Seizure-Refractory Period After a Single Stimulation and Inhibition of Seizures After Repetitive Stimulation in the Gerbil: Effects on Blood Cortisol Levels

Summary: Purpose: To determine the epileptic response of gerbils to external shock stimulus, assessing blood cortisol levels as a parameter to determine stress conditions.
Methods: Five sets of two-month-old Mongolian gerbils were stimulated to elicit seizures by the clapping of a sheaf of papers. Stimulation was done once a week over a 10-week period to obtain a stable situation and a similar response in all the animals. Four of the sets were killed to collect blood samples: those not manipulated; those stimulated twice a day for 5 days; those stimulated once to obtain samples immediately after seizure recovery; and those stimulated once to obtain samples 30 min after seizure recovery. Blood samples from the fifth set of animals were taken in vivo from the retro-orbital plexus.
Results: Eliciting seizures with this stimulus, twice a day in a repetitive way, prevented further induced seizures from the second day of stimulation on. Changes in the gerbils'behavior—from exploratory to escape mode—were also observed. The blood cortisol levels found in the sets of animals killed without induced seizures were similar to the others, regardless of whether the animals had been subjected to repetitive stimulation. Additionally, significant decreases in blood cortisol levels were detected in the animals killed immediately and 30 min after recovering from an induced epileptic episode.
Conclusions: The normal refractory period in gerbils can be estimated at 1 h. The lack of correlation between cortisol levels and the inhibition of seizure-elicitation through repetitive stimulation supports the environmental and exploratory hypothesis of seizure generation rather than a stress hypothesis.