Fall in the number of intracardiac neurons in aging rats

The neurons of whole cardiac atria were stained using a NADH-diaphorase technique in young adult (3 months old) (GI) and aging rats (20 months old) (GII). Light microscopy revealed differences in the appearance of the neurons in the two groups. In GI, most ganglia contained 50-100 neurons while in GII, most ganglia usually contained 20 neurons. The mean total number of neurons in the atria of GII was 245+/-31, i.e. only 23% of the mean value in GI (1086+/-203). The mean size of the ganglionic neurons (area of maximum cell profile) was 702 microm2 in GI and 1065 microm2 in GII. Histological sections of the ganglia revealed that a capsule of collagen fibers sheaths each ganglion in both groups. In GII, the density of collagen fibers increases in the capsule and in the septa within the ganglia; yellow or red, type I collagen fibers predominate in this group. No elastic fibers were present in the cardiac ganglia of either group. It is suggested that in aging rats, structural changes and reorganization of the remnant neurons accompany neuron reduction.