Ultrastructural localisation of TGF-beta exposure in dentine by chemical treatment

Transforming growth factor- (TGF-) sequestered in dentine matrix has an important role in dental tissue repair after injury and its exposure at sites of injury may stimulate tertiary dentinogenesis. This study aimed to investigate the expression of TGF- isoforms in mature human dentine matrix and the ability of chemical treatments to expose TGF- on the cut surface of dentine using gold immunolabelling and subsequent scanning electron microscopy examination. TGF-1 was the only isoform that could be detected in human dentine and the nature of the chemical treatment of the tissue influenced its detection. EDTA treatment provided good exposure of TGF-1 on the dentine surface, whilst citric acid and sodium hypochlorite treatments revealed lesser amounts of this isoform. Only minimal staining for TGF-1 was observed in samples treated with phosphate-buffered saline. TGF-2 and -3 could not be detected in the specimens with any of the treatments. This study suggests that TGF-1 is the only TGF- isoform expressed by human odontoblasts to be sequestered in dentine implying that differences in isoform–extracellular matrix interactions may exist. Information on chemical treatment of tissue specimens for immunostaining may provide a useful basis for selection of tissue preparation techniques for clinical restorative treatment procedures to facilitate TGF- mediated reparative processes at sites of dental injury.     

Über den Einfluß des Salzgehaltes auf die photosynthetische Leistung verschiedener Standortformen vonDelesseria sanguinea undFucus serratus

Zusammenfassung 1. Es wurde untersucht, welchen Einfluß kurzfristige und langfristige Salzgehaltsveränderungen auf verschiedene Standortformen der RotalgeDelesseria sanguinea und der BraunalgeFucus serratus haben. Als Kriterium des Lebenszustandes wurde die photosynthetische Leistung gewählt. Die Algen wurden folgenden Salzgehaltskonzentrationen ausgesetzt: 0, 5, 10, 15, 20, 30, 40, 50 S.2. Die Versuche ergaben, daß kurzfristige Konzentrationsveränderungen (30 min) — sowohl Erniedrigung als auch Erhöhung des Salzgehaltes — die photosynthetische Leistung stimulieren. Ein langfristiger Aufenthalt (24 Std) unter den veränderten Bedingungen bewirkt, sofern diese innerhalb der Toleranzgrenzen der Algen liegen, einen Ausgleich der anfänglichen Stimulation. Außerhalb der Toleranzgrenzen liegende Konzentrationen rufen nach der Stimulation eine Leistungsdepression hervor. Bei Rückübertragung in den Ausgangssalzgehalt sind die Depressionen teilweise reversibel.3. Im hypotonischen Milieu verhalten sich die Delesserien der verschiedenen Standorte (Helgoland, Kattegat, Kieler Bucht) gleich: in 5 S treten starke Depressionen auf. Nordsee-Delesserien sind im hypertonischen Milieu weniger empfindlich, sie zeigen noch bei 50 S eine gesteigerte photosynthetische Leistung. In diesem Bereich sind die Ostseeformen schon schwer geschädigt. Am empfindlichsten gegenüber allen Konzentrationsänderungen ist die BrackwasserformDelesseria sanguinea formalanceolata aus der Kieler Bucht.4.Fucus serratus aus dem Litoral von Helgoland zeichnet sich im Gegensatz zu der submers lebenden Form der Ostsee, die sich ähnlich wieDelesseria verhält, in allen untersuchten Konzentrationsbereichen durch eine unveränderte photosynthetische Leistung aus. Die beiden Standortformen vonFucus entsprechen gemäß der Einteilung vonMontfort (1931) dem resistenten Typ und dem Stimulations-Depressionstyp.

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On the influence of salinity on photosynthetic performance of various ecotypes ofDelesseria sanguinea andFucus serratus

