Taste neophobia in individually and socially reared male rats

Behavioural Inhibition and the Age at Social Isolation in Rats

Rats that were socially isolated or group-housed at weaning were re-housed at 51 days of age in either the same housing condition or the opposite housing condition until 91 days and throughout subsequent behavioural testing. Increased resistance to extinction of running in an alley and poorer Hebb-Williams maze learning were found only after social isolation between 23 and 51 days of age. In contrast, slower running to reach the water reward during alley training and lower rearing activity at the beginning of open field testing were evident only in rats that were isolated at the time of testing. As in previous studies, open field hyperactivity was found in rats isolated at weaning but slower emergence latency was found in animals isolated at the time of testing. These findings confirm that the many behavioural effects of social isolation at different ages do not reflect a unitary aetiology. The behaviour of rats isolated at weaning is suggestive of a “disinhibition syndrome” but the precise nature of this syndrome is as yet unclear.

Social learning in a high-risk environment: incomplete disregard for the 'minnow that cried pike' results in culturally transmitted neophobia

Many prey species rely on conspecifics to gather information about unknown predation threats, but little is known about the role of varying environmental conditions on the efficacy of social learning. We examined predator-naive minnows that had the opportunity to learn about predators from experienced models that were raised in either a low- or high-risk environment. There were striking differences in behaviour among models; high-risk models showed a weaker response to the predator cue and became neophobic in response to the control cue (a novel odour, NO). Observers that were previously paired with low-risk models acquired a strong antipredator response only to the predator cue. However, observers that interacted with high-risk models, displayed a much weaker response to the predator odour and a weak neophobic response to the NO. This is the first study reporting such different outcomes of social learning under different environmental conditions, and suggests high-risk environments promote the cultural transmission of neophobia more so than social learning. If such a transfer can be considered similar to secondary traumatization in humans, culturally transmitted neophobia in minnows may provide a good model system for understanding more about the social ecology of fear disorders.

Behavioral effects of bovine lactoferrin administration during postnatal development of rats

We tested the hypothesis that rats consuming bovine lactoferrin (bLf) during postnatal development would show better performance of stressful tasks during adolescence. In the first study, we orally administered bLf (750 mg/kg) once daily between postnatal days 16-34. Rats then underwent a battery of behavioral tests: open field (forced exploration of risky environment), light-dark emergence (voluntary exploration of risky environment), baited holeboard (working and reference memory), food neophobia (preference for familiar versus novel food), forced swim (test for antidepressant efficacy), and shuttle-box escape (learning to escape footshock). bLf-supplemented rats showed less exploration of the risky environment, greater preference for the familiar food odor, and faster escape responses. The effect of bLf on forced-swim behavior depended on sex: immobility increased for males and decreased for females. In the next study, we replaced the forced-swim test with an escape-swim test in which rats learned to use a visual cue to locate an escape platform, and we tested the dose response of bLf on this and the shuttle-box escape test, with subjects receiving vehicle or bLf at 500, 1,000, or 2,000 mg/kg. Under this modified testing battery, improvement of escape from footshock was not observed at any dose. However, males, but not females, showed a significant dose-dependent effect of bLf on acquisition of the water-escape task. On average, males receiving a higher dose mastered the task 20-25 % sooner than rats receiving a lower dose or vehicle. These results offer preliminary evidence that bLf supplementation during development can improve subsequent cognitive performance during stress.

Behavioural and neurochemical effects of post-weaning social isolation in rodents-relevance to developmental neuropsychiatric disorders

Exposing mammals to early-life adverse events, including maternal separation or social isolation, profoundly affects brain development and adult behaviour and may contribute to the occurrence of psychiatric disorders, such as depression and schizophrenia in genetically predisposed humans. The molecular mechanisms underlying these environmentally induced developmental adaptations are unclear and best evaluated in animal paradigms with translational salience. Rearing rat pups from weaning in isolation, to prevent social contact with conspecifics, produces reproducible, long-term changes including; neophobia, impaired sensorimotor gating, aggression, cognitive rigidity, reduced prefrontal cortical volume and decreased cortical and hippocampal synaptic plasticity. These alterations are associated with hyperfunction of mesolimbic dopaminergic systems, enhanced presynaptic dopamine (DA) and serotonergic (5-HT) function in the nucleus accumbens (NAcc), hypofunction of mesocortical DA and attenuated 5-HT function in the prefrontal cortex and hippocampus. These behavioural, morphological and neurochemical abnormalities, as reviewed herein, strongly resemble core features of schizophrenia. Therefore unravelling the mechanisms that trigger these sequelae will improve our knowledge of the aetiology of neurodevelopmental psychiatric disorders, enable identification of longitudinal biomarkers of dysfunction and permit predictive screening for novel compounds with potential antipsychotic efficacy.

