Simplified drug efficacy screening system for sleep-disorder drugs using non-human primates

Mice with deficiency in Pcdh15, a gene associated with bipolar disorders, exhibit significantly elevated diurnal amplitudes of locomotion and body temperature

Genetic factors significantly affect the pathogenesis of psychiatric disorders. However, the specific pathogenic mechanisms underlying these effects are not fully understood. Recent extensive genomic studies have implicated the protocadherin-related 15 (PCDH15) gene in the onset of psychiatric disorders, such as bipolar disorder (BD). To further investigate the pathogenesis of these psychiatric disorders, we developed a mouse model lacking Pcdh15. Notably, although PCDH15 is primarily identified as the causative gene of Usher syndrome, which presents with visual and auditory impairments, our mice with Pcdh15 homozygous deletion (Pcdh15-null) did not exhibit observable structural abnormalities in either the retina or the inner ear. The Pcdh15-null mice showed very high levels of spontaneous motor activity which was too disturbed to perform standard behavioral testing. However, the Pcdh15 heterozygous deletion mice (Pcdh15-het) exhibited enhanced spontaneous locomotor activity, reduced prepulse inhibition, and diminished cliff avoidance behavior. These observations agreed with the symptoms observed in patients with various psychiatric disorders and several mouse models of psychiatric diseases. Specifically, the hyperactivity may mirror the manic episodes in BD. To obtain a more physiological, long-term quantification of the hyperactive phenotype, we implanted nano tag® sensor chips in the animals, to enable the continuous monitoring of both activity and body temperature. During the light-off period, Pcdh15-null exhibited elevated activity and body temperature compared with wild-type (WT) mice. However, we observed a decreased body temperature during the light-on period. Comprehensive brain activity was visualized using c-Fos mapping, which was assessed during the activity and temperature peak and trough. There was a stark contrast between the distribution of c-Fos expression in Pcdh15-null and WT brains during both the light-on and light-off periods. These results provide valuable insights into the neural basis of the behavioral and thermal characteristics of Pcdh15-deletion mice. Therefore, Pcdh15-deletion mice can be a novel model for BD with mania and other psychiatric disorders, with a strong genetic component that satisfies both construct and surface validity.

Effect of chronic intermittent hypoxia on ocular and intraoral mechanical allodynia mediated via the calcitonin gene-related peptide in a rat

STUDY OBJECTIVES

Obstructive sleep apnea, a significant hypoxic condition, may exacerbate several orofacial pain conditions. The study aims to define the involvement of calcitonin gene-related peptide (CGRP) in peripheral and central sensitization and in evoking orofacial mechanical allodynia under chronic intermittent hypoxia (CIH).

METHODS

Male rats were exposed to CIH. Orofacial mechanical allodynia was assessed using the eyeblink test and the two-bottle preference drinking test. The CGRP-immunoreactive neurons in the trigeminal ganglion (TG), CGRP-positive primary afferents projecting to laminae I-II of the trigeminal spinal subnucleus caudalis (Vc), and neural responses in the second-order neurons of the Vc were determined by immunohistochemistry. CGRP receptor antagonist was administrated in the TG.

RESULTS

CIH-induced ocular and intraoral mechanical allodynia. CGRP-immunoreactive neurons and activated satellite glial cells (SGCs) were significantly increased in the TG and the number of cFos-immunoreactive cells in laminae I-II of the Vc were significantly higher in CIH rats compared to normoxic rats. Local administration of the CGRP receptor antagonist in the TG of CIH rats attenuated orofacial mechanical allodynia; the number of CGRP-immunoreactive neurons and activated SGCs in the TG, and the density of CGRP-positive primary afferent terminals and the number of cFos-immunoreactive cells in laminae I-II of the Vc were significantly lower compared to vehicle-administrated CIH rats.

CONCLUSIONS

An increase in CGRP in the TG induced by CIH, as well as orofacial mechanical allodynia and central sensitization of second-order neurons in the Vc, supported the notion that CGRP plays a critical role in CIH-induced orofacial mechanical allodynia.

Phenotypes for general behavior, activity, and body temperature in 3q29 deletion model mice

Whole genome analysis has identified rare copy number variations (CNV) that are strongly involved in the pathogenesis of psychiatric disorders, and 3q29 deletion has been found to have the largest effect size. The 3q29 deletion mice model (3q29-del mice) has been established as a good pathological model for schizophrenia based on phenotypic analysis; however, circadian rhythm and sleep, which are also closely related to neuropsychiatric disorders, have not been investigated. In this study, our aims were to reevaluate the pathogenesis of 3q29-del by recreating model mice and analyzing their behavior and to identify novel new insights into the temporal activity and temperature fluctuations of the mouse model using a recently developed small implantable accelerometer chip, Nano-tag. We generated 3q29-del mice using genome editing technology and reevaluated common behavioral phenotypes. We next implanted Nano-tag in the abdominal cavity of mice for continuous measurements of long-time activity and body temperature. Our model mice exhibited weight loss similar to that of other mice reported previously. A general behavioral battery test in the model mice revealed phenotypes similar to those observed in mouse models of schizophrenia, including increased rearing frequency. Intraperitoneal implantation of Nano-tag, a miniature acceleration sensor, resulted in hypersensitive and rapid increases in the activity and body temperature of 3q29-del mice upon switching to lights-off condition. Similar to the 3q29-del mice reported previously, these mice are a promising model animals for schizophrenia. Successive quantitative analysis may provide results that could help in treating sleep disorders closely associated with neuropsychiatric disorders.

