A Neurotracing Study For The Efferent Pathway From Hypothalamus To Autonomic Nerve Endings In The Anterior Chamber Of The Eyes

Purpose: Besides trigeminal ganglion(TG)nerve endings,the possible baroreceptor of the intraocular pressure(IOP),the anterior chamber(AC)of the eye is also richly innervated by autonomic nerve endings,which were proposed to play an efferent role in IOP regulation by affecting the aqueous humor formation and outflow.Previous research has shown that hypothalamus is the possible modulation center of IOP neural control.Our study is designed to determine the efferent pathway from the nuclei of hypothalamus to the autonomic nerve endings distributing in the AC.Methods: In this study,Sprague-Dawley(SD)rats were injected with pseudorabies virus(PRV),a retrograde trans-multisynaptic tracer,to label the autonomic efferent pathways that dominate the AC.Fifteen SD rats were divided into three groups.For the first group(n = 5),a non-trans-synaptic tracer,FAST Dil,was injected into the right AC of the rats as a control.For animals in the second group(n = 5),PRV531 expressing green fluorescent protein was injected into the right AC.For the last group,PRV531 and PRV724 expressing green or red fluorescent protein was injected into the right and left AC of five rats,respectively.FAST Dil-injected rats survived for 7 days and PRV-infected animals survived for 4.5 days.After they were sacrificed,the rats were perfused,and then bilateral autonomic ganglia,including superior cervical ganglia(SCG),pterygopalatine ganglia(PPG)and ciliary ganglion(CG),and the brain tissue were obtained.Then frozen sections were prepared and immunohistochemical staining was performed.Fluorescence signals in autonomic ganglia and the nuclei of hypothalamus were observed under a slide scanner and confocal microscope.Results: Seven days after FAST Dil was injected into right AC,FAST Dil-labeled(red)neurons were observed in the ipsilateral autonomic ganglia,including the SCG,PPG and CG,but not in hypothalamic nuclei.Four and a half days after PRV531 right AC injection,PRV531-labeled(green)neurons could be observed in the ipsilateral autonomic ganglia and bilateral hypothalamic nuclei,especially in the suprachiasmatic nucleus(SCN),paraventricular nucleus(PVN),dorsomedial hypothalamus(DMH),perifornical hypothalamus(Pe F),and ventral mammillary nucleus(VMN).Four and a half days after PRV531 right AC and PRV724 left AC injection,PRV531-labeled(green),PRV724-labeled(red)and double-labeled(yellow)neurons could be observed in the abovementioned bilateral hypothalamic nuclei.Conclusion: Our results indicate that there exist efferent pathways from the nuclei of hypothalamus to the autonomic nerve endings distributing in the AC,providing anatomic evidence for hypothalamus regulating IOP.There exist interactive efferent pathways from some neurons in the bilateral hypothalamic nuclei to the autonomic nerve endings in the bilateral AC,which provide a reasonable explanation for the phenomenon of the consensual ophthalmotonic reaction(COR).