Early social isolation decreases the expression of calbindin D-28k and dendritic branching in the medial prefrontal cortex of the rat

Social isolation in rodents is the most well characterized animal model for early stressful experiences and their neurobehavioral consequences. The present study analyzed the effects of early social isolation on the expression of the calcium binding protein calbindin-D28k (CAD) and dendritic arborization in the medial prefrontal cortex (mPFC) of the rat. Sprague-Dawley male rats were reared either under isolation or social conditions from 21 to 51 postnatal days. At the end of this period the animals were behaviorally evaluated in the open-field test, sacrificed, and mPFC serial sections were processed either for immunocytochemical labeling against CAD or Golgi-Cox-Sholl staining. Isolated-reared rats exhibited a dramatic decrease in the number of CAD immunoreactive neurons and a significant dendritic atrophy of layer II/III pyramidal cells in association with a reduced exploratory behavior.

Differential basis of strain and rearing effects on open-field behavior in Fawn Hooded and Wistar rats

Open-field behavior was examined under several conditions in isolation-reared, and socially reared, Fawn Hooded (FH) and Wistar rats. Lighting conditions (red or white light) and complexity (object or no object) were varied: Experiment 1, white light, no object; Experiment 2, red light, no object; Experiment 3, white light, object; Experiment 4, red light, object. The plasma corticosterone (CORT) response to open-field exposure was examined two further experiments. Observation of differences in open-field behavior, resulting from strain or rearing condition, was dependent on both lighting condition and complexity. Differences in exploratory behavior exhibited by isolation-reared rats were best explained by changes in response to novelty, while those in FH, relative to Wistar, rats were primarily due to increased anxiety. Supporting these conclusions, FH rats had enhanced stimulated CORT levels, while isolation rearing was without effect.

Taste preferences, body weight gain, food and fluid intake in singly or group-housed rats

Two behavioral experiments were performed to determine if the housing conditions modify taste preferences, body weight gain, food and fluid intake, and alimentary diurnal pattern in adult male rats. In Experiment 1, a two-bottle 24-h preference test (salt, sweet, sour, bitter solutions versus deionized water) was performed in singly, dually or multiply housed rats. In Experiment 2, the same sapid solutions as Experiment 1 and water were contemporaneously offered to singly, dually, or multiply housed rats. Crowded rats drank more water, sweet solution, and total fluid, but less salt solution than singly or dually housed rats during dark and whole-day periods. All rats preferred sour solution, but not bitter solution, to water. In both experiments, crowded rats gained less body weight and ate less food than dually or isolated rats. These results suggest that the housing conditions influence taste preferences, food and fluid intake, body weight gain, but not alimentary diurnal pattern in rats. An important implication of these results is that in experiments in which appetite and taste are dependent variables, all rats should be housed under the same social and environmental conditions.

Behavioural comparisons between individually- and group-housed male rats: effects of novel environments and diurnal rhythm

Individually-housed rats, when compared with group-housed controls, have been previously shown to be hyper-reactive when exposed to an openfield at the beginning of the dark-phase; this was not due to elevated spontaneous activity. In the present experiments locomotor and rearing activities were determined immediately after exposing animals to a novel environment, and after 6 and 24 h of habituation to the test-environment. Additionally, after 24 h of adaptation, animals' responses towards a modification of the test-environment were examined. Four parallel experiments were carried out, each starting at a different time in the light/dark cycle. Individually-housed rats were hyper-reactive in novel environments and showed a slower habituation at all time points tested. Part of behavioural parameters show clearcut day/night variations, but differences between individually- and group-housed rats do not seem to be influenced by the time of day.