A new model for photochemically induced thrombosis in the inner ear microcirculation and the use of hearing loss as a measure for microcirculatory disorders

Increased Risk of Sensorineural Hearing Loss as a Result of Exposure to Air Pollution

Whether exposure to air pollution is associated with developing sensorineural hearing loss (SHL) remains controversial. Using data from the National Health Insurance Research Database, we recruited a total of 75,767 subjects aged older than 20 years with no history of SHL from 1998 to 2010, and they were followed up until SHL was observed, they withdrew from the National Health Insurance program, or the study ended. The subjects were evenly exposed to low-level, mid-level, and high-level carbon monoxide (CO) and nitrogen dioxide (NO₂). The incidence rate ratio of SHL for patients exposed to high-level CO was 1.24 (95% confidence interval (CI) = 1.14–1.36). The NO₂ pollutants increased the incidence rate ratios of SHL in mid-level NO₂ and high-level NO₂ exposures by 1.10 (95% CI = 1.10–1.32) and 1.36 (95% CI = 1.24–1.49) times, respectively. The adjusted hazard ratio (adj. HR) of SHL in patients exposed to high-level CO was 1.45 (95% CI = 1.31–1.59), relative to that of patients exposed to low-level CO. Compared to patients exposed to low-level NO₂, patients exposed to mid-level NO₂ (adj. HR = 1.40, 95% CI = 1.27–1.54) and high-level NO₂ (adj. HR = 1.63, 95% CI = 1.48–1.81) had a higher risk of developing SHL. The increased risk of SHL following the increased concentrations of air pollutants (CO and NO₂) was statistically significant in this study. In conclusion, the subjects’ exposure to air pollution exhibited a significantly higher risk of developing SHL in Taiwan.

Urokinase-type plasminogen activator and plasminogen mediate activation of macrophage phagocytosis during liver repair in vivo

Urokinase-type plasminogen activator (u-PA) and plasminogen play a primary role in liver repair through the accumulation of macrophages and alteration of their phenotype. However, it is still unclear whether u-PA and plasminogen mediate the activation of macrophage phagocytosis during liver repair. Herein, we investigated the morphological changes in macrophages that accumulated at the edge of damaged tissue induced by a photochemical reaction or hepatic ischaemia-reperfusion in mice with u-PA ( u-PA-/- ) or plasminogen ( Plg-/- ) gene deficiency by using transmission electron and fluorescence microscopy. In wild-type mice, the macrophages aligned at the edge of the damaged tissue and extended a large number of long pseudopodia. These macrophages clearly engulfed cellular debris and showed well-developed organelles, including lysosome-like vacuoles, nuclei, and Golgi complexes. In wild-type mice, the distribution of the Golgi complex in these macrophages was biased towards the direction of the damaged tissue, indicating the extension of their pseudopodia in this direction. Conversely, in u-PA-/- and Plg-/- mice, the macrophages located at the edge of the damaged tissue had few pseudopodia and less developed organelles. The Golgi complex was randomly distributed in these macrophages in u-PA-/- mice. Furthermore, interferon γ and IL-4 were expressed at a low level at the border region of the damaged tissue in u-PA-/- mice. Our data provide novel evidence that u-PA and plasminogen are essential for the phagocytosis of cellular debris by macrophages during liver repair. Furthermore, u-PA plays a critical role in the induction of macrophage polarity by affecting the microenvironment at the edge of damaged tissue.

Nitric oxide production and blood corpuscle dynamics in response to the endocrine status of female rats

INTRODUCTION

Menopause is associated with marked changes in the endocrine profile, and increases the risk of vascular disease. However, the effect of hormones on the vascular system is still unclear. Therefore, the aim of this study was to examine the effects of endocrine status in female rats on nitric oxide (NO) production, inflammatory reactions and thrombus organization potency in the mesenteric microcirculation.

