A reliable, standardized method for ultrastructural electron microscopic radioautography

Autoradiography of mossy fiber terminals in the fastigial nucleus of the cat

Terminal boutons of mossy fiber collaterals in the fastigial nucleus originating from the nucleus reticularis tegmenti pontis, the bulbar reticular formation, and the medial vestibular nucleus were studied with high-resolution autoradiography in order to examine their ultrastructural features and synaptic relations. Labeled mossy fiber boutons ranged in size from 0.5 to 5 micron in diameter, and they all contained clear and spherical vesicles in an electron-lucent matrix, mitochondria, and some fine tubular elements. These boutons form asymmetric synapses with dendritic profiles of different sizes. No evidence was found for mossy fiber termination on the soma of fastigial neurons. Two types of mossy fiber terminals were distinguished on the basis of the aggregation of synaptic vesicles: one type with clustered vesicles and one type with densely packed vesicles, occurring in equal number from all sources. Furthermore, the applicability of the congruity hypothesis is confirmed for the general identification of terminals.

Synthesis and migration of 3H-fucose-labeled glycoproteins in the retinal pigment epithelium of albino rats, as visualized by radioautography

3H-fucose was injected into the vitreous body of the eye(s) of 250-gm rats, which were then killed by means of an intracardiac perfusion with glutaraldehyde after intervals of 10 min, 1 and 4 hr, and 1 and 7 days. The eyes were removed and further fixed, and pieces of retina were processed for light and electron microscope radioautography. Light microscope radioautography showed that the pigment epithelial cells actively incorporated 3H-fucose label. The intensity of reaction peaked at 4 hr after injection of the label and then slowly declined. Quantitative electron microscope radioautography revealed that, at 10 min after 3H-fucose injection, over 70% of the label was localized to the Golgi apparatus, indicating that fucose residues are added to newly synthesized glycoproteins principally at this site. With time the proportion of label associated with the Golgi apparatus decreased, but that assigned to the infolded basal plasma membrane, the apical microvilli, and various apical lysosomes increased. These results indicate that in retinal pigment epithelial cells newly synthesized glycoproteins continuously migrate from the Golgi apparatus to lysosomes and to various regions of the plasma membrane. In this case, the membrane glycoproteins may play specific roles in receptor functions of the basal plasma membrane or phagocytic activities at the apical surface. Very little label migrated to Bruch's membrane, indicating either a very slow turnover or a paucity of fucose-containing glycoproteins at this site.

The role of secretory granules in the transport of basement membrane components: radioautographic studies of rat parietal yolk sac employing 3H-proline as a precursor of type IV collagen

Biosynthesis of type IV collagen in the parietal endodermal cells of 12 day gestant Sherman rats was examined following intraconceptal injection of 3H-proline. The concepti were removed at times varying from 2 minutes to 24 hours after the injection. The parietal wall of the yolk sac, including endodermal cells and the associated basement membrane known as Reichert's membrane were processed for electron microscopic radioautography. Silver grains were counted over the organelles of endodermal cells as well as over Reichert's membrane. Radioactivity was high in endodermal cells during the first 2 hr after 3H-proline injection and later dropped to some extent, while radioactivity rose in Reichert's membrane. Examination of endodermal cell organelles showed some early labeling over rER and Golgi apparatus without a clear-cut trend, except for a drop in Golgi label at late times after 3H-proline injection. The density of silver grains over secretory granules rose significantly by 40 min, reached a high peak by 4 hr and then declined at the time when radioactivity increased over Reichert's membrane. Furthermore, the radioactively-labeled secretory granules were localized mainly at the trans Golgi face soon after injection and near the cell surface adjacent to Reichert's membrane at later times. Biochemical reports indicate that a substantial amount of the proline taken up by the 12-14.5 day rat embryo endodermal cells is incorporated into type IV collagen. Since there is high labeling of the secretory granules from 40 min to 4 hr and the labeled granules are associated with the Golgi apparatus at early times, it is proposed that collagen precursors are processed through rER and Golgi apparatus, packaged into secretory granules and then transported to the cell surface where type IV collagen or its precursors are released and subsequently deposited into Reichert's membrane.

Calcitonin receptor binding as a marker of osteoclast heterogeneity in osteopetrotic rodents

We have employed a radioautographic technique to examine in vivo receptor binding of calcitonin to osteoclasts in four rodent mutants with osteopetrosis. 125I-Labeled calcitonin was injected intravenously alone or with excess unlabeled calcitonin to osteopetrotic (op/op), osteosclerotic (oc/oc), and microphthalmic (mi/mi) mice and to incisor absent (ia/ia) rats. Similar experiments were performed simultaneously in phenotypically normal littermates. Specific binding of calcitonin to receptors on osteoclasts and osteoclast morphology were then examined by light and electron microscope radioautography. Calcitonin binding was increased in mi/mi mice, where osteoclasts were abundant but reduced in size, and was also increased in op/op mice in association with an undulated and redundant osteoclast cell membrane. Binding of the hormone was markedly diminished on osteoclasts of oc/oc mice and ia/ia rats. Thus, in these rodent models of osteopetrosis all of which manifest reduced skeletal remodeling and share a recessive pattern of inheritance, considerable heterogeneity of osteoclast characteristics was demonstrable. Although calcitonin may play no primary pathogenetic role in most forms of this disease, calcitonin receptor binding is a morphological and functional marker of osteoclasts that can be used in assessing the pathophysiology of disorders of bone remodeling.

Osteodentin formation in rat incisor as visualized by radioautography after 3H-proline administration

Osteodentin formation was studied in rat incisor pulp after adriamycin administration. Male Sprague Dawley rats (100 +/- 5 gm) were injected intravenously with adriamycin (5 mg/kg body weight), and after 7 days they were again injected intravenously with 3H-proline (3 microCi/gm). These animals were killed in groups of three from 5 minutes to 4 hours after proline injection by perfusion with 3% phosphate-buffered formaldehyde followed by 2.5% phosphate-buffered glutaraldehyde. Control animals injected with only physiological saline, and 7 days later with 3H-proline (3 microCi/gm), and were killed at the same time intervals. Radioautography on sections showing osteodentin formation revealed that at 5 minutes after 3H-proline injection the labeling was located over the cells associated with the osteodentin matrix. At 1 hour after injection the labeling was located over the cells and the matrix, while at 4 hours the labeling was seen only over the matrix. It therefore appears that at least a proline-containing component of the osteodentin matrix is synthesized and secreted by the cells associated with it.

