Norwin H. Becker

FINE STRUCTURE OBSERVATIONS OF THE UPTAKE OF INTRAVENOUSLY INJECTED PEROXIDASE BY THE RAT CHOROID PLEXUS

The uptake by the choroid plexus of adult rats of intravenously injected horseradish peroxidase has been investigated by electron microscopy. Within 4 min, the injected protein passes the capillary and is rapidly distributed through extracellular space and choroidal cells. Peroxidase enters the choroidal cells within coated vesicles which act as pinocytotic vesicles. At 15 min, peroxidase activity is present in numerous membrane-bound vesicles, multivesicular bodies, dense bodies and what appear to be segments of smooth endoplasmic reticulum. None of the peroxidase-containing organelles is seen to empty to the ventricular surface. Egress of the extracellular peroxidase into the cerebrospinal fluid is apparently blocked by apical zonulae occludentes between the choroidal cells.

A comparison of the fine structure of small blood vessels in intracranial and retroperitoneal malignant lymphomas

SummaryThe fine structure of the blood vessels of an apparently primary intracerebral malignant lymphoma was compared with those in another malignant lymphoma in a retroperitoneal lymph node. The essential features of the blood vessels in both cases were the same. They resembled the blood vessels found in normal lymph nodes and were both distinctly different from those seen in normal brain. It was concluded that the direction of differentiation of the blood vessels which arise to nourish the neoplastic tissue is determined by the nature of the tumor rather than the vessels from which they originate.The fine structure of the blood vessels of an apparently primary intracerebral malignant lymphoma was compared with those in another malignant lymphoma in a retroperitoneal lymph node. The essential features of the blood vessels in both cases were the same. They resembled the blood vessels found in normal lymph nodes and were both distinctly different from those seen in normal brain. It was concluded that the direction of differentiation of the blood vessels which arise to nourish the neoplastic tissue is determined by the nature of the tumor rather than the vessels from which they originate.

ISOLATION OF THE PERIAXONAL SPACE OF THE CENTRAL MYELINATED NERVE FIBER WITH REGARD TO THE DIFFUSION OF PEROXIDASE

Horseradish peroxidase was implanted into rat forebrains and the distribution with respect to the periaxonal space was examined. The peroxidase filled the extracellular spaces. Usually, however, the flow stopped at the junction of the outer loop and the outermost lamella of the myelin sheath and at the outermost lateral loop at the node of Ranvier. Therefore, in most cases, the periaxonal space was devoid of peroxidase. Occasionally, however, peroxidase in small amounts evidently penetrated the junctions and could sometimes be clearly demonstrated within the periaxonal space.

Evidence for the functional polarization of micropinocytotic vesicles in the rat choroid plexus.

domie to test its validity have been described elsewhere (Graham and Karnovsky. J. Histochem. Cytochem. 14: 291. 1966; J. Exp. Med. 124: 1123. 1966). The localization of reactioml product in the remial glomerulus resembled somewhat that described previously with MPO (Graham and Karnovsky. J. Exp. Med. 124: 1123. 1966). ImI mice killed 1-7 mimi after imijection, reaction product was present throughout the basement membrane, with the greatest concemitration seemi at the interface betweeni the basement membramie amid the epithehum. The degree of accumulation at this interface was less marked thami that scent previously imi mice injected with MPO. Comisiderable amoumits of reactiomi prodtmct were presemit in the mesamigial spongy areas. By 15 ruin after LPO imijection, reactiomi prodtmct was mio lomuger apparent in the glomerular basememit membrane. Small amounts were still seen in mesamigial spongy areas, and vacuoles contaimiing reaction product were presemit in mesamigial cells. At miomie of the imitervals studied was reactiomi product seen withimi the cytoplasm of glomerular epithelial cells. Uptake of LPO in the apical portiomis of proximal tubular cells (Fig. 2) appeared similar to that described previously with HRPO (Graham and Karmiovsky J. Histochem. Cytochem. 14: 291. 1966), amid is miot described in detail. Reactiomi product appeared first on brush border membramies amid in apical tubular invagimiations. Soomi thereafter it was seen in apical vacuoles, where it was progressively concentrated. In the liver, there was evidence of uptake of LPO by parenchymal cells (Fig. 3). Early, reactiomi product filled the space of Disse, amid many pinocytotic vesicles filled with reaction product were observed. Later, most of the reactiomi product was seen imi larger vacuoles, many of which were near bile camialicuhi. At all imitervals, uptake of LPO by Kupffer cells was prominent. Studies on the uptake of peroxidases in the liver are continuing amid will be considered in detail in a separate report. The use of peroxidases as proteimi tracers offers a number of advantages, some of which have been discussed previously (Graham and Karnovsky. J. Histocheni. Cytochem. 14: 291. 1966; J. Exp. Med. 124: 1123. 1966). Prominemit amomig these is the sensitivity afforded by the amplifyimig effect of enzymatic activity, wherein a few molecules of enzyme can gemierate increasing amounts of reaction product as incubation proceeds. Imi additiomi, peroxidases exist which are comparable mumolecular weight to certain of the plasma proteins, thus making them preferable to large proteins such as ferritimi. The existemice of several peroxidases of differemit molecular weights should be advamitageous in the study of the relationship between molecular size amid proteini transport. Umitil now, however, HRPO, which is smaller thami any of the commomi plasma proteins, has been the omily peroxidase generally available for use as a tracer. Thus the present demonstration that LPO cami be used successfully as a tracer is of some importance, since its molecular weight of 82,000 is slightly greater than that of plasma albumimi. Much remaimis to be learmied before data obtained with peroxidase tracers cami be used with comifidence imi understandimig miaturally occurrimig protein transfer. All available peroxidases are of plant or heterologous animal origimu. At present, no technique exists for comparing the structural bases by which heterologous and homologous proteins are handled by the organism. Although the need for a satisfactory homologous tracer remains, it would appear that the peroxidase tracer method represents the best of the available techniques for the study of the structural basis of protein transfer. The fact that LPO can be used as a tracer is significant in that the fate of proteins of different sizes can miow be compared comiveniently. We thank Miss Sarajayne Limpert, who helped with the development of the cytochemical method and did much of the electron microscopy, amid Miss Claranne Cicarelli, who helped with the preparation of the enzyme.