The phaeophyceanF. serratus and the rhodophyceanD. sanguinea came from the North Sea (30 S) and the Baltic Sea (15 S). The activity of photosynthesis was taken as a criterion of algae vitality. Experiments were made in salinity concentrations of 0, 5, 10, 15, 20, 30, 40 and 50 S. Thirty-minute exposures to sub- or supranormal salinities stimulate photosynthesis. Within their physiological salinity ranges the algae assume normal photosynthetic rates within 24 hours. Extreme salinities cause a reduction in photosynthetic activity; this reduction mostly disappears, however, after re-transfer into normal salinity conditions. At 5 S all test individuals ofDelesseria from different locations exhibit a reduction of photosynthetic rates. At 50 SDelesseria from the North Sea still show increased activity, whileDelesseria from the Baltic are already severely damaged. The brackish-water formD. sanguinea (formalanceolata) is most sensitive to salinity variations. The photosynthetic activity ofF. serratus from Helgoland does not vary in all salinities employed. The range of test salinities corresponds to that of the habitat in the littoral zone, where high salinities occur during air exposure, and low salinities, during rainfall. By contrast, inF. serratus from the Baltic Sea occurring only in the sublittoral zone, photosynthetic rates are similarly affected by salinity as inDelesseria.

     

Slowly adapting stretch-receptor organs: Periodic stimulation with and without perturbations

The length of isolated slowly adapting stretch-receptor organs (SAO) from crayfish was submitted to approximately sinusoidal modulations of 0.030–0.800 mm at frequencies of about 0.2, 1.0 or 3.0 cps. Sines were imposed either by themselves (clean) or mixed with (perturbed by) fast irregular length fluctuations or jitter. The amplitude of the latter remained within a specified fraction of the modulation, usually two-thirds (or x0.66), though from one twentieth to twice (or x0.05–2.00) were explored. The afferent impulse discharge was recorded: rate over bins of about 1/10 of the period was plotted as function of ongoing time. Within stationary epochs, average cycles were analyzed primarily in terms of lengths and discharge intensities. Each point in the displays corresponded to a particular bin along the average cycle, the abscissa and the ordinate being the length and the corresponding discharge rate, respectively; points were numbered in the order of their generation. Similar displays were constructed for rate vs velocity, rate vs acceleration, and rate-change vs velocity. Experiments without jitter. The non-perturbed state. With 0.2 and 1.0 cps, the rate vs length display had a clockwise loop with a flat extension to the left. The SAO at its shortest did not discharge and remained silent for some time. As length augmented, it eventually started firing, reaching maximum rate while being stretched (lead) or at maximum length. While length decayed, the organ fired less, slowing down, stopping at a length greater than where it had started, and then remaining silent until the end of the cycle. With 3.0 cps, the display had a counterclockwise loop with a flat extension on the left. The SAO did not discharge at its shortest, and fired more during relaxation than during stretching, peaking when relaxing (lag) and stopping at a length greater than where it had started. Artificial introduction of time separations between length and rate converted displays into acceptably straight lines only in a few, usually 0.2 cps, cases. The rate vs length relation exhibited consistent departures from monotonic increase and from linearity: departures were large fractions of the overall swings involving flat extensions, leads, lags, saturation effects, asymmetric rate sensitivities, and locking (which was frequent with 1.0 or 3.0 cps and could conceivably be more common with faster modulations). Other experimental paradigms have demonstrated multivaiued steady-state-rate-length relations. The variability from cycle to cycle of the rate in a particular bin was high or low for bins with low or high rates, respectively. Rate vs velocity plots were counter-clockwise loops with a base upon the abscissae, higher rates when velocity was decaying than when augmenting, and maxima at non-negative velocities. Rate-change vs velocity plots showed shortening associated with either discharge, decreases or small changes, and lengthenings associated with discharge increases, greater when augmenting if at 0.2 cps or when decaying if at 3.0 cps. Rate vs stimulus acceleration plots were, for the three tested frequencies, counterclockwise loops with a base upon the abscissae and higher rates when acceleration was decaying than when augmenting, suggesting a particular role in sensing accelerations. The sensitivity to length was evaluated by comparing the rate-swings at each frequency using identical bin-widths and depths. This procedure is considered to be most meaningful physiologically. Sensitivity was contingent upon the bin-width: with small bins (30 and 120 ms) it was highest for 3.0 cps, with intermediate bins (160 ms) it was highest for 1.0 cps, and with larger bins it was practically uniform. Differences involved factors of under x1.7. Experiments with jitter. The perturbed state. Jitter changed radically the rate vs length displays, converting all of them into clockwise folium-like loops, which implied a shift from lag to lead at 3.0 cps. Introduction of appropriate lags brought points acceptably close to straight, positively sloped segments: this occurred often at 0.2 cps, sometimes at 1.0 cps, and exceptionally at 3.0 cps. Jitter altered the variability profile along the cycle, decreasing peak variability and not affecting or increasing the minimum; variability along the cycle was thus reduced and uniformed and identification of stimuli on the basis of discharges was improved. Jitter amplitude was an important issue. The larger ones, about the modulation size, increased the lowest bin-rates, particularly at 0.2 and 1.0 cps, and increased the peaks at 0.2 cps, decreasing them at 1.0 and 3.0 cps. The smaller jitter, about 1/10 of the modulation, affected the lowest rates little, but increased the peak rate at 0.2 cps, decreasing it at 1.0 and 3.0 cps; display shapes changed little. A qualitative model of the SAO involves subsystems with linear features, as well as rectification, stiction-like and saturation-like properties. Depending upon back-ground length, modulation depth, jitter and several other issues, the organ can perform frankly nonlinearly, piece-wise linearly or linearly. Within each context, a particular stimulus is of interest and can be referred to as the signal; others are not, and can be referred to as noise, acting as perturbations. Small, erratic perturbations influence strongly transduction of large steps or sines, simplifying and making it more proportionate. Large regular perturbations act upon small signals too, but their influence has been explored less extensively.Supported by grants from NIH and NSF     