MATERIALS AND METHODS

Female Wistar rats were divided into four groups: proestrus, metestrus, ovariectomized (OVX) and OVX plus estradiol treatment (OVX+E2). NO was imaged using an NO-sensitive dye. The leukocyte and platelet velocities relative to the erythrocyte velocity (VW/VRC and VP/VRE, respectively) and thrombi sizes created by laser radiation were measured as thrombogenesis indices.

RESULTS

Changes in endocrine status did not affect vascular function in the arterioles. However, in venules, NO production, VW/VRC and VP/VRE were decreased in the OVX group compared with the proestrus and metestrus states. Thrombus size was significantly greater in the OVX group than in the proestrus and metestrus states. Administration of E2 for 2 weeks restored NO production, VW/VRC and VP/VRE to control levels.

CONCLUSIONS

Changes in endocrine status did not affect arterioles. In contrast, in venules, reduced estrogen levels led to a decrease in NO production, thereby increasing thrombogenesis. Estrogen replacement restored NO production and leukocyte and platelet velocities, reducing thrombus formation relative to OVX. Although it is unclear how E2 reduces thrombus formation, our results indicate that leukocyte and platelet adhesion to the endothelium is a target for E2 via NO.

Urokinase-type plasminogen activator contributes to heterogeneity of macrophages at the border of damaged site during liver repair in mice

Urokinase-type plasminogen activator (u-PA) plays an important role in tissue remodelling through the activation of plasminogen in the liver, but its mechanisms are less well known. Here, we investigated the involvement of u-PA in the accumulation and phenotypic heterogeneity of macrophages at the damaged site during liver repair. After induction of liver injury by photochemical reaction in mice, the subsequent pathological responses and expression of phenotypic markers in activated macrophages were analysed histologically. Fibrinolytic activity at the damaged site was also examined by fibrin zymography. In wild-type mice, the extent of damage decreased gradually until day 14 and was associated with an accumulation of macrophages at the border of the damaged site. In addition, the macrophages that accumulated near the damaged tissue expressed CD206, a marker of highly phagocytic macrophages, on day 7. Further, macrophages that were adjacent to CD206-positive cells expressed inducible nitric oxide synthase (iNOS), a pro-inflammatory marker. u-PA activity increased at the damaged site on days 4 and 7, which distributed primarily at the border region. In contrast, in u-PA-deficient mice, the decrease in damage size and the accumulation of macrophages were impaired. Further, neither CD206 nor iNOS was expressed in the macrophages that accumulated at the border region in u-PA-deficient mice. Mice deficient for the gene encoding either u-PA receptor (u-PAR) or tissue-type plasminogen activator experienced normal recovery during liver repair. These data indicate that u-PA mediates the accumulation of macrophages and their phenotypic heterogeneity at the border of damaged sites through u-PAR-independent mechanisms.

Plasminogen is essential for granulation tissue formation during the recovery process after liver injury in mice

SUMMARY BACKGROUND

The involvement of plasminogen in liver repair has been reported, but its exact role in promoting this process is unknown.

OBJECTIVE

To elucidate the underlying mechanism, we examined the dynamics of liver repair by using a reproducible liver injury model in plasminogen gene-deficient mice and their wild-type littermates.

METHODS

Liver injury was induced by photochemical reaction and the subsequent responses were histologically analyzed.

RESULTS

In wild-type animals, the area of the damage successively decreased, and the repair process was associated with macrophage accumulation at its border. Neutrophils were also attracted to the damaged region on day 1 and were evident only at its border by day 4, which spatially and temporally coincided with the expression of macrophage chemoattractant protein-1 (MCP-1). Neutrophil depletion suppressed recruitment of macrophages at the border between the damaged and the normal tissues. These changes were followed by activated hepatic stellate cell accumulation, collagen fiber deposition and angiogenesis at the boundaries of the injured zone. In contrast, in plasminogen gene-deficient mice, the decrease in the area of damage, macrophage accumulation, late-phase neutrophil recruitment, hepatic stellate cell accumulation, collagen fiber deposition and angiogenesis were all impaired.

CONCLUSION

Our data suggest that accumulated neutrophils at the border of the damaged area may contribute to macrophage accumulation at granulation tissue via the production of MCP-1 after liver injury. The plasminogen system is critical for liver repair by facilitating macrophage accumulation and triggering a cascade of subsequent repair events.

