Analysis of ultrasonic vocalizations emitted by intruders during aggressive encounters among rats (Rattus norvegicus).

Determined the ultrasonic vocalizations produced by intruders during aggressive interactions and investigated the role of these signals in agonistic behavior of rats. In Exp I, 7 experienced resident male Long-Evans rats were paired with both devocalized and intact vocalizing naive intruder males (n?=?14). Devocalization of the intruder males resulted in a drastic decrease in 50-kHz vocalizations and the elimination of all 22-kHz vocalizations. This almost total absence of ultrasonic vocalizations was not accompanied by any change in resident aggressive behavior or intruder defensive and submissive behavior. In Exp II, 16 naive intruders were tested with either deafened or intact resident males (n?=?8). Similarly, preventing residents from hearing intruder ultrasounds had no detectable effect on any aggressive behavior. These experiments are not consistent with the correlative evidence that intruder-produced 22-kHz vocalizations inhibit the aggressive behavior of the resident. Results show that most of the ultrasonic vocalizations emitted during aggressive encounters were probably produced by the intruder. (10 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Analysis of ultrasonic vocalizations emitted by residents during aggressive encounters among rats (Rattus norvegicus).

Determined the extent to which aggressive resident rats emit 40–70-kHz vocalizations and the effect of these signals on intruders. In Exp I, 16 deafened and intact intruder male Long-Evans rats were given 2 encounters with 8 resident Ss. Deafened intruders engaged in a higher duration of immobile or freezing postures than intact Ss. Exp II indicated that the augmentation of freezing found among deafened intruders was not due to an inability to detect ultrasounds made by residents since intruders encountering devocalized resident males showed no reliable differences in specific motor patterns from intruders paired with intact residents. Results demonstrate that 40–70-kHz vocalizations were produced almost entirely by intruding Ss since there were no significant changes in occurrence of these calls when resident males were devocalized. (13 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Transitive inference in rats (Rattus norvegicus).

Although Piagetian theory proposes that the ability to make transitive inferences is confined to humans above age 7 yrs, recent evidence has suggested that this logical ability may be more broad based. In nonverbal tests, transitive inference has been demonstrated in preschool children and 2 species of nonhuman primates. In these experiments, evidence of transitive inference in rats is demonstrated. An ordered series of 5 olfactory stimuli (A??E and A?>?F). The possibility that logical transitivity may reflect a form of spatial paralogic rather than formal deductions from a syllogistic–verbal system is discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Food stealing by young Norway rats (Rattus norvegicus).

Six experiments were undertaken to explore factors affecting young rats' (Rattus norvegicus) frequencies of stealing food from conspecifics when identical food is available in surplus. It was found that (a) rats would walk across a bed of pellets to steal the particular pellet a peer was eating, (b) frequency of stealing within a pair did not decrease over days, (c) rats stole unfamiliar foods more frequently than familiar foods, (d) younger rats stole from older rats more frequently than older rats stole from younger ones, (e) hungry rats stole more frequently than replete rats, and (f) rats that had stolen a pellet of unfamiliar food from an anesthetized conspecific subsequently exhibited an enhanced preference for that food. Results suggest that food stealing is a mode of active seeking of information about what foods to eat. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Numerical discrimination by rats (Rattus norvegicus) using body and vibrissal touch.

Three experiments were performed to test if tactile stimuli could serve as the basis for a numerical discrimination in rats (Rattus norvegicus). In Experiment 1, touch delivered symmetrically to both sides of the animal's body yielded no evidence of numerical discrimination. In Experiment 2, the restriction of tactile cues to one side of the animal's body resulted in marginally better results, although performance remained below conventional levels of significance. In Experiment 3, tactile contact with the animal's vibrissae yielded statistically significant evidence of numerical processing. Subjects learned to enter one arm of a Y-maze when three vibrissal deflections were presented, and the other arm when either two or four stimuli occurred. The demonstration of a two-three-four discrimination extends the use of this relatively complex intermediate number procedure from a previous demonstration in rats involving auditory stimuli (Davis & Albert, 1986) and indicates for the first time in any species that touch may be used as the basis for numerical behavior. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Responsiveness to estrous chemostimuli in male rats (Rattus norvegicus) of different ages.

