Showing papers by "Rockefeller University published in 1972"

Dynamics of Encoding in a Population of Neurons

Abstract: A simple encoder model, which is a reasonable idealization from known electrophysiological properties, yields a population in which the variation of the firing rate with time is a perfect replica of the shape of the input stimulus. A population of noise-free encoders which depart even slightly from the simple model yield a very much degraded copy of the input stimulus. The presence of noise improves the performance of such a population. The firing rate of a population of neurons is related to the firing rate of a single member in a subtle way.

The enzymatic iodination of the red cell membrane.

Abstract: An enzymatic iodination procedure utilizing lactoperoxidase (LPO), radioactive iodide, and hydrogen peroxide generated by a glucose oxidase-glucose system has been described and utilized for a study of the red cell membrane. 97% of the incorporated isotope is in the erythrocyte ghost and 3% is associated with hemoglobin. No significant labeling of the red cell membrane occurs in the absence of LPO or by the deletion of any of the other reagents. A 6 million-fold excess of chloride ions inhibits iodination by no more than 50%. Incorporation of up to 1 x 106 iodide atoms into a single erythrocyte membrane results in no significant cell lysis. The incorporated label is exclusively in tyrosine residues as monoiodotyrosine. 10–15% of the trichloroacetic acid-precipitable radioactivity can be extracted with lipid solvents but is present as either labeled protein or 125I. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of solubilized membrane proteins reveals only two labeled protein bands out of the 15 present, and the presence of 50-1 x 106 iodide atoms per ghost does not alter this pattern. Component a has a molecular weight of 110,000, is carbohydrate poor, and represents 40% of the total label. Component b has an apparent molecular weight of 74,000, contains all of the demonstrable sialic acid, and accounts for 60% of the total label. Trypsinization of iodinated, intact red cells results in the disappearance of only component b, the appearance of labeled glycopeptides in the medium, and the absence of smaller, labeled peptides remaining in the membrane. Pronase treatment hydrolyzes component b in a similar fashion, but also cleaves component a to a 72,000 mol wt peptide which is retained in the membrane. A combination of protease treatment and double labeling with 125I and 131I does not reveal the appearance of previously unexposed proteins.

INTERACTION OF AGGREGATED γ-GLOBULIN WITH B LYMPHOCYTES

Abstract: Specific binding of aggregated gamma-globulin to a subpopulation of lymphocytes was demonstrated. This subpopulation was identified as the Ig-staining or B lymphocytes. The binding was irreversible and independent of complement, pH, temperature, protein content of the medium, and divalent cations. Aggregates of large size were needed for optimal visualization. Evidence was obtained that the site on the lymphocyte membrane responsible for binding aggregates was distinct from surface Ig.

The interaction between Toxoplasma gondii and mammalian cells. II. The absence of lysosomal fusion with phagocytic vacuoles containing living parasites.

Abstract: Electron microscope methods have been used to study delivery of macrophage primary or secondary lysosomal contents to phagocytic vacuoles containing living or dead toxoplasmas. Secondary lysosomes were labeled by culturing the cells in colloidal thorium dioxide (thorotrast) or in ferritin. Acid phosphatase cytochemistry was employed for detection of primary as well as secondary lysosomal constituents. These various lysosomal labels were present in nearly all vacuoles containing toxoplasmas killed with glutaraldehyde, or in vacuoles containing those parasites undergoing degeneration 1 hr after the uptake of living toxoplasmas. In contrast, at times ranging from 1 to 20 hr after infection, no vacuoles containing morphologically normal, apparently viable toxoplasmas were thorotrast or ferritin positive, and only rarely did these vacuoles react for acid phosphatase. In many instances vacuoles containing viable toxoplasmas and no lysosomal markers were situated in the same cell nearby to vacuoles containing degenerating toxoplasmas and lysosomal constituents, thus indicating that the determinants of lysosomal fusion were operating locally in the immediate vicinity of the phagocytic vacuole, and not operating to influence general cell function. Thus, some toxoplasmas are able to prevent the delivery of lysosomal contents, and apparently the phagocytic vacuole provides for these parasites a sheltered microenvironment ideal for their growth. Morphologic evidence indicated that living toxoplasmas altered the phagocytic vacuolar membrane in macrophages, fibroblasts, and HeLa cells. Within minutes after phagocytosis, the vacuole became surrounded by closely apposed strips of endoplasmic reticulum and mitochondria; somewhat later, microvillous protrusions of the membrane into the vacuole were seen. These morphologic features of phagocytic vacuoles containing living toxoplasmas may be of importance in relation to the absence of lysosomal fusion, or they may serve some function in protecting the host cell or in nourishing the parasite.

