Dopaminergic lateralisation in the forebrain: relations to behavioural asymmetries and anxiety in male Wistar rats

Neurochemical lateralisation has been demonstrated in dopaminergic systems in the rat brain, and it has been suggested that such lateralisation might contribute to asymmetric and emotional behaviour. Here, we investigated dopaminergic brain lateralisation in relation to spontaneous and drug-induced behavioural asymmetries, and to emotional behaviour in a sample of 24 male Wistar rats. Asymmetric behaviour was measured in the open field in the undrugged state and after a systemic challenge with the muscarinic receptor antagonist scopolamine (0.5 mg/kg). Emotional behaviour was measured in the elevated plus-maze. Dopaminergic lateralisation was assessed by means of a post-mortem analysis of tissue dopamine (DA) and dihydroxyphenyl acetic acid (DOPAC) content. We found higher DOPAC/DA ratios in the neostriatum, ventral striatum, frontal cortex and amygdala of the right hemisphere. In the open field, the complete sample of rats did not show a left/right asymmetry in spontaneous behaviour, whereas systemic scopolamine induced a left-sided preference in thigmotactic scanning. A correlational analysis yielded individual relationships between behaviour and post-mortem neurochemistry, since lateralisation of DOPAC/DA ratios in favour of the right ventral striatum was related to right-side thigmotaxis. Furthermore, a right dopaminergic lateralisation in the frontal cortex was associated with lower anxiety. The study indicates that asymmetries in ventral striatal dopamine might contribute to side preferences in thigmotactic scanning while frontal dopaminergic lateralisation might influence emotional processing.