The short-term toxicity of ethanol to neurons in rat cerebral cortex tested by topical application in vivo, and a note on a problem in estimating ethanol concentrations in tissue

Abstract

In rats anesthetized with ethanol 4.0 g/kg i.p. the dura overlying the parietal cortex was exposed and superfused with 100% ethanol for 1 h. After 6 days survival the underlying cortex was stained with a silver method that is selective for degenerating axons and their terminals. No degeneration was found in the superfused cortex, although heat-lesioned tissue stained concurrently showed axonal degeneration and so validated the technique. Electron microscopy after 3-20 days survival did not show any degeneration, and synapses of normal appearance were present immediately beneath the cortical surface. In other rats the ethanol concentration in the superfused tissue was assayed in 0.4 mm thick discs sectioned with a vibratome from a 4-mm diameter core cut with a trocar from the cortex immediately after 1 h of superfusion. The ethanol was eluted in 2% TCA, and an aliquot assayed enzymatically. A second elution of the tissue disc contributed a further 5% of the ethanol content indicating a partition coefficient for ethanol between wet brain tissue and 2% TCA of about 10. The total concentration of ethanol in the superficial cortex was found to be about 0.82 M or 3.8%. This estimation was confirmed by superfusion with 14C-labelled ethanol and scintillation counting. Thus neurons in the cerebral cortex did not degenerate after exposure for 1 h to a concentration of ethanol that was 3 times greater than the concentration that causes death in a rat by paralysis of the respiratory centre (1.2%).