Lack of Interference in Long-Term Memory for Socially Learned Food Preferences in Rats (Rattus norvegicus).

Outside the laboratory, rats (Rattus norvegicus) are likely both to interact with several conspecifics that have eaten various foods and to eat a variety of foods themselves before they encounter any particular food for which they have a socially enhanced preference. Here the authors examine the stability of rats' socially learned food preferences following 6 days of potentially disruptive ingestive experiences. The authors found that 6 days of (a) eating unfamiliar foods, (b) interacting with demonstrators that had eaten unfamiliar foods, or (c) both eating unfamiliar foods and interacting with demonstrators that had eaten those foods had no measurable effect on rats' socially learned food preferences. The stability of socially enhanced food preferences over time and despite potentially disruptive experiences is consistent with the view that social learning about foods is an important determinant of the food choices of free-living Norway rats. (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)     

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)     

Effects of spatial food distribution on search behavior in rats (Rattus norvegicus).

To analyze how search strategies are adapted according to the geometric distribution of food sources, the authors submitted rats to a search task in which they had to explore 9 food trays in an open field and avoid visiting already-depleted trays. Trays were spatially arranged in 4 independent configurations: a cross, a 3 × 3 matrix, 3 clusters of 3 trays each, and a random configuration. Rats exhibited differential search efficiency as a specific effect of the susceptibility of the configurations to being explored in a principled way: Crosses were first, matrices or clusters were in the middle, and random configurations were last. Although no exhaustive searches or highly principled patterns were observed in any of the configurations, performances improved as the sessions went by. Thus, structural affordances of the environment influence the construction not only of search strategies but also of information linked to where the reward is. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Sex differences in urinary odors produced by young laboratory rats (Rattus norvegicus).

Examined the responses of 75 primiparous Long-Evans rat dams and 20 nonmaternal Long-Evans females to male and female pup urine in 3 experiments. Investigatory sniffing of male and female pup urine deposits by maternal Ss was compared in a series of simultaneous choice tests given at 3-day intervals between Day 2 and Day 17 postpartum. Male urine was consistently preferred. Introduction of male but not female pup urine to the nest was found to significantly elevate maternal licking of anogenital regions of pups. Thus, urine from pups of various ages contains sex-identifying odors that differentially elicit spontaneous maternal interest. The odor of male urine may provide a sufficient stimulus to account for the greater anogenital licking that males of this species normally receive. Nonmaternal, naive, adult Ss behaved like maternal Ss, preferring male urine in the choice test, which indicates that the maternal condition of a dam is not necessary either for the olfactory discrimination or for the male odor preference. (13 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The influence of preexperimental experience on social discrimination in rats (Rattus norvegicus).

The authors used laboratory rats (Rattus norvegicus) of known relatedness and contrasting familiarity to assess the potential effect of preexperimental social experience on subsequent social recognition. The authors used the habituation-discrimination technique, which assumes that multiple exposures to a social stimulus (e.g., soiled bedding) ensure a subject discriminates between the habituation stimulus and a novel stimulus when both are introduced simultaneously. The authors observed a strong discrimination if the subjects had different amounts of preexperimental experience with the donors of the 2 stimuli but a weak discrimination if the subjects had either equal amounts of preexperimental experience or no experience with the stimuli. Preexperimental social experience does, therefore, appear to influence decision making in subsequent social discriminations. Implications for recognition and memory research are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Sex and social play in juvenile rats (Rattus norvegicus).

Four experiments were conducted to examine the effects of pretest social isolation, sex of the social stimulus, and test cage familiarity on sex differences in play fighting in 156 juvenile Long-Evans rats. Reliable sex differences were found only when Ss were tested after 6 days of isolation in undisturbed cages (Exp III). In contrast to weak sex effects, pretest isolation and test cage familiarity were robust variables influencing levels of play fighting in juveniles of both sexes. Results are discussed in reference to procedural differences among experimental approaches that have examined sex differences in social play. It is suggested that social investigatory behavior and play behavior appear to be reciprocally related. Hence, the sex difference in social play is accompanied by an apparent reversal in the sex effect seen with social investigation. (28 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Interdose interval effects on the development of contextual tolerance to nicotine's analgesic effects in rats (Rattus norvegicus).

