This group includes such alkaloids as nicotine, lobeline and cytisine. They have a two-phase action on N-cholinoceptors (excitatory stage is alternated with inhibitory effect). Nicotine is an alkaloid of tobacco leaves. It does not have any therapeutic value. It is used in experimental pharmacology. Nicotine affects both peripheral and central N-cholinoceptors. N-cholinoceptors of the autonomic ganglia, on which nicotine has a two-phase effect, are especially sensitive to it. The first phase (excitation) is characterized by a depolarization of the ganglionic neu­ronal membranes, the second one (inhibition), are provided by competitive antagonism with acetylcholine. Nicotine does not affect the release and hydrolysis of acetylcholine.