Cognitive impairment in a young marmoset reveals lateral ventriculomegaly and a mild hippocampal atrophy: a case report

Sleep Disturbance and Severe Hydrocephalus in a Normally Behaving Wistar Rat With Traumatic Brain Injury

We report on a case study of a Wistar rat that was investigated in detail because it exhibited no N3 sleep in electroencephalography (EEG) after lateral fluid-percussion injury (FPI)-induced traumatic brain injury (TBI). The rat (#112) belonged to a cohort of 28 adult Wistar rats exposed to lateral FPI. Rats were monitored by continuous video EEG for 30 days to follow-up on the evolution of sleep disturbances. The beam walking test was used to measure post-TBI functional recovery. Severity of the cortical lesion area, total brain volume, and cortical volume were measured from histological brain sections. Rat #112 had a normal body and skull appearance. Its baseline body weight did not differ from that of the rest of the cohort. At baseline, rat #112 crossed the beam in 6.3 sec (score range for the rest of the cohort, 4.7-44.3) and showed no evident slipping of the paws, scoring a 5.3 (score range for the rest of cohort, 4.3-6.0). On day 30 post-TBI, however, rat #112 was the only rat with a score of 0 on the beam. Histological analysis at 30 days post-TBI revealed a small 0.6-mm² post-TBI lesion in the somatosensory cortex (lesion size range for the rest of the cohort, 1.2-10.9). The brain volume of rat #112 was 2-fold larger than the mean volume of the rest of the cohort (1592 vs. 758 mm³), the ventricles were remarkably enlarged, and the layered cerebral cortex was very thin. Analysis of the sleep EEG revealed that rat #112 had rapid eye movement sleep and wakefulness, but no N3 sleep, during the 72-h EEG epoch analyzed. This case report demonstrates that brain abnormalities presumably unrelated to the impact-induced cortical lesion, such as presumed pre-existing hydrocephalus, may worsen TBI-induced behavioral and electrographical outcome measures and complicate the assessment of the cause of the abnormalities.

Atrophic astrocytes in aged marmosets present tau hyperphosphorylation, RNA oxidation, and DNA fragmentation

Astrocytes perform multiple essential functions in the brain showing morphological changes. Hypertrophic astrocytes are commonly observed in cognitively healthy aged animals, implying a functional defense mechanism without losing neuronal support. In neurodegenerative diseases, astrocytes show morphological alterations, such as decreased process length and reduced number of branch points, known as astroglial atrophy, with detrimental effects on neuronal cells. The common marmoset (Callithrix jacchus) is a non-human primate that, with age, develops several features that resemble neurodegeneration. In this study, we characterize the morphological alterations in astrocytes of adolescent (mean 1.75 y), adult (mean 5.33 y), old (mean 11.25 y), and aged (mean 16.83 y) male marmosets. We observed a significantly reduced arborization in astrocytes of aged marmosets compared to younger animals in the hippocampus and entorhinal cortex. These astrocytes also show oxidative damage to RNA and increased nuclear plaques in the cortex and tau hyperphosphorylation (AT100). Astrocytes lacking S100A10 protein show a more severe atrophy and DNA fragmentation. Our results demonstrate the presence of atrophic astrocytes in the brains of aged marmosets.

The Japan Monkey Centre Primates Brain Imaging Repository of high-resolution postmortem magnetic resonance imaging: the second phase of the archive of digital records

A comparison of neuroanatomical features of the brain between humans and our evolutionary relatives, nonhuman primates, is key to understanding the human brain system and the neural basis of mental and neurological disorders. Although most comparative MRI studies of human and nonhuman primate brains have been based on brains of primates that had been used as subjects in experiments, it is essential to investigate various species of nonhuman primates in order to elucidate and interpret the diversity of neuroanatomy features among humans and nonhuman primates. To develop a research platform for this purpose, it is necessary to harmonize the scientific contributions of studies with the standards of animal ethics, animal welfare, and the conservation of brain information for long-term continuation of the field. In previous research, we first developed a gated data-repository of anatomical images obtained using 9.4-T ex vivo MRI of postmortem brain samples from 12 nonhuman primate species, and which are stored at the Japan Monkey Centre. In the present study, as a second phase, we released a collection of T2-weighted images and diffusion tensor images obtained in nine species: white-throated capuchin, Bolivian squirrel monkey, stump-tailed macaque, Tibet monkey, Sykes' monkey, Assamese macaque, pig-tailed macaque, crested macaque, and chimpanzee. Our image repository should facilitate scientific discoveries in the field of comparative neuroscience. This repository can also promote animal ethics and animal welfare in experiments with nonhuman primate models by optimizing methods for in vivo and ex vivo MRI scanning of brains and supporting veterinary neuroradiological education. In addition, the repository is expected to contribute to conservation, preserving information about the brains of various primates, including endangered species, in a permanent digital form.

