Figure 7. Effects of i.c. microinjection with β-FNA, naltrindole or nor-BNI into the contralateral thalamic MD nucleus on bilateral noxious mechanical- and heat-evoked paw withdrawal reflexes during the exposure to the i.m. noxious 46°C single heating-needle stimulation.

Bilateral mechanical hyperalgesia elicited by the 30 min 46°C heating-needle stimulation was depressed significantly by the i.c. microinjection with μ-opioid receptor antagonist β-FNA into the contralateral MD nucleus. It is suggested that the μ-opioid receptor is involved in thalamic MD nucleus-mediated descending facilitation of mechanically evoked nociception.*P < 0.05 compared with the 46°C i.m. single heating-needle stimulation group. #P < 0.05 compared with the vehicle (0.9% saline) treatment group. BO, baseline response before the i.c. catheterization; B, baseline response before the i.m. heating-needle stimulation; p, post i.c. injection. n = 8 for each group.