Species-specific immunostaining of embryonic corneal nerves: techniques for inactivating endogenous peroxidases and demonstration of lateral diffusion of antibodies in the plane of the corneal stroma.

Species-specific and species-common monoclonal antibodies (MAbs) to nerve-specific cell surface epitopes were used to compare pre-treatment techniques for nerve staining. Endogenous peroxidases were inactivated in four ways: (1) 0.3% hydrogen peroxide (H2O2); (2) 1% periodic acid (PA) (pH 1.85-1.95); (3) sodium meta-periodate (10-40 mM, pH 4.5); or (4) HCl (pH 1.80). Staining of chick and quail corneal nerves and dorsal root ganglia (DRG) nerves with the MAbs was species-specific. Staining of chick and quail corneal nerves was unaffected by pre-treatment with 0.3% H2O2, but was eliminated by pre-treatment with 1% PA. Chick and quail DRG nerve staining tolerated 0.3% H2O2, and at least one epitope also tolerated 1% PA. Corneal nerves of both chick and quail displayed concentration-dependent sensitivity to pre-treatment with sodium meta-periodate; DRG nerves were not sensitive to such pre-treatment. Corneal nerves tolerated pre-treatment with HCI (pH 1.80), whereas DRG nerves did not. These findings indicate sensitivity of corneal nerve epitopes to oxidation, in contrast with sensitivity of DRG nerve epitopes to low pH. Results also indicate that tissue trimming regulated whole-mount staining of corneal nerves, suggesting that antibodies cannot diffuse across corneal basement membranes, even after detergent extraction. However, antibodies are able to diffuse laterally into the stroma from any cut edge.