Differential movement patterns but not amount of activity in unconditioned motor behavior of Fischer, Lewis, and Sprague-Dawley rats

Welfare Challenges Influence the Complexity of Movement: Fractal Analysis of Behaviour in Zebrafish

The ability to assess welfare is an important refinement that will ensure the good condition of animals used in experimentation. The present study investigated the impact of invasive procedures on the patterns of movement of zebrafish (Danio rerio). Recordings were made before and after fin clipping, PIT tagging and a standard pain test and these were compared with control and sham handled zebrafish. The fractal dimension (FD) from the 3D trajectories was calculated to determine the effect of these treatments on the complexity of movement patterns. While the FD of zebrafish trajectories did not differ over time in either the control or sham group, the FDs of the treatment groups reduced in complexity. The FD of fish injected with different strengths of acetic acid declined in a dose-dependent manner allowing us to develop an arbitrary scale of severity of the treatments. The 3D trajectory plots from some groups indicated the presence of repetitive swimming patterns akin to stereotypical movements. When administered with lidocaine, which has analgesic properties, the movement complexity of fin clipped fish reverted to a pattern that resembled that of control fish. Fractal analysis of zebrafish locomotion could potentially be adopted as a tool for fish welfare assessment.

Patterns of motor activity in spontaneously hypertensive rats compared to Wistar Kyoto rats

BACKGROUND

Increased motor activity is a defining characteristic of patients with ADHD, and spontaneously hypertensive rats have been suggested to be an animal model of this disorder. In the present study, we wanted to use linear and non-linear methods to explore differences in motor activity patterns in SHR/NCrl rats compared to Wistar Kyoto (WKY/NHsd) rats.

METHODS

A total number of 42 rats (23 SHR/NCrl and 19 WKY/NHsd, male and female) were tested. At PND 51, the animals' movements were video-recorded during an operant test procedure that lasted 90 min. Total activity level and velocity (mean and maximum), standard deviation (SD) and root mean square successive differences (RMSSD) were calculated. In addition, we used Fourier analysis, autocorrelations and two measures of complexity to characterize the time series; sample entropy and symbolic dynamics.

RESULTS

The SHR/NCrl rats showed increased total activity levels in addition to increased mean and maximum velocity of movements. The variability measures, SD and RMSSD, were markedly lower in the SHR/NCrl compared to the WKY/NHsd rats. At the same time, the SHR/NCrl rats displayed a higher complexity of the time series, particularly with regard to the total activity level as evidenced by analyses of sample entropy and symbolic dynamics. Autocorrelation analyses also showed differences between the two strains. In the Fourier analysis, the SHR/NCrl rats had an increased variance in the high frequency part of the spectrum, corresponding to the time period of 9-17 s.

CONCLUSION

The findings show that in addition to increased total activity and velocity of movement, the organization of behavior is different in SHR/NCrl relative to WKY/NHsd controls. Compared to controls, behavioral variability is reduced in SHR/NCrl at an aggregate level, and, concomitantly, more complex and unpredictable from moment-to-moment. These finding emphasize the importance of the measures and methods used when characterizing behavioral variability. If valid for ADHD, the results indicate that decreased behavioral variability can co-exist with increased behavioral complexity, thus representing a challenge to current theories of variability in ADHD.

Locomotory patterns, spatiotemporal organization of exploration and spatial memory in serotonin transporter knockout mice

