Behaviour of marmoset monkeys in a T-maze: comparison with rats and macaque monkeys on a spatial delayed non-match to sample task

Testing spatial working memory in pigs using an automated T-maze

Pigs are an important large animal model for translational clinical research but underutilized in behavioral neuroscience. This is due, in part, to a lack of rigorous neurocognitive assessments for pigs. Here, we developed a new automated T-maze for pigs that takes advantage of their natural tendency to alternate. The T-maze has obvious cross-species value having served as a foundation for cognitive theories across species. The maze (17' × 13') was constructed typically and automated with flanking corridors, guillotine doors, cameras, and reward dispensers. We ran nine pigs in (1) a simple alternation task and (2) a delayed spatial alternation task. Our assessment focused on the delayed spatial alternation task which forced pigs to wait for random delays (5, 60, 120, and 240 s) and burdened spatial working memory. We also looked at self-paced trial latencies, error types, and coordinate-based video tracking. We found pigs naturally alternated but performance declined steeply across delays (R2 = 0.84). Self-paced delays had no effect on performance suggestive of an active interference model of working memory. Positional and head direction data could differentiate subsequent turns on short but not long delays. Performance levels were stable over weeks in diverse strains and sexes, and thus provide a benchmark for future neurocognitive assessments in pigs.

Cognitive rescue in aging through prior training in rats

Cognitive decline in spatial memory is seen in aging. Understanding affected processes in aging is vital for developing methods to improve wellbeing. Daily memory persistence can be influenced by events around the time of learning or by prior experiences in early life. Fading memories in young can last longer if a novel event is introduced around encoding, a process called behavioral tagging. Based on this principle, we asked what processes are affected in aging and if prior training can rescue them. Two groups of aged rats received training in an appetitive delayed matching-to-place task. One of the groups additionally received prior training of the same task in young and in mid-life, constituting a longitudinal study. The results showed long-term memory decline in late aging without prior training. This would reflect affected encoding and consolidation. On the other hand, short-term memory was preserved and novelty at memory reactivation and reconsolidation enabled memory maintenance in aging. Prior training improved cognition through facilitating task performance, strengthening short-term memory and intermediate memory, and enabling encoding-boosted long-term memory. Implication of these findings in understanding brain mechanisms in cognitive aging and in beneficial effects of prior training is discussed.

Innate immunity stimulation via CpG oligodeoxynucleotides ameliorates Alzheimer's disease pathology in aged squirrel monkeys

Alzheimer's disease is the most common cause of dementia and the only illness among the top 10 causes of death for which there is no disease-modifying therapy. The failure rate of clinical trials is very high, in part due to the premature translation of successful results in transgenic mouse models to patients. Extensive evidence suggests that dysregulation of innate immunity and microglia/macrophages plays a key role in Alzheimer's disease pathogenesis. Activated resident microglia and peripheral macrophages can display protective or detrimental phenotypes depending on the stimulus and environment. Toll-like receptors (TLRs) are a family of innate immune regulators known to play an important role in governing the phenotypic status of microglia. We have shown in multiple transgenic Alzheimer's disease mouse models that harnessing innate immunity via TLR9 agonist CpG oligodeoxynucleotides (ODNs) modulates age-related defects associated with immune cells and safely reduces amyloid plaques, oligomeric amyloid-β, tau pathology, and cerebral amyloid angiopathy (CAA) while promoting cognitive benefits. In the current study we have used a non-human primate model of sporadic Alzheimer's disease pathology that develops extensive CAA-elderly squirrel monkeys. The major complications in current immunotherapeutic trials for Alzheimer's disease are amyloid-related imaging abnormalities, which are linked to the presence and extent of CAA; hence, the prominence of CAA in elderly squirrel monkeys makes them a valuable model for studying the safety of the CpG ODN-based concept of immunomodulation. We demonstrate that long-term use of Class B CpG ODN 2006 induces a favourable degree of innate immunity stimulation without producing excessive or sustained inflammation, resulting in efficient amelioration of both CAA and tau Alzheimer's disease-related pathologies in association with behavioural improvements and in the absence of microhaemorrhages in aged elderly squirrel monkeys. CpG ODN 2006 has been well established in numerous human trials for a variety of diseases. The present evidence together with our earlier, extensive preclinical research, validates the beneficial therapeutic outcomes and safety of this innovative immunomodulatory approach, increasing the likelihood of CpG ODN therapeutic efficacy in future clinical trials.

