Experiments on the effects of a continuous 16.7 Hz magnetic field on melatonin secretion, core body temperature, and heart rates in humans.

The present study investigated the hypothesis that a strong extremely low frequency magnetic field partially suppresses the synthesis of melatonin and subsequently elevates the core body temperature. Seven healthy young men (16-22 years) took part in a control and in an exposure session. Three men experienced first the control and then the exposure session, four men experienced the sessions in reverse order. Control sessions were performed as constant routines, where the participants spent 24 hour periods continuously in bed while air temperature was 18 degrees C, illumination less than 30 lux, and the sound pressure level 50 dBA. The exposure sessions differed from that protocol only between 6 pm and 2 am when a strong extremely low frequency magnetic field was continuously applied (16.7 Hz, 0.2 mT). Assuming that the participants were unable to perceive the field consciously, they were blind against the actual condition. Salivary melatonin levels were determined hourly; body core temperatures and heart rates were registered continuously throughout. Neither of these parameters revealed alterations that can be related to the influence of the magnetic field. The present results, taken together with other investigations using that particular field, lead to the hypothesis that the effects most likely, occur, only after repetitive exposures to intermittent fields.     

Turnover of Brain Monoamine Oxidase Measured In Vivo by Positron Emission Tomography Using l-[11C]Deprenyl

The distribution of carbon-11-labeled L-deprenyl, an irreversible inhibitor of monoamine oxidase type B (MAO-B), was determined in the baboon brain by positron emission tomography. The irreversible blood-to-brain transfer constant (influx constant, K_i) was measured using a complete metabolite-corrected arterial plasma concentration curve. This influx constant was used as a measure of functional enzyme activity for sequential determinations of MAO-B recovery following a single high dose of unlabeled l -deprenyl. The half-life for turnover of MAO-B was thus determined to be 30 days. Using appropriate irreversible inhibitors, this procedure should be generally useful for determining enzyme turnover rates in any organ in vivo and can be applied to some human studies as well.     

Activation of Dopamine Receptors Does Not Affect Phosphoinositide Turnover in NCB-20 Cells

Dopamine inhibits and serotonin stimulates adenylate cyclase activity in a neuroblastoma X Chinese hamster brain explant cell line (NCB-20). The inhibition of cyclic AMP accumulation by dopamine was blocked by pretreatment of the cells with pertussis toxin. Carbachol and bradykinin stimulated the accumulation of water-soluble inositol phosphates whereas thyrotropin-releasing hormone, vasopressin, neurotensin, and phenylephrine were without effect. Dopamine and serotonin had no significant effect on carbachol-induced phosphoinositide hydrolysis or the levels of the parent lipids within the membrane. Forskolin induced a much larger stimulation of cyclic AMP than did serotonin, and caused an increase in the levels of phosphatidylinositol-4-phosphate and phosphatidyl inositol-4,5-bisphosphate in the cell membrane.     

Distribution,length and weight of roots in young plantations ofEucalyptus grandis W. Hill ex Maiden irrigated with recycled water

Summary The root systems ofEucalyptus grandis W. Hill ex Maiden, irrigated with recycled municipal effluent at two sites in north-western Victoria, Australia, were studied by excavation and coring. Trees at Robinvale were four years-old and were irrigated using micro-sprays that covered only 70% of the ground surface area, whereas at Mildura, effuent was uniformly was uniformly applied to six years-old trees by flood and sprinkler irrigation. At Mildura where roots were excavated from a 2.80×2.80×1.20 m block of soil, a total root length of 1193 m.m⁻² and a total root weight of 3.1 kg m⁻² were estimated in the top metre. For roots >1 mm diameter, 77% of intercepts were at 0–30 cm, whereas only 50% were in the 50–100 cm soil horizon. At both sites where roots in the top 30 cm were studied by coring, the vertical distributions of root intercepts, length and weight were similar. Root length was greatest in the 0–10 cm soil horizon at both sites, and intercepts of roots <1 mm diameter comprised 73% and 81% of all roots at Mildura and Robinvale respectively. Roots <1 mm diameter contributed 85% of total length at both sites, but only 19% and 21% of total weight at Mildura and Robinvale respectively. The horizontal distribution of roots differed at the two sites. With uniform application of effuent at Mildura, root intercepts and length were concentrated in the centre of the irrigation bay, but at Robinvale, the concentration occurred closer to the tree row due mainly to the different method of irrigation. Root weight at both sites was highest within 50 cm of the tree row. Root densities of 0.11 to 0.57 cm cm⁻³ were estimated in the two plantations; these were similar to root densities measured inPinus radiata D. Don plantations up to 46 months old, but were considerably lower than those estimated for pastures. The implications of the results for the management of irrigated plantations of eucalypts are discussed.     