A study of the vascular arrangement in the rat adrenal gland using non-radioactive microspheres

Summary The intra-glandular vascular arrangement in the adrenal has been studied using non-radioactive microspheres injected by three different routes: in-vivo injection into the left ventricle under pentobarbital anesthesia, postmortem orthograde, and postmortem retrograde injection. The doses of microspheres were 10⁵ (average size 24.7 m), 10⁶ (15.8 m) and 10⁷ (9.9 m). The entrapment rate of microspheres by the medulla as compared with the whole gland was measured in the serially sectioned tissue (section thickness 60 m).The entrapment rates of 25-m microspheres differed between the orthograde and retrograde injections, while the entrapment rates for 15-m microspheres were essentially similar irrespective of the route of injection.Our results support the conclusion from previous microangiographic studies that the adrenal cortex and medulla are supplied by different arteries but have a common venous outflow, and that direct communication between cortical and medullary sinusoids is not likely. The medullary blood flow per gram tissue weight is estimated to be larger than cortical blood flow.     

Male swarms at landmarks and scramble competition polygyny inPolistes gallicus (Hymenoptera: Vespidae)

At the end of summer, males of Polistes gallicusfly in swarms around vertical landmarks and land in clusters on their favorite perches, where they drag their legs and abdomen. Here males occasionally crowd around a perched female; they make no effort to defend an exclusive mating territory but instead attempt to copulate by displacing rivals from the female. In this work we describe this spatial-nuptial system, which entails site fidelity without territoriality, unisexual swarms, common patrol routes, collective sexual approaches, and scramble competition polygyny. Mating success is evaluated in relation to the familiarity with flight paths (routine patrollers versus newcomers), to the type of sexual approach (single males versus in- group males), and, in the laboratory, to the individual activity level.     

Ultrastructural studies on the adrenal medulla of golden hamster: Origin and fate of secretory granules

Summary Several different fixatives were used in order to obtain the best preservation of fine structure in the chromaffin cells of hamster adrenal medulla. The best fixative for both immersion-fixation and perfusion-fixation contained glutaraldehyde (2.5%) and formaldehyde (4%). After fixation by immersion of the gland, both dark and light cells are found, but glands fixed by perfusion contain a homogeneous population of light cells, which were very well preserved.The plasma membrane along the free surface of chromaffin cells showed a large number of omega-shaped invaginations that usually contained a dense core or fibre-like material; the extracellular dense cores were very similar to those of intact secretory granules. Rarely, the extracellular dense cores were very large and resembled the contents of a secondary lysosome. Several coated pits were found on the inner surface of each omega-shaped invagination.A prominent Golgi zone, containing many coated vesicles, is typical of these chromaffin cells. The coated vesicles are of two kinds, one with and one without electron-dense contents. Coated vesicles were frequently found in close contact with, or fused with, pro-secretory granules.Both authors are Wellcome Research Fellows. This work is supported by a grant from the Medical Research Council. We appreciate the technical assistance of Mr. P. T. Edwards.     

