Study On Thermo-Biological Effect Of CO₂ Laser Irradiation On The Cochlea Of Guinea Pigs

ObjectiveTo study the relationship among the expression of the inducible nitric oxide synthase(iNOS), heat shock protein 70 (HSP70) ,the change of ultrastructure and hearing function of the cochlea after the irradiation of the different power densities carbon dioxide laser(CO₂) in guinea pigs,in order to explore the appropriate power density of carbon dioxide laser applying in the ear surgery, and estimate the possible traumatic mechanisms of inner ear after irradiation of carbon dioxide laser.Methods48 guinea pigs after the fenestration on the cochlea with the left ear were equally divided into 4 groups(A,B,C and D), irradiated with carbon dioxide laser with 1w(A), 2w(B), 3w(C) and 0w(D),Dgroup (only do surgery without fenestration) as controls. Auditory brainstem response(ABR) were recorded preoperation and antemortem respectively. After irradiation the animals were decapitated in batch. Scanning electron microscopies were performed to observe the morphological alteration .The expression of the iNOS and HSP70 were detected by SABC immunohistochemistry method and average gray densities were quantified with a light microscope image analysis system.ResultsIt was elucidated that the thresholds of ABR immediately after irradiation were higher than those preoperative in A, B and C groups(p<0.05), the ABR thresholds three weeks later were higher than those before irradiation in group B and C(p<0.05),no significance was noted in group A and D(p>0.05). Three weeks later, through scanning electron microscopiesjt was found that cochlea hair cells were slightly affected by low power(lw) CO2 laser irradiation,the same as D group.However, with 2w CO2 laser irradiation .the outer hair cells and stereocilia in the Corti's organ were disarranged , collapsing hair cells were also observed, with 3w CO2 laser irradiation, regional disorder or serious loss of stereocilia .The level of iNOS immunoreactivity in cochlea immediately after irradiation was higher than that in the control group (p<0.05),including Corti's organ, spiral ganglion cells, spiral ligment and the stria vascularis in three groups, iNOS was present in B and C group three weeks after irradiation were stronger than that in control group(p<0.05), whereas no difference was observed in A group(p>0.05). The rise of the ABR thresholds in guinea pigs was correlated with the strong expression of the iNOS both immediately and three weeks laser after irradiation in A > B and C group (p<0.05).The level of HSP70 immunoreactivity in guinea pig cochlea immediately after irradiation was higher than that in the control group (p<0.05),including Cortis organ, spiral ganglion cells in three groups, Hsp70 was present in B and C group three weeks after irradiation were stronger than that in control group(p<0.05), whereas no difference was observed in A group(p>0.05). The rise of the ABR thresholds in guinea pigs was correlated with the strong expression of the Hsp70 both immediately and three weeks laser after irradiation in A and B group (p<0.05),and immediately after irradiation in C group(p<0.05),but no significance was noted three weeks laser after irradiation in group C(p>0.05).Conclusions...