Parametric analysis of dynamic postural responses

A detailed theoretical understanding of postural control mechanisms must be preceded by careful quantification of both the deterministic and stochastic aspects of postural behavior of normal and abnormal subjects under various dynamic conditions. Toward this end, concise parametric transfer function plus noise models were derived for both shoulder and waist position data obtained by applying a linear anteriorposterior bandlimited pseudorandom disturbance to the base of support of human subjects. Model orders as well as model parameters were determined empirically. One advantage of this modeling procedure is the conciseness of the postural models, permitting easy statistical analysis of the data obtained under different dynamic conditions from many subjects. Model features, including pole and zero locations, from 6 normal subjects each tested on 5 consecutive days under 3 input amplitudes and eyes open and closed conditions are presented. The resulting transfer function models consist of only 1 or 2 poles near the integration position on the Z plane unit circle and 0 to 2 zeros. Locations of the poles indicate that the eyes closed responses are more oscillatory, less damped, and with higher gains than the eyes open responses. These transfer functions are similar to nonparametric ones of other authors. The noise model orders are also small. Their spectra are those of low pass systems. Also, the quantity and frequency range of the postural noise is positively related to the amplitude of platform motion as well as related to the presence or absence of vision. Present address: Kresge Hearing Research Institute, University of Michigan Medical School, 1301 E. Ann St., Ann Arbor, MI 48109, USA     

Head regeneration and polarity reversal inHydra attenuata can occur in the absence of DNA synthesis

Summary Regeneration in hydra is considered to be morphallactic because it can occur in the absence of cell division. Whether DNA synthesis is required for regeneration or other repatterning events is not known. The question was investigated by blocking DNA synthesis with hydroxyurea and examining several developmental processes. Head regeneration, reversal of regeneration polarity and battery cell differentiation all took place in the absence of DNA synthesis. Hence, morphallactic regulation in hydra is independent of both DNA synthesis and mitosis.     

The effect of renal vasodilation and hypotonic volume expansion on water excretion in dogs after anesthesia and surgery

The possible effects of renal vasoconstriction from anesthesia and surgery on water excretion after hypotonic volume expansion (HVE) were studied in 18 well conditioned anesthetized dogs, with and without the infusion of phenoxybenzamine and acetylcholine into the renal artery of the cannulated kidney. In 6 dogs (Group 1 - Control) whose renal artery was infused with isosmotic saline, HVE resulted in a bilateral increase in GFR and UV (p < .05). ERPF, Cosm, C_H2O, U_NaV, U_KV, RBF, RVR and MAP did not change significantly. In 6 other dogs (Group 2), whose cannulated kidney was infused with phenoxybenzamine 50 μg/min before and during HVE, GFR increased on the infused side while CH₂O and UV increased bilaterally (p < .05). ERPF, Cosm, U_NaV, U_KV, RBF, RVR and MAP were not affected significantly. The addition of ADH, 2 mu/min into the phenoxybenzamine infusate, decreased ERPF, RBF and RVR bilaterally and CH₂O on the infused side (p < .05). It had no effect upon GFR, Cosm, U_NaV, U_KV and MAP. In another 6 dogs, (Group 3), whose cannulated renal artery was infused with acetylcholine (20 μg/min) before and during HVE, C_H2O, UV and RVR increased bilaterally (p < .05). ERPF and RBF decreased bilaterally (p < .05), whereas GFR, Cosm, U_NaV and MAP were unaffected. U_KV decreased on the infused side (p < .05). The addition of ADH (2 mu/min)_into the acetylcholine infusate, decreased C_H2O bilaterally and increased Cosm and U_KV on the control side (p < .05). It had no effect on ERPF, GFR, UV, U_NaV, RBF, RVR and MAP. These observations suggest that anesthesia and surgery produce renal vasoconstriction and this together with increased ADH release, interfere with water excretion by the kidney. Previous renal vasodilation prevents these influences of anesthesia and surgery.     

Caprine Arthritis-Encephalitis Virus Is Distinct from Visna and Progressive Pneumonia Viruses as Measured by Genome Sequence Homology

Competitive inhibition of hybridization between ¹²⁵I-labeled caprine arthritis-encephalitis viral RNA and homologous cDNA by heterologous viral RNA shows that the caprine retrovirus shares <20% genome sequence homology with visna and progressive pneumonia viruses. These viruses, however, are indistinguishable in immunodiffusion reactions involving the major structural protein (p28).     

Physiological Adaptation to the Loss of Amino Acid Transport Ability

A strain of Neurospora crassa devoid of constitutive amino acid transport ability can utilize arginine as the sole nitrogen source. Nitrogen starvation, presence of arginine, and mutational inactivation of the general permease are key factors in signaling production of an extracellular enzyme which removes the alpha-amino group from the amino acid.     

