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PubMed1980

Ultracytochemical identification of catecholamine-containing vesicles in the ligated sciatic nerve of the rat. Comparison with sympathetic nerve terminals.

Using the fixation procedure of Tranzer, three kinds of granular vesicles were identified in certain unmyelinated fibres of rat sciatic nerves proximal to a ligature: (1) small vesicles (SGV:30-60 nm in diameter), (2) large vesicles (LGV:60-100 nm in diameter), and (3) large elongated vesicles (LEV:60-100 nm in diameter). A comparative study concerning the distribution of these granular vesicles was carried out using a cytopharmacological method (reserpine) and employing different fixatives (aldehydes + OSO4, or OSO4 alone) in periarterial nerve plexus of the femoral artery, vas deferens and the pineal organ. Use of Tranzer's method allows preservation in almost all granular vesicles of a strongly electron-dense core, while with the other fixatives mainly small, eccentric dense cores occur in the vesicles. Two main features were observed in ligated sciatic nerves: (i) a clear increase in the number of LGV, and (ii) the presence of LEV, considered as a variety of LGV rather than a new population of granular vesicles. Reserpine caused the cores of SGV to disappear almost completely, while LGV and LEV remained only partly depleted. The original method combining Tranzer's fixation procedure with radioautography revealed radioautographic labelling only in the unmyelinated fibres of ligated sciatic nerves and mainly superimposed over SGV, LGV and LEV. It is suggested that (i) SGV, LGV and also LEV represent possible storage sites of catecholamines, and (ii) a local morphogenesis of SGV from the large vesicles occurs in ligated sympathetic nerve fibres.

Animals↗

PubMed1984

Evidence for glutamate as a neurotransmitter in the cat vestibular nerve: radioautographic and biochemical studies.

Evidence that glutamate acts as a neurotransmitter in vestibular nerve fibers was sought (1) by electron microscope radioautographic identification of the uptake sites of [3H]-glutamic acid after incubation of slices of cat vestibular nuclei, and (2) by measuring changes in sodium-dependent high affinity glutamate uptake in nerve endings containing homogenates from normal and deafferented vestibular nuclei 8 to 11 days after unilateral vestibular nerve lesion. Electron microscopic radioautography revealed that glutamate had been taken up by numerous nerve endings projecting over the whole vestibular nuclear complex. The biochemical approach indicated that after section of the vestibular nerve, a significant decrease in high affinity glutamate uptake occurred in the vestibular nuclei, which lost their exclusively ipsilateral projection. This decrease varied from one area of the deafferented vestibular nuclei to another, reaching -58% in the lateral area of the central part corresponding to the ventral lateral vestibular nucleus and the rostral part of the descending vestibular nucleus. It is concluded that glutamate (or aspartate) is used by the vestibular nerve fibers as a neurotransmitter in the vestibular nuclei.

Animals↗

PubMed1983

Characterization of lactogen binding sites in choroid plexus.

Prolactin binding sites have been demonstrated previously in rat choroid plexus using in vivo radioautography (Walsh et al. 1978). In the present study we have employed this procedure to characterize further the binding specificity of these sites. Following the injection of 125I-hGH or 125I-oPRL an intense radioautographic reaction was observed over the choroid plexus. The reaction was significantly reduced by coinjecting excess unlabeled hGH or oPRL but not bGH. The specific binding of 125I-oPRL to choroid plexus from rat, rabbit, sheep and pig was demonstrated by in vitro assays. Subsequently a survey of 125I-oPRL specific binding in a number of regions of pig brain indicated that the highest binding was in choroid plexus. A detailed study of the characteristics of 125I-oPRL binding to pig choroid plexus was undertaken. Specific binding increased with choroid plexus homogenate protein to a maximum of 30% (3.0 mg protein/tube). Binding was maximum at 4 degrees C by 30-40 h of incubation. During the incubation the integrity of 125I-oPRL in the incubation medium declined steadily to 50% after 20 h and 35-40% after 48 h. Radioactivity eluted from binding sites was fully intact as judged by rebinding to lactogen receptor-enriched membranes. Binding showed a broad pH optimum of 5.5-7.5. On cell fractionation of choroid plexus binding sites were enriched in microsomes. The binding of 125I-oPRL and 125I-hGH was inhibited in a dose-dependent manner by unlabeled lactogens and was of high affinity. hGH and oPRL were equipotent inhibitors of the binding of both radioligands whereas bGH and a variety of structurally unrelated peptides were non-inhibitory.

