The terminal innervation patterns in young and old guinea pig heart valves: a quantitative analysis using...

The objective of this study was to determine whether and to what extent age-related changes occur in atrioventricular (AV) heart valve innervation. The AV valves from three young adult (3 months) and three older (> 24 months) female guinea pigs were studied. An acetylcholinesterase (AChE) localization method was used to prepare valve whole mounts for analysis. Two methods were used to assess nerve fiber density. Segments of the valves were drawn using a camera lucida/Nikon optiophot system. The density of nerve fibers was calculated from digitized images. The density of nerve fibers was also calculated by counting the points at which the nerve plexus intersected with the grid lines of an ocular graticule. In the bicuspid and tricuspid valves of the older guinea pigs, we observed a marked diminution in the densities of the nerve plexus, particularly in the basal zone, towards the free edges of the valve cusps, and in the chordae tendineae. Whole mount preparations such as those used in our morphological studies of the AV innervation may assist in elucidating the changes in other autonomic nerve plexuses with aging. Further work is required to establish whether and to what extent the loss of valve innervation influences the effectiveness of closure of the valves.