Reversibility of Compound Action Potential during the Acute Phase after Transitory Local Ischemia

Abstract

We investigated the reversibility of compound action potential (CAP) changes induced after transitory local ischemia induced by rose bengal photochemically induced thrombosis of the rat anterior inferior cerebellar artery (AICA). Cochlear blood flow (CBF) was measured with a laser-Doppler flowmeter positioned on the lateral bony wall of the basal turn of the cochlea, and the CAP to an 8-kHz half-wave of sinusoid sound at 100 dB sound pressure level was monitored. The irradiation was started 5 minutes before the rose bengal administration and continued through the thrombosis formation. Tissue-type plasminogen activator (t-PA, 1 mg/kg) dissolved in saline was injected intravenously 2 minutes after complete photothrombotic blockade of the AICA in the rats presenting complete abolition of CAPs just after the vascular occlusions. Nineteen of the 51 rats presented complete abolition of the CAP just after the AICA occlusion, and the thrombosed AICA was successfully reperfused by t-PA administration in 11 of the 19 rats. The result showed that duration of ischemia was the more important determinant for the reversibility of CAPs during the acute phase (p = .00001), and the residual level of cochlear blood flow during ischemia was also an important factor (p = .066). It appeared that the critical time of ischemia for the complete recovery of CAPs was around 5 minutes, and that the critical limit for the irreversibility of CAPs within the acute phase was between 20 and 25 minutes.