The total AChE activity in different areas of the brain was estimated as done earlier . The brain tissues were homogenized in a Potter–Elvehjem homogenizer by using 0.1M phosphate buffer (pH 8) at a temperature of 0 ◦C. The homogenate was centrifuged at 10,000×g for 5 min at 4 ◦C. The activity of AChE in the aliquot of the homogenate was estimated by the method followed by Ellman et al. (1961). The aliquot was mixed with phosphate buffer (pH 8). To this, the substrate
acetylthiocholine iodide and dithiobisnitrobenzoic acid (DTNB) reagent (Sigma, USA) were added. Acetylthiocholine iodide was hydrolyzed to thiocholine and acetate by AChE. Thiocholine reacted with DTNB reagent to produce yellow color. The rate of color development is the measure of the AChE activity. A kinetic profile of the enzyme activity was studied spectrophotometrically at 412m at the interval of 15 s. The enzyme activity is expressed as the mol of substrate hydrolyzed/min/g tissue.