The trajectory of a stiff rod in a curved potential energy trough

The equilibrium trajectory of the axis of a rod subject to an externally imposed curved potential energy trough tends to conform to the shape of the curved trough, but also tends to be straight because of elastic resistance to bending. The actual path of the axis is a balance between the two extremes. We consider a potential energy trough centered along a circular arc of radiusR. For a rod of small length compared toR, we show that the axis at equilibrium forms an arc of a circle of radius greater thanR. The value of the radius of the axial path depends on the relative values of the Hooke’s Law bending constant for the rod and the depth and width of the trough. Motivation for the calculation is provided by nucleosomal DNA, which conforms to the surface of a roughtly cylindrical histone core at physiological ionic strength, but is observed to unwind into a partially extended conformation at very low ionic strength. We suggest that the rigidity to bending of short DNA segments becomes sufficiently great at low ionic strength to overcome attractive interactions with the histone surface. Alternately, of course, if during the cell cycle mutually attractive forces between DNA and histone core are weakened at constant ionic strength, the same type of unfolding would be expected to occur as the strength of the DNA-histone contacts drops below the level required to overcome elastic resistance to bending of the DNA rod.     

The influence of mineral salts on fecundity of the water flea (Daphnia magna) and the implications on toxicity testing of industrial wastewater

The effects of mineral salts constituting water hardness on fecundity ofDaphnia magna were assessed. Of the salts tested, increased concentrations of NaHCO₃ and MgSO₄ had no effect on fecundity, CaSO₄ significantly increased fecundity, and KCl significantly reduced fecundity. The number of offspring produced per daphnid was correlative to the CaSO₄ concentration at CaSO₄ concentrations between 91 and 2100 mg/ℓ. The effects of CaSO₄ on daphnid fecundity could influence the interpretive outcome of industrial wastewater toxicity tests using this species when the waste and dilution waters contain different concentrations of CaSO₄. It is recommended that when performing these tests, dilution water be sampled at the intake site of the industry's water source, thus assuring initial comparability of the waste and dilution waters. The CaSO₄ content of the water prior to and after industrial use should be determined to identify any alterations of CaSO₄ concentration during use. Identification of CaSO₄ concentration differences can aid in the interpretation of effects associated with the wastewater.     

Endogenous phosphorylation of retinal photoreceptor outer segment proteins by calcium phospholipid-dependent protein kinase

A calcium phospholipid-dependent protein kinase (C-kinase) activity was detected in the soluble fraction of rod outer segments (ROS) of the bovine retina. The enzyme required calcium, phosphatidylserine (PS) and diacylglycerol for maximal activity. In the presence of calcium and PS, C-kinase endogenously phosphorylated proteins with molecular weights of 95,000, 91,000, 31,000, 21,000, 19,000, 18,000, 16,000, 14,000 and 11,000. Addition of diolein in the reaction mixture further enhanced the endogenous phosphorylation of these proteins. Retinal was found to inhibit the phosphorylation of endogenous proteins by C-kinase in a concentration dependent manner. Half-maximal inhibition of enzyme activity was obtained at a retinal concentration of about 12μM. These results suggest that calcium, phospholipids and the C-kinase enzyme may play an important role in the functional regulation of rod photoreceptors and, with retinal, perhaps in the visual process as well.     

Histophotometric Evaluation of Glutamate Dehydrogenase Activity of the Rat Hippocampal Formation During Postnatal Development,with Special Reference to the Glutamate Transmitter Metabolism

Transmitter glutamate/aspartate synthesis is known to proceed along different metabolic pathways. In this light, the functional relevance of glutamate dehydrogenase in postnatally maturing glutamatergic/aspartatergic structures was studied by means of quantitative enzyme histochemistry. The basic requirements concerning the kinetics and calibration of the histochemical glutamate dehydrogenase reaction used were proved to be met in order to obtain valid quantitative data. The histochemically demonstrable activity of glutamate dehydrogenase (EC 1.4.1.3) in the hippocampal formation of the rat increased markedly during postnatal development. On day 30, the distribution pattern observed was similar to that in adult animals. While the enzyme activity rose within cell body layers from day 0 to day 30 by 240-285%, the increase in neuropil layers was found to be up to 830%. Maximum values were seen in the stratum lacunosum-moleculare of CA1 and CA3 and the stratum moleculare of the dentate fascia on day 30. Since the hippocampal neuropil is supposed to be copiously provided with glutamatergic (and aspartatergic?) structures which become functional in rats during the first weeks of postnatal life, the increase in enzyme activity is discussed to be primarily a consequence of maturing synaptic systems using glutamate and/or aspartate as transmitters.     

Central projections of labellar taste hairs in the blowfly,Phormia regina Meigen

Summary We have traced the central projections of the receptor neurons associated with each of the eleven largest taste hairs on the labellum of the blowfly, Phormia regina (Meigen), by staining them with cobaltous lysine. The eleven hairs fall into three groups which reflect their peripheral locations and their branching patterns in the subesophageal ganglion. Group 1, consisting of the anterior hairs (numbers 1 and 2) and Group 3, consisting of the posterior hairs (numbers 9–11) project bilaterally, while Group 2, consisting of the middle hairs (numbers 3–8) projects primarily ipsilaterally. The central projections of the hairs within a single group are similar. Each hair houses four chemoreceptors, which have differing chemical sensitivities and behavioral roles, and one mechanoreceptor. In some cases, there were indications that the different cells within a single hair have different central branching patterns. For some hairs, however, it was clear that a single central branching region and pattern was shared by more than one receptor cell. We failed to find either a continuous somatotopic representation of a hair's position on the periphery, or an anatomical segregation of receptors coding for different modalities. Behavioral experiments indicate that the fly is informed both of the identity of the hair stimulated and of the chemical nature of the stimulus. Our results suggest that this information is not represented on a gross anatomical level.     

