Spontaneous spike-wave discharges in rat neocortex and their relation to behaviour

A certain proportion of laboratory rats of various strains show spontaneous nonconvulsive ECoG seizures in the form of bursts of spike-and-wave discha rges (SWD). Since in the majority of behavioural experiments the EEG is not controlled, the experimenter is usually unaware of this fact. The purpose of the present work was to find out whether the SWD trait is related to the rats behavioural performance in selected test situations. The experiment w as performed on two groups of male Wistar rats, outbreds, aged six (group 6 M, n = 17) and 24 months (group 24M, n = 14). First, in both groups the fol lowing forms of behaviour were assessed: (1) seeking water reward in an 8-a rm radial maze, (2) exploration of a new object, (3) inhibition of a locomo tor response (passive avoidance), and (4) paw-lick response to a thermal st imulus (54.5 degrees C) applied to the feet before and after intermittent f ootshock. The rats were then implanted with intrabrain electrodes and the l evel of SWD activity was assessed. Rats of the 24M group, compared with tho se of the 6M one, showed a significantly shorter exploratory response to a new object and diminished responsiveness to heat. The groups did not differ , however, in passive avoidance and radial maze performance. The analysis o f 3-h ECoG sections revealed SWD bursts in 73% and nearly 93% of rats from groups 6M and 24M, respectively. The groups did not differ in the number of bursts or in the total duration of SWD activity. A correlation analysis of pooled data from both groups revealed that the exploration time of a new o bject was significantly (negatively) correlated with the number of SWD epis odes. The total duration of SWD activity, and the number of perseveration e rrors in the radial maze, was significantly (positively) correlated with th e total duration of SWD activity. The results suggest that SWD rats are beh aviourally impaired in some test situations.