Localization and expression of three nitric oxide synthase isoforms in the cochlea of guinea pigs and the effects in the hearing process of inner ear

Aimei WANG; Hao TANG; Zhongming ZHANG; Lianming LI; Hua MU

ABSTRACT

BACKGROUND:

Nitric oxide (NO) is synthesized by catalysis of nitric oxide synthase (NOS). Three distinct isoforms of NOS have been detected in different structures of the guinea pig cochlea. However, there are still rather controversies about the definite localization and expression of NOS isoforms in guinea pig cochlea.

OBJECTIVE:

To investigate localization and expression of three NOS isoforms in the cochlea of guinea pigs, and to explore the effect of NO on auditory physiology and pathophysiology of inner ear.

DESIGN:

An observed and controlled study.

SETTING:

Department of Physiology, Jinzhou Medical College; Department of Orthopedics, the Second Affiliated Hospital of Jinzhou; Department of Otorhinolaryngology, Jinzhou Central Hospital.MATERIALS The study was performed in Hearing Research Laboratory of China Medical University from May to November 2000. Ten healthy male albino guinea pigs, with body mass of 250-300 g, with sensitive Preyer's reflexes and normal drum membrane and external auditory canal,were selected.

METHODS:

After anesthesia, guinea pigs were decapitated and the temporal bones were removed immediately. The round and oval windows were opened, perfused with 40 g/L paraformaldehyde, and the specimens were immersed in the same fixative solution for 2 hours. Decalcification of the cochleae was performed in 100 g/L EDTA solution for 1 week. Then the specimens were placed in 250 g/L sucrose solution overnight and embedded in OCT. Cryostat (20 μm) sections were prepared for immunohistochemistry.MAIN OUTCOME

MEASURES:

Localization and expression of three NOS isoforms in the cochlea of guinea pigs.

RESULTS:

All data of ten guinea pigs was entered the final analysis without any loss. [1] Neuronal-type nNOS and endothelial-type eNOS immunoreactivity were localized in inner and outer hair cells of the organ of Corti, as well as in spiral ganglion cells. In addition, staining for nNOS and eNOS were also seen in the marginal cells of stria vascularis, spiral ligament cells, and in nerve fibers. [2] Inducible-type iNOS immunoreactivity was also detected in above each structure of the guinea pig cochlea under physiological conditions.

CONCLUSION:

NO may play an important role in neurotransmission,blood flow regulation, and cytotoxicity.