Reexamination of spectral mechanisms in the rat (Rattus norvegicus).

Studied the spectral mechanisms of Long-Evans and Zucker rats in electrophysiological and behavioral experiments. The photopic electroretinogram was recorded (a) to rapidly flickering lights, (b) during the cone phase of dark adaptation, and (c) with a flicker photometric procedure. The consistent conclusion from both experiments is that the rat retina contains only a single photopic spectral mechanism. (34 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Paternal behavior in the male Long-Evans rat (Rattus norvegicus).

Five studies examined the paternal behavior of monogamously housed male and female, individually housed male, and virgin male and female Long-Evans rats. Findings indicate that males cohabiting monogamously with females showed low levels of pup contact and parental behavior, and the frequency of these behaviors did not increase with experience, possibly because the lactating females kept the males away from the pups. When presented with pups in their own cage, sexually experienced and naive males did not differ in the latency or frequency of parental behavior, and both groups showed more parental behavior than monogamously housed males. Males that had formerly exhibited infanticide showed as much parental behavior as noninfanticidal males. The frequency of pup contact and parental behavior increased as the pups grew older. Although virgin males showed the same latency as virgin females to exhibit parental behaviors, females showed these behaviors more frequently than males. Results suggest that the responsiveness of noninfanticidal male rats to infants may depend on the test situation and the age of the infants. (45 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Cyclic motor activity in the fetal rat (Rattus norvegicus).

Rat fetuses were observed on Day 20 of gestation using a technique that permits direct observation of fetal behavior. The resulting time series was analyzed to assess cyclic organization in fetal movement. Fetal activity did not occur randomly but showed significant cyclic variation with a mean frequency of 0.61 cycle/min. This finding agrees with studies of human fetuses, which also exhibit short-period cyclicity in motor activity. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Loudness bisection and masking in the rat (Rattus norvegicus).

The bisection method of animal psychophysical scaling was examined as a measurement procedure. The critical assumptions of bisection scaling, as described by J. Pfanzagl (1968), were tested to determine if a valid equal-interval scale could be derived. A valid scale was derived in which loudness for the rat (n?=?13) was a power function of sound pressure for 4-kHz tones. Masking noise reduced the discriminability of tonal stimuli but did not affect the bisection point. This result is consistent with an interval scale representation of loudness and demonstrates scale meaningfulness. Loudness bisection data that have been reported in the literature for 3 species (humans, rats, and pigeons) are in substantial agreement with these results. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Acoustic startle threshold of the albino rat (Rattus norvegicus).

The startle threshold of the albino Sprague-Dawley rat runs parallel to the curve of the hearing threshold. The difference between the startle and hearing threshold is 87 dB (SPL) at a background noise level of 75 dB (SPL). At 110 dB (SPL), the threshold has a range from 2 kHz to 50 kHz with a minimum at 10 kHz and a second minimum at 40 kHz. Amplitude and latency of the startle response are not only dependent on the sensation level of the acoustic stimulus but also on the frequency. At threshold, only the head movement component of the startle response is elicited. (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)     

Milk availability modulates weaning in the Norway rat (Rattus norvegicus).

Beginning on Day 14 postnatally, 368 Sprague-Dawley rat pups were exposed to different levels of milk supply by changing litter size of 10 dams from 8 to 4 or 12 (Exp I) or limiting temporally Ss' access to a lactating dam (1 of 36) to 8, 14, or 24 hrs/day (Exp II). Both manipulations accelerated weaning in milk-deprived Ss. By adding solid food and water to their diet, early weaning Ss compensated for the negative energy consequences of milk reduction and achieved premanipulation growth rates. Milk availability thus appears to affect weaning, and it is suggested that the developmental changes in the nutritive energy balance between mother and offspring contribute to the emergence of independent ingestion. (43 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Development of directional responses to sounds in the rat (Rattus norvegicus).

Exp I examined the tendency of 48 Sprague-Dawley rat pups to approach auditory stimulation. Tests were conducted in a circular maze with a central start area and 8 response areas at the periphery. Stimuli were played back over a loudspeaker behind 1 of 8 response areas. Signals included species calls at high and low intensities. Ss showed a tendency to approach the low-intensity playback of a species "social" vocalization but did not approach the other stimuli. Exp II investigated the importance of binaural cues for localization. 24 pups were tested with 1 or both ears blocked or neither ear blocked. Only the binaurally blocked and normal controls approached the sound source at above chance levels. The failure of Ss in the monaural group to approach the sound probably resulted from a disruption of binaural cues. The ability of Ss to localize sounds and process binaural cues is discussed in relation to the onset of hearing and in terms of physiological responses that are present early in ontogeny. (76 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Olfactory conditioning of sexual behavior in the male rat (Rattus norvegicus).

