Showing papers by "Johns Hopkins University School of Medicine published in 1970"

Embryonic vertebrate central nervous system: Revised terminology

Abstract: The layers and cells of the early developing central nervous system lack direct counterparts in the adult and must be designated by a special terminology. The inconsistent and inaccurate language now in use leads to misunderstanding and a revision is proposed in which the four fundamental zones are termed the ventricular, subventricular, intermediate, and marginal zones. Each is defined according to the form, behavior, and fate of its constituent cells. All neurons and macroglia of the central nervous system can be derived from these developmental zones.

Organization of the outer plexiform layer of the primate retina: electron microscopy of Golgi-impregnated cells.

Abstract: Golgi-impregnated retinae of rhesus monkeys have been examined by serial section electron microscopy to establish in a quantitative manner the neural connexions in the outer plexiform layer. The results have shown that there are two types of midget bipolar cell, here called the invaginating midget bipolar and the flat midget bipolar. Both types of midget bipolar are exclusive to a single cone. The invaginating midget bipolar has been found to fit a dendritic terminal process into every invagination in the cone pedicle base. The flat midget bipolar has dendritic terminals that make superficial contact on the cone pedicle base. There are twice as many dendritic terminals and points of contact with the cone pedicle on a flat midget bipolar top as compared with an invaginating midget bipolar top. These observations, together with light microscope counts of the numbers of the two types of midget bipolars, suggest that there are two midget bipolars per cone. The diffuse cone bipolar (the flat bipolar) also makes superficial contacts on the cone pedicle base, and serial sections have shown that a flat bipolar contacts about six cones. Rod bipolars connect exclusively to rods and their dendritic terminals always end as one of the central processes that penetrate the invagination. Horizontal cell dendrites end exclusively in cone pedicles and their axon terminals end in rod spherules. The point of contact with both the types of receptor is as the lateral elements of the invaginations. A single small horizontal cell contacts about seven cones and a large horizontal cell contacts about twelve cones. The numbers of contacts per cone pedicle decrease from the centre to the periphery of the horizontal cell's dendritic field, suggesting there is an overlap of four to six horizontal cells onto a single cone pedicle. The horizontal cell axon terminals are too numerous to assess in absolute numbers but there is only one terminal to a given rod spherule from any particular axon.

Organization of vertebrate retinas.

Abstract: JL he vertebrate retina is a portion of nervous tissue that has long been of interest both to investigators of brain function and of the visual process. It is one of the most accessible parts of the central nervous system; it can be easily and precisely stimulated with patterns of light; and its output, via the optic nerve, can be readily monitored. Recent studies employing electron microscopy and intracellular recording techniques have described the synaptic contacts in the vertebrate retina and the electrical responses of the six principal types of retinal cells. This new information, coupled with the knowledge of the retinal cells derived from light microscopy, permits us to infer probable sites of interaction and major synaptic pathways that occur within the vertebrate retina. In this paper I shall review some of this recent

The inner plexiform layer of the vertebrate retina: A quantitative and comparative electron microscopic analysis

Abstract: The inner plexiform layer of human, monkey, cat, rat, rabbit, ground squirrel, frog and pigeon retinas was studied by electron microscopy. All showed the same qualitative synaptic arrangements: bipolar cells made dyad ribbon synapses onto amacrine and ganglion cells; amacrine cells made conventional synaptic contacts onto bipolar, ganglion cells; amacrine cells montage of electron micrographs through the full thickness of the inner plexiform layer were made for each species and were scored for synaptic contacts. Both absolute and relative quantitative differences were found between species. The ratio of amacrine cell (conventional) synapses to bipolar cell (ribbon) synapses, the absolute number of amacrine cell synapses and the number of inter-amacrine cell synapses were all found to be higher in those animals which are known to have relatively complex retinal ganglion cell receptive field properties. It is suggested that the amacrine cell is involved in mediating complex visual transformations in certain vertebrate retinas.

Concentrations of putrescine and polyamines and their enzymic synthesis during androgen-induced prostatic growth.