The rat ear vein model for investigating in vivo thrombogenicity of ultrafine particles (UFP)

Recent studies in rodents indicate that intravenous or intratracheal administration of ultrafine particles (UFP) increases thrombogenesis in a surgically exposed peripheral vein after photodynamic excitation of intravenously injected rose bengal (RB). We sought to adapt the invasive peripheral vein RB model to a noninvasive monitoring of ear veins under an inverted microscope. Animals received one of the following: an intraperitoneal, intravenous bolus, or intravenously infused dose of RB. An ear vein was illuminated by a green laser, and formation of a thrombus was captured with a digital camera. Only continuous intravenous infusion produced a steady-state RB plasma level and reproducible thrombus responses in different ear veins of the same rat. This system was then used to study the thrombogenic effects of iv-administered positively or negatively charged 60-nm ultrafine polystyrene particles (PSP). Significant dose-dependent enhancement of thrombus formation was found, as indicated by decreased laser illumination time to 33% of baseline values at 0.5 mg/kg. Negatively charged PSP of the same size failed to affect thrombus formation. We also studied the thrombogenic effect of PSP without the use of RB. The findings were the same as with RB, although the illumination time had to be increased. When 0.5 mg/kg was instilled intratracheally, the laser illumination time to form a thrombus was decreased to 42% of the baseline value, suggesting translocation of UFP into the bloodstream. These results are consistent with previous findings using the invasive model, and they validate the use of this non-invasive ear vein model to evaluate thrombogenic effects of UFP deposition in the respiratory tract.

Fish oil inhibits photochemically induced thrombosis in the guinea pig in a dose dependent manner

The dose-response effect of dietary fish oil was investigated in the photochemically induced thrombosis model in guinea pigs. In this arterial thrombosis model thrombus formation was evaluated by determination of different occlusion parameters (percentage of occlusion, area under the blood flow curve, time to first occlusion, spontaneous reflow). Sixty guinea pigs (7 weeks old) were randomly assigned to and fed a 40 energy % diet containing increasing amounts (0, 5.5, 17 and 36 energy %) of fish oil for four weeks. Arterial thrombosis was induced in the femoral artery by free radical damage and subsequent thrombus formation. Increasing fish oil concentrations in the diet were associated with a linear decrease (p<0.001) in the percentage of occlusion (calculated as a decrease in blood flow) and a linear increase in area under the blood flow curve/begin flow (p<0.001). The time to thrombus formation was not significantly prolonged in any group. However the frequency of animals in which complete occlusion of the femoral artery was not obtained during the thrombosis induction and subsequent observation period was higher in the groups receiving the two highest doses of fish oil. Spontaneous reflow correlated positively (p<0.013) with increasing dietary fish oil content. In conclusion, our data indicates that dietary fish oil inhibits photochemically induced thrombosis in this animal model of arterial thrombosis in a dose dependent manner.

Photochemically induced equilibrium dysfunction in the hamster model with evaluation by means of a new globe rotatory test system

Thrombosis in the inner ear is regarded as one of the causes of equilibrium dysfunction. We have established an experimental thrombosis model by producing a photochemical reaction between rose bengal and green light, and have evaluated the dysfunction with a new rotatory test system. Hamsters were treated with tissue-type plasminogen activator (tPA) in doses of 0, 0.13, 0.26, and 0.52 mg/kg. The equilibrium dysfunction of the hamsters was evaluated by scoring their behavior according to visual observation and by measuring their time on the rotatory test system. Treatment of animals with sufficient tPA (> or = 0.26 mg/kg) caused a significant amelioration of the behavior and a concomitant significant prolongation of time on the rotating globe. These findings suggest that the equilibrium dysfunction induced by the photochemical reaction was due to the thrombi formed, and that our test system may provide a useful tool for evaluating equilibrium dysfunction in hamsters.

