Ibotenic acid was injected into the nucleus basalis magnocellularis region of rat brain in order to study whether an elevation of lipase activities was associated with the degeneration of cholinergic neurons in this potential animal model of Alzheimer's disease. Two plasma membrane fractions were prepared from different regions of ibotenate injected (right hemisphere) and non-injected (left hemisphere) rat brain. One plasma membrane fraction was from synaptosomes (SPM) and the other from glial and neuronal cell bodies (PM). Activities of mono- and diacylglycerol lipases in these plasma membrane fractions were markedly increased (3- to 5-fold) in hippocampus, midbrain and frontal cortical regions of rat brain at 10 days after the injection of ibotenate. The activity of choline acetyltransferase was decreased in frontal cortex but unchanged in hippocampus and midbrain. Our results suggest that the increase in lipase activity is much more widespread and non-specific than is the decrease in cholinergic function.