Mohammad, 2005). In an initial attempt, Alias and Mohammad (2005) applied the electrometric method for measuring plasma and tissue cholinesterase activities in four indigenous wild birds (quail, large pin-tailed sand grouse, starling and rock dove) in northern Iraq (Mosul). The method of in vitro cholinesterase inhibition has various toxicological applications and it is used to assess the potential anticholinesterase activity of insecticides (Iyaniwura, 1990; Khan et al., 1990; Karanth & Pope, 2003; Mohammad et al., 2006; 2007a,b). The purpose of the present study was to further examine cholinesterase activity in wild birds (quail (Coturnix coturnix), collard dove (Streptopelia decaocto) and rock dove (Columba livia gaddi) in Mosul, Iraq, as well as the potential sus- ceptibility of plasma or whole brain cholinesterases to in vitro inhibition by selected organophosphate (dichlorvos, malathion and monocrotophos) and carbamate (carbaryl) insecticides. Materials and methods Animals The birds used in the present study were apparently healthy adults of both sexes of quail (Coturnix cotur- nix), collard dove (Streptopelia decaocto) and rock dove (Columba livia gaddi), which were captured in Mosul, Iraq. The birds were obtained from regions in which there were no activities of insecticide application for at least two months. The birds of each species were separately kept in captivity cages (80×60×70 cm) at about 25 °C with water and poultry feed available ad libitum for 3–7 days before experiments. The Scientific Committee of the College of Veterinary Medicine at the University of Mosul (Iraq) has approved the present study. All the experiments complied with institutional regulations addressing animal use, and proper attention and care were given to the birds used in this study. Eight apparently healthy birds from each species (3–5 from each sex) were euthanized by decapitation and blood samples were collected using heparinized test tubes (Coles, 1986). Plasma was separated from erythrocytes by centrifugation at 3 000 rpm (Centurion, U.K.) for 15 min. The whole brain was excised from each bird. All plasma samples and brains were kept frozen at –20 °C pending analysis within one week. Electrometric method for measurement of cholinesterase activity The whole brain was homogenized on an ice bath by a teflon homogenizer (Karl Kolb, Germany) using 25% of the maximum velocity of the homogenizer. The homogenization of the whole brain was performed in a pH 8.1 barbital-phosphate buffer solution (1.237 g sodium barbital, 0.163 g potassium dihydrogen phosphate and 35.07 g sodium chloride/L of distilled water) at 3 ml/100 mg wet weight (Mohammad, 2007; Al-Badrany & Mohammad, 2007). We determined cholinesterase activ- ity in the plasma and brain samples by an electrometric method (Alias & Mohammad, 2005; Mohammad 2007; Interdisciplinary Toxicology. 2011; Vol. 4(3): 144–148 Also available online on PubMed Central 145 Al-Badrany & Mohammad, 2007). The reaction mixture of the enzyme in a 10-ml vial contained 3 ml of the pH 8.1 barbital-phosphate buffer, 0.2 ml plasma or whole brain homogenate and 3 ml of distilled water. Initial pH of the mixture (pH 1) was measured with a glass electrode using a pH meter (Hanna, Romania), then 0.10 ml of the aque- ous solution of the substrate 7.5% acetylthiocholine iodide was added to the mixture which was incubated at 37 °C for 30 min. At the end of the incubation period, the pH of the reaction mixture (pH 2) was measured. The enzyme activ- ity expressed as ΔpH/30 min was calculated as follows: Cholinesterase activity: (ΔpH/30 min.) = (pH 1–pH 2) – Δ pH of blank. The blank was without the plasma or brain homogenate aliquot. In vitro cholinesterase inhibition Plasma and whole brain samples from each bird species were also used for in vitro cholinesterase inhibition. We used the method of inhibitor-cholinesterase incubation at 37 °C for 10 min to cause in vitro inhibition of plasma and whole brain cholinesterase activities of the birds (Mohammad et al., 1997; 2006; 2007a,b). The commercial insecticides used were the organophosphates dichlorvos (50%, Super Nogos, Pacific Agriscience, Australia), mala- thion (50%, VAPCO, Jordan) and monocrotophos (40%, Green River, Italy) and the carbamate insecticide carbaryl (85%, Sociedad Anonima De Agroquimicos, Spain). The insecticides were prepared in distilled water and individu- ally added in a volume of 0.1 ml to the reaction mixtures of the plasma or whole brain homogenate and the final reaction volume in control and inhibited samples was 6.3 ml (Mohammad et al., 2007a). The final concentra- tions of dichlorvos, malathion and monocrotophos were 0.5 and 1.0 μM and those of the carbaryl were 5 and10 μM in the enzyme reaction mixture. Control reaction mix- tures did not contain any insecticide, and they were used for measurement of base-line cholinesterase values. The reaction mixtures were incubated at 37 °C for 10 minutes and the residual cholinesterase activity in the mixtures was measured as described above. The % of inhibition of cholinesterase activity was calculated as follows: % Cholinesterase inhibition = [Cholinesterase activity (without insecticide) – Cholinesterase activity (with insecticide) / Cholinesterase activity (without insecti- cide)] × 100. Statistics The data were presented as means + SE and they were subjected to analysis of variance followed by the least significant difference test (Petrie & Watson, 1999). The accepted level of statistically significant difference level was at p<0.05. Results Mean plasma cholinesterase activities of the birds in descending order were observed in the rock dove, collard Copyright © 2011 Slovak Toxicology Society SETOX