Cg-ZI Circuit And Explorative Locomotion

Exploratory locomotion,by which animals effectively capture key factors in novel environments(for instance,food or threat),is critical for animal survival and species continuance.After entering a new environment,animals actively explore the surroundings to avoid danger or search for food and water.Previous studies have identified that the pedunculopontine tegmental nucleus(PPTg)regulates exploratory locomotion.The zona incerta(ZI),a prominent upstream nucleus of PPTg,raises our interests in its role in this behavior.ZI is a subthalamic nucleus in which GABAergic neurons predominate.Based on the cytoarchitecture,morphology,and neurochemical properties of neurons in this nucleus,ZI in rodents is divided into four sectors including the rostral part of ZI(rZI),the ventral part of ZI(vZI),the dorsal part of ZI(dZI),and the caudal part of ZI(cZI).The extensive efferent and afferent projections from or to the ZI provide a rigid structural foundation for versatile functions of the ZI in the regulation of various physiological functions,such as sleep-promoting,attention,posture and movement,and cortical development.Notably,ZI reciprocally connects with locomotion-related nuclei,such as substantia nigra(SN),periaqueductal gray(PAG),and PPTg,and deep brain stimulation of ZI has been a trending therapeutic option for patients with Parkinson's disease.These pieces of evidence suggest that ZI may regulate exploratory locomotion but little is known about the neural circuitry involved.In order to answer that question,we applied retrograde CTB and anterograde AAV tracing as well as optogenetics to dissect out the neuronal connections of ZI in exploratory locomotion control.Our results reveal that pharmacological inhibition of AMPAR in ZI neurons reduces locomotion thus indicating that the ZI is involved in locomotion.The retrograde and anterograde tracing results suggest that nitricoxide synthase-positive(Nos+)neurons in the rZI and dZI receive glutamatergic projection from the cingulate cortex(Cg).Meanwhile,optogenetic activation of the Cg-ZI circuit promotes exploratory locomotion behavior.Our study,for the first time,reveal that the Cg mediates exploratory locomotion behavior through its projections to the ZI.Future investigations into this pathway may provide new insights into the underlying mechanisms of locomotion execution.