A simple neural network generating an interactive memory

Abstract: A model of a neural system where a group of neurons projects to another group of neurons is discussed. We assume that a trace is the simultaneous pattern of individual activities shown by a group of neurons. We assume synaptic interactions add linearly and that synaptic weights (quantitative measure of degree of coupling between two cells) can be coded in a simple but optimal way where changes in synaptic weight are proportional to the product of pre-and postsynaptic activity at a given time. Then it is shown that this simple system is capable of “memory” in the sense that it can (1) recognize a previously presented trace and (2) if two traces have been associated in the past (that is, if trace f was impressed on the first group of neurons and trace ḡ was impressed on the second group of neurons and synaptic weights coupling the two groups changed according to the above rule) presentation of f to the first group of neurons gives rise to f plus a calculable amount of noise at the second set of neurons. This kind of memory is called an “interactive memory” since distinct stored traces interact in storage. It is shown that this model can effectively perform many functions. Quantitative expressions are derived for the average signal to noise ratio for recognition and one type of association. The selectivity of the system is discussed. References to physiological data are made where appropriate. A sketch of a model of mammalian cerebral cortex which generates an interactive memory is presented and briefly discussed. We identify a trace with the activity of groups of cortical pyramidal cells. Then it is argued that certain plausible assumptions about the properties of the synapses coupling groups of pyramidal cells lead to the generation of an interactive memory.

The interaction of soluble horseradish peroxidase with mouse peritoneal macrophages in vitro

Abstract: The in vitro interaction of soluble horseradish peroxidase (HRP) with homogeneous mono layers of mouse macrophages has been studied using sensitive biochemical and cytochemical techniques. The compartmentalization of HRP in extracellular and intracellular sites has been quantitatively evaluated. A significant fraction is bound to a serum-derived layer, which coats the surface of culture vessels and may be removed by appropriate washes. Macrophages interiorize HRP as a solute in pinocytic vesicles without appreciable binding of the glycoprotein to the plasma membrane. Uptake is directly proportional to the concentration of HRP in the culture medium. 1 x 106 cells ingest 0.0025% of the administered load per hr over a wide range of concentrations. Cytochemically, all demonstrable HRP is sequestered within the endocytic vesicles and secondary lysosomes of the vacuolar apparatus. After uptake, the enzymatic activity of HRP is inactivated exponentially with a half-life of 7–9 hr, until enzyme is no longer detectable. When macrophages have pinocytosed trace-labeled HRP-125I, cell-associated isotope disappears with a t ½ of 20–30 hr and they release monoiodotyrosine-125I into the culture medium. We were unable to obtain evidence that significant amounts of HRP (>2%) can be exocytosed after uptake, can exist intact on the cell surface, or can be digested extracellularly. It is difficult to reconcile these observations with several of the postulated mechanisms whereby macrophages are thought to play a prominent role in the induction of an immune response.

Lysosomes of the arterial wall i. isolation and subcellular fractionation of cells from normal rabbit aorta

Abstract: Smooth muscle cells were dissociated from normal rabbit aorta by incubating the tissue in Hanks' solution containing elastase, collagenase, and hyaluronidase. The isolated cells contained significant amounts of the following acid hydrolases: N-acetyl-beta-glucosaminidase, N-acetyl-beta-galactosaminidase, beta-galactosidase, beta-glucuronidase, alpha-mannosidase, beta-glucosidase, acid phosphatase, and cathepsins C and D. The cells were disrupted and fractionated by isopycnic centrifugation on sucrose density gradients in the Beaufay automatic zonal rotor. Lysosomes with a modal density of 1.16 were identified by the distribution of these acid hydrolases and by the latency of N-acetyl-beta-glucosaminidase and beta-galactosidase. Other particulate enzymes studied in these sucrose gradients included cytochrome oxidase and monoamine oxidase (mitochondria), 5'-nucleotidase and leucyl-beta-naphthylamidase (plasma membrane), and catalase (? peroxisome). This microanalytical subcellular fractionation technique is applicable to the study of milligram quantities of many other tissues, both normal and pathological.