Autoradiographic studies of the synthesis of RNA and protein as a function of cell volume in Streptococcus faecium

Mid-exponential-phase cultures were either labeled continuously with tritiated leucine and uracil or pulse-labeled with tritiated leucine. The amount of leucine and uracil incorporated into protein or RNA per cell was determined by grain counts of autoradiographs of cells seen in electron micrographs; the volume of each cell was determined by three-dimensional reconstruction. The average number of autoradiographic grains around cells continuously labeled with uracil and leucine increased linearly with cell volume. In contrast, while the average grain count around cells pulse-labeled with leucine increased in a near-linear fashion over most of the volume classes, less than the expected number of grains were seen around cells in large- and small-size classes. The distribution of grains around cells from both the continuously and pulse-labeled populations could be fit at the 5% confidence level with a Poisson distribution modified to take into consideration the volume distribution of each population of cells analyzed. These findings suggested that large changes in the density of RNA and protein do not occur in most cells as they increase in size; however, there may be decreases in the rate of protein synthesis in some large and small cells. The decrease in the rate of protein synthesis appears consistent with the hypothesis that new sites of envelope growth must be introduced into cells that are close to the division event to restore rapid growth.

Evidence for a pool of non-recycling transferrin receptors in peripheral sheep reticulocytes

Sheep reticulocytes from phlebotomized animals have a total transferrin binding potential that may exceed by an order of magnitude the surface binding capacity. Steady state uptake of transferrin at 37 degrees C is generally less than 50% of the total transferrin binding capacity. During long-term incubation of the reticulocytes, all transferrin binding ability is lost, the ability to internalize being lost most rapidly. The loss in ability to bind transferrin during long-term incubation is independent of the number of surface transferrin binding sites, since removal of surface receptors with pronase does not affect the rate of loss of the internal pool of receptors during long-term incubation. Moreover, after removing surface receptors with pronase, only a fraction of the original number of receptors is restored to the surface, despite the presence of a large pool of internal receptors. These data suggest that only a fraction of the internal pool of receptors is capable of recycling to the cell surface in sheep reticulocytes.

In vivo demonstration by radioautography of binding sites for insulin in liver, kidney, and calcified tissues of the rat

An in vivo binding assay using radioautography was employed to visualize insulin receptors in rat tissues. Two and one-half minutes after the intravenous injection of 125I-insulin, free hormone was separated from bound hormone by whole body perfusion with lactated Ringer's solution followed by perfusion with glutaraldehyde. The localization of bound hormone, fixed in situ by perfusion with glutaraldehyde, was determined. Nonspecific binding of labeled insulin was noted in the proximal convoluted tubules of the kidney cortex, prebone and adjacent bone, predentin and adjacent dentin, and enamel. Specific binding sites were observed at the periphery of hepatocytes, over osteoblasts, and in relation to the endothelial cells of fenestrated capillaries within the papillary layer of the maturation zone of the incisors.

Glycoprotein synthesis in the Golgi apparatus of spermatids during spermiogenesis of the rat

During steps 1-7 of spermiogenesis the Golgi apparatus contributes to the formation of the acrosomic system which develops at the surface of the nucleus. Later, in step 8, the Golgi apparatus detaches from the acrosome and remains suspended in the elongated cytoplasm until it degenerates during step 16. Using 3H-fucose as a tracer and the radioautographic technique, we observed that the Golgi apparatus incorporates the tracer and delivers the labeled glycoproteins to the developing acrosomic system during steps 1-7 of spermiogenesis, to multivesicular bodies during steps 1-9, and to the remaining cytoplasm and plasma membrane during steps 1-15. Throughout these steps of spermiogenesis the Golgi apparatus does not show major changes in structure; it is composed of a cortex made up of connected stacks of saccules and a medulla showing a loose aggregate of vesicular profiles. Glycoprotein synthesis in this Golgi apparatus, before and after it contributes lysosomal glycoproteins to the growing acrosomic system, was quantitatively assessed in electron microscope EM radioautographs of tissue sections from animals sacrificed at 1, 4, 8, and 24 h of 3H-fucose injection. The incorporation of the labeled sugar was found to remain quantitatively similar during steps 1-15 of spermiogenesis, and therefore, no shift in glycoprotein synthesis took place following separation of the Golgi apparatus from the acrosomic system. Throughout these steps, fucose molecules are first incorporated in the cortex of the organelle and subsequently transported to the medulla, where they temporarily accumulate before being delivered, depending on the step of spermiogenesis, to the acrosomic system, to the multivesicular bodies, and also, presumably, to the plasma membrane.

Quantitative analyses of axonal endings in the central nucleus of the inferior colliculus and distribution of 3H-labeling after injections in the dorsal cochlear nucleus

Quantitative analyses of electron microscopic (EM) autoradiographs were used to identify the afferents from the dorsal cochlear nucleus in the central nucleus of the inferior colliculus (IC) in the cat. In order to localize the sources of radioactivity, material from axonal transport experiments was analyzed by means of a hypothetical grain procedure which takes the cross-scatter of beta particles into account. Measurements of the synaptic vesicles in axonal endings and a cluster analysis were used to identify different groups of endings. In order to determine which types of endings arise in the dorsal cochlear nucleus, axonal endings labeled after axonal transport and unlabeled endings were characterized and compared to the groups defined by the cluster analysis. Axonal endings with round synaptic vesicles were labeled with more than 2 grains/micron2 which was about 30% of the radioactivity in the central nucleus of the IC. This was six to seven times greater than if the radioactivity had been randomly distributed. Other tissue compartments usually had less radioactivity. Some myelinated and unmyelinated axons were labeled, but, as a group they had lower amounts of radioactivity than predicted by random labeling. In most cases, only low levels of activity were found in glial and postsynaptic structures. Five groups of axonal endings in the medial part of the central nucleus were identified by an analysis which clustered similar types of endings. The variance of the longest axis, the mean diameter, the variance of area, and the mean area of the synaptic vesicles were the variables most useful in distinguishing these five groups. Axonal endings with round synaptic vesicles were classified as either small, or large, or very large, while endings with pleomorphic vesicles were either large or small. Using measurements of the cross-sectional diameter of dendritic microtubules, samples of digitized axonal endings from normal and experimental cases were normalized and could be compared directly to the groups defined by the cluster analysis. Microtubules were 21.7 nm (+/- 1.6) in average diameter. After injections of 3H-leucine and/or proline in the dorsal cochlear nucleus, most of the labeled endings in the IC contained small, round vesicles (less than 47 nm in diameter) although a very small number of endings with large, round vesicles also were labeled.(ABSTRACT TRUNCATED AT 400 WORDS)

SERGE, the subcellular site of initial hepatic glycogen deposition in the rat: a radioautographic and cytochemical study