Animals↗

PubMed1980

Ultrastructural cytochemistry of atrial muscle cells. VIII. Radioautographic study of synthesis and migration of proteins.

Sections of atrial cardiocytes from young rats were subjected to radioautography after a single intravenous injection of L-leucine-4,5 3H to identify the sites of synthesis and to follow the migration of newly-formed proteins. As early as 2 min after injection of L-leucine 3H, the label was highest in the rough endoplasmic reticulum (RER), suggesting that cisternal ribosomes are sites of protein synthesis. By 5 min, most of the label had migrated from the RER to the Golgi complex. Some label had migrated from the RER to the Golgi complex. Some label was already present over specific granules by 2 min but the peak was reached at 1 h. By 4 h, the label over the specific granules had diminished, possibly indicating a release of newly-synthetized secretory material outside the cell. The label over myofilaments and Z-bands was relatively high at most time intervals, suggesting an early and important incorporation of leucine into the contractile and structural proteins of these organelles. The label over the cytosol was initially high and increased even further at 5 and 20 min but decreased to a very low level at 4 h. In contrast, the label over the cell surface rose continuously and peaked at 4 h. The pattern of increment of the label over the cell surface suggests that the newly-formed proteins of these sites are also synthetized in the RER, pass through the Golgi complex and are transported in the cytosol before reaching their destination.

Animals↗

PubMed1989

Degeneration and graft-induced restoration of dopamine innervation in the weaver mouse neostriatum: a quantitative radioautographic study of [3H]dopamine uptake.

A recently introduced quantitative radioautographic technique was used to characterize the striatal dopaminergic deficit in weaver mutant mice and to evaluate the extent of DA reinnervation resulting from cell suspension grafts of fetal ventral mesencephalic tissue. Brain slices from normal mice and unilaterally grafted weaver mice were incubated in [3H]DA, in the presence of desipramine and pargyline 3-5 months after graft surgery. Semi-thin sections from the fixed and resinembedded slices were subsequently exposed on tritium sensitive film and afterwards dipped in nuclear emulsion for light microscope radioautography. Alternative slices were embedded in Epon for post-embedding tyrosine hydroxylase (TH) immunocytochemistry. The grain density of the film radioautographs matched well the distribution of TH positive fibers. Both methods revealed an almost complete absence of DA axons in the dorsomedial quadrant of the weaver neostriatum and an increasing density of DA innervation towards the ventrolateral areas. In the light microscope radioautographs, only the ventral striatum (i.e. nucleus accumbens and olfactory tubercle) and a narrow ventral and periventricular zone of the caudate-putamen were covered by silver grain clusters typical of DA varicosity labeling. Such labeled varicosities were nevertheless found in reduced numbers the lateral portion of both nucleus accumbens and the olfactory tubercle. The remaining neostriatum was overlaid by diffuse silver grains. suggesting a deficient DA uptake and storage mechanism in the residual DA fibers in this region. Immunocytochemistry using antibodies specific for DA or TH provided further evidence that the residual DA innervation in the weaver neostriatum was biochemically defective. Weaver mice with grafts of ventral mesencephalic tissue in the right neostriatum showed an amphetamine-induced rotational bias to the contralateral side, which was not seen in the sham-operated animals. In contrast to the intrinsic weaver neostriatal DA innervation, DA fibers of graft origin exhibited the normal, clustered type of varicosity labeling. The computerized image analysis of silver grain density in film radioautographs was calibrated by counting these labeled varicosities in selected areas of light microscope radioautographs from the same sections. Results showed a mean DA reinnervation of neostriatal tissue surrounding the graft of about 20%, in some cases up to 80%, of the density seen in wild type mice, with a gradual decrease with distance up to 1-1.4 mm from the graft. The ventral parts of the neostriatum, which contained higher numbers of residual intrinsic DA fibers, were much more sparsely reinnervated than the dorsal and dorsomedial areas.(ABSTRACT TRUNCATED AT 400 WORDS)