Rat Brain Binds Adrenal Steroid Hormone: Radioautography of Hippocampus with Corticosterone

Abstract: Tritiated corticosterone injected subcutaneously into adrenalectomized male rats 1 hour before killing produced intense labeling of the hippocampus in radioautograms prepared by a method that reduced or prevented diffusion of the radioactive material The pyramidal neurons of the cornu ammonis and the granule neurons of the gyrus dentatus contained more radioactivity than did other regions of the brain; however, the intensity of labeling varied among adjacent neurons The nuclei of many neurons were clearly labeled but radioactivity was relatively sparse in the cytoplasm, in the axons where they branch from cell bodies, and in adjacent neuropil

The interaction between Toxoplasma gondii and mammalian cells. I. Mechanism of entry and intracellular fate of the parasite.

Abstract: Macrophage, fibroblast, and HeLa cell cultures have been infected with Toxoplasma gondii, and observations have been made on parasite entry and fate. A special procedure was devised for studying the entry of toxoplasmas by electron microscopy. Toxoplasmas were centrifuged onto the cells in the cold; fixation 1-3 min after warming yielded specimens showing numerous examples of parasites in the process of entering cells. The mechanism of entry into macrophages, fibroblasts, and HeLa cells was in all cases by phagocytosis. Micropseudopods were extended by the cells to envelop the attached parasites in a typical phagocytic vacuole. Apparently the toxoplasmas stimulated this response of HeLa cells and fibroblasts, cell types not usually phagocytic. No instance was seen of penetration of toxoplasmas through the cell membrane, or of parasites located free in the cytoplasm. Essentially all of the toxoplasmas that entered HeLa cells divided with a generation time of 9 hr; the parasites formed large rosettes situated in vacuoles, eventually leading to host cell rupture. Macrophages took in larger numbers of toxoplasmas than did HeLa cells, but approximately half of the parasites inside of macrophages degenerated within a few hours. The surviving toxoplasmas in macrophages divided every 8 hr, forming rosettes and eventually rupturing the cells.

Depletion of vesicles from frog neuromuscular junctions by prolonged tetanic stimulation.

Abstract: Curarized cutaneous pectoris nerve muscle preparations from frogs were subjected to prolonged indirect stimulation at 2/sec while recording from end plate regions. At the ends of the periods of stimulation, the curare was removed and the preparations were fixed for electron microscopy or treated with black widow spider venom to determine the degree to which their stores of transmitter had been depleted. After 6–8 hr of stimulation the nerve terminals were almost completely depleted of their stores of transmitter and of their population of vesicles. Most of the transmitter release occurred during the first 4 hr of stimulation, and after this time most (about 80%) of the fibers were depleted of about 80% of their transmitter. The organization of the nerve terminals in 4-hr preparations appeared normal and the terminals still contained many vesicles. When peroxidase was present in the bathing medium, terminals from stimulated preparations showed many vesicles that contained peroxidase, whereas the rested control preparations showed few such vesicles The fact that after 4 hr the total number of vesicles is not markedly changed while a large fraction (up to 45%) contained peroxidase suggests that in our experiments vesicles were continuously fusing with and reforming from the axolemma.

Interactions of signal and background variables in visual processing

Abstract: Three variables which determine the opportunities for signal-noise confusions, display size (D), number of redundant signals per display (N), and number of alternative signals (A) were studied in relation to nature of the noise elements, confusable or nonconfusable with signals. Data were obtained in a forced-choice visual detection situation, the displays being linear arrays of letters on a CRT screen. For all three performance measures used, frequency of correct detections and correct and error latencies, strong interactions were obtained between all of the other variables and signal-noise confusability. The functions obtained, together with other data bearing on the role of confusions and on spatial relations among characters within the display, suggest a model whose initial phase is a parallel feature extraction process involving inhibitory relations among input channels.

