Quantitative morphological charateristics of developing neurons of the brain-stem reticular formation

Two types of neurons — reticular (with few branches) and multipolar giant (densely ramified) were distinguished in the brain-stem reticular nuclei of the brain in Golgi preparations from cat fetuses aged 45–55 days and kittens aged 1–5 and 30 days. The quantitative morphological characteristics of these neurons at different stages of development were determined from the dimensions of their bodies, the number, length, and ramification of their dendrites, and the overall ramification of the cell. The types of neurons described above differed in both qualitative and quantitative indices and in the character of their maturation. Maximal ramification of dendrites of giant multipolar neurons was observed in the embryonic period. Foci of maximal ramification in reticular neurons were close to the cell bodies. In gaint multipolar neurons in fetuses and 30-day-old kittens foci of maximal ramification were located on the proximal and distal portions of the dendrites, but in the newborn kittens on the proximal segments only. These facts are examined in connection with differences in the spike activity of the growing neuron.Institute of Higher Nervous Activity and Neurophysiology, Academy of Sciences of the USSR, Moscow. Brain Institute, Academy of Medical Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 12, No. 1, pp. 53–61, January–February, 1980.     

Quantitative freeze-fracture analysis of the frog neuromuscular junction synapse – II. Proximal–distal measurements

Neurotransmitter release from different parts of frog motor nerve terminals is often non-uniform. There is a decrease in release efficacy from the distal regions of frog motor nerve terminal branches. Since release is thought to occur near the double arrays of large intramembranous particles that constitute the pre-synaptic active zones (AZs), we have examined quantitatively the proximal–distal distribution of AZ structure, using a novel freeze-fracture technique that produces replicas of large fractions of terminals, including the region of nerve entry. This enables us to know the proximal–distal orientation of each branch. From 23 end-plates we have obtained fractures of 72 branches. For 27 of these branches we have obtained continuous fractures both greater than 25 μm in length and with sufficient information to determine their proximal–distal polarity. Only a few of these branches showed a marked distal decrease in AZ length/unit length of terminal, while several junctions had short regions (5–10 μm), either proximally or distally, that exhibited amounts of AZ that were substantially greater or smaller than the mean value for that terminal branch. The terminal area, post-synaptic gutter width and nerve terminal width all exhibit some distal decline concomitant with the distal tapering of nerve terminal branches. AZ length tends to have the least decline compared to the other parameters. Thus, the vast majority of frog motor nerve terminal branches do not display a significant proximal-distal gradient in the amount of AZ structure/μm terminal length. The present data do not provide an obvious ultrastructural correlate for the distal decline in transmitter release that some authors have observed.     

Patterns of on-shoot positioning of seed cones in relation to shoot length and position in the crowns of young Picea mariana

Summary Patterns of distribution of seed cones along the length and around the circumference of shoots were determined for young black spruce [Picea mariana (Mill.) B.S.P.] trees aged 9–17 years. Seed cone production averaged 5, 30, 62, 95, and 112 per tree of ages 9, 11, 13, 15, and 17 years, respectively. Cone distribution was restricted to distal and medial 1-year-old branches at age 9 and spread to distal 3-year-old branches by age 17. Sequentially, shoots of 0–25, 26–100, 101–250, 251–325, and 326–375 mm bore more cones in terminal, distal, medial, proximal, and basal positions along shoots, respectively. The uppermost and longest distal 1-year-old shoots bore most of their cones proximally and medially. On the shortest and innermost proximal order 2 shoots, cones were often terminal. The percentages of cones borne on upper, lower, and each of the two side surfaces of shoots were 31, 22, and 21, respectively, and 5% of the cones were terminal. Cones on lower surfaces were most common on the longest shoots near the apex of trees. Cones on upper surfaces became prevalent downward and outward in the crown. On-shoot positioning therefore varied in a predictable manner with shoot length, and thus with pattern of shoot-length distribution in the crown.     