Amphetamines↗

PubMed1988

Reinnervation of dopamine neurons by regenerating serotonin axons in the rat medial zona incerta. A combined radioautographic and immunocytochemical ultrastructural study.

Cellular relationships between serotonin (5-HT) axons and tyrosine hydroxylase (TH)-containing neurons were examined by combined (3H)5-HT uptake radioautography and TH immunocytochemistry in the medial zona incerta (ZI) of adult rats, 7 and 50 days after an intracerebral injection of 5,7-Dihydroxytryptamine (5,7-DHT). Seven days post-lesion, only rare, scattered (3H)5-HT-labeled axon terminals were apparent in the zone of the medial ZI accessible to intraventricularly injected (3H)5-HT. In contrast, in sham-injected animals (3H)5-HT-labeled varicosities were numerous and often observed adjacent to TH-immunoreactive perikarya and dendrites. Fifty days post 5,7-DHT injection, the density of (3H)5-HT-labeled terminals approximated that seen in sham-treated animals. At the ultrastructural level, these regenerated 5-HT axons were similar in size, shape and content to those observed in sham-operated rats. Also, as in sham, some of the (3H)5-HT-labeled axons were directly apposed to TH-immunopositive labeled profiles. The latter included large dendritic shafts and dendritic spines, but only rare perikarya. In both sham- and 5,7-DHT-treated animals a few of the contacts between (3H)5-HT-labeled and TH-immunoreactive profiles exhibited an asymmetric synaptic differentiation. These results indicate that 5-HT fibers in the medial ZI, following regeneration, can reestablish normal relationships and even synapses with a given population of chemically identified cells.

5,7-Dihydroxytryptamine↗

PubMed1976

Production of specific antibody to purified prostatic acid phosphatase.

Prostatic acid phosphatase may well be a prime antigenic protein in prostatic tissue and fluid. Extraction of the enzyme in highly purified form from prostatic fluid and benign hypertrophic prostatic tissue provides a unique antigen capable of inducing a prompt and specific antibody response in the goat and rabbit as amnifested by immunodiffusion, immunoelectrophoresis, and immunofluorescence techniques. In prostatic cancer patients with elevated serum acid phosphatase levels it is possible to detect humoral circulating PAP antigen by standard immunoelectrophoretic methods and to confirm the existence of the enzyme by radioautography, L-tartrate inhibition, and the Gomori or Burstone staining procedures. Preliminary indirect prostatic immunofluorescence studies consistently demonstrated characteristic fluorescent foci in the paranuclear areas of benign prostatic epithelial cells, the presumed area of synthesis of prostatic acid phosphatase. Consideration has been given to the possibility of the development of a radioimmunoassay for prostatic acid phosphataase utilizing a heterolologous antiserum to the enzyme extracted from human prostatic fluid.

Acid Phosphatase↗

PubMed1993

Stability of elastin in the developing mouse aorta: a quantitative radioautographic study.