Serotonin transporter knockout (SERT-/-) mice are extensively used as a genetic model of several neuropsychiatric disorders, and consistently display anxiety-like behaviors and inactivity in different tests. To better understand how these mice organize their behavior, we assessed the open field and elevated plus maze spatiotemporal patterning of activity in adult male SERT wild type (+/+), heterozygous (+/-) and -/- mice on C57BL/6J genetic background using new videotracking and analytic procedures. In addition, we analyzed their spatial memory, assessing within- and between-trial habituation, and examined specific motor characteristics of their movement in these two tests. In the open field test, SERT-/- mice showed reduced vertical exploration throughout the arena, reduced central (but not peripheral) horizontal exploration, unaltered within-trial habituation, and slightly poorer between-trial habituation for horizontal activity. In the elevated plus maze, SERT-/- mice demonstrated anxiety-like avoidance of open arms, hypoactivity, as well as unaltered within-trial and between-trial habituation (except for poorer between-trial habituation of total horizontal activity). In both tests, SERT-/- mice showed greater prevalence of horizontal over vertical dimension of their exploration in the areas protected by the walls (open field periphery, plus maze closed arms), but not in open aversive areas, such as the center of the open field or center or open arms of the maze. In both arenas, SERT-/- mice consistently displayed increased turning behavior, potentially representing a perseverance-like phenotype or aberrant spatial strategies in novel environments. Overall, using a fine-graded behavioral analysis in two different novelty tests, this study revealed alterations in motor and spatiotemporal patterning of activity in SERT-/- mice. Given the relevance of exploratory strategies to human personality traits and brain disorders, our data may be useful for developing further neurobehavioral models using these mice.

Early androgen treatment influences the pattern and amount of locomotion activity differently and sexually differentially in an animal model of ADHD

Higher testosterone level in males is one of the most obvious possibilities for the development of a clear gender difference in ADHD. The present study focused on the influence of excessive androgen exposure in the developmental stage on the hyperactivity feature of ADHD. The study used the spontaneously hypertensive rat (SHR) as an animal model. The amount of locomotion activity previously used as an over-activity measure in the SHR has resulted in a complicated picture. While the general activity level of SHR was significantly higher than its progenitor-the Wistar Kyoto rat (WKY), comparative differences with the Wistar rat could be observed only under certain experimental conditions. The present study applied the scaling approach to assess open field behaviors from a qualitative aspect. Although SHR and Wistar rats showed similar locomotion amounts, movement patterns differed significantly, as indicated by the spatial scaling exponent. Androgen treatment during the early postnatal developmental stage significantly increased total path lengths only in the male SHR. Effects of the hormone manipulation were not expressed in the scaling measurement. The scaling approach conclusively provides a different aspect of open field behaviors and also reacts differently as the total path length to excessive early testosterone exposure.

Differential Effects of Alcohol Consumption and Withdrawal on Circadian Temperature and Activity Rhythms in Sprague-Dawley, Lewis, and Fischer Male and Female Rats

BACKGROUND

Hypothalamic synthesis and secretion of corticotropin-releasing hormone (CRH), a putative mediator of various behavioral and physiological responses to ethanol (EtOH), is defective in inbred Lewis (LEW) rats in comparison with their genetically related inbred Fischer 344 (F344) and outbred Sprague-Dawley (S-D) strains. We aimed to characterize the effects of continuous EtOH consumption and withdrawal on circadian patterns of body temperature and spontaneous locomotor activity in males and females of these 3 strains.

METHODS

Adult LEW, F344, and S-D males and randomly cycling females were fed an EtOH-containing liquid diet or the control (pair-fed or lab chow and water) diet for 14 days. Biotelemetric body temperature data for the last 3 days of EtOH diet feeding and the first 3 days of withdrawal were subjected to cosinor analysis of the circadian rhythm parameters of midline-estimating statistic of rhythm (MESOR), amplitude, and acrophase. Mean dark-phase activity during these periods was also computed.

RESULTS

In the control diet condition, the MESORs and amplitudes of LEW males were lower than those of F344 males. MESORs of rhythms of LEW females were lower than those of both F344 and S-D females. Ethanol consumption caused hypothermia with reduced MESORs and amplitudes of LEW and F344 males and amplitudes of F344 and S-D females. Upon withdrawal, MESORs of the males increased during each day as the amplitudes decreased, reflective of their initial withdrawal-induced dark-phase hypothermia, which was most pronounced in the LEW males, followed by light-phase hyperthermia. MESORs of females were not affected by withdrawal; their amplitudes were differentially affected. Acrophase of LEW males shifted from dark to light on the first day of withdrawal. All rats responded to EtOH exposure with a reduction of dark-phase spontaneous locomotor activity and an immediate increase upon withdrawal.

