Neotic preferences in laboratory rodents: Issues, assessment and substrates

Developmental cascades linking stress inoculation, arousal regulation, and resilience

Stressful experiences that are challenging but not overwhelming appear to promote the development of arousal regulation and resilience. Variously described in studies of humans as inoculating, steeling, or toughening, the notion that coping with early life stress enhances arousal regulation and resilience is further supported by longitudinal studies of squirrel monkey development. Exposure to early life stress inoculation diminishes subsequent indications of anxiety, increases exploration of novel situations, and decreases stress-levels of cortisol compared to age-matched monkeys raised in undisturbed social groups. Stress inoculation also enhances prefrontal-dependent cognitive control of behavior and increases ventromedial prefrontal cortical volumes. Larger volumes do not reflect increased cortical thickness but instead represent surface area expansion of ventromedial prefrontal cortex. Expansion of ventromedial prefrontal cortex coincides with increased white matter myelination inferred from diffusion tensor magnetic resonance imaging. These findings suggest that early life stress inoculation triggers developmental cascades across multiple domains of adaptive functioning. Prefrontal myelination and cortical expansion induced by the process of coping with stress support broad and enduring trait-like transformations in cognitive, motivational, and emotional aspects of behavior. Implications for programs designed to promote resilience in humans are discussed.

Operant sensation seeking engages similar neural substrates to operant drug seeking in C57 mice

Novelty and sensation seeking have been associated with elevated drug intake in human and animal studies, suggesting overlap in the circuitry mediating these behaviors. In this study, we found that C57Bl/6J mice readily acquired operant responding for dynamic visual stimuli, a phenomenon we term operant sensation seeking (OSS). Like operant studies using other reinforcers, mice responded on fixed and progressive ratio schedules, were resistant to extinction, and had sustained responding with extended access. We also found that OSS, like psychostimulant self-administration, is sensitive to disruption of dopamine signaling. Low doses of the dopamine antagonist cis-flupenthixol increased active lever responding, an effect reported for psychostimulant self-administration. Additionally, D1-deficient mice failed to acquire OSS, although they readily acquired lever pressing for food. Finally, we found that one common measure of novelty seeking, locomotor activity in a novel open field, did not predict OSS performance. OSS may have predictive validity for screening compounds for use in the treatment of drug addiction. In addition, we also discuss the potential relevance of this animal model to the field of behavioral addictions.

Regulation of food intake through hypothalamic signaling networks involving mTOR

To maintain normal activity, single cells must assure that their energy needs and utilization are continuously matched. Likewise, multicellular organisms must constantly coordinate energy intake and expenditure to maintain energy homeostasis. The brain, and the hypothalamus in particular, plays a critical role in integrating and coordinating several types of signals, including hormones and nutrients, to guarantee such homeostasis. Like single cells, the hypothalamus also profits from intracellular pathways known to work as fuel sensors to maintain energy balance. One such pathway is the mammalian target of rapamycin (mTOR). mTOR integrates different sensory inputs to regulate protein synthesis rates in individual cells, and it has recently been implicated in the central nervous system to regulate food intake and body weight as well. This review provides an overview of the role of hypothalamic intracellular fuel sensors in the overall control of energy balance and discusses the potential contribution of these fuel-sensing mechanisms to the metabolic dysregulation associated with obesity.

Structure of rat behavior in hole-board: I) multivariate analysis of response to anxiety

Aim of present paper was to carry out an analysis of rat behavior in hole-board following different multivariate approaches. Thirty male Wistar rats were observed in a hole-board apparatus and their behavior recorded for 10 min through a digital videocamera for a following frame-by-frame analysis. Both descriptive and multivariate analyses were used. Descriptive analysis showed that roughly 85% of the whole behavioral structure encompassed six patterns appearing during the first minute of observation: walking, climbing, rearing, immobile-sniffing, edge-sniff and head-dip. As to multivariate approach, cluster analysis showed three main dyadic associations: [edge-sniff/head-dip], [walking/climbing], [face-grooming/body-grooming]. Path diagram, obtained on the basis of relative frequencies of transitions among behavioral patterns (stochastic analysis), emphasized cluster analysis results. Adjusted residuals confirmed, from a statistical point of view, the strong relationships among specific patterns. Results demonstrate that immobile-sniffing has a crucial role in rat behavioral organization and head-dip is closely related with edge-sniff which is suggested to be a specific sniffing activity of holes edge never properly considered. Present research shows that multivariate approaches, revealing patterning among different behavioral elements in hole-board, could improve test reliability, providing a more useful tool to investigate behavioral effects of anxiolytic drugs.

