Showing papers by "Dalhousie University published in 1978"

A comparison of methods of determining organic carbon in marine sediments, with suggestions for a standard method

Abstract: The yield of organic C or total organic matter from a standard carbonate-free marine sediment containing 23.04% N-acetyl glucosamine (10% organic C) was determined using 1) a CHN analyzer on untreated sediment, 2) CHN analysis of acidified and filtered sediment, 3) CHN analysis of acidified centrifuged sediment, 4) wet oxidation by the Walkley and Black method, and 5) loss on ignition at 475–500°C. 100% of the organic C added was recovered by CHN analysis of untreated sediment, but after treatment with acid (necessary to remove carbonates from most sediments) only 0.19% and 1.32% of the C added could be recovered. Wet oxidation yielded only 76.6% organic C. Loss on weight after combustion in a muffle furnace yielded 100% of the total organic matter. It is very difficult to avoid carbonate interference if simple techniques of analysis are used. For most work by marine ecologists organic carbon and nitrogen may be measured by a combination of CHN analysis and loss of weight on ignition of sediments freed of organic matter by precombustion below 500°C.

Vertical zonations of marsh foraminifera as accurate indicators of former sea-levels

Abstract: MANY attempts to reconstruct the pattern of apparent sea-level rise that took place during the Holocene have used salt-marsh deposits as indicators of former sea level1,2. Contemporary mature salt marshes occupy a vertical range covering the upper half of the tidal range, from mean sea level to higher high water3,4, and geologists have arbitrarily equated ancient marsh deposits with various fixed elevations within this range. This method, disregarding any other source of inaccuracy, can introduce an error of 1–5 m depending on the tidal range. Apparent sea level movements during the late Holocene (2,000–3,000 yr BP) have been of the order of 1–2 m; hence such a method introduces errors larger than the movements being measured. Even less adequate sea-level estimates are derived from other commonly used indicators such as raised beaches, oyster beds, and submerged or emerged terraces and deltas. We describe here how marsh foraminifera can be used to delimit small-scale vertical zones along modern marsh surfaces generally corresponding to the floral zones in vertical range. This relationship was first established in the marshes of southern California5, and has recently been shown to be valid in other areas6.

Phytoplankton Photosynthetic Response to Vertical Movement in a Mixed Layer

Abstract: 14C uptake was measured in experimental bottles suspended at a series of fixed depths (using subsamples from one sample depth), and was compared with estimates obtained from bottles provided with vertical movement similar to that which might occur in Langmuir circulations. In most experiments, the vertically cycled bottles gave estimates of integral photosynthesis 19 to 87% higher than estimates from the control series. Evidence from laboratory experiments detailing the change in photosynthesis over time at various irradiance levels shows that a higher lightsaturated photosynthetic rate under variable light conditions could account for the enhanced integral photosynthesis found in the bottles provided with vertical movement.

Genetic variation associated with growth rate in the american oyster (crassostrea virgin ica).

Abstract: Several studies on the amount and the geographical distribution of enzyme variability in marine molluscs have revealed that the frequencies of heterozygotes were often lower than expected under HardyWeinberg equilibrium. The most extensively studied locus is the one coding for the enzyme leucine animopeptidase (Lap). An excess of homozygosity in this locus was observed in several populations of Mytilus edulis (Milkman and Beaty, 1970; Koehn and Mitton, 1972; Boyer, 1974; Koehn et al., 1976), Mytilus californianus (Tracey et al., 1975) and Modiolus demissus (Koehn and Mitton, 1972). Other enzyme loci in which an excess of homozygosity was observed include tetrazolium oxidase (To) in Modiolus demissus (Koehn et al., 1973), aminopeptidase (Ap) in Mytilus edulis (Koehn et al., 1976), malic dehydrogenase (Mdh) and phosphoglucose isomerase (Pgi) in Mytilus californianus (Tracey et al., 1975) and esterase in Littorina sexatilis and Littorina obtusata (Newkirk and Doyle, pers. comm.). The amount by which homozygosity exceeds the levels predicted by the HardyWeinberg equilibrium varies among populations, and within the same population it seems to be negatively correlated with shell size. Again, this is an observation made by various authors surveying different enzyme loci in different organisms. Koehn et al. (1973) found it to be true for the To locus of Modiolus demissus. The same phenomenon was observed by Tracey et al. (1975) for three loci (Mdh, Lap, and Pgi) in Mytilus californianus, and by Koehn et al. (1976) for the Lap locus of Mytilus edulis. These observations are of interest for various reasons. First, their validity is not affected by the limitations of electrophoresis in distinguishing different allozymes. Although a more powerful method of recording genic variation will definitely elevate the amount of heterozygosity, one expects that observed homozygosity will still be higher than expected from the new set of allelic frequencies. Second, difference in shell size in marine molluscs may indicate differences in the rate of growth as well as difference in age. It is possible, therefore, that heterozygotes have a higher growth rate. This would mean that not only viability but also time to sexual maturity and fertility may be correlated with the degree by which homozygosity exceeds equilibrium levels. In oysters there can be a great amount of variation in shell size among individuals of same age growing under uniform conditions. We observed this to be true in a population established for breeding purposes (see MATERIALS AND METHODS). This observation induced us to ask whether we could detect, among oysters of same age but of different size, differences in heterozygosity comparable to those observed between mussels of different age. It is obvious, of course, that for species of commercial value, as the oyster, studies relating growth rates to genetic factors may prove to be of considerable economical significance.