The common marmoset as a model of neurodegeneration

Human life expectancy has increased over the past few centuries, and the incidence of dementia in the older population is also projected to continue to rise. Neurodegenerative diseases are complex multifactorial conditions for which no effective treatments are currently available. Animal models are necessary to understand the causes and progression of neurodegeneration. Nonhuman primates (NHPs) offer significant advantages for the study of neurodegenerative disease. Among them, the common marmoset, Callithrix jacchus, stands out due to its easy handling, complex brain architecture, and occurrence of spontaneous beta-amyloid (Aβ) and phosphorylated tau aggregates with aging. Furthermore, marmosets present physiological adaptations and metabolic alterations associated with the increased risk of dementia in humans. In this review, we discuss the current literature on the use of marmosets as a model of aging and neurodegeneration. We highlight aspects of marmoset physiology associated with aging, such as metabolic alterations, which may help understand their vulnerability to developing a neurodegenerative phenotype that goes beyond normal aging.

Blood-brain barrier disruption and ventricular enlargement are the earliest neuropathological changes in rats with repeated sub-concussive impacts over 2 weeks

Repeated sub-concussive impact (e.g. soccer ball heading), a significantly lighter form of mild traumatic brain injury, is increasingly suggested to cumulatively alter brain structure and compromise neurobehavioural function in the long-term. However, the underlying mechanisms whereby repeated long-term sub-concussion induces cerebral structural and neurobehavioural changes are currently unknown. Here, we utilised an established rat model to investigate the effects of repeated sub-concussion on size of lateral ventricles, cerebrovascular blood-brain barrier (BBB) integrity, neuroinflammation, oxidative stress, and biochemical distribution. Following repeated sub-concussion 3 days per week for 2 weeks, the rats showed significantly enlarged lateral ventricles compared with the rats receiving sham-only procedure. The sub-concussive rats also presented significant BBB dysfunction in the cerebral cortex and hippocampal formation, whilst neuromotor function assessed by beamwalk and rotarod tests were comparable to the sham rats. Immunofluorescent and spectroscopic microscopy analyses revealed no significant changes in neuroinflammation, oxidative stress, lipid distribution or protein aggregation, within the hippocampus and cortex. These data collectively indicate that repeated sub-concussion for 2 weeks induce significant ventriculomegaly and BBB disruption, preceding neuromotor deficits.

Location and temporal memory of objects declines in aged marmosets (Callithrix jacchus)

Episodic memory decline is an early marker of cognitive aging in human. Although controversial in animals and called “episodic-like memory”, several models have been successfully developed, however they rarely focused on ageing. While marmoset is an emerging primate model in aging science, episodic-like memory has never been tested in this species and importantly in aged marmosets. Here, we examined if the recall of the what-when and what-where building blocks of episodic-like memory declines in ageing marmosets. We developed a naturalistic approach using spontaneous exploration of real objects by young and old marmosets in the home cage. We implemented a three-trial task with 1 week inter-trial interval. Two different sets of identical objects were presented in sample trials 1 and 2, respectively. For the test trial, two objects from each set were presented in a former position and two in a new one. We quantified the exploratory behaviour and calculated discrimination indices in a cohort of 20 marmosets. Young animals presented a preserved memory for combined what-where, and what-when components of the experiment, which declined with aging. These findings lead one to expect episodic-like memory deficits in aged marmosets.

The Importance of Complementary Collaboration of Researchers, Veterinarians, and Husbandry Staff in the Successful Training of Marmoset Behavioral Assays

Interest in marmosets as research models has seen exponential growth over the last decade, especially given that the research community is eager to improve on gaps with historical animal models for behavioral and cognitive disorders. The spectrum of human disease traits that present naturally in marmosets, as well as the range of analogous human behaviors that can be assessed in marmosets, makes them ideally suited as translational models for behavioral and cognitive disorders. Regardless of the specific research aims of any project, without close collaboration between researchers, veterinarians, and animal care staff, it would be impossible to meet these goals. Behavior is inherently variable, as are marmosets that are genetically and phenotypically diverse. Thus, to ensure rigor, reliability, and reproducibility in results, it is important that in the research environment, the animal's daily husbandry and veterinary needs are being met and align with the research goals while keeping the welfare of the animal the most critical and highest priority. Much of the information described herein provides details on key components for successful behavioral testing, based on a compendium of methods from peer-reviewed publications and our own experiences. Specific areas highlighted include habituation procedures, selection of appropriate rewards, optimization of testing environments, and ways to integrate regular veterinary and husbandry procedures into the research program with minimal disruptions to the behavioral testing plan. This article aims to provide a broad foundation for researchers new to establishing behavioral and cognitive testing paradigms in marmosets and especially for the veterinary and husbandry colleagues who are indispensable collaborators of these research projects.

