Intrathecal administration of SSP-saporin

[Sar⁹, Met(O₂)¹¹]-substance P-saporin, a SP-positive nociceptor neurotoxin (SSP-Saporin, Advanced Targeting Systems, San Diego, CA) was prepared in saline (5 ng/μL), and 20 μL was injected intrathecally, 14 days before the nociceptive tests [4; 7]. The addition of [Sar⁹, Met(O₂)¹¹] to substance P conjugated to saporin makes the agent more stable and a more potent toxin than when substance P alone is bound to saporin. The pre-treatment interval and dose were established by Wiley and colleagues [59] and Choi and colleagues [18], who observed prominent loss of neurons expressing the neurokinin 1 (NK1) receptor in the laminae 1 of the lumbar dorsal horn after using this protocol [32; 34; 56; 58].