Hormonal control of hepatic glycogen and blood glucose levels is one of the major homeostatic mechanisms in mammals: glycogen is synthesized when portal glucose concentration is sufficiently elevated and degraded when glucose levels are low. We have studied initial events of hepatic glycogen synthesis by injecting the synthetic glucocorticoid dexamethasone (DEX) into adrenalectomized rats fasted overnight. Hepatic glycogen levels are very low in adrenalectomized rats, and DEX causes rapid deposition of the complex carbohydrate. Investigation of the process of glycogen deposition was performed by light and electron microscopic (EM) radioautography using [3H]galactose as a glycogen precursor. Rats injected with DEX for 2-3 h and [3H]galactose one hour before being killed displayed an increasing number of intensely labeled hepatocytes. EM radioautography revealed silver grains over small (+/- 1 micron) ovoid or round areas of the cytosome that were rich in smooth endoplasmic reticulum (SER) and contained a high concentration of small dense particles. These distinct areas or foci of SER and presumptive glycogen (SERGE) were most numerous during initial periods of glycogen synthesis. After longer exposure to DEX (4-5 h) more typical deposits of cytoplasmic glycogen were evident in the SERGE regions. Several criteria indicated that the SERGE foci contained glycogen or presumptive glycogen: resemblance of the largest dense particles to beta-glycogen particles in EM; association of 3H-carbohydrate with the foci; removal of particles and label with alpha-amylase; and positive reaction with periodic acid-chromic acid-silver methenamine. The concentration of SER in the small foci and the association of newly formed glycogen particles with elements of SER suggest a role for this organelle in the initial synthesis of glycogen.

An EM-autoradiographic and EM-HRP study of the commissural projection of the superior colliculus in the cat

Terminals of the commissural projection in the cat were characterized ultrastructurally by autoradiographic and horseradish peroxidase methods. The results of the two studies are complementary. Terminals of commissural cells are present in the intermediate and deep layers of the cat superior colliculus. Two distinct populations of terminals are present: one containing mostly round vesicles and forming asymmetric specializations, and a second containing mostly pleomorphic vesicles and forming symmetric specializations. Both populations contact small dendrites or dendritic appendages. The two populations, mostly round and mostly pleomorphic, are present in the ratio of 2:1. Terminals measure approximately 1.1 micron in mean diameter and contact profiles ranging in size from 0.2 to 4.6 micron. There is no significant difference between the two populations in either pre- or postsynaptic profile size. The colocalization of terminals of commissural neurons with other afferent and efferent projections of the intermediate layers of the superior colliculus is discussed.

Dynamic histology of the antral epithelium in the mouse stomach: II. Ultrastructure and renewal of isthmal cells

The isthmus of typical mucous units of the pyloric antrum was investigated in 3- to 4-month-old CD1 mice using light and electron microscopy as well as 3H-thymidine radioautography. On the average, the isthmus measured 25 microns in length and was composed of 36 isthmal cells and two enteroendocrine cells. Isthmal cells generally displayed features found in embryonic cells, such as many free ribosomes, scant organelles, and a large reticulated nucleolus, and were, therefore, at an immature stage of development. Isthmal cells could be devoid of secretory granules ("granule-free cells," 2%) or contain a few small, spherical, PA-Schiff-positive, mucous granules in their apex. The granules in some of the cells had a variegated appearance and a diameter averaging 235 nm ("mottled granule cells," 39%); in other cells, the granules had a large diameter, 278 nm, with a pale background and a dense core ("core granule cells," 28%); while in still others they were homogeneously dark and measured 264 nm ("dense granule cells," 12%). Finally, some cells included a mixture of core and dense granules ("mixed granule cells," 14%). One hour after a single injection of 3H-thymidine, 37% of the isthmal cells were labeled. Each of the five isthmal cell types could acquire label and, therefore, divide. After one or more days of continuous 3H-thymidine infusion, all isthmal cells were labeled. Their turnover time was estimated to be 16.1 hr (t1/2 = 11.2 hr). The isthmus is thus composed of several cell types which are turning over rapidly. While all are relatively immature, the various types are thought to represent different developmental stages in the life history of an isthmal cell. A model devised on this basis proposes that the granule-free cells are stem cells, from which mottled granule cells are derived. These in turn evolve into either the dense granule cells of the upper isthmus or the core granule cells of the lower isthmus, or into the mixed granule cells (which are believed to develop eventually into dense granule cells or core granule cells). Maintenance of a steady state requires that the rapid production of isthmal cells be associated with rapid emigration; the dense granule cells presumably going to the pit and the core granule cells to the gland. The turnover of isthmal cells is accordingly described as following a "bidirectional pattern" of renewal.

NH2-terminal specificity and axonal localization of adrenocorticotropin binding sites in rat median eminence

Adrenocorticotropin binding sites in the rat median eminence have been localized in vivo. These binding sites occur in the basalar zone, which is rich in axonal endings. Using competitive binding and quantitative light-microscope radioautography, we found that the median-eminence binding site, in contradistinction to the adrenal receptor, binds specifically the residue 4-10 region of the adrenocorticotropin molecule. Using quantitative electron-microscope radioautography and median-eminence deafferentation, we localized the binding sites to axon terminals in this region. In time-delayed uptake studies using light-microscope radioautography, we failed to observe concentration of radiolabel in neurons of the medial basal hypothalamus after the direct injection of radioiodinated adrenocorticotropin(1-24) into the median eminence.

The application of cobalt labelling to electron microscopic investigations of serial sections

The cobalt labelling technique can be applied to ultrathin serial sections and subsequent electron microscopical investigations with the following modifications: a prolonged, up to 12 h, fixation of the tissue in aldehydes; a shortened, 15 min, postfixation in OsO4; embedding in soft resin block by using a higher proportion of plasticizer in the polimerizing mixture; mounting of 5 micrometers thick serial sections between two layers of Agar-Agar coatings; performing the intensification of the Agar section-Agar sandwich with a physical developer containing a low percentage of the reductive agent; reembedding selected thick sections for ultrathin serial sectioning and staining with uranile acetate and lead citrate. The technique unambiguously shows all labelled profiles, and preserves the fine structural details of the surrounding tissues.

Reduction due to ageing of TSH-stimulated thyroid hormone release in the cream hamster

The in vitro secretion by thyroid lobes from young (2-month-old) and from "aged" (more than 21 months old) male cream hamsters was estimated by measuring the butanol-extractable 125I (BE-125I) released into the medium after 2 and 4 h of incubation in the presence or absence of thyroid stimulating hormone (TSH). Lobes were fixed at the end of incubation for examination by both light and electron microscopy. Other lobes from both groups were collected for estimation of cyclic AMP contents. BE-125I release by lobes from aged animals after TSH stimulation was significantly lower than that of young animals. Similarly, pseudopods resorbing colloid, the morphological markers of secretion, were much less prominent in the aged group than in the young group. As this observation and the reduced BE-125I release contrast with an equivalent increase of cyclic AMP in both the young and aged groups, it is suggested that the age-dependent defect resulting in reduced hormone secretion is located at a step beyond the generation of cyclic AMP in the cascade of events occurring between binding of TSH to plasma membrane receptors on the target cell and hormone release.