Free Ia Eα chain expression in the E α + :E β − : recombinant strain A.TFR5

Molecular and biochemical techniques have been used to explore the reasons behind low E chain expression in the E ⁺ E ^– I-region recombinant strain, A.TFR5. A.TFR5 (A ^f E ^k, ap5), a recombinant between A.CA (A ^f E ^f) and A.TL (A ^k E ^k), carries the E ^k subregion. Previous results have shown that it expresses the E chain, but at reduced levels relative to E ⁺ E ⁺ strains. No E chains were detected, which is consistent with the A.TFR5E gene being derived from the A.CA parent, which carries the null E ^f allele. In this paper, the defect in E-chain expression is explored. Restriction fragment length polymorphism analysis has localized the recombination event in A.TFR5 approximately 30 kb upstream of E, in the region of the large intervening sequence of E. Northern blot analysis of total RNA from A.TFR5 shows normal amounts of the E message, but no E message. Two-dimensional gel analysis of 15 min pulse-labeled A.TFR5, A.CA, and A.TL E immunoprecipitates shows decreased levels of the intracellular E chain in A.TFR5 relative to A.TL. However, analysis of total cell extracts shows normal levels of this protein. A glycoprotein fraction isolated from total cell extracts of 5 h labeled cells contains normal amounts of intracellular E, but decreased amounts of the mature cell-surface protein. These data suggest that in the absence of E, the E chain (1) takes on an altered conformation that is not as efficiently recognized by alloantibodies, and (2) is found in normal levels as the partially glycosylated intracellular precursor, but is not processed and/or transported efficiently to the cell surface.     

Teratogenicity of retinoic acid and its effects on TGF-β2 expression in the developing cerebral cortex of the rat

Vitamin A metabolites are potent teratogens in a wide variety of species, including man. Transforming growth factor betas (TGF-s) are involved in several mammalian prenatal developmental processes. The aim of this study was to determine the effects of exogenous and excessive all-trans retinoic acid on TGF2 expression in the developing cerebral cortex of the rat. Many of the malformations including exencephaly, exophtalmus, abdominal wall defects, extremity reduction defects observed in this study were dependent on the time of administration of retinoic acid. TGF-2 was diversely expressed, as revealed immunohistochemically, in the cerebral cortex and plexus choroideus. The diversity depended on the gestational day and the was affected by the administration of retinoic acid. In the 15-day-old fetus from mothers who had been fed by gavage a single dose of 60mg/kg body weight of all-trans retinoic acid on the 8th day of gestation, TGF-2 immunoreactivity in the brain was decreased. However, by the 18th day of gestation, TGF-2 expression increased. The expression of TGF-2 in fetuses whose mothers had been given all-trans retinoic acid after the neurulation period (on day 12 of gestation) was generally similar to that in a control group. We conclude that all-trans retinoic acid leads to severe congenital malformations if administered before neurulation whereas if given after neurulation, it is not so teratogenic. Further, retinoic acid has a variable effect on the expression of TGF-2.     

Influence of thyroid hormones on the human ATP synthase β-subunit gene promoter

The action of thyroid hormones on the expression of the mitochondrial ATP synthase -subunit gene (ATPsyn) is controversial. We detected a binding site for the thyroid hormone receptor between-366 and-380 in the human ATPsyn gene by DNase I footprint analysis and band-shift assays. However, expression vectors in which the chloramphenicol acetyl transferase (CAT) reporter gene is driven by the 5 upstream region of ATPsyn gene were unresponsive to T₃ when transiently transfected to HepG2 or GH4C1 cells. CAT constructs driven by the rat phosphoenolpyruvate carboxykinase (PEPCK) or the growth hormone (GH) promoters were stimulated several fold by T₃ in parallel experiments. It is proposed that the biological effects of thyroid hormones on the ATPsyn expression occur through indirect mechanisms.     

Organ-specific crystalline structures of ferritin cores inβ-thalassemia/hemoglobin E

Summary The cores of ferritins isolated from different organs of human subjects with-thalassemia/hemoglobin E (-thal/HbE) disease have different size distributions and crystallinities depending on the source organ. These patients have not been treated by hypertransfusion regimen or iron chelation therapy.-Thal/HbE spleens and livers yield ferritin cores which are less crystalline than those isolated from normal spleens and livers, reflecting the more rapid deposition of iron in the diseased state. Ferritins isolated from the hearts and pancreases of-thal/HbE subjects were found to have larger, more crystalline cores than those from the-thal/HbE livers and spleens, possibly as a consequence of the role of the heart and pancreas as long-term iron deposition sites in this iron overload pathology.     