Effect of short-term variations in light intensity on photosynthesis of a marine phytoplankter: A laboratory simulation study

Abstract: Parameters of photosynthesis and growth were measured for a marine diatom (Lauderia borealis) grown in axenic continuous culture under three different light regimes: constant, simulated diurnal variation, and fluctuating. The light fluctuations were systematic increases and decreases in light intensity superimposed on the diurnal regime. In the first two regimes, a morning maximum and an afternoon depression in photosynthesis were observed. In the fluctuating light regime, the afternoon depression was less pronounced and the morning maximum was enhanced. The results may be explained by postulating a time-dependent value for the light-saturated rate of photosynthesis. Light utilization [mmol O2 cell-1 (E m-2)-1] was the same for the diurnally varying and fluctuating regimes, despite the fact that the peak light intensity in the fluctuating regime was double that of the diurnally varying regime.

The evolution of sedimentary basins on a viscoelastic lithosphere: theory and examples

Abstract: Summary. A systematic approach is suggested for modelling the development of sedimentary basins. The theory, which partitions basin formation into initiating and isostatic adjustment processes, is applicable to all modes of basin formation if these processes are linear, or can he represented with sufficient accuracy in an incrementally linear form. The dynamics of regional isostatic adjustment are characterized by the Heaviside space-time Green functions for the response of elastic and viscoelastic (Maxwell) thin plate models of the lithosphere. It is shown, by convolving the Heaviside—Green functions with cylindrical surface loads, that the rate of isostatic adjustment on a viscoelastic lithosphere is a function of the wavelength of the surface load, long wavelengths being compensated most rapidly. Six archetypal initiating processes for sedimentary basin development are presented. These processes are those responsible for the subsidence of the Earth's surface which creates a depression in which water and sediments collect. Isostatic amplification of subsidence by sediment and water loads is cast in the form of an integral equation with isostatic Heaviside—Green functions as kernel. Specific examples, the basins that result from a graben initiating process, are compared with the largest scale structure of the North Sea Basin, a basin that is known to be underlain by a graben system. A model, in which a 50-km wide graben subsides exponentially with a time constant of 5 × 107yr during the interval 180–100 Myr bp, is shown to be consistent with the largest scale structure of the North Sea Basin if the underlying lithosphere is viscoelastic with a flexural rigidity of ∼5 × 1025 Nm and relaxation time constant ∼ 106 yr.