Structure, development, and cytochemical properties of the nucleolus-associated "round body" in rat spermatocytes and early spermatids

The "round body," a spherical structure typically associated with a nucleolus in male germ cells of the rat, has been examined in the electron microscope using routine and cytochemical methods to determine its structure, composition, and mode of development. Cytochemical analysis indicates that the round body includes neither nucleic acid nor lipid, but is composed of nonhistone protein which appears in the form of 1.6-nm-wide fibrils. Development begins in late leptotene, when a single round body appears in each spermatocyte as an irregular spheroid located along the inner surface of the nuclear envelope. During subsequent stages of the meiotic prophase, the round body leaves the nuclear envelope, becomes a regular sphere, and gradually enlarges from a diameter of 0.4 micron in leptotene to 1.6 micron in diplotene. Concurrently, lacunae appear within its substance and enlarge. At each maturation division, the amount of round-body material is decreased by about half, presumably because the constituent proteins are dissociated at metaphase, distributed between the two daughter cells at telophase, and reconstituted into half-sized round bodies. As spermiogenesis proceeds, the round body shrinks gradually and disappears at step 8. Soon after its appearance at leptotene, the round body becomes associated with and is surrounded by the pars granulosa of one of the nucleoli. Moreover, 3H-uridine incorporation into nucleolar RNA is high as long as the size of the round body increases, but is low or absent when it decreases. It is possible, therefore, that the round body exerts some control on nucleolar activity in meiotic cells.

Assessment of resolution by half distance values for tritium and radioiodine in electron microscopic radioautographs using Ilford L4 emulsion developed by "solution physical" or D-19b methods

Half distance values for electron microscopic (EM) radioautographs with the isotopes 3H and 125I were determined using Ilford L4 emulsion processed with either fine grain, solution physical development, or filamentous grain, chemical development with D-19b. 3H- and 125I-line sources, obtained by cutting perpendicular sections from sections of 3H-labeled methacrylate or 125I-labeled thyroid glands, were processed for EM radioautography. The distribution of silver grains around a line source was determined by measuring their distance from the source in photographs of EM radioautographs. The number of silver grains per unit distance from the line source was plotted on graphs and half distance values were calculated. With solution physical development, the half distance value was 74 nm for 3H and 80 nm for 125I; whereas with D-19 b development it was 187 nm for 3H and 157 nm for 125I. Since solution physical development produced a reduction of about 50% in the half distance values for both isotopes, it is concluded that the production of fine grain by this method provides better resolution for EM radioautography than filamentous grain development with D-19b.

Lobular and cellular patterns of early hepatic glycogen deposition in the rat as observed by light and electron microscopic radioautography after injection of 3H-galactose

Very low hepatic glycogen levels are achieved by overnight fasting of adrenalectomized (ADX) rats. Subsequent injection of dexamethasone (DEX), a synthetic glucocorticoid, stimulates marked increases in glycogen synthesis. Using this system and injecting 3H-galactose as a glycogen precursor 1 hr prior to sacrifice, the intralobular and intracellular patterns of labeled glycogen deposition were studied by light (LM) and electron (EM) microscopic radioautography. LM radioautography revealed that 1 hr after DEX treatment, labeling patterns for both periportal and centrilobular hepatocytes resembled those in rats with no DEX treatment: 18% of the hepatocytes were unlabeled, and 82% showed light labeling. Two hours after treatment with DEX, 14% of the hepatocytes remained unlabeled, and 78% were lightly labeled; however, 8% of the cells, located randomly throughout the lobule, were intensely labeled. An increased number of heavily labeled cells (26%) appeared 3 hr after DEX treatment; and by 5 hr 91% of the hepatocytes were intensely labeled. Label over the periportal cells at this time was aggregated, whereas centrilobular cells displayed dispersed label. EM radioautographs showed that 2 to 3 hr after DEX injection initial labeling of hepatocytes, regardless of their intralobular location, occurred over foci of smooth endoplasmic reticulum (SER) and small electron-dense particles of presumptive glycogen, and in areas of SER and distinct glycogen particles. After 5 hrs of treatment with DEX, the intracellular distribution of label reflected the glycogen patterns characteristic of periportal or centrilobular regions.

Radioautographic visualization of differences in the pattern of [3H]uridine and [3H]orotic acid incorporation into the RNA of migrating columnar cells in the rat small intestine

The epithelium of rat small intestine was radioautographed to examine whether RNA is synthesized by the salvage pathway as shown after [3H]uridine injection or by the de novo pathway as shown after [3H]orotic acid injection. The two modes of RNA synthesis were thus investigated during the migration of columnar cells from crypt base to villus top, and the rate of synthesis was assessed by counting silver grains over the nucleolus and nucleoplasm at six levels along the duodenal epithelium--that is, in the base, mid, and top regions of the crypts and in the base, mid, and top regions of the villi. Concomitant biochemical analyses established that, after injection of either [5-3H]uridine or [5-3H]orotic acid: (a) buffered glutaraldehyde fixative was as effective as perchloric acid or trichloracetic acid in insolubilizing the nucleic acids of rat small intestine; (b) a major fraction of the nucleic acid label was in RNA, that is, 91% after [3H]uridine and 72% after [3H]orotic acid, with the rest in DNA; and (c) a substantial fraction of the RNA label was in poly A+ RNA (presumed to be messenger RNA). In radioautographs of duodenum prepared after [3H] uridine injection, the count of silver grains was high over nucleolus and nucleoplasm in crypt base cells and gradually decreased at the upper levels up to the villus base. In the rest of the villus, the grain count over the nucleolus was negligible, while over the nucleoplasm it was low but significant. After [3H]-orotic acid injection, the number of silver grains over the nucleolus was negligible at all levels, whereas over the nucleoplasm the number was low in crypt cells, but high in villus cells with a peak in mid villus. The interpretation is that, except for a small amount of label incorporated into DNA from either precursor by crypt cells, the bulk of the label is incorporated into RNA as follows. In the crypts, cells make almost exclusive use of uridine, that is, of the salvage pathway, for the synthesis of ribosomal RNA in the nucleolus and of messenger and transfer RNA in the nucleoplasm. However, when cells pass from crypt to villus, they mainly utilize orotic acid--i.e., the de novo pathway--for the synthesis of messenger and transfer RNA within the nucleoplasm.