Learning models of associative and nonassociative drug tolerance predict that the development of contextual tolerance to drug effects is disrupted when the drug is delivered at short interdose intervals (IDIs). The authors examined the impact of 1 long IDI and 2 short IDIs in the development of contextual nicotine tolerance. Associative tolerance was investigated by giving rats (Rattus norvegicus) 10 subcutaneous injections of nicotine at either long (72-hr) IDIs or short (6-hr and 4.5-hr) IDIs. The delivery of nicotine was either explicitly paired or explicitly unpaired with a distinctive context. A 3rd group of rats was exposed to the experimental procedures but received only saline. Associative tolerance to nicotine's analgesic effects was defined as a shift to the right of the dose-response curve (DRC) of rats in the explicitly paired condition with respect to the DRC of rats in the explicitly unpaired condition. Analgesia was assessed with the tail-flick and hot-plate devices. In the tail-flick assessment, associative tolerance was evident in the 72-hr and the 6-hr IDI conditions only. In the hot-plate assessment, associative tolerance was present in the 72-hr IDI condition only. The findings suggest that contextual tolerance to nicotine's analgesic effects are positively related to IDI length and are more readily demonstrated with the tail-flick method than with the hot-plate method. Overall, the results supported the thesis that nicotine tolerances that develop to different IDIs are qualitatively different and may be mediated by different psychological and physiological mechanisms. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Temporal integration as a function of signal and gap intensity in rats (Rattus norvegicus) and pigeons (Columba livia).

Previous data suggest that rats (Rattus norvegicus) and pigeons (Columba livia) use different interval-timing strategies when a gap interrupts a to-be-timed signal: Rats stop timing during the gap, and pigeons reset their timing mechanism after the gap. To examine whether the response rule is controlled by an attentional mechanism dependent on the characteristics of the stimuli, the authors manipulated the intensity of the signal and gap when rats and pigeons timed in the gap procedure. Results suggest that both rats and pigeons stop timing during a nonsalient gap and reset timing after a salient gap. These results also suggest that both species use similar interval-timing mechanisms, influenced by nontemporal characteristics of the signal and gap. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Contributions of endothermy to huddling behavior in infant Norway rats ( Rattus norvegicus) and Syrian golden hamsters ( Mesocricetus auratus).

Infant Syrian golden hamsters (Mesocricefus auratus) do not exhibit endogenous heat production before 3 weeks of age and do not huddle effectively during cold exposure, gaining little thermoregulatory benefit from the presence of multiple littermates. In contrast, infant Norway rats (Rattus norvegicus) produce heat endogenously and are effective at maintaining elevated body temperatures by huddling. Therefore, the ineffective huddling of infant hamsters may be due to the absence of endogenous heat production. The huddling behavior of infants in mixed huddles of 8-day-old hamsters and weight-matched 4-5-day-old rats was observed to explore this possibility. The results indicate that hamsters, even when cold, effectively gain access to heat-producing rats, supporting the idea that endothermy contributes to the behavior of huddling by providing heat to each individual and thermal stimuli to other infants to support aggregation. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Habituation of the hiding response to cat odor in rats (Rattus norvegicus).

