The potential for grass-fed livestock: resource constraints

Using pasture and grazed forest-range for a system of producing live-stock by feeding grass alone reduces the inputs of energy about 60 percent and land resources about 8 percent, but also reduces by about half the production of animal protein in the United States. Under a system in which only grass was fed, livestock would be restricted to beef, milk, and lamb production. The amount of grain fed to U.S. livestock is about 135 million tons (metric) or about ten times the amount consumed by the U.S. population.     

Lipoprotein uptake by neuronal growth cones in vitro

Macrophages that rapidly enter injured peripheral nerve synthesize and secrete large quantities of apolipoprotein E. This protein may be involved in the redistribution of lipid, including cholesterol released during degeneration, to the regenerating axons. To test this postulate, apolipoprotein E-associated lipid particles released from segments of injured rat sciatic nerve and apolipoprotein E-containing lipoproteins from plasma were used to determine whether sprouting neurites, specifically their growth cones, possessed lipoprotein receptors. Pheochromocytoma (PC12) cells, which can be stimulated to produce neurites in vitro, were used as a model system. Apolipoprotein E-containing lipid particles and lipoproteins, which had been labeled with fluorescent dye, were internalized by the neurites and their growth cones; the unmetabolized dye appeared to be localized to the lysosomes. The rapid rate of accumulation in the growth cones precludes the possibility of orthograde transport of the fluorescent particles from the PC12 cell bodies. Thus, receptor-mediated lipoprotein uptake is performed by the apolipoprotein B,E(LDL) (low density lipoprotein) receptors, and in the regenerating peripheral nerve apolipoprotein E may deliver lipids to the neurites and their growth cones for membrane biosynthesis.     

Cloning of complementary DNA for GAP-43, a neuronal growth-related protein

GAP-43 is one of a small subset of cellular proteins selectively transported by a neuron to its terminals. Its enrichment in growth cones and its increased levels in developing or regenerating neurons suggest that it has an important role in neurite growth. A complementary DNA (cDNA) that encodes rat GAP-43 has been isolated to study its structural characteristics and regulation. The predicted molecular size is 24 kilodaltons, although its migration in SDS-polyacrylamide gels is anomalously retarded. Expression of GAP-43 is limited to the nervous system, where its levels are highest during periods of neurite outgrowth. Nerve growth factor or adenosine 3',5'-monophosphate induction of neurites from PC12 cells is accompanied by increased GAP-43 expression. GAP-43 RNA is easily detectable, although at diminished levels, in the adult rat nervous system. This regulation of GAP-43 is concordant with a role in growth-related processes of the neuron, processes that may continue in the mature animal.     

Neuronal cytomechanics: the actin-based motility of growth cones

The patterns of synaptic connection that underlie brain function depend on the elaborate forms characteristic of neurons. It is therefore a central goal of neuroscience to understand the molecular basis for neuronal shape. Neuronal pathfinding during development is one major determinant of neuronal shape: growing nerve axons and dendrites must navigate, branch, and locate targets in response to extracellular cue molecules within the embryo. The leading tips of growing nerve processes, structures known as growth cones, contain especially high concentrations of the ubiquitous mechanochemical protein actin. Force generation involving this cytoskeletal molecule appears to be essential to the ability of growing nerve fibers to respond structurally to extracellular cues. New results from electronically enhanced light microscopy of living growth cones are helping to show how actin-based forces guide neurite growth and synapse formation.     

Nerve growth factor attenuates neurotoxic effects of taxol on spinal cord-ganglion explants from fetal mice

Most neurons in organotypic cultures of dorsal root ganglia from 13-day-old fetal mice require high concentrations of nerve growth factor for survival during the first week after explanation. These nerve growth factor-enhanced sensory neurons mature and innervate the dorsal regions of attached spinal cord tissue even after the removal of exogenous growth factor after 4 days. In cultures exposed for 4 days to nerve growth factor and taxol (a plant alkaloid that promotes the assembly of microtubules) and returned to medium without growth factor, greater than 95 percent of the ganglionic neurons degenerated and the spinal cord tissues were reduced almost to monolayers. In contrast, when the recovery medium was supplemented with nerve growth factor, the ganglionic neurons and dorsal (but not ventral) cord tissue survived remarkably well. Dorsal cord neurons do not normally require an input from dorsal root ganglia for long-term maintenance in vitro, but during and after taxol exposure they become dependent for survival and recovery on the presence of neurite projections from nerve growth-factor-enhanced dorsal root ganglia.     

Nerve growth factor: relationship to the cyclic AMP system of sensory ganglia

Nerve growth factor and N(6),O(2)' dibutyryl adenosine 3',5'-monophosphate both stimulate neurite elongation by explanted ganglia. However, the addition of nerve growth factor does not lead to increased amounts of adenosine 3',5'-monophosphate in intact ganglia, nor does it stimulate adenylate cyclase activity in broken ganglia cells.     