CONCLUSIONS

Body temperature rhythms of the males were generally more affected by EtOH consumption and withdrawal than the females; within each sex, LEW and F344 rats differed significantly. The specific hormonal factors that mediate the differential temperature responses remain to be defined.

Fractal analysis of animal behaviour as an indicator of animal welfare

Animal welfare assessment commonly involves behavioural and physiological measurements. Physiological measures have become increasingly sophisticated over the years, while behavioural measurements, for example duration or frequency, have changed little. Although these measures can undoubtedly contribute to our assessment of an animal's welfare status, a more complex analysis of behavioural sequences could potentially reveal additional and valuable information. One emerging methodology that could provide such information is fractal analysis, which calculates measures of complexity in continuous time series. Its previous application in medical physiology suggested that it could reveal ‘hidden’ information in a dataset beyond that identified by traditional analyses. Consequently, we asked if fractal analysis of behaviour might be a useful non-invasive measure of acute and chronic stress in laying hens and in pigs. Herein, we outline our work and briefly review some previous applications of fractal analysis to animal behaviour patterns. We successfully measured novel aspects of complexity in the behavioural organisation of hens and pigs and found that these were stress-sensitive in some circumstances. Although data collection is time consuming, the benefit of fractal analysis is that it can be applied to simple behavioural transitions, thereby reducing subjective interpretation to a minimum. Collectively, the work to date suggests that fractal analysis — by providing a novel measure of behavioural organisation — could have a role in animal welfare assessment. As a method for extracting extra information from behavioural data, fractal analysis should be more widely examined in animal welfare science.

The relative playfulness of juvenile Lewis and Fischer-344 rats

The relative playfulness of inbred Lewis and Fischer-344 rats was characterized. Fischer rats were consistently less playful than Lewis rats, with rats of this strain less likely to initiate playful interactions with either responsive or unresponsive partners and also less likely to respond playfully when playful solicitations were directed to them. While less playful, Fischer rats were more socially inquisitive than Lewis rats when tested with an unresponsive partner, suggesting that Fischer rats are less likely to escalate a social encounter into a playful one. Strain differences in playful responsiveness were present with or without prior social isolation, suggesting that this aspect of play represents a relatively stable trait difference. Unlike play responsiveness, strain differences in play solicitation were only apparent after a period of social isolation. Low levels of play were still present in Fischer rats that had been reared by Lewis dams, suggesting a genetic source for the altered play in rats of this strain. Further studies of play behavior in Lewis and Fischer rats could illuminate relevant neural involvement in rough-and-tumble play and also help understand the genetic bases for this complex social behavior.

Genetic differences in NMDA and D1 receptor levels, and operant responding for food and morphine in Lewis and Fischer 344 rats

Previously, we have shown that Lewis (LEW) rats acquire faster than Fischer 344 (F344) rats operant food- and morphine-reinforced tasks under fixed-ratio schedules of reinforcement. The first purpose of the present work has been to study if differences in operant responding behavior may participate in the reported differences in morphine self-administration behavior between both inbred rat strains. To this end, we have analyzed the microstructure of responding obtained under a variable-interval (VI) of food reinforcement by calculating the inter-response time (IRT) for each rat strain. LEW rats exhibited shorter IRTs than F344 rats, suggesting that LEW rats may have an inherent high or compulsive operant responding activity. When subjects of both inbred rat strains were submitted to a schedule of morphine reinforcement of high responding requirements such as progressive ratio schedules, LEW rats also reached significantly higher breaking points and final response ratio than F344 rats for i.v. morphine self-administration. Given that there are neurochemical differences between both rat strains and that glutamatergic N-methyl-D-aspartate (NMDA) and dopaminergic D(1) receptors have been involved in operant responding behavior, a second purpose of this work has been to measure basal NMDA and D(1) receptor levels in these rat strains by quantitative receptor autoradiography. Compared to F344 rats, LEW rats showed higher basal NMDA receptor levels in frontal and cingulate cortex, caudate putamen, central amygdaloid nuclei, and intermediate white layer of superior colliculus, and higher basal D(1) receptor levels in several areas of hippocampus and thalamus, and substantia nigra pars reticulata. Taken together, these results suggest that an inherent high operant responding activity of LEW rats may have a role in the previous reported faster acquisition of opiate-reinforced behavior in operant self-administration paradigms under fixed-ratio schedules of reinforcement. In addition, a basal higher NMDA and D(1) receptor levels of LEW rats compared to F344 rats may participate in the neurochemical background that mediates the behavioral differences between both inbred rat strains.

