Aim: 

Hyperactivity is considered a typical manifestation of functional injury of the brain after peri- and neonatal hypoxia/ischaemia. However, in our previous experiments, we found inhibition of motor activity of the rats subjected to neonatal anoxia tested in a one-day session. In the present study we evaluated the effect of perinatal anoxia on the intensity of exploratory behaviour of the rat offspring in repeated testing in the open field.

Methods: 

Female pregnant rats were sacrificed on day 20 of gestation. The uteruses were placed in 37°C water bath for 20 min. After the anoxic insult the pups were adopted by foster mothers. On day 28 and 180 of age, exploratory behaviour of the rats (intensity of motor activity and rearings) was tested in the repeated open field test (5 consecutive days, 10 min session). Results:

After weaning, the study showed different courses of habituation of intensity of motor activity and rearings in anoxic animals compared to controls. There was a decrease of motor activity on day 1 of testing and an increase on days 3, 4 and 5 in the anoxic group compared to controls (sum of the activity counts on days 3, 4 and 5 for anoxic group: 1848 ± 169, for controls: 1279 ± 150, p < 0.05).

Conclusions: 

The study revealed the need of a complex approach to the evaluation of motor activity after hypoxic- ischemic insults. Single testing can conceal the phenomenon of hyperactivity, which can be detected during repeated testing of the animals in a novel environment.

Study was supported by the grant VEGA No. 2/5052/27