Materials and Methods
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Boxing behavior was shown by rats in the isolation-induced fighting tests, especially following attack sequences, as well as during the shock-induced fighting tests. Calculation of strain differences was made difficult, however, by the experimental design which usually matched home rats against intruders of unlike strains and by the fact that the upright posture of one rat apparently triggers upright posture in the opponent. In order to control for the matching of unlike strains, a comparison was made between the number of minutes of boxing of those pairs of strains which had shown boxing in response to footshock (DA-Irish. DA-DA, and Irish-Irish combinations) to all other pairs of strain combinations. The former combinations averaged 8.0 minutes with boxing in the 20 minute test, while the latter combinations averaged 2.2 minutes with boxing, a difference which was significant at p<.01 by analysis of variance. Hence, strain differences in boxing in response to footshock were paralleled by data from isolation-induced fighting tests.
In the restraint-induced biting tests, isolated animals were significantly more reactive than were animals which had been living together with cagemates. With the exception of Fischer rats, no biting was ever observed in response to restraint of non-isolated males. Among the isolated males, Irish and Fischer rats showed biting, struggling, and vocalization in a significantly higher percentage of cases than did the other strains (78% and 75% biting respectively compared to 0-10%). Whenever biting occurred it was accompanied by struggling, and in all but one case by vocalization as well. Struggling and vocalization, on the other hand, occurred in many cases without biting.
Fischer, Lewis. DA, and Irish home rats showed both bite-and-kick attack and offensive sideways posture. The percentages of Fischer and Lewis rats with bite-and-kick attack (86% and 70%, respectively) were significantly greater than WAG-Rij, and the percentages of Fischer, Lewis, and DA rats in offensive sideways posture (86%,60% and 60% respectively) were also significantly greater. Aggressive behavior was not shown by intruder rats.
WAG-Rij home rats showed deficits in olfactory investigation and scent-marking behavior as shown in Table 2 and Table 3, which may have been related to their deficits in isolation-induced fighting. WAG-Rij intruder rats showed normal levels of olfactory investigation, but home rats showed significantly lower percentages with olfactory investigation during the initial five minutes of the test than did home rats of other strains. The deficit was across three different acts and postures: sniff ano-genital region; sniff-Petri-dish; and aggressive groom. The latter behavior has been included here as olfactory investigation because the active rat appeared to lick and sniff the back of the other rat's neck and head while "grooming" it.
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