Long-term changes in off-lesion endocochlear potential after induction of localized lesions in the lateral wall

Localized lesions were produced in various turns of the guinea pig cochlea by means of a photochemical reaction between systemically administered rose bengal dye and green light illumination. The endocochlear potential (EP) was measured at various off-lesion sites, and a morphological examination was performed. In a previous study, this same investigation was done at 3 days, at which time all sites apical to the lesion showed significant EP depression, and damage to the stria vascularis at the lesion was ongoing. In the present 2-week study, the apical EP values were not different from the basal values, and all experimental values were essentially the same as the EP values found in control animals. Morphological examination revealed that the previously damaged structures were greatly repaired. Localized damage and early apical EP depression followed by damage repair and eventual EP recovery could account for the clinical course of certain cases of idiopathic sudden hearing loss involving low-tone deafness.

Endocochlear potential in focal lesions of the guinea pig cochlea

To estimate the correlation between the cochlear lateral wall and endocochlear potential (EP), the EP was measured at different time intervals up to 3 weeks at cochlear focal lesions made in the guinea pig. Lesions were produced by a photochemical reaction between systemically administered Rose Bengal and green light illumination in the second cochlear turn. Focal strial lesions (mean diameter 975 microm) became apparent under a scanning electron microscope 60 min after illumination, and degeneration of the organ of Corti was recognized at 3 days. The EP was measured continuously for 1 h following onset of the reaction in eight ears. In the other ears, EP measurements were done after various intervals of time up to 3 weeks. The EP showed two declines from pre-illumination level. The first started soon after illumination, reached a minimum value at 25 min, and then slightly recovered by 1 h. The second decline appeared at 3 days after illumination. In contrast to evident focal morphological degeneration 2 weeks post illumination, the EP values had recovered to almost normal. We suggest that the sequential changes in the EP were produced depending on the degeneration and then repairing processes of the endolymphatic boundary tissues.

Effects of corticosteroid, contrast medium and ATP on focal microcirculatory disorders of the cochlea

We evaluated the ability of various drugs to prevent the decrease in focal cochlear blood flow induced by photochemical reaction and investigated the mechanisms underlying this decrease. By means of a photochemical reaction, which produces reactive oxygen species, focal lesions measuring about 1 mm in diameter were induced in the lateral wall of the guinea pig cochlea. The protective effects of hydrocortisone, amidotrizoate and ATP on cochlear blood flow and cochlear vascular conductance changes were evaluated by using a non-contact laser flowmeter. Cochlear blood flow and cochlear vascular conductance were decreased to 65.1+/-4.9% (mean +/- S.E.M.) and 57.0+/-3.7% (mean +/- S.E.M.) of the initial level 30 min after the start of the photochemical reaction, respectively. Hydrocortisone significantly prevented the decline in the cochlear blood flow and cochlear vascular conductance and reduced the area of stria vascularis degeneration in a dose-dependent manner. Neither amidotrizoate nor ATP significantly prevented the decrease in cochlear blood flow or cochlear vascular conductance. Hydrocortisone was more effective than vasodilators or other agents which increase cochlear blood flow in preventing the photochemically induced decrease in cochlear blood flow. This might be due to the antioxidative effects of hydrocortisone.

Milrinone, a phosphodiesterase inhibitor, suppresses intimal thickening after photochemically induced endothelial injury in the mouse femoral artery

The effect of milrinone, a phosphodiesterase (PDE) inhibitor, on intimal thickening after endothelial denudation was investigated. Intimal thickening was induced in the femoral arteries of mice by a photochemical reaction between rose bengal and transluminal green light which caused endothelial injury followed by platelet adhesion, aggregation, and formation of an occlusive thrombus in the irradiated segment of the mouse femoral artery. In this model, intimal thickening occurred following spontaneous thrombolysis. The intima/media ratio at 21 days after irradiation was 0.556+/-0.104 in the untreated group. Oral administration of milrinone (0.3-3.0 mg/kg) for 3-21 days suppressed intimal thickening by up to 56% in a dose- and time-dependent manner. In an in vivo experiment using bromodeoxyuridine incorporation, milrinone suppressed cell proliferation at 1.0 mg/kg p.o. On the other hand, the minimum doses of milrinone for suppression of ex vivo platelet aggregation induced by collagen (0.8 microg/ml) or ADP (0.5 microM) were 3.0 and 10.0 mg/kg, respectively. These results indicate that milrinone may not suppress intimal thickening by inhibiting platelet function but by preventing vascular smooth muscle cell (VSMC) proliferation, probably through a mechanism mediated via 3', 5'-adenosine cyclic monophosphate (cAMP).

