Objective—To localize substance P (SP) and neurokinin
A (NKA) and their receptors in the insertion of
the distal sesamoidean impar ligament (DSIL), deep
digital flexor tendon (DDFT), and dorsal hoof wall of
healthy feet of horses.
Sample Population—18 healthy feet from horses.
Procedure—Samples from the dorsal hoof wall and
insertion of the DSIL and DDFT of 10 feet were
processed for immunocytochemical analysis, using
rabbit polyclonal antisera raised against SP and NKA.
Tissue sections from 8 feet were incubated with
I125-labeled SP to localize tachykinin receptors and
their specificity and with control solutions of radioactive
SP and excess nonradioactive SP to identify areas
of nonspecific binding.
Results—Many nerves immunoreactive for SP and
NKA were localized to the region of the insertion of
the DSIL and DDFT and the accompanying microvasculature
and arteriovenous complexes (AVC) as well
as to the microvasculature of the dorsal hoof wall.
Specific neurokinin 1 receptors were localized over
the microvessels and AVC of the insertion zone and
small microvessels of the hoof wall.
Conclusions and Clinical Relevance—These results
document that the microvasculature of the equine
foot is richly innervated and has specific receptors
for tachykinins. Distributions of these tachykinin
receptors on the microvasculature suggest that they
form an important vasodilatory mechanism for controlling
blood flow through the DSIL-DDFT insertion
and dorsal hoof wall. (Am J Vet Res 2002;63:222–228)
Objective—To describe microanatomic characteristics
of the insertion of the distal sesamoidean impar
ligament (DSIL) and deep digital flexor tendon (DDFT)
on the distal phalanx in horses.
Sample Population—Healthy feet obtained from 62 horses of various breeds.
Procedure—Feet from 23 horses were used to histologically
examine the insertion of the DSIL and DDFT
(n = 7), its vasculature (10), and neural elements (6).
In 39 other horses, the insertion zone was examined
Results—The insertion of the DSIL and dorsal half of
the DDFT contained bundles of collagen fibers with
intervening loose connective tissue septa with arteriovenous
complexes (AVC) and nerve fibers.
Microscopic examination revealed adaptive changes in
the insertion with regard to proteoglycan content. In
young adult horses, little or no staining for proteoglycans
was evident, whereas in middle-aged horses,
moderate proteoglycan staining was seen. Six older
horses had slight proteoglycan staining at the insertion.
Conclusions and Clinical Relevance—The study
revealed that this region contained a rich neurovascular
complex between the collagen bundles. A gradual
increase in production of proteoglycan, evident at the
insertion of the DSIL and DDFT on the distal phalanx,
indicates that adaptive responses to stress rather
than age alone may be the primary determining factor.
These observations indicate that this insertion site
may be susceptible to stress during stance and
impact loading, because this region appears to be
strategically situated to regulate important neurovascular
functions of the foot. (Am J Vet Res 2002;63:215–221)