Elastic lamina growth during development and the ultimate stability of elastin in the mouse aortic media was investigated by light and electron microscopic radioautography. Following a single subcutaneous injection of L-[3,4-3H]valine at 3 days of age, animals were killed at 9 subsequent time intervals up to 4 months of age. One day after injection, radioautographic silver grains were primarily observed over the elastic laminae; however, silver grains were also seen over the smooth muscle cells and extracellular matrix. By 21 to 28 days of age, the silver grains were almost exclusively located over the elastic laminae. From 28 days to 4 months of age, the distribution of silver grains appeared relatively unchanged. Quantitation of silver grain number/micron2 of elastin showed a steady decrease in the concentration of silver grains associated with the elastic laminae from 4 to 21 days of age. After this time, no significant difference in silver grain concentration was observed. Since the initial decrease in grains/micron2 of elastin corresponds to a period of rapid post-natal growth, the decrease is likely to be a result of dilution of the radiolabel due to new elastin synthesis. With the assumption that little or no significant turnover occurs during this time, a constant growth rate of 4.3% per day was predicted by linear regression analysis. Since no significant difference in the concentration of silver grains was observed from 28 to 118 days of age, no new growth or turnover of elastin can be said to occur during this time period. This is supported by the observation that animals injected with radiolabeled valine at 28 days and 8 months of age showed no significant incorporation of radiolabel into the elastic laminae. The results from this study present the first long-term radioautographic evidence of the stability of aortic elastin and emphasize that initial deposition of elastin and proper assembly of elastic laminae is a critical event in vessel development.

Aging↗

PubMed1991

Repair and reconstruction of the cortical plate following closed cryogenic injury to the neonatal rat cerebrum.

A cryogenic lesion was induced in the parietal cortex of neonatal rats at postnatal day 2, and the chronological sequence of cellular events during repair and reconstruction of the cortical plate examined. Serial sections of cerebra obtained at varying intervals ranging from 1 to 60 days postinjury were studied by light and electron microscopy and by immunocytochemistry for fibronectin, laminin, type IV collagen, vimentin and glial fibrillary acidic protein. In addition, localization of heavily labeled neurons (generated on embryonic day 20) in the cerebral cortical plate was examined by [3H]thymidine radioautography. Repair of a well-defined coagulative lesion was accomplished with little or no mesenchymal cell proliferation in either the necrotic zone or the leptomeninges. Eventually, fusion of the adjacent cortical plates took place with the formation of a microsulcus. Migration of neurons continued to take place along the outer margins of the lesion, and postmigratory neurons accumulated within the upper cortical layers. Around the microsulcus, heavily labeled neurons aligned themselves with layers II-III of the adjacent normal cortical plate. Irregular clusters of neurons closely abutting the leptomeningeal surface were frequently noted when repair took place without an intervening molecular layer and/or a well-defined pial-glial barrier. Supplementing intrinsic information inherent in migrating neurons, local environmental signals provided by the radial glia, glia limitans, basal lamina and pial-glial barrier appear to influence the polarity and final positioning of postmigratory neurons within the cortical plate. The necrotic zone within the deeper layers of the cortex eventually healed with a cell-sparse gliotic layer. The end result was a histological pattern that, in many respects, resembled that of human micropolygyria.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1991

Discrimination of two fibroblast progenitor populations in early explant cultures of hamster gingiva.

Numerous metabolic studies have demonstrated heterogeneity of fibroblast populations in culture, yet little is known about the structure of fibroblast populations in adult tissues in vivo. To determine if populations of both cycling and non-cycling cells are present in gingiva, hamsters were labelled with [3H]-thymidine to label cycling cells in vivo, and explanted biopsies were subsequently incubated with bromodeoxyuridine to label cycling cells in vitro. Cycling cells were identified by combined immunohistochemistry and radioautography. Fibroblasts were recognized by the presence of vimentin and the absence of keratin as determined by immunofluorescence. The largest proportion of cells were double-labelled with [3H]-thymidine and bromodeoxyuridine (43.8%) indicating the presence of actively cycling populations that maintained their proliferative status upon explanation. Cultures also exhibited a second population of cells labelled only with bromodeoxyuridine (38.7%) that did not cycle in vivo, but retained the capacity for proliferation in vitro. However, limiting dilution analysis of single-cell suspensions revealed only a single class of progenitors capable of forming large colonies in vitro. Approximately 1 in 190 plated cells was capable of colony-formation, indicating that, upon explanation, a subset of the cycling cells in vitro exhibits extensive proliferative capacity. There was also a small population of cells unlabeled with either [3H]-thymidine or bromodeoxyuridine (9.4%) that appeared to be terminally differentiated. Different substrates, including glass and thin films of gelatin and collagen, did not significantly alter the fraction of cells labelled with [3H]-thymidine. These data demonstrate the existence of 2 separate progenitor-cell populations with different capacities for proliferation in vivo and in vitro.

