Entopeduncular Nucleus Affects Corticosterone And Learning In Rats

Stress is an unavoidable event in life which is marked by increase of glucocorticoid.Glucocorticoid affects many aspects of brain functions,and is often related to several psychological disorders.Previous studies find that exercise significantly modulates the release of glucocorticoid.However,it is not clear which stage of exercise modulates glucocorticoid,at planning of movement,at execution of movement,or influence of exercise?The underlying mechanism remains elusive.The Internal globus pallidus acts as the output nucleus of the basal ganglia and plays a very important role in the preparation and maintenance of exercise.In our previous study,the GABA_A receptor agonist muscimol was injected into the rat’s entopeduncular nucleus(EP),and induced self-mutilation accompanied by increase in serum corticosterone in rats and effect fear memory acquisition in rats.Thus we hypothesized that.EP could modulate the release of glucocorticoid.In this experiment,we used virologic,optogenetics,electrophysiologic,immunologic,and behavioral methods to explore the effects of rat EP on HPA axis and behavior.We found:1.Projections Projected from EP to paraventricular nucleus(PVN)via several brain areas:AAV2/9-hsyn-mCherry was injected into EP,AAVRetro-hsyn-eGFP was injected into hypothalamic paraventricular nucleus(PVN).we found that there was a large amount of fluorescence overlap in ventral sector of zona incerta(ZIV),dorsal sector of zona incerta(ZID),subthalamic nucleus(STh)and reticular thalamic nucleus(Rt),and very little fluorescence overlap in EP.2.Verification of modulation of light on EP activity:The total frequency of neuron firing in EP area increased significantly,single unit recording also showed the neuron’s spike well followed light exposure in the presence of blue light in AAV-2/9-hsyn-ChR2-mCherry rats.3.Corticosteroid level and behavior Effected by EP activity:Photoactivation of EP increased serum corticosterone level,but photoinactivation of EP didn’t affect serum corticosterone level.Photoactivation of EP impaired freezing time on retrieval stage,subsequent experiment showed that the freezing time were also impaired in the absence of light exposure.But photoinactivation of EP had no effect.The time spent in center and open arm were not affected by either light exposure in open field test and elevated cross maze.4.Corticosteroid level Effected by EP-ZI pathway:Photoactivation of EP-ZI pathway increased serum corticosterone level,but photoinactivation of EP-ZI pathway didn’t affect serum corticosterone level.photostimulation of EP had no effect on fear memory on retrival stage.Our study revealed that EP could regulate HPA activity and fear memory.EP might regulate HPA axis activity by the axon terminals EP projected to ZI,But EP couldn’t regulate fear memory by these axon terminals.