Horseradish peroxidase uptake in Vivo by neuronal and glial lysosomes

Uptake and transport of lectins from the cerebrospinal fluid by cells of the immature mouse brain

40 mice (C57BL/6J) 2, 3, 6, and 10 d old were injected intraventricularly with 2% wheat germ agglutinin (WGA) or soybean agglutinin (SBA). The transport of lectins from the ventricular cerebrospinal fluid (CSF) into brain parenchyma was studied by an unlabelled antibody technique ( BORGES and SIDMAN 1982). The granule product of the immunohistochemical reaction was found in the cytoplasm of ventricular ependymal cells, the choroid plexus and meninges in all age groups studied. Penetration of lectins into brain parenchyma was higher in younger animals and at more immature-cell-surrounded parts of lateral and the IVth ventricle. The stain product was dispersed throughout the neuropil excepting cell nuclei. Higher concentration of lectins appeared in nerve cell cytoplasm of some regions of the brain of younger animals (P2 to P3); in 10 d old mice granules of stain appeared in the cytoplasm of PURKINJE cells and pyramidal neurons of the hippocampus. A fiber-like staining, apparent especially in large commissures adjacent to brain ventricles (corpus callosum, fornix hippocampi) in all age groups, suggests that lectins are transported within axons, even at the earliest postnatal ages. Unlike WGA, densely stained glial cells appeared in parenchyma of SBA injected animals, especially of the younger age group (P3 to P6). The results of this study confirm earlier findings that macromolecules within the ventricular CSF can penetrate into brain parenchyma but suggest that the penetration is higher in less mature animals and at the ventricle regions surrounded by less differentiated parenchyma.(ABSTRACT TRUNCATED AT 250 WORDS)

Transport of pinocytic vesicles in the eye of a snail, Helix aspersa

The heads of small adult snails, Helix aspersa, were injected with horseradish peroxidase (HRP) for one to five hours before extirpating the eyes and preparing them cytochemically for electron microscopy. There was internalization of tracer by pinocytic vesicles (pinosomes) at the bases of types-I and -II sensory cells, ganglion cells and, in lesser amounts, by pigmented supportive cells. Vesicles and vacuoles filled with HRP were transported in two directions: lensward as far distad as the ends of the cells (retrograde) and brainward down the optic nerve (anterograde). We believe that the numerous reacted vacuoles in the cell somata are formed by fusion of vesicles, tubules and C-shaped organelles filled with tracer; we present evidence that they become secondary lysosomes. Sensory cell type II possesses more HRP-reacted vacuoles distally than the other retinal cells. Other vesicles are also described. There was no uptake of tracer by the distal ends of the retinal cells following injection HRP into the hemolymph. The swelling of the optic nerve, immediately behind the eye, contains more HRP-filled pinosomes and vacuoles than does the nerve below the dilatation. The significance of endocytosis and transport of pinosomes within the eye and down the optic nerve is discussed.

Prenatal development of the optic projection in albino and hooded rats

The development of retinofugal projections has been examined in albino and hooded rat embryos from embryonic day 16 to birth (E21.5). Horseradish peroxidase (HRP) was injected intraocularly through the uterine wall and its anterograde transport revealed with TMB and DAB. The retrograde transport of HRP or the fluorescent dyes Nuclear yellow, Fast blue and propidium iodide from optic tract, superior colliculus (SC) or lateral geniculate body (LG) injections was used to demonstrate the origin of the projections. Superficial projections to the contralateral SC were first identified at E16. A light projection to the entire medio-lateral extent of the ipsilateral SC could be detected a day later. The optic axons grow over the surface of the diencephalon at E16 and it was only at later stages that the fibers were observed to invade successively deeper parts of the LG. A superficial projection to the ipsilateral LG could first be detected at E17. Both the ipsilateral and contralateral projections grew through the entire dorso-ventral extent of the lateral geniculate body: some restriction of the axons to their normal adult termination zones could be detected by E21. No difference in the distribution of projections could be detected between the albino and pigmented rats although the projections were lighter, and possibly because of this were detected later, in the albino rats. At all the ages examined in this study labeled retinal ganglion cells were observed in the non-injected eyes after injection of label into the contralateral eye. The use of persistent fluorescent dyes showed that these retinal ganglion cells did not survive for more than 5 days postnatally. The projection to the uninjected eye came preferentially from ganglion cells in the lower nasal retina while the ipsilateral central projections came predominantly but not exclusively from the lower temporal retina of the injected eye. It appears, therefore, that the initial projections of optic axons in the rat are not limited to their normal termination zones and that the choice of pathway at the chiasm appears to be only loosely controlled.

