Acetylcholinesterase measurement in various brain regions and muscles of juvenile, adolescent, and adult rats

Several insecticides, chemicals, and drugs are known to inhibit acetylcholinesterase (AChE) activity, responsible for the cleavage of the neurotransmitter acetylcholine. The administration of AChE inhibitors leads to typical parasympathomimetic (toxic) symptoms in rats. In order to differentiate between compounds acting in various regions of the brain or in peripheral nerves, regulatory authorities demand the measurement of AChE activity in different compartments and the study of potential toxicity at different developmental stages. In the present paper, instructions are given for the necropsy of various regions of the brain depending on rat age. Furthermore, a method validation procedure is described for measuring AChE in these parts of the brain as well as peripheral nerves, serum, and erythrocytes in juvenile, adolescent, and adult rats according to the US EPA method. All investigations were performed within the frame of a regulatory extended one-generation reproductive study (EOGRTS, OECD TG 443). AChE activity increases age dependently in parts of the forebrain (cortex, hippocampus, striatum, but decreases in the mid-and hindbrain (cerebellum, brain stem, medulla oblongata) as well as in peripheral nerves (heart, diaphragm, gastrocnemius muscle). Sex-dependent differences of the AChE activity occur after an age of 11 weeks. The implication of AChE measurement in different brain regions of various age groups is discussed regarding the assessment of AChE inhibitors.