Branching of central neurons: intracellular cobalt injection for light and electron microscopy

Cobalt chloride can be injected into an identified nerve cell body in an insect ganglion and reacted with ammonium sulfide to stain the soma and its branches with a black precipitate. The stained cell body and its branches throughout the neuropil are visible in both the light and electron microscope. In whole mount preparations, the resolution of neurites within the neuropil is of a quality that permits the comparison of branching patterns between cells and during various functional states.     

Protrudin induces neurite formation by directional membrane trafficking

Guanosine triphosphatases of the Rab family are key regulators of membrane trafficking, with Rab11 playing a specific role in membrane recycling. We identified a mammalian protein, protrudin, that promoted neurite formation through interaction with the guanosine diphosphate (GDP)-bound form of Rab11. Phosphorylation of protrudin by extracellular signal-regulated kinase (ERK) in response to nerve growth factor promoted protrudin association with Rab11-GDP. Down-regulation of protrudin by RNA interference induced membrane extension in all directions and inhibited neurite formation. Thus, protrudin regulates Rab11-dependent membrane recycling to promote the directional membrane trafficking required for neurite formation.     

Extensive dendritic sprouting induced by close axotomy of central neurons in the lamprey

Massive dendritic sprouting was induced in identified giant reticulospinal neurons of the lamprey by axotomy close to the soma. An axonal lesion slightly farther from the cell body induced new growth from both dendrites and axon. The amount of new growth per cell was the same whether it originated from the dendrites alone or from axonal and dendritic compartments. The location of the axonal lesion therefore determines where, in the neuron, membrane is inserted to produce the new neurites. The dendritic tree of a differentiated vertebrate central neuron was shown to have sufficient plasticity to extend new growth for several millimeters beyond the normal dendritic domain.     

Aplysia californica: analysis of nuclear DNA in individual nuclei of giant neurons

The nuclei of the giant neurons of the marine mollusk Aplysia californica can contain more than 0.2 microgram of DNA. This is more than 200,000 times as much DNA as the haploid amount found in Aplysia sperm. On the basis of nuclear DNA content, the giant neurons R-2, P-1, and L-6 of adult animals can each be divided into at least two populations. The mean DNA content of these two populations (0.067 and 0.131 microgram of DNA) are approximately related by a factor of 2. This suggests that much and perhaps all of the genome replicates repeatedly (up to 16 times) during the growth and development of these neurons and that each replication is synchronous. The enormous amount of DNA in these cells opens up the possibility of characterizing the DNA and other constituents of chromatin from individual but phenotypically different neurons.     

Formation of retinal ganglion cell topography during prenatal development

A fundamental feature of the mammalian visual system is the nonuniform distribution of ganglion cells across the retinal surface. To understand the ontogenetic processes leading to the formation of retinal ganglion cell topography, changes in the regional density of these neurons were studied in relation to ganglion cell loss and the pattern of retinal growth in the fetal cat. Midway through the gestation period, the density of these neurons was only two to three times greater in the area centralis than in the peripheral retina, whereas shortly before birth this central-to-peripheral difference was nearly 20-fold. Age-related changes in the ganglion cell distribution were found not to correspond in time or magnitude to the massive loss of ganglion cells that occurs during prenatal development. Rather, the formation of ganglion cell density gradients can be accounted for by unequal expansion of the growing fetal retina-peripheral regions expand more than the central region, thereby diluting the peripheral density of ganglion cells to a greater degree. Nonuniform growth, in conjunction with differential periods of neurogenesis of the different types of retinal cells, appears to be a dominant factor regulating overall retinal topography. These results suggest that the differential regional expansion of the fetal retina underlies the formation of magnification factors in the developing visual system.     

Sulfur dioxide: episodic injection shows evidence for active venus volcanism

Pioneer Venus ultraviolet spectra from the first 5 years of operation show a decline (by more than a factor of 10) in sulfur dioxide abundance at the cloud tops and in the amount of submicron haze above the clouds. At the time of the Pioneer Venus encounter, the values for both parameters greatly exceeded earlier upper limits. However, Venus had a similar appearance in the late 1950's, implying the episodic injection of sulfur dioxide possibly caused by episodic volcanism. The amount of haze in the Venus middle atmosphere is about ten times that found in Earth's stratosphere after the most recent major volcanic eruptions, and the thermal energy required for this injection on Venus is greater by about an order of magnitude than the largest of these recent Earth eruptions and about as large as the Krakatoa eruption of 1883. The episodic behavior of sulfur dioxide implies that steady-state models of the chemistry and dynamics of cloud-top regions may be of limited use.     

THE PROBLEMS OF AGING AND OF VASCULAR DISEASES

The increase in death rate with increasing age over that at the age of ten accounts for over a million deaths each year in the United States. To what extent these deaths are due to the aging process remains to be determined, but the progressive loss of resistance to nearly all diseases appears to play a large role even in youth and middle life. Since loss of resistance to disease, as well as loss of ability, seems to result from an underlying aging process we may look upon aging as constituting our greatest medical problem. Second in importance to the aging problem is that of the vascular and renal diseases, since these are involved in nearly 50 per cent. of the deaths after the age of ten (in addition to the effect of aging). Until more is known about aging and vascular diseases we are not justified in predicting what can or can not be done about them. A new experimental method in which healthy animals of different ages are killed by a known measurable cause offers possibilities for determining the nature of the aging process. Our two outstanding medical problems are being neglected largely because of the lack of funds to support both the long-term research and the raising of old animals needed for adequate investigation in this field. New endowments as well as changes in the policies of existing foundations are urgently needed.     