Strain differences in response to escapable and inescapable novel environments and their ability to predict amphetamine-induced locomotor activity

RATIONALE

Locomotor response to novelty predicts locomotor and reinforcing effects of psychostimulant drugs in outbred rats. Among Lewis and Fischer 344 (F344) inbred rats this association is less clear, perhaps due to strain-selective differences in responses to novelty.

OBJECTIVE

We examined responses to novel inescapable and escapable environments and to novel objects in these strains.

METHODS

Experiment 1 utilized a place conditioning procedure. Rats were confined to one side for 8 days and then allowed access to both this (familiar) and the novel sides. Experiment 2 assessed locomotor response within an inescapable environment. On another occasion, contacts with novel objects within a novel environment were tabulated. Corticosterone levels and fecal boli were measured. Whether these responses predicted amphetamine-induced locomotor activity was determined. To further assess genetic contributions to this association, experiment 3 assessed novelty responses in F1 hybrid Lewis-F344 rats.

RESULTS

Lewis rats showed greater novelty-seeking behavior in the escapable environment but lower locomotor activity in the inescapable environment compared to F344 rats. There were no strain differences in novel object contacts, corticosterone, or fecal boli responses. Baseline corticosterone levels and activity levels in the novel environment were positively correlated with amphetamine activity based on data from all rats. However, novelty and amphetamine-induced activity showed non-significant negative correlations in F344 and Lewis rats. Yet, F1 rats showed a significant positive correlation between these variables, even though some of their other responses were Lewis-like or F344-like.

CONCLUSIONS

These data suggest that responses to different novelty situations are strain-dependent.

Nurr1-null heterozygous mice have reduced mesolimbic and mesocortical dopamine levels and increased stress-induced locomotor activity

Nurr1, an orphan nuclear receptor, is essential for the differentiation of the midbrain dopamine (DA) neurons; however, its function in adult midbrain DA neurons has not been determined. The present study compared regional brain levels of catecholamines and spontaneous and pharmacologically induced locomotor behaviors between mice heterozygous for the Nurr1-null allele (+/-) and wild type (+/+) littermates. The Nurr1 +/- mice had significantly lower levels of DA in whole brain, midbrain, prefrontal cortex and nucleus accumbens, although no significant differences were observed in the striatum, olfactory bulb or hippocampus. Nurr1 +/- mice displayed significantly greater locomotor activity in a novel open field and after saline injection with no significant difference in activity after treatment with amphetamine (2.5 or 5.0 mg/kg) or MK 801 (0.2 or 0.4 mg/kg). A similar elevation in locomotor activity was observed in Nurr1 +/- mice at 35 days old as was found in 70 days old adults. These data demonstrate that the loss of a single Nurr1 allele results in reduced DA levels in mesolimbic and mesocortical pathways and increased locomotor activity in response to mild stress. The involvement of Nurr1 in DA neurotransmission and the implications for schizophrenia are discussed.

