Differential roles of spinal cholera toxin- and pertussis toxin-sensitive G proteins in nociceptive responses caused by formalin, capsaicin, and substance P in mice

The aim of the present study is to characterize the roles of spinal cholera toxin (CTX)- and pertussis toxin (PTX)sensitive G proteins in the regulation of various nociceptive responses. The effects of intrathecal (i.t.) pretreatments with CTX and PTX on the formalin (subcutaneous)-, capsaicin (i,t,)-, and substance P (SP; i,t,)-induced nociceptive behaviours were examined in mice. Pretreatment with CTX (i.t.; 24 h before) significantly and dose-dependently (0.05-0.5 mug) suppressed both the first and second phases of the formalin-induced nociceptive behaviour. On the other hand, pretreatment with PTX (i.t,, 6 days before) at the same doses (0.05-0.5 mug) did not affect the formalin-induced response. Capsaicin (i.t,, 0.5 mug)and SP (i.t., 0.7 mug)-induced nociceptive behaviours were attenuated by the pretreatment with CTX, In addition, SP-induced nociceptive response was also attenuated by the pretreatment with PTX, However, the capsaicin-induced nociceptive response was not influenced by PTX pretreatment. These findings suggest that, at the spinal cord level, CTX-sensitive G-proteins are involved in the formalin-, capsaicin-, and SP-induced nociceptive behavioural responses, whereas PTX-sensitive G proteins are involved in SP-induced nociceptive response, (C) 2001 Elsevier Science Inc.