Our laboratory aims to propose a happy environment of humans and animals and presents three themes.
" To assess the environmental factor which cause behavioral dysfunctions, e.g. chemical compounds, and stress. "
" To identify methods for acquiring new beneficial body characteristics, e.g. stress tolerance. "
" To clarify the neuroendocrine mechanism regulating behaviors such as anxiety, sociality, learning and food intake. "

As part of the themes mentioned above, we expose rats to estrogenic compounds within hours of birth, and then assess the effects on behavior. There are various chemical compounds in the environment that can affect humans and domestic animals. Some of these chemicals mimic the effects of natural hormones and so can interfere with endocrine systems. Domestic animals can be exposed to these endocrine disruptors in the form of hormone preparations, ingredients or preservatives contained in animal feed, as well as some pesticide residues. One of these endocrine disruptors is estrogen. It can cause formative and functional changes in rodent brains.

The formative effect of estrogen is irreversible and happens during the developmental stage. It acts on the nervous system when it is undeveloped and rich in plasticity, and the resulting form of the neuron and neural network cannot subsequently be altered. Thus, normal differentiation of the brain can be inhibited by exposure to chemical compounds having estrogenic activity during the developmental period. On the other hand, the functional effect of estrogen stimulates neuron and neural network activity, and many of these activities are reversible. There are a wide range of neural mechanisms affected by estrogen, such as those related to reproduction, food intake, emotion, high-order function. However, the precise timing and mechanisms underlying these effects is not yet fully understood. Therefore, in this study we focused on estrogen exposure to female rats within 24 hours of birth, and analyzed the effects on learning behavior, anxiety-related behavior, feeding behavior and sexual behavior. From these studies we have revealed that a single neonatal exposure to 17α-ethinyl estradiol (EE) (2 mg/kg) disturbs the normal development of the female brain. It resulted in impaired sexual behavior (Komine et al, 2017. Journal of Applied Toxicology.), and also a decline in passive avoidance performance that was apparent even at a 1/100 dose level (0.02 mg/kg EE) (Shiga et al, 2016. PLoS One. 11:e0146136.).

Introduction of research methods

In our laboratory, we have mainly been working on research using an ethological analysis approach.
Some of the experimental methods being used in our laboratory are listed below.

Elevated plus maze test　

The elevated plus maze test measures anxiety-related behavior in rodents. It is conducted using cross-shaped apparatus that is elevated 50-60 cm above the floor. The cross shape is formed by two open arms and 2 closed arms. The test measures the number of entries and the time spent on each arm. Anxiety is demonstrated by the animal spending more time in the closed arms, and thus anxiety-related behavior can be examined. Our research indicate that arm structure (presense/absense of ledges on the open arm and/or the transparency/opaqueness of walls on the closed arm) significantly influences maze-exploratory behavior in rats (Horii et al, 2015. Behavioral Brain Res. 294: 131-40).

Maternal separation-induced ultrasonic vocalization test

This anxiety-related behavior, test focuses on infant animals. Infant rats produce ultrasonic vocalizations (USV) when they are separated from their mother and litter. This is a specific response of pups during the early postnatal period that prompts mothers to retrieve the vocalizing pups when they are scattered outside the nest. It appears to be a valid index of pup anxiety-related behavior, social behavior and stress response.

Y-maze test

The Y-maze test, which uses Y-shaped apparatus consisting of three arms, is used to study how the rodents function with memory and spatial learning. Rodents typically prefer to investigate a new arm of a maze rather than returning to one that they had previously visited. Based on this characteristic, the animal's memory function is tested by monitoring the preference to spend time in a newly uncovered arm or in 'known' arms that the animal had previously visited.

Rat preference test

Rat preference test has been used to determine whether a female finds different types of sexual interaction rewarding. The female is placed into a test chamber which is divided into three compartments linked by a tunnel. Test rat is allowed free moving between two areas. We measure time spent in each area, and evaluated which area the rat stayed in longer.