The ability to learn and change future behaviour based on past experiences is crucial for the life and survival of animals. For various behaviours exhibited by animals it is clear that in a seemingly homogeneous population not all individuals behave the same way, even in invertebrates. In crickets (Gryllus bimaculatus), a model system for the mechanisms of intra-specific aggression, agonistic experiences with the underlying impact of neuromodulators have been identified as a cause of inter-individual differences. For mammals and humans, the experience of adversity and stress can have detrimental effects on cognitive abilities and chronic defeat stress is used as a model for depression. In crickets the equivalent, the chronic social defeat stress paradigm, has been established. This thesis first sets out to construct a new model for measuring a conditioned response from multiple behavioural aspects and quantify learning in individual crickets. Video tracking of responses revealed behavioural variables that were included in a binary logistic regression analysis, whereas the resulting multi-variable model proves to be superior to other models constructed and can give the probability of an individual exhibiting a conditioned response. With this, learning indices can be calculated for each individual trained in a differential appetitive olfactory paradigm. With the method at hand, this thesis reveals that the experience of chronic social stress impairs learning in crickets, susceptible and resilient to defeat stress alike. The experience of multiple wins, however, does neither improve nor decrease learning abilities, but a long-term winner effect on aggression could be shown. Although inter-individual differences in learning are present, the aggressive state of crickets is not correlated to the learning indices. The application of serotonergic drugs that block receptors or act as re-uptake inhibitors reveal the influence of serotonin on learning within this paradigm. In addition to maintaining reduced aggressiveness, serotonin promotes the impairment of learning after the experience of chronic social defeat stress.:1 INTRODUCTION.....................................................................................................1 2 MATERIALS AND METHODS............................................................................... 8 2.1 Experimental animals...................................................................................... 8 2.2 Appetitive olfactory conditioning..................................................................... 8 2.2.1 Odour application and rewarding....................................................... 8 2.2.2 Absolute conditioning paradigm........................................................ 10 2.2.3 Differential conditioning paradigm.................................................... 11 2.3 Experimental setup for video-tracking.............................................................. 12 2.4 Binary logistic regression model....................................................................... 13 2.4.1 Binary groups for model building...................................................... 13 2.4.2 Variables of a behavioural response................................................... 14 2.4.3 Calculating a conditioned odour response probability (Presp) ............ 15 2.5 Evaluation of learning with the binary logistic model...................................... 17 2.6 Evaluation of aggression with a standardised fight.......................................... 18 2.7 Multiple agonistic experiences......................................................................... 19 2.7.1 Chronic social defeat stress................................................................ 19 2.7.2 Multiple wins..................................................................................... 20 2.8 Serotonin......................................................................................................... 20 2.8.1 Pharmacological treatments............................................................... 20 2.8.2 Methiothepin and ketanserin.............................................................. 21 2.8.3 Fluoxetine with non-chronic defeat................................................... 21 2.9 Additional data analysis and statistic................................................................ 22 3 RESULTS............................................................................................................ 23 3.1 Binary logistic regression model for quantifying learning............................... 23 3.1.1 Behavioural variables of a conditioned odour response.................... 23 3.1.2 Model building and selection............................................................. 29 3.1.3 Odour response probabilities (Presp)................................................... 31 3.1.4 Application of the regression model to assess the quantification of learning.................................................................................................... 34 3.2 The influence of agonistic experiences on aggression and learning................. 39 3.2.1 Chronic social defeat stress................................................................ 39 3.2.2 Multiple experiences of winning........................................................ 46 3.2.3 Correlation of aggression and learning............................................... 48 3.2.4 Summary of learning capacities – multiple experiences.................... 50 3.3 The influence of serotonergic drugs on learning after chronic defeat.............. 51 3.3.1 Methiothepin and ketanserin.............................................................. 