgetting when time-periods are close to or exceed one month. Moreover, changes in the morphology and functionality of neocortical areas, hippocampus, and other subcortical structures, such as the thalamus, have been extensively observed as a result of spatial memory retrieval. In conclusion, apart from an increasingly neocortical recruitment in remote spatial retrieval, the hippocampus seems to participate in the retrieval of fine spatial details. These results help to better understand the timing of memory maintenance and normal forgetting, outlining the underlying brain areas implicated.

The physiological control of eating: signals, neurons, and networks

During the past 30 yr, investigating the physiology of eating behaviors has generated a truly vast literature. This is fueled in part by a dramatic increase in obesity and its comorbidities that has coincided with an ever increasing sophistication of genetically based manipulations. These techniques have produced results with a remarkable degree of cell specificity, particularly at the cell signaling level, and have played a lead role in advancing the field. However, putting these findings into a brain-wide context that connects physiological signals and neurons to behavior and somatic physiology requires a thorough consideration of neuronal connections: a field that has also seen an extraordinary technological revolution. Our goal is to present a comprehensive and balanced assessment of how physiological signals associated with energy homeostasis interact at many brain levels to control eating behaviors. A major theme is that these signals engage sets of interacting neural networks throughout the brain that are defined by specific neural connections. We begin by discussing some fundamental concepts, including ones that still engender vigorous debate, that provide the necessary frameworks for understanding how the brain controls meal initiation and termination. These include key word definitions, ATP availability as the pivotal regulated variable in energy homeostasis, neuropeptide signaling, homeostatic and hedonic eating, and meal structure. Within this context, we discuss network models of how key regions in the endbrain (or telencephalon), hypothalamus, hindbrain, medulla, vagus nerve, and spinal cord work together with the gastrointestinal tract to enable the complex motor events that permit animals to eat in diverse situations.

Combination of dasatinib and quercetin improves cognitive abilities in aged male Wistar rats, alleviates inflammation and changes hippocampal synaptic plasticity and histone H3 methylation profile

Aging is associated with cognitive decline and accumulation of senescent cells in various tissues and organs. Senolytic agents such as dasatinib and quercetin (D+Q) in combination have been shown to target senescent cells and ameliorate symptoms of aging-related disorders in mouse models. However, the mechanisms by which senolytics improve cognitive impairments have not been fully elucidated particularly in species other than mice. To study the effect of senolytics on aging-related multifactorial cognitive dysfunctions we tested the spatial memory of male Wistar rats in an active allothetic place avoidance task. Here we report that 8 weeks treatment with D+Q alleviated learning deficits and memory impairment observed in aged animals. Furthermore, treatment with D+Q resulted in a reduction of the peripheral inflammation measured by the levels of serum inflammatory mediators (including members of senescent cell secretome) in aged rats. Significant improvements in cognitive abilities observed in aged rats upon treatment with D+Q were associated with changes in the dendritic spine morphology of the apical dendritic tree from the hippocampal CA1 neurons and changes in the level of histone H3 trimethylation at lysine 9 and 27 in the hippocampus. The beneficial effects of D+Q on learning and memory in aged rats were long-lasting and persisted at least 5 weeks after the cessation of the drugs administration. Our results expand and provide new insights to the existing knowledge associated with effects of senolytics on alleviating age-related associated cognitive dysfunctions.

The Role of the Medial Septum-Associated Networks in Controlling Locomotion and Motivation to Move

The Medial Septum and diagonal Band of Broca (MSDB) was initially studied for its role in locomotion. However, the last several decades were focussed on its intriguing function in theta rhythm generation. Early studies relied on electrical stimulation, lesions and pharmacological manipulation, and reported an inconclusive picture regarding the role of the MSDB circuits. Recent studies using more specific methodologies have started to elucidate the differential role of the MSDB's specific cell populations in controlling both theta rhythm and behaviour. In particular, a novel theory is emerging showing that different MSDB's cell populations project to different brain regions and control distinct aspects of behaviour. While the majority of these behaviours involve movement, increasing evidence suggests that MSDB-related networks govern the motivational aspect of actions, rather than locomotion per se. Here, we review the literature that links MSDB, theta activity, and locomotion and propose open questions, future directions, and methods that could be employed to elucidate the diverse roles of the MSDB-associated networks.

Noradrenergic enhancement of object recognition and object location memory in mice

Extensive evidence indicates that noradrenergic activation is essentially involved in mediating the enhancing effects of emotional arousal on memory consolidation. Our current understanding of the neurobiological mechanisms underlying the memory-modulatory effects of the noradrenergic system is primarily based on pharmacological studies in rats, employing targeted administration of noradrenergic drugs into specific brain regions. However, the further delineation of the specific neural circuitry involved would benefit from experimental tools that are currently more readily available in mice. Previous studies have not, as yet, investigated the effect of noradrenergic enhancement of memory in mice, which show different cognitive abilities and higher endogenous arousal levels induced by a training experience compared to rats. In the present study, we investigated the effect of posttraining noradrenergic activation in male C57BL/6J mice on the consolidation of object recognition and object location memory. We found that the noradrenergic stimulant yohimbine (0.3 or 1.0 mg/kg) administered systemically immediately after an object training experience dose-dependently enhanced 24-h memory of both the identity and location of the object. Thus, these findings indicate that noradrenergic activation also enhances memory consolidation processes in mice, paving the way for a systematic investigation of the neural circuitry underlying these emotional arousal effects on memory.LAY SUMMARY: The current study successfully validated the effect of noradrenergic activation on both object recognition and object location memory in mice. This study thereby provides a fundamental proof-of-principle for the investigation of the neural circuitry underlying noradrenergic and arousal effects on long-term memory in mice.

