Innervation of the mitral valve is strikingly depleted with age

Previous reports demonstrated that mammalian atrioventricular (AV) valves p ossess a dense nerve plexus, consisting of nerve subpopulations which diffe r from each other in densities and patterns of distribution in the valves, and which may have sensory or motor roles in valve function. Although there is extensive evidence that age-related changes occur in autonomic nerves o f animals and humans (Daly et al. J. Pharm; Exp. Ther., 1988;245(3):798-803 ; Ingall et al. Aust. NZ J. Med., 1990;20:570-577; Tumer et al. Exp. Geront ol., 1992;27:301-307), and that these changes contribute to changes in card iac function (Klausner and Schwartz Clin. Geriat. Med., 1985;1(1):119-114), there is little information about age-related changes in heart valve inner vation. In this study, we used acetylcholinesterase (AChE) histochemistry t o localize and compare qualitative and quantitative changes in the innervat ion of the mitral valves in young adult and aged animals of three species. Young adult and aged guinea pigs, mice, and Wistar and Fischer 344 rats wer e anesthetized with Nembutal, the hearts removed, and the mitral valves dis sected out and processed for AChE localization. Camera lucida drawings of t he AChE-positive nerves in representative segments of valve cusps were made directly fr-om slides; these drawings were digitized and subjected to comp uter-assisted image analysis to obtain quantitative information about nerve plexus density in the valves. All three animal species showed profuse AChE -positive innervation in the mitral valves of young adult animals, and decr eases in the density of this innervation in aged animals. The most striking loss of innervation, compared to the young adult, occurred in the mitral v alves of aged Fischer 344 rats, in which large regions of the valves appear ed virtually devoid of nerves. Further studies are needed to investigate wh ether and to what extent age-related losses in heart valve innervation affe ct valvular structure and function. Anat Rec 255:252-260, 1999. (C) 1999 Wi ley-Liss, Inc.