Less invasive, simultaneous, and continuous measurements of locomotor activity and body temperature using the nano tag® small accelerometer device in cynomolgus monkeys

Locomotor activity and body temperature evaluations of cynomolgus monkeys are useful to understand the effects of drugs on the central nervous system. Here, we describe a simple, inexpensive, and less invasive evaluation method using the nano tag® (KISSEI COMTEC Co., Ltd.), a small three-axis accelerometer device with a temperature sensor. Nano tags® were subcutaneously implanted in four cynomolgus monkeys that had been intraperitoneally implanted with a telemetry transmitter. Then, body temperature and locomotor activity counts were simultaneously and continuously measured by both the nano tag® and telemetry transmitter for 14 days after nano tag® implantation. The invasiveness of the implantation surgery was evaluated by recovery after surgery, and the validity of each nano tag® parameter was evaluated by comparison with the telemetry system data. Additionally, locomotor activity and body temperature changes induced by treatment with ketamine, a noncompetitive N-methyl-d-aspartate receptor antagonist, were evaluated by the nano tag®. Recovery from nano tag® implantation surgery was observed at 7 days postoperative, indicating that nano tag® was less invasive than a telemetry transmitter. Both of the parameter profiles measured by nano tag® were approximately comparable to those of the telemetry system. Moreover, the nano tag® could detect ketamine-induced pharmacological changes of decreases in both parameters. The present study demonstrates that nano tag® is an effective, simple, and less invasive tool for locomotor activity and body temperature evaluations in cynomolgus monkeys. This proposed easier method could help researchers evaluate central nervous system effects in cynomolgus monkeys.

Regular Low-Intensity Exercise Prevents Cognitive Decline and a Depressive-Like State Induced by Physical Inactivity in Mice: A New Physical Inactivity Experiment Model

Regular exercise has already been established as a vital strategy for maintaining physical health via experimental results in humans and animals. In addition, numerous human studies have reported that physical inactivity is a primary factor that causes obesity, muscle atrophy, metabolic diseases, and deterioration in cognitive function and mental health. Regardless, an established animal experimental method to examine the effect of physical inactivity on physiological, biochemical, and neuroscientific parameters is yet to be reported. In this study, we made a new housing cage, named as the physical inactivity (PI) cage, to investigate the effect of physical inactivity on cognitive function and depressive-like states in mice and obtained the following experimental results by its use. We first compared the daily physical activity of mice housed in the PI and standard cages using the nano-tag method. The mice’s physical activity levels in the PI cage decreased to approximately half of that in the mice housed in the standard cage. Second, we examined whether housing in the PI cage affected plasma corticosterone concentration. The plasma corticosterone concentration did not alter before, 1 week, or 10 weeks after housing. Third, we investigated whether housing in the PI cage for 10 weeks affected cognitive function and depressive behavior. Housing in an inactive state caused a cognitive decline and depressive state in the mice without increasing body weight and plasma corticosterone. Finally, we examined the effect of regular low-intensity exercise on cognitive function and depressive state in the mice housed in the PI cage. Physical inactivity decreased neuronal cell proliferation, blood vessel density, and gene expressions of vascular endothelial growth factors and brain-derived neurotrophic factors in the hippocampus. In addition, regular low-intensity exercise, 30 min of treadmill running at a 5–15 m/min treadmill speed 3 days per week, prevented cognitive decline and the onset of a depressive-like state caused by physical inactivity. These results showed that our novel physical inactivity model, housing the mice in the PI cage, would be an adequate and valuable experimental method for examining the effect of physical inactivity on cognitive function and a depressive-like state.

Sleep Disturbances and Depression Are Co-morbid Conditions: Insights From Animal Models, Especially Non-human Primate Model

The incidence rates of depression are increasing year by year. As one of the main clinical manifestations of depression, sleep disorder is often the first complication. This complication may increase the severity of depression and lead to poor prognosis in patients. In the past decades, there have been many methods used to evaluate sleep disorders, such as polysomnography and electroencephalogram, actigraphy, and videography. A large number of rodents and non-human primate models have reproduced the symptoms of depression, which also show sleep disorders. The purpose of this review is to examine and discuss the relationship between sleep disorders and depression. To this end, we evaluated the prevalence, clinical features, phenotypic analysis, and pathophysiological brain mechanisms of depression-related sleep disturbances. We also emphasized the current situation, significance, and insights from animal models of depression, which would provide a better understanding for the pathophysiological mechanisms between sleep disturbance and depression.