A model for signal detection based on an adaptive filter

A model for the detection of brief stimuli based on a change detection algorithm and a random walk traversed by the residuals generated by an adaptive filter is proposed. A linear relationship between mean RT and response proportion measures obtained in a simulation of the model was consistent with data obtained in psychophysical discrimination tasks using human observers. In this way the role of the sensory system as a detector of change in ambient stimulation could be incorporated into a signal detection model.     

Replication of bacteriophage lambda DNA. Examination of variants containing double origins and observation of a bias in directionality

Bacteriophage λ variants have been constructed that possess two λ ori sites. Replicative intermediates resulting from infection with these phages have been investigated. We find that initiation of replication from the ori site on an EcoRI fragment (containing all the DNA sequences from within the red gene to the middle of gene O) cloned in the inverted orientation is predominantly bidirectional but occurs at a decreased frequency. Double initiations were observed at low frequency. However, a second cloned ori fragment (carrying two large deletions and a small insertion) cloned in the normal orientation demonstrated insignificant levels of replication from the cloned site unless the normal ori had already initiated.A bias in directionality of λ replication has been observed. Molecules that replicate unidirectionally propagate to the right more often than to the left. If the cloned ori-containing EcoRI fragment is inserted with reversed polarity, then the bias is towards the left. Bidirectional λ replicative intermediates also appear to show a similar bias but this is superimposed on a large, apparently random, effect that results in asymmetric growing-point propagation.     

Effects of butylated hydroxyanisole on the aryl hydrocarbon hydroxylase of rats and mice

The effects of butylated hydroxyanisole (BHA) and butylated hydroxytoluene (BHT) on the aryl hydrocarbon hydroxylase (AHH) activities in the liver, lung and skin of rats and mice have been studied to examine the possible mechanisms of the anticarcinogenic actions of these compounds. Both compounds inhibit the hydroxylase activities of hepatic microsomes and nuclei, with BHA a more potent inhibitor than BHT. The AHH of lung microsomes is inhibited to a lesser extent by BHA and BHT than that of the liver. The AHH activities of both liver and lung microsomes become less susceptible to the inhibition after pretreatment of the animals with 3-methylcholanthrene (MC) or 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) but phenobarbital (PB) pretreatment does not produce such an effect. In skin homogenates, however, the AHH activities of control rats and mice are not inhibited by BHA and BHT. The only skin sample which is inhibited by BHA and BHT is that from TCDD-pretreated mice. It has been established that the extent of inhibition with different samples is related to the concentration of BHA in the incubation but not to the amounts or specific activities of microsomes used. Double reciprocal plots suggest that BHA exerts a mixed inhibition on the hydroxylase of liver microsomes with a K_i of 7.7 μM. Analysis of the metabolites of benzo[a]pyrene (BP) shows that BHA inhibits the formation of various metabolites uniformly without changing the regio-selectivity of the enzyme system. The mechanism of inhibition has also been studied with a reconstituted AHH system consisting of cytochrome P-450 (P-450), reductase and phospholipid. The system with P-450 isolated from PB-induced microsomes is inhibited to a much greater extent than that with MC-induced P-450. The results indicate that the inhibitory action of BHA is dependent on the species of the animal, tissue types and treatment with inducers.     

Specificity