The structure of glycophorins of animal erythrocytes

Glycophorins are red cell membrane sialoglycoproteins, which contain multipleO-linked oligosacchride chains and carry most of the cell surface sialic acid. Due to this high content of sialic acid the glycophorins are strongly stained with periodic acid-Schiff (PAS) reagent after sodium sodicylsulfate-polyacrylamide gel electrophoresis (SDS-PAGE). The term glycophorin was proposed initially for human red cell sialoglycoproteins [1,2] and now it is also used for sialoglycoproteins in animal red cell membranes. Furthermore, similar glycoproteins of non-erythrocyte origin have also been identified and given the same name [3], although the terms leukosialin and sialophorin were proposed for a major sialoglycoproteins of human leukocytes [4,5]. In this article the term glycophorin will be used only for sialoglycoproteins existing in the erythrocyte membrane.Glycophorins of human erythrocytes, carrying blood group MN, Ss and other determinants, have been thoroughly studied and their properties described in several review articles [3,6,7,8]. The aim of this article is to summarize studies carriedout on the structure of non-human glycophorins, although some data concerning human glycophorins are included for comparative purposes.Abbreviations SDS-PAGE sodium dodecylsulphate-polycrylamide gel electrophoresis - PAS periodic acid-Schiff - LIS lithium diiodosalicylate     

Ultrastructure of carotenoid deprivation in photoreceptors of Manduca sexta: myeloid bodies and intracellular microvilli

Summary The ultrastructural effects of carotenoid (vitamin A) deprivation were studied in the adult photoreceptors of the tobacco hornworm moth Manduca sexta. Moths were reared on a deprived diet, which lacked the carotenoid sources of the photopigment chromophore, 3-hydroxy retinal, or on a control, fortified diet, containing ample carotenoid. The latter supported normal levels of visual function, whereas visual pigment and sensitivity were reduced by at least 3 log units in moths reared on the deprived diet. Myeloid bodies, massed cisternae of hypertrophied smooth endomembrane, filled the cytoplasm in the receptors of deprived animals. The myeloid bodies assumed various configurations that included lamellate stacks of parallel cisternae, and tubular networks in a paracrystalline form. Freeze-fracture preparations of myeloid membranes revealed a high density of P-face particles. Vacuoles containing microvilli similar to those of the rhabdomere were also present in deprived photoreceptors. We suggest that the elaboration of smooth endoplasmic reticulum as myeloid bodies in chromophore-deprived photoreceptors may stem from the hypertrophy of a biochemical system for processing the chromophore or the interruption of the intracellular pathway that normally carries visual pigment to the rhabdomere.     

Zum Problem der nucleolären Stoffabgabe

Summary An electron microscopical investigation of the nucleolo-cytoplasmic pathway was carried out in pilocarpine-stimulated exocrine pancreatic acinar cells. About 200 nuclei with peripheral nucleoli were investigated. In previous experiments it has been shown by means of radioautography that these nucleoli release considerable amounts of RNA or RNA-containing substances directly into the cytoplasm.Only in a very few cases do the peripheral nucleoli touch the inner nuclear membrane. In general a narrow zone of chromatin seperates the nucleolus from the nuclear envelope. Frequently the peripheral nucleoli are in direct contact with the so-called intranuclear channels of the pore complex. Without exception the nuclear envelope is closed in the vicinity of peripheral nucleoli and shows its typical structure. An extrusion of nucleolar substances could not be demonstrated in electron micrographs. The functional significance of the displacement of the nucleolus from the center to the peripheral region of the nucleus is discussed.It is suggested that the homogeneous appearance of the karyoplasm, as usually obtained after osmium fixation, gives a very good image of the intravital situation in the normal interphase nucleus. Lack of homogeniety of the karyoplasm, found sometimes after osmium fixation and regularly after aldehyde fixation, seems to be due to the method of tissue preparation. Especially the appearance of nucleolus associated chromatin as commonly described seems to be the result of fixation procedure. The fact, that the so-called intranuclear channels of the pore complex become visible seems to be another consequence of the method of preparation.

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Herrn Prof. Dr. F. Büchner zum 70. Geburtstag gewidmet.     

Fehlender Einfluß von Licht auf die Reversion der UV-induzierten spektralen Veränderung von Cytidylsäure

Zusammenfassung Das Lichtprodukt, welches nach Belichtung von UV-bestrahlter Cytidylsäure (CMP) in früheren Versuchen zu entstehen schien und über das von Park u. Kaplan berichtet worden war, konnte in neuen Versuchen des zweiten Autors nicht wiedergefunden werden. Nachbehandlung mit Licht wie auch Dunkelheit bei ca. 25°C ergaben offenbar die gleiche Substanz mit dem Absorptionsspektrum von normalem CMP.