Examined the development of behavioral responsiveness to estrous chemostimuli in 48 male Norway rats from late infancy to adulthood. Preweanling, adolescent, and adult Ss were observed for 20 min in the presence of an anesthetized estrous or an anesthetized diestrous female. This was, for adolescent and adult Ss, the 1st heterosexual encounter since weaning. Ss in each age group responded differentially according to female state, but in distinct, age-related ways: Preweanling Ss spent more time investigating the female's body if she was estrous. Adults expressed the same affinity but by more focused investigation directed perivaginally. Adolescents showed no female-directed bias but groomed themselves more if the female was estrous. These data identify developmental continuities and discontinuities in male rat behavior toward sexually receptive females. (38 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Landmark use by navigating rats (Rattus norvegicus) contrasting geometric and featural information.

Place navigation in the rat is based on an allocentric localization process in which places are recognized in reference to the surrounding environment. However, the nature of the spatial information used for such a process remains unclear. In particular, the relative importance of environmental geometry and of individual landmarks is still a matter of debate. This issue was addressed in rats (Rattus norvegicus, Long-Evans strain) by means of a water maze experiment in which the importance of the identity of landmarks and of their geometric arrangement were compared. Results showed that place navigation appears to be primarily based on the geometric arrangement of landmarks. These results are discussed in the more general context of the construction of spatial representations in rodents. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Recognition of food by individual, food-naive, weaning rats (Rattus norvegicus).

To control and observe first feeding experiences, pups were reared without access to food. At weaning age, individual pups received simultaneous access to a palatable, noncaloric diet and a similar diet containing starch. Each diet contained a flavor cue. Within 20 min of sampling both diets pups preferentially ingested the caloric alternative. Further tests indicated that pups learned a preference for flavor cues paired specifically with ingestion of starch. In caloric discrimination tests in which the diets were not distinguished by artificial flavors, pups did not show the rapid preference for the caloric diet seen in earlier experiments. We suggest that recognition and preference for the caloric diet is based on its rapid postingestive effects rather than readily preferred sensory features of the starch. Our findings demonstrate the abilities of individual, food-naive pups to rapidly recognize food and indicate a role for associative learning in the onset of independent feeding. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Penile responses of rats (Rattus norvegicus) in extended ex copula tests.

Conducted prolonged tests of male Long-Evans rats' penile responses outside the context of copulation (ex copula) to facilitate analysis of these penile components of copulatory behavior. Penile erections and flips were evoked for 1 hr following penile sheath retraction (SR), and Ss were retested for 30 min after a rest interval of 5 min to 4 hr. The number of penile responses declined sharply over the course of 1 hr. Following a 5-min rest, there was little likelihood of additional responses. Within 2 hrs, some measures of penile response potential approached their original high asymptotes: other measures were still depressed after the 4-hr rest. In control tests, the penile sheath was unretracted (SU) during the 1st 60 min, and hence few or no penile responses occurred. This condition caused no reduction in the number of erections and flips in the subsequent 30-min SR test; hence, the reduction in response to potential during and after SR tests was due to the responses displayed, not to the conditions of restraint. Ejaculation occurred frequently in the SU condition but rarely in SR tests. These results suggest that SR may normally inhibit ejaculation in ex copula tests and during copulation. (41 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Visits to starts, routes, and places by rats (Rattus norvegicus) in swimming pool navigation tasks.

