Expression of Exploratory Activity of Rat Offspring Depends on the Expression of Exploratory Activity of Their Parents at the Moment of Mating.

The aim of this work was to study the, so far, unexplored possibility that non-genetic inheritance of animal behavioral characteristics could depend on the state of the parents at the time of conception. In this study, we measured the levels of motor and exploratory activity in rats at the ages of 2 and 5 months. Male and female rats were mated at the age of 5 months. The following groups were used: male and female rats with high motor activity at ages of 2 and 5 months (ACT+); male and female rats with high activity at the age of 2 months, but low activity at the age of 5 months (ACT-); male and female rats with low activity at the ages of 2 and 5 months (PAS-); male and female rats with low activity at the age of 2 months, but high activity at the age of 5 months (PAS+). It was found that both males and females ACT+ had significantly higher motor activity, which was observed in the first 10minutes, in the next 20-60minutes, in the center of the cage and more rearings as compared with PAS-rats. Significant differences in the severity of exploratory activity were found between the male offspring of ACT+ and ACT- rats. Differences between the offspring of PAS+ and PAS- rats were observed in both the male and female rats. The motor activity of animals in the period from 20minutes after the start of registration did not differ between groups. Thus, it can be considered that individual characteristics of general motor activity are due to genetically inherited factors, while differences in the level of exploratory activity, apparently, are formed due to non-genetic influences from parents during mating.

Cross-Generational Impact of Epigenetic Male Influence on Physical Activity in Rat.

The aim of this work was to study whether epigenetic events at conception influence the formation of behavioral features found in adult rats. First generational inheritance of activity level, anxiety like behavior, and learning ability was studied. To separate genetic and non-genetic inheritance, mating of males and females with average motor activity was carried out in the presence anesthetized or conscious males with high or low activity. Our results show that offspring of parents who mated in the presence of males with a high motor activity were significantly more active than offspring of parents that were paired in the presence of males with low activity. Anxiety like behavior and learning ability were not inherited in this way. It is possible that the phenomenon we discovered is important for maintaining a certain level of activity of specific populations of animals. It counteracts natural selection, which should lead to a constant increase in the activity of animals.

Age-Related Individual Behavioural Characteristics of Adult Wistar Rats.

The aim of this work was to study age-related changes in the behaviour of adult Wistar rats using the open field (OF) and elevated plus maze (EPM) tests. Behavioural changes related to motor activity and anxiety were of particular interest. Results showed that as male and female rats progressed from 2 to 5 months of age, there was a decrease in the level of motor and exploratory activities and an increase in their level of anxiety. Age-related changes were dependent upon initial individual characteristics of behaviour. For example, animals that demonstrated high motor activity at 2 months become significantly less active by 5 months, and animals that showed a low level of anxiety at 2 months become more anxious by 5 months. Low-activity and high-anxiety rats did not show any significant age-related changes in OF and EPM tests from 2 to 5 months of age, except for a decrease in the number of rearings in the EPM. Thus, the behaviour of the same adult rat at 2 and 5 months of age is significantly different, which may lead to differences in the experimental results of physiological and pharmacological studies using adult animals of different ages.

Endogenous opioid dependence after intermittent use of glucose, sodium chloride, and monosodium glutamate solutions.

In 2002, Colantuoni et al described the possibility of dependency in rats after intermittent, excessive consumption of a 25% glucose solution over a one-week period. We hypothesized that the intermittent consumption of any tasty solution can lead to endogenous opioid dependency. Another aim was to determine whether dependency is connected to the taste of the consumed substance or with its physiological significance. Rats were maintained on chow and cyclic glucose, NaCl, or monosodium glutamate (MSG) solution for 8 days. On day 9, after a 12-hr deprivation period and administration of intraperitoneally (IP) naloxone, the general withdrawal index was calculated as the sum of teeth chattering, head shaking, forepaw tremors, and wet dog shakes. Motor activity was also documented. After the intermittent consumption of any tasty solution, rats were found to demonstrate signs of endogenous opioid dependence. The development of dependence was not related to taste preferences or the amount of solution consumed. Intermittent use of essential substance with a pleasant taste, as glucose and sodium chloride, leads to the rapid development of endogenous opioid dependence. Withdrawal syndrome following the consumption of MSG solution is associated with the presence of sodium ions in the MSG molecule.