Seizure-refractory period after a single stimulation and inhibition of seizures after repetitive stimulation in the gerbil: Effects on blood cortisollevels

Purpose: To determine the epileptic response of gerbils to external shock s timulus, assessing blood cortisol levels as a parameter to determine stress conditions. Methods: Five sets of two-month-old Mongolian gerbils were stimulated to el icit seizures by the clapping of a sheaf of papers. Stimulation was done on ce 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; th ose stimulated once to obtain samples immediately after seizure recovery; a nd those stimulated once to obtain samples 30 min after seizure recovery. B lood samples from the fifth set of animals were taken in vivo from the retr o-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 kille d without induced seizures were similar to the others, regardless of whethe r the animals had been subjected to repetitive stimulation. Additionally, s ignificant decreases in blood cortisol levels were detected in the animals killed immediately and 30 min after recovering from an induced epileptic ep isode. Conclusions: The normal refractory period in gerbils can be estimated at 1 h. The lack of correlation between cortisol levels and the inhibition of se izure-elicitation through repetitive stimulation supports the environmental and exploratory hypothesis of seizure generation rather than a stress hypo thesis.