The rate of recovery of vision after early monocular deprivation in kittens

Abstract: 1. Fifteen kittens were monocularly deprived of vision by suturing the lids of the right eye together for various periods of time at different ages. A simple behavioural technique was used to assess the immediate effects of the period of monocular deprivation on the visual acuity of the deprived eye as well as the time course of any subsequent recovery.2. The extent of the recovery of vision was measured under conditions where the animal was either forced to use its deprived eye by performing a reverse suture or where the animal had both eyes open after the initial period of monocular occlusion.3. The initial effects of monocular deprivation were graded in severity according to the age at which the deprivation was imposed, ranging from apparent blindness in animals deprived at 6 weeks of age to only a small loss of acuity in kittens deprived at 12 weeks of age.4. The effects of deprivation imposed from birth were particularly severe, leading to a temporary blindness. Nevertheless after a period of time that became progressively longer with increasing deprivation, all animals showed some recovery of pattern vision over the course of the next 2 or 3 months. The extent of this recovery became progressively less as the period of deprivation was prolonged. There was even some recovery of vision (an acuity of 2.5 cycles/deg) in animals that were deprived throughout the duration of the ;critical period' to 4 months of age.5. Direct comparison of the rate of behavioural recovery between animals that were reverse sutured with that of litter-mates that received binocular input after monocular occlusion to either 45 or 60 days of age proved to be remarkably similar, although the acuity that was eventually attained by the reverse sutured animals was always slightly higher.6. The recoveries observed after reverse suturing were reasonably well correlated with changes observed in the ocular dominance of visual cortical cells under similar circumstances.7. Although the recovery in these animals can be accounted for by the simple notion of a competitive interaction between the two eyes, the recovery observed in animals that had both eyes open after the initial period of deprivation cannot be so readily explained. Evidently there must be an additional non-competitive mechanism of recovery.

Release of atp from a synaptosomal preparation by elevated extracellular k+ and by veratridine

Abstract: — A technique was developed which permitted the release of ATP from synaptosomes by elevated extracellular K+ or by veratridine to be directly and continuously monitored. The released ATP interacted with firefly luciferin and luciferase in the incubation medium to produce light which could be detected by a photomultiplier. The assay system was specific for ATP, in that similar concentrations of adenosine, AMP or ADP did not produce chemiluminescence. Moreover, the maximum peak of light emission correlated linearly with the concentrations of ATP present in the medium, so that semiquantitative estimates of ATP release could be made. Elevating the extracellular K+ concentration produced a graded release of ATP from synaptosomes. Rb+ also released ATP but Na+, Li+ and choline did not. The response to elevated K+ was not blocked by tetrodotoxin (TTX), indicating that this effect was not mediated by the opening of Na+-channels in synaptosomal membranes. Veratridine (50 μM) caused a graded release of ATP which was larger and more prolonged than that caused by elevated K+. The release of ATP by veratridine was blocked by TTX indicating that the opening of Na+-channels was involved. Neither veratridine nor elevated K+ released ATP from microsomal or mitochondrial fractions, showing that the release of ATP probably did not originate from microsomal, vesicular or mitochondrial contaminants of the synaptosomal preparation. Release of ATP by elevated K+ was diminished in a medium lacking CaCl+ or when EGTA was added to chelate Ca2+. In contrast, release by veratridine appeared to be augmented in Ca2+-free media or in the presence of EGTA. The K+-induced release of ATP, which is Ca2+ dependent, closely resembles the exocytotic release of putative neurotransmitters from presynaptic nerve-terminals. On the other hand, the apparent lack of a Ca2+ requirement for veratridine's action suggests that this process could originate from other sites, or involve mechanisms other than conventional neurotransmitter release processes.

Effects of nitrate concentration on the growth and physiology of laminaria saccharina (phaeophyta) in culture1,2

Abstract: Laminaria saccharina Lamour. sporophytes were grown in enriched and synthetic media through a range of nitrate concentrations, There was an approximately linear relationship between growth and nutrient concentration up to 10 μ substrate concentration. The half-saturation constant (K2) was ca. 1.4 μ NO3-. The internal levels of NO3- increased at substrate concentrations above 10 μM b>3- and reached levels several thousand times higher than the surrounding medium. Thus there is evidence for luxury consumption of NOsb>3-. The chlorophyll content and photosynthetic capacities of plants also increased with increasing external NO3- The ecological implications of this work are considered.

Neurones in cat parastriate cortex sensitive to the direction of motion in three-dimensional space