Abstract: 1 Castration of adult rats resulted in marked decreases in the amounts of putrescine, spermidine and spermine in the ventral prostate gland Spermidine concentrations decline rapidly over the first 11 days after androgen withdrawal, reaching a value of only 12% of normal controls Spermine concentrations diminish more slowly, reaching 24% of normal within 11 days The spermidine/spermine molar ratio falls from 09 to 046 under these conditions Putrescine concentrations decrease by 70% at 7 days after castration and then remain constant for some days 2 After daily injections of testosterone propionate to rats castrated 7 days previously, prostatic spermidine and putrescine concentrations increase significantly within 24h; normal or even greater values are observed within 8 and 4 days respectively In contrast, the spermine concentration does not increase until 5 days after commencement of androgen treatment 3 The activities of two enzymes involved in polyamine biosynthesis (ornithine decarboxylase and a putrescine-activated S-adenosyl-l-methionine decarboxylase system) were greatly decreased soon after castration: after 7 days the respective values were 15% of normal for ornithine decarboxylase and 7% of normal for putrescine-dependent decarboxylation of S-adenosyl-l-methionine Injection of testosterone propionate into animals castrated 7 days previously induced a rapid increase in both enzymic activities: ornithine decarboxylase was doubled in 6h, and increased three- to four-fold within 48h, whereas the putrescine-dependent decarboxylation of S-adenosyl-l-methionine doubled in 3h and increased tenfold within 48h of commencement of daily androgen treatments 4 The activity of these enzyme systems was very low in the ventral prostates of hypophysectomized rats and was increased by administration of testosterone in a manner similar to that found in castrated rats 5 Alterations in the activity of two ventral-prostate enzymes involved in ornithine production (arginase) and utilization (ornithine-2-oxoglutarate transaminase) that result from changes in the androgenic status of rats are described 6 The findings presented suggest that the activities of ornithine decarboxylase and the putrescine-dependent S-adenosyl-l-methionine decarboxylase system, rather than ornithine concentrations, are rate-limiting for the formation of putrescine and polyamines in rat ventral prostate 7 The relation of polyamines to androgen-induced prostatic growth is discussed with particular reference to the biosynthesis of proteins and nucleic acids

Amphetamine: Differentiation by d and l Isomers of Behavior Involving Brain Norepinephrine or Dopamine

Abstract: d-Amphetamine is markedly more potent an inhibitor of catecholamine uptake by norepinephrine neurons in the brain than is 1-amphetamine, whereas the two isomers are equally active in inhibiting catecholamine uptake by the dopamine neurons of the corpus striatum. In behavioral studies, d-amphetamine is ten times as potent as 1-amphetamine in enhancing locomotor activity, while it is only twice as potent in eliciting a compulsive gnawing syndrome. This suggests that the locomotor stimulation induced by amphetamine involves central norepinephrine, while dopamine neurons play an important role in the induced compulsive gnawing behavior. Assessment of differential actions of d- and 1-amphetamine may be an efficient method to differentiate behaviors involving norepinephrine or dopamine in the brain.

The rate of decline of diphenylhydantoin in human plasma

Abstract: The rate of disappearance of diphenylhydantoin from plasma was studied in 70 healthy volunteers by giving them 100 mg. orally 3 times daily for 3 days and measuring the plasma diphenylhydantoin concentration for 4 consecutive days after the last dose of the drug. The mean plasma half‐life was 22.0 ± 9.0 hours and the difference between that of Negro and Caucasian males, 26.5 and 18.5 hours, respectively, was Significant. Dose dependency of the half‐life was demonstrated in 10 subjects studied. The decline in plasma diphenylhydantoin concentration in many subfects was not exponential and the disappearance of the drug from plasma was not always a first‐order process. The diphenylhydantoin half‐life in some subjects was shorter after long‐term administration than after short‐term administration of the drug. Saturation, autoinduction, or product inhibition, singly or in combination, of the drug‐metabolizing enzyme system are possible mechanisms involved in the dose dependency and nonexponential decline of plasma diphenylhydantoin concentration.