The effect of beta-aminoproprionitrile on the periodontal ligament: II. Radioautographic study of collagen secretion from fibroblasts

Fibroblasts are distributed evenly throughout the periodontal ligament (PDL) of normal mice. In mice fed beta-aminoproprionitrile (beta-APN) the fibroblasts undergo aggregation to form palisades of closely juxtaposed cells abutting pools of acellular collagenous matrix. Individual fibroblasts within these aggregates retain their polarized cytoplasmic organization and continue to synthesize and secrete collagen. However, unlike normal PDL fibroblasts, the beta-APN-treated cells appear immobilized by well-developed cell-to-cell adherens-type junctions along their lateral surfaces. We studied collagen secretion from beta-APN-treated fibroblasts by light and electron microscopic radioautography after injection of 3H-proline. Newly synthesized collagen was secreted from the distal ends of the beta-APN-aggregated fibroblasts as a distinct band of labeled material, resembling the pattern of matrix deposition seen in osteogenesis and dentinogenesis. The radioactive band of collagenous matrix was displaced further away from the fibroblasts at 2 and 4 days after 3H-proline injection as more collagen was secreted. This pattern of radiolabeled collagen secretion confirmed previous observations that PDL fibroblasts are highly polarized and that collagen secretory granules are extruded from the distal or secretory pole of the cell. In normal PDL the even distribution of fibroblasts and the complex interrelationship of their distal cell processes leads to a diffuse pattern of silver grain deposition, masking the oriented flow of new collagen from the distal ends of individual fibroblasts. Analysis of electron microscopic radioautographs revealed that newly synthesized collagen was packaged and secreted from beta-APN-treated fibroblasts via the normal cytoplasmic pathways but at a slower rate.

Inhibition of the glutamate uptake in the excitatory neuromuscular synapse of the locust by delta-philanthotoxin; a component of the venom of the solitary wasp Philanthus triangulum F. A high resolution autoradiographic study

Glutamate uptake in insect neuromuscular junctions is inhibited by delta-philanthotoxin. Two other components of the philanthus venom (beta- and gamma-philanthotoxin) do not affect this glutamate uptake. No synergism between the active delta-philanthotoxin and the two inactive components had to be assumed to explain the inhibition by the Philanthus venom.

Two anatomical pathways for the renewal of surface glycoproteins in chloride cells of fish gills

The cytoplasm of chloride cells found in the epithelium lining the gills of guppies (Lebistes reticulatus) contains, in addition to the Golgi apparatus and cisternae of endoplasmic reticulum, two distinct membranous components, the vesiculotubular and the tubular systems. While the latter is connected to the laterobasal plasma membrane, the former, made up of small vesicles and short membranous tubules, is seen mainly between the Golgi apparatus and the apical cavity which invaginates the apex of the cell. The role of these two systems in the transport of glycoproteins from the Golgi apparatus to the cell surface was investigated in fishes maintained in fresh and salt water, injected with 3H-fucose, and sacrificed at various intervals thereafter (10 and 30 min; 2.5, 8, 15.5, 24, and 48 hours). The distribution of the label was analyzed by quantitative radioautography in sections examined with the light and electron microscopes. The light microscopic data suggested that the label incorporated in the supranuclear region, where the Golgi apparatus is located, migrated toward the apical and the laterobasal regions of the chloride cells. The relative concentration of the tracer over the various components of the cytoplasm of these cells was calculated from data collected on electron microscope radioautographs at various intervals after 3H-fucose injection. The curves obtained supported the view that glycoproteins synthesized in the Golgi apparatus were transported to the apical surface via the vesiculotubular system, and to the laterobasal membrane via the tubular system.

Structure of the piriform cortex of the opossum. III. Ultrastructural characterization of synaptic terminals of association and olfactory bulb afferent fibers

Terminals of olfactory bulb afferent (OB) and association (ASSN) fibers within the piriform cortex were characterized ultrastructurally. Identification was by electron microscopic (EM) autoradiography following injections of tritiated amino acids into the olfactory bulb and anterior piriform cortex. The results show that terminals of both fiber systems contain round vesicles and make asymmetrical synaptic contacts predominantly onto dendritic spines. Profiles with pleomorphic vesicles do not appear to be labeled from either site. Since there is strong evidence that both fiber systems generate excitatory postsynaptic potentials (EPSPs) in pyramidal cells, these results provide additional examples in the mammalian CNS of terminals with round vesicles and asymmetrical contacts that mediate an excitatory effect. Percentage density analysis and quantitative study of a large number of heavily labeled terminals revealed that while OB and ASSN terminals are similar in terms of vesicle shape and contact type, they differ in many morphological details including pre- and postsynaptic profile size, the packing density and distribution of synaptic vesicles, synaptic contact shape, and the presence of overlying neuroglial lamellae. However, large variations in appearance of different terminals of the same type are also present so that a small percentage of OB and ASSN terminals are indistinguishable morphologically in the absence of label. An important finding of the quantitative analysis is that spines contacted by lateral olfactory tract (LOT) terminals appear to be of two types based on a bimodal distribution in size and differences in morphology, while spines contacted by ASSN terminals appear to be of a single type. Comparison of these data with results from Golgi analysis indicates that ASSN terminals predominantly contact pyramidal cell spines while OB terminals contact both pyramidal and semilunar cell spines. Quantitative analysis of synaptic vesicles revealed that histograms of vesicle size for OB and ASSN terminals are virtually identical in shape, but peaks are slightly displaced (ASSN vesicles are 5% larger; significant with P less than .002). An analysis of the laminar distribution of OB and ASSN synaptic terminals revealed that while most OB terminals are segregated in layer Ia and most ASSN terminals in layer Ib, occasional OB terminals are observed up to approximately 50 micro deep to the Ia-Ib boundary and occasional ASSN terminals up to approximately 50 micro superficial to this boundary.

Ultrastructural characteristics of progenitor cell populations in the periodontal ligament

Electron microscope radio-autography was used in an attempt to identify any relationship between the location and degree of differentiation of progenitor cells in the periodontal ligament (PDL). Ligament fibroblasts were classified on the basis of their nuclear/cytoplasmic ratio and their distance to the closest blood vessel measured. It was determined that an undifferentiated paravascular progenitor cell population exists, and that the PDL also contains progenitor cells showing a range of cytodifferentiation.

Variations in the retinal synapses of the cat superior colliculus revealed using quantitative electron microscope autoradiography

This study has examined the retinal synapses of the cat superior colliculus using electron microscope autoradiography and morphometric techniques. The depth of each retinal synapse was measured using a computer-based EM plotter. The area, perimeter, and synapse contact density of selected synapses were calculated using a computer-based digitizer. Pale mitochondria were found to be an accurate cytological marker of retinal input to the colliculus. Fifty-eight percent of pale mitochondria terminals were labeled in the colliculus contralateral to eye injections. Ten percent of pale mitochondria terminals were labeled in the ipsilateral colliculus. A few labeled terminals contained dark mitochondria. The labeled retinal terminals in the contralateral colliculus were concentrated in a 60 microns wide dense band at the top of the superficial gray layer. They were also found within the deep superficial gray and upper optic layers. This distribution corresponded exactly to a larger population of pale mitochondria terminals. The cross-sectional area and synaptic contact density of selected pale mitochondria terminals varied with depth. Within the upper superficial gray, the terminals were small (mean area = 1.26 microns squared) and had high contact densities (mean = 0.25 per microns). These small terminals were also found deeper within the colliculus. Below the upper subdivision of the superficial gray, some labeled terminals were much larger and had lower contact densities. These results suggest there may be two subpopulations of retinal terminal in the cat superior colliculus: (1) small terminals with scalloped contours and complex synaptic relationships which may correspond to W-type input; and (2) larger terminals with simpler synaptic relationships which are distributed deeper and may correspond to Y-type input.