Effect of lipo-pro-prostaglandin E1, AS-013 on rat inner ear microcirculatory thrombosis

We investigated effects of lipo-pro-prostaglandin E1 (lipo-[11alpha, 13E, 15S]-11,15-dihydroxy-9-[1-oxobutoxy]-prosta-8, 13-dien-1-oic acid butyl ester), AS-013 in two models of hearing disturbance and equilibrium dysfunction induced by rat inner ear microcirculatory thrombosis. Inner ear microcirculatory thrombosis was induced by photochemical reaction between systemic injection of Rose Bengal and irradiation of green light to the cochlea and vestibule. Photochemical reaction causes endothelial injury followed by platelet adhesion, aggregation and formation of a platelet- and fibrin-rich thrombus. In the hearing disturbance model, a compound cochlear nerve action potential was recorded by electrocochleography every minute. Photochemical reaction induced inner ear microcirculatory thrombosis, followed by disappearance of the action potential. AS-013 significantly (P<0.05) prolonged time to disappearance of the action potential compared with control group. In the equilibrium dysfunction model, the irradiation to the vestibule was applied for 10 min after Rose Bengal injection. The behavior of rats in the swimming test and nystagmus were observed 24 h after the completion of irradiation. In the swimming test, two of 12 animals treated with AS-013 showed no rotating about their longitudinal axes, which indicates equilibrium dysfunction and the duration of well-balanced swimming prolonged. AS-013 suppressed the appearance of nystagmus. These results suggest that lipo-pro-prostaglandin E1, AS-013 may prevent hearing disturbance and equilibrium dysfunction due to inner ear microcirculatory disorders.

Photochemically induced focal cochlear lesions in the guinea pig: I. DAB staining and SEM study

A photochemical reaction was used to produce focal microcirculation disorders in the guinea pig cochlea. Temporal bones were removed at various intervals between 5 minutes and 1 month after infusion of rose bengal (RB) and illumination. Infused but unilluminated contralateral cochleae served as controls. Dissected cochlear structures were stained by 3,3'-diaminobenzidine (DAB) peroxidase substrate medium. After observation by light microscopy (LM), the same specimens were processed and observed by scanning electron microscopy (SEM). Dilation of strial capillaries and destruction of strial epithelial cells became apparent at 1 hour after illumination. Tightly packed red blood cells were found filling the severed end of markedly dilated strial capillaries at 24 hours after the procedure. DAB staining of the osseous spiral lamina indicated vascular change with vessel dilation in the illuminated area. At 1 week after illumination, the lesion area of the stria vascularis and spiral prominence was replaced by a layer of larger, flat cells. At 1 month after illumination, all vascular supply to the cochlear lateral wall disappeared at the site of illumination. All lesions remained focal and showed no sign of expansion or reduction throughout the observation period. The cochlear duct of the guinea pig appears to be segmentally nourished by the capillary system. Observation of DAB stained tissue by LM and SEM proved to be informative in the study of microcirculation disorders of the inner ear.