Striatal activity underlies novelty-based choice in humans

The desire to seek new and unfamiliar experiences is a fundamental behavioral tendency in humans and other species. In economic decision making, novelty seeking is often rational, insofar as uncertain options may prove valuable and advantageous in the long run. Here, we show that, even when the degree of perceptual familiarity of an option is unrelated to choice outcome, novelty nevertheless drives choice behavior. Using functional magnetic resonance imaging (fMRI), we show that this behavior is specifically associated with striatal activity, in a manner consistent with computational accounts of decision making under uncertainty. Furthermore, this activity predicts interindividual differences in susceptibility to novelty. These data indicate that the brain uses perceptual novelty to approximate choice uncertainty in decision making, which in certain contexts gives rise to a newly identified and quantifiable source of human irrationality.

Delay-dependent involvement of the rat entorhinal cortex in habituation to a novel environment

Evidence has accumulated that the entorhinal cortex (EC) is involved in memory operations underlying formation of a long-term memory. Because entorhinal-lesioned rats are impaired for long delays in delayed matching and non-matching to sample tasks, it has been proposed that EC contributes to the maintenance of information in short-term memory. In the present study, we asked whether such a time-limited role applies also when learning complex spatial information in a novel environment. We therefore examined the effects of EC lesions on habituation in an object exploration task in which a delay of either 4min or 10min is imposed between successive sessions. EC-lesioned rats exhibited a deficit in habituation at 10min but not 4min delays. Following habituation, reactions to spatial change (object configuration) and non-spatial change (novel object) were also examined. EC-lesioned rats were impaired in detecting the spatial change but were able to detect a non-spatial change, irrespective of the delay. Overall, the results suggest that EC is involved in maintaining a large amount of novel, multidimensional information in short-term memory therefore enabling formation of long-term memory. Switching to a novelty detection mode would then allow the animal to rapidly adapt to environmental changes. In this mode, EC would preferentially process spatial information rather than non-spatial information.

The exploratory behaviour of rats in the hole-board apparatus: is head-dipping a valid measure of neophilia?

The exploratory behaviour of laboratory rodents is of interest within a number of areas of behavioural pharmacology. However, how best to measure exploratory behaviour in rodents remains a contentious issue. Many unconditioned tests, such as the open field, potentially confound general locomotor activity with exploration. The hole-board apparatus appears to avoid this confound, as head-dipping into holes in the floor is assumed to be a valid measure of the subject's attraction towards novelty (neophilia). This study aimed to investigate whether head-dipping should be considered a valid measure of neophilia by comparing performance of adult male and female Lister hooded rats on the hole-board task (a) over repeated sessions and (b) when novel objects were absent or present underneath the holes. The results show that head-dipping initially decreased across repeated exposures, while time spent in the aversive central area increased. No change in head-dipping was seen in response to objects being placed underneath the holes. Rather than being a measure of neophilia, these results support the hypothesis that head-dipping represents an escape response, which declines as the subject becomes less fearful. These results are compared with previous studies of repeated exposure to other novel environments.

Increased emotional reactivity in rats following exposure to caffeine during adolescence

From 45 to 55 days after birth, male and female rats were treated via daily intraperitoneal injections with either isotonic saline, or 15 or 30 mg/kg caffeine. When 72-82 and 112-122 days old, their activity and emotional reactivity were assessed by means of frequencies of rearing, ambulation, immobility, defecation and urination recorded in an open field, as well as their occupancy of corners and center squares of the field, and their partial emergence and latencies to fully emerge from a small darkened chamber into a brightly lit arena. Rats treated with caffeine were probably more emotionally reactive than untreated controls as suggested by more immobility and defecation and urination. There were also effects on rearing and ambulation that might have arisen from increased impulsivity. Further evidence of caffeine treatment-induced higher emotional reactivity was found in the heavier adrenal glands of a small number of 10 months-old males. This occurred in the absence of any caffeine treatment effects on spatial reference memory measured by ability to identify a novel Y-maze arm. Changes between the two testing ages in rearing and emergence latencies, and sex-dependent changes in ambulation, defecation and corner and center squares occupancy, along with immobility for 30 mg/kg caffeine-treated subjects, were discussed in the light of possible changes in emotional reactivity. Sex differences in open-field rearing and ambulation, and testing age-dependent sex differences in corner and center squares occupancy were ascribed to higher emotional reactivity in males.