Abstract: 1. On psychophysical grounds, Beverley & Regan suggested that in man different neural mechanisms mediate the binocular perception of movement in depth and the binocular perception of positional (static) depth. They proposed that the human visual pathway contains several neural mechanisms, each sensitive to a different direction of motion in space. These mechanisms compute the direction of motion from the relative speeds and directions of movement of the left and right retinal images. 2. We have recorded from 101 units in area 18 of cat visual cortex, searching for neurones tuned to the direction of motion in three dimensions, with properties that could account for the proposed directionally tuned binocular motion detectors in man. The cat's left eye viewed one bar, while its right eye simultaneously viewed a second bar. Single units were stimulated by independently oscillating the bars from side to side. The apparent direction of movement in three dimensions was altered by varying the relative speeds of the bars and their relative directions of motion. The mean (positional) disparity of the bars could also be varied. 3. For one class of neurone (twenty cells), binocular stimulation inhibited firing for trajectories parallel to the frontoparallel plane over a large volume of space. Strong firing was produced by oppositely directed bar movements. Some of these neurones were especially narrowly tuned to the direction of movement in depth, responding only to a range of 2-3°, i.e. to moving bodies that would hit or only narrowly miss the cat. These cells emphasized the direction of movement at the expense of positional information. 3. These units occurred in clusters. On the perpendicular penetrations in which they were found, they comprised a substantial majority of all cells encountered. 5. For a second class of neurone (nine cells), binocular facilitation produced selective responses to objects moving along trajectories that missed the head. 6. The two classes of neurone provide a basis for four proposed directionally tuned binocular motion detectors. 7. A third class of neurone (seventeen cells) was selectively sensitive to movements parallel to the frontoparallel plane. There was strong binocular facilitation when the bars moved at the same speeds in the same directions: oppositely directed movements might be more than 100 times less effective. These neurones may signal positional disparity. 8. These three classes of neurone cut across established categories. Only when both eyes were stimulated simultaneously with targets moving in different speeds and directions was it possible to demonstrate the binocular interactions described here.

Culture and sociobiology.

Abstract: Sociobiological concepts are easily misapplied to human behavior because the latter is culturally as well as biologically organized. Because biological and cultural evolution are two linked but conceptually distinct processes, sociobiology is more readily applied to the evolution of cultural capacity than to contemporary cultural behavior. The extent to which the latter is consistent with sociobiological expectation must be determined empirically, although there are theoretical grounds for predicting a limited degree of concordance. [sociobiology, culture, evolution, reductionism, biosocial anthropology]

Perception of a phonetic contrast in multisyllabic utterances by 2-month-old infants

Abstract: In the present study, three aspects of the 2-month-old’s perception of multisyllabic utterances were explored. First, do infants perceive phonetic contrasts occurring either in the initial (Bada-Gada) or medial (Daba-Daga) positions of multisyllabic utterances? Second, are infants more likely to perceive these contrasts in stressed as opposed to unstressed syllables? Third, will infants detect a difference between two stress patterns? Our results indicate the following: (1) Two-month-olds are sensitive to place-of-articulation differences occurring in either the initial or medial positions of multisyllabic stimuli. (2) Whether the contrast occurred between stressed or unstressed syllables had little or no effect on the infant’s ability to detect it. (3) Infants as young as 2-months old respond to differences between stress patterns.

Antibody-Linked Cytotoxic Agents in the Treatment of Cancer: Current Status and Future Prospects

Abstract: Antibodies against tumor cell surface antigens have been used as selective carriers of anticancer drugs, which themselves lack selectivity. Although such antibodies have been demonstrated in tumor hosts, xenogeneic antitumor sera should provide larger yields of better-defined antitumor antibodies for therapeutic purposes. This review examined factors that influence the immune response to tumor-associated transplantation antigens (TATA) and the methods for rendering tumor cells more immunogenic. Consideration was also given to techniques for elimination of irrelevant immunoglobulin molecules. These could involve purification of both antitumor sera and TATA fractions for immunization, as well as tailoring of the immunization protocol. Various toxic agents that have been linked to antitumor globulins with retention of agent and antibody activity were tabulated: alkylating drugs, antibiotics, antimetabolites, cell surface agents, protein synthesis inhibitors, and unconventional anticancer agents that selectively convert nontoxic arsenicals or halides into cytocidal derivatives. The methods by which effective conjugates can be produced and their possible mode of action were described for the different types of agents. Several problems inherent in this modality of tumor therapy include: 1) the necessity of binding therapeutically effective amounts of antitumor agent, 2) ensuring of delivery of drug in active form to target sites, 3) avoidance of host reactions to foreign proteins, and 4) possible emergence of resistant tumor cell populations. Antibody-linked cytotoxic agents may find their greatest use in the eradication of small numbers of circulating tumor cells and micrometastases remaining after removal of primary tumors.

