Microinjection of L-NAME into dorsal raphe nucleus inhibits nociceptive response in sigmoid pain model of rats / 生理学报

ABSTRACT

By means of Fos immunocytochemistry, nicotinamide adenine dinucleotide phosphate-diaphorase (NADPH-d) histochemistry and microinjection methods, the role of nitric oxide synthase (NOS) of dorsal raphe (DR) neurons in the modulation of rats sigmoid pain was studied. The results showed (1) Rats exhibited aversive behavioral responses related to visceral pain after injecting formalin into the sigmoid wall. NOS neurons in DR were up-regulated, in addition, about 8% of NOS-labeled neurons were Fos positive. By contrast, there were no Fos/NOS double-labeled neurons in the control group. (2) Formalin-induced sigmoid pain scores and the expression of Fos in the spinal cord at S1 segment were decreased after microinjecting L-NAME into the DR. These findings suggest that NOS neurons are involved in the modulation of formalin-induced sigmoid pain and that NO may play an important role in the transmission of visceral nociceptive message in the midbrain.