Developmental markers of psychiatric disorders as identified by sensorimotor gating

Prepulse inhibition (PPI) of the acoustic startle reflex is an operational measure of sensorimotor gating that is amenable to cross-species comparisons. Deficits in PPI have been repeatedly reported in patients with schizophrenia or other psychiatric disorders characterized by abnormalities in sensory, cognitive, or motor gating. Because some forms of schizophrenia appear to be attributable to early developmental perturbations, many animal studies have examined the influences of various developmental manipulations on PPI in adulthood. For example, isolation rearing of rats from weaning into adulthood leads to a reorganization of brain circuitry including changes in monoamine systems that modulate PPI. Isolation rearing of rats leads to deficits in PPI that are not evident pre-puberty, are enduring in adulthood, and are developmentally specific, in that isolation of adult rats does not affect PPI. The PPI deficits in isolation-reared rats are reversed by typical or atypical antipsychotic treatments, including raclopride, haloperidol, clozapine, olanzapine, quetiapine, and even the putative antipsychotic M100907. In contrast, other psychoactive drugs, such as chlordiazepoxide, diazepam, prazosin, or amitriptyline, do not normalize PPI in isolation-reared rats. Hence, the isolation-rearing model may help identify novel antipsychotics. Thus, social isolation rearing of rats provides a developmentally specific, non-pharmacological manipulation that leads to deficits in sensorimotor gating that mimic those observed in schizophrenia patients and are responsive to antipsychotic medications.

Effects of reversible inactivation of the neonatal ventral hippocampus on behavior in the adult rat

Rats with neonatal excitotoxic damage of the ventral hippocampus display in adulthood a variety of abnormalities reminiscent of schizophrenia and are used as an animal model of this disorder. In the present study, we hypothesized that transient inactivation of ventral hippocampal activity during a critical developmental period may be sufficient to disrupt normal maturation of relevant brain systems and produce similar lasting behavioral changes. We infused tetrodotoxin (TTX) or artificial CSF into the ventral hippocampus on postnatal day 7 (P7) and assessed behavioral changes in response to stress, amphetamine, and (+)-5-methyl-10,11-dihydro-5H-dibenzo [a,d] cyclohepten-5,10-imine maleate in juvenile (P35) and young adult (P56) rats. In adulthood, rats infused neonatally with TTX displayed motor hyperactivity after pharmacological stimulation and after stress compared with sham controls. Analogous TTX infusions in adult animals did not alter these behaviors later in life. These data suggest that transient loss of ventral hippocampal function during a critical time in maturation of intracortical connections permanently changes the development of neural circuits mediating certain dopamine- and NMDA-related behaviors. These results represent a potential new model of aspects of schizophrenia without involving a gross anatomic lesion.

HPA axis function and drug addictive behaviors: insights from studies with Lewis and Fischer 344 inbred rats

Much research supports a link between stress and its concomitant hypothalamic-pituitary-adrenal (HPA) axis responses with behavioral sensitivity to psychoactive drugs. Our research demonstrates that Lewis inbred rats more readily acquire drug self-administration than Fischer 344 (F344) inbred rats and, compared to this strain, Lewis rats have hyporesponsive HPA axis responses to stress exposure. This association appears to conflict with investigations using outbred rats and suggests that the relationship between drug sensitivity and HPA axis responsiveness is more complicated than originally thought. It is essential to better understand this relationship because of its relevance to vulnerability and relapse to drug abuse. Thus, this paper reviews the literature in which these two inbred strains have been compared. We discuss strain differences in HPA axis function, in characteristics of the mesolimbic dopamine system, and in behaviors thought to reflect emotionality. Strain differences in unconditioned and conditioned effects of psychoactive drugs are then reviewed. Next, we discuss the possible role of sex and gonadal hormones on responsiveness to psychoactive drugs in these strains. Finally, a comparison of results obtained from these strains to three other comparator groups (e.g., high and low responders) suggests that a non-monotonic relationship between behavioral sensitivity to drugs and HPA axis responsiveness can explain much of the discrepancies in the literature.

