The Fine Structure of Neurons

891

223

Rat liver, liver homogenates, and microsome fractions separated therefrom were examined systematically in the electron microscope in sections of OsO4-fixed, methacrylate-embedded tissue and pellets. It was found that most microsomes are morphologically identical with the rough surfaced elements of the endoplasmic reticula of hepatic cells. They appear as isolated, membrane-bound vesicles, tubules, and cisternae which contain an apparently homogeneous material of noticeable density, and bear small, dense particles (100 to 150 A) attached to their outer aspect. In solutions of various osmolar concentrations they behave like osmometers. The findings suggest that they derive from the endoplasmic reticulum by a generalized pinching-off process rather than by mechanical fragmentation. The microsome fractions contain in addition relatively few vesicles free of attached particles, probably derived from the smooth surfaced parts of the endoplasmic reticula. Dense, peribiliary bodies represent a minor component of the same fractions. The microsomes derived from 1 gm. wet weight liver pulp contained (averages of 10 experiments) 3.09 mg. protein N, 3.46 mg. RNA (RNA/protein N = 1.12), and 487 µg. phospholipide P. They displayed DPNH-cytochrome c reductase activity and contained an alcohol-soluble hemochromogen. The microsome preparations proved resistant to washing and "aging." Treatment with versene and incubation with ribonuclease (30 minutes at 37°C.) resulted in appreciable losses of RNA and in partial or total disappearance of attached particles. Treatment with deoxycholate (0.3 to 0.5 per cent, pH = 7.5) induced a partial clarification of the microsome suspensions which, upon centrifugation, yielded a small pellet of conglomerated small, dense particles (100 to 150 A) with only occasionally interspersed vesicles. The pellet contained ∼80 to 90 per cent of the RNA and ∼20 per cent of the protein N of the original microsomes. The supernatant accounted satisfactorily for the materials lost during deoxycholate treatment. The findings suggest that the microsomal RNA is associated with the small particles whereas most of the protein and nearly all of the phospholipide, hemochromogen, and DPNH-cytochrome c reductase activity are associated with the membrane or content of the microsomes.

Section: Morphology Of the Cytoplasm In Parenchymatous Liver Cellsmentioning

confidence: 58%

Section: Discussionmentioning

confidence: 99%

Liver Microsomes

Palade

Siekevitz

1956

891

223

“…These structures have no evident connection with other submicroscopic structures. They are similar to the dense particles found in other tissues by Palade (13) and seem to be particularly concentrated in the nerve cells (14,15). The following statement of the Wiener equation for rod birefringence is based upon the fact that (na + no) is approximately equal to 2ni.…”

Section: Ob Servationsmentioning

confidence: 68%

Polarization and Electron Microscope Study of Frog Nerve Axoplasm

Thornburg

Robertis

1956

1. The submicroscopic organization of nerve axons from R. pipiens and R. catesbiana has been studied by means of polarizing and electron microscopes. 2. In measurements on a series of 85 fresh myelinated axons from which the sheaths had been removed average values were obtained for the total birefringence, +2.5 x 10–4, the form birefringence, +1.4 x 10–4, and the refractive index of the oriented component, 1.523. The average partial volume occupied by axially oriented filaments was computed to be 0.69 per cent. 3. Electron micrographs of fixed myelinated axons demonstrate an average of 93 axially oriented neuroprotofibrils per square micron of cross-section. The neuroprotofibrils are approximately 90 A in diameter, of indefinite length, and occupy a computed partial volume of 0.59 per cent. 4. Mitochondria, neuroprotofibrils, endoplasmic reticulum, and dense particles are seen in electron micrographs of both myelinated and unmyelinated nerve axons. 5. It is concluded that the neuroprotofibrils are present in the living nerve, that they play an important but undetermined role in nerve function, and that these structures are not an artifact of osmium tetroxide fixation.

“…He pointed out that in this cell such cytoplasmic structures are centres of organization of the ergastoplasm. Palay and Palade (14), also noticed similar structures in the cytoplasm of mammalian nerve cells; they considered them to be the Nissl substance or a specialized part of the endoplasmic reticulum. In neither of these studies was there an attempt to correlate the electron microscopy with histochemical studies on the same type of cell.…”

Section: Discussionmentioning

confidence: 97%

The Fine Structure of the Adipose Cell of the Leech Glossiphonia complanata

Bradbury¹,

Meek²

1958

The two distinct types of cytoplasm seen with the light microscope in the adipose cell of the leech Glossiphonia complanata have been identified in the electron microscope image of this cell.One of these, the basophil cytoplasm, contains many well oriented, paired mere-:branes which are much more clearly evident when calcium ions are added to the fixative. The membranes sometimes appear as concentric arrays of lamellae and are thought to represent sections through a phospholipide-containing body. The paired membranes and the concentric lamellae have granules attached to them and resemble in size and structure the membranes of the endoplasmic reticulum encountered in many mammalian cells. Small dense cytoplasmic particles are present throughout the cell; they may be ferritin molecules, derived from the breakdown of haemoglobin taken in as food.On the basis of 'a previous histochemical study and the present electron microscope investigation, it is suggested that these paired membranes are similar to the organized type of mammalian ER and the results seem to confirm the belief that these membranes are composed of layers of phospholipoprotein together with attached particles of ribonucleoprotein.During a recent investigation of the connective tissue of the pond leech, Glossiphonia complanata, histochemical studies were made on the adipose cell, which acts as the main centre for storage of reserve food substances (Bradbury (4)). This cell is interesting, as it contains two distinct cytoplasmic regions, one of which colours intensely with basic dyes, and surrounds the fat drops and the nucleus and is sharply marked off from the second, the peripheral cytoplasm of the cell. This basophil cytoplasm has been termed "ergastoplasm" by Bobin (3), but as no evidence about its submicroscopic structure was then available, a new name was suggested--the " s u r r o u n d " --w h i c h had no functional implications (Bradbury (4)). When the cell is studied with the light microscope, very little structure is visible in this region of the cytoplasm, though by means of the acid haematein test of Baker (1) phospholipide droplets or bodies are found embedded in it; histochemical tests showed also in the same region of the cell the presence of much ribonucleic acid and protein.