The formation and function of single transmitter release sites at mature amphibian motor—nerve terminals

The extent of quantal transmitter release from single sites of synaptic vesicle accumulations along the length of motor-nerve terminal branches at the amphibian neuromuscular junction has been investigated. Such a determination involves development of a model for the generation of quantal potential fields at single styryl-dye stained sites along the length of a branch. Successful testing and application of this model indicates that the extent of quantal release at a dye-stained site is proportional to the total length of active zone at the site. The stability of these sites and of their ensheathing terminal Schwann cell processes was also investigated. Following simultaneous injection of the terminal Schwann cell and nerve terminal with different fluorescent dyes, terminal branches were observed to show dynamic changes in their length, with these occurring in relatively short periods of hours or less. Redistribution of styryl dye stained sites at the ends of branches also occurred in such short periods of time. These were accompanied by changes in the configuration of terminal Schwann cells, which generally occurred prior to changes in the length of nerve terminal branches.     

Effect of shade stress on growth,morphology, and carbon dynamics of loblolly pine branches

Summary Shade treatments were applied to the terminal portions of branches in loblolly pine trees to test whether portions of branches were autonomous with respect to carbohydrates. The shade treatments reduced light by 50% and 72% compared with full sun conditions resulting in significant reductions in net photosynthesis. Branch growth (branch diameter and length, branch and needle biomass) decreased significantly within the shaded portion of the branch. Branch and needle morphology were also affected by shading. Lateral branches subtending terminal shoots were labelled with ¹⁴C 2 times during the growing season. No movement of ¹⁴C into the terminal portions of the branch was evident during the first growth flush. However, during the second flush of growth small but statistically significant amounts of ¹⁴C were imported into the terminal portion of the shaded branches from subtending laterals. It was concluded that loblolly pine shoots were usually autonomous with respect to carbohydrate supply, but that carbohydrate movement into the terminal shoot from subtending foliage could occur under conditions of very high stress.     

Quantitative morphological characteristics of developing neurons of the sensory trigeminal nuclei in kittens

Five types of neurons were distinguished in the sensory nuclei of the trigeminal nerve, stained by Golgi's method, in kittens aged 1–5 days and 30 days: reticular and short-dendritic cells (with few branches), and multipolar giant cells, arborescent, and bushy neurons (densely branching). Yet another special type of cell, with a few short dendrites and one long dendrite, was distinguished in preparations from the brain of newborn kittens. Analysis of the dimensions of the bodies, the number, length, and ramification of the dendrites, and the total ramification of the cell yielded quantitative morphological characteristics of these neurons at different times of development. These types of neurons differed in their qualitative and quantitative parameters and in the features of their maturation.Bushy neurons underwent regressive changes during development. Foci of maximal ramification of dendrites of densely branched neurons changed their location during the first months of life relative to the cell body, moving into the more distal regions of the dendrites. Differences in orientation of dendrites with foci of maximal ramification were found relative to neighboring brain formations, which depended on the types of cells and the animal's age. The high level of maturity of trigeminal neurons at birth was demonstrated.Institute of Higher Nervous Activity and Neurophysiology, Academy of Sciences of the USSR, Moscow. Brain Institute, Academy of Medical Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 14, No. 6, pp. 592–600, November–December, 1982.     

Human coronary arteries. II. Branching anatomical pattern and arterial wall microarchitecture

A study on 22 pairs, including subjects of similar age, sex and cause of death but with different branching anatomical patterns, shows, that the amount and structural organization of elastic and muscular tissue of the thickened intima are strongly influenced by (a) the size, length, mode of ramification of the parent vessels of the coronary tree; (b) the number of branch orifices in a given arterial segment, and (c) the collateral or terminal character of certain daughter branches.     

