Cardiac responses activated by nicotine in canine ganglial plexus between aorta and pulmonary artery

In order to study the location and function of nicotine-sensitive neurons of cardiac ganglial plexuses, microdissections of collections of fat pads were carried out, and nicotine (100 micrograms) was injected into the ganglial plexus between aorta and pulmonary artery (A-PGP) in 30 anesthetized open-chest dogs. There were numerous ganglia or neurons in A-PGP. Either positive or negative inotropic and chronotropic responses were elicited following injections of nicotine into A-PGP. Control injections of 0.1 ml saline into A-PGP and injections of nicotine (100 or 200 micrograms) into right marginal ganglial plexus did not elicit any cardiac responses. After acute decentralization, nicotine (100 micrograms) was again injected into the same locus of A-PGP. Some positive and negative responses could still be induced, but their frequencies were reduced. These suggest that nicotine can directly activate the efferent parasympathetic and sympathetic neurons and indirectly activate them by stimulating the afferent neurons existing on the surface of dog heart.