Dopaminergic and serotonergic correlates of stimulation-induced circling

Rotation induced by electrical stimulation of the medial forebrain bundle at the level of the lateral hypothalamus was associated with increases in dopamine (DA), 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) in the striatum ipsilateral to the site of stimulation (i.e. contralateral to direction of turning). The concentrations of DA, DOPAC and HVA within the nucleus accumbens (NAS) were not altered. In the olfactory tubercle (OT), concentrations of DA and both metabolites were, in general, elevated ipsilateral to the electrode. However, relative to non-stimulated controls, HVA concentrations were increased bilaterally in rats exhibiting circling. Stimulation-induced circling also resulted in a bilateral enhancement of striatal serotonin (5-HT) metabolism as indicated by elevated 5-hydroxyindoleacetic acid: 5-HT ratios. No changes in 5-HT metabolism were observed in the NAS. The utilization of 5-HT was elevated in the OT ipsilateral to the electrode in rats that exhibited stimulation-induced rotation. While most subjects that exhibited contraversive rotation in response to the stimulation demonstrated enhanced DA activity, the neurochemical changes were not observed in all subjects. As such, it is concluded that while stimulation of the mesotelencephalic DA system can be associated with stimulation-induced rotation it is not necessary for its elicitation.