Growth of Hyphal Branching Systems in Coprinus disseminatus

Apical portions of hyphal branching systems of Coprinus disseminatuswere observed at the margins of colonies extending at a constantrate under one set of environmental conditions. Growth was consistentlymonopodial, the main hyphae continuing to extend in the colonymargin at a constant rate. Primary branch initiation occurredat regular intervals, closely associated with cell divisionof the parent hypha, and initiation of secondary branches tookplace in the older parts of the system. Extension rates of main,primary branch, and secondary branch hyphae were distinct, beingin the proportions 100: 66: 18. In the majority of systems successivebranches of the same category closely resembled one anotherand changes in extension rate of primary branches were smallfrom soon after initiation up to a length of 750µ. Ina minority of systems branch behaviour was less regular, somebranches increasing in extension rate whilst others decreased.Changes in older parts of the systems were not followed. young primary branch hyphae were consistently narrower thanmain hyphae. Although extension rate was correlated with hyphaldiameter for main and for branch hyphae separately, the extensionrate of equally wide hyphae was significantly higher for mainas compared with branch hyphae. Furthermore the wider, faster-extendingbranch hyphse temded tp arise from the wider, faster-extendingmain hyphae. The significance of these findings is discussed.     

Complex nerve terminal formation in the phasic muscles of frogs

Synapses with complex nerve terminals consisting of several terminal arbors of a single axon divided by myelin segments were investigated using histological and electrophysiological techniques during experiments on the cutaneous-pectotoralis muscles of different aged frogs. Numbers of synapses with complex nerve terminals were shown to increase during the postnatal developmental process. The relationship between the complexity of nerve terminals, summated length of terminals, and size of muscle fiber is described. Some terminal arborizations at complex nerve terminals originate from nodes of Ranvier; these are marked by low quantal secretion and a distinctive pattern of sodium current decay along the path of the terminals. The causes and mechanisms governing increased complexity of nerve endings in phasic muscles are discussed, together with transmitter release patterns at these endings. It is postulated that growth and myelination processes occur in parallel at the nerve terminal.A. A. Ukhtomskii Physiological Institute, Leningrad State University; S. A. Kurashov Medical Institute, RSFSR Ministry of Health, Kazan'. V. I. Ul'yanov State University, Kazan'. Translated from Neirofiziologiya, Vol. 22, No. 1, pp. 99–107, January–February, 1990.     

The single nerve ending of the frog sartorius muscle: its ultrastructural characteristics and mediator secretion

Electron microscopy and extracellular recordings were used for the investigation of structural and functional peculiarities of single frog sartorius muscle nerve terminal. It has been found that the diameter, length of the synaptic contact and quantity of synaptic vesicles decreased from proximal to distal parts of the nerve terminal. A number of varicosities, separated from each other by schwann cells, have been revealed along the course of the nerve terminal. This indicates the existence of an interrupted synaptic contact. Both the evoked and spontaneous transmitter release decreased from the initial to the end parts of the nerve terminal. The data obtained suggest that there is a correlation between structural heterogeneity and the differences in the transmitter release.     

Pre-synaptic and post-synaptic factors influencing the synchronism in the transmitter secretion and the amplitude and temporal parameters of a postsynaptic response in the neuromuscular junction: a model study

Using a model of the frog neuromuscular junction, we studied the influence of pre-synaptic and post-synaptic factors on the amplitude and temporal parameters of end-plate currents (EPC). A nerve terminal (NT) was supposed to include linearly distributed active zones (AZ) that are able to release a transmitter quantum with a definite temporal distribution of the release probability (AZ DRP) after successive activation of these zones by a spreading action potential (AP). An increase in the length of a terminal, distance between AZ, and time constant of the DRP decline, or a decrease in the AP conduction velocity along the NT determines a decrease in the EPS amplitude and prolongation of its rising phase. These effects result from an increased asynchronism in the transmitter release. An expansion of the temporal parameters of minature EPC leads to an increase in the EPC amplitude, i.e., provides minimization of its loss. Various EPC models are compared, and contributions of the examined pre-synaptic and post-synaptic factors in modifications of the amplitude and temporal EPC parameters are evaluated.Neirofiziologiya/Neurophysiology, Vol. 27, No. 3, pp. 163–179, May–June, 1995.     