Autoradiographic study of3H-methylated elastase in hamster lungs

An emphysemalike condition can be induced in animal lungs by the instillation of a single dose of elastase. Autoradiography was used to determine the location of 3H-methylated porcine pancreatic elastase in hamster lungs at four time points. Six hours after instillation of radiolabeled enzyme the distribution of silver grains was very patchy, but in heavily labeled areas grains were concentrated over macrophages, connective tissue areas and over some fibroblasts. By 24 hr the labeling of connective tissue areas was no longer evident and almost all silver grains were associated with macrophages or with the edema fluid that filled many alveoli at this time. By 4 days only macrophages exhibited concentrations of silver grains. The labeling of macrophages was still evident at 7 days. Elastase inactivated by N-acetyl-(L-alanyl)3-L-alanine chloromethyl ketone showed a different distribution 6 hr after instillation. Silver grains were concentrated over macrophages and alveolar type II cells but showed no affinity for connective tissue areas or fibroblasts. By 24 hr almost all grains were located over heavily labeled macrophages.

Effect of colchicine on internalization of prolactin in female rat liver: an in vivo radioautographic study

Binding and internalization of 125I-ovine prolactin into hepatocytes of female rats was visualized by the in vivo radioautographic method (Bergeron, J. J. M., G. Levine, R. Sikstrom, D. O'Shaughnessey, B. Kopriwa, N. J. Nadler, and B. I. Posner, 1977, Proc. Natl. Acad. Sci. USA, 745:051-5055). Receptor-mediated internalization of label was observed into lipoprotein-filled vesicles in the Golgi/bile canalicular region of the hepatocyte. Colchicine treatment had no effect on the internalization of label into the lipoprotein-filled vesicles. However, the location of the radio-labeled lipoprotein-filled vesicles was altered from the Golgi/bile canalicular region to subsinusoidal. Radioactive content of hepatocytes decreased as a function of time after injection of 125I-prolactin; however, colchicine treatment markedly retarded this loss of label. Subcellular fractionation experiments indicated that colchicine treatment led to decreased levels of 125I-prolactin accumulation in microsomes but augmented the accumulation of label in the L fraction. It is concluded that in normal female rats prolactin is internalized into lipoprotein-filled vesicles in the Golgi region before degradation of the hormone. Colchicine treatment accumulates labeled lipoprotein-containing vesicles in a subsinusoidal region and retards hormone catabolism. The labeled vesicles observed after colchicine treatment may correspond to the unique vesicles previously observed in the L fraction and found to be enriched in prolactin receptors (Khan, M. N., B. I. Posner, A. K. Verma, R. J. Khan, and J. J. M. Bergeron, 1981, Proc. Natl. Acad. Sci. USA, 78:4980-4981).

Synthesis and assembly of connecting-piece proteins as revealed by radioautography

The synthesis and assembly of connecting-piece proteins have been studied during spermiogenesis in the rat by electron microscopy and radioautography following intratesticular injection of radiolabeled amino acids [3H]proline and [3H]cystine. Early in spermiogenesis (steps 1-7) the two centrioles that give rise to the connecting piece are essentially unmodified. During the 6.5-day period between steps 8 and 15, the major elements of the connecting piece (striated columns and capitulum) gradually become assembled from an electron-dense material that is deposited around the walls of the centrioles; throughout this period, protein molecules containing proline and cystine are synthesized by the step 8-15 spermatids and incorporated into the developing neck region. These proteins subsequently become permanent structural components of the connecting piece. Following completion of the major elements in step 15, few additional proteins are added to the connecting piece during the final steps 16-19 of spermiogenesis.

Regeneration and retrograde degeneration of axons in the rat optic nerve

The retinal stump of the rat optic nerve was examined histologically 1-64 weeks after intracranial section of the nerve with or without grafting of autologous peripheral nerve segments. Single unmyelinated axons and bundles of unmyelinated axons appeared in cut optic nerves and were most abundant 2-4 weeks after section. With light and electron microscope radioautography after injection of tritiated amino acids into the globe, it was confirmed that many unmyelinated fibres arose from the optic nerve rather than from nearby peripheral nerves and it was estimated that some axons regenerated as far as 0.5 mm. At or near the end of retinofugal axons, structures resembling growth cones were seen at 2 weeks and vesicle-containing swellings similar to synapses were found at 1-2 months. Outgrowth from optic nerve axons was not obviously enhanced by peripheral nerve grafts although a few retinofugal axons became ensheathed by Schwann cells. Retrograde axonal degeneration was rapid in both cut and grafted optic nerves, the number of nerve fibres near the globe falling to less than 10% of normal after 4 weeks. A few myelinated and unmyelinated fibres were still present 64 weeks after nerve transection. In conclusion, some cut axons in the rat optic nerve display a transient regenerative response before undergoing retrograde degeneration.

Kinetics of fibrous sheath formation in the rat spermatid

The morphogenesis of the fibrous sheath in the rat spermatid has been studied by electron microscopy and by EM radioautogaphy following injection of 3H-proline. The appearance of the developing fibrous sheath from the distal to proximal end of the principal piece has been examined in spermatids in each of the 19 steps of spermiogenesis. The precise timing of the various steps of its formation has been established and related to radioautographic observations on the synthesis and incorporation of proteins into the developing fibrous sheath. The longitudinal columns form slowly over a period of 15 days, appearing first at the distal end of the principal piece in step 2 and gradually extending in a proximal direction, ending at the level of the annulus in step 17. Throughout this 15-day period, proline-containing proteins are synthesized and incorporated into the growing columns. All of the ribs, on the other hand, arise from anlagen which are assembled along the length of the principal piece during a much shorter (4.5-day) period between steps 11 and 15 of spermiogenesis. New rib anlagen seemingly originate from bundles of proteinaceous filamentous material which are synthesized in the cytoplasm of step 11-15 spermatids and become aligned along the plasma membrane of the principal piece, starting at the distal end. These observations suggest that the two components of the fibrous sheath are assembled by means of two independent mechanisms that proceed asynchronously except during an overlap period of 2.5 days between steps 12 and 14.

