A new gerbil model of hindbrain ischemia by extracranial occlusion of the bilateral vertebral arteries

A new rat model of reversible global cerebral ischemia

A new rat model of global cerebral ischemia-reperfusion was proposed via reversible occlusion of the major vessels originating from the aortic arch and supplying the brain. This technique can be used for the search and study of exogenous (pharmacological) and endogenous methods of brain protection from ischemia-reperfusion injury.

Protection against ischemic cochlear damage by intratympanic administration of AM-111

OBJECTIVE

AM-111, a cell-permeable peptide inhibitor of c-Jun N-terminal kinase, was investigated for its protective effects against ischemic damage of the cochlea in gerbils.

METHODS

Transient cochlear ischemia was introduced in animals by occluding the bilateral vertebral arteries for l5 minutes. Then, 10 μl of AM-111 at a concentration of l, 10, or 100 μM in hyaluronic acid gel formulation was applied onto the round window 30 minutes after the insult. Gel without active substance was used in a control group. Treatment effects were evaluated by auditory brainstem response (ABR) and histology of the inner ear.

RESULTS

In controls, transient cochlear ischemia caused a 25.0 ± 5.0 dB increase in the ABR threshold at 8 kHz and a decrease of 13.3 ± 2.3% in inner hair cells at the basal turn on Day 7. Ischemic damage was mild at 2 and 4 kHz. When the animals were treated with AM-111 at 100 μM, cochlear damage was significantly reduced: the increase in ABR threshold was 3.3 ± 2.4 dB at 8 kHz, and the inner hair cell loss was 3.1 ± 0.6% at the basal turn on Day 7. The effects of AM-111 were concentration dependent: 100 μM was more effective than 1 or 10 μM.

CONCLUSION

Direct application of AM-111 in gel formulation on the round window was effective in preventing acute hearing loss because of transient cochlear ischemia.

Gender differences in myogenic regulation along the vascular tree of the gerbil cochlea

Regulation of cochlear blood flow is critical for hearing due to its exquisite sensitivity to ischemia and oxidative stress. Many forms of hearing loss such as sensorineural hearing loss and presbyacusis may involve or be aggravated by blood flow disorders. Animal experiments and clinical outcomes further suggest that there is a gender preference in hearing loss, with males being more susceptible. Autoregulation of cochlear blood flow has been demonstrated in some animal models in vivo, suggesting that similar to the brain, blood vessels supplying the cochlea have the ability to control flow within normal limits, despite variations in systemic blood pressure. Here, we investigated myogenic regulation in the cochlear blood supply of the Mongolian gerbil, a widely used animal model in hearing research. The cochlear blood supply originates at the basilar artery, followed by the anterior inferior cerebellar artery, and inside the inner ear, by the spiral modiolar artery and the radiating arterioles that supply the capillary beds of the spiral ligament and stria vascularis. Arteries from male and female gerbils were isolated and pressurized using a concentric pipette system. Diameter changes in response to increasing luminal pressures were recorded by laser scanning microscopy. Our results show that cochlear vessels from male and female gerbils exhibit myogenic regulation but with important differences. Whereas in male gerbils, both spiral modiolar arteries and radiating arterioles exhibited pressure-dependent tone, in females, only radiating arterioles had this property. Male spiral modiolar arteries responded more to L-NNA than female spiral modiolar arteries, suggesting that NO-dependent mechanisms play a bigger role in the myogenic regulation of male than female gerbil cochlear vessels.

