Sex is an important factor in understanding the clinical presentation, management, and developmental trajectory of children with neuropsychiatric disorders. While much is known about the clinical and neurobehavioral profiles of males with neuropsychiatric disorders, surprisingly little is known about females in this respect. Animal models may provide detailed mechanistic information about sex differences in autism spectrum disorder (ASD) in terms of manifestation, disease progression, and development of therapeutic options. This review aims to widen our understanding of the role of sex in autism spectrum disorder, by summarizing and comparing behavioral characteristics of animal models. Our current understanding of how differences emerge in boys and girls with neuropsychiatric disorders is limited: Information derived from animal studies will stimulate future research on the role of biological maturation rates, sex hormones, sex-selective protective (or aggravating) factors and psychosocial factors, which are essential to devise sex precision medicine and to improve diagnostic accuracy. Moreover, there is a strong need of novel strategies to elucidate the major mechanisms leading to sex-specific autism features, as well as novel models or methods to examine these sex differences.

Autism spectrum disorder (ASD) remains unexplained and untreated despite the high attention of research in recent years. Aside from its various characteristics is the baffling male preponderance over the female population. Using a validated animal model of ASD which is the telomerase reverse transcriptase overexpressing mice (TERT-tg), we conducted ASD-related behavioral assessments and protein expression experiments to mark the difference between male and females of this animal model. After statistically analyzing the results, we found significant effects of TERT overexpression in sociability, social novelty preference, anxiety, nest building, and electroseizure threshold in the males but not their female littermates. Along these differences are the male-specific increased expressions of postsynaptic proteins which are the NMDA and AMPA receptors in the prefrontal cortex. The vGluT1 presynaptic proteins, but not GAD, were upregulated in both sexes of TERT-tg mice, although it is more significantly pronounced in the male group. Here, we confirmed that the behavioral effect of TERT overexpression in mice was male-specific, suggesting that the aberration of this gene and its downstream pathways preferentially affect the functional development of the male brain, consistent with the male preponderance in ASD.

Despite some innate limitations, animal models are a potent investigative tool when used to model specific symptoms of a disorder. For example, MK-801, an N-methyl-D-aspartate receptor antagonist, is used as a pharmacological tool to induce symptoms found in some neuropsychiatric disorders. However, a close examination of literature suggests that the application window of MK-801 doses is relatively narrow between individual behavioral paradigms, necessitating careful characterization of the evoked behavioral aberrations and the doses used to induce them. Moreover, variation in behaviors depending on the animal strain, gender of the subject, and the timing of administration is observed, making it difficult to compare the behavioral characteristics reported in different studies. We aim to characterize the behavioral aberrations induced by different doses of MK-801 in CD-1 mice and create a ready reference for future studies. We used CD-1 mice to recapitulate behavioral impairments resulting from acute administration of MK-801. In 0.1 mg kg-1 , we observed diminished spontaneous alteration during the Y-maze test, while 0.12 mg kg-1 resulted in hyperlocomotion and social deficit. Mice treated with 0.2 and 0.3 mg kg-1 of MK-801 demonstrated a decreased self-grooming. Finally, all doses significantly impaired cliff avoidance behaviors suggesting increased impulsivity. These results affirm that MK-801 can effectively model various symptoms of different neuropsychiatric disorders in a dose-dependent manner. The observed sensitivity against spatial-memory impairment and impulsive behaviors at low concentration of MK-801 suggest that MK801 may modulate cognitive function and impulsivity in even lower concentration before it can modulate other behavioral domains.

Behavioral analysis in mice provided important contributions in helping understand and treat numerous neurobehavioral and neuropsychiatric disorders. The behavioral performance of animals and humans is widely different among individuals but the neurobehavioral mechanism of the innate difference is seldom investigated. Many neurologic conditions share comorbid symptoms that may have common pathophysiology and therapeutic strategy. The forced swim test (FST) has been commonly used to evaluate the “antidepressant” properties of drugs yet the individual difference analysis of this test was left scantly investigated along with the possible connection among other behavioral domains. This study conducted an FST-screening in outbred CD-1 male mice and segregated them into three groups: high performers (HP) or the active swimmers, middle performers (MP), and low performers (LP) or floaters. After which, a series of behavioral experiments were performed to measure their behavioral responses in the open field, elevated plus maze, Y maze, three-chamber social assay, novel object recognition, delay discounting task, and cliff avoidance reaction. The behavioral tests battery revealed that the three groups displayed seemingly correlated differences in locomotor activity and novel object recognition but not in other behaviors. This study suggests that the HP group in FST has higher locomotor activity and novelty-seeking tendencies compared to the other groups. These results may have important implications in creating behavior database in animal models that could be used for predicting interconnections of various behavioral domains, which eventually helps to understand the neurobiological mechanism controlling the behaviors in individual subjects.

No abstract