Animals↗

PubMed1987

Human foetal kidney explants in serum-free organ culture.

The purpose of the work was to develop an in vitro model for the study of human kidney development. Human metanephric explants from foetuses 10-18 weeks of gestational age were cultured in serum-free Leibovitz L-15 medium without hormones. Under the current minimal conditions for growth, the system permitted to maintain the renal tissues in culture for periods up to 9 days, although no evident sign of morphological differentiation was observed. However, during the studied period the overall architecture of the explants was preserved as well as the ultrastructural features of cytoplasmic organelles. The incorporation of 3H-thymidine and 3H-leucine indicated that DNA and protein synthesis was maintained or increased. Glycoprotein synthesis evaluated by 3H-glucosamine incorporation and radioautography continued in mesangium as well as in glomerular and tubular basement membranes. Alkaline phosphatase, gamma-glutamyltranspeptidase (brush border) and catalase (peroxisomes) activities remained histochemically active. The proposed organ culture system appears as a reliable and promising model that will provide basic data on the morphology and functional characteristics of the developing kidney. Since it is achieved in a completely controlled environment, it will permit to study the role of growth factors and hormones in proliferation and differentiation of the cell populations during development of the human foetal kidney.

Alkaline Phosphatase↗

PubMed1987

Human fetal colon in organ culture.

Human fetal colon (14-16 weeks gestation) was cultured as explants for 15 days in serum-free Leibovitz L-15 medium at 37 degrees C. The overall morphology of the colonic explants was well maintained throughout the culture period and all epithelial cell types retained their ultrastructural characteristics. The incorporation of [3H]-leucine continued and even increased, reflecting sustained synthesis of proteins. Even though the incorporation of [3H]-thymidine into the total DNA decreased during culture, the synthesis of DNA continued. The sites of [3H]-thymidine incorporation into the different layers of the colonic wall were studied by radioautography. The incorporation of the radioactive precursor occurs mainly in the epithelium and to lesser degrees in the mesenchyme and the muscular layer. Labeled epithelial nuclei were located in the intervillous areas but not on the villi. The labeling index of the epithelial cells remained constant throughout the culture period indicating the preservation of the proliferative capacity of the epithelium. Brush-border hydrolytic activities, namely those of sucrase, maltase, lactase, trehalase, glucoamylase and alkaline phosphatase, were assayed in the colonic tissue. These enzymic activities generally decreased in the tissue and increased in the medium during the course of culture. These observations clearly demonstrate that fetal colon can be maintained viable for at least 15 days in a serum-free medium. Organ culture now provides the opportunity to study the normal function and metabolism of human colon during its development.

Autoradiography↗

PubMed1987

Radioautographic study of glycoprotein synthesis and fate in the hypothalamo-neurohypophyseal system of vasopressin-deficient Brattleboro rats.

