Male and Female Rats Show Different Brain Responses to Enriched Environment

Neurobiologists from Immanuel Kant Baltic Federal University found out differences of educability level and processes of formation of spatial memory of adult male and female rats, that live together in large cages and played with toys. Such conditions imitating natural habitat can help formation of new nerve cells in adult animals' brain, that reveals in improving of special memory and cognitive abilities, and also in immunity improvement. The difference in reaction of male and female rats on the habitat enables to suggest which brain region and which cells and molecules in it can lead to changes in animal's behavior. That helps to elaborate new drugs and methods of treating brain diseases, that are caused by stresses and cerebrovascular insults. The results of the research are published in magazine Biomedicine.

Conditions in which a person or animal lives influence his immunity, cognitive abilities and development of brain. American psychologist Mark Rozencwaig in 1960-ies elaborated a method of research of psychophysiological changes among animals in enriched environment – complex, often changing conditions, that imitate life in natural habitat. Such conditions include social cooperation of animals with each other, physical activity, and also various visual, acoustical, and tactile stimuli in form of toys. In some variants the enriched habitat can include cooperation of males and females.

Rozencwaig's experiments showed that rats, that were kept in enriched environment, lived longer, were ill more rarely and surpassed their fellows, that lived in small cages by two, as far as cognitive abilities are concerned. Such results confirm that adult brain is characterized by brain plasticity – the ability to form new nerve cells and neural connections. However, apart from external factors there are many internal ones, such as hormone fluctuations, specific for males and females, that influence the processes in adult brain. That gives scientists an ability to observe various behavioral reactions among animals of different gender, and also to reveal which molecular and cells mechanisms in brain lead to concrete changes in behavior.

Scientists from Immanuel Kant Baltic Federal University (Kaliningrad) compared changes, that occurred in brain of adult male and female rats, that lived in the enriched environment. To conduct the research, they divided more than 80 rats, one month old, into experimental and control group with approximately equal number of males and females in each. Gnawers from the control group lived by two in standard laboratory cages. Rats from experimental group were put into the conditions of enriched environment: 6-9 animals of each gender lived in large three-storied cages with wheels for running, stairs and toys, that were changed every three days. After two months scientists compared cognitive abilities of animals with the help of behavioral tests and compared results of rats of each gender from these two groups.

Authors found out essential differences between male and females from the experimental group in the course of passing Barnes maze. For that purpose, animals were let on the illuminated platform with twenty holes, under one of which there was a dark container for hiding. Animals have to remember this hiding-place during some trainings, in order to find it as quickly as possible during control test. Rats can orientate in space with the help of signs in form of colored figures, situated around the platform. Males who lived in the enriched environment, passed the test twice better, than rats from the control group. The female rats dominated their control fellows in 1.8 times. By this rats from the control group didn't have any essential differences as far as gender was concerned.

For development of spatial memory answers hippocamp – brain region that plays part in sensory perception, emotionality and cognitive abilities. Besides this, adult animals and men have in that brain region a center, where new neurons are formed from stem cells. The plasticity of brain is in many respects defined by their embedding into the structure of hippocamp. Scientists examined biochemical changes that took place in the hippocamp of experimental rats. The male rats that lived in the enriched environment showed insignificant difference as compared with control group. At the same time females' amount of immature stem cells increased in five times as compared with control group. In future it can influence the improvement of their cognitive abilities. Besides this scientist found out that female rats have 12 microRNA – specific molecule-markers that pointed to the intensive formation of new neurons. The male rats have only 4 such markers activated.

We suggest that differences between male and females are explained by work of reproductive hormones. Possibly, we examined hippocamp of animals at that moment when formation of new nerve cells from stem ones in the organisms of females had just begun, and figures of spatial memory of males were improved due to the fact that their cells had already grown and acquired "specialty". However, gender differences in brain reactions help us to know which cells and molecules in nerve system are connected with definite behavioral reactions. In future that enables to find molecular targets for drugs, that will help to recover brain plasticity of people who had suffered from severe stress or damage of brain, such as insult."

Oksana Tuchina, Ph.D, Biology, head of the laboratory for synthetic biology of Immanuel Kant Baltic Federal University

On the next stage of the research scientists are planning to examine how living in the enriched environment influences work of rats' hippocamp. In particular, they plan to detect changes in transferring of nerve impulses with the help of intermediary matters – neurotransmitters, such as serotonin and noradrenalin.