HRP, as a retrograde and anterograde tracer of neuronal connections, increased the sensitivity for detecting the chromagin.[1]
In vitro, treatment with 1 ug of complexed HRP, macrophages interiorized complexes formed in a wide range of HRP/anti-HRP ratios, while FDC's associated with complexes formed in HRP excess only. [2] In vitro kinetic experiment shown that the soluble HRP had more affinity toward guiacol and H2O2 than immobilized HRP. [5]
In vivo, mice were injected 100 mg/ml HRP after 30 sec, enzyme reaction products were weakly detected in interstitium around some thick blood vessels of corticomedullary boundary areas, but within capillaries of cortical areas. After injection 30 min, phagocytosis of HRP by macrophages was scattered throughout the interstitium, which was accompanied by decrease of HRP reaction intensity in interstitial matrices.[3] In vivo test it demonstrated that WGA-HRP (horseradish peroxidase conjugates of either the lectin wheat germ agglutinin) injection resulted in labeling of primary afferents mainly in the substantia gelatinosa of the trigeminal subnucleus caudalis. While B-HRP (choleragenoid) injection, it was found labeling only existed in the magnocellular zone and innermost part of the substantia gelatinosa.[4] In vivo efficacy test it exhibited that the HRP-diaminobenzidine reaction products were heavily distributed in the OVLT and surrounding brain tissues 10 and 60 min after the injection of HRP (50 mg/kg, i.v.) in rabbits, and also were retained in the parenchymal tissues at 24 h post-injection.[6]
References:
[1] Wilczynski W, et al. Transcellular transfer of HRP in the amphibian visual system. Brain Res. 1982 May 6;239(1):29-40.
[2] Chen LL, et al. Distribution of horseradish peroxidase (HRP)-anti-HRP immune complexes in mouse spleen with special reference to follicular dendritic cells. J Cell Biol. 1978 Oct;79(1):184-99.
[3] Wu B, et al. Immuno- and Enzyme-histochemistry of HRP for Demonstration of Blood Vessel Permeability in Mouse Thymic Tissues by "In Vivo Cryotechnique". Acta Histochem Cytochem. 2014;47(6):273-88.
[4] Robertson B, et alTransganglionic transport of wheat germ agglutinin-HRP and choleragenoid-HRP in rat trigeminal primary sensory neurons. Brain Res. 1985 Nov 25;348(1):44-51.
[5] Alshawafi WM, et al. Immobilization of horseradish peroxidase on PMMA nanofibers incorporated with nanodiamond. Artif Cells Nanomed Biotechnol. 2018;46(sup3):S973-S981.
[6] Yamaguchi K, Sieber NC. The capillary of the organum vasculosum laminae terminalis (OVLT) in rabbits is more permeable to horseradish peroxidase (HRP) than that in rats. J Electron Microsc (Tokyo). 2000;49(6):783-91.