Wild common marmosets (Callithrix jacchus) employ spatial cognitive abilities to improve their food search and consumption: an experimental approach in small-scale space

The ability of an animal to integrate and retain spatial information of resources often depends on the spatial memory and the speed at which this memory crystallizes. These become especially important once foragers reach their target area. However, very little is known about how wild common marmosets encode spatial information when feeding rewards are near to each other in a small-scale space. With this in mind, we performed field experiments to test foraging decisions related to a small-scale space setting. Specifically, we tested the (i) short- and (ii) long-term spatial memory, as well as (iii) the ability to remember the spatial location of resources after a single visit (one-trial spatial learning). The study was conducted with four groups of wild common marmosets (Callithrix jacchus) living in a semiarid Caatinga environment. We observed that individuals were able to retain spatial information of food sources on both a short- and long-term basis and to learn the spatial location of these resources after a single visit. We suggest that such abilities during foraging can improve the search for scattered resources with fluctuations of food availability. Presumably, this would be particularly advantageous in Caatinga, with its vegetation exhibiting asynchronous phenological patterns. Altogether, our results demonstrate that common marmosets employ all three studied spatial cognitive abilities to improve their food search and consumption.

A Method to Train Marmosets in Visual Working Memory Task and Their Performance

Learning and memory processes are similarly organized in humans and monkeys; therefore, monkeys can be ideal models for analyzing human aging processes and neurodegenerative diseases such as Alzheimer's disease. With the development of novel gene modification methods, common marmosets (Callithrix jacchus) have been suggested as an animal model for neurodegenerative diseases. Furthermore, the common marmoset's lifespan is relatively short, which makes it a practical animal model for aging. Working memory deficits are a prominent symptom of both dementia and aging, but no data are currently available for visual working memory in common marmosets. The delayed matching-to-sample task is a powerful tool for evaluating visual working memory in humans and monkeys; therefore, we developed a novel procedure for training common marmosets in such a task. Using visual discrimination and reversal tasks to direct the marmosets' attention to the physical properties of visual stimuli, we successfully trained 11 out of 13 marmosets in the initial stage of the delayed matching-to-sample task and provided the first available data on visual working memory in common marmosets. We found that the marmosets required many trials to initially learn the task (median: 1316 trials), but once the task was learned, the animals needed fewer trials to learn the task with novel stimuli (476 trials or fewer, with the exception of one marmoset). The marmosets could retain visual information for up to 16 s. Our novel training procedure could enable us to use the common marmoset as a useful non-human primate model for studying visual working memory deficits in neurodegenerative diseases and aging.

The marmoset monkey as a model for visual neuroscience

The common marmoset (Callithrix jacchus) has been valuable as a primate model in biomedical research. Interest in this species has grown recently, in part due to the successful demonstration of transgenic marmosets. Here we examine the prospects of the marmoset model for visual neuroscience research, adopting a comparative framework to place the marmoset within a broader evolutionary context. The marmoset's small brain bears most of the organizational features of other primates, and its smooth surface offers practical advantages over the macaque for areal mapping, laminar electrode penetration, and two-photon and optical imaging. Behaviorally, marmosets are more limited at performing regimented psychophysical tasks, but do readily accept the head restraint that is necessary for accurate eye tracking and neurophysiology, and can perform simple discriminations. Their natural gaze behavior closely resembles that of other primates, with a tendency to focus on objects of social interest including faces. Their immaturity at birth and routine twinning also makes them ideal for the study of postnatal visual development. These experimental factors, together with the theoretical advantages inherent in comparing anatomy, physiology, and behavior across related species, make the marmoset an excellent model for visual neuroscience.

A modified light-dark box test for the common marmoset

The common marmoset (Callithrix jacchus) has attracted extensive attention for use as a non-human primate model in biomedical research, especially in the study of neuropsychiatric disorders. However, behavioral test methods are still limited in the field of marmoset research. The light-dark box is widely used for the evaluation of anxiety in rodents, but little is known about light-dark preference in marmosets. Here, we modified the light-dark test to study this behavior. The modified apparatus consisted of three compartments: one transparent open area and two closed opaque compartments. The closed compartments could be dark or light. We found that both adult and young marmosets liked to explore the open area, but the young animals showed more interest than adults. Furthermore, when one of the closed compartments was light and the other dark, the adult marmosets showed a preference for the dark compartment, but the young animals had no preference. These results suggest that the exploratory behavior and the light-dark preference in marmosets are age-dependent. Our study provides a new method to study exploration, anxiety, and fear in marmosets.