Bud and crown architecture of white spruce and black spruce

Needle primordia in buds and branch lengths were assessed in the crown of a plantation-grown white spruce tree. There was a gradation in needle primordia in buds in branches within the crown. The largest number of primordia was in the terminal bud of the leading main stem shoot, with the number in first-order whorl lateral shoot terminal buds decreasing from whorl 1 to whorl 4, below which buds contained a similar small number of primordia (about one-third as many as in the terminal shoot). Previous year's shoot elongation followed a similar pattern (i.e., elongation of whorl branches was greater closer to the top of the tree and elongation in the fourth through ninth whorls was about one-third that of the main stem leader). Higher order branches within whorls had within-branch gradation in shoot elongation and number of needle primordia, with older branches having as few as 16–30 primordia in buds and 3–4 cm elongation for high-order branches on older main stem whorls. There were strong correlations between the number of primordia in branch terminal buds and branch length/diameter and bud length/diameter/volume. In both black spruce and white spruce, there were strong correlations of number of needle primordia in main stem leader terminal buds with number of needle primordia in terminal buds of first and second whorl leaders.     

Effect of prolonged inactivity on skeletal motor nerve terminals during aestivation in the burrowing frog, <Emphasis Type="Italic">Cyclorana alboguttata</Emphasis>

This study examined the effect of prolonged inactivity, associated with aestivation, on neuromuscular transmission in the green-striped burrowing frog, Cyclorana alboguttata. We compared the structure and function of the neuromuscular junctions on the iliofibularis muscle from active C. alboguttata and from C. alboguttata that had been aestivating for 6 months. Despite the prolonged period of immobility, there was no significant difference in the shape of the terminals (primary, secondary or tertiary branches) or the length of primary terminal branches between aestivators and non-aestivators. Furthermore, there was no significant difference in the membrane potentials of muscle fibres or in miniature end plate potential (EPP) frequency and amplitude. However, there was a significant decrease in evoked transmitter release characterised by a 56% decrease in mean EPP amplitude, and a 29% increase in the failure rate of nerve terminal action potentials to evoke transmitter release. The impact of this suite of neuromuscular characteristics on the locomotor performance of emergent frogs is discussed.     

Crown alterations induced by decline: a study of relationships between growth rate and crown morphology in beech (Fagus sylvatica L.)

One of the first symptoms expressed by declining trees is reduced growth in stem diameter and length increment. The possibility of a relationship between length increment and crown thinning in beech (Fagus sylvatica L.) was investigated by developing a computer model to simulate first order branching patterns of the apical 2 m of monopodially branching beech trees, 70–100 years old, for a range of length increment rates. The model was based on values for branching angle, main axis and branch length increment, number of branches produced per year and branch mortality rates for six healthy and declining trees. Shoot growth rates in the apical 2 m of the sample trees ranged from about 5 cm/year (decline class 3) to 43 cm/ year (healthy). Simulations of branching patterns in the apical 2 m of trees growing at different rates indicated that, when growth rate exceeded about 20 cm/year, total first order branch length and area explored were independent of growth rate. When growth rates fell below this value there was a reduction in total area explored and first order branch length due primarily to the formation of fewer branches. More acute branching angles contributed to a reduction in the area explored. Growth rate-related crown thinning could increase the risk of bark necrosis and secondary pathogen infection during dry and/or hot spells.     

Crown development in Norway spruce [<Emphasis Type="Italic"> Picea abies </Emphasis>(L.) Karst.]

This study tests whether crown and stem development in Norway spruce could be described using a modified profile theory. 29 trees from three age-groups (25, 67, 86) with different treatments (unthinned, normally and intensively thinned) were destructively sampled. Crown ratio and crown length varied between age groups and treatments. Crown width was positively correlated with crown length, but branch length along the crown depended on tree age and growing space. Foliage mass density peaked at a relative crown height of 50–70% in middle-aged and mature stands, while young crowns were densest and widest at the base. Foliage mass was predictable from branch and stem cross-sectional area, provided the distance from the top was included. The ratio of foliage mass to branch cross-sectional area increased for 2–4 m down from the tip of the crown, then started to decrease. The relationship between cumulative foliage mass and stem cross-sectional area was non-linear along the stem in the upper crown, but the ratio of cumulative branch to stem cross-sectional area was linear. Trees in the mature and unthinned stands had more cross-sectional area in branches relative to stems than in the young and thinned stands. We conclude that the profile theory needs modification regarding (1) crown shape which varies with age and growing space, and (2) the ratio of foliage mass to branch area which varies along the stem. Both aspects emphasise the need to include impacts of disuse of sapwood pipes in models of crown and stem development.     

