Features of the involvement of the dopamine and serotonin brain systems in positive and negative emotional states in rats

Abstract

The aim was to study the effect of rewarding and aversive stimulation of lateral hypothalamus on the turnover of monoamines in the terminal structures of the mesocorticolimbic and nigrostriatal systems: the nucleus accumbens (NAc) and striatum (St). The Wistar male rats were implanted electrodes in the lateral hypothalamus and further trained in self-stimulation test. Animals were also selected on aversive emotional reactions were observed after pressing the pedal for self-stimulation. Subsequently, forced stimulation was performed for 5 minutes and the animals were decapitated. The content of norepinephrine, dopamine (DA) and its metabolites 3,4-dioxiphenylacetic acid (DOPАС) and homovanilinic acid, serotonin (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) in the nucleus accumbens and striatum were determined by high performance liquid chromatography with electrochemical detection. Positive and aversive stimulation of lateral hypothalamus decreased the level of DA in the NAc, however, only stimulation of the positive emotiogenic zone increased the DA and 5-HT turnover in the NAc, as evidenced by an increase in the DOPАС/DA and 5-HIAA/SER ratios, respectively. Rewarding and aversive stimulation decreased the level of 5-HT in St, however, only rewarding stimulation decreased the St level of 5-HIAA compared to control and animals with aversive stimulation. Rewarding stimulation increased the turnover of serotonin in St, as evidenced by the increase of 5-HIAA/5-HT ratios. The activity of the noradrenergic system did not change after rewarding and aversive stimulation. Thus, both rewarding and aversive electrical stimulation increases the turnover of DA and 5-HT in NAc and St. However, these changes are more significant after rewarding stimulation. DA turnover increases more in NAc, and 5-HT turnover in St. The data obtained indicate the specificity of the dopaminergic and serotonergic involvement for the formation of a modality of emotional reactions. Data may provide guidance for developing treatment strategies for neuropsychiatric diseases related to the malfunction of the reward system.