3,4-diaminopyridine alters acetylcholine metabolism and behavior during hypoxia

Abstract

Low oxygen (hypoxia) decreases the release and synthesis of acetylcholine (ACh) as well as behavioral performance (i.e., tight rope test scores). These hypoxic-induced impairments are partially reversed by 3,4-diaminopyridine (3,4-DAP). With mouse brain slices, the Ca++-dependent-K+-stimulated synthesis of ACh from [U-14C]glucose decreased 45% under 2.5% oxygen and 80% under 0% oxygen. During hypoxia, 3,4-DAP (10 nM) increased in vitro ACh synthesis 67% (2.5% oxygen) and 63% (0% oxygen). The Ca++-dependent-K+-stimulated release of ACh declined by 55 or 67% under 2.5 or 0% oxygen, respectively.3,4-DAP partially reversed this hypoxic impaired release of ACh under 2.5 (+69%) or 0% (+226%) oxygen. In vivo, chemical hypoxia (i.e., NaNO2-induced methemoglobinemia) reduced ACh synthesis from [U-14C]glucose in striatum (-82%), cortex (-68%) and hippocampus (-55%). During hypoxia, 3,4-DAP (10 pmol/kg) increased [U-14C]glucose incorporation into ACh in the hippocampus (+62%) and striatum (+36%). Tight rope test performance decreased 89% during hypoxia and 3,4-DAP diminished this decline to only 55%. These findings demonstrate that the hypoxic-induced deficits in ACh metabolism and behavior can be partially reversed by interaction with Ca++ homeostasis. The therapeutic usefulness of 3,4-DAP in the treatment of human metabolic encephalopathies remains to be evaluated.