In active females, motor activity decreased with age in the OF test (U = 0.01; Z = 3.06; p = 0.002). However, these changes were less pronounced than in males. In females that were passive in the OF, only a decrease in the number of rearings in the EPM was noted (U = 7.50 Z = 2,108,293 p = 0.035006)

The active and passive males in the OF test at the age of 2 months differed only in the level of horizontal (U = 0.01; Z = −3.07; p = 0.02) and vertical activity (U = 0.01; Z = −3.06; p = 0.002) (Table 1). At the age of 5 months, these differences diminished. In active and passive females at the age of 5 months, the differences observed at 2 months in the level of motor activity in the OF (U = 0.01; Z = −3.06; p = 0.002) also receded (Table 2).

In males that were active in the EPM, a significant decrease with age in motor activity was also observed, both in the OF (U = 0.01; Z = 3.06; p = 0.002) and in the EPM (U = 0.01; Z = 3.06; p = 0.002). The number of rearings also decreased in the OF (U = 8; Z = 2.04; p = 0.04) and in the EPM (U = 1.0; Z = 2.9; p = 0.003) tests. There were no age-related differences in the level of anxiety.

In males that were passive in the EPM, no significant age-related changes in the levels of motor and exploratory activities were

In females active in the EPM, motor activity significantly decreased with age in the OF (U = 7.50; Z = 2.11; p = 0.03) and EPM (U = 1; Z = 2.94; p = 0.003) tests, and the number of rearings in the EPM decreased (U = 2; Z = 2.81; p = 0.005). No significant age-related changes were observed in passive females

Males, both active and passive in the EPM at the age of 2 months significantly differed in the number of intersections of the maze compartments (U = 0.01; Z = −3.07; p = 0.002). At 5 months, these differences were not apparent.

EPM motor activity in females at 2 months was significantly greater compared to passive females (U = 0.01; Z = −2.93; p = 0.003). They also spent longer time in the open arms (U = 1.50; Z = −2.71; p = 0.007) than rats that were passive in the EPM. At 5 months, these differences between active and passive females in the EPM were not apparent.

4. Age-Related Changes in Rats with High (HA) and Low Levels of Anxiety (LA) in the OF and EPM Tests

Despite the fact that we did not reveal age-related differences in the level of anxiety in the general population of Wistar rats, LA in the OF test males, at the age of 2 months, demonstrated a low level of anxiety (spent a longer time in the centre of the OF), and had a significantly increased level of anxiety by the fifth month (U = 11.50; Z = 2.10; p = 0.036). In addition, in LA males in the OF, by the fifth month, motor activity decreased both in the OF (U = 0.01; Z = 3.31; p = 0.0009) and in the EPM (U = 7; Z = 2.57; p = 0.01) tests, and the number of rearings in the OF (U = 8.50; Z = 2.41; p = 0.02) and in the EPM (U = 8; Z = 2.47; p = 0.01) also decreased (Table 5). Those males that demonstrated a high level of anxiety at age 2 months had no reliable age-related changes in levels of motor activity and anxiety. We observed only a significant decrease in the number of rearings in the EPM (U = 3.0; Z = 2.68; p = 0.007).

In both LA and HA in the OF test females, no significant age-related changes in the studied parameters were observed, except for a decrease in the number of rearings in the EPM in calm (U = 3.5; Z =2.62; p =0.009) and in anxious animals (U =7.5; Z = 2.11; p = 0.035)

The observed significant differences between LA and HA in the OF test in males at the age of 2 months in motor activity (U =1; Z = −3.07; p = 0.002), the number of rearings (U =5.5; Z = −2.55; p = 0.01), and the time spent in the centre of the arena (U = 0.01; Z = −3.18; p = 0.001) was not present by the fifth month. The observed significant differences between LA and HA 2-month-old females in terms of the time spent in the centre of the OF (U = 0.01; Z = −3.07; p = 0.002) was also not apparent at the age of 5 months.

Males who, at the age of 2 months, demonstrated a low level of anxiety in the EPM (prolonged time spent in open arms), by 5 months significantly reduced the time spent on open arms (U = 7.0; Z = 2.17; p = 0.03). Motor and exploratory activity of LA in EPM males, both in the EPM (U = 7.5; Z = 2.11; p =0.035) and in the OF (U = 1; Z = 2.94; p = 0.003) also significantly decreased with age. In males that demonstrated a high level of anxiety at the age of 2 months, the number of rearings in the EPM decreased with age (U = 2.5; Z = 2.75; p = 0.006). No other significant age-related changes in behaviour were observed In males that demonstrated a high level of anxiety in the EPM at the age of 2 months, practically no significant age-related changes in behaviour were observed.

Females showing a low level of anxiety in the EPM at the age of 2 months also significantly reduced the time spent on open arms by 5 months (U = 4.0; Z = 2.555; p = 0.01). In addition, with age, they had a decrease in the number of rearings in the EPM (U = 2.5; Z = 2.75; p = 0.006). In females showing a high level of anxiety in the EPM, by the fifth month the time spent in the open arms did not change. However, the number of rearings in the EPM significantly decreased (U = 3.0; Z = 2.68; p = 0.007)

Males with high and low anxiety in the EPM differed at the age of 2 months in the duration of stay in the open arms of the maze (U = 0.01; Z = −3.07; p = 0.002). By the fifth month, significant differences between groups were not observed.

Females with high and low anxiety in the EPM at 2 months significantly differed in the time spent on the open arms of the maze (U = 0.0 1; Z = −3.07; p = 0.002), as well as in the level of motor activity in the EPM (U = 3; Z = −2.68; p = 0.007). These differences were not found at the fifth month.

5. Conclusions

4. In male and female Wistar rats there is a decrease in the level of motor and exploratory activities from 2 to 5 months of age.
5. Age-related changes in adult Wistar rats depend on their initial individual characteristics of behaviour.
6. Animals that demonstrate high motor activity at 2 months become significantly less active by 5 months.
7. Animals that show a low level of anxiety at the age of 2 months become more anxious by 5 months.
8. Low-activity and high-anxiety rats do not exhibit 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.

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