Cholinergic, dopaminergic, noradrenergic, or glutaminergic stimulation ventral to the anterior septum does not specifically suppress defensive behavior.

Three experiments investigated neurotransmitters which might function in the neural system ventral to the anterior septum modulating defensiveness in the rat. In the first experiment, a dose dependent suppression of defensive behavior to the experimenter was produced by intracranial infusion of carbachol or physostigmine but not dopamine, norepinephrine, or glutamate. The suppression of defensiveness did not occur when a carbachol-atropine sulfate mixture was infused. In a second experiment the cholinergic antagonists, atropine methyl nitrate or atropine sulfate, did not increase reactivity when infused ventral to the anterior septum although the nonspecific blocking agent lidocaine was effective. In a final experiment, the infusion of carbachol ventral to the anterior septum which had suppressed defensiveness was found to suppress eating and general activity as well, thus suggesting that the effect of carbachol on defensiveness was the result of a non-specific suppression of behavior. It is concluded that the specific modulation of defensiveness by the neural system ventral to the anterior septum is not mediated by acetylcholine, dopamine, noradrenaline, or glutamate.