Focal microcirculation disorder induced by photochemical reaction in the guinea pig cochlea

A small region of microcirculation disorder in the cochlea of the guinea pig could be induced by a photochemical reaction. Photoillumination to the cochlea was done after systemic infusion of Rose Bengal (RB). The lateral wall of the second or third turn of the cochlea was illuminated for 10 min with a 1 mm diameter focused green light supplied by a xenon lamp. Degeneration of the stria vascularis (SV) was observed by a scanning electron microscope at 60-300 min after illumination. The range of length of degenerated area in the SV was from 111 to 1800 microns, with a mean of 760 microns. The organ of Corti along the illuminated lesion of the SV was well preserved in all animals at 60-300 min. In contrast, degeneration of sensory hair cells and scar formation in the SV were observed in the focal lesions of the three animals killed 1 week after illumination. The increase of diameter in the vessel of the SV from the radiating arteriole, the vessel of basilar membrane (VSBM) and limbus vessel (LVS) were observed in the illuminated area with diaminobenzidine (DAB) staining. These findings suggest that segmental microcirculation damage occurred in the SV and modiolus. In physiological studies, compound action potentials (CAP) were evaluated. Endocochlear potentials (EP) were also measured at the second turn under three different situations (groups A, B and C). A photochemically induced lesion was created at the site of EP measurement (group A), a site in the second turn 1 mm from the EP measurement site (group B) and a site in the third turn adjacent to the EP measurement site (group C). Threshold shift of CAP (up to 5.6 +/- 1.8 dB SPL) and reduction of EP (down to 11.4 +/- 10.7 mV) in the photochemically injured location were detected during about 15 min. EP did not recover to the predamaged level (79.9 +/- 3.7 mV) during 20 min. The morphological and physiological changes were not observed in the control group with illumination only. There were no significant decreases in EP values at the sites 1 mm from the lesion (group B) and at the inferior turn adjacent to the lesion (group C) compared to the marked decrease at the site of the photochemically induced lesion (group A). These findings suggest that CAP and EP are significantly affected by the interruption of segmental blood supply in the cochlea and remarkable decrease of EP occurs in the focal region of the guinea pig cochlea. We conclude that a localized blood circulation disorder induced by the photochemical reaction can make a focal lesion in guinea pig cochlea morphologically and physiologically.

Effect of prostaglandin E1 on the rat inner ear microvascular thrombosis

1. The effect of prostaglandin E1 was investigated with a two-rat model of hearing disturbance and equilibrium dysfunction associated with inner ear microvascular thrombosis. 2. The inner ear microvascular thrombosis was induced by photochemical reaction between Rose Bengal and transmural green light (540 nm). Photochemical reaction causes endothelial injury followed by platelet adhesion, aggregation, and formation of a platelet- and fibrin-rich thrombus. 3. Under anesthesia, the cochlea or the vestibule was irradiated with green light to induce hearing disturbance or equilibrium dysfunction. 4. In the hearing disturbance model, a compound cochlear nerve action potential was recorded by electrocochleography every minute after the beginning of photoirradiation in the presence of Rose Bengal. 5. In the equilibrium dysfunction model, the photoirradiation was applied for 10 min after Rose Bengal administration. The behavior of rats was observed in the swimming test, and nystagmus was observed 24 hr after the end of photoirradiation. 6. Prostaglandin E1 significantly (P < 0.05) prolonged the time required to suppress the action potential. In the swimming test, 3 of the 6 animals treated with prostaglandin E1 did not rotate about their longitudinal axes (equilibrium dysfunction) and the duration of well-balanced swimming was significantly prolonged (P < .001). Prostaglandin E1 significantly (P < 0.05) suppressed the appearance of nystagmus. 7. In conclusion, prostaglandin E1 potentially prevents hearing disturbance and equilibrium dysfunction due to inner ear microvascular disorders.

Effect of focal cochlear vascular lesion on endocochlear potential in guinea pigs