Visual Adaptation in the Retina of the Skate

Abstract: The electroretinogram (ERG) and single-unit ganglion cell activity were recorded from the eyecup of the skate (Raja erinacea and R. oscellata), and the adaptation properties of both types of response compared with in situ rhodopsin measurements obtained by fundus reflectometry. Under all conditions tested, the b-wave of the ERG and the ganglion cell discharge showed identical adaptation properties. For example, after flash adaptation that bleached 80% of the rhodopsin, neither ganglion cell nor b-wave activity could be elicited for 10–15 min. Following this unresponsive period, thresholds fell rapidly; by 20 min after the flash, sensitivity was within 3 log units of the dark-adapted level. Further recovery of threshold was slow, requiring an additional 70–90 min to reach absolute threshold. Measurements of rhodopsin levels showed a close correlation with the slow recovery of threshold that occurred between 20 and 120 min of dark adaptation; there is a linear relation between rhodopsin concentration and log threshold. Other experiments dealt with the initial unresponsive period induced by light adaptation. The duration of this unresponsive period depended on the brightness of the adapting field; with bright backgrounds, suppression of retinal activity lasted 20–25 min, but sensitivity subsequently returned and thresholds fell to a steady-state value. At all background levels tested, increment thresholds were linearly related to background luminance.

Diffuse neonatal hemangiomatosis

Abstract: Two infants with diffuse neonatal hemangiomatosis are presented. One infant developed thrombocytopenia and bleeding while the other infant with more widely diffuse lesions succumbed to extensive central nervous system involvement. Steroid therapy caused no obvious alteration in either of the patient9s course. The vascular lesion in this disease is possibly congenital absence of vessel wall pericytes. Six previous cases of diffuse neonatal hemangiomatosis are briefly reviewed in relation to the sites of the lesions, cause of death and malignant potential.

An electron microscopic characterization of classes of synaptic vesicles by means of controlled aldehyde fixation

Abstract: Examination of variables of aldehyde fixation that may affect the shape of agranular synaptic vesicles has revealed that even brief storage of aldehyde-perfused nervous tissue pieces in cacodylate buffer, prior to hardening in osmium tetroxide, has an unusually severe flattening effect on agranular vesicles of a particular type. These are the vesicles of peripheral cholinergic axon endings, and of certain central synaptic bulbs. Types of synaptic bulbs can now be further defined on the basis of shape of agranular synaptic vesicles under controlled conditions of aldehyde fixation. Previously described "S" bulbs in the spinal cord contain uniformly spheroid vesicles, which are wholly resistant to flattening. Previously described "F" bulbs contain somewhat smaller agranular vesicles that are flattened after aldehyde fixation, even when this is followed by prompt hardening in osmium tetroxide solution. A third type, previously characterized as having irregularly round agranular vesicles after the above treatment, contains only severely flattened vesicles when the osmium tetroxide hardening is preceded by even a brief wash with sodium cacodylate buffer containing sucrose. Moreover, the "third" type is characteristic of all cholinergic peripheral axon endings examined, as well as the large axosomatic ("L") synaptic bulbs of the spinal cord.

Biosynthese von 6‐Methylsalicylsäure

Abstract: An extract was prepared from Penicillium patulum grown in submerged culture, which converted acetyl-CoA and malonyl-CoA into 6-methylsalicylic acid in the presence of NADPH. The enzyme was very labile in the crude extract, but appeared stable after acetone precipitation. A 100-fold purification was achieved by ammonium sulfate fractionation, sedimentation in the ultracentrifuge, and sucrose-density gradient centrifugation. The enzyme was a single particle with a molecular weight of 1.1–1.5 × 106 as determined by gradient centrifugation with catalase and fatty acid synthetase as standards. In the first steps of purification, fatty acid synthetase from Penicillium patulum migrated with the methylsalicylic acid synthetase complex. A separation of the two enzyme systems was accomplished by sucrose-density gradient centrifugation. The purified enzyme represents a new multienzyme complex which shares several common properties with fatty acid synthetase. Methylsalicylic acid synthetase is inhibited by iodoacetamide and N-ethylmaleinimide. The incubation of enzyme with acetyl-CoA and malonyl-CoA in the absence of NADPH led to triacetic acid lacton. This indicates that in 6-methylsalicylic acid synthesis reduction occurs at the triacetic acid level before the final condensation with malonyl-CoA. Triacetic acid lacton was produced by the enzyme at 10% of the rate of 6-methylsalicylic acid synthesis in the complete system. This rate of lacton synthesis, however, is an order of magnitude greater than that catalysed by fatty acid synthetase. A possible explanation for this difference in behavior is given. Covalent linkage of substrates and intermediates to SH-groups of the protein during the synthesis of 6-methylsalicyslic acid is suggested. A reaction scheme leading to 6-methylsalicylic acid is proposed and the partial reactions of this synthesis are discussed with respect to similar reactions of fatty acid biosynthesis.

