Comparative quantitative study of the intrinsic cardiac ganglia and neurons in the rat, guinea pig, dog and human as revealed by histochemical staining for acetylcholinesterase

Abstract

This study was conducted to determine the overall number of intrinsic neurons distributed through-out the entire heart, in which most neurons are located inside of intramural ganglia and are hidden to observers. For this reason, we attempted to ascertain: (1) how the number of neurons located inside of intrinsic cardiac ganglion is related to its area, and (2) whether this relationship is dependent on age and species of animals. Hearts of rats, guinea pigs, dogs and humans were used to examine intramural ganglia stained histochemically for acetylcholinesterase (AChE). The number and parameters of neurons located inside of 104 ganglia were estimated in serial sections. Although the revealed intrinsic cardiac ganglia varied extremely in shape and size, two different types were identified: the globular and plain ones. In the plain ganglia, perikarya of side by side situated neurons were always intensely stained for AChE and, being clearly discernible, they could be reliably counted in any plain ganglia on total heart preparations using a contact microscope. Contrarily, neuron somata in the globular ganglia were densely packed above one another and their perikarya were almost indiscernible for the observer. Counting of neurons located inside of globular ganglia was possible in serial sections only. The largest cardiac ganglia were revealed in dogs, in which some globular ganglia containing up to 2000 neurons occupied more than 1 mm2. In spite of evident species-dependent differences with respect to frequency of large ganglia, the majority of intrinsic cardiac ganglia both in humans and animals were comparatively small, involved approximately 100-200 nerve cells and occupied an area ranging from 0.01 to 0.17 mm2. Overall, the number of neurons located inside of globular ganglion was related to its area (correlation coefficient = 0.82). However, the correlation coefficients between the globular ganglion area and its neuron number were unequal in different species.