No abstract

The domestication of gray Norway rats through more than 55 generations by Dr. Helen Dean King (1) has not changed fundamentally their feral nature, which, as demonstrated by Keeler and King (2), is associated with coat color genes. Every gray rat of this strain is born with a characteristically wild and savage temperament. However, reports in the literature (3, 4) and experience in our colony (5) have shown that the behavior of the animal may be modified readily by training. Although an untamed rat of this strain will attack anyone attempting to touch it, a young gray handled before weaning becomes accustomed to the treatment within a week or less, and may thereafter, with occasional exceptions, be handled safely with bare hands.Even when tamed, however, a gray Norway rat exhibits behavior that distinguishes it from a Wistar albino rat. One characteristic of the former is a distaste for restraint by hand or in a confining enclosure, which stimulates the animal to more or less vigorous attempts at escape. Another difference may be seen in the effect of sound upon rats of the two strains. Slight noises that elicit little or no observable response in an albino will startle a gray Norway. In general, gray rats, tamed or otherwise, react with overt behavior to stimuli that leave albinos apparently unmoved. Even when the savage element (i.e., tendency to bite) of the gray Norway temperament is suppressed by training, some residuum of wildness, in the sense of ready excitability of the nervous system, remains. Observers familiar with tamed gray rats look upon them as (in anthropomorphic terms) sensitive, nervous, excitable and emotional.As a step in analyzing the temperament of gray Norway rats and in evaluating quantitatively, if possible, the difference in behavior between them and albinos, animals of both strains were subjected to Hall's test of emotionality (6). This test is based upon excretion as a sign of psychic disturbance in animals and is a reliable criterion of individual differences in emotionality. It was anticipated that the rating or scores of gray Norway rats would be uniformly high, indicating extreme emotionality, while those of albinos would range from low to high, with a preponderance of low scores. Actually, the gray rats also covered the entire range of possible scores, with a preponderance of high ones. MATERIAL AND METHODS73 Wistar albino rats (40 males, 33 females) and 73 gray Norways (33 males, 40 females) were tested. The latter were descendants of rats of the forty-third generation of captive gray rats from Dr. Helen Dean King's colony. Ail of the 1 Aided in part by a grant from the Samuel S. Feis Fund.

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.

No abstract

In experiments on audiogenic seizures, we have tested by air blast two strains of inbred rats, the Wistar albino and gray Norway. The latter strain showed, on the average, a decidedly greater frequency of attacks. Analysis of the individual records demonstrated a preponderance of highly susceptible animals among the gray Norways.Rats in these two strains exhibit marked differences in temperament and behavior. The inherited wildness and savageness of gray Norway rats is well known (1,2,3). Gray rats, in order to be made manageable for experimentation, require a regime of handling begun before weaning, which nevertheless does not completely eradicate their innate wildness. It seems likely that the high incidence of audiogenic seizures in gray Norway rats is related in some way to their temperament.