RESUMO
Radix Polygalae (RP) has been used to relieve psychological stress in traditional oriental medicine. Recently, cell protective, antiamnestic and antidepressant-like effects were disclosed but the possible application of RP to post-traumatic stress disorder, in which exaggerated fear memory persists, has not yet been explored. For this purpose, the effects of RP on fear behavior was examined in a mouse model of single prolonged stress and conditioned fear (SPS-CF), previously shown to mimic key symptoms of post-traumatic stress disorder. Male mice received daily oral dose of RP extract or vehicle during the SPS-CF procedure. Then fear-related memory (cohort 1, n=25), non-fear-related memory (cohort 2, n=38) and concentration-dependent effects of RP on fear memory (cohort 3, n=41) were measured in 3 separate cohort of animals. Also working memory and anxiety-like behaviors were measured in cohort 1. RP-treated SPS-CF mice exhibited attenuated contextual but not cued freezing and no impairments in the working memory and spatial reference memory performances relative to vehicle-treated SPS-CF controls. RP-treated SPS-CF and naive mice also demonstrated no difference in anxiety-like behavior levels relative to vehicle-treated SPS-CF and naive controls, respectively. In the hippocampus of SPS-CF mice, expression of BAG1, which regulates the activity of GR, was decreased, whereas RP increased expression of BAG1 in naïve and SPS-CF mice. These results suggest that RP exerts some symptomatic relief in a mouse with exaggerated fear response. RP and its molecular components may thus constitute valuable research targets in the development of novel therapeutics for stress-related psychological disorders.
RESUMO
Radix Polygalae (the root of Polygala tenuifolia) is a herb widely used in traditional Asian medicine that is thought to exert a variety of neuropsychiatric effects. Radix Polygalae extract can protect against N-methyl D-aspartate (NMDA) neurotoxicity and induce brain-derived neurotrophic factor (BDNF) expression, suggesting modulatory roles at glutamatergic synapses and possible antidepressant action. In accordance with this hypothesis, Radix Polygalae extract demonstrated antidepressant-like effects in 8-week-old male C57Bl/6 mice by decreasing behavioral despair in the forced swim and tail suspension tasks and increasing hedonic-like behavior in the female urine sniffing test 30 minutes after a single oral administration of 0.1 mg/kg. Reduced latency to acquire a food pellet in the novely suppressed feeding paradigm, without change in anxiety-like behaviors suggested a rapid-onset nature of the antidepressant-like effect. In addition, it decreased the number of failed escapes in the learned helplessness paradigm after two oral administrations 24 hours and 30 minutes before the first test. Finally, it reversed anhedonia as measured by saccharin preference in mice exposed to the chronic stress model after two administrations of 0.1 mg/kg, in contrast to the repeated administration generally needed for similar effect by monoamergic antidepressants. Immobility reduction in tail suspension task was blocked by the α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor antagonist NBQX, a pattern previously demonstrated by ketamine and other ketamine-like rapid-onset antidepressants. Also similarly to ketamine, Radix Polygalae appeared to acutely decrease phosphorylation of GluR1 serine-845 in the hippocampus while leaving the phosphorylation of hippocampal mTOR serine 2448 unchanged. These findings serve as preclinical evidence that Radix Polygalae extract exerts rapid-onset antidepressant effects by modulating glutamatergic synapses in critical brain circuits of depression and may be worthy of further evaluation as a safe substitute to other rapid-onset antidepressants known to have unacceptable side effects.