The role of classical conditioning in the copulatory preferences of male Long-Evans rats (Rattus norvegicus) was examined by pairing a neutral olfactory stimulus (almond odor) with female reproductive status. During training trials, the males were given access to scented or unscented females that were either sexually receptive or unreceptive. Subsequently, copulatory preferences were tested in males given simultaneous access to 2 receptive females, 1 scented and 1 not. Males trained with scented-receptive females displayed an ejaculatory preference for the scented female. Males trained with scented-unreceptive females or with unscented-receptive females displayed an ejaculatory preference for the unscented female. Males displayed no preference when scent and reproductive status were paired randomly. These results demonstrate that classical conditioning produces an ejaculatory preference. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Development of the auditory orientation response in the albino rat (Rattus norvegicus).

The development of head orientation to auditory stimulation was examined in rat pups at Postnatal Days 8, 11, 14, 17, and 20. The animals were tested in a quiet environment with single bursts of 65 dB (SPL) broad-band noise. A reflexive head turn toward the sound was first seen on Postnatal Day 14 and subsequently on Days 17 and 20. This result demonstrates that the onset of directional auditory responses occurred between Day 11 and Day 14. The role of binaural cues in early sound orientation was examined in 17-day-old pups with monaural ligation of the external meatus. These animals were unable to localize a sound source and consistently turned toward the side of the unligated ear regardless of the position of the stimulus. Thus binaural cues were shown to be important for head orientation to sound in early development. In a separate study, head orientation to high and low frequency tone pips was examined. Directional responses were first seen on Day 12 for a 16-kHz tone and Day 14 for a 2-kHz tone. These results indicate an earlier onset for orientation to high frequency sounds in the rat. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Variability in general activity and the expression of complex behavior in the fetal rat (Rattus norvegicus).

Rat fetuses exhibit intrinsic fluctuations in general motor activity and respond to an artificial nipple (AN) with mouthing and oral grasping behavior. The present study examined the relation between the organization of general activity and the expression of these specific responses to an AN on Embryonic Day 21. In Experiment 1, continuous exposure to the AN resulted in nonspecific behavioral activation characterized by an increase in amplitude and high-frequency variability. In Experiment 2, increased amplitude and variability in general activity preceding discrete presentations of the AN resulted in more mouthing and oral grasping responses to the AN. These results suggest that presentation of the AN triggers behavioral reorganization in which the level and variability of overall activity may facilitate expression of well-defined action patterns. (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)     

Individual differences in the behavior of rats (Rattus norvegicus).

Male and female hooded rats were evaluated individually for performance in burrowing, food hoarding, exploration, and insect predation in the laboratory. The results were that (a) performance in each of these behaviors was distributed over a wide range; (b) females as a group had significantly better burrowing and insect predation performance than did males; (c) there were significant correlations between individual performance in each of these behaviors in two series of tests held 30 days apart; and (d) no evident and systematic correlations between individual performance in different kinds of behavior were detected. These and other results in the literature support the idea that behavioral performance in nonprimate mammals is not stereotyped. On the contrary, individuals tend to have conspicuous behavioral interactions with the environment, and this characteristic tends to be stable, under our conditions, for periods of at least 1 month. (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)     

Midline and lateral field sound localization in the albino rat (Rattus norvegicus).

Estimated the normal sensory capacity of 6 albino Sprague-Dawley rats for sound localization in the lateral fields and related this ability to the effects of brain damage on sound localization, as demonstrated in previous studies. Each of the Ss performed at high levels on a midline task but had great difficulty with tests in the left and right fields. Minimum audible angles for midline localization were obtained for 2 Ss and were estimated as 11.5° and 13.5°. Performance levels on the hemifield tests for each of the 6 Ss, however, were too low to permit estimates of threshold even with speakers separated by 60°. It is suggested that for animals that do not have the capacity for detailed sound localization, subcortical mechanisms may be sufficient. For animals that do have the ability to resolve multiple positions in the horizontal plane, auditory cortex may be essential for both lateral field and midline localization. (29 ref) (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)     

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)     

Maternal contributions to sensory experience in the fetal and newborn rat (Rattus norvegicus).

Using videographic analyses, maternal contributions to the sensory environment of the perinatal rat were identified and quantified by analyzing, from the offspring's perspective, the dam's activities during gestation, labor, and delivery. The observations indicate that pregnant females remain highly active during the final week of gestation, as compared with nonpregnant control animals. Exploratory movements, feeding, drinking, self-grooming, and other activities of the rat dam pitch, turn, accelerate, and expose fetuses to mechanical pressures. During parturition uterine contractions and maternal licking and handling provide vigorous tactile and vestibular stimuli to pups. Newly born pups are exposed to intense thermal stimulation, cooling rapidly to the temperature of the postnatal environment. Results suggest that fetal and newborn rats are exposed during development to a broad range of maternally produced stimuli. (PsycINFO Database Record (c) 2010 APA, all rights reserved)