Progressive loss of DA neurons following PQ injections. (A) The experimental plan demonstrating the injection regime and treatment schedule. Immunohistochemistry performed using anti-tyrosine hydroxylase antibodies on the brain sections of animals. (B) Representative images of midbrain sections showing TH positive neurons at lower and higher magnifications from saline injected control group rats, PQ injected rats dissected 24 hours after the last injection (PQ1 group), PQ injected rats dissected four weeks after the last injection (PQ2 group), PQ injected rats dissected eight weeks after the last injection (PQ3 group). The area of SN which is to be counted is selected in every 6th section of the midbrain (sectioned at 30 microns thickness). (C) The total number of TH positive neurons in the SNpc region was counted at higher magnification using the stereology software purchased from the Stereology Resource Centre, Inc., Florida. There is a significant decrease in the number of TH - positive neurons (*p < 0.05) in the rats sacrificed four weeks and (**p < 0.05) eight weeks after the last injection in comparison with saline injected control group and no significance in rats sacrificed immediately after the last injection verses saline injected control groups. (D) The percentage decrease in TH positive neurons between the saline injected control and PQ groups. There is 43.3% and 47% decrease in the TH positive neurons in the rats sacrificed four and eight weeks after the last injection and only a 17.8% decrease in the number of TH positive neurons in the rats sacrificed 24 hours after the last injection. The bars in the upper (low magnification) panel are 200 μm and in the lower (high magnification) panel 20 μm.