Repeated acquisition of a spatial navigation task in mice: effects of spacing of trials and of unilateral middle cerebral artery occlusion

Two spaced training trials induce associative ERK-dependent long term memory in Neohelice granulata

Memory formation depends upon several parametric training conditions. Among them, trial number and inter-trial interval (ITI) are key factors to induce long-term retention. However, it is still unclear how individual training trials contribute to mechanisms underlying memory formation and stabilization. Contextual conditioning in Neohelice granulata has traditionally elicited associative long-term memory (LTM) after 15 spaced (ITI = 3 min) trials. Here, we show that LTM in crabs can be induced after only two training trials by increasing the ITI to 45 min (2t-LTM) and maintaining the same training duration as in traditional protocols. This newly observed LTM was preserved for at least 96 h, exhibiting protein synthesis dependence during consolidation and reconsolidation as well as context-specificity. Moreover, we demonstrate that 2t-LTM depends on inter-trial and post-training ERK activation showing a faster phosphorylation after the second trial compared to the first one. In summary, we present a new training protocol in crabs through a reduced number of trials showing associative features similar to traditional spaced training. This novel protocol allows for intra-training manipulation and the assessment of individual trial contribution to LTM formation.

Reptilian Cognition: A More Complex Picture via Integration of Neurological Mechanisms, Behavioral Constraints, and Evolutionary Context

Unlike birds and mammals, reptiles are commonly thought to possess only the most rudimentary means of interacting with their environments, reflexively responding to sensory information to the near exclusion of higher cognitive function. However, reptilian brains, though structurally somewhat different from those of mammals and birds, use many of the same cellular and molecular processes to support complex behaviors in homologous brain regions. Here, the neurological mechanisms supporting reptilian cognition are reviewed, focusing specifically on spatial cognition and the hippocampus. These processes are compared to those seen in mammals and birds within an ecologically and evolutionarily relevant context. By viewing reptilian cognition through an integrative framework, a more robust understanding of reptile cognition is gleaned. Doing so yields a broader view of the evolutionarily conserved molecular and cellular mechanisms that underlie cognitive function and a better understanding of the factors that led to the evolution of complex cognition.

Spaced training improves learning in Ts65Dn and Ube3a mouse models of intellectual disabilities

Benefits of distributed learning strategies have been extensively described in the human literature, but minimally investigated in intellectual disability syndromes. We tested the hypothesis that training trials spaced apart in time could improve learning in two distinct genetic mouse models of neurodevelopmental disorders characterized by intellectual impairments. As compared to training with massed trials, spaced training significantly improved learning in both the Ts65Dn trisomy mouse model of Down syndrome and the maternally inherited Ube3a mutant mouse model of Angelman syndrome. Spacing the training trials at 1 h intervals accelerated acquisition of three cognitive tasks by Ts65Dn mice: (1) object location memory, (2) novel object recognition, (3) water maze spatial learning. Further, (4) spaced training improved water maze spatial learning by Ube3a mice. In contrast, (5) cerebellar-mediated rotarod motor learning was not improved by spaced training. Corroborations in three assays, conducted in two model systems, replicated within and across two laboratories, confirm the strength of the findings. Our results indicate strong translational relevance of a behavioral intervention strategy for improving the standard of care in treating the learning difficulties that are characteristic and clinically intractable features of many neurodevelopmental disorders.

Assessment of behavioral flexibility after middle cerebral artery occlusion in mice

Middle cerebral artery occlusion (MCAO) is the most common animal model of cerebral ischemia and induces various functional impairments. Long-lasting deficits resulting from MCAO however, remain insufficiently characterized, especially regarding cognition. Yet, behavioral flexibility, a prominent cognitive process is found impaired after stroke in humans. We thus used an operant-based task to assess behavioral flexibility in mice after MCAO. Three weeks after 30 min MCAO surgery, mice were subjected to a battery of sensorimotor tests (rotarod, vertical pole test, spontaneous locomotion and grip-strength test). Behavioral flexibility was then assessed in an operant task, in which mice, rewarded according to a FR5 schedule of reinforcement, had to alternate their operant responses between two levers from trial to trial. Regarding sensory and motor functioning, only the pole test yielded a significant difference between MCAO and sham mice. In the operant flexibility task, results showed a behavioral flexibility deficit in MCAO mice; neither the operant response acquisition nor the appeal for food rewards was altered. In conclusion, our operant-based task revealed a long-lasting behavioral flexibility deficit after MCAO in mice.

