Daily changes in pentylenetetrazol-induced convulsions and open-field behavior in rats.

Susceptibility to pentylenetetrazol (PTZ)-induced clonic convulsions was measured in rats over the 24-hr light-dark cycle at four-hour intervals. The results showed a higher sensitivity to PTZ around 2200 hr. Other groups of rats were exposed to a four-min open-field session. In the first two min of the session the animals were submitted to open-field environmental stimuli. The next two-min observation occurred with sound and light presented to the animals. Differences through the 24-hr period of the day for both sessions were seen. A reduction in rearing at 2200 hr and increase in defecation at 2200 hr and 0200 hr was observed.