Alkyl phosphotriester modified oligodeoxyribonucleotides. VI. NMR and UV spectroscopic studies of ethyl phosphotriester (Et) modified Rp-Rp and Sp-Sp duplexes, (d[GGAA(Et)TTCC])2.

1H NMR chemical shift assignments for the title compounds were made for all but a few H5' and H5" signals using two-dimensional nuclear Overhauser effect (2D-NOE) data, which was also used for the first time to assign absolute configuration at phosphorus. The chemical shifts were, in general, similar to those reported [Broido, M.S., et al. (1985) Eur. J. Biochem. 150, 117-128] for the B-like conformation of the unmodified, parent duplex, [d(GGAATTCC)]2. Differences in chemical shifts for corresponding protons were mostly localized to the AA(Et)TT region, and showed some stereochemical dependence. Unambiguous assignment of the phosphotriester 31P signals was achieved in a novel way using selective insensitive nucleus enhancement by polarization transfer (selective INEPT) NMR. The Rp-Rp duplex melted ca. 11 degrees C lower than either the Sp-Sp or parent duplexes, as evidenced by Tm and variable temperature 1H/31P NMR measurements. The 2D-NOE data for the Rp-Rp duplex suggested possible steric interactions between the ethyl group and the H3' of the flanking A residue. At low ionic strength, the Sp-Sp and parent duplexes had similar stability but at high ionic strength the Sp-Sp duplex was less stable.     

Discrimination of calling song models by the cricket,Teleogryllus oceanicus: the influence of sound direction on neural encoding of the stimulus temporal pattern and on phonotactic behavior

Summary Recordings were made from an identified auditory neuron, the omega neuron, in the cricketTeleogryllus oceanicus. Models of the conspecific calling song and of the song of another species were presented either singly or simultaneously, and the degree to which the temporal pattern of the conspecific model was encoded in the neuron's spike train was determined. When a single stimulus was presented alone, its temporal pattern was faithfully reflected by the cells's spiking activity, no matter what the azimuth of the broadcasting loudspeaker (Fig. 3). When two stimuli were presented simultaneously from opposite sides, encoding of the pattern ipsilateral to the recorded neuron was interfered with only slightly by the contralateral pattern, as long as the two loudspeakers were sufficiently separated (Figs. 2, 3, 4). When the loudspeakers were each 15° from the cricket's midline, however, the encoding of the temporal pattern of the ipsilateral song model was severely disrupted (Figs. 3, 4). Bilateral interactions are important in determining the response level of the neuron, but do not appear to contribute to the direction-selective encoding of the stimulus temporal pattern (Figs. 5, 6).Phonotactic steering movements of tethered, flying crickets were recorded under stimulus conditions similar to those used in the neurophysiological tests. Under one-stimulus conditions, crickets attempted to turn towards the conspecific model for all tested speaker locations. The heterospecific model elicited reliable steering behavior when it was broadcast from azimuths of 90° and 60°, but often failed to elicit consistent responses when the speaker was positioned closer to the cricket's midline (Figs. 7, 8A and 8B). Responses to the heterospecific pattern were smaller in amplitude than those to the conspecific song model (Figs. 7, 8B). Under two-stimulus conditions, the conspecific model was consistently preferred over the heterospecific song for all tested speaker locations in half the tested crickets. In the remaining animals, preference for the conspecific pattern was only evident for the larger loudspeaker azimuths (Figs. 7, 8C).These results demonstrate that simultaneouslypresented stimuli can be represented separately in the nervous system as a consequence of auditory directionality. It is postulated that the cricket's ability to choose between these stimuli may result from the interactions between two bilaterallypaired song recognizers, each of which may be driven primarily by sound stimuli from one side.     

Similarity of EPR Signal IIf rise and P-680+ decay kinetics in Tris-washed chloroplast Photosystem II preparations as a function of pH

The rise time, of Signal II_f and the decay time of P-680⁺ have been measured kinetically as a function of pH by using EPR. The Photosystem II-enriched preparations which were used as samples were derived from spinach chloroplasts, and they evolved oxygen before Tris washing. The onset kinetics of Signal II_f are in agreement, within experimental error, with the fast component of the decay of an EPR signal attributable to P-680⁺. The signal II_f rise kinetics also show good agreement with published values of the pH dependence of the decay of P-680⁺ measured optically (Conjeaud, H. and Mathis, P. (1980) Biochim. Biophys. Acta 590, 353–359). These results are consistent with a model where the species Z (or D₁) responsible for Signal II_f is the immediate electron donor to P-680⁺ in tris-washed Photosystem II fragments.     

Theoretical significance of the condition δ=2μ in bacterial chemotaxis

First-order spatial gradients are reliquished in the Schrödinger-Bloch equation for bacterial chemotaxis if and only if the flux coefficient-motility ratio equals 2, the precise value measured in recent experiments onEscherichia coli attracted by oxygen. Moreover, for δ/μ=2 the Schrödinger-Bloch function Ψ is simply equal to the number of bacteria cells per unit volume divided by the chemoattractant concentration.