Effects of amphetamine and medial septal lesions on acquisition and retention of radial maze learning in rats

Models of anxiety: responses of rats to novelty in an open space and an enclosed space

Exposure to novelty has been shown to induce anxiety responses in a variety of behavioural paradigms. The purpose of the present study was to investigate whether exposition of naïve rats to novelty would result in a comparable or a different pattern of responses in an open space versus enclosed space with or without the presence of an object in the centre of the field. Lewis and Wistar rats of both genders were used to illustrate and discuss the value and validity of these anxiety paradigms. We examined a wide range of measures, which cover several aspects of animals' responses. The results of this study revealed significant differences between the behaviour of animals in an open space and in the enclosed space. It also revealed significant differences in animal's responses to the presence and absence of an object in the open space and in the enclosed space. In the enclosed space, rats spent most of their time in the outer area with lower number of exits and avoided the object area except when there was an object, while in the open space rats displayed frequent short duration re-entries in the outer area and spent longer time in the object area in presence of an object. The time spent in the inner area (away from the outer area and the object area) was significantly longer and the number of faecal boli was significantly higher in the open space than in the enclosed space. In the present report, we will discuss the fundamental differences between enclosed space and open space models, and we will examine some methodological issues related to the current animal models of human behaviour in anxiety. In the enclosed space, animals can avoid the potential threat associated with the centre area of a box and chose the safety of walls and corners, whereas, in the open space animals have to avoid every parts of the field from which there was no safe escape. The response of animals to novelty in an open space model appears more relevant to anxiety than in an enclosed space. The present studies revealed no correlations between the measures of behaviour in enclosed space and the measures of behaviour in open space, which suggest that these two models do not involve the same construct. Our results suggest that the enclosed space model involves avoidance responses while the open space model involves anxiety responses. The open space model can be very useful in understanding the underlying neural mechanisms of anxiety responses, and in assessing the effects of potential anxiolytic drugs.

Detailed analysis of the behavior of Lister and Wistar rats in anxiety, object recognition and object location tasks

The present study, examines some issues in the measure and analysis of behavior in animals. Two strains of rats of both genders were used to illustrate and discuss these issues. We examined to what extent various behavioral measures reflect different or identical emotional or cognitive factors and, how sensitive are the various parameters of a task to differences between strains and genders. Wistar and Lister males and females rats were tested in an anxiety test then in the object recognition task followed by the object location task. Taking advantage of a simple computer program it is possible to: (1) record several parameters of theses tasks and examine the pattern of animal responses toward novelty and/or familiarity; (2) examine whether different measurements of the same response would reflect anxiety response to novelty and, can they discriminate between novelty and familiarity responses to objects; and (3) examine if changes in the pattern of animal responses are reflected by these measurements and, whether anxiety or discrimination is evident mainly during the first minute of the test. The results on the anxiety test show that different measures of the same response proved concordant and revealed significant differences between Lister males and Wistar males. Lister males approached more frequently an object and spent more time on an object in each approach compared to Wistar males in the first 5 min of test and in the total 10 min. They have also shorter latencies between approaches compared to Wistar males. The examination of performance over different time bins was significant with the measure of frequency. Lister male rats approached less frequently the object in the last 5 min of the test compared to the first 5 min. Their performance, however, did not differ from that of the other groups in this last 5 min. In the memory tasks, the measure of the frequency of approaches suggests that Lister male rats were able to discriminate between novel and familiar objects and, between novel and familiar location of objects. The measure of latency of first approach shows that Wistar female rats were able to discriminate between objects only in the spatial memory test. Discrimination in the object recognition task was observed in the first and second minute, and in the total 3 min sessions. Discrimination in the object location task was observed with the measure of frequency of approaches, in the first minute, and in the total 3 min sessions. Results from the total 3 min sessions were more concordant between the different measures of discrimination than results from separate 1 min bins. The results from the two memory tasks show that novelty prevented habituation to re-exposure to the testing environment. In many cases, novelty increased exploration of the objects in the choice phase compared to the sample phase. However, this lack of habituation or increased exploration in the choice phase is not concordant with most results of discrimination between novelty and familiarity from the same type of measurements.

The hippocampal formation--orbitomedial prefrontal cortex circuit in the attentional control of active memory

The long held view that the hippocampal formation is not only essential, but also solely responsible for declarative memory in humans (and by analogy non-human primates) has come into question. Based on extensive reciprocal connection patterns between the hippocampal formation and the orbitoventromedial prefrontal cortex in primates and rats, a central role for the hippocampal formation in the attentional control of behavior is emerging. In this paper, evidence is reviewed showing that the hippocampal-orbitomedial prefrontal cortex circuit may be involved in attentional monitoring of the internal sensorium. This attentional monitoring system, in a sense, is the working memory of viscero-emotional processing. The hippocampal formation can thus be viewed as a discrepancy detector with respect to the relative activational status of cognitive/emotional set in the orbitomedial prefrontal cortex. Discrepancies between the current representation of the internal milieu and the "just-prior" representation held "on-line" in orbitomedial prefrontal cortex associative working memory, are signaled from the hippocampus to the prefrontal cortex prospective attentional systems to activate, process, and reconcile internal (past) with external (present) environments, and finally to effectively alter active working emotional "sets" to exert cognitive-emotional control of behavior.