Pattern and predictability in memory formation: from molecular mechanisms to clinical relevance

Most long-term memories are formed as a consequence of multiple experiences. The temporal spacing of these experiences is of considerable importance: experiences distributed over time (spaced training) are more easily encoded and remembered than either closely spaced experiences, or a single prolonged experience (massed training). In this article, we first review findings from studies in animal model systems that examine the cellular and molecular properties of the neurons and circuits in the brain that underlie training pattern sensitivity during long-term memory (LTM) formation. We next focus on recent findings which have begun to elucidate the mechanisms that support inter-trial interactions during the induction of LTM. Finally, we consider the implications of these findings for developing therapeutic strategies to address questions of direct clinical relevance.

Six-month ischemic mice show sensorimotor and cognitive deficits associated with brain atrophy and axonal disorganization

AIMS

To identify long-term sensorimotor and cognitive deficits and to evaluate structural alterations in brain ischemic mice.

METHODS

C57Bl/6J male mice were subjected to 30 min transient middle cerebral artery occlusion (tMCAo) or sham surgery. Sensorimotor deficits, exploratory behavior, and cognitive functions were evaluated up to 6 months. Cortical and subcortical damage were analyzed by MRI multiparameter analysis and histopathology.

RESULTS

tMCAo mice showed significant sensorimotor deficits in the rotarod, negative geotaxis, neuroscore, and beam walk tests. They also showed impairment in exploratory behavior in the open field test and in spatial learning in the Morris water maze. T2-weighted MRI revealed a volume reduction in injured brain areas at 12 and 24 weeks postinjury. Brain atrophy was shown by MRI and conventional postmortem analysis. Diffusion tensor imaging on the external capsule showed increased values of axial and radial diffusivity. Fiber tracking revealed a reduction in the number and length of ipsilateral fibers.

CONCLUSIONS

tMCAo in mice induces sensorimotor and cognitive impairments detectable at least up to 6 months postinjury, associated with brain atrophy, and axonal and myelin damage of the external capsule. These behavioral tests and anatomical investigations may represent important tools in translational studies in cerebral ischemia.

Massed versus spaced visuospatial memory in cognitively healthy young and older adults

BACKGROUND

The present study examined the effect of massed versus spaced learning trials on 24-hour delayed recall for a visuospatial learning task. To determine the utility of measuring the incremental benefit of spaced training as a cognitive assay that may be useful in early clinical trials, we used a within-subject crossover design, with two small samples (typical sample sizes for phase I clinical trials).

METHODS

Young adults and cognitively healthy older adults without significant physical, neurological, or psychiatric illness were trained on a visuospatial paired-associate learning task under a massed condition (learning trials were presented in immediate succession) and a spaced condition (learning trials were presented with 15-minute intertrial delays).

RESULTS

Statistically significant differences between training conditions on the visuospatial task, such that young adult participants performed better on delayed recall after spaced training, were identified. Large effect sizes for young and older adults on this task suggest meaningful differences between training conditions, reflecting the expected "spacing effect." The role of amyloid aggregation was also considered for a subset of participants; as amyloid levels increased, the benefit of spaced training decreased, suggesting that the effect of this training paradigm is modulated by disease burden.

CONCLUSIONS

The utility of this paradigm as a potential assay for phase I proof-of-concept trials, targeting molecular mechanisms that are central to the encoding and consolidation of new learning, is discussed.

Evaluation of animal models of neurobehavioral disorders

Animal models play a central role in all areas of biomedical research. The process of animal model building, development and evaluation has rarely been addressed systematically, despite the long history of using animal models in the investigation of neuropsychiatric disorders and behavioral dysfunctions. An iterative, multi-stage trajectory for developing animal models and assessing their quality is proposed. The process starts with defining the purpose(s) of the model, preferentially based on hypotheses about brain-behavior relationships. Then, the model is developed and tested. The evaluation of the model takes scientific and ethical criteria into consideration.Model development requires a multidisciplinary approach. Preclinical and clinical experts should establish a set of scientific criteria, which a model must meet. The scientific evaluation consists of assessing the replicability/reliability, predictive, construct and external validity/generalizability, and relevance of the model. We emphasize the role of (systematic and extended) replications in the course of the validation process. One may apply a multiple-tiered 'replication battery' to estimate the reliability/replicability, validity, and generalizability of result.Compromised welfare is inherent in many deficiency models in animals. Unfortunately, 'animal welfare' is a vaguely defined concept, making it difficult to establish exact evaluation criteria. Weighing the animal's welfare and considerations as to whether action is indicated to reduce the discomfort must accompany the scientific evaluation at any stage of the model building and evaluation process. Animal model building should be discontinued if the model does not meet the preset scientific criteria, or when animal welfare is severely compromised. The application of the evaluation procedure is exemplified using the rat with neonatal hippocampal lesion as a proposed model of schizophrenia.In a manner congruent to that for improving animal models, guided by the procedure expounded upon in this paper, the developmental and evaluation procedure itself may be improved by careful definition of the purpose(s) of a model and by defining better evaluation criteria, based on the proposed use of the model.

