Alteration of shock titration thresholds in the cat following intrathecal substance P administration

Substance P (SP) was injected intrathecally (10 or 100 micrograms) into cats previously implanted with nerve-stimulating electrodes and the effect on shock titration thresholds was evaluated. Elevated shock thresholds were observed in 5 of 8 cats following the 100 micrograms dose of SP. In addition, one cat exhibited a decreased threshold and two cats showed a triphasic (increase, decrease, increase) response. Overt behavioral effects of intrathecal SP were mild, but suggested that injection of the drug was aversive.