Clin Exp Otorhinolaryngol.  2012 Sep;5(3):117-121. 10.3342/ceo.2012.5.3.117.

Decreased Immunoreactivities of the Chloride Transporters, KCC2 and NKCC1, in the Lateral Superior Olive Neurons of Kanamycin-treated Rats

• Suh MW
• Ahn SC

• KMID: 2134593
• DOI: http://doi.org/10.3342/ceo.2012.5.3.117

Abstract

OBJECTIVES
From our previous study about the weak expressions of potassium-chloride (KCC2) and sodium-potassium-2 chloride (NKCC1) co-transporters in the lateral superior olive (LSO) in circling mice, we hypothesized that partially damaged cochlea of circling mice might be a cause of the weak expressions of KCC2 or NKCC1. To test this possibility, we reproduced the altered expressions of KCC2 and NKCC1 in the LSO of rats, whose cochleae were partially destroyed with kanamycin.
METHODS
Rat pups were treated with kanamycin from postnatal (P)3 to P8 (700 mg/kg, subcutaneous injection, twice a day) and sacrificed for immunohistochemical analysis, scanning electron microscope (SEM) and auditory brain stem response.
RESULTS
The SEM study revealed partially missing hair cells in P9 rats treated with kanamycin, and the hearing threshold was elevated to 63.8+/-2.5 dB SPL (4 ears) at P16. Both KCC2 and NKCC1 immunoreactivities were more prominent in control rats on P16. On 9 paired slices, the mean densities of NKCC1 immunoreactivities were 118.0+/-1.0 (control) and 112.2+/-1.2 (kanamycin treated), whereas those of KCC2 were 115.7+/-1.5 (control) and 112.0+/-0.8 (kanamycin treated).
CONCLUSION
We concluded that weak expressions of KCC2 and NKCC1 in circling mice were due to partial destruction of cochleae.

Keyword

KCC2; NKCC1; Lateral superior olive; Kanamycin; Cochlea

MeSH Terms

Animals
Brain Stem
Cochlea
Electrons
Hair
Hearing
Injections, Subcutaneous
Kanamycin
Mice
Neurons
Olea
Rats
Symporters
Kanamycin
Symporters

Figure

• 

  Fig. 1 Scanning electron microscopic image of the cochlea on postnatal (P)9, after 6 days of kanamycin treatment (P3 to P8). In the picture at the top, box areas indicate the areas where the lower photographs (A-C) were taken. Missing hair cells were identified in several areas of the apical (A) and middle (B) turn. In contrast, the hair cells in basal (C) turn were relatively preserved. In the top picture, '1.5 mm' indicates the length between the wedge shape marks at the lateral margins of the picture.

• 

  Fig. 2 The threshold change of auditory brainstem response (ABR), after 6 days of kanamycin treatment (postnatal 3 to postnatal 8). According to waves III and V of ABR, the hearing threshold was near 10-20 dB SPL in the control (A) and near 60 dB SPL in the kanamycin-treated rat (B).

• 

  Fig. 3 The localization of potassium-chloride (KCC2) immunoreactivity in the lateral superior olive (LSO) of control (A, C) and kanamycin-treated rat (B, D). At postnatal 16, KCC2 immunoreactivities were observed in LSO of both groups (A, B). The selected areas (dashed-line box) in A and B are magnified in C and D, respectively. The arrows indicate that KCC2 immunoreactivity was confined to the cell membrane (C, D). A&B scale bar=100 µm; C&D=50 µm.

• 

  Fig. 4 The localization of sodium-potassium-2 chloride (NKCC1) immunoreactivity in the lateral superior olive (LSO) of control (A, C) and kanamycin-treated rat (B, D). At postnatal 16, NKCC1 immunoreactivities were observed in LSO of both groups (A, B). The selected areas (dashed-line box) in A and B are magnified in C and D, respectively. A&B scale bar=100 µm; C&D=50 µm.

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