Motor innervation of muscle fibers in thyrotoxic myopathy]

In patients and test animals similar changes in innervation have been revealed. Degeneration of some preterminal axons has been shown. The most manifested feature's increased ramification of distal axons. No signs of real reinnervation have been found. New collateral branches of preterminal, terminal and ++ultra-terminal axons usually have their ends at the same muscle fiber in the form of additional nervous terminals. Decreased average diameter of motor end-plates, revealed in the test animals, depends not on their degeneration, but on formation of new small motor end plates as a result of immature axonal ramification of distal axons. Acetylcholinesterase activity in the end-plates is decreased. A suggestion is made that excess of thyroid hormones in the skeletal muscle disturbs both the system of cyclic nucleotides and mechanisms of muscular contraction, connected with it and axoplasmic transport, respectively. The changes of the terminal intramuscular innervation revealed, structures of the motor end-plates with a decrease of acetylcholinesterase activity are supposed to result from disturbances of neurotrophic regulation of the muscle fibers because of the disturbances of the axoplasmic current as the excess of thyroid hormones.     

Oxygen regulation of airway branching in Drosophila is mediated by branchless FGF.

The Drosophila tracheal (respiratory) system is a tubular epithelial network that delivers oxygen to internal tissues. Sprouting of the major tracheal branches is stereotyped and controlled by hard-wired developmental cues. Here we show that ramification of the fine terminal branches is variable and regulated by oxygen, and that this process is controlled by a local signal or signals produced by oxygen-starved cells. We provide evidence that the critical signal is Branchless (Bnl) FGF, the same growth factor that patterns the major branches during embryogenesis. During larval life, oxygen deprivation stimulates expression of Bnl, and the secreted growth factor functions as a chemoattractant that guides new terminal branches to the expressing cells. Thus, a single growth factor is reiteratively used to pattern each level of airway branching, and the change in branch patterning results from a switch from developmental to physiological control of its expression.     

Transmitter release in proximal and distal parts of a nerve terminal of the frog sartorius muscle

Evoked synaptic potential were recorded extracellularly in experiments on a nervemuscle preparation of the frog sartorius muscle. A decrease in evoked transmitter release was found from the proximal to the distal parts of the nerve ending, due to a decrease in the probability of transmitter quantum release. The terminal portions of the synapse are less sensitive than the proximal parts to changes in Ca⁺⁺ concentration, they show less marked facilitation of transmitter release during paired and repetitive stimulation, and exhibit deeper and more rapidly developing depression. It is concluded that differences in transmitter release in the terminal parts of the synapse are due to the low reserves of transmitter and the lower premeability of the presynaptic membrane to Ca⁺⁺.     

Topological differences along mammalian motor nerve terminals for spontaneous and alpha-bungarotoxin-induced sprouting

Spontaneous sproutings can be observed in end plates from normal adult vertebrate muscles and motor end plates develop increased growth signs and sprouts when target muscle cells become less active or paralysed. Nevertheless, very little is known about where in the motor nerve terminal arborization spontaneous and experimentally induced sprouts originate, their similarities and differences and also about their final maturation or elimination. In this study we investigate the topological properties of both spontaneous and alpha-bungarotoxin-induced sprouts (during different periods of intoxication and after recovery) along the motor nerve terminal branches of the Levator auris longus muscle of Swiss mice (between 48-169 day old). Muscles were processed for immunocytochemistry to simultaneously detect postsynaptic AChRs and axons. This procedure permits us to make an accurate identification of the fine sprouts and a morphometric study of the presynaptic branching pattern profile in control muscles, during the toxin action and after recovery from paralysis. The results show that in normal muscles, the initial and trunk segments (those between branch points) of the terminal arborization sprouted proportionally more branches when taking their relative lengths into account than the distal free-end segments. In contrast, every micrometer of alpha-bungarotoxin-treated muscles throughout the full terminal arborization have the same probability of generating a sprout. Moreover, the toxin-induced sprouts can consolidate as new branches once recovered from the paralysis without changing the total length of the nerve terminal arborization.