On the role of the baseline firing rate in determining the responsiveness of cingulate cortical neurons to iontophoretically applied substance P and acetylcholine.

The relationship between baseline firing rate and the magnitude of excitatory responses to iontophoretically applied substance P (SP) and acetylcholine (ACh) was determined for neurons in the anterior cingulate cortex of the rat. Whereas the size of responses to ACh was positively correlated with the level of ongoing neuronal activity, no correlation, either positive or negative, could be demonstrated for responses to SP. It seems unlikely that the excitatory effects of SP in this brain area result from release of endogenous ACh.