Object discrimination and reversal learning in infant and juvenile non-human primates in a non-clinical laboratory

Evaluation of changes in the cognitive function of adult cynomolgus monkeys under stress induced by audio-visual stimulation by applying modified finger maze test

Stress in life is ubiquitous and unavoidable. Prolonged exposure to severe stress can lead to physical intolerance and impair cognitive function. Non-human primates are considered to be the best animal model for studying cognitive function, especially memory and attention. The finger maze test, with the advantages of short training time and lower cost, is recommended to evaluate learning and memory in non-human primates. In this study, we modified the finger maze test method to evaluate the cognitive function of single-housed cynomolgus monkeys. The flexibility and attention of cynomolgus monkeys were assessed by performing the complex task test and the stranger intrusion interference test, respectively, which increased the difficulty of obtaining rewards, and the ability of long-term memory was also evaluated by the memory test. Furthermore, the changes in cognitive function of the cynomolgus monkeys were tested by using the finger maze test after audio-visual stimulation, and the changes in the cortisol levels during stimulation were also analyzed. We found that, after completing the learning test, there was no significant decrease in their success rate when monkeys processed multitasks at the same time. In the stranger intrusion interference test, all subjects were distracted, but the accuracy did not decrease. The monkeys completed the memory tests in the 1st and 2nd months after the learning tests, with a high success rate. However, the success rate decreased significantly at the end of the 4th month. During audio-visual stimulation, the plasma cortisol level significantly increased in the first 2 months and was maintained at a high level thereafter. One month after audio-visual stimulation, the accuracy of the memory test was significantly reduced, and the total time of distraction was significantly prolonged. In conclusion, chronic audio-visual stimulation can increase blood cortisol levels and impair cognitive function. The modified finger maze test can evaluate many aspects of cognitive function and assess the changes in the cognitive function of adult cynomolgus monkeys under stress.

Infant isoflurane exposure affects social behaviours, but does not impair specific cognitive domains in juvenile non-human primates

BACKGROUND

Clinical studies show that children exposed to anaesthetics for short times at young age perform normally on intelligence tests, but display altered social behaviours. In non-human primates (NHPs), infant anaesthesia exposure for several hours causes neurobehavioural impairments, including delayed motor reflex development and increased anxiety-related behaviours assessed by provoked response testing. However, the effects of anaesthesia on spontaneous social behaviours in juvenile NHPs have not been investigated. We hypothesised that multiple, but not single, 5 h isoflurane exposures in infant NHPs are associated with impairments in specific cognitive domains and altered social behaviours at juvenile age.

METHODS

Eight Rhesus macaques per group were anaesthetised for 5 h using isoflurane one (1×) or three (3×) times between postnatal days 6 and 12 or were exposed to room air (control). Cognitive testing, behavioural assessments in the home environment, and provoked response testing were performed during the first 2 yr of life.

RESULTS

The cognitive functions tested did not differ amongst groups. However, compared to controls, NHPs in the 3× group showed less close social behaviour (P=0.016), and NHPs in the 1× group displayed increased anxiety-related behaviours (P=0.038) and were more inhibited towards novel objects (P<0.001).

CONCLUSIONS

5 h exposures of NHPs to isoflurane during infancy are associated with decreased close social behaviour after multiple exposures and more anxiety-related behaviours and increased behavioural inhibition after single exposure, but they do not affect the cognitive domains tested. Our findings are consistent with behavioural alterations in social settings reported in clinical studies, which may guide future research.

Bridging the species gap in translational research for neurodevelopmental disorders

The prevalence and societal impact of neurodevelopmental disorders (NDDs) continue to increase despite years of research in both patient populations and animal models. There remains an urgent need for translational efforts between clinical and preclinical research to (i) identify and evaluate putative causes of NDD, (ii) determine their underlying neurobiological mechanisms, (iii) develop and test novel therapeutic approaches, and (iv) translate basic research into safe and effective clinical practices. Given the complexity behind potential causes and behaviors affected by NDDs, modeling these uniquely human brain disorders in animals will require that we capitalize on unique advantages of a diverse array of species. While much NDD research has been conducted in more traditional animal models such as the mouse, ultimately, we may benefit from creating animal models with species that have a more sophisticated social behavior repertoire such as the rat (Rattus norvegicus) or species that more closely related to humans, such as the rhesus macaque (Macaca mulatta). Here, we highlight the rat and rhesus macaque models for their role in previous psychological research discoveries, current efforts to understand the neurobiology of NDDs, and focus on the convergence of behavior outcome measures that parallel features of human NDDs.

