The early Miocene onset of a ventilated circulation regime in the Arctic Ocean

Deep-water formation in the northern North Atlantic Ocean and the Arctic Ocean is a key driver of the global thermohaline circulation and hence also of global climate. Deciphering the history of the circulation regime in the Arctic Ocean has long been prevented by the lack of data from cores of Cenozoic sediments from the Arctic's deep-sea floor. Similarly, the timing of the opening of a connection between the northern North Atlantic and the Arctic Ocean, permitting deep-water exchange, has been poorly constrained. This situation changed when the first drill cores were recovered from the central Arctic Ocean. Here we use these cores to show that the transition from poorly oxygenated to fully oxygenated ('ventilated') conditions in the Arctic Ocean occurred during the later part of early Miocene times. We attribute this pronounced change in ventilation regime to the opening of the Fram Strait. A palaeo-geographic and palaeo-bathymetric reconstruction of the Arctic Ocean, together with a physical oceanographic analysis of the evolving strait and sill conditions in the Fram Strait, suggests that the Arctic Ocean went from an oxygen-poor 'lake stage', to a transitional 'estuarine sea' phase with variable ventilation, and finally to the fully ventilated 'ocean' phase 17.5 Myr ago. The timing of this palaeo-oceanographic change coincides with the onset of the middle Miocene climatic optimum, although it remains unclear if there is a causal relationship between these two events.     

Forecasting for the generation of trading signals in financial markets

In this paper we show that optimal trading results can be achieved if we can forecast a key summary statistic of future prices. Consider the following optimization problem. Let the return r_i (over time i=1, 2, ..., n) for the ith day be given and the investor has to make investment decision d_i on the ith day with d_i=1 representing a ‘long' position and d_i=0 a ‘neutral' position. The investment return is given by r=Σⁿ_i=1r_id_i−cΣⁿ⁺¹_i=1∣d_i−d_i−1∣, where c is the transaction cost. The mathematical programming problem of choosing d₁, ..., d_n to maximize r under a given transaction cost c is shown to have an analytic solution, which is a function of a key summary statistic called the largest change before reversal. The largest change before reversal is recommended to be used as an output in a neural network for the generation of trading signals. When neural network forecasting is applied to a dataset of Hang Seng Index Futures Contract traded in Hong Kong, it is shown that forecasting the largest change before reversal outperforms the k‐step‐ahead forecast in achieving higher trading profits. Copyright © 2000 John Wiley & Sons, Ltd.     

Lack of gravity effect on the speed of amoeboid locomotion inNaegleria gruberi

Summary The speed of amoeboid locomotion was the same for amoebae moving on the top surface and bottom surface of a horizontal perfusion chamber i.e. cell-substrate adhesive forces must be considerably greater than the gravitational force acting on the locomoting amoeba.Acknowledgments. We would like to thank Les Cooper for technical assistance, and the Science Research Council for support.     

Sequence and expression of a frog brain complementary DNA encoding a kainate-binding protein

Excitatory amino acids (EAAs) are important neurotransmitters in the vertebrate central nervous system. Electrophysiological and ligand-binding studies indicate that at least three different receptor subtypes for EAAs exist--N-methyl-D-aspartate, kainate and quisqualate receptor subtypes--on the basis of the preferred agonist of the receptors. We recently purified a kainate-binding protein (KBP) from frog (Rana pipiens berlandieri) brain by domoic acid (a high-affinity kainate analogue) affinity chromatography, and showed that the kainate-binding activity was associated with a protein of relative molecular mass 48,000 (Mr 48 K). The pharmacological properties and the anatomical distribution of KBP were consistent with those of a kainate receptor-ionophore complex. We have now isolated a complementary DNA encoding KBP of Mr 48 K. The deduced amino-acid sequence of the KBP has similar hydrophobic profiles to those found in other ligand-gated ion channel subunits, and shows some amino-acid sequence similarities to the corresponding regions of brain nicotinic acetylcholine receptor subunits. Localization of the KBP messenger RNAs by in situ hybridization histochemistry is compatible with the results of immunohistochemistry and receptor autoradiography studies. COS-7 cells transfected with the cDNA encoding the KBP show high-affinity kainate-binding activity with pharmacological properties similar to those of the biochemically purified KBP. These results provide the first molecular characterization of an EAA-binding site and raise the possibility that the KBP cDNA encodes a ligand-binding subunit of a kainate receptor-ionophore complex.     

Female visual displays affect the development of male song in the cowbird

The role of social stimulation in avian vocal learning is well documented. The separate contribution of social, as opposed to vocal, stimulation has been difficult to address, however, because in almost all cases both tutor and pupil sing. The opportunity to isolate such effects arose in cowbirds (Molothrus ater ater) after discovering that males housed with non-singing female cowbirds made vocal changes which related directly to the female preferences for native song. Here we report how females communicate with males about songs. We describe a visual display by females, a wing stroke, that is elicited by specific vocalizations. The songs that trigger wing strokes are in turn highly effective releasers of copulatory postures, and thus this previously unnoticed female display has biological significance. The data not only provide the first evidence of the tutorial role of male-female interactions during song ontogeny, they also clearly implicate visual stimulation in song learning, a process that has until now been assumed to be affected only by auditory information.     

Identifying individuals by sequencing mitochondrial DNA from teeth.

Mitochondrial DNA (mtDNA) was extracted from teeth stored from 3 months to 20 years, including teeth from the semi-skeletonized remains of a murder victim which had been buried for 10 months. Tooth donors and/or their maternal relatives provided blood or buccal cells, from which mtDNA was also extracted. Enzymatic amplification and direct sequencing of roughly 650 nucleotides from two highly polymorphic regions of mtDNA yielded identical sequences for each comparison of tooth and fresh DNA. Our results suggest that teeth provide an excellent source for high molecular weight mtDNA that can be valuable for extending the time in which decomposed human remains can be genetically identified.     

Afferent respiratory pathways in the avian vagus

Résumé Nous avons enregistré 88 afférences respiratoires du nerf vague chez le poulet. Quelques unes se déclenchaient au cours de l'inspiration eupnéique, d'autres au cours de l'expiration. Jusqu'à présent, on a l'impression qu'il existe plus de types d'activité afférente respiratoire chez l'oiseau que chez le mammifère, mais de nouvelles analyses seront nécessaires pour mieux les préciser. Nous croyons que c'est ici la première preuve évidente de l'existence d'un contrôle afférent vagal de la respiration chez l'oiseau.

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This work was supported by a grant from the British Egg Marketing Board.     

Effect of trifluoperazine and calcium ions on gregarine gliding

Summary The drug trifluoperazine (TFP) inhibits the gliding motility of gregarine protozoans. This suggests that the Ca⁺⁺ binding protein, calmodulin, plays a role in the motility process. However the presence of extracellular Ca⁺⁺ was not required for gliding to occur.Acknowledgments. We should like to thank L. Cooper for technical assistance, Smith, Kline and French for the gift of trifluoperazine, and Terry Preston for valuable discussion.