The use of a T-maze to measure cognitive-motor function in cats (Felis catus)

Few tests have been developed to test the cognitive and motor capabilities of domestic cats, in spite of the suitability of cats for specific studies of neuroanatomy, infectious diseases, development, aging, and behavior. The present study evaluated a T-maze apparatus as a sensitive and reliable measure of cognition and motor function of cats. Eighteen purpose-bred, specific-pathogen-free, male, neutered domestic shorthair cats (Felis catus), 1-2 years of age, were trained and tested to a T-maze protocol using food rewards. The test protocol consisted of positional discrimination training (left arm or right arm) to criterion followed by two discrimination reversal tests. The two reversal tests documented the ability of the subjects to respond to a new reward location, and switch arms of the T-maze. Data were collected on side preference, number of correct responses, and latency of responses by the subjects. Aided by a customized computer program (CanCog Technologies), data were recorded electronically as each cat progressed from the start box to the reward arm. The protocol facilitated rapid training to a high and consistent level of performance during the discrimination training. This learning was associated with a decrease in the latency to traverse the maze to a mean of 4.80 ± 0.87 s indicating strong motivation and consistent performance. When the rewarded side was reversed in the test phase, cats required more trials to reach criterion, as expected, but again showed reliable learning. The latency to reward in the first session of reversal increased 86% from the first to the last trial indicating that it may provide a useful index of cognitive processing. Latencies subsequently decreased as the new reversal paradigm was learned. This paradigm provides a relatively rapid and reliable test of cognitive motor performance that can be used in various settings for evaluation of feline cognitive and motor function.

Maze model to study spatial learning and memory in freely moving monkeys

Many types of mazes have been used in cognitive brain research and data obtained from those experiments, especially those from rodents' studies, support the idea that the hippocampus is related to spatial learning and memory. But the results from non-human primates researches regarding the role of the hippocampus in spatial learning and memory are controversial and inconsistent with those obtained in rodents. This might be due to the differences of the methods used in non-human primates and rodents. Several kinds of maze models including two-dimensional computerized visual maze models and three-dimensional maze models have been developed for non-human primates, but they all have some defects. Therefore, development of a maze model for non-human primates that is comparable with those used in rodents is necessary to solve the controversy. This paper describes a large-scale, three-dimensional outdoor maze model for non-human primates which can be used to study spatial learning and memory. Monkeys learn to use the maze quickly compared with two-dimensional computerized visual mazes. It has many advantages which could make up the limits of the existing three-dimensional mazes in non-human primates, and can be comparable with radial arm mazes used in rodents. Based on the results, we believe that the new maze model will be valuable in many research areas, especially in studies involving spatial learning and memory in freely moving monkeys.

Effects of the mGluR2/3 agonist LY354740 on computerized tasks of attention and working memory in marmoset monkeys

RATIONALE

LY354740 is a recently developed metabotropic glutamatergic receptor 2 and 3 (mGluR2/3) agonist. A high density of mGluR2 has been reported in terminal fields of the perforant path in rodents and humans, suggesting its involvement in cognitive functions mediated by the temporal lobe, including memory. A small number of in vivo studies in rodents have assessed the effects of LY354740 on memory tasks, reporting the induction of impaired memory for spatial orientation in a water maze task and for delayed match and non-match to position in an operant version of these tasks.

OBJECTIVE

In the present primate study, we used radioautography to describe the distribution and intensity of (3)H-LY354740 binding in the hippocampal formation of the common marmoset monkey (Callithrix jacchus) relative to the rat. In the major, in vivo part of the study, the effects of systemic LY354740 on computerized tasks of attention and memory were investigated.

METHODS

Adult common marmosets were trained to perform a five-choice serial reaction time (5-CSRT) task and a concurrent delayed match-to-position (CDMP) task from the Cambridge Neuropsychological Automated test Battery (CANTAB). Filter tests of LY354740 effects on motor dexterity and motivation for reward revealed high inter-individual variation in sensitivity; therefore, on the 5-CSRT, subjects were tested at a dose range of 3--10 mg/kg, and on the CDMP, subjects were tested at 1--3 or 3--10 mg/kg.

RESULTS

Radioautography revealed a relatively low level of (3)H-LY354740 binding in the marmoset hippocampal formation compared to the rat. Despite low binding, LY354740 reduced sustained-attention accuracy in the 5-CSRT, and reduced accuracy in two stages of the CDMP.

CONCLUSIONS

The current study provides novel evidence for the importance of mGluR2/3 in the regulation of primate cognitive functioning.