Activation and blockade of basolateral amygdala 5-HT6 receptor produce anxiolytic-like behaviors in an experimental model of Parkinson's disease

Although the basolateral amygdala (BLA) and serotonin6 (5-HT6) receptor are involved in modulation of anxiety, their roles in Parkinson' disease (PD)-related anxiety are still unknown. Thus we perform this study to examine the involvement of BLA 5-HT6 receptor on anxiety in unilateral 6-hydroxydopamine-induced PD rats. The lesion of the medial forebrain bundle (MFB) induced anxiety-like behaviors, and decreased the basal firing rate of BLA glutamate neurons and dopamine (DA) levels in tissues of the medial prefrontal cortex (mPFC), amygdala and ventral part of hippocampus (vHip) in rats. Activation of BLA 5-HT6 receptor by local infusion of WAY208466 induced anxiolytic-like effects and increased extracellular γ-aminobutyric acid (GABA) level in the BLA in the lesioned rats. Blockade of BLA 5-HT6 receptor by SB258585 produced anxiolytic-like effects and increased extracellular GABA levels in the BLA in two groups of rats. Activation and blockade of BLA 5-HT6 receptor resulted in increases in DA levels and decreases in noradrenaline levels in tissues of the mPFC, amygdala and vHip in two groups of rats, and induced opposite effects on the firing activity of glutamate neurons between sham-operated and the lesioned rats. The results suggest that decreased DA levels in the limbic brain regions and the enhanced sensitivity of the 5-HT6 receptor on the BLA neurons might be etiological and pathophysiological factors for anxiety in PD. The anxiolytic-like effects may due to elevated extracellular GABA levels in the BLA and altered monoamine levels in the limbic regions, which were induced by WAY208466 and SB258585 through different mechanisms.