Uptake, intra-axonal transport and fate of horseradish peroxidase in embryonic spinal neurons of the chick

Horseradish peroxidase (HRP) was injected in ovo into the ventral muscle mass of the hind limb of 5- to 7-day-old chick embryos or into the gastrocnemius muscle of 8- to 18-day embryos and localized histochemically. HRP is extensively incorporated via endocytosis into axonal growth cones or presynaptic terminals in the proximity of the injection site. Much of the tracer is taken up in vesicles and small vacuoles. Most of these are smooth-surfaced and only a few are bristle-coated. A small amount of the tracer is also incorporated into the axon terminal through the openings between the axolemma and an intricate membrane channel. The majority of the tracer-laden vesicles and vacuoles rapidly fuse with one another to become large vacuoles, some of which are transformed into multivesicular bodies (MVBs). In axon shafts, many labeled vacuoles and MVBs are transferred to tubule-like organelles, which appear to be the primary carrier for transporting the tracer back to the cell bodies in the lumbar spinal cord. HRP arrives in the sensory ganglia about 0.5-1 hour earlier than in the motoneurons of the lateral motor column. The maximal rate of the retrograde axoplasmic transport is about 3.5 mm/hour. After arriving in the cell bodies, HRP is transferred from tubule-like organelles to discrete vacuoles of various sizes and appearance. Lysosomal dense bodies and HRP-labeled vacuoles can be distinguished ultrastructurally. A fusion of HRP-labeled vacuoles with lysosomal dense bodies or Golgi vesicles was occasionally observed and the density of HRP-labeled vacuoles diminished after 2 to 3 days. Most of the HRP-labeled organelles were found to contain acid phosphatase activity. Therefore, the complete disappearance of HRP by 4 days postinjection is most likely related to lysosomal degradation. Neuronal cell bodies diffusely labeled with HRP were only observed prior to day 6. After day 6, despite various attempts to injure the peripheral axons, only granularly labeled cell bodies were found. This difference may imply that "mature" neurons have a more efficient mechanism for the sequestration of "free" HRP in the cytoplasmic matrix into membrane-bounded organelles. A mature-like retrograde transport mechanism appears to exist at the earliest stages of axonal growth in vivo.

An electron microscopic study of neurones in the lateral geniculate nucleus of the monkey labelled by retrograde transport of horseradish peroxidase

In a previous report horseradish peroxidase (HRP) reaction product has been described as accumulating in a restricted part of neurones in the lateral geniculate nucleus following injections of HRP into the visual cortex of the primate. With the aid of long series of ultrathin sections from the same material labelled neurones have been partially reconstructed in the present study, and it has been confirmed that HRP reaction product aggregates as a group of electron-dense lysosome-like bodies which form a cap to one side of the nucleus.

Endocytic activity of subependymal microglial cells in the toad brain: a cytochemical study of peroxidase uptake

A population of microglial cells that rapidly incorporate extracellular material introduced into the ventricular system has been identified just beneath the ependyma of all four cerebral ventricles in the toad (Bufo marinus). In untreated tissue these cells appear to be scattered, possess few processes and have an elongate shape with their long axes lying parallel to the ventricular surface. Their most distinctive ultrastructural features are nuclei containing clumps of chromatin, cytoplasmic dense bodies and single strands of granular endoplasmic reticulum. When horseradish peroxidase (HRP) is perfused through the ventricular system and the tissue processed using the DAB cytochemical method, the cells change shape and incorporate HRP into cytoplasmic structures. Even after very short perfusion periods (2-5 minutes) cells become rounded, the surface is ruffled and pseudopodia develop that contain characteristic flocculent material. Reaction product for HRP is contained in plain and coated vesicles, tubules, vacuoles and long structures composed of two closely apposed membranes. At these early times, relatively few multivesicular bodies and dense bodies contain reaction product, but when the cells are viewed at longer time periods after the ventricular perfusion of HRP an increasing proportion of the multivesicular bodies and dense bodies contain reaction product. By 320 minutes reaction product is found almost exclusively in these two organelles. In addition, many pseudopodia containing dense bodies with peroxidase activity are found in the neurophile; some, but not all, can be traced from the subependymal microglial cells. The cell bodies have resumed their flattened shape. When compared to the subependymal microglial cells, other brain cells--oligodendrocytes, astrocytes, ependymal cells and neurons--contain relatively little reaction product at short time intervals; only by 320 minutes are moderate amounts of HRP present. Because of the position of the microglial cells and their ingestive capacity, it is suggested that they function to protect the brain from foreign substances entering from the CSF.

Absorption of free and antibody-conjugated horseradish peroxidase to fixed glial cells in tissue culture, a possible source of error in immunohistochemistry

Incubation of cellular preparations with antibody-conjugated peroxidase result in a very strong unspecific staining, for one electropolar binding of the basic enzymic protein with the cell structures. In immunohistochemical practice, it may represent an evil as import as when dealing with immunofluorescence techniques. This background can to a great extent be avoided by rinsing the preparations in buffer at pH = 6.2.

Electron microscopic observations of horseradish peroxidase transported from the caudoputamen to the substantia nigra in the rat: possible involvement of the agranular reticulum

The intracellular distribution of horeseradish peroxidase (HRP) transported intraaxonally from the caudoputaminal complex to the substantia nigra has been examined with the electron microscope. The reciprocal axonal connections between the caudoputamen and the substantia nigra permitted observation not only of HRP transported retrogradely from axons and axon terminals in the caudoputamen to the cell bodies of origin in the pars compacta of the substantia nigra, but also provided information suggesting that HRP may be transported anterogradely by neurons of the caudoputamen to their terminals, which are especially numerous in the pars reticulata of the substantia nigra. Special attention was focused on observations which might elucidate the manner in which exogenous proteins are compartmentalized and transported intracellularly. It is suggested that the agranular reitculum is involved in the retrograde transport of proteins which are pinocytosed near the axon terminal and ultimately reach lysosomes in the perikaryon. A possible anterograde movement of HRP may also involve the agranular reticulum. The implications such findings have on the use of HRP in neuroanatomical tracing techniques are also discussed.