L-3H-fucose was injected into the lateral cerebral ventricle of vasopressin-deficient Brattleboro and control Long-Evans rats which were subsequently killed at several time intervals after the injection. The hypothalamus and the neurohypophysis were processed for light- and electronmicroscopic radioautography. Other complementary experiments using immunocytochemical and enzyme-histochemical techniques were also undertaken. L-3H-fucose was incorporated into newly synthesized glycoproteins in the Golgi apparatus of supraoptic and paraventricular neurons, and later on labelled glycoproteins migrated to lysosomes and the plasma membrane surrounding the perikaryon. The Golgi apparatus of the vasopressin-deficient neurons remained heavily labelled as long as 3 days after injection, in sharp contrast with the normal neurons in which there was a remarkable decrease of label in the Golgi region between 4 and 24 h after the isotope administration. Labelled glycoproteins also migrated to the neurohypophysis and were mainly found in the axonal plasma membrane, vesicles and axoplasm. The renewal of glycoproteins in the neurohypophysis of Brattleboro rats was faster than in the normal rats and this was attributed to the lack of formation of products which are normally packaged in secretory granules in the perikaryon and released at the axon terminal in the neurohypophysis. Colchicine caused a disturbance in the topography of the organelles of the perikaryon and the most striking features were the displacement of Golgi stacks to the periphery of the perikaryon and an accumulation of mitochondria in this neuronal region. No secretory granules were observed in the vasopressin-deficient neurons of untreated or colchicine-treated Brattleboro rats. By contrast, secretory granules (most of them labelled with 3H-fucose) were concentrated in the perikaryon of colchicine-treated Long-Evans rats. In these rats, colchicine caused a severe block in the migration of 3H-fucose-labelled glycoproteins to the neurohypophysis, but this did not occur in the Brattleboro rats. The results of the experiments were interpreted in the light of the genetic defect known to occur in Brattleboro rats which causes the inability to produce vasopressin and also remarkable morphological and physiological changes in the affected neurons.

Acid Anhydride Hydrolases↗

PubMed1982

Appearance and distribution "in situ" of nicotinic acetylcholine receptors in cervical myotomes of young chick embryos. Radioautographic studies by light and electron microscopy.

Localization of the acetylcholine (nicotinic) receptor sites was investigated in the developing cervical myotomes of the early chick embryo by radioautography at the light and electron microscope level, using 125I-alpha-bungarotoxin. The presence of cholinergic receptor sites was detected in situ as early as 60 hours of incubation (stage 17); their relative density increased in the myotome during the differentiation of the somite. Specific labeling of these receptor sites was detected in the myotomal tissue but not in the notochord, spinal cord or periaxial mesenchyme. The distribution of the receptor sites was uniform in the myotome at 3 days in ovo. An anterior-posterior asymmetry of the density appeared at 4 days in ovo and developed up to the 6th day. The highest density of these toxin-binding receptor sites was observed near the spinal motor nerve bundle as revealed by silver staining. These observations, made in situ, are discussed with respect to the possible neurotrophic or physical effects of the early motor innervation.

Animals↗

PubMed1991

Variations in the level of transferrin and SGP-2 mRNAs in Sertoli cells of vitamin A-deficient rats.

Stage-specific levels and long-term effects of vitamin A deficiency on transferrin and sulfated glycoprotein-2 (SGP-2) mRNAs were analyzed in normal rats and in rats fed a vitamin A-deficient diet for 49 days (49 day VAD) and 77 days (77 day VAD). Histological sections of testes from these animals were hybridized in situ with single stranded 3H-labeled RNA probes complementary to the transferrin and SGP-2 (clusterin) mRNAs prepared from specific cDNAs subcloned in the SP65 vector. In all cases the probes were visualized and quantified by radioautography. Vitamin A deficiency (49 day VAD rats) differentially affected the levels of these mRNAs by increasing significantly the level of SGP-2 transcripts and decreasing the level of transferrin mRNA. However, in both cases the stage-specific pattern characteristic of the normal testes remained cyclic indicating that the specific interactions between germ cells and Sertoli cells may play an important role in modulating the cyclic activities of Sertoli cells. The data also indicated that dividing spermatocytes, secondary spermatocytes and steps 13-14 spermatids were associated with Sertoli cells expressing high levels of transferrin mRNA, while steps 7, 8 and particularly 19 spermatids were associated with Sertoli cells expressing high levels of SGP-2 mRNA. In contrast to the shorter term, a longer term of vitamin A deficiency (77 day VAD rats) produced a significant decrease in the levels of both transferrin and SGP-2 mRNAs.