Neural coding in the sense of touch: human sensations of skin indentation compared with the responses of slowly adapting mechanoreceptive afferents innvervating the hairy skin of monkeys.

Abstract: The human capacity to scale the intensity of brief mechanical indentations of the hairy skin was measured by the method of subjective magnitude estimation. The afferent discharges evoked by nearly identical stimuli delivered to comparable locations on the hairy skin in monkeys were recorded in a number of types of first-order mechanoreceptive afferents. It was shown that of these only those which adapt slowly to mechanical stimuli possess sufficient dynamic range of response to account for the range of human pressure sensation. Two such afferents innervating the hairy skin, previously identified by others as the Type I and Type II afferents, were studied in detail as regards their responses to brief mechanical stimuli of different intensities. The relation of the human subject's estimate of intensity to stimulus magnitude is described by a power function with an exponent of about 0.4. Using impulse frequency in the “early steady state” as a measure, the responses of both types of slowly adapting mechanoreceptive afferents are related to stimulus magnitudes by power functions with exponents averaging about 0.5. On the assumption that the stimuli used elicit similar patterns of discharge in the first-order afferents innervating the hairy skin of men and monkeys, the results support the general proposition, now shown to hold for a number of senses, that the intensity of human sensation is determined by the functional properties of the first-order sensory fibers, and that the final behavioral output in the form of a subjective estimate of magnitude is a linear function of the frequency of discharge in those first-order fibers.

Analogues of methionine as substrates and inhibitors of the methionine adenosyltransferase reaction. Deductions concerning the conformation of methionine.

Abstract: Steric, electronic, and conformational requirements are described for analogues of L-methionine essential to their function as substrates or inhibitors of the methionine adenosyltransferase reaction (ATP: L-methionine S -adenosyltransferase, EC [2.4.2.13][1]). With the aid of partially purified transferase preparations from Escherichia coli , bakers' yeast, and rat liver, a systematic study of substrate analogues has been undertaken. Inhibitors of the enzyme fall into three categories: (a) straight carbon chain amino acids, such as L-2-amino-4-hexenoic acid ( trans but not the cis isomer) and L-2-amino-4-hexynoic acid, which are the most potent inhibitors; (b) cyclic amino acids, among which 1-aminocyclopentanecarboxylicacid and one of the four isomers of 1-amino-3-methylcyclopentanecarboxylic acid (either the 1R, 3R or the 1S, 3R isomer) are the most powerful; and (c) O -acetyl-L-serine- O -carbamyl-L-serine, and S -carbamyl-L-cysteine. Since inhibitors belonging to groups (a) and (b) possess considerable conformational rigidity by virtue of the presence of unsaturations or cyclic structures, it has been possible to draw conclusions with respect to the conformation of L-methionine at the active site of the adenosyltransferase reaction. A number of the inhibitors of the methionine adenosyltransferase reaction, such as 1-aminocyclopentanecarboxylic acid and S -carbamyl-L-cysteine, are known to be inhibitors of the growth of certain microorganisms and tumors. The possibility is suggested that these inhibitory activities may be mediated at least in part through the inhibition of the synthesis of S -adenosyl-L-methionine. ACKNOWLEDGMENTS The authors are deeply grateful to Drs. E. Bueding and C. H. Robinson for advice, and to Mrs. Mary Karen Burch for technical assistance. [1]: pending:yes

Growth Hormone Induction of Ornithine Decarboxylase in Rat Liver

Abstract: The effect of growth hormone on hepatic ornithine decarboxylase (L-ornithine carboxy- lyase, EC 4.1.1.17) (ORD) activity was studied in adult and weanling rats. Single injections of growth hormone produced up to 30-fold increases in ORD activity in both adults and weanlings. However, with lower doses of growth hormone, a greater increase in ORD activity occurred in weanlings than in adults. Both adult and weanling rats showed the same time course of ORD activity enhancement after growth hormone with peak enzymatic activity at 4 hr and a decline to basal levels by 8 hr after hormone administration. In weanling rats, cycloheximide completely prevented the elevation of ORD activity at 4 hr after growth hormone if administered any time up to 3 hr after the hormone. If given simultaneously with growth hormone, actinomycin D almost totally supressed the enhanced ORD activity 4 hr after growth hormone. However, the ability of actinomycin D to prevent increased ORD activity decreased as the time after growth horm...

