Effects of substance P analogues on spinal dorsal horn neurons

The effects of iontophoretically applied (D-Pro2, D-Phe7, D-Trp9)-SP and (D-Pro2, D-Trp7,9)-SP on the spontaneous and evoked activity of functionally identified cat spinal dorsal horn neurons have been investigated in vivo by means of extracellular single unit recording technique. In addition, the rat spinal cord slice preparation has been used to study the actions of (D-Pro2, D-Trp7,9)-SP and (D-Arg1, D-Pro2, D-Trp7,9, Leu11)-SP on the resting membrane potential of dorsal horn neurons and also on their responses to dorsal root stimulation and exogenous SP application. We have observed that both (D-Pro2, D-Phe7, D-Trp9)-SP and (D-Pro2, D-Trp7,9)-SP produced an excitation of about 15% of all neurons tested and had a weak antagonistic effect against SP in the cat spinal cord. (D-Pro2, D-Trp7,9)-SP suppressed the SP-induced excitation in 63% of examined cells. In addition, depression of the glutamate-induced excitation and spontaneous activity was evident in 10% and 19% of the cat dorsal horn neurons tested, respectively. In the spinal cord slice preparation (D-Arg1, D-Pro2, D-Trp7,9, Leu11)-SP proved to be a more potent antagonist of the SP-induced depolarization and the dorsal root-elicited slow depolarization, if compared with (D-Pro2, D-Trp7,9)-SP.