ABSTRACT
Background Recently,there were many studies on corneal innervations during mammalian development.However,there were fewer studies on discussing corneal innervations before and after mouse eye openings.Objective The present study was to investigate the change in the regulation of corneal nerve fiber length and density before and after mouse eye openings to offer a basis for clinical research in human.Methods Thirty SPF C57BL/6 mice were divided into postnatal 1 day(P1 d),P7 d,P13 d(1 day before eye opening),P14 d(eye halfopened),P17 d(1 day after eye opening)and P23 d(7 day after eye opening)groups,with 5 mice and 10 eyes for each group.Entire corneal stretches were prepared and immunostaining with an anti-neuron-specific β-Ⅲ tubulin antibody was performed to label the corneal nerve fibers.Confocal microscopic pictures from the corneal dorsal-nasal region (DN),dorsal-temporal(DT),ventral-nasal region(VN)and ventral-temporal(VT)were taken using Delta Vision Core.From these pictures,the mouse corneal area,total length and density of nerve fibers in the 4 regions were calculated.The use of the animals complied with Statement of ARVO.Results Corneal areas of P1 d,P7d,P13 d,P14 d,P17 d and P23 d mice were(0.404±0.007),(1.362±0.154),(1.573±0.080),(1.603±0.046),(1.847±0.052),(2.445±0.798)mm2,respectively ; the total lengths of nerve fibers were(3.718±1.044),(19.065±3.350),(23.687±0.907),(27.309±2.477),(31.989±3.976),(41.214±1.573)mm,respectively ; the densities of nerve fibers were(9.592±1.138),(14.506±1.908),(15.088±1.241),(16.772±1.897),(16.821±2.102),(17.660±1.216)mm/mm2,respectively,all showing significant increases with age(F =22.906,P =0.000 ; F =0.424,P =0.000 ; F =2.375,P=0.000).A positive correlation of the increasing corneal areas and increasing lengths of nerve fibers was found(r=0.983,P＜0.01).Nerve fiber densities in the four corneal regions significantly increased with age(DN region:F =0.159,P =0.000 ; DT region:F =2.1 72,P =0.001 ; VN region:F =1.998,P =0.000 ; VT region:F=2.352,P=0.000).From P13 d to P14 d,the corneal nerve fiber densities in the DN region decreased by 6.0％ without significant difference(t =0.589,P =0.572); and the corneal nerve fiber densities in the DT region,VN region and VT region decreased by 4.6％,5.5％ and 0.1％,respectively,without significant difference from P14 d to P17 d(t=0.549,P=0.596;t=0.701,P=0.501 ;t=-0.100,P=0.919).Conclusions The development of nerve fibers in the whole cornea or the four corneal regions is influenced by eye opening in mouse to various extents.From P13 d to P14 d,the corneal nerve fiber densities in the DN region decreased by 6.0％ without significant difference.From P14 d to P17 d,the corneal nerve fiber densities in the DT region,VN region and VT region decrease by 4.6％,5.5％ and 0.1％,respectively,without significant difference.Afterwards,the growth of nerve fibers increased in pace and the growth rate is recovered.