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Keywords:

  • horse;
  • sensory nerves;
  • neuropeptides;
  • equine foot;
  • lamellated corpuscles

Summary

Sensory innervation of the equine distal forelimb was examined using several different anatomical techniques with each revealing a different morphological component of the sensory apparatus in the foot. Electron microscopic examination of the medial palmar nerve (N. digitalis communis II) revealed predominantly unmyelinated nerve fibres with a ratio of unmyelinated/ myelinated nerves at the level of the metacarpophalangeal joint of 3.67:1. Sensory peptides (substance P, neurokinin A, calcitonin gene-related peptide and peptide histidine isoleucine) were observed immunocytochemically to innervate much of the equine foot, including the dermis of the dorsal wall and sole, the suspensory ligaments (ligamenta sesamoidea collateralia) (CSL) and the distal sesamoidean impar ligament (ligamentum sesamoideum distale impar), the synovial cavities and bones. These sensory peptides were usually associated with the adventia of the arterial vessels rather than the muscularis layer in contrast to neuropeptide Y. None or only scant immunoreactivity was present in the venules and capillary beds. Lamellated corpuscles in the loose connective tissues proximal to CSL appeared to be innervated by myelinated nerves. These different morphological components of sensory nerves innervating the equine digit suggest that these nerves are functionally complex in that during neurotransmission they have effects both within the spinal cord and within the peripheral tissues.