Cat odor-induced hiding was examined in rats (Rattus norvegicus) using an apparatus with a "hide box" at one end and a piece of a worn cat collar at the other end. Rats spent most of their time hiding on exposure to the cat collar, but this response gradually habituated over repeated daily exposures. Hiding was reversed by administering the anxiolytic drug midazolam (0.375 mg/kg). Rats showed increased anxiety on the elevated plus-maze after exposure to the collar. This response was absent in habituated rats, suggesting that habituation of hiding reflects decreased odor-induced anxiety. It was established that rats located in the hide box of the apparatus might not have detected the odor of the cat collar placed at the other end of the apparatus. This implies that habituation occurs after relatively modest levels of odor exposure. Overall, the results cast some doubt on claims that predatory odors in rats are akin to phobic stimuli in humans. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Influence of sex, estrous cycle, and drug-onset age on cocaine self-administration in rats (Rattus norvegicus).

The influence of sex, phase of the estrous cycle, and age of drug onset on cocaine self-administration was examined. Adult male, adult female, and adolescent male rats (Rattus norvegicus) were evaluated using low fixed-ratio (FR) schedules of drug delivery with a single fixed cocaine unit dose or a range of cocaine unit doses with a single FR schedule. Sex differences in adults were observed for mg/kg consumption of the 3.0-mg/kg unit dose, with consumption being significantly less in estrus females than in males. Over the estrous cycle, mg/kg consumption of this unit dose was significantly less during estrus than during metestrus-diestrus. Differences due to age of drug onset were also observed, with mg/kg consumption of the 3.0-mg/kg unit dose being significantly less in adolescent males than adult males or adult females during metestrus-diestrus. In contrast, these various groups did not have significantly different mg/kg intakes of cocaine unit doses     

Effects of neonatal handling on playfulness by means of reversal of the desire to play in rats (Rattus norvegicus).

In the present study the authors sought to establish whether the range of effects of neonatal handling stimulation (H), that is, brief daily periods of infant isolation, could be extended to the domain of social motivation. With this aim, the authors studied the innate motivation to engage in rough-and-tumble play (R&T) in adolescent rats (Rattus norvegicus) by means of a reversal design, in which half of the rats were first housed in isolation (Days 1–3), and then in company (Days 4–6), while the other half followed the reverse sequence of housing conditions. Results showed in a clear-cut manner that H fuelled playfulness, as measured by pin and dorsal contact episodes, with (relative) independence of trait-based differences in fearful behavior between handled and nonhandled rats. Given that the different levels of the rat’s social brain are apparently sensitive to tactile stimulation in infancy, the authors propose that the vibrant R&T reported here could reflect an enduring alteration of genetically based, motivational systems underlying playfulness and, perhaps, positive social emotions like joy. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Exposure to various stressors alters preferences for natural odors in rats (Rattus norvegicus).

Male Sprague-Dawley rats were given choice tests (Test 1) in a maze with the odors of clean bedding, citronella, an alpha colony (ACO), shocked conspecifics (SCO), or a predator cat (PCO). In Exps 1–3, groups were exposed to no stress, defeat by a conspecific, or shocks. During subsequent tests (Test 2), nonstressed rats showed no change in odor preferences; defeated rats showed a nonsignificant reduction in preference for ACO; and shocked rats showed significant preference reductions for SCO and PCO and a significant increase in preference for ACO. In Exp 4, odors of isolated, nonstressed conspecifics (CO) were preferred more than ACO, for rats given shock before Test 2. In Exp 5, rats significantly preferred CO over ACO when exposed to a caged cat during Test 2. Because of exposure to stress, rats later avoided certain fear odors and showed strong preferences for the odors of nonstressed CO. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Comparison of spatial learning in woodmice (Apodemus sylvaticus) and hooded rats (Rattus norvegicus).

The spatial learning of woodmice and rats was examined in two different experiments. In the Morris place navigation task, the woodmice were slower to escape and took more circuitous routes than did the rats. However, in a special probe trial their accuracy in swimming repetitively through the position of the absent training platform was comparable to that of the rats. In the second experiment, subjects were allowed to escape from a large arena through a hole connected with their home cage. Rats and woodmice learned this task in few trials. In a special trial with no connected hole, subjects of both species showed accurate searching behavior in and around the hole of the training location. However, only the rats developed direct approaches in a systematic manner. These differences are discussed in the contexts of the species specific constraints that might affect the acquisition of direct approaches in a wild species. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of caloric, protein, and sodium deprivation on the affiliative behavior of Norway rats (Rattus norvegicus).