In 2 studies, 40 young adult female Sprague-Dawley rats were trained to escape to visible or to hidden platforms in a swimming pool and then given probe trials, which required that they searched for a platform that had been removed or repositioned. Results indicate that to solve the tasks, Ss simultaneously used a number of behavioral strategies including position responses, cue responses, and place responses. On the probe trials, they not only displayed behaviors that were reinforced during training but also displayed novel behaviors. Ss trained on the place task (hidden platform) made more swims across the platform's previous location, whereas Ss trained on the cue task (visible platform) made more returns to previously used start points. Increases in the number of start points produced more returns to start points, whereas increases in the number of platform locations produced more searches for platforms. It is concluded that rats make coextensive use of all relevant strategies to solving spatial navigation tasks and that their search patterns on probe trials reflect both previously reinforced behaviors and novel unconditioned search behaviors. (34 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Cooperative behavior of laboratory rats (Rattus norvegicus) in an instrumental task.

Cooperation is a cognitively demanding, complex social behavior, found primarily in primates. Here we investigated mutualism in rats (Rattus Norvegicus), a simple form of cooperation in which two subjects work on operant task, receiving immediate and simultaneous sucrose reward for a joint action. To receive the sucrose reward, familiar pairs of rats were required to nose poke simultaneously. Following 44 training days, we examined the relation of social contact and ultrasonic vocalizations to the rat's cooperative behavior by testing the effects of inserting opaque, wire-mesh, or no partition - between subjects. Cooperative behavior (simultaneous nose-poking): (a) increased gradually during initial training; (b) decreased with the opaque partition (restricting visual, acoustic, and physical communication); (c) increased with a wire mesh partition restricting only physical contact); and (d) increased with the number of 50 kHz USV “happy” calls and the intensity of social interaction. The possibility of studying the development of cooperative behavior in laboratory rats using a simple procedure based on commercially available equipment may prove useful in modeling determinants of social behavior. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Social identification of toxic diets by Norway rats (Rattus norvegicus).

48 naive female Long-Evans rats (observers) interacted with 2 conspecifics (demonstrators [n?=?96]) that had recently eaten a diet unfamiliar to the observer; ate 2 unfamiliar foods in succession, one of which was the food its demonstrators had eaten; suffered toxicosis; and were offered a simultaneous choice between the 2 diets they had eaten prior to toxicosis induction. During the choice test, observers exhibited an aversion to that diet their respective demonstrators had not eaten. It is suggested that exposure of a rat to conspecifics that have eaten a diet can act, as does actual ingestion of a diet, to reduce that diet's subsequent associability with toxicosis and that interaction with conspecifics may provide an alternative to individual trial-and-error learning in identification of toxic foods by rats that ingest a number of novel foods in succession before becoming ill. (12 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Sexual free behavior in male rats (Rattus norvegicus).

Male rats ( Rattus norvegicus) were given continuous access to estrous female rats for 24 hrs each day for 10 days. During the 1st 12 hrs, the rats achieved an average of 10 ejaculations, followed by a 1- to 2-day period with little sexual activity. During the last 7 days, the rats maintained a reasonably stable equilibrium level of 3 ejaculations per day. These occurred predominantly during the dark phase of the diurnal cycle, they frequently occurred in a cluster, and they usually occurred shortly after the introduction of a novel estrous female. Except for quantitative differences, these results are generally consistent with conventional research but systematically extend the generality of the results to the context of the free behavior situation. The availability of sexual activity had no appreciable effect on food and water intake, but it did decrease the amount of running activity. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The von Restorff effect in rats (Rattus norvegicus).

Two experiments examined the functional equivalence of memory in the rat (Rattus norvegicus) with memory in humans for serially presented items. Memory was assayed with an 8-arm radial maze, in which rats were allowed access to 5 arms of the maze and were then removed. Following a retention interval of 16 min, the rats were replaced in the maze and allowed to retrieve pellets from the 3 unvisited arms. The errors in reentering previously visited arms were noted. Both primacy and recency effects were found as with humans. Presenting a stimulus change after entry to 1 of the maze arms improved recall for that arm relative to when no change occurred. This effect was found using both handling and tone cues, and irrespective of whether the change consisted of presentation or nonpresentation of the cue. These results suggest that rats are subject to a von Restorff-like effect similar to that in humans. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Postsuckling behavioral arousal in weanling rats (Rattus norvegicus).