Autoradiographic studies of protein and polysaccharide synthesis during vitellogenesis in Drosophila

Quantitative light- and electron-microscopic autoradiography was used to evaluate metabolic processes that occur during late developmental stages (10-14) of oogenesis in Drosophila melanogaster. Major differences in radiolabelling patterns were found after in vivo (10-45 min) uptake of [3H]-monosaccharides and [3H]-L-lysine. Several different methods of data analysis were required to facilitate interpretation of these patterns. [3H]-L-lysine produced extensive cytoplasmic labelling at all developmental stages. In addition, about 15% of alpha yolk spheres were intensely labelled at stage 10, reflecting the incorporation of radiolabelled vitellogenins synthesized during the incubation period. Subsequent stages showed low silver grain density over alpha yolk spheres until stage 14, when a burst of [3H]-L-lysine incorporation by most alpha spheres was observed, possibly indicative of a maturation process for embryogenesis. [3H]-D-glucose and [3H]-D-galactose (10 min, in vivo) both induced intense labelling of the beta yolk spheres in a manner suggesting in situ assembly beginning at early stage 13. Inasmuch as the polysaccharide of beta yolk spheres has the properties of glycogen (e.g., rosette structure digested by alpha-amylase) and the radiolabelled monosaccharides were introduced intra-abdominally, it is evident that transport systems as well as enzymes utilizing glucose and galactose for glycogenesis must be readily available. It is notable that wide-spread labelling of egg chambers was elicited by [3H]-D-glucose and [3H]-D-galactose (e.g., nurse cells, follicle cells, chorion, vitelline membrane), but the labelling induced by [3H]-N-acetylmannosamine was restricted mainly to the endochorion. A possible role of microtubules in distribution and assembly of yolk spheres was inferred when colchicine, admixed to the culture medium (2-5 ppm), produced abnormal distribution and diminution in number of both alpha and beta yolk spheres. In addition to revealing previously unknown metabolic events of vitellogenesis, the results provide additional criteria for stage characterization as well as a means to specifically label certain macromolecules for purposes of isolation.

A quantitative analysis of the ipsilateral retinocollicular projection in the cat: an EM degeneration and EM autoradiographic study

The ipsilateral projection to the binocular segment of the superior colliculus in the cat was quantified by means of electron microscopic (EM) degeneration and electron microscopic autoradiography. Because of the patchy distribution of ipsilateral terminals, contiguous samples were taken across the mediolateral extent of the colliculus. The results from both EM degeneration and EM autoradiography are in substantial agreement: In the binocular segment, the ipsilateral projection represents 5.3% and 5.6%, respectively, of the total retinal input to the superior colliculus. As the contralateral projection extends over the whole colliculus but is greatest in the caudal region, while the ipsilateral projection is restricted to the middle one-third of the colliculus, it follows that the total ipsilateral retinocollicular projection is less than earlier estimates (5--10%, Kanaseki and Sprague, '74) and probably closer to 1%, as suggested by Sterling ('73) on the basis of an electron microscopic degeneration study. A significant finding is that there are many more terminals per axon in the contralateral than in the ipsilateral superficial gray. The ratio of degenerated terminals in SGS1 and SGS2 to degenerated axons in SGS3 is 3.1 contralaterally, while in the ipsilateral colliculus the figure is 1.2. This may reflect a difference in the arborization pattern of Y-type and W-type retinal ganglion cells in the colliculus.

Peripheral nerve autografts to the rat spinal cord: studies with axonal tracing methods

In young adult female rats, autologous sciatic nerve segments were transplanted to the thoracic region of the spinal cord. The grafts became well innervated but led to no obvious functional improvement. The origin and termination of axons in the grafts was studied by retrograde neuronal labeling with horseradish peroxidase (HRP) and radioautographic axonal tracing. Studies with HRP indicated that some axons in the grafts originated from intrinsic CNS neurons with their cell bodies in nearby segments of the spinal cord and that others arose from dorsal root ganglia at the level of the grafts and at least 7 segments distal to them. After tritiated amino acids were injected into lumbar dorsal root ganglia, labeled axons could be followed into the grafts but not into the rostral spinal cord stumps. Together with other experimental observations, these results demonstrate a correlation between success or failure of elongation of dorsal root fibers and peripheral or central ensheathment at the axonal tip. The corticospinal tract was studied both with radioautography and retrograde axonal transport of HRP but no extension of its axons into peripheral nerve grafts was detected under these experimental conditions. The findings implicate both neuroglial and axonal factors in the feeble regenerative response usually seen after injury to the spinal cord.

A cytochemical study of the Golgi apparatus of the spermatid during spermiogenesis in the rat

The reactivity of the various components of the Golgi apparatus of rat spermatids for three phosphatase activities (nicotinamide adenine dinucleotide phosphatase, NADPase; thiamine pyrophosphatase, TPPase; cytidine monophosphatase, CMPase) and the incorporation of 3H-fucose by the spermatids was analyzed at the 19 steps of spermiogenesis, i.e., during and after this organelle elaborated the glycoprotein-rich acrosomic system. During steps 1-3, the Golgi apparatus produced, in addition to the proacrosomic granules, multivesicular bodies that became associated with the chromatoid body. NADPase was located within the four of five intermediate saccules of Golgi stacks, and TPPase was found in the last one or two saccules on the trans aspect of the stacks from steps 1 to 17 of spermiogenesis. CMPase was located within the thick saccular GERL elements found in the trans region of the Golgi apparatus from steps 1 to 7 of spermiogenesis, but the CMPase-positive GERL disappeared from the Golgi apparatus after its detachment from the acrosomic system at step 8. Th acrosomic system itself was reactive from CMPase and TPPase but was negative for NADPase, while the multivesicular bodies were CMPase and NADPase positive but unreactive for TPPase. Tritiated-fucose was readily incorporated within the Golgi apparatus of steps 1-17 spermatids; in steps 1-7 it was subsequently incorporated within the acrosomic system and multivesicular bodies. These various data indicated (1) that the Golgi apparatus of spermatids, although it loses its CMPase-positive GERL element in step 8, retains evidence of functional capacity until it degenerates in step 17; (2) that in early spermatids the various saccular components of the Golgi are specialized with respect to enzymatic activities; and (3) that each Golgi region may contribute in a coordinated fashion to the formation of the acrosomic system and multivesicular bodies.

Formation of the outer dense fibers during spermiogenesis in the rat

The morphogenesis of the outer dense fibers (ODF) in rat spermatids has been studied by electron microscopy, and the synthesis and incorporation of proteins into the ODF during this process have been followed by radioautography using 3H-proline and 3H-cystine as precursors for ODF proteins. In the first phase (step 8-14), nine very fine fibers termed anlagen of the ODF develop in association with the microtubule doublets. These first appear along the most proximal portion of the axoneme in step 8 of spermiogenesis; during steps 9-14 they gradually increased in length in a proximal-to-distal direction, being first observable along the forming midpiece and later along the principal piece as well. In the second phase (steps 15-16), the rudimentary fibers suddenly increase in diameter, with the most dramatic growth occurring in step 16, and assume a close resemblance to the mature ODF. This striking transformation, which appears to result from simultaneous deposition of electron-dense material along the length of anlagen of the ODF, coincides with a period of rapid incorporation of 3H-proline-and 3H-cystine-containing proteins, which become permanent structural components of the ODF. These proteins, which comprise the bulk of the ODF, are synthesized in the cytoplasm of spermatids during the acrosome and early maturation phases. In the final phase (steps 17-19) the fibers continue to enlarge very slowly, assuming their definitive form in step 19 of spermiogenesis. Thus formation of the ODF in the rat is a lengthy multistep procedure, requiring from step 8-19 of spermiogenesis and utilizing proteins synthesized throughout most of this period.

