Restoring Spinal Noradrenergic Inhibitory Tone Attenuates Pain Hypersensitivity in a Rat Model of Parkinson’s Disease

Figure 2

The development of pain hypersensitivity in the 6-OHDA-lesioned rats. After testing the baseline response to heat and mechanical stimuli, rats received a bilateral dorsal CPu injection of 6-OHDA or vehicle. (a) Paw thermal withdrawal threshold was significantly decreased in the 6-OHDA-treated rats () than in the sham control rats () on the 4th and 5th weeks after operation. ((b)–(d)) 4 g, 8 g, and 15 g von Frey filament were used to evaluate mechanical hypersensitivity. The 6-OHDA-lesioned rats () showed mechanical hypersensitivity from the 4th and 5th week after the 6-OHDA lesion compared with the sham rats (). , , and compared to the sham animals. ((e)-(f)) At the 5th week after 6-OHDA microinjection, we used the formalin test to determine the changes of chemical-induced pain. There was a significant increase in both phase 1 (0–10 min) and phase 2 (10–60 min) in 6-OHDA-treated rats () compared to the sham animals () (, , and compared to the sham animals).

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