The maintenance of shore-level size gradients in an intertidal snail (Littorina sitkana)

Summary The size of many intertidal animals varies with tidal height. These size gradients could be produced by growth or survival varying with tidal height, or by animals moving to a preferred tidal level. The body size of the snail, Littorina sitkana, increases steadily with tidal height in rocky high intertidal habitats of British Columbia. To determine how size gradients were maintained in L. sitkana, I quantified how growth, survival, and snail movement varied with tidal height. I studied populations of L. sitkana found on sheltered pebble beach and exposed basaltic shelf habitats. Mark-recapture studies and experimental transplants showed that growth could not have produced the size gradients because snail growth rates in both habitats were as fast or faster at low tidal levels (where the snails were the smallest) than at high tidal levels. However, survival rates were lowest at low tidal levels. On pebble beaches, this was due to size selective predation on large snails by the pile perch, Rhacochilus vacca. On basaltic shelves, heavy wave action at low tidal levels may have caused the poor survival rates. Transplanted snails moved homeward on pebble beaches, but not on basaltic shelves. Reduced survival rates at low tidal levels cause size gradients in both habitats, and snail movement helps to maintain size gradients on pebble beaches.     

Cellular basis for tentacle adherence in the Portuguese man-of-war (Physalia physalis)

The fishing tentacles of Physalia physalis (Portuguese man-of-war) adhere to prey and human victims by the penetration of a barbed tubule connected to an intracellular nematocyst. The nematocyst is surrounded by a fibrillar system of microtubules and microfilaments that terminate in hemidesmosomal processes which anchor the nematocyst to the acellular mesoglea of the tentacle.     

Incorporation of3H-thymidine into DNA and the activity of alkaline phosphatase in zinc-deficient fetal rat brains

The incorporation of³H-thymidine into DNA in the brains of the 17-day and 20-day old rat fetuses was significantly reduced by maternal zinc restriction during pregnancy. The activity of the enzyme thymidine kinase (EC 2.7.1.21) was similarly reduced in the zine-deprived fetal brains on days 14 and 20 of gestation, but not on day 17. Fetal brain alkaline phosphatase (EC 3.1.3.1) was significantly depressed by maternal zinc deprivation on days 17 and 20 of pregnancy. The data suggest an association between thymidine kinase and the reduced incorporation of³H-thymidine into DNA in the brains of 20-day old fetuses but not in animals on day 17. Alkaline phosphatase was however depressed at this stage. The suggestion is made that because of the complexity of brain development, future biochemical studies in this area should concern specific structures in the brain at particular critical stages during neurogenesis.     

Kinetic studies of the binding of inhibitors to thermolysin

The K_I values for inhibition of thermolysin activity by N-β-phenylpropionyl-aliphatic amino acids (Gly, Ala, Val, Leu, Ile) are correlated by π, the hydrophobic substituent parameter for the amino acid side chain (log K_I = ?0.73π ?1.80, correlation coefficient = 0.990). By contrast, the K_I values for the corresponding benzyloxycarbonyl amino acids are poorly correlated by π, but show a good correlation with the steric parameter E_s(log K_I = 0.880E_s ? 3.086, correlation coefficient = 0.985). Binding of β-phenylpropionyl-l-alanine is associated with an acidic residue of pK 7.3 and a basic residue of pK 8.0 in the E · I complex, and appears to raise the pK of Glu-143 by 2 units. Binding of benzyloxycarbonyl-Ala and -Phe is associated with an acidic residue of pK 8.0 and two basic residues, both with pK 8.3. Three similar pK values are observed with benzyloxycarbonyl-Phe. These results are interpreted in terms of different modes of binding of β-phenylpropionyl and benzyloxycarbonyl inhibitors.     

Immunological and biochemical analysis of a null mutant of α-glycerolphosphate dehydrogenase from Drosophila melanogaster

Summary A Drosophila null mutant(BO-1-4) of -glycerolphosphate dehydrogenase induced by ethylmethane sulfonate(EMS) was analyzed by double immunodiffusion, enzyme immuno-inactivation, immunoelectrophoresis and two-dimensional electrophoresis. Based on all the immunological evidence, this mutant appears to express no protein that can cross-react with the antiserum specific to -glycerolphosphate dehydrogenase. A protein spot corresponding to -glycerolphosphate dehydrogenase was identified on two-dimensional gels of the soluble fly homogenates. The absence of this protein spot on two-dimensional gels of this null mutant further supported the immunological data. The activities of seven other enzymes in the related metabolic pathways were determined for the mutant and the control Drosophila. The null mutant does not show significant alterations in activities of these enzymes. The relationship between the deficiency of this enzyme and the inability for the sustained flight of the null mutant was discussed in terms of cellular metabolic regulations.Abbreviations used -GPD -glycerolphosphate dehydrogenase (EC 1.1.1.8) - EMS ethylmethane sulfonate - TEMED N,N,N,N-tetramethylene diamine - pI isolectric point - CRM immunological cross-reacting material