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Summary The photoproduct after illumination of UV-irradiated Cytidylic acid (CMP) reported by Park and Kaplan earlier could not be reproduced by the 2^nd author. Both, postincubation with and without light at about 25°C led to the formation of obviously the same substance with the absorption spectrum of normal CMP.

     

Human high-affinity FcγRI (CD64) gene mapped to chromosome 1q21.2-q21.3 by fluorescence in situ hybridization

The human FcRI gene encodes for a highaffinity Fc receptor that plays pivotal roles in the immune response. We have used fluorescence in situ hybridization analysis to localize the FcRI gene to human chromosome 1. The human FcRI (CD64) gene has been assigned to human chromosome 1q21.2-q21.3 using R-banded human (pro)metaphase chromosomes.     

Cytoplasmic effects on the tissue culture response of callus from winter wheat mature embryos

A simple and reliable method was established for the maintenance of a permanent stock of several Medicago truncatula genotypes selected from a general seed stock by their in vitro culture amenability and embryogenic capacity. In the first step, multiple shoots were induced from the cotyledon axillary meristem meristem of pre-germinated seeds in Murashige and Skoog medium supplemented with cytokinins (9.3 M zeatin, 22.2 M benzylaminopurine or 4.5 M thidiazuron). In the second step, the induced shoots were allowed to develop in growth-regulator-free medium. Benzylaminopurine at 22.2 M supported the best combination of shoot quality and number of shoots produced. Rooting of microshoots depended on the cytokinin used for shoot induction and was faster for zeatin-treated shoots. In this work a propagation system was devised where the addition of growth regulators was restricted to the induction phase therefore reducing the risks of epigenetic and somaclonal variation.     

Early development of the self-fertilizing mangrove killifish <Emphasis Type="Italic">Rivulus marmoratus</Emphasis> reared in the laboratory

The mangrove killifish Rivulus marmoratus was reared at 25°±1°C and 17ppt salinity from 0 to 100 days after hatching (DAH), and its early development was described by examining growth and morphometric parameters, meristic characters (vertebral and fin-ray counts), bone-cartilage development, and pigmentation. Growth was isometric for preanal length, head length, snout length, body depth, pectoral-fin length, dorsal-fin length, anal-fin length, and caudal-peduncle depth. Negative allometric growth was observed in eye diameter and gape size. Meristic counts (mean±SD) for vertebrae (34.2±0.4) and dorsal- (8.6±0.5), anal- (11.4±0.5), and caudal-fin rays (30.2±0.8) were complete at 0 DAH (n=5), whereas pectoral-fin rays and pelvic-fin rays were complete by 30 DAH (14.5±0.4, n=5) and 60 DAH (4.2±0.8, n=5). Full ossification of meristic elements proceeded in the following sequence: vertebrae (by 30 DAH), caudal-, dorsal-, and anal-fin rays (by 60 DAH), pectoral-fin rays (between 60 DAH and 100 DAH), and pelvic-fin rays (by 100 DAH). Both morphological characters and meristic counts indicate that this species can be considered to be a juvenile after 9.8mm in standard length (20 DAH).     

Crayfish stretch-receptor organs: Effects of length-steps with and without perturbations