Membrane fusion and glycosylation in the rat hepatic Golgi apparatus

When purified Golgi fractions were incubated with UDP-[3H]galactose in the absence of Triton-X-100, radioactivity was incorporated into an endogenous lipid and several peptide acceptors. Electron microscope analysis of Golgi fractions incubated in the endogenous galactosyl transferase assay medium revealed extensive fusion of Golgi saccules. Systematic removal of constituents in the galactosyl transferase assay medium showed enhanced (minus beta-mercaptoethanol) or reduced (minus ATP, minus sodium cacodylate buffer or minus MnCl2) fusion of Golgi membranes compared to the complete medium, Stereologic analysis revealed a correlation between membrane fusion and galactosyl transferase activity (r = 0.99, P less than 0.001). Electron microscope radioautography was carried out after incubation of Golgi fractions with UDP-[3H]galactose. Silver grains were not observed over trans elements of Golgi but were revealed mainly over large fused saccules with the number of silver grains being proportionate to membrane fusion (r = 0.92, P less than 0.001). Bilayer destabilization at points of Golgi membrane fusion may act to translocate galactose across the Golgi membrane and thereby provide a fusion regulated substrate for terminal glycosylation.

Ultrastructural studies on the intracellular fate of 125I-nerve growth factor in cultured rat sympathetic neurons

Primary cell cultures of sympathetic neurons from rat were exposed to 125I-nerve growth factor (NGF) and the fate of the NGF in the cell was followed using electron microscopic autoradiography. The intracellular localization of NGF was determined in the cell bodies and in the proximal neurites of neurons that had been grown in three-chamber dishes, following 5 or 24 hr of retrograde transport of NGF from the distal portions of the neurites. Label in the proximal neurites was predominantly associated with lysosomes and multivesicular bodies (MVBs), and at 5 hr elongated tubular elements were especially heavily labeled. Most of the label in the cell bodies was concentrated in lysosomes and MVBs. Lysosomes accounted for the largest fraction (45-60%) of the grains in the cell body, with a labeling density (LD = % grains/% area) of 3-5, while MVBs accounted for 5-10% of the grains with an LD of 5-20. We observed no evidence of nuclear labeling after 5 or 24 hr of retrograde transport. Mass cultures of neurons were incubated for 22 hr with NGF in the presence of the lysosomal inhibitors chloroquine (CQ, 0.05 mM) or methylamine (MA, 10 mM). In both agents the lysosomes were swollen with membranous material but still sequestered NGF, especially in CQ where the lysosomes were associated with almost 65% of the grains and had an LD of 6. CQ and MA had different effects on the morphology of the MVBs: in CQ they were few in number and compact while in MA they were numerous and appeared swollen and vacuolated. We observed no evidence for the nuclear accumulation of NGF even in the presence of the lysosomotropic agents.

Neurons and glia in cat superior colliculus accumulate [3H]gamma-aminobutyric acid (GABA)

We have examined by autoradiography the labeling pattern in the cat superior colliculus following injection of tritiated gamma-aminobutyric acid (GABA). Silver grains were heavily distributed within the zonal layer and the upper 200 micrometer of the superficial gray. Fewer grains were observed deeper within the superficial gray, and still fewer were found within the optic and intermediate gray layers. The accumulation of label was restricted to certain classes of neuron and glia. Densely labeled neurons were small (8-12 micrometer in diameter) and located primarily within the upper 200 micrometer. Dark oligodendrocytes and astrocytes showed a moderate accumulation of label while pale oligodendrocytes and microglia were unlabeled. Label was also selectively accumulated over several other types of profile within the neuropil, including presynaptic dendrites, axons, and axon terminals.

Effect of aging on the morphology and function of the thyroid gland of the cream hamster. Further evidence for two different mechanisms of hormone secretion

The effect of aging on the morphology and function of the thyroid gland of the cream hamster was studied by light and electron microscopy coupled with autoradiography or histochemistry. Morphologically, aging induces an accumulation of lysosomal dense bodies and a loss of the phagocytosis of colloid droplets after stimulation with TSH. Iodine uptake and organification occur normally and thyroglobulin synthesis, estimated by autoradiography with 3H-leucine, is not different from that observed in young animals. The basal T4 and T3 plasma levels are lower in the old animals. A low iodine diet administered for several months prevents the age related accumulation of lysosomal dense bodies. Hormone secretion seems to proceed by two different mechanisms; phagocytosis of colloid droplets, the classical mechanism that decreases with age, and an additional mechanism, probably micropinocytosis, that is maintained during the whole lifespan.

Identification and distribution of retinocollicular terminals in the cat: an electron microscopic autoradiographic analysis

The electron microscopic (EM) autoradiographic method has been used to determine the size, distribution, and ultrastructure of retinocollicular axon terminals following intraocular injection of either (3H)-leucine or (3H)-proline. In the contralateral colliculus, retinal terminals are most numerous in the uppermost sublamina of the superficial grey, SGS1. The mean diameter of terminals in the contralateral SGS1 and SGS2 is 1.3 micron +/- 0.33, and 1.45 micron +/- 0.37, respectively. The mean diameter of terminals in the deepest contralateral sublamina, SGS3 (1.85 micron +/- 0.62), is significantly larger than the mean diameter of those in the contralateral SGS1 or SGS2. By contrast, the mean diameter of terminals in different sublayers of the ipsilateral superficial grey is relatively constant, ranging from 1.56 micron +/- 0.45 to 1.63 micron +/- 0.60. Most ipsilateral retinal terminals are located in the uppermost part of SGS2. It is postulated that there are two populations of retinal terminals in the superficial grey: a population of smaller terminals present in the contralateral SGS1 and SGS2, and a population of larger terminals present in the contralateral SGS3. Both populations appear to be present in the ipsilateral sublaminae. While all labeled retinocollicular terminals contain round vesicles and asymmetric membrane thickenings, two morphological features appear to be correlated with retinal terminal size: (1) the population of smaller retinal terminals more frequently contacts postsynaptic profiles containing scattered round vesicles; and (2) large, dense-core vesicles are more commonly associated with the presynaptic profiles of the population of larger terminals. A comparison of these morphological findings with available physiological data (Hoffman, '73; Fukuda and Stone, '74; McIlwain and Lufkin, '76 McIlwain, '78) suggests that the smaller terminals may be those of W-retinal ganglion cells, and the larger terminals those of Y-retinal ganglion cells.