MRI monitoring of macaque monkeys in neuroscience: Case studies, resource and normative data comparisons

Information from Magnetic Resonance Imaging (MRI) is useful for diagnosis and treatment management of human neurological patients. MRI monitoring might also prove useful for non-human animals involved in neuroscience research provided that MRI is available and feasible and that there are no MRI contra-indications precluding scanning. However, MRI monitoring is not established in macaques and a resource is urgently needed that could grow with scientific community contributions. Here we show the utility and potential benefits of MRI-based monitoring in a few diverse cases with macaque monkeys. We also establish a PRIMatE MRI Monitoring (PRIME-MRM) resource within the PRIMatE Data Exchange (PRIME-DE) and quantitatively compare the cases to normative information drawn from MRI data from typical macaques in PRIME-DE. In the cases, the monkeys presented with no or mild/moderate clinical signs, were well otherwise and MRI scanning did not present a significant increase in welfare impact. Therefore, they were identified as suitable candidates for clinical investigation, MRI-based monitoring and treatment. For each case, we show MRI quantification of internal controls in relation to treatment steps and comparisons with normative data in typical monkeys drawn from PRIME-DE. We found that MRI assists in precise and early diagnosis of cerebral events and can be useful for visualising, treating and quantifying treatment response. The scientific community could now grow the PRIME-MRM resource with other cases and larger samples to further assess and increase the evidence base on the benefits of MRI monitoring of primates, complementing the animals’ clinical monitoring and treatment regime.

The role of MRI in applying the 3Rs to non-human primate neuroscience

Magnetic resonance imaging is playing a significant role in applying the 3Rs to neuroscience studies using non-human primates. MRI scans are contributing to refinement by enhancing the selection and assignment of animals, guiding the manufacture of custom-fitted recording and head fixation devices, and assisting with the diagnosis of health issues and their treatment. MRI is also being used to better understand the impact of neuroscience procedures on the welfare of NHPs. MRI has helped to optimise NHP use and make greater scientific progress than would otherwise be made using larger numbers of animals. Whilst human fMRI studies have replaced some NHP studies, their potential to directly replace NHP electrophysiology is limited at present. Given the considerable advantages of MRI for electrophysiology experiments, including improved welfare of NHPs, consideration should be given to focusing NHP electrophysiology laboratories around MRI facilities. Greater sharing of MRI data sets, and improvements in MRI contrast and resolution, are expected to further advance the 3Rs in the future.

Memory deficits in Sprague Dawley rats with spontaneous ventriculomegaly

INTRODUCTION

Spontaneous ventriculomegaly has been observed in rats that were presumed normal. Because the external phenotype of these animals is unremarkable, they can be inadvertently included in behavioral experiments, despite the considerable enlargement of the ventricular system, reduced cortical thickness, and hippocampal atrophy upon imaging. Given the role of such structures in memory consolidation, we evaluated long-term memory retention while decision making in rats with spontaneous ventriculomegaly.

METHODS

We studied adult male Sprague Dawley rats, identified as having spontaneous ventriculomegaly, while performing baseline magnetic resonance imaging scanning intended for a different research protocol. Control (n = 7) and experimental (n = 6) animals were submitted to a delayed-alternation task (no delay, 30, 60, and 180 s) and an object-in-context recognition task. During the first task, we evaluated the number of correct choices as well as the latency to reach any of the cavities located at the end of each branch arm during each trial. The second task assessed the rodents' ability to remember where they had previously encountered a specific object, calculating the context recognition index.

RESULTS

When compared to control animals, rats with spontaneous ventriculomegaly required significantly more training sessions to reach the 80% criterion during the training phase. Moreover, they showed reduced delayed-alternation performance in the evaluated times, reaching significance only at 180 s. Increased latencies while trying to reach the cavity were also observed. Evaluation of the long-term memory formation during the object-in-context recognition task showed that subjects with ventriculomegaly spent less time investigating the familiar object, resulting in a significantly decreased recognition index value.

CONCLUSION

Our results are the first to show how spontaneous ventriculomegaly-induced cerebral structural damage affects decision-making behaviors, particularly when comparing between immediate and delayed trials. Moreover, this lesion disrupts the animals' ability to recall or express contextual information.

The common marmoset: An overview of its natural history, ecology and behavior

Callithrix jacchus are small-bodied Neotropical primates popularly known as common marmosets. They are endemic to Northeast Brazil and occur in contrasting environments such as the humid Atlantic Forest and the dry scrub forest of the Caatinga. Common marmosets live in social groups, usually containing only one breeding pair. These primates have a parental care system in which individuals help by providing assistance to the infants even when they are not related to them. Free-ranging groups use relatively small home ranges (0.5-5 hectares) and have an omnivorous diet. Because of the shape of their teeth, they actively gouge tree bark to extract and consume exudates. When foraging for live prey, they adjust their strategy according to the type of prey. The successful use of appropriate hunting strategies depends not only on age but also on prey type and seems to be mediated by learning and experience. Indeed, common marmosets have shown unexpected cognitive abilities, such as true imitation. All these aspects seem to have contributed to the ecological success of this species. Callithrix jacchus has been widely studied, especially in captivity; even so, a number of questions remain to be answered about its biology, ecology, and behavior, both in captivity and the wild. A richer understanding of marmosets' natural behavior and ecology can have a significant impact on shaping ongoing and future neuroscience research. © 2016 Wiley Periodicals, Inc. Develop Neurobiol 77: 244-262, 2017.