Seasonal growth in Laminaria longicuris: Relations with reserve carbohydrate storage and production

Abstract: Growth rates of Laminaria longicruris increase during January and February, and the role of carbohydrate reserves as a carbon source for this growth was investigated. Seasonal variations in the levels of laminaran and mannitol showed maximum values for both in late summer. Minimum values occurred in February at the time when growth rates were increasing rapidly. Erosion of the blades in winter carried away much of the tissue containing carbohydrate reserves accumulated during the previous summer. Experimental reduction of carbohydrate reserves by fertilization with sodium nitrate during the summer did not affect subsequent winter growth rates. Truncation of the plants in November significantly reduced growth rates. The lower rate of growth is attributed to a reduction in photosynthetic area rather than a loss of storage products.

In vitro formation of polyunsaturated fatty acids by desaturation in rat brain: some properties of the enzymes in developing brain and comparisons with liver.

Abstract: —In vitro desaturation of [1-C14]linolenic, linoleic, oleic, and icosatrienoic acids was determined using homogenates and subcellular fractions of developing rat brain and liver. Linolenic, linoleic, and oleic acids were desaturated in the δ6-position and activity was optimal in the presence of CoA, ATP, MgCl2, and NADH in a citrate-phosphate buffer at pH 6.0. Icosatrienoic acid was desaturated in the δ5-position with a much broader pH optimum. The unstable desaturation systems of brain were protected by reduced glutathione and niacinamide and markedly inhibited by dithiothreitol, p-chloromercuribenzoate, sodium cyanide or bathophenanthroline sulfonate. With brain homogenate of neonatal rats, the relative rates of desaturation of these substrates were 18:3(n - 3) > 18:2(n - 6) > 20:3(n - 6) > 18:l (n - 9). Specific activity of brain enzymes was greatest in neonatal rats with fluctuations in activity between 3 and 6 days of age. During this period, liver enzyme appeared to alter in a reciprocal manner. Total desaturation capacity of brain was maximal and fairly constant between 4 and 20 days of age, whereas liver activity increased dramatically after weaning. The activity of crude microsomal preparations from neonatal brain, like that of liver microsomes, was stimulated by a heat-labile component of the cytosolic fraction. These results demonstrate that brain has a high capacity for desaturation of the essential fatty acids during crucial stages of brain development when liver activity is relatively low.

Origin of lamination in deep sea, fine-grained sediments

Abstract: Many mechanisms have been proposed for the origin of lamination in deep sea sediments, but without general agreement. Experiments in other environments have suggested that several different processes may operate in particle flow conditions. Those relevant to deep water conditions are briefly discussed, and a new quantitative model developed for lamina formation in fine-grained sediments on a continental margin.

The development of vision in cats after extended periods of dark-rearing.

Abstract: The time course of development of visual acuity for square wave gratings was measured behaviourally in a number of cats that were reared in total darkness until they were either 4 (5 cats) or 6 (1 cat) months of age. Less extensive measurements were also made on animals reared in a similar manner until they were either 1 1/2 or 10 months old. Initially, all the animals appeared to be blind, but signs of vision became evident after periods of time in an illuminated environment that ranged from a few days, in the case of animals dark-reared for only 1 1/2 to 4 months, to 1 to 2 months for those animals that were deprived for 6 months or more. Thereafter, visual acuity as measured on a jumping stand progressively improved, reaching, in the case of animals deprived for 4 months, values that were comparable to those of normal animals (6.9 cycles/deg) after 4 months of exposure to light. The animal deprived for 6 months remained apparently blind for a month and eventually attained an acuity (5.7 cycles/deg) that was somewhat less than that of normal animals. The fact that such high acuities can be achieved after periods of binocular deprivation that extend throughout the classically defined “critical period” suggest that the effect of dark-rearing is somehow to impede the natural decline with age in the degree to which cortical neurones are susceptible to environmental modification.

Recovery of function in free muscle transplants using microneurovascular anastomoses

Abstract: Using the rectus femoris muscle of the rabbit, the functional capabilities of the normal and replanted muscle were studied after tenotomy, simple neurovascular repair, and orthotopic and heterotopic transplantation. Tenotomy alone altered the function more than did neurovascular repair, and although a muscle survived after replantation, it never achieved the functional capability of the normal muscle, maximum working capacity being only one fourth of the normal.