Strain difference in behavioral response to a new environment in rats

Behavioral differences between late preweanling and adult female Sprague-Dawley rat exploration of animate and inanimate stimuli and food

The late preweanling rat has potential as a preclinical model for disorders initially manifested in early childhood that are characterized by dysfunctional interactions with specific stimuli (e.g., obsessive-compulsive disorder and autism). No reports, however, of specific-stimulus exploration in the late preweanling rat are found in the literature. We examined the behavioral responses of normal late preweanling (PND 18-19) and adult rats when presented with exemplars of categorically-varied stimuli, including inanimate objects systematically varied in size and interactive properties, biological stimuli, and food. Preweanlings were faster to initiate specific stimulus exploration and were more interactive with most specific stimuli than adults; the magnitude of these preweanling-adult quantitative differences ranged from fairly small to very large depending upon the stimulus. In contrast, preweanlings were adult-like in their interaction with food and prey. Preweanling response to some stimuli, for example to live pups, was qualitatively different from that of adults; the preweanling behavioral repertoire was characterized by pup-seeking while the adult response was characterized by pup-avoidance. The specific stimulus interactions of preweanlings were less impacted than those of adults by the time of day of testing and placement of a stimulus in an anxiety-provoking location. The impact of novelty was stimulus dependent. The differences in interactions of preweanlings versus adults with specific stimuli suggests that CNS systems underlying these behavior patterns are at different stages of immaturity at PND 18 such that there may be an array of developmental trajectories for various categories of specific stimuli. These data provide a basis for the use of the preweanling as a preclinical model for understanding and medicating human disorders during development that are characterized by dysfunctional interactions with specific stimuli.

Animal models of gene-environment interactions in schizophrenia

The pathogenesis of schizophrenia and related mental illnesses likely involves multiple interactions between susceptibility genes of small effects and environmental factors. Gene-environment interactions occur across different stages of neurodevelopment to produce heterogeneous clinical and pathological manifestations of the disease. The main obstacle for mechanistic studies of gene-environment interplay has been the paucity of appropriate experimental systems for elucidating the molecular pathways that mediate gene-environment interactions relevant to schizophrenia. Recent advances in psychiatric genetics and a plethora of experimental data from animal studies allow us to suggest a new approach to gene-environment interactions in schizophrenia. We propose that animal models based on identified genetic mutations and measurable environment factors will help advance studies of the molecular mechanisms of gene-environment interplay.

Rat strain differences in sleep after acute mild stressors and short-term sleep loss

Genetic and physiological diversity amongst rodent strains provide the potential for developing models that may give insight into factors that regulate sleep in response to environmental challenges. We examined home cage activity, behavioral performance in the open field and sleep after a number of mild stressors (cage change [CC], open field [OF]) and after 1 and 4h of sleep deprivation (1hSD and 4hSD) in rat strains (Fischer 344 [F344], Lewis [LEW], Wistar [WST] and Sprague-Dawley [Sp-D], n=16 per strain) that differ in behavior and sleep. F344 and WST rats had greater home cage locomotion than LEW and Sp-D rats, but F344 rats exhibited the least relative locomotion in OF. In 24h baseline recordings of sleep, strain rankings were LEW=WST=Sp-D>F344 in rapid eye movement sleep (REM), and LEW=Sp-D>F344 and LEW>WST in non-REM (NREM). Compared to baseline, total sleep was reduced in all four strains after CC, OF and 1hSD, but not after 4hSD, in the first hour after treatment. Afterwards, increases in REM and NREM were seen after all treatments with the amount and time course varying across treatments and strains. CC induced the weakest and 4hSD the largest effects on sleep, whereas OF and 1hSD had intermediate effects. Among strains, the more anxious F344 rats exhibited the greatest sleep increases during the light period after OF, 1hSD and 4hSD. The results are discussed with respect to the relationship between behavioral and sleep responses to stressors, and to potential mechanisms underlying the strain differences.

Different effects of diazepam in Fischer rats and two stocks of Wistar rats in tests of anxiety

The behaviour of animals in tests of anxiety varies between strains, even in identical tests and surroundings. To evaluate the results obtained, a more detailed knowledge of the behaviour of different rat strains is indispensable. Identically raised Fischer 344 rats and two stocks of Wistar rats were examined in two animal tests of anxiety: the X-maze and a modified open-field test following diazepam treatment (0.5-4.0 mg/kg). Harlan-Wistar rats were the least 'anxious' when the behaviour of vehicle treated controls was compared. The largest effect of the anxiolytic diazepam, however, was observed in Harlan-Fischer rats. To determine possible reasons for strain and stock differences, plasma concentrations of diazepam and metabolites and concentrations of serotonin (5-HT) in the CNS were measured. Plasma concentrations of diazepam and metabolites differed between the strains with the Harlan-Fischer rats showing higher diazepam concentrations. 5-HT levels in discrete brain regions varied with Harlan-Fischer rats having higher 5-HT concentrations. Strain differences influence the anxiety-associated behaviour of untreated animals and the effect of anxiolytics.