Habitat selection and burrow construction by wild Rattus norvegicus in a landfill.

A portion of a large sanitary landfill that had recently harbored a population of wild Rattus norvegicus was examined for signs of rat activity. All sites of digging activity by rats were excavated, and detailed measures on 36 chambered burrows were recorded. Ss selected burrow sites that minimized the travel distance to the major food source and a permanent water supply. They also invariably chose to dig burrows on sloping terrain and exhibited a strong preference for constructing burrows in loose soil that was easy to dig. (10 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Defensive behaviors of laboratory and wild Rattus norvegicus..

Examined in 2 studies, with 29 wild rats, 15 Long-Evans laboratory rats, and 11 1st-generation offspring from 3 sets of wild-trapped parents, the defensive repertoire of wild rats in a variety of situations and compared these behaviors with those of domestic rats under identical conditions. Analysis of the defensive behaviors of wild rats to an inescapable approaching threat stimulus (the experimenter) indicated a pattern of freezing to distant stimuli, giving way to vocalization, jumps, and jump attacks at shorter defensive distances. Comparisons of the defensive reactions of wild-trapped and laboratory-bred wild rats to a variety of threatening stimuli, in escapable and inescapable situations, indicated that the 2 wild strains were similar and consistently more defensive than laboratory rats to both human and conspecific threat stimuli. Results suggest that the defensive behaviors of rats have been substantially reduced during the process of domestication, with relatively little of this reduction being attributable to housing in standard laboratory conditions. (29 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Life-span changes in the copulatory behavior of male rats (Rattus norvegicus).

Studied the copulatory behavior of 36 5-, 10-, 15-, and 20-mo old sexually naive male Long-Evans rats during 2-hr tests with receptive females. There was no apparent change in sexual arousal as measured by latency to initiate copulation across age, with Ss from all groups exhibiting comparable latencies to 1st mount and 1st mount with intromission. The numbers of ejaculations achieved were also similar across ages. Significant age differences were found for frequency of mounts, with 20-mo olds having the highest mean frequency. The persistent mounting by older Ss appeared to account for significant group differences in interintromission interval and ejaculation latency. It is suggested that motor deficits may impair the ability of older Ss to achieve intromission, increasing the number of mount bouts as well as the number of mounts for each bout, thus extending the length of each copulatory series. (31 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Ultrasonic vocalizations of defeated male rats.

Used the resident–intruder aggression paradigm in 6 experiments to investigate the conditionability of 20–25 kHz vocalizations of defeated male Long-Evans hooded rats (territorial intruders). 90% of intruding males consistently emitted ultrasounds in the presence of an inaccessible aggressive male with which they had received repeated defeat experiences (4–22 attacks). Intruders tested 1 wk after initial conditioning emitted 20–25 kHz calls of comparable latency and number in the presence of familiar and unfamiliar aggressors. Defeated Ss emitted few or no ultrasonic calls in response to male or female castrates, immobilized aggressive males, anosmic males, or the soiled bedding material of an aggressor's home cage. Vocalizations by aggressors (45–70 kHz) were not required to stimulate production of 20–25 kHz signals of defeated Ss. Though olfactory cues alone were not sufficient to elicit ultrasonic vocalizations, they appeared to be an important part of the stimulus complex capable of consistent elicitation. (42 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effect of lysine-8-vasopressin on retention and retrieval of a discrimination reward task in the rat.

The effect of vasopressin on memory of a brightness discrimination reward task was investigated in 20 male Sprague-Dawley rats. Two measures of retention were used: resistance to extinction and savings scores on a reacquisition task given 45 days after the completion of extinction training. The effect of the peptide on both memory consolidation and retrieval was assessed. There were 2 major findings: (a) The peptide enhanced memory consolidation of the task whether measured after a short time interval (6 days) or after a long time interval (45 days after completion of extinction training) using a measure of trials to relearn the task, and (b) the peptide had no effect on memory retrieval. These results were compared to those of other studies designed to access memory consolidation and retrieval on appetitive tasks. The mechanisms of the peptide's effect on memory was briefly discussed with respect to three theories on the subject. This study extends the vasopressin research on memory consolidation by suggesting that it pertains to appetitive as well as to aversive tasks. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Structure, contents, and distribution of roof rat (Rattus rattus) burrows in a rain forest.

Examined roof rat burrows in a 50-acre area of rain forest on the island of Oahu, Hawaii. All burrows were constructed on sloping ground and were spaced farther apart from one another than were other sites of digging activity. Few burrows contained nest material or food, but clusters of opened macadamia and kukui nuts were found at feeding stations that were assumed to protect the animal from predation while it was eating. Comparisons of the present data with those from several studies of Rattus norvegicus indicate that the burrows of both species are similar in overall construction and design. (30 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Time course of postpartum aggression in rats (Rattus norvegicus).

The time course of postpartum aggression was examined in primiparous Long-Evans rats (N?=?77). Individually housed lactating females (n?=?7 per condition) were randomly assigned to 1 of 11 conditions (day of testing), with each subject tested once between Day 0 (the day of parturition) through Day 20 postpartum. Duration of aggression was highest and latency to attack was shortest on Day 0, with all dams attacking an unfamiliar intruding male during 10-min tests. The proportion of dams engaging in attack remained high through the end of the first week of lactation, but decreased sharply during the third week postpartum. The findings indicate that the probability and intensity of maternal aggression is closely associated with the time since parturition at which tests are given. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Copulation and intermale aggression in rats.

Exp I observed attack behavior of 9 reliably aggressive male Long-Evans rats against unfamiliar male intruders immediately following copulation to one or more ejaculations. Copulatory series to 5 ejaculations did not differ from copulation to a single ejaculation or from a noncopulatory control in affecting aggressive behavior. Repetitive biting attacks occurred in all conditions, with comparable wounding. Evidently, the male postejaculatory state of insensitivity to sexual stimuli does not extend to stimuli eliciting intermale aggression. A 2nd experiment determined the attack-eliciting capacity of foreign males placed in the home cage of an actively copulating S. As intromissions increased and the interval to ejaculation decreased, the probability of intermale aggression and interruption of copulation diminished. Findings suggest that a postejaculatory mechanism for behavioral inhibition exists in the male rat, preventing his interference with fertilization but without affecting his capacity to prevent other males from attempting to displace the fruits of his labors. (34 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)