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Fig. 4. Survey of a cross-cryosection (5 µm thickness) of nasal gland tissue
stained with Hemalaun and Eosin (A), description of structural correlates
(c.f. Butler et al., 1991) (B)
and immunohistochemical detection of AQP1 (C,D) or AQP5 (E–H),
respectively, in nasal gland tissue obtained from naïve (C,E) or
osmotically stressed (D,G) ducklings. Specific signals at the sites of
antibody binding are visible as brownish precipitates, which are products of
the peroxidase-reactions with diaminobenzidine and hydrogen peroxide as
substrates. The dark speckles within some of the capillaries are red blood
cells (RBCs). Control experiments, in which cryosections were preincubated
with (C1,D1) or without (C2,D2) 3% hydrogen peroxide-solution for 30 min at
room temperature before immunostaining without primary antibody, revealed that
endogenous peroxidases of RBCs reacted non-specifically with the peroxidase
substrates. Note the presence of AQP1 in capillary endothelial cells in tissue
of naïve animals (C). Epithelial cells of the secretory tubules or the
ducts are devoid of AQP1-related signals. Note the expression of AQP5 in
individual cells lining the primary and central ducts. Apical as well as
basolateral plasma membrane compartments of ductal cells in glands of
naïve ducklings are labelled (F). Much less immunostaining was observed
in nasal gland cryosections obtained from osmotically stressed ducklings using
AQP1-(D) or AQP5-specific (G,H) antibodies, respectively.
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