Cardiovascular response to the injection of acetylcholine into the anterior cingulate region of the medial prefrontal cortex of unanesthetized rats.

Injection of acetylcholine (ACh) (2.5-60 nmol) into the anterior cingulate cortex caused dose-dependent hypotensive responses (Emax = -25.3 mmHg) and no change in the heart rate. The hypotensive response to 30 nmol of ACh was blocked by local pretreatment with atropine (3 nmol) or 4-DAMP (6.7 nmol), a non-tropine muscarinic antagonist. When the same dose of atropine was injected i.v., no changes were observed in the hypotensive response to intracortical ACh. This observation rules out the possible leakage of ACh into the peripheral circulation and favors the idea of a cortical site of action. The injection of the same dose of ACh into the corpus callosum or the occipital cortex did not cause changes in the cardiovascular system. The present results confirm earlier evidence that the cingulate cortex is involved in the control of the autonomic system and indicate that cholinergic muscarinic receptors in the cingulate cortex mediate a hypotensive response without a change in heart rate.