Animals↗

PubMed1993

Ultrastructural radioautographic analysis of neurogenesis in the hypothalamus of the adult frog, Rana temporaria, with special reference to physiological regeneration of the preoptic nucleus. I. Ventricular zone cell proliferation.

The localization and fine structure of proliferating cells in the hypothalamic preoptic area were studied by light- and electron-microscopic radioautography 1-2 h following single application of 3H-thymidine to adult Rana temporaria taken from their natural habitat in the spring and autumn. 3H-thymidine uptake by proliferating cells was much more pronounced in frogs caught in May/June, i.e., a month after the breeding period (labeled cells represent about 10% of the total ventricular zone cell population), compared to animals caught in mid-September, when it was very low. In both 3H-thymidine treatment groups the vast majority of labeled cells are found exclusively within the preoptic recess ventricular zone. With regard to ultrastructure, it contained proliferating cells of at least 4 types, ranging from immature forms (bipolar stem cells) to more differentiated elements (tanycyte-like ependymoblasts, "classical" ependymoblasts). All of them showed label over their nuclei indicating that these cells are capable of DNA synthesis and mitosis. The possible role of the preoptic recess ventricular zone as a source of precursor cells for new peptidergic neurosecretory cells, conventional neurons and glial cells in the hypothalamic preoptic area of the adult frog is discussed.

Animals↗

PubMed1993

Ultrastructural radioautographic analysis of neurogenesis in the hypothalamus of the adult frog, Rana temporaria, with special reference to physiological regeneration of the preoptic nucleus. II. Types of neuronal cells produced.

Light- and electron-microscopic radioautography was used to identify the newly formed neuronal cells in the hypothalamic preoptic area of the frog. Adult Rana temporaria that had been caught in May/June received repeated 3H-thymidine injections and were sacrificed 30 days later. Heavily labeled cells were found in 1-micron plastic coronal sections of the preoptic area and then analysed in electron-microscopic radioautographs of neighbouring thin sections. The cells were identified as newly generated by the presence of 3H-thymidine label over the nucleus. All frogs showed considerable numbers of new peptidergic neurosecretory cells, small conventional neurons, and glia in the preoptic area. Some new ependymally located cells contacting the cerebrospinal fluid displaying ultrastructural characteristics of monoaminergic cells were also revealed. We conclude that prominent ventricular neurogenesis normally exists in the intact adult frog hypothalamus. The birth of small hypothalamic neurons seems to represent a case of sustained growth leading to a net increase in neuron numbers without loss. Conversely, the birth of large peptidergic neurosecretory cells, in which the increased secretory activity often leads to natural death of some cells, is considered as a neuronal replacement phenomenon, referred to as physiological regeneration of the magnocellular preoptic nucleus. The possible significance of this phenomenon in adult Anamnia is discussed.

Animals↗

PubMed1992

The de novo and salvage pathways for the synthesis of pyrimidine residues of RNA predominate in different locations within the mouse duodenal epithelium.

RNA synthesis was examined by radioautography in mouse duodenal epithelium using 3H-uridine as a tracer of the salvage pathway and 3H-orotic acid as a tracer of the de novo pathway. The incorporation of the two precursors was estimated by counting silver grains in light-microscopic and electron-microscopic radioautographs at successive levels of crypt and villus. With both precursors, silver grains were found over all epithelial nuclei, but in numbers varying by location. Thus, after 3H-uridine injection, the number of grains was high over nucleolus and nucleoplasm in the base of the crypt, declined gradually in the middle and top of the crypt, and was low along the villus. After 3H-orotic acid, the number of grains was fairly low throughout, but peaked over the nucleoplasm in lower villus cells. The 3H-uridine reaction over nucleolus and nucleoplasm in crypt cells was interpreted as synthesis by the salvage pathway of ribosomal RNA and heterogeneous RNA, respectively, whereas the 3H-orotic acid reaction over the nucleoplasm of some villus cells indicated that these cells synthesized heterogeneous RNA by the de novo pathway.

Animals↗