The effects of olfactory bulb removal on single-pellet skilled reaching task in rats

We focused on how the rat uses olfactory cues in a single-pellet reaching task, which is composed of three successive learned responses, Orient, Transport, and Withdrawal. Orient comprised: front wall detection, slot localisation, and nose poke until reach start. High-speed video-recording enabled us to describe the temporal features of this sequence in controls vs. 3-5 and 12-14 days after bilateral bulbectomy in trials with (P trial) vs. without (no-P trial) pellet. In controls, the full sequence was complete in P trials, while it was interrupted after Orient in no P-trials. After bulbectomy, the full sequence was seen in both P and no-P trials at days 3-5 and 12-14 and there was an increase in Orient duration due to the increased time in slot/shelf localisation. Unlike in controls, in anosmic rats, the first nose contact with the front wall took place below the slot/shelf level, and the number of nose touches together with the number of whisker cycles was significantly higher at 3-5 but not at 12-14 days. The relationship between nose touches and whisker cycles was linear in all experimental conditions. Bulbectomy resulted in no changes in the Transport duration or the time the paw spent out of the slot. These findings suggest that olfaction allows the animal to orient itself in pellet localisation, and offers insight into the contribution of olfaction during different stages of natural behaviour in skilled reaching task.

Effects of repetitive gentle handling of male C57BL/6NCrl mice on comparative behavioural test results

Mice are the most commonly used laboratory animals for studying diseases, behaviour, and pharmacology. Behavioural experiment battery aids in evaluating abnormal behaviour in mice. During behavioural experiments, mice frequently experience human contact. However, the effects of repeated handling on mice behaviour remains unclear. To minimise mice stress, methods of moving mice using transparent tunnels or cups have been recommended but are impractical in behavioural tests. To investigate these effects, we used a behavioural test battery to assess differences between mice accustomed to the experimenter’s handling versus control mice. Repeatedly handled mice gained slightly more weight than control mice. In behavioural tests, repeatedly handled mice showed improved spatial cognition in the Y-maze test and reduced anxiety-like behaviour in the elevated plus-maze test. However, there was no change in anxiety-like behaviour in the light/dark transition test or open-field test. Grip strength, rotarod, sociability, tail suspension, Porsolt forced swim, and passive avoidance tests revealed no significant differences between repeatedly handled and control mice. Our findings demonstrated that mice repeatedly handled by the experimenter before behavioural tests showed reduced anxiety about high altitudes and improved spatial cognition, suggesting that repeated contact can affect the results of some behavioural tests.

Understanding Addiction Using Animal Models

Drug addiction is a neuropsychiatric disorder with grave personal consequences that has an extraordinary global economic impact. Despite decades of research, the options available to treat addiction are often ineffective because our rudimentary understanding of drug-induced pathology in brain circuits and synaptic physiology inhibits the rational design of successful therapies. This understanding will arise first from animal models of addiction where experimentation at the level of circuits and molecular biology is possible. We will review the most common preclinical models of addictive behavior and discuss the advantages and disadvantages of each. This includes non-contingent models in which animals are passively exposed to rewarding substances, as well as widely used contingent models such as drug self-administration and relapse. For the latter, we elaborate on the different ways of mimicking craving and relapse, which include using acute stress, drug administration or exposure to cues and contexts previously paired with drug self-administration. We further describe paradigms where drug-taking is challenged by alternative rewards, such as appetitive foods or social interaction. In an attempt to better model the individual vulnerability to drug abuse that characterizes human addiction, the field has also established preclinical paradigms in which drug-induced behaviors are ranked by various criteria of drug use in the presence of negative consequences. Separation of more vulnerable animals according to these criteria, along with other innate predispositions including goal- or sign-tracking, sensation-seeking behavior or impulsivity, has established individual genetic susceptibilities to developing drug addiction and relapse vulnerability. We further examine current models of behavioral addictions such as gambling, a disorder included in the DSM-5, and exercise, mentioned in the DSM-5 but not included yet due to insufficient peer-reviewed evidence. Finally, after reviewing the face validity of the aforementioned models, we consider the most common standardized tests used by pharmaceutical companies to assess the addictive potential of a drug during clinical trials.