The tendency of food-deprived, protein-deprived, and sodium-deprived Norway rats (Rattus norvegicus) and their respective controls to affiliate with conspecifics deprived of either food, protein, or sodium was examined. We found that (a) independent of internal state, focal rats offered a forced choice between protein-deprived and protein-replete target rats spent more time near replete than deprived target rats; and (b) both food-deprived and sodium-deprived focal rats offered a forced choice between food-deprived and replete target rats spent less time near fasted rats than did well-fed and sodium-replete focal rats. The data indicate that (a) rats can distinguish both food-deprived and protein deprived rats from replete rats and (b) the deprivation states of rats can affect their willingness to affiliate with deprived conspecifics. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Developmental expression of defensive responses during exposure to conspecific adults in preweanling rats (Rattus norvegicus).

Examined preweanling rats' (Rattus norvegicus) expression of ultrasounds and secretion of adrenocorticotrophic hormone (ACTH) when exposed to unfamiliar adult male rats or to their mothers. Pups at 7 days of age produced similar levels of ultrasonic vocalization near both unfamiliar males and mothers. However, these pups could discriminate familiar from unfamiliar adults because ACTH was significantly higher in pups near adult males than in those near mothers. At 14 days of age, pups avoided adult males but not their mothers; therefore, adult males represented a significant threat. Importantly, 14-day-old rats significantly reduced ultrasound production only when near adult males. Pups at 21 days of age no longer emitted ultrasounds when socially isolated or when near conspecific adults. In addition, 14- and 21-day-old rats produced similar elevated ACTH levels across stimulus conditions. Results show significant changes in preweanling rats' responses to conspecific adults. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Sex differences in investigatory and grooming behaviors of laboratory rats (Rattus norvegicus) following exposure to novelty.

Prior research suggested that during exposure to novel stimuli, rodent investigation and self-grooming behaviors may be sexually dimorphic and interact with ambient illumination. To test this notion we compared the behavior of adult male and female groups of Long-Evans hooded rats in normal room lighting (860 lx) and in very dim, red light (0.2 lx) following exposure to a novel juvenile conspecific. Illuminance level had little or no effect, but investigatory and subsequent self-grooming behaviors of males were substantially greater than those of females, and females engaged in greater ambulatory activity than did males. In a second experiment adult males and females were exposed to a novel inanimate object. No reliable sex differences were observed. We conclude that social novelty, as provided by exposure to a juvenile conspecific, stimulates greater investigation and postinvestigatory self-grooming than exposure to a novel inanimate object and that exposure to novel conspecifics presents a useful method for the investigation of sex differences, gonadal hormone effects, and interactions of hormones with neurotransmitter systems governing motor control systems. (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)     

Combined glossopharyngeal and chorda tympani nerve transection elevates quinine detection thresholds in rats (Rattus norvegicus).

Using a conditioned shock avoidance procedure, behavioral quinine hydrochloride thresholds were measured before and after glossopharyngeal (GLX), chorda tympani (CTX), or combined glossopharyngeal and chorda tympani (GLX?+?CTX) transection, as well as after sham surgery. In Experiment 1, thresholds in the sham, CTX, and GLX rats (Rattus norvegicus) either improved (lowered) or remained the same after surgery. In Experiment 2, GLX?+?CTX caused a pronounced 1.5 log?0 unit increase in presurgically measured thresholds. Neither the glossopharyngeal nor the chorda tympani nerve is necessary for normal sensitivity to low quinine concentrations provided the other is intact. When both of these nerves are transected, however, the remaining afferent input is not sufficient to maintain normal detection performance. (PsycINFO Database Record (c) 2010 APA, all rights reserved)