Genetic Inactivation of the α-Galactosidase Locus in Carriers of Fabry's Disease

Abstract: Skin fibroblasts from a patient with Fabry's disease showed deficient activity of alpha-galactosidase. Fibroblasts from his mother and sister had two distinct clonal populations, one with enzymatic activity and the other enzyme deficient. This provides evidence of genetic inactivation at the alpha-galactosidase locus and makes possible the detection of carriers of Fabry's disease even when the enzymatic activity in their leukocytes and uncloned fibroblasts is within the range of controls.

Comparative studies on mitochondria isolated from neuron-enriched and glia-enriched fractions of rabbit and beef brain

Abstract: Fractions enriched in neuronal and glial cells were obtained from dispersions of whole beef brain and rabbit cerebral cortex by large-scale density gradient centrifugation procedures. The fractions were characterized by appropriate microscopic observation. Mitochondria were then isolated from these fractions by differential centrifugation of their homogenates. The two different types of mitochondria were characterized with respect to certain enzyme activities, respiratory rate, rate of protein synthesis, and their buoyant density in sucrose gradients. The mitochondria from the neuron-enriched fraction were distinguished by a higher rate of incorporation of amino acids into protein, higher cytochrome oxidase activity, and a higher buoyant density in sucrose density gradients. Mitochondria from the glia-enriched fraction showed relatively high monoamine oxidase and Na+- and K+-stimulated ATPase activities. The rates of oxidation of various substrates and the acceptor control ratios did not differ appreciably between the two types of mitochondria. The difference in the buoyant density of mitochondria isolated from the neuron-enriched and glia-enriched cell fractions was utilized in attempts to separate neuronal and glial mitochondria from the mixed mitochondria obtained from whole brain homogenates in shallow sucrose gradients. The appearance of two peaks of cytochrome oxidase, monoamine oxidase, and protein concentration in such gradients shows the potential feasibility of such an approach.

The essential fatty acids.

Abstract: Publisher Summary This chapter explains structural requirements, metabolism of action, and the role of the essential fatty acids. These acids are metabolized in ways common to other unsaturated fatty acids. In addition, the unsaturated acids possessing the 9, 12 double bond system (C18 acids) or the 11–14 double bond system (C20 acids) possesses special properties that are essential to the animal. Presumably, they function in esterified forms rather than as free fatty acids, and their essential roles may be determined by relative concentrations of phospholipids, glycerides, and sterol esters, which in turn seem to involve hormonal regulation. There is evidence to suggest that they are concerned, via phospholipids, in membrane integrity. This may be related to certain biochemical lesions that have been reported in connection with a deficiency of essential fatty acids in cases where membranes possess recognized biochemical activity, for example, in mitochondria. The essential fatty acids are the precursors of the prostaglandins, but the relationships of the latter to the classical deficiency symptoms is not certain and there is no evidence suggesting a relationship of this hormone family to the reported biochemical lesions of the deficiency.

Neuronal populations in the human brain.

Abstract: THE deterioration of mental function in old age may be due to loss of neurones or decay of their function. Several studies support the former view1,2 but sample sizes and the number of cases reviewed were small. Accordingly we studied the ventral cochlear nucleus (VCN) because it is well defined and small enough to make accurate counts feasible.

Uptake and Subcellular Localization of Neurotransmitters in the Brain

Abstract: Publisher Summary Nerve terminals in the brain possess specialized uptake mechanisms for a variety of putative neurotransmitters, such as dopamine (DA), norepinephrine (NE), serotonin, γ-aminobutyric acid (GABA) and, possibly, for glutamic acid and glycine. This chapter describes the specific uptake mechanisms for several putative neurotransmitters in the brain and their use in labeling and separating synaptosomes storing different putative neurotransmitters. The chapter proposes to use these uptake systems for labeling the endogenous transmitter pools with exogenous, radioactive neurotransmitters, labeling one class of synaptosomes with 3 H-transmitter and another with 14 C-transmitter. Kinetic studies elucidate the optimal conditions for nerve endings in brain slices or in isolated, pinched-off form (synaptosomes) to accumulate selectively their specific transmitter. The synaptosomal populations are separated with density gradient centrifugal procedures in the same brain region storing different transmitters or in different brain region storing the same transmitter. The electron microscopic studies reveal specific morphological features for the varying synaptosomal populations.