Behavior and severity of adjuvant arthritis in four rat strains

Previous research has suggested that behavioral traits of the histocompatible Lewis and Fischer strains of rats could be related to the difference in their susceptibility to adjuvant arthritis (AA). In the present study, the predictive value of behavioral markers in susceptibility to AA was investigated in nonhistocompatible inbred DA, Lewis, Albino Oxford (AO), and outbred Wistar strain. Behavioral profiles (open filed test and forced swim test) were determined prior to immunization with a single intradermal injection of complete Freund's adjuvant. Animals were daily scored for clinical signs of AA. The occurrence of certain behaviors and clinical indices of AA was significantly associated with strain membership. Discriminant analysis identified strain-related behavioral and illness profiles with very few overlaps among the phenotypes. Discriminant classification significantly exceeded the proportion of cases, which could have been correctly classified on the basis of chance. Open field behavior, in particular, exploration and grooming, differentiated among AA-susceptible and AA-resistant strains. Multiple regression analysis indicated that severity of AA (maximum clinical sign) can be predicted by the latency time and grooming behavior in the open field independently of strain membership. No clear distinction between AA-susceptible and AA-resistant strains was found with respect to forced swim test immobility. It was concluded that (a) strain-related genetic predisposition is important for the expression of certain behavioral traits and for susceptibility to AA and (b) open field behaviors, particularly grooming and latency, predict susceptibility to AA across different rat strains.

Morphine-induced conditioned taste aversions in the LEW/N and F344/N rat strains

Previous reports have shown that the LEW/N and F344/N inbred rat strains display a differential sensitivity to cocaine in a number of preparations, with the LEW/N rats displaying an increased sensitivity to both the reinforcing and aversive effects of cocaine (relative to the F344/N rats). Given that the LEW/N rats are also more sensitive to the reinforcing effects of morphine than the F344/N strain, the present experiment examined the ability of morphine to condition taste aversions in the LEW/N and F344/N strains to determine if the general sensitivity to cocaine generalizes to another drug of abuse. Specifically, on four conditioning trials, 35 LEW/N and 33 F344/N female rats were allowed access to a novel saccharin solution and then injected with varying doses of morphine (0, 10, 32 and 56 mg/kg). On intervening recovery days, subjects were allowed 20-min access to water. Following the fourth trial, a final aversion test was administered. The F344/N rats, but not the LEW/N rats, rapidly acquired morphine-induced taste aversions at all doses of morphine. Pharmacokinetic differences between the strains were also assessed. Specifically, 10 mg/kg morphine (or vehicle) was administered to subjects of both strains and plasma morphine levels were analyzed at 0.5, 2 and 4 h postinjection. No differences in plasma levels between the strains were observed. Unlike with cocaine, the LEW/N rats do not seem generally sensitive to morphine (relative to the F344/N rats). Rather, the differential sensitivity of the two strains to these compounds seems to be preparation dependent. Possible mechanisms underlying the differential sensitivity evident in the strains were discussed.

Differential Fos expression in the paraventricular nucleus of the hypothalamus, sacral parasympathetic nucleus and colonic motor response to water avoidance stress in Fischer and Lewis rats

The responsiveness of hypothalamic CRF to various stressors is reduced in the young female Lewis relative to the histocompatible Fischer rat. Whether such a difference impacts the brain-gut response to water avoidance stress was investigated by monitoring Fos immunoreactivity in the brain and sacral spinal cord and fecal pellet output. Exposure for 60 min to water avoidance stress increased the number of Fos positive cells in the paraventricular nucleus of the hypothalamus (PVN), nucleus tractus solitarius (NTS), and the parasympathetic nucleus of the lumbo-sacral spinal cord (L6-S1) in both Lewis and Fischer rats compared with non stress groups. The Fos response was lower by 32.0% in the PVN, and 63% in sacral parasympathetic nucleus in Lewis compared with Fischer rats while similar Fos expression was observed in the NTS. Stress-induced defecation was reduced by 52% in Lewis compared with Fischer rats while colonic motor response to CRF injected intracisternally resulted in a similar pattern and magnitude of defecation in both strains. The CRF receptor antagonist [D-Phe12,Nle(21,38)C(a)MeLeu(37)]-CRF(12-41) injected intracisternally antagonized partly the defecation response in Lewis and Fischer rats. These data indicate that a lower activation of PVN and sacral parasympathetic nuclei in Lewis compared with Fisher rats may contribute to the differential colonic motor response and that the blunted CRF hypothalamic response to stress, unlike responsiveness to central CRF plays a role.