A reproducible model of middle cerebral artery occlusion in mice: hemodynamic, biochemical, and magnetic resonance imaging

A reproducible model of thread occlusion of the middle cerebral artery (MCA) was established in C57 Black/6J mice by matching the diameter of the thread to the weight of the animals. For this purpose, threads of different diameter (80 to 260 microns) were inserted into the MCA of animals of different weights (18 to 33 g), and the success of vascular occlusion was evaluated by imaging the ischemic territory on serial brain sections with carbon black. Successful occlusion of the MCA resulted in a linear relationship between body weight and thread diameter (r = 0.46, P < 0.01), allowing precise selection of the appropriate thread size. Laser-Doppler measurements of CBF, neurological scoring, and 2,3,5-triphenyltetrazolium chloride staining confirmed that matching of animal weight and suture diameter produced consistent cerebral infarction. Three hours after MCA occlusion, imaging of ATP, tissue pH, and cerebral protein synthesis allowed differentiation between the central infarct core, in which ATP was depleted, and a peripheral penumbra with reduced protein synthesis and tissue acidosis but preserved ATP content. Perfusion deficits and ischemic tissue alterations could also be detected by perfusion- and diffusion-weighted magnetic resonance imaging, demonstrating the feasibility of dynamic evaluations of infarct evolution. The use of multiparametric imaging techniques in this improved MCA occlusion model opens the way for advanced pathophysiological studies of stroke in gene-manipulated animals.

Brainstem auditory evoked potentials during brainstem ischemia and reperfusion in gerbils

To evaluate the reversibility of neural function in the brainstem following ischemia, we investigated the effect of transient brainstem ischemia on the brainstem auditory evoked potential in gerbils. Brainstem ischemia was produced by bilateral extracranial occlusion of vertebral arteries. Local cerebral blood flow was measured by quantitative autoradiography after 5 min of ischemia and was reduced to less than 3 ml/100 g per min in the pons and lower midbrain, indicating severe and reproducible brainstem ischemia. During brainstem ischemia, brainstem auditory evoked potential waveforms disappeared completely. After a brief ischemic insult (5 min), all four brainstem auditory evoked potential components recovered to normal. After longer ischemic insults (10-30 min), brainstem auditory evoked potential components never recovered to normal. Microtubule-associated protein 2 immunoreactivity revealed differential vulnerability of the acoustic relay nuclei in the brainstem. Neurons in the lateral lemniscus were most vulnerable, followed in order by neurons in the trapezoid body, the superior olive and the cochlear nucleus. We also demonstrated a close relationship between the reversibility of ischemia-induced changes on brainstem auditory evoked potential and ischemic lesions of these relay nuclei. These data may be useful for evaluating the therapeutic window of thrombolytic therapy during acute vertebrobasilar occlusion.

The isolated in vitro perfused spiral modiolar artery: pressure dependence of vasoconstriction

We developed a new technique, the isolated in vitro perfused spiral modiolar artery, which allowed the continuous measurement of the vascular diameter and control of the intravascular pressure. An isolated section of the spiral modiolar artery from the gerbil was perfused on one end with a set of concentric pipettes and occluded on the other end in order to apply a defined intravascular pressure in the range between 10 and 230 cm H2O. The preparation was continuously superfused with a NaCl solution. The diameter of the spiral modiolar artery in NaCl solution displayed little dependence on the applied intravascular pressure. The diameter was 73 +/- 10 microm (n = 5) at 10 cm H2O and increased with pressure to 85 +/- 7 microm (n = 5) at the highest applied pressure (220 or 230 cm H2O). Elevation of the K+ concentration from 3.6 to 150 mM in the superfusate caused a transient vasoconstriction. The amplitude of the K+-induced vasoconstriction depended strongly on the applied intravascular pressure. At 10 cm H2O the amplitude was maximal and the outer diameter decreased transiently by 49 +/- 9% (from 73 +/- 10 to 38 +/- 9 microm; n = 5). The amplitude of K -induced vasoconstriction was nearly maximal at pressures lower than 30 cm H2O, declined at higher pressures, and was not significantly different from zero at pressures larger than 100 cm H2O. These observations in conjunction with an estimation of the intravascular pressures in vivo suggest that cochlear blood flow can be regulated on two levels: (1) cochlear blood flow can be regulated by controlling the vascular diameter of the spiral modiolar artery (intracochlear blood flow regulation) and (2) intracochlear blood flow regulation can be modulated by altering the perfusion pressure which is controlled by the vasculature upstream of the cochlea.