THE BASEMENT-MEMBRANE AT THE EQUINE HOOF DERMAL-EPIDERMAL JUNCTION

In the equine hoof, the basement membrane connects the heavily keratinised hoof wall to the dense connective tissue of the distal phalanx, a region able to withstand considerable mechanical stress. This study investigated the properties of this important anatomical and physiological structure. In contrast to haematoxylin and eosin, the connective tissue stains, periodic acid Schiff, periodic acid silver methenamine and Azan showed good resolution of lamellar basement membrane. The lamellar basement membrane cross-reacted with mouse monoclonal antibodies raised against human laminin, thereby providing evidence that component of the equine basement membrane. ultrastructure of the equine hoof basement membrane was essentially the same as in other animals but appeared to have many anchoring fibrils and extensions of the lamina densa into the adjoining connective tissue, an arrangement interpreted to convey extra strength to the region. Large areas of the surface of the hoof wall basement membrane could be exposed to examination with the scanning electron microscope by treating tissue blocks with detergent/enzyme or sodium bromide, When epidermal lamellae were separated from their dermal counterparts the basement membrane stayed with the dermis and the dermal lamellae retained their natural shape despite the absence of an adjacent epidermis. The exposed surface of the lamellar basement membrane was generally smooth and unbroken, marked with small indentations and fine wrinkles. At the cut edges of the lamellae, a mesh of fine connective tissue fibres were attached to the inner surface of the basement membrane. The basement membrane of both the coronary and terminal papillae was folded into numerous longitudinal ridges, all parallel to the long axis of the papillae. Like the folds in the basement membrane of the lamellae (the so-called secondary lamellae) the longitudinal ridges of the papillae are probably an adaptation to increase the surface area of attachment of the dermis to the inner hoof wall. The architecture of the equine basement membrane and the tissues adjacent to it is severely disrupted as the pathology of laminitis develops. A study of the basement membrane using the techniques described in this study may add to our understanding of the pathophysiology of equine laminitis.