Focal damage to cochlear microcirculation measured using a non-contact laser blood flowmeter in guinea pigs

Adiponectin deficiency exacerbates age-related hearing impairment

Obesity-related disorders are closely associated with the development of age-related hearing impairment (ARHI). Adiponectin (APN) exerts protective effects against obesity-related conditions including endothelial dysfunction and atherosclerosis. Here, we investigated the impact of APN on ARHI. APN-knockout (APN-KO) mice developed exacerbation of hearing impairment, particularly in the high frequency range, compared with wild-type (WT) mice. Supplementation with APN prevented the hearing impairment in APN-KO mice. At 2 months of age, the cochlear blood flow and capillary density of the stria vascularis (SV) were significantly reduced in APN-KO mice as compared with WT mice. APN-KO mice also showed a significant increase in terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL)-positive apoptotic cells in the organ of Corti in the cochlea at 2 months of age. At the age of 6 months, hair cells were lost at the organ of Corti in APN-KO mice. In cultured auditory HEI-OC1 cells, APN reduced apoptotic activity under hypoxic conditions. Clinically, plasma APN levels were significantly lower in humans with ARHI. Multiple logistic regression analysis identified APN as a significant and independent predictor of ARHI. Our observations indicate that APN has an important role in preventing ARHI.

The effect of vascular pedicle preservation on blood flow and clinical outcome following ulnar nerve transposition

PURPOSE

To evaluate the efficacy of a technique to preserve the extrinsic vascular supply to the ulnar nerve after transposition and its effect on blood flow and clinical outcome.

METHODS

We included 36 patients with cubital tunnel syndrome. The patients were randomly selected to undergo vascular pedicles-sparing surgery for anterior ulnar nerve transposition (VP group) or nerve transposition and artery ligation (non-VP group). Blood flow to the ulnar nerve was estimated intraoperatively at 3 locations in the cubital tunnel before and after transposition using a laser Doppler flowmeter. Clinical results at 3, 6, and 12 months after surgery were also compared between the 2 groups.

RESULTS

The blood flow before ulnar nerve transposition was not significantly different between the groups. Blood flow at all 3 locations after the ulnar nerve transposition was significantly higher in the VP group than in the non-VP group. Blood flow in the non-VP group reduced to values between 28% and 52% from the pre-transposition baseline values. After surgery, no significant differences were observed in the clinical results between the groups, except for the Disabilities of the Arm, Shoulder and Hand scores at 12 months after surgery, which was greater in the non-VP group.

CONCLUSIONS

The procedure of preserving the extrinsic vascular pedicles can prevent compromise of blood flow to the ulnar nerve immediately after nerve transposition. However, this procedure had no correlation to improved recovery of ulnar nerve function after surgery.

TYPE OF STUDY/LEVEL OF EVIDENCE

Therapeutic II.

NOS inhibition enhances myogenic tone by increasing rho-kinase mediated Ca2+ sensitivity in the male but not the female gerbil spiral modiolar artery

Cochlear blood flow regulation is important to prevent hearing loss caused by ischemia and oxidative stress. Cochlear blood supply is provided by the spiral modiolar artery (SMA). The myogenic tone of the SMA is enhanced by the nitric oxide synthase (NOS) blocker L-N^G-Nitro-Arginine (LNNA) in males, but not in females. Here, we investigated whether this gender difference is based on differences in the cytosolic Ca²⁺ concentration and/or the Ca²⁺ sensitivity of the myofilaments. Vascular diameter, myogenic tone, cytosolic Ca²⁺, and Ca²⁺ sensitivity were evaluated in pressurized SMA segments isolated from male and female gerbils using laser-scanning microscopy and microfluorometry. The gender difference of the LNNA-induced tone was compared, in the same vessel segments, to tone induced by 150 mM K⁺ and endothelin-1, neither of which showed an apparent gender-difference. Interestingly, LNNA-induced tone in male SMAs was observed in protocols that included changes in intramural pressure, but not when the intramural pressure was held constant. LNNA in male SMAs did not increase the global Ca²⁺ concentration in smooth muscle cells but increased the Ca²⁺ sensitivity. This increase in the Ca²⁺ sensitivity was abolished in the presence of the guanylyl cyclase inhibitor ODQ or by extrinsic application of either the nitric oxide (NO)-donor DEA-NONOate or the cGMP analog 8-pCPT-cGMP. The rho-kinase blocker Y27632 decreased the basal Ca²⁺ sensitivity and abolished the LNNA-induced increase in Ca²⁺ sensitivity in male SMAs. Neither LNNA nor Y27632 changed the Ca²⁺ sensitivity in female SMAs. The data suggest that the gender difference in LNNA-induced tone is based on a gender difference in the regulation of rho-kinase mediated Ca²⁺ sensitivity. Rho-kinase and NO thus emerge as critical factors in the regulation of cochlear blood flow. The larger role of NO-dependent mechanisms in male SMAs predicts greater restrictions on cochlear blood flow under conditions of impaired endothelial cell function.

Photochemically induced double lateral wall lesions in the guinea pig cochlea

OBJECTIVE

Multiple patches of atrophy have been reported in the stria vascularis (SV) in elderly persons with presbycusis The aim of this study was to investigate the correlation between sensorineural hearing loss and this strial condition.

MATERIALS AND METHODS

We established a new animal model comprising two small lesions in the SV in the second turn of the cochlea by means of photochemical reaction. Using this model, we investigated morphological and physiological changes in the cochlea at 3, 7 and 14 days after SV damage.

RESULTS

Scanning electron microscopy studies revealed that the strial cells between the two damaged areas of the SV remained intact, although the outer hair cells (OHCs) facing the intact SV area were damaged. Furthermore, damage to the first and second rows of OHCs gradually progressed throughout the 14-day observation period. The endocochlear potential (EP) measured at a point midway between the 2 lesions at 3 and 7 days was found to be significantly lower compared with control values, but had returned to a normal level at 14 days

CONCLUSION

The reversible EP change and localized OHC loss seen in the present investigation may help to understand acute idiopathic or progressive sensorineural hearing loss.

Role of nitric oxide in focal microcirculation disorder of guinea pig cochlea

This study was designed to evaluate the role of endogenous nitric oxide (NO) in focal microcirculation disorder of the guinea pig cochlea. Focal microcirculation disorder was induced by a photochemical reaction at the lateral wall of the second cochlear turn. Saline or N omega-nitro-L-arginine methyl ester (L-NAME) was administered before the onset of photochemical reaction. Cochlear blood flow (CBF) was measured at the focal lesion (ischemic core), 1 mm from the lesion in the apical and basal direction (ischemic border zone) by using a novel non-contact laser blood flowmeter. NO synthase activities were measured by radioenzymeassay. In the saline pretreatment group, CBF was significantly decreased to 58.8+/-4.4% of the baseline at the ischemic core 30 min after the onset of photochemical reaction (P<0.01), while CBF showed no significant change at the ischemic border zone. In the L-NAME pretreatment group, CBF was significantly decreased not only at the focal lesion (48.3+/-6.5%, P<0.01), but also at the ischemic border zone (apical, 49.3+/-2.3%, P<0.05; basal, 58.7+/-7.1%, P<0.05, respectively). NO synthase III activity of cochlea was increased significantly (P<0.01) 15 min after microcirculation disorder. These findings suggest that formation of endogenous NO plays a key role in the maintenance of CBF in acute focal cochlear microcirculation disorder.