Temperament - a psychobiological approach to harm avoidance and novelty seeking

Abstract

This thesis explores if rats can be said to have a temperament, and if that is the case, how it changes with age and how it is related to brain neurochemistry. Using the hole board and canopy tests (considered to measure exploration and anxiety respectively), behaviour was studied in Wistar rats. In Study I Principal Components Analysis (PCA) revealed two temperamental dimensions reflecting Harm Avoidance and Novelty Seeking. Sex differences were apparent, in that nonestrous females were more active than males and nose poked more in the hole board. In regard to the two temperamental dimensions, sex differences could also be observed, with males exhibiting high levels of Harm Avoidance, and more females exhibiting a high Novelty Seeking/low Harm Avoidant profile. In Study II, a longitudinal study, behaviour was observed from the age of 6 to 52 weeks. Correlation analyses showed substantial behavioural consistency over time, with subjects showing considerable rank order consistency in behavioural measures from their 11th week and on. PCA analysis revealed two temperamental dimensions in adult rats. However, only one dimension reflecting Harm Avoidance was present in the juvenile and older rats. Several behavioural variables showed age-bound mean level profiles. In Study III connections between brain monoamines and temperamental dimensions were analysed using multivariate techniques. Harm avoidant subjects had low levels of striatal dopamine, and high levels of cortical noradrenaline and amygdaloid 5- hydroxyindoleacetic acid. High Novelty Seeking scores were linked to low levels of brainstem serotonin and dopamine, and to low levels of 5-hydroxyindoleacetic acid in amygdala and accumbens. Moreover, rats scoring high on Novelty Seeking had higher-than-average levels of noradrenaline in the thalamus and of serotonin in the amygdala. Study IV went on to explore potential similarities in behaviour between male sibling rats, finding small and non-significant correlations. In contrast to this, weight correlated highly between siblings both at the start and the end of the testing period. Overall the findings in this thesis support the position that temperament is a temporally enduring dimension but that it also changes over the course of an organism’s life cycle. Tentative connections between chemistry and temperamental dimensions are made, and findings on siblings in Harm Avoidance and Novelty Seeking point in the direction of little or no temperamental similarity. Keywords: Harm Avoidance – Novelty Seeking – Continuity – Longitudinal– Monoamines - Siblings