Sex and increasing age as factors in the frequency of audiogenic seizures in albino rats.

Abstract

In a previous paper (1) we reported that the frequency of audiogenic seizures in Wistar albino rats varied with age. This conclusion was based on the observation that in 234 individuals the number of s-nimftls showing one or more attacks in the first five consecutive air blast trials was greatest in a three-week old group, less in a year-old group, and least in a twenty-month group. In the present investigation we have determined the effect of repeated stimulation over a prolonged period. We find that the number of rats reacting, and the number of reactions per rat, decreased as the animals grew older. A sex difference was noted in the susceptibility to attacks. PROCEDURETwo series of albino rats comprising 143 individuals, reared in the Wistar Institute animal colony, were used in this investigation. The first group (Series I), composed of 38 males and 38 females, was subjected to air blasting from 21 to 240 days of age. Similar treatment of Series II (33 males and 34 females) was terminated at 120 days of age. The method of testing was described previously in detail (1), and consists of five minute daily exposures to the sound of an air blast for five days a week.The age of the rats from 21 days on was divided into five day periods.. The total number of attacks in each period was divided by the total possible reactions in the period (i.e., total exposures to the air blast), and the result multiplied by 100 to give the per cent of responses. These data for Series I and II were combined in fig. 1, since both groups have responded thus far in essentially similar fashion. In fig. 2 the per cent of responses was calculated for 20 day periods. Beyond the 120th day the figures belong to Series I animals only.

Effects of early experience upon the behavior of animals.

“…Because of the young animal's unfamiliarity with its environment, and its lack of a learned repertoire of fear-reducing responses, fear in infancy is probably of a greater intensity than similarly produced fear later in life. It is known, for example, that incidence of seizure reactions to air blasts is a decreasing function of age in rats (30,34). In the same manner, defeat in a fight, as occurred in Kahn's study of mice (67), may be a more intense experience for a young animal than for an older one; and for this reason, its traumatic effects might last longer and have a greater influence on subse-quent behavior.…”

The susceptibility of albino and gray Norway rats to audiogenic seizures.

“…The reactions of the grays far exceed those of the albinos. The decrease in percentage of attacks with age, reported by us previously (5) is apparent in the case of the albinos, but is delayed beyond 100 days of age in the grays. The sex difference (i.e., greater susceptibility of the males at an early age) is more pronounced in the grays (5).…”

Effects of oral administration of dilantin sodium on abnormal behavior in the rat.

“…7. During the course of the experiment, there appears to have been a gradual decrease in the incidence of attacks, which may have been due either to adjustment with repeated testing (20), to decreased susceptibility with increase in age (20,21), or less plausibly, to a residual action of the drug.…”