FIGURE 7. Poly(I:C) injection increases vulnerability to nigral DA neuron loss induced by low-dose 6-OHDA.

(A) Experimental timeline: rats received a single intra-nigral injection of 20 μg poly(I:C) and 12 days later an intra-striatal injection of 5 μg 6-OHDA. The lesion was allowed to progress for 3 weeks after which animals were sacrificed for post mortem analyses. (B) Unbiased stereological analysis indicates that rats exposed to poly(I:C) injection, followed by a low-dose injection of 6-OHDA, had significant reduction of TH⁺ neurons in the SNc when compared to animals injected with low-dose 6-OHDA. The loss of TH⁺ neurons was reflected in the loss of NeuN⁺ neurons, confirming true neuronal loss. Either vehicle or poly(I:C) injection alone did not induce neuronal cell loss. (C) Unbiased stereological analysis indicates no loss of TH⁺ or NeuN⁺ neurons in the VTA in any of the groups. (D-G) Images of TH immunohistochemistry from single coronal sections of rats injected with vehicle, poly(I:C) alone, 6-OHDA alone or combined insult. (H-K) Images of TH (brown) and NeuN (red) immunohistochemistry from single coronal sections of rats injected with vehicle, poly(I:C) alone, 6-OHDA alone or combined insult. Scale bar: 1.0 mm (D-G); 0.25 mm (H-K). SNc, substantia nigra pars compacta; SNr, substantia nigra pars reticulata; VTA, ventral tegmental area; CP, cerebral peduncle. Animals/group: vehicle/vehicle n=8, poly(I:C)/vehicle n=8, vehicle/6OHDA n=8, poly(I:C)/6OHDA n=8; * p<0.05, *** p<0.001, One-way Anova.