The alteration endocochlear potential (EP) in response to total cochlear ischemia induced by various experimental manipulations has been studied. However, the effect of restricted areal damage to the microvessels (restricted to small area in the lateral wall of a cochlear turn) on the EP value is still unknown. In the current investigation we adopted a photochemical method to produce a focal (i.e., restricted area) microvessel injury in the lateral wall of the guinea pig cochlea and examined the effect of these insults on EP recorded in the same region. The small area of the microvessel lesion (small fenestra: approximately 0.2 x 0.4 mm2) induced by photoactivation did not yield significant EP changes, suggesting that damage to such a small area of microcirculation in the lateral wall of the cochlea has no statistically significant effects on EP values. In subjects with a large area of the microvessel lesion (large fenestra: approximately 0.2 x 0.8 mm2), a decrease in the EP value (mean +/- SEM 7.9 +/- 0.8 mV) was noted. However, the control group animals with a large fenestra but without microvessel lesion also displayed a decrease (8.6 +/- 0.8 mV) in EP. In the current study we were unable to differentiate whether the EP changes in animals with the large fenestra microvessel lesions were caused by the cochlear blood flow decrease or by the surgical preparation. However, the results of this study indicated if the EP value was affected by the large area of the microvessel lesion, the level of decrease would not be large. That is, the EP decrease was less than the EP change in the control group (mean: 8.6 mV). Considering the dependence of EP on blood flow, the data of this study suggest that compensatory mechanisms in the cochlea may maintain the EP following a focal lesion in the lateral wall of the cochlea. This study also indicates that the photochemical method provides a reliable approach to produce the animal model with the focal microvessel lesion in the lateral wall of the cochlea.

Cochlear blood flow measured by averaged laser Doppler flowmetry (ALDF)

This report describes a new approach to estimate the hydromechanical properties of a vascular system. Averaged laser Doppler flowmetry (ALDF) was developed by averaging the flux signal of a laser Doppler flowmeter (LDF) synchronized to the heart cycle. The usefulness of this method was verified by manipulation of the cochlear microvasculature. Twelve pigmented guinea pigs under pentobarbital/fentanyl anesthesia were used. The cochlea was surgically exposed and the LDF probe placed on the bony surface of the first turn to monitor cochlear blood flow (CBF). The LDF flux signal (0.2 s time constant) was sampled by an A/D board at 2 kHz for 255 ms and averaged with synchronization to the heart beat. The mean blood flow, peak to peak amplitude, and time (phase) delay of pulsatile flow were measured from the averaged signal. According to a transmission line model of the vascular system, under a given perfusion pressure, mean flow reflects resistance while amplitude and time delay of the pulsatile flow are related to the reactance component of the impedance of the vascular system. During the formation of photochemically-induced thrombosis in the cochlear microvasculature, there was a dramatic mean flux decrease (90.1 +/- 3.4% from baseline (BL), N = 6). Additionally, a time-dependent decrease in amplitude and time delay of pulsatile flow were indicated by ALDF. These results suggest a large increase in vascular resistance and significant decrease in compliance.(ABSTRACT TRUNCATED AT 250 WORDS)

Autoradiographic measurement of regional brainstem blood flow: occlusion of the anterior inferior cerebellar artery

Autoradiography was used to measure regional brainstem blood flow in Wistar rats following permanent left anterior inferior cerebellar artery (AICA) occlusion. With the AICA occluded, blood flow to the left vestibular nucleus decreased 31% while flow to the left cochlear nucleus decreased 47% when compared to the right (unobstructed) side. In the rat, the median pontine branch of the basilar artery was found to provide the principal blood supply to the vestibular nucleus. Electrocochleography was also used to measure the action potential (AP), summating potential (SP) and cochlear microphonics (CM) during left AICA occlusion. The AP disappeared completely after at least 7 min, while the SP polarity changed from negative to positive. Findings also showed that CM2 did not disappear completely in pre-mortem animals.

Effect of a Ca2+ entry blocker, nilvadipine, on hearing disturbances and equilibrium dysfunction caused by microcirculatory disorders of the rat inner ear

