Seizing by Magnesium-Deprived Mongolian Gerbils Given Open Field Tests

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Abstract
Epileptiform seizures of unknown etiology are exhibited by small percentages of Mongolian gerbils in samples drawn from the randomly bred Tumblebrook Farm colony, the major source for these animals in the United States. Because the tendency to seize is heritable, the higher seizure rates reported by several investigators may result from selection and breeding practices used to develop daughter colonies. Seizing has been labelled “spontaneous” in occurrence inasmuch as trivial events can trigger the activity in susceptible gerbils. Further, attempts to relate tendency to seize with visceral or central nervous system disorders, with middle ear infections, and with gross departures from normal dietary status have proved unproductive. Nonetheless, accounts of seizure episodes in gerbils resemble descriptions of magnesium (Mg) tetany in other rodents. In the present study, the effect of Mg-deprivation upon seizure incidence in Tumblebrook Farm gerbils was explored. At age 60 days, 80 gerbils were placed either in an Experimental Group (N = 40) or in two equally sized control groups. All groups held as many males as females. The Experimental Group (Mg-deprived) and Control Group 1 (Mg-repleted) were given open field tests at four-day intervals during 32 days of deprivation/repletion. Control Group 2 (Mg-deprived) was observed in the home cages, but was not otherwise tested. The combination of predisposing factors secondary to hypomagnesaemia and of precipitating factors (field tests) led to a total of 34 seizures by 25 gerbils and to 24 deaths within the Experimental Group. In contrast, a single animal in the two control groups seized during the 32-day period, and only one gerbil died. The findings permit speculation that the inherited tendency to seize “spontaneously” in certain gerbils fed stock rations is associated with inefficient magnesium metabolism.