Pain mechanismDescending facilitation from the rostral ventromedial medulla maintains nerve injury-induced central sensitization
Section snippets
Experimental procedures
Male, Sprague–Dawley rats (Harlan, Indianapolis, IN, USA), weighing 200–300 g at the time of surgery were maintained in a climate-controlled room on a 12-h light/dark cycle (light on at 07:00 h). Food and water were available ad libitum. All testing and surgeries were performed in accordance with the policies and recommendations of the International Association for the Study of Pain and the National Institutes of Health guidelines for the handling and use of laboratory animals. These studies
Microinjection sites
Histological verification at the end of the experiments demonstrated the injection sites and cannula tracks as shown in Fig. 1. These microinjection sites have previously been shown to reduce the mRNA signal for the mu opioid receptor in the RVM and surrounding areas including the nucleus gigantocellularis (NGC) (Porreca et al., 2001).
Dermorphin–saporin microinjection and behavioral hypersensitivity
Rats (n=8 per group) received a single bilateral microinjection of distilled water (0.5 μl), dermorphin (3 pmol), saporin (3 pmol), or dermorphin–saporin
Discussion
In the present study, repetitive non-noxious tactile stimulation of the hindpaw produced an increase in the number of FOS-positive cells in the ipsilateral spinal dorsal horn of animals that had received SNL when compared with FOS expression in animals that received sham surgery. The increase in FOS-positive cells was seen in both the superficial and deep dorsal horn laminae and correlated in time with the expression of nerve injury-induced mechanical and thermal hypersensitivity, behaviors
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