Breeding system ofDaphniopsis ephemeralis: adaptations to a transient environment

Populations of the vernal cladoceranDaphniopsis ephemeralis are found in woodland ponds throughout southern Ontario. The species reproduces by cyclic parthenogenesis, and genotype frequencies at allozyme loci are ordinarily in good agreement with Hardy-Weinberg expectations. Occasional heterozygote deficiencies are apparently the consequence of admixture of ephippial hatchlings produced in temporally separated bouts of sexual reproduction. Considerable heterogeneity in genotypic frequencies exists among local populations in southwestern Ontario, indicating that gene flow among populations is restricted. Inbreeding coefficients suggest that populations receive an average of 0.3 migrants per generation. The completion of a sexual life cycle is made possible despite the brief persistence of populations by the emergence of males from ephippial eggs and by the production of equal numbers of male and female progeny in the first parthenogenetic brood.     

Endosymbiotic origin and codon bias of the nuclear gene for chloroplast glyceraldehyde-3-phosphate dehydrogenase from maize

Summary The nuclei of plant cells harbor genes for two types of glyceraldehyde-3-phosphate dehydrogenases (GAPDH) displaying a sequence divergence corresponding to the prokaryote/eukaryote separation. This strongly supports the endosymbiotic theory of chloroplast evolution and in particular the gene transfer hypothesis suggesting that the gene for the chloroplast enzyme, initially located in the genome of the endosymbiotic chloroplast progenitor, was transferred during the course of evolution into the nuclear genome of the endosymbiotic host. Codon usage in the gene for chloroplast GAPDH of maize is radically different from that employed by present-day chloroplasts and from that of the cytosolic (glycolytic) enzyme from the same cell. This reveals the presence of subcellular selective pressures which appear to be involved in the optimization of gene expression in the economically important graminaceous monocots.     

2-Amino-7-Phosphonoheptanoic Acid Inhibits Insulin-Induced Convulsions and Striatal Aspartate Accumulation in Rats with Frontal Cortical Ablation

Pretreatment of rats with the excitatory amino acid antagonist 2-amino-7-phosphonoheptanoic acid (2-APH; 0.5 mmol/kg, i.p.) protected against insulin-induced clonic seizures. Complete protection was observed in 38% of the rats and partial protection in an additional 50%. Lesioning of the corticostriatal pathway by frontal cortical ablation caused decreases in the striatal levels of aspartate (-28%) and glutamate (-18%), an increase in striatal glutamine level (45%), and decreased high-affinity uptake of D-[3H]aspartate (-27%) in the lesioned dorsal neostriatum. Insulin-induced hypoglycemia caused a predicted sharp increase in aspartate level (165%) and decreased glutamate (-20%) and glutamine (-38%) levels in the intact striatum. Pretreatment of rats with 2-APH significantly reversed the insulin-induced changes in striatal aspartate, glutamate, and glutamine levels, especially in the intact hemisphere. In normoglycemic control rats, the "metabolic," i.e., concentration in the lesioned hemisphere, aspartate pool constituted 72% and the "synaptic," i.e., the concentration difference between the intact and lesioned hemispheres, 28% of the total striatal aspartate pool. 2-APH had no effect on the level of "metabolic" aspartate in the striata of normoglycemic rats but caused an almost complete suppression of "synaptic" aspartate. Following insulin-induced hypoglycemia, the "metabolic" aspartate pool doubled, whereas the "synaptic" aspartate pool increased 3.5-fold in the absence of 2-APH. The insulin-induced rise in "synaptic" aspartate level was almost completely blocked by 2-APH (a 5% rise instead of a 3.5-fold rise).(ABSTRACT TRUNCATED AT 250 WORDS)     

Age,growth and reproductive biology of the silky shark,Carcharhinus falciformis,and the scalloped hammerhead,Sphyrna lewini,from the northwestern Gulf of Mexico