51 3.3.2 Fluoxetine........................................................................................... 57 3.3.3 Summary of learning capacities – chronic defeat and serotonin........ 60 4 DISCUSSION....................................................................................................... 63 4.1 The semi-automated measurement of olfactory learning in individually assayed crickets................................................................................................................... 64 4.2 The influence of multiple agonistic experiences on learning........................... 71 4.3 The role of serotonin in chronic social defeat influenced learning................... 77 4.4 Overall conclusion and outlook........................................................................ 80 5 SUMMARY........................................................................................................... 82 6 ZUSAMMENFASSUNG........................................................................................ 87 7 REFERENCES.................................................................................................... 93 8 APPENDIX................................................................................................... 106 8.1 Figures and tables................................................................................... 106 8.2 Publications and published abstracts....................................................... 108 8.3 Curriculum vitae....................................................................................... 109 8.4 Acknowledgements.................................................................................. 111

Drug abuse is becoming an increasing problem in Kenya. A number of studies carried out in the country show that almost every Kenyan youngster at one time or another experiments with drugs, especially beer and cigarettes. The major cause of concern is that a significant proportion of these young people eventually get addicted posing a threat to their own health and safety, while creating difficulties for their families and the public at large into difficulties. This study sought to establish the current trend of drug abuse among students in Kenyan secondary schools, and to analyze the strategies used to address the problem. The ultimate aim was to propose a programme for prevention and intervention. The study is a descriptive survey. In view of this, the field survey method was adopted to collect quantitative and qualitative data, using questionnaires and interviews. Both qualitative and quantitative approaches were used in data analysis, thus there was a mixed model research design approach to data analysis. The analysis of structured items was mainly done using the Statistical Package for Social Sciences (SPSS). The key findings from the study were that drug abuse among students is common; both boys and girls have abused drugs with the majority being in boys‟ schools; the greatest ratio of drug abusers to non-abusers among the sampled schools are aged between 20 and 22 years; there is a significant relationship between drug abuse and age, use of drugs by other family members and easy access to drugs. A variety of factors contribute to drug abuse with the majority of students citing curiosity, acceptance by peers and ignorance as to the dangers of drug abuse as the main reasons. Both the school administrators and teachers face a number of challenges in an attempting to curb drug abuse in schools. The study makes a number of recommendations for policy and further research. A number of guidelines are proposed for developing a programme for prevention and intervention. / Educational Studies / D. Ed. (Socio-Education)

Drug abuse is becoming an increasing problem in Kenya. A number of studies carried out in the country show that almost every Kenyan youngster at one time or another experiments with drugs, especially beer and cigarettes. The major cause of concern is that a significant proportion of these young people eventually get addicted posing a threat to their own health and safety, while creating difficulties for their families and the public at large into difficulties. This study sought to establish the current trend of drug abuse among students in Kenyan secondary schools, and to analyze the strategies used to address the problem. The ultimate aim was to propose a programme for prevention and intervention. The study is a descriptive survey. In view of this, the field survey method was adopted to collect quantitative and qualitative data, using questionnaires and interviews. Both qualitative and quantitative approaches were used in data analysis, thus there was a mixed model research design approach to data analysis. The analysis of structured items was mainly done using the Statistical Package for Social Sciences (SPSS). The key findings from the study were that drug abuse among students is common; both boys and girls have abused drugs with the majority being in boys‟ schools; the greatest ratio of drug abusers to non-abusers among the sampled schools are aged between 20 and 22 years; there is a significant relationship between drug abuse and age, use of drugs by other family members and easy access to drugs. A variety of factors contribute to drug abuse with the majority of students citing curiosity, acceptance by peers and ignorance as to the dangers of drug abuse as the main reasons. Both the school administrators and teachers face a number of challenges in an attempting to curb drug abuse in schools. The study makes a number of recommendations for policy and further research. A number of guidelines are proposed for developing a programme for prevention and intervention. / Educational Studies / D. Ed. (Socio-Education)