Isolated slowly and fast adapting stretch receptor organs (SROs) of crayfish were submitted to step-like length changes separated by prolonged stations with constant lengths. At times they were perturbed by a small-amplitude, fast length variation representing natural pertubations and referred to as jitter. Stimulus cycles depended on the sequence of lengths and on whether jitter was present. First-order afferent discharges were recorded from the dorsal nerve. Firing intensity, measured by the rate over bins of about 1 s, was displayed along ongoing time. Quantification involved estimation of cycle histograms, and trend tests for fully adapted discharges and preparation stability. The behaviour perturbed by jitter differed quantitatively in both organs from that without jitter, apart from more intense and irregular firing. Differences were also qualitative in the rapidly adapting organ (RAO), that jitter kept firing almost unccasingly and changed from a transient detector to a tonic receptor. Jitter effects varied with background stretch. The slowly adapting organ (SAO) and the perturbed RAO behaved quite similarly and exhibited features of lead-lag linear systems that implied joint sensitivity to length and velocity, like lively accelerations after stretches and lively slowings after relaxations with subsequent adaptation to steady discharges. Shortenings provided as important stimuli as lengthenings. At constant lengths, discharges eventually reached full adaptation: full adaptation cannot be proven experimentally, but can be accepted in practice using statistically sound and physiologically pragmatic criteria. When fully adapted, the SAO and the perturbed RAO had length-dependent discharges. Both SROs exhibited also prominent non-linear features besides the expected limiter behavior. Responses to symmetric stimuli were asymmetric: e.g. lengthenings produced greater rate changes and more durable transients than shortenings. The coding from steady lengths to fully-adapted discharges was multivalued (except in the unperturbed RAO): discharges were more or less intense depending on whether the particular length had been reached through lengthening or shortening, respectively (hysteresis). The anatomical and physiological reasons for many of these linear or nonlinear features are not yet identified fully. Discharge profiles deviated (in mean squared error) from the corresponding stimuli less with jitter than without. This happened, in spite of increased fluctuations in successive bins, because of reductions in transient effects and in delays to full adaptation. Length identification on the basis of the afferent discharges was improved by jitter, because of the above and because of reduction of the multivaluedness. The consequences of this more faithful representation are contingent on the neuronal analyzer to which the discharges are presented. The issues discussed, like full adaptation, multivaluedness, and the implications of the perturbations are relevant to mechanoreceptors in general, and even to all receptors.The authors acknowledge gratefully the generous support of the Fogarty Center of the National Institutes of Health (USA) and of the Fundación E. Rodríguez Pascual (España). The cooperation of the Instituto de Conservación de la Naturaleza was indispensable     

Carboxyl-terminal modification alters the subunit interactions and assembly pathways of normal and sickle hemoglobins

Parallel isofocusing studies established that carboxypeptidase A removal of the His-146 (HC3) and Tyr-145 (HC2) residues of heme subunits affected the assembly properties of both Des (A) and Des (S) with heme chains, albeit to differing degrees. Indeed, the rate of Des (A) oligomer dissociation (k ₁), as determined by visible spectroscopy, was 4.3-fold faster than that of its native (A) counterpart. Furthermore, Soret spectral studies have affirmed distinct rates of normal (HbA), sickle (HbS), and Des HbA hemoglobin assembly (k₂) from their and [Des (A)] heme-containing monomers. Matching kinetic analysis of Des (A) and Des (S) chain assembly (with an identical chain) revealed 4.6- and 7.8-fold faster combination rates than those seen for (A) and (S) chains, respectively. This 3-fold disparity in rates strongly supports the critical role of the -6 (A3) residue, and its amino-terminal region, in chain partner recognition and subsequent human hemoglobin assembly.     

Dynamic and static hysteresis in crayfish stretch receptors

This report calls attention to the magnitude and pervasiveness of hysteresis in the coding from length to afferent discharges in crayfish stretch receptor organs (SRO's). The influence of previous lengths on the rate that corresponded to a particular length L was manifest by a substantial excess of that encountered when L was arrived at from a shorter value over that when arrived at from a longer one. Hysteretic loops were present under dynamic conditions when length was modulated quasi-sinusoidally in the length vs. rate Lissajous plots of both the slowly and the fast-adapting organs (SAO, FAO), either not perturbed or perturbed. Loops became narrower with increasing frequency (except for when 1 to 1 locking appeared, Diez Martínez and Segundo, 1983). Hysteretic loops were present under static conditions when length changes were step-like, and fully adapted rates were noted in the SAO and in the perturbed FAO.Earlier reports suggest that hysteresis reflects jointly at least mechanical and electrogenic factors in the length-to-local dendritic effects and in the generator potential to discharge stages.Several models, either mechanical or mathematical, reveal hysteretic behavior. Detailed analysis has not been performed except for one instance (Chua and Bass, 1972) where, for example, loop-narrowing at higher frequencies occurs only with certain weighting functions whose physiological significance is as yet obscure.Hysteresis may be more widespread than suspected in sensory (and perhaps other) systems: it involves a multi-valuedness that raises the issue of how central mechanisms infer stimulus magnitude retrospectively from the discharge.Supported by funds from the Brain Research Institute and by a scholarship to ODM from the Departmento de Becas, Universidad Nacional Autónoma de México (UNAM)