Differences in Ethanol Sensitivity of Brain NMDA Receptors of Long‐Sleep and Short‐Sleep Mice

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Abstract
Long-Sleep (LS) and Short-Sleep (SS) mice, selectively bred mice that differ in the duration of anesthesia produced by an acute dose of ethanol, were used to determine the possible association of differing ethanol sensitivity of brain NMDA receptors with differing sensitivity to the anesthetic effects of ethanol in vivo. NMDA receptor-mediated responses were determined by measurement of L-glutamate-stimulated increases in free intracellular calcium concentration (Cai) using the fluorescent indicator for Cai, Indo 1, in microsacs (a cell-free brain membrane vesicle preparation) isolated from hippocampi or cerebral cortices of the two mouse lines. In the absence of added drugs, NMDA responses did not differ between the two lines in hippocampal or cerebrocortical microsacs. However, a high concentration of ethanol (200 mM) inhibited NMDA responses in hippocampal microsacs from LS mice. In contrast, a moderate concentration of ethanol (50 mM) stimulated NMDA responses in hippocampal microsacs isolated from SS mice. In cerebrocortical microsacs, ethanol inhibited NMDA responses in the two lines to an equivalent degree. MK-801, a noncompetitive blocker of NMDA receptors, blocked NMDA responses at lower concentrations in hippocampal microsacs from LS mice than in SS mice, but produced a similar degree of inhibition of NMDA responses in cerebrocortical microsacs from the two lines. A high concentration of ethanol (200 mM) increased resting Cai in hippocampal microsacs from LS mice but not in hippocampal microsacs from SS mice, and increased resting Cai in cerebrocortical microsacs isolated from both lines of mice equally. The small change in resting Cai produced by MK-801 in cerebrocortical microsacs did not differ between the two lines.(ABSTRACT TRUNCATED AT 250 WORDS)