Rhodiola rosea L. Improves Learning and Memory Function: Preclinical Evidence and Possible Mechanisms

Rhodiola rosea L. (R. rosea L.) is widely used to stimulate the nervous system, extenuate anxiety, enhance work performance, relieve fatigue, and prevent high altitude sickness. Previous studies reported that R. rosea L. improves learning and memory function in animal models. Here, we conducted a systematic review and meta-analysis for preclinical studies to assess the current evidence for R. rosea L. effect on learning and memory function. Ultimately, 36 studies involving 836 animals were identified by searching 6 databases from inception to May 2018. The primary outcome measures included the escape latency in Morris water maze (MWM) test on behalf of learning ability, the frequency and the length of time spent on the target quadrant in MWM test representing memory function, and the number of errors in step down test, dark avoidance test and Y maze test on behalf of memory function. The secondary outcome measures were mechanisms of R. rosea L. for learning and/or memory function. Compared with control, the pooled results of 28 studies showed significant effects of R. rosea L. for reducing the escape latency (P < 0.05); 23 studies for increasing the frequency and the length of time spent on the target quadrant (P < 0.05); and 6 studies for decreasing the number of errors (P < 0.01). The possible mechanisms of R. rosea L. are largely through antioxidant, cholinergic regulation, anti-apoptosis activities, anti-inflammatory, improving coronary blood flow, and cerebral metabolism. In conclusion, the findings suggested that R. rosea L. can improve learning and memory function.

Spatial learning and long-term memory impairments in RasGrf1 KO, Pttg1 KO, and double KO mice

BACKGROUND

RasGrf1 is a guanine-nucleotide releasing factor that enhances Ras activity. Human PTTG1 is an oncoprotein found in pituitary tumors and later identified as securin, a protein isolated from yeast with a reported role in chromosome separation. It has been suggested that RasGrf1 is an important upstream component of signal transduction pathways regulating Pttg1 expression and controlling beta cell development and their physiological response. At memory formation level, there are contradictory data regarding the role of RasGrf1, while Pttg1 has not been previously studied. Both proteins are expressed in the mammalian hippocampus, which is one of the key brain areas for spatial learning and memory.

OBJECTIVE

The aim of this work was to study a potential link between RasGrf1 and Pttg1 in memory formation.

METHOD

Spatial learning and memory test in the Pttg1 KO, RasGrf1 KO, and Pttg1-RasGrf1 double KO and their correspondent WT mice using a Barnes maze.

RESULTS

In comparison with the WT control mice, Pttg1 KO mice learned how to solve the task in a less efficient way, suggesting problems in memory consolidation. RasGrf1 KO mice performance was similar to controls, and they learned to use the best searching strategy. Double KO mice reached a better spatial learning level than WT.

CONCLUSION

A role for Pttg1 in memory consolidation/formation is suggested, while our RasGrf1 KO mice do not show hippocampus associated memory defects.

Comparing Mouse and Rat Hippocampal Place Cell Activities and Firing Sequences in the Same Environments

Hippocampal place cells are key to spatial representation and spatial memory processing. They fire at specific locations in a space (place fields) and fire in precise patterns during theta sequences and during ripple-associated replay events. These phenomena have been extensively studied in rats, but to a less extent in mice. The availability of versatile genetic manipulations gives mice an advantage for place cell studies. However, it is unknown how place fields and place cell sequences in the same environment differ between mice and rats. Here, we provide a quantitative comparison in place field properties, as well as theta sequences and replays, between rats and mice as they ran on the same novel track and as they rested afterwards. We found that place cells in mice display less spatial specificity with more but smaller place fields. Theta oscillations, theta phase precession and aspects of theta sequences in mice are similar as those in rats. The ripple-associated replay, however, is relatively rare during stopping on the novel track in mice. The replay is present during resting after the track running, but is weaker in mice than the replay in rats. Our results suggest that place cells in mice and rats are qualitatively similar, but with substantial quantitative differences.

The Effect of Gentle Handling on Depressive-Like Behavior in Adult Male Mice: Considerations for Human and Rodent Interactions in the Laboratory

Environmental factors play a significant role in well-being of laboratory animals. Regulations and guidelines recommend, if not require, that stressors such as bright lighting, smells, and noises are eliminated or reduced to maximize animal well-being. A factor that is often overlooked is handling and how researchers interact with their animals. Researchers, lab assistants, and husbandry staff in animal facilities may use inconsistent handling methods when interacting with rodents, but humans should be considered a part of the animal's social environment. This study examined the effects of different handling techniques on depressive-like behavior, measured by the Porsolt forced swim test, in adult C57BL/6J male mice. The same two researchers handled the mice in a gentle, aggressive, or minimal (control) fashion over approximately two weeks prior to testing. The results demonstrated a beneficial effect of gentle handling: gentle handling reduced swimming immobility in the forced swim test compared to mice that were aggressively or minimally handled. We argue that gentle handling, rather than methodical handling, can foster a better relationship between the handlers and rodents. Although handling is not standardized across labs, consistent gentle handling allows for less challenging behavioral testing, better data collection, and overall improved animal welfare.