Neurogenesis and the spacing effect: learning over time enhances memory and the survival of new neurons

Information that is spaced over time is better remembered than the same amount of information massed together. This phenomenon, known as the spacing effect, was explored with respect to its effect on learning and neurogenesis in the adult dentate gyrus of the hippocampal formation. Because the cells are generated over time and because learning enhances their survival, we hypothesized that training with spaced trials would rescue more new neurons from death than the same number of massed trials. In the first experiment, animals trained with spaced trials in the Morris water maze outperformed animals trained with massed trials, but there was not a direct effect of trial spacing on cell survival. Rather, animals that learned well retained more cells than animals that did not learn or learned poorly. Moreover, performance during acquisition correlated with the number of cells remaining in the dentate gyrus after training. In the second experiment, the time between blocks of trials was increased. Consequently, animals trained with spaced trials performed as well as those trained with massed, but remembered the location better two weeks later. The strength of that memory correlated with the number of new cells remaining in the hippocampus. Together, these data indicate that learning, and not mere exposure to training, enhances the survival of cells that are generated 1 wk before training. They also indicate that learning over an extended period of time induces a more persistent memory, which then relates to the number of cells that reside in the hippocampus.

A simple integrated circuit device for measuring distances traveled and determining speed in open-field environments

An easily constructed and inexpensive device for measuring distance and determining mean speed, which utilizes an integrated circuit (IC) photosensor system, is described. It was designed for evaluating activity of small animals in open-field environments, being used in conjunction with a video-recording system. The horizontal locomotor path of the animal is manually tracked directly from the video monitor image or from a tracing made of the image.

Cognitive and behavioral assessment in experimental stroke research: will it prove useful?

Stroke in humans is associated with deficits in sensorimotor and cognitive function. Consequently, many stroke researchers recently have expanded their techniques to assess cognitive and behavioral correlates of histologically-determined stroke damage in animal models. Although the incorporation of functional outcome assessment represents an important step forward in stroke research, reports of middle cerebral artery occlusion (MCAO) induced behavioral deficits often conflict, and a significant correlation between post-stroke histology and behavior has been reported in few stroke studies. Discrepancies in behavioral outcomes among studies may be due to several factors, such as method of MCAO, duration of occlusion, strain, the timing and method of the behavioral testing and the laboratory environment. Furthermore, proper experimental and control groups, necessary to rule out potential confounding factors during cognitive testing, often are not incorporated. The goal of this review is: (1) to provide a description of the techniques most commonly employed to assess functional outcome after (MCAO) in rodents and (2) to identify potential confounding factors that may interfere with a clear interpretation of the behavioral data.

Early onset of axonal degeneration in double (plp-/-mag-/-) and hypomyelinosis in triple (plp-/-mbp-/-mag-/-) mutant mice

Double (plp-/-mag-/-) and triple (plp-/-mbp-/-mag-/-) null-allelic mouse lines deficient in proteolipid protein (PLP), myelin-associated glycoprotein (MAG), and myelin basic protein (MBP) were generated and characterized genetically, biochemically, and morphologically including their behavioral capacities. The plp-/-mag-/- mutant develops a rapidly progressing axon degeneration in CNS with severe cognitive and motor coordinative deficits but has a normal longevity. CNS axons of the plp-/-mbp-/-mag-/- mouse are hypomyelinated and ensheathed by "pseudomyelin" with disturbed protein and complex lipid composition. The shiverer trait in the plp-/-mbp-/-mag-/- similar to the plp-/-mbp-/- mutant is significantly ameliorated, and its lifespan is considerably prolonged. The longevity of these dysmyelinosis mouse mutants recommends them as suitable models for the long-term evaluation of stem cell therapeutic strategies.