Variations in atrioventricular valve innervation in four species of mammals

Abstract

In this series of studies, the innervation patterns of whole-mount preparations of bicuspid and tricuspid valves were studied by light microscopy in the mouse, rat, guinea pig, and opossum. The acetylcholinesterase-positive networks of nerve fibers showed many similarities in the basic patterns of valve innervation in all of the species studied, but several interspecies variations were observed. The basal zone of the valve adjacent to the fibromuscular atrioventricular ring displayed the most dense plexus of nerves, with acetylcholinesterase-positive fibers being seen across the width of the valve. In the intermediate zone of the valve, less dense plexuses of nerve fibers were found; and these were more numerous in the cuspal areas and less numerous in the intervening commissural areas. In the distal portions of the valve, nerve networks arborized extensively, with some of their nerve fibers extending toward the chordae tendineae and the free edges of the valve cusps. Only in the guinea pig and opossum did these fibers reach the free margin of the valve cusp, where they either ended directly as free nerve endings or lay parallel to the free edge of the cusp, often running between adjacent chordae tendineae. Although the patterns of innervation were similar in both bicuspid and tricuspid valves, the innervation density of the bicuspid valve was greater than that of the tricuspid valve for each species examined. A distinguishing feature of guinea pig and opossum tricuspid valves was that their chordae tendineae were relatively more prominent and more densely innervated than the bicuspid chordae tendineae. Free nerve endings with no light microscopic evidence of specialization were present throughout the bicuspid and tricuspid valves of all species studied. Some nerve endings in the opossum showed evidence of specialization, with brush-like arborizations leading to presumed free terminals seen chiefly in the distal zone of the valve cusps. Although some general tendencies were apparent, we have demonstrated that interspecies heterogeneity exists in the terminal networks of the atrioventricular valves of mouse, rat, guinea pig, and opossum.

Active stiffening of mitral valve leaflets in the beating heart

“…Our working hypothesis is that mechanoreceptors in the leaflet may monitor leaflet stretch and that leaflet sensory (afferent) nerves transmit this information for local reflex and/or central processing. Anterior leaflets are known to be richly innervated with sensory and motor nerves (1,19,20,36,(43)(44)(45) [adrenergic and cholinergic (6, 8 -10)], with unmyelinated axons (18) and thick myelinated fibers (8,18,29,(43)(44)(45) (which may serve as mechanoreceptors) coursing through the atrial subendocardial plexus. Leaflet contractile elements could thus be appropriately activated via motor nerves to maintain constant anterior MV leaflet shape and position immediately before and during valve closure over the wide range of LV operating pressures and volumes.…”

“…Black springs, collagen; red arrows, valvular interstitial cells; red interdigitating symbols, leaflet atrial muscle. (29)], annulus, leaflet, chordae, and papillary muscles (1,6,8,10,12,18,26,(43)(44)(45) to carry this stimulus from the aorticmitral continuity into the anterior leaflet. Within the anterior leaflet, however, no myoneural junctions are observed (18,39), the neuromuscular distance being Ͼ50 nm and filled with connective tissue (8,18); thus contractile myofibers in the leaflet are not directly innervated, and paracrine action is most consistent with our findings.…”

Changes in peptidergic nerves in the atrioventricular valves of streptozotocin-induced diabetic rats: A confocal microscopy study

“…Although recent studies have reported PGP 9.5, TH, NPY, SP and CGRP-like immunoreactive nerves in the atrioventricular valves (Ahmed et al, 1997), the changes of peptidergic nerves in the atrioventricular valves of the diabetic rat have not been studied. The zones of the atrioventricular valves were termed as basal, intermediate and distal zones in previous studies (Williams et al, 1990;Jew et al, 1996;Ahmed et al, 1997;Jew and Williams, 1999). The changes of peptidergic nerves in the atrioventricular valves at 24 months post-diabetes was increased compare with that at 12 months post-diabetes.…”

“…This has been well documented in the human cardiac valves with age from 3 months to 21 years (Marron et al, 1996). The networks of the atrioventricular valves were termed as "primary plexus" and "secondary plexus" in previous studies (Williams et al, 1990 andAhmed et al, 1997). In the diabetic rat, there were less NPY-like immunoreactive nerve fibres in the atrioventricular valves and chordae tendinae.…”

“…The presence of dense plexuses of NPY-like immunoreactive nerve fibres in the rat atrioventricular valves and chordae tendinae confirms a previous study (Ahmed et al, 1997). Early studies described the density of nerve fibres of the mitral valve was greater than that of the tricuspid valve (Williams et al, 1990) and the nerve density within the anterior leaflet was greater than the posterior leaflet of the mitral valve (Marron et al, 1996). A recent study has reported degenerated acetylcholinesterase (AchE)-like profiles of nerve fibres in the aged mitral valves (Jew and Williams, 1999).…”