Synopsis The silky shark, Carcharhinus falciformis, and scalloped hammerhead, Sphyrna lewini, represent >80% of the shark by-catch of the winter swordfish/tuna longline fishery of the northwestern Gulf of Mexico. This catch represents a potential supplemental fishery, yet little is known of the life histories of the two species. This report relates reproductive biology data to age and growth estimates for 135 C. falciformis and 78 S. lewini. Unlike other regional populations, C. falciformis in the Gulf of Mexico may have a seasonal 12 month gestation period. Males mature at 210–220 cm TL (6–7 yr); females at >225 cm TL (7–9 yr). Application of age at length data for combined sexes produced von Bertalanffy growth model parameter estimates of L_∞ = 291 cm TL, K = 0.153, t₀ = −2.2 yr. Adult male S. lewini outnumbered adult females in catches because of differences in the distributions of the sexually segregated population. Males mature at 180 cm TL (10 yr); females at 250 cm TL (15 yr). von Bertalanffy parameter estimates for combined sexes of this species were L_∞ = 329 cm TL, K = 0.073, t_o = −2.2 yr.     

Pollination systems in a warm temperate evergreen broad-leaved forest on Yaku Island

Animal pollination in a warm temperate evergreen broad-leaved forest was observed on Yaku-shima Island, south of Kyushu, Japan. Three groups of plants were categorized: canopy-flowering tree species, understory-flowering tree species, and climber and epiphyte species. Each of these formed different pollination systems. The canopy-flowering tree species had shallow, dish-shaped flowers and utilized various types of opportunistic pollinators. Most of the climber and epiphyte species had deep, tube-shaped flowers and specialized pollinators, although some climber species which bloomed in the canopy especially in winter, had opportunistic pollinators. The understory-flowering tree species had large dish- or funnel-shaped flowers and endothermic pollinators able to tolerate the dark and cold conditions under the canopy. The individual trees of canopy-flowering tree species produced large numbers of flowers simultaneously (mass-flowering) and had a well synchronized flowering period. Each canopy-flowering tree species segregated its flowering time from those of the anothers. Climber and epiphyte species and most of the understory-flowering tree species produced small numbers of flowers sequentially (extended flowering) and showed a long flowering period.     

Evidence for slow turnover in a fraction of Photosystem II complexes in thylakoid membranes

We used two different techniques to measure the recovery time of Photosystem II following the transfer of a single electron from P-680 to Q_A in thylakoid membranes isolated from spinach. Electron transfer in Photosystem II reaction centers was probed first by spectroscopic measurements of the electrochromic shift at 518 nm due to charge separation within the reaction centers. Using two short actinic flashes separated by a variable time interval we determined the time required after the first flash for the electrochromic shift at 518 nm to recover to the full extent on the second flash. In the second technique the redox state of Q_A at variable times after a saturating flash was monitored by measurement of the fluorescence induction in the absence of an inhibitor and in the presence of ferricyanide. The objective was to determine the time required after the actinic flash for the fluorescence induction to recover to the value observed after a 60 s dark period. Measurements were done under conditions in which (1) the electron donor for Photosystem II was water and the acceptor was the endogenous plastoquinone pool, and (2) Q₄₀₀, the Fe²⁺ near Q_A, remained reduced and therefore was not a participant in the flash-induced electron-transfer reactions. The electrochromic shift at 518 nm and the fluorescence induction revealed a prominent biphasic recovery time for Photosystem II reaction centers. The majority of the Photosystem II reaction centers recovered in less than 50 ms. However, approx. one-third of the Photosystem II reaction centers required a half-time of 2–3 s to recover. Our interpretation of these data is that Photosystem II reaction centers consist of at least two distinct populations. One population, typically 68% of the total amount of Photosystem II as determined by the electrochromic shift, has a steady-state turnover rate for the electron-transfer reaction from water to the plastoquinone pool of approx. 250 e⁻ / s, sufficiently rapid to account for measured rates of steady-state electron transport. The other population, typically 32%, has a turnover rate of approx. 0.2 e⁻ / s. Since this turnover rate is over 1000-times slower than normally active Photosystem II complexes, we conclude that the slowly turning over Photosystem II complexes are inconsequential in contributing to energy transduction. The slowly turning over Photosystem II complexes are able to transfer an electron from P-680 to Q_A rapidly, but the reoxidation of Q⁻_A is slow (t1/2 = 2 s). The fluorescence induction measurements lead us to conclude that there is significant overlap between the slowly turning over fraction of Photosystem II complexes and PS II_β reaction centers. One corollary of this conclusion is that electron transfer from P-680 to Q_A in PS II_β reaction centers results in charge separation across the membrane and gives rise to an electrochromic shift.