Sm. Lopez et al., P75 AND TRKA NEUROTROPHIN RECEPTORS IN HUMAN SKIN AFTER SPINAL-CORD AND PERIPHERAL-NERVE INJURY, WITH SPECIAL REFERENCE TO SENSORY CORPUSCLES, The Anatomical record, 251(3), 1998, pp. 371-383
Human skin, including nerves and sensory corpuscles, displays immunore
activity (IR) for low- (p75) and high-affinity (TrkA-like) receptors f
or nerve growth factor (NGF), the best characterized member of the fam
ily of neurotrophins. This study was designed to analyze the changes i
nduced by spinal cord and peripheral nerve injuries in the expression
of neurotrophin receptors in digital skin, with special reference to n
erves and sensory corpuscles. Skin biopsy samples were obtained from 1
) the hand and toes of normal subjects, 2) below the level of the lesi
on of patients with spinal cord injury affecting dorsal and lateral fu
niculi, 3) the cutaneous territory of entrapped peripheral nerves (med
ian and ulnar nerves), and 4) the cutaneous territory of sectioned and
grafted nerves (median nerve). The pieces were formalin fixed and par
affin-embedded, cut in serial sections, and processed for immunohistoc
hemistry using antibodies against human p75 and TrkA proteins. The per
centage of sensory corpuscles displaying IR for p75 and TrkA-like, as
well as the intensity of IR developed within them, was assessed using
quantitative image analysis. Spinal cord severance causes a decrease i
n p75 IR in Meissner and Pacinian corpuscles, whereas TrkA-like IR did
not vary. In other nonnervous tissues (i.e., epidermis, sweat glands)
, both p75 and TrkA-like IR was diminished or even absent. Similar but
more severe changes were encountered in the skin from the territory o
f entrapped nerves. Finally, in subjects with sectioned-grafted nerves
, p75 IR was found close to controls in nerves, reduced in Meissner co
rpuscles, and absent in the inner core of the Pacinian ones; TrkA-like
IR was in the perineurium, a small percentage of Meissner corpuscles
(about 7%), and the outer core and capsule of the Pacinan corpuscles.
In the nonnervous tissues, p75 IR was practically absent, whereas TrkA
-like IR did not change. No changes in the expression of neurotrophin
receptors were observed in Merkel cells of the different groups. Prese
nt results show the following: 1) expression of nerve p75 IR in human
cutaneous sensory corpuscles is sensitive to central deafferentation,
to blockade or difficulty in axonal transport, and to disruption of ax
onal continuity independently of possible restoration of axonal integr
ity due to grafts; 2) expression of TrkA-like IR in nerves and sensory
corpuscles is sensitive only to nerve transection; 3) the corpuscular
Schwann-related cells are the only cells involved in the above modifi
cations, the perineurial cells remaining unchanged; 4) the expression
of p75 and TrkA-like IR by Merkel cells is independent of normal inner
vation; 5) an adequate innervation of the skin seems to be necessary f
or the expression of p75 but not TrkA-like in nonneuronal cells, espec
ially in the epidermis. A role for NGF in the maintenance of epidermis
integrity is discussed. Anat. Rec. 251:371-383, 1998. (C) 1998 Wiley-
Liss, Inc.