The effects of mercaptoethanol and of peritoneal macrophages on the antibody-forming capacity of nonadherent mouse spleen cells in vitro

Abstract: Nonadherent mouse spleen cells exhibited poor viability and little or no capacity to form antibodies to sheep red cells in the Mishell-Dutton culture system. Viability and antibody-forming capacity could be restored by addition to these cultures of low concentrations of mercaptoethanol (10(-4)-10(-5)M), or by addition of appropriate numbers of mouse peritoneal macrophages. Macrophage concentrations lower than optimal resulted in lower lymphoid cell viability and correspondingly fewer plaque-forming cells, whereas excess macrophages resulted in marked inhibition of antibody formation despite good viability of the lymphocytes. Restoration of the nonadherent cells with mercaptoethanol was thus much simpler and more reproducible than it was with macrophages; furthermore, the number of plaque-forming cells developed in cultures restored with mercaptoethanol was approximately fourfold higher than it was in cultures restored with optimal numbers of macrophages. In the presence of mercaptoethanol, the plaque-forming capacity of the nonadherent spleen cells was not increased when small numbers of macrophages were added to the system, nor was it decreased when the few macrophages present in the nonadherent cells were further reduced or eliminated. Excess macrophages inhibited antibody formation in the cultures containing mercaptoethanol as they did in control cultures. Optimal restoration of plaque-forming capacity to the nonadherent spleen cells with mercaptoethanol required the reducing agent to be present throughout the 4 or 5 day culture period. Addition of mercaptoethanol 1 or more days after initiation of culture, or transfer of the cells to a medium free of mercaptoethanol before completion of the culture resulted in a reduction in the numbers of plaque-forming cells. The results suggest that mouse lymphoid cells do not require macrophages in order to form antibodies to sheep red cells in vitro, provided mercaptoethanol is present in the culture medium. The mechanism of action of mercaptoethanol under these conditions is not completely clear, but one of its effects is to promote the viability of lymphoid cells in the cultures.

PERMEABILITY OF INTESTINAL CAPILLARIES : Pathway followed by Dextrans and Glycogens

Abstract: The pathway followed by macromolecules across the wall of visceral capillaries has been studied by using a set of tracers of graded sizes, ranging in diameter from 100 A (ferritin) to 300 A (glycogen). Polysaccharide particles, i.e. dextran 75 (mol wt ∼75,000; diam ∼125 A), dextran 250 (mol wt 250,000; diam ∼225 A), shellfish glycogen (diam ∼200 A) and rabbit liver glycogen (diam ∼300 A), are well tolerated by Wistar-Furth rats and give no vascular reactions ascribable to histamine release. Good definition and high contrast of the tracer particles were obtained in a one-step fixation—in block staining of the tissues by a mixture containing aldehydes, OsO4 and lead citrate in phosphate or arsenate buffer, pH 7.4, followed by lead staining of sections. The glycogens and dextrans used move out of the plasma through the fenestrae and channels of the endothelium relatively fast (3–7 min) and create in the pericapillary spaces transient (2–5 min) concentration gradients centered on the fenestrated sectors of the capillary walls. The tracers also gained access to the plasmalemmal vesicles, first on the blood front and subsequently on the tissue front of the endothelium. The particles are temporarily retained by the basement membrane. No probe moved through the intercellular junctions. It is concluded that, in visceral capillaries, the fenestrae, channels, and plasmalemmal vesicles, viewed as related parts in a system of dynamic structures, are the structural equivalent of the large pore system.

Structure of the Ribonucleoprotein of Influenza Virus

Abstract: The ribonucleoprotein (RNP) internal components of influenza virus were separated into distinct size classes by sedimentation in glycerol gradients and examined by electron microscopy by using positive staining with uranyl acetate. The large RNP have a peak in length distribution at 90 to 110 nm, the medium, at 60 to 90 nm, and the small, at 30 to 50 nm. These lengths can be correlated with the estimated molecular weights of the ribonucleic acids contained in the various RNP size classes. The RNP structure appears to consist of a strand which is folded back on itself and coiled in a regular double-helical arrangement.

Slow Conduction and Reentry in the Ventricular Conducting System I. RETURN EXTASYSTOLE IN CANINE PURKINJE FIBERS

Abstract: Depression of excitability and responsiveness provoked by the action of high K + and epinephrine on short bundles of excised canine Purkinje fibers yields reentrant excitation. An impulse entering a depressed area undergoes marked slowing of conduction; the impulse then may continue forward while also returning through the pathway by which the initiating impulse entered the depressed area. The impulse may be delayed or blocked in either the forward or the retrograde direction. The reentrant excitation can occur in the absence of premature excitation. Various methods of depression of excitability produce return extrasystoles in Purkinje fibers. The common factor is very slow conduction which depends upon the abolition of the fast upstroke and the appearance of a low-voltage, slowly propagated action potential that is readily blocked.