We evaluated the effects of Ca2+ entry blockers, nilvadipine and flunarizine, on microcirculatory disorders of the inner ear and on blood flow in the inner ear of rats. Under sodium pentobarbital anesthesia, the middle ear was opened by a ventrolateral approach. A green light (wave length 540 nm) was applied to the cochlea or the vestibule to induce a hearing disturbance or equilibrium dysfunction as a result of inner ear microcirculatory disorders, while rose bengal solution was infused intravenously. In a hearing disturbance model, a compound cochlear nerve action potential was recorded by electrocochleography every minute after the beginning of illumination. The sound stimulus was an 8 kHz sine wave 100 dB normal hearing level. The action potential was calculated 128 times. The action potential disappeared about 12 min after the beginning of illumination. In another model of equilibrium dysfunction, the photoillumination was applied for 40 min under the infusion of rose bengal. The behavior of rats was observed in the swimming test and nystagmus was recorded 24 h after the completion of photoillumination. In a separate experiment, blood flow in the inner ear was measured with a laser Doppler flowmeter under sodium pentobarbital anesthesia. In this study, both nilvadipine and flunarizine prolonged the time required for complete suppression of the action potential, prevented equilibrium dysfunction in the swimming test and reduced the occurrence of nystagmus. Flunarizine significantly increased inner ear blood flow and nilvadipine failed to decrease blood flow in the inner ear, despite a reduced systemic blood pressure. In conclusion, Ca2+ entry blockers may prevent microcirculatory disorders of the inner ear in rats.

Effect of ibudilast on microcirculation thrombosis in rat inner ear

The effect of ibudilast (0.1, 0.3 mg/kg), which has cerebral vasodilating and antiplatelet effects, was evaluated in two models of rat inner ear microcirculation thrombosis by using the photochemical reaction between green light (wave length: 540 nm) and intravenous injection of rose bengal. Furthermore, the inner ear blood flow was measured by a laser-Doppler flowmeter. In the hearing disturbance model, under anesthesia, the compound action potential of the cochlear nerve (AP) was measured by an electrocochleogram. The sound stimulus was an 8-kHz sine wave at 80 dB SPL. The AP was calculated 128 times. In the controls, the AP disappeared about 4 min after the intravenous injection of rose bengal (20 mg/kg). The time required to completely suppress the AP in the animals treated with ibudilast (0.1, 0.3 mg/kg) was significantly prolonged as compared with that in the controls. In the equilibrium dysfunction model, ibudilast (0.1, 0.3 mg/kg) reduced the time of abnormal swimming in the swimming test 24 hr after the completion of photo-illumination. Ibudilast (0.3 mg/kg) increased the inner ear blood flow during the 10-min observation period as compared with the controls, while it did not affect the mean blood pressure. In conclusion, ibudilast increased the inner ear blood flow and was effective in two models of rat inner ear microcirculation thrombosis.

Photochemically induced thrombosis model in rat femoral artery and evaluation of effects of heparin and tissue-type plasminogen activator with use of this model

We report a new and reproducible model of thrombosis in the rat femoral artery. The thrombosis is initiated by endothelial injury subsequent to photochemical reaction between systemically injected rose bengal (10 mg/kg, i.v.) and transillumination of filtered xenon lamp (wave length: 540 nm) from the outside of the vessel. The blood flow of the femoral artery, which was monitored by a pulsed doppler flow meter, was fully stopped in 348.68 +/- 36.18 sec (n = 12) after i.v. injection of rose bengal under irradiation with green light. The formation of massive thrombosis was readily evident by visual inspection. The processes of primary endothelial injury and the subsequent formation of thrombosis during this manipulation were observed by light microscopy and analysed by the scanning and transmission electron microscopy. Pretreatment with heparin (30, 100 or 300 units/kg, i.v.) 10 min before rose bengal injection dose-dependently prolonged the time required to interrupt the blood flow. The thrombolytic activity of a tissue-type plasminogen activator (tPA) was also investigated. After the establishment of stable thrombotic occlusion of the femoral artery, infusion of tPA was started from the contralateral femoral vein for 30 min at the rate of 30 or 100 micrograms/kg/min. The occluded artery was reperfused in 2 out of 10 rats and in 9 out of 12 at the lower and higher rates of tPA infusion, respectively. That heparin could prevent the arterial occlusion and that tPA could reperfuse the occluded artery are observations consistent with the histopathological ones that the primary lesion of endothelium injured photochemically activates the platelet aggregation to form platelet-rich thrombus with extensions of erythrocyte-rich lesions. This model is expected to be a useful tool for evaluating the antithrombotic and thrombolytic agents.