Autism-like behaviours and germline transmission in transgenic monkeys overexpressing MeCP2

Methyl-CpG binding protein 2 (MeCP2) has crucial roles in transcriptional regulation and microRNA processing. Mutations in the MECP2 gene are found in 90% of patients with Rett syndrome, a severe developmental disorder with autistic phenotypes. Duplications of MECP2-containing genomic segments cause the MECP2 duplication syndrome, which shares core symptoms with autism spectrum disorders. Although Mecp2-null mice recapitulate most developmental and behavioural defects seen in patients with Rett syndrome, it has been difficult to identify autism-like behaviours in the mouse model of MeCP2 overexpression. Here we report that lentivirus-based transgenic cynomolgus monkeys (Macaca fascicularis) expressing human MeCP2 in the brain exhibit autism-like behaviours and show germline transmission of the transgene. Expression of the MECP2 transgene was confirmed by western blotting and immunostaining of brain tissues of transgenic monkeys. Genomic integration sites of the transgenes were characterized by a deep-sequencing-based method. As compared to wild-type monkeys, MECP2 transgenic monkeys exhibited a higher frequency of repetitive circular locomotion and increased stress responses, as measured by the threat-related anxiety and defensive test. The transgenic monkeys showed less interaction with wild-type monkeys within the same group, and also a reduced interaction time when paired with other transgenic monkeys in social interaction tests. The cognitive functions of the transgenic monkeys were largely normal in the Wisconsin general test apparatus, although some showed signs of stereotypic cognitive behaviours. Notably, we succeeded in generating five F1 offspring of MECP2 transgenic monkeys by intracytoplasmic sperm injection with sperm from one F0 transgenic monkey, showing germline transmission and Mendelian segregation of several MECP2 transgenes in the F1 progeny. Moreover, F1 transgenic monkeys also showed reduced social interactions when tested in pairs, as compared to wild-type monkeys of similar age. Together, these results indicate the feasibility and reliability of using genetically engineered non-human primates to study brain disorders.

Feasibility of repeated testing for learning ability in juvenile primates for pediatric safety assessment

Assessment of learning ability in nonhuman primate (NHP) models is sometimes requested by regulatory authorities. The double choice object discrimination task using a Wisconsin General Testing Apparatus (WGTA) approach is typically being applied. In this study, the WGTA approach was performed on 66 juvenile cynomolgus monkeys aged 8-9 months in the predose phase of juvenile toxicity assessment. In addition, reversal learning data of seven control animals/gender were obtained for the weeks 25 and 52 of dosing. Gender differences in the number of days required to pass the habituation, learning or reversal learning phases were statistically comparable, males and females may be combined for statistical analysis. At first instance, the habituation phase was passed on average after 6.4 days, and the learning test on average after 8.6 days with improvement to 2.0-2.6 days for habituation and 6.4-6.7 days for learning in weeks 52. Power analysis (α = 0.05, one-sided t-test) revealed a sample size of 8 and 41 to predict a 50% and 20% difference, respectively. In conclusion, examination for learning ability, but not for memory ability (during repeated testing) is feasible in juvenile NHPs using the WGTA approach.

Developmental toxicity assessment of tanezumab, an anti-nerve growth factor monoclonal antibody, in cynomolgus monkeys (Macaca fascicularis)

Two intravenous studies with tanezumab, an anti-nerve growth factor monoclonal antibody, were conducted in pregnant cynomolgus monkeys to assess potential effects on pregnancy and pre- and postnatal development. Study 1 evaluated infants up to 12 months of age following weekly maternal dosing (0, 0.5, 4 or 30 mg/kg; 18 per group) from gestation day (GD) 20 through parturition. Study 2 evaluated infants 2 months postnatally following weekly maternal dosing (0, 0.5 or 30 mg/kg; 20-21 per group) from GD 20 through 48. In the absence of maternal toxicity, tanezumab increased stillbirth and post-birth infant mortality/morbidity, decreased infant growth and resulted in microscopic changes in the peripheral sympathetic and sensory nervous system of the infants at all doses. Decreased primary antibody responses and increased incidences in skin changes in infants were also observed. The no-observed-adverse-effect-level for maternal toxicity was 30 mg/kg and <0.5 mg/kg for developmental toxicity.