Suppression of neurite elongation and growth cone motility by electrical activity

Electrical activity may regulate a number of neuronal functions in addition to its role in transmitting signals along nerve cells. The hypothesis that electrical activity affects neurite elongation in sprouting neurons was tested by stimulating individual snail neurons isolated in cell culture. The findings demonstrated that growth cone advance, and thus neurite elongation, is reversibly stopped during periods when action potentials are experimentally evoked. A decrease in filopodial number and growth cone area was also observed. Thus, action potentials can mediate the cessation of neurite outgrowth and thereby may influence structure and connectivity within the nervous system.     

冀东滨海盐碱区耕层土壤盐碱变化规律研究

采取定点、定期取样方法,研究了冀东滨海盐碱区地下水以及0~5 cm、5~10 cm、10~20 cm和20~30 cm耕层土壤的盐碱变化。结果表明:0~5 cm耕层含盐量最高,平均达到了0.66%,是其他3个耕层含盐量的4~5倍,而其他3个耕层的含盐量差异不大。从盐分季节性变化看,5月中旬~6月中旬耕层土壤含盐量较高。而耕层土壤pH值较稳定,基本维持在7.8水平,且季节性变化不大。说明土壤碱性不是影响该区作物生长的主要因子,在实际生产措施中应以降低土壤盐分为主。     

Regeneration in spinal neurons: proteosynthesis following nerve growth factor administration

Incorporation of H(3)-leucine into dorsal root ganglion cells in rats was markedly increased over that of controls following section of sciatic and femoral nerves. Crush lesion of dorsal roots did not increase the H(3)-leucine uptake of these cells except in animals which had received nerve growth factor after the operation.     

苦楝不同种源苗期生长性状和生长节律研究

通过观测苦楝10个种源生长性状,分析苗高、地径和冠幅的生长节律,采用Logistic方程拟合其苗高、地径和冠幅生长过程。结果表明,拟合方程的决定系数为0.969~0.998,符合"S"型生长曲线;不同苦楝种源在苗高、地径和冠幅的物候期和生长参数上存在比较明显的差异,各种源前期生长量小于后期;不同种源速生期起始时间变动幅度为5—6月,最早与最晚时间在种源间相差20 d左右;速生期结束时间变动幅度为8—10月,最早与最晚时间在种源间相差50 d左右;速生期生长量占总生长量的比例均在58%以上,速生期生长量最大种源约为最小种源的2倍左右;地径和冠幅速生期起始时间相差不大,且均早于苗高;冠幅速生期结束最早,其次是苗高,最晚为地径;在速生期起始时间上,北方种源早于南方种源,在速生期结束时间上,北方种源晚于南方种源。     

Nerve growth factor: stimulation of regenerative growth of central noradrenergic neurons

The growth of new axonal sprouts was studied from transected, ascending noradrenergic axons into transplants of iris tissue in the caudal hypothalamus of the rat. A single intraventricular injection of nerve growth factor, given at the time of axonal damage, resulted in an increased formation and growth of new noradrenaline sprouts 7 days later. The effect seemed to be proportional to the administered dose of nerve growth factor.     

Micro-optical sectioning tomography to obtain a high-resolution atlas of the mouse brain

The neuroanatomical architecture is considered to be the basis for understanding brain function and dysfunction. However, existing imaging tools have limitations for brainwide mapping of neural circuits at a mesoscale level. We developed a micro-optical sectioning tomography (MOST) system that can provide micrometer-scale tomography of a centimeter-sized whole mouse brain. Using MOST, we obtained a three-dimensional structural data set of a Golgi-stained whole mouse brain at the neurite level. The morphology and spatial locations of neurons and traces of neurites could be clearly distinguished. We found that neighboring Purkinje cells stick to each other.     

Garfish olfactory nerve: easily accessible source of numerous long, homogeneous, nonmyelinated axons

The olfactory nerve of the garfish, Lepisosteus, is about 1 millimeter in diameter and about 20 centimeters long, depending on the size of the fish; it is easily prepared by breaking off successive scored segments of the rostrum. It consists of a relatively homogeneous population of about 10(7) nonmyelineated nerve fibers, each about 0.24 micrometer in diameter. In most other nerves each fiber is separated from all others by an enfolding Schwann cell, but in the olfactory nerve the fibers are directly in contact with one another in groups of several hundred fibers. The Schwann cell, not directly concerned with propagation of the nerve impulse, forms a thin layer at the periphery of the group and makes up a small proportion of the total cellular material. The volume of axon cytoplasm is about five times greater than that of Schwann cell cytoplasm, and the axon surface is about 30 times the Schwann cell surface. The ratio of surface to volume for axons of a typical olfactory nerve is about 5400 times that for the squid axon of the same diameter. The large proportion of axonal membrane recommends this nerve for use in chemical and physical studies of properties of axon membranes.