Early signs of neurolipidosis-related behavioural alterations in a murine model of metachromatic leukodystrophy

Arylsulfatase A (ASA)-deficient mice represent an animal model for the lysosomal storage disorder metachromatic leukodystrophy (MLD). Although the model has been applied in pathophysiological and therapeutic studies, the behavioural phenotype of ASA(-/-) mice is only partially characterized, and the most decisive outcome measures for therapy evaluation only emerge beyond 1 year of age. Presently, ASA(-/-) mice and ASA(+/-) control mice were studied at 6 and 12 months of age on an extensive battery including tests of neuromotor ability, exploratory behaviour, and learning and memory. Overt signs of ataxia were not observed in 6-month-old ASA(-/-) mice, but quantitative gait analysis during open-field exploration revealed that ASA(-/-) mice displayed increased hind base width and increased stride lengths for all paws. Their covert motor incoordination was evident in a correlation analysis which unveiled decreased harmonisation of concurrent gait parameters. For example, while ASA(+/-) controls demonstrated substantial convergence of front and hind base width (r=0.54), these variables actually diverged in ASA(-/-) mice (r=-0.37). Furthermore, various behavioural observations indicated emotional alterations in ASA(-/-) mice. Six-month-old ASA(-/-) mice also showed decreased response rates in scheduled operant responding. The present findings could provide relevant behavioural outcome measures for further use of this murine MLD model in preclinical studies.

Sex does matter: comments on the prevalence of male-only investigations of drug effects on rodent behaviour

Despite abundant evidence of sex differences in the effects of drugs on nonsexual behaviour in rats and mice, most researchers continue to investigate male animals exclusively. This was evident from a survey of all relevant research reports published during the period February 2005-September 2006 (inclusive) in recent issues of five representative behavioural pharmacological journals. Reasons for excluding female animals from most studies are discussed along with attempts to justify the use of either male or female animals only, and the value of including both sexes (especially when a drug effect is poorly understood). Although there are other factors that can influence the effects of drugs, such as strain, age and social density, the sex of experimental animals is the easiest to control and thus is well suited to inclusion in pharmacological investigations. It is accordingly suggested that, as has been recommended many times in the past, animals' sex should play a more important part in future research than is still currently the case.

Development of a mouse test for repetitive, restricted behaviors: relevance to autism

Repetitive behavior, a core symptom of autism, encompasses stereotyped responses, restricted interests, and resistance to change. These studies investigated whether different components of the repetitive behavior domain could be modeled in the exploratory hole-board task in mice. Four inbred mouse strains, C57BL/6J, BALB/cByJ, BTBR T+tf/J, and FVB/NJ, and mice with reduced expression of Grin1, leading to NMDA receptor hypofunction (NR1neo/neo mice), were tested for exploration and preference for olfactory stimuli in an activity chamber with a 16-hole floor-board. Reduced exploration and high preference for holes located in the corners of the chamber were observed in BALB/cByJ and BTBR T+tf/J mice. All inbred strains had initial high preference for a familiar olfactory stimulus (clean cage bedding). BTBR T+tf/J was the only strain that did not demonstrate a shift in hole preference towards an appetitive olfactory stimulus (cereal or a chocolate chip), following home cage exposure to the food. The NR1neo/neo mice showed lower hole selectivity and aberrant olfactory stimulus preference, in comparison to wildtype controls. The results indicate that NR1neo/neo mice have repetitive nose poke responses that are less modified by environmental contingencies than responses in wildtype mice. 25-30% of NMDA receptor hypomorphic mice also show self-injurious responses. Findings from the olfactory studies suggest that resistance to change and restricted interests might be modeled in mice by a failure to alter patterns of hole preference following familiarization with an appetitive stimulus, and by high preference persistently demonstrated for one particular olfactory stimulus. Further work is required to determine the characteristics of optimal mouse social stimuli in the olfactory hole-board test.