New screening tool for analyzing behavior of laboratory animals

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This invention relates to a screening tool which enables the investigator to test complex behavioral effects of pharmaceutical compounds and to behavioral test procedures for psychopharmacological animal models employing this screening tool.

The screening tool of the invention, a modified hole board, allows to differentially analyse the behavior in small laboratory animals, in particular rodents such as mice and rats, tree shrews (Tupaia belangeri) and small primates and to evaluate behavioral effects induced by pharmacological manipulation.

Furthermore, the screening tool according to the invention may also be used to evaluate the behavioral alteration induced by selective breeding or genetic manipulation of laboratory animal strains or evaluate learning and memory functions of laboratory animals and influences thereon by a drug.

A variety of test procedures are used in preclinical research on behavioral pharmacology (for review see Lister, 1990; Menard & Treit, 1999). Most of these procedures are considered to be predictive of one specific type of therapeutic activity, such as anxiolytic, sedative or antidepressant effects. In rodents, the most widely used animals in preclinical research, these effects can be assessed by behavioral alterations, for instance in anxiety-related behavior, risk assessment, locomotor activity, and exploration.

To assess drug effects, tests of spontaneous unconditioned behavior are often used. In these tests locomotor behavior plays a crucial role and, thus, it seems to be difficult to reliably dissociate locomotion from indices of anxiety or exploration (Sheldon, 1968). To differentially investigate the behavioral effects of compounds, correlational models with behavioral data obtained from a whole series of different independent tests need to be performed (Treit, 1985). Thus, the evaluation of potential behavioral properties of pharmacologically active compounds is in need of a series of specific behavioral tests, resulting in cost-intensive and time-consuming procedures. Moreover, it has to be considered that an animal's behavior is context-specific and, therefore, the fact that a drug exerts an anxiolytic effect in one test-specific context does not necessarily imply that it will exert a similar effect in another context (for review see Lister, 1990). Studies based on behavioral tests which allow to investigate a wide range of behavioral forms and which are focussed on a more detailed ethological analysis of experimental animals in a single complex paradigm may overcome these disadvantages (Cruz et al., 1994; Rodgers et al., 1997).

In recent years, considerable progress has been made in fields such as combinatorial chemistry and the genomic based research, providing an immense number of new chemical entities with potential clinical use. There is thus a growing need for the pharmaceutical industry for a simple, fast throughput screening method which avoids the need of a complicated time-consuming battery of separate behavioral tests.

It is appreciated that also hole numbers and diameters will be adapted to the size of the respective laboratory animals to be used.

The experiments described below establish that the mHB is a reliable test for behavioral characterization in rodents like mice and rats (as well as in other small laboratory animals such as tree shrews and small primates) in a single experimental setting.

In LABs, at first glance, acute treatment with diazepam seemed to produce an anxiogenic action: Opposing the effects observed in HABs, ‘latency board’ was rather increased and ‘entries on board’ were decreased in LABs. However, the concomitant tendency towards reduced locomotion and the lack of changes in risk assessment behavior point towards a sedative rather than an anxiogenic action of diazepam in non-anxious animals. Taken together, these results provide evidence for anxiolytic effects of diazepam in hyper-anxious individuals only but a rather sedative effect in hypo-anxious individuals, thus suggesting the feasibility of the mHB to assess the predictive value of a psychopathological animal model.

Although chronic treatment with the selective serotonin-reuptake inhibitor paroxetine revealed no effects on parameters indicating anxiety of unprotected areas, the abolition of the basal line-difference in risk assessment behavior after chronic treatment with paroxetine indicates a mild anxiolytic action in HABs. This is in accordance with the hypothesis that risk assessment behavior is more sensitive to the effects of atypical anxiolytics, such as paroxetine, than are more traditional indices of anxiety (Griebel et al., 1997). However, recent studies on the behavior of rats in the elevated plus-maze both after chronic treatment with antidepressants (Beaufour et al., 1999) and chronic treatment with the serotonin reuptake-inhibitor fluoxetine (Silva & Brandao, 2000) revealed neither changes in classical indicators of anxiety nor in risk assessment behavior. The observation of treatment-induced changes in risk assessment behavior in the mHB suggests that the stress-reduced characteristic of this test allows to discover more subtle treatment effects than other tests of unconditioned behavior.

As can be clearly derived from the above it is possible to differentially analyze the basal behavior in rodents and to evaluate behavioral effects induced by different pharmacological treatments under stress-reduced conditions using the mHB test. Behaviors such as anxiety, exploration, and locomotor activity can be dissociated and investigated by thorough monitoring and analysis of behavioral parameters obtained in this behavioral test. Hence, the mHB represents a significant improvement over the prior art, which requires a whole battery of separate tests. The finding that even subtle differentiation of behavioral profiles may be determined by a single simple test is surprising and contrary to the conventional teaching.

The mHB thus provides a simple and expedient screening tool suitable for high throughput screening.

Finally, due to its stress-reduced characteristic by avoiding social separation, the mHB test enables the investigator to evaluate subtle behavioral modulations such as mild changes in anxiety-related behavior or changes in the exploratory motivation.

Thus, the mHB represents an effective tool for high throughput-screening for potential therapeutic agents in preclinical research and for the assessment of genetically induced behavioral effects in particular laboratory animal strains. It is simple and cost-efficient and moreover, the number of laboratory animals needed may be significantly reduced, combining for the first time avoidance of stress due to social partition. It still allows the clear differentiation between the individual behavioral parameters in a single experimental setting, as opposed to conventional paradigms. Thus, for example in the open field paradigm, the locomotor activity cannot be clearly dissociated from exploration. Moreover the test arrangement and experimental procedures employing the mHB of the invention can also be used for motoric tests or habituation tests, as well as for memory and learning, e.g. by assessing visual and olfactorial discrimination in small laboratory animals, for example by the introduction of food into the hole compartment.