Evaluation of innervation of the mitral valves and the effects of myxomatous degeneration in dogs.
OBJECTIVE
To map aspects of the innervation of the mitral valve complex and determine any association with the development or progression of myxomatous mitral valve disease (MMVD) in dogs.


METHODS
Septal mitral valve leaflets from 11 dogs aged 6 months to > 10 years.


METHODS
Expression of protein gene product 9.5 (general neuronal marker), tyrosine hydroxylase (adrenergic innervation marker), vasoactive intestinal peptide (parasympathetic innervation marker), and calcitonin gene-related peptide (sensory innervation marker) was assessed by use of a standard immunohistochemical technique. Innervation was assessed qualitatively and semiquantitatively. Differences between valvular zones and between groups were analyzed statistically.


RESULTS
MMVD was present in leaflets of all dogs > or = 5 years of age. Innervation was confirmed in all leaflets but was markedly reduced in leaflets of dogs > 10 years of age. Innervation was most dense at the base of valves and mainly associated with the epimysial, perimysial, and endomysial layers of the muscle and blood vessels within the valve. Innervation was reduced within the middle zone of the valve and lacking at the free edge. Innervation was not identified at the tip of the leaflet, the free edge, or the chordae. Nerve fibers were mostly sympathetic, with the remainder being parasympathetic or sensory. Existence of MMVD did not alter the pattern or density of innervation.


CONCLUSIONS
Mitral valve leaflets in the study dogs were innervated, with most of the nerve fibers associated with the myocardium in the valve base. Development of MMVD appeared to precede the reduction of innervation associated with advancing age.
Culshaw
Geoff J
GJ
Division of Veterinary Clinical Sciences, Royal (Dick) School of Veterinary Studies, The University of Edinburgh, EH25 9RG, Scotland. Geoff.Culshaw@ed.ac.uk
French
Anne T
AT
Han
Richard I
RI
Black
Alexander
A
Pearson
Geoff T
GT
Corcoran
Brendan M
BM
D000818:Animals; D004283:Dog Diseases / Q000473:pathology*; D004285:Dogs; D005260:Female; D008297:Male; D008943:Mitral Valve / Q000294:innervation*; D008944:Mitral Valve Insufficiency / Q000473:pathology / Q000662:veterinary*