Twenty-day-old litters and their dams were observed in seminatural habitats consisting of a nest compartment and adjacent open field that contained powdered rat chow. It was found that pups displayed marked bursts of activity after suckling. Independent feeding reliably followed nursing bout termination (Experiment 1). Nipple withdrawal, with or without milk transfer, induced behavioral arousal whereas withdrawal of thermotactile and conspecific odor cues did not (Experiments 2-3). Increased thermogenesis was observed following milk transfer (Experiment 4). Finally, preweanling pups (10- to 12-day-olds) also displayed postsuckling arousal within the confines of the nest; full locomotor expression of this arousal was not evident until weaning age (Experiment 5). It was concluded that postsuckling arousal in weanlings functions to stimulate activities performed away from the nest and suckling, propelling pups into the field where feeding begins. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Risk aversion in rats (Rattus norvegicus) under varying levels of resource availability.

Five male Wistar rats chose between a certain prospect and an uncertain prospect having equal expected value under varying levels of resource (water) availability. In contrast to results found with granivorous birds and common shrews (Sorex araneus), the rats did not switch from risk aversion (choosing the certain prospect) to risk preference (choosing the uncertain prospect) as resource availability varied from surplus to deficit, even though deficits were maintained for extended periods of time. Rather, Ss displayed an approximately constant level of risk aversion throughout. Explanations for these differences are offered in terms of procedural differences between this and earlier studies and in terms of differential behavioral patterns of relatively large organisms with large internal resource stores relative to their daily resource requirements. (15 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Recognition of conspecific odors by laboratory rats ( Rattus norvegicus) does not show context specificity.

This experiment investigated how contextual cues affect recognition of conspecific odors in laboratory rats (Rattus norvegicus). Rats received 5 encounters with the same odor in the same context. For the 6th test encounter, all rats received a simultaneous presentation of the original odor and a novel odor. The authors tested 1 group of rats (context same) in the same context as before. For the remaining 2 groups, the test encounter was in a different context that 1 group (context different) had experienced but that 1 group (context novel) had not. A significant preference to investigate the novel odor by context-same and context-different rats, but not by context-novel rats, suggests that odor recognition can occur following transfer to a different, but familiar, test context, indicating a lack of context specificity. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Olfactory discrimination of individual littermates in rats (Rattus norvegicus).

Tested the ability of 4 adult male Sprague-Dawley rats to use odors in discrimination among littermates living as a group. Ss were trained in a Y-maze to discriminate the presence of a littermate from its absence. Results from transfer of training in 3 subsequent testing periods indicated that the animals were capable of distinguishing among individuals when relatedness and familiarity were held constant, that this ability was not due to training, and that performance was based solely on odor cues. Results suggest that laboratory rats exhibit odor sensitivities conmensurate with very complex social processes. (17 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)     

Numerical competence in rats (Rattus norvegicus): Davis and Bradford (1986) extended.

The task of rats (Rattus norvegicus) was to enter 1 box of a defined ordinal number among an array of boxes. In Experiments 1 and 2, the rats correctly chose the 4th box from arrays of 6 and 12 boxes, respectively. In Experiments 3 and 4, in which the ordinal number of the correct box was increased in a graduated fashion, they were able to select the correct box even when its position was higher than 10th among 12 and 18 boxes, respectively. In Experiment 5, the possibility that the rats had used cues to the openability of the box doors was ruled out. In Experiments 6 and 7, the rats succeeded in the task even when the total number of boxes was varied from trial to trial. In Experiment 8, both small- and large-sized boxes were used to control for the possibility of using the cumulative length of the boxes as a cue. Overall, the results suggest that performance was based on numerical cues. Intentional acts were occasionally observed but appeared not to be essential for solving the task. (PsycINFO Database Record (c) 2010 APA, all rights reserved)