Animal models of psychiatric disorders

Challenges in the use of animal models and perspectives for a translational view of stress and psychopathologies

The neurobiology and development of treatments for stress-related neuropsychiatric disorders rely heavily on animal models. However, the complexity of these disorders makes it difficult to model them entirely, so only specific features of human psychopathology are emulated and these models should be used with great caution. Importantly, the effects of stress depend on multiple factors, like duration, context of exposure, and individual variability. Here we present a review on pre-clinical studies of stress-related disorders, especially those developed to model posttraumatic stress disorder, major depression, and anxiety. Animal models provide relevant evidence of the underpinnings of these disorders, as long as face, construct, and predictive validities are fulfilled. The translational challenges faced by scholars include reductionism and anthropomorphic/anthropocentric interpretation of the results instead of a more naturalistic and evolutionary understanding of animal behavior that must be overcome to offer a meaningful model. Other limitations are low statistical power of analysis, poor evaluation of individual variability, sex differences, and possible conflicting effects of stressors depending on specific windows in the lifespan.

The Role of Microglial CX3CR1 in Schizophrenia-Related Behaviors Induced by Social Isolation

According to the microglial hypothesis of schizophrenia, the hyperactivation of microglia and the release of proinflammatory cytokines lead to neuronal loss, which is highly related to the onset of schizophrenia. Recent studies have demonstrated that fractalkine (CX3CL1) and its receptor CX3CR1 modulate the function of microglia. Thus, the present study aimed to determine whether microglial CX3CR1 plays a role in schizophrenia-related behaviors. A classical animal model of schizophrenia, social isolation (from postnatal days 21-56), was used to induce schizophrenia-related behaviors in C57BL/6J and CX3CR1-/- mice, and the expression of the microglial CX3CR1 protein was examined in several brain areas of the C57BL/6J mice by Western blot analysis. The results revealed that social isolation caused deficits in the prepulse inhibition (PPI) in the C57BL/6J mice but not in the CX3CR1-/- mice and increased locomotor activity in both the C57BL/6J mice and the CX3CR1-/- mice. Moreover, the CX3CR1 protein level was increased in the medial prefrontal cortex, nucleus accumbens, and hippocampus of the isolated C57BL/6J mice. These findings suggested that the function of microglia regulated by CX3CR1 might participate in schizophrenia-related behaviors.

DIY-NAMIC Behavior: A High-Throughput Method to Measure Complex Phenotypes in the Homecage

Complex behavioral assessment is necessary to comprehensively assess in vivo manipulations in rodent models for neuropsychiatric disorders. Operant behavioral paradigms provide rich datasets and allow for the careful analysis of behavioral phenotypes. However, one major limitation in these studies is the expense and work-load that are required using traditional methods. The equipment for commercial operant boxes can be prohibitively expensive, and the daily experimenter effort and mouse costs required for these studies is extensive. Rodents are generally trained on task-specific paradigms for months, tested every day for 5–7 d/week. Additionally, appetitive paradigms usually require food restriction and are also commonly run in the non-active light phase of the rodent circadian rhythm. These limitations make operant behavioral testing especially difficult during adolescence, a time period of interest with regards to the development of adult-like phenotypes and a high-risk period for the development of neuropsychiatric disorders, including those which involve impulsive behavior. In order to address these issues, we developed an automated, inexpensive, open-source method which allows the implementation of most standard operant paradigms in the homecage of rodents in shorter time frames without food restriction, and with much less experimenter effort. All construction and code for the do-it-yourself Nautiyal Automated Modular Instrumental Conditioning (DIY-NAMIC) system are open source. We demonstrate their utility here by measuring impulsive behavior in a pharmacology experiment, as well as in adolescent mice.

Impaired Dopamine-Dependent Locomotory Behavior of C. elegans Neuroligin Mutants Depends on the Catechol-O-Methyltransferase COMT-4

Neurexins and neuroligins are neuronal membrane adhesion molecules that have been involved in neuropsychiatric and neurodevelopmental disorders. The nrx-1 and nlg-1 genes of Caenorhabditis elegans encode NRX-1 and NLG-1, orthologue proteins of human neurexins and neuroligins, respectively. Dopaminergic and serotoninergic signalling control the locomotory rate of the nematode. When well-fed animals are transferred to a plate with food (bacterial lawn), they reduce the locomotory rate. This behavior, which depends on dopamine, is known as basal slowing response (BSR). Alternatively, when food-deprived animals are moved to a plate with a bacterial lawn, further decrease their locomotory rate. This behavior, known as enhanced slowing response (ESR), is serotonin dependent. C. elegans nlg-1-deficient mutants are impaired in BSR and ESR. Here we report that nrx-1-deficient mutants were defective in ESR, but not in BSR. The nrx-1;nlg-1 double mutant was impaired in both behaviors. Interestingly, the nlg-1 mutants upregulate the expression of comt-4 which encodes an enzyme with putative catechol-O-methyltransferase activity involved in dopamine degradation. Our study also shows that comt-4(RNAi) in nlg-1-deficient mutants rescues the wild type phenotypes of BSR and ESR. On the other hand, comt-4(RNAi) in nlg-1-deficient mutants also recovers, at least partially, the gentle touch response and the pharyngeal pumping rate that were impaired in these mutants. These latter behaviors are dopamine and serotonin dependent, respectively. Based on these results we propose a model for the neuroligin function in modulating the dopamine-dependent locomotory behavior in the nematode.