Slow Conduction and Reentry in the Ventricular Conducting System: II. SINGLE AND SUSTAINED CIRCUS MOVEMENT IN NETWORKS OF CANINE AND BOVINE PURKINJE FIBERS

Abstract: Depression of excitability and responsiveness provoked by the action of high K+ and epinephrine on short bundles of excised canine Purkinje fibers yields reentrant excitation. An impulse entering a depressed area undergoes marked slowing of conduction; the impulse then may continue forward while also returning through the pathway by which the initiating impulse entered the depressed area. The impulse may be delayed or blocked in either the forward or the retrograde direction. The reentrant excitation can occur in the absence of premature excitation. Various methods of depression of excitability produce return extrasystoles in Purkinje fibers. The common factor is very slow conduction which depends upon the abolition of the fast upstroke and the appearance of a low-voltage, slowly propagated action potential that is readily blocked.

Radioautographic analysis of the secretory process in the parotid acinar cell of the rabbit.

Abstract: Intracellular transport of secretory proteins has been studied in the parotid to examine this process in an exocrine gland other than the pancreas and to explore a possible source of less degraded membranes than obtainable from the latter gland. Rabbit parotids were chosen on the basis of size (2–2.5 g per animal), ease of surgical removal, and amylase concentration. Sites of synthesis, rates of intracellular transport, and sites of packaging and storage of newly synthesized secretory proteins were determined radioautographically by using an in vitro system of dissected lobules capable of linear amino acid incorporation for 10 hr with satisfactory preservation of cellular fine structure. Adequate fixation of the tissue with minimal binding of unincorporated labeled amino acids was obtained by using 10% formaldehyde-0.175 M phosphate buffer (pH 7.2) as primary fixative. Pulse labeling with leucine-3H, followed by a chase incubation, showed that the label is initially located (chase: 1–6 min) over the rough endoplasmic reticulum (RER) and subsequently moves as a wave through the Golgi complex (chase: 16–36 min), condensing vacuoles (chase: 36–56 min), immature granules (chase: 56–116 min), and finally mature storage granules (chase: 116–356 min). Distinguishing features of the parotid transport apparatus are: low frequency of RER-Golgi transitional elements, close association of condensing vacuoles with the exit side of Golgi stacks, and recognizable immature secretory granules. Intracelular processing of secretory proteins is similar to that already found in the pancreas, except that the rate is slower and the storage is more prolonged.

Conduction of the Cardiac Impulse III. Characteristics of very slow conduction

Abstract: The excitability of short segments (5–7 mm) of bundles of canine Purkinje fibers was depressed by exposure to 15–18 mM K+, to 15–18 mM K+ plus 5 x 10-6 epinephrine or norepinephrine, to low K+, and to low Na+. The depressed segment was in the center chamber of a three-chamber bath; the ends of the bundle were exposed to normal Tyrode solution. Each method of depression resulted in slow and probably decremental conduction with an effective conduction velocity in the middle chamber of about 0.05 m/sec, or one-way block, or two-way block with summation of the graded responses in the depressed region. The action potential in the depressed segment (the slow response) differs from the normal action potential in its response to applied stimuli. A second active depolarization can be evoked by cathodal stimulation during much of the slow response. The response in the depressed segment is graded. The response of depressed fibers may depend on excitatory events similar to those responsible for the slow component of the cardiac action potential. It is suggested that the slow response can propagate, at least decrementally, in fibers in which the rapid, Na+-dependent upstroke is absent, and can cause reentrant excitation by so doing.

Activation of b lymphocytes by locally concentrated concanavalin a.

Abstract: B lymphocytes are not stimulated by soluble concanavalin A (Con A). However, Con A cross-linked at the bottom of tissue culture petri dishes could activate DNA synthesis in B cells. Addition of free Con A to such cultures inhibited the proliferative response to insoluble Con A. T lymphocytes were not activated by locally concentrated Con A, although they responded to soluble Con A. In the presence of both soluble and cross-linked Con A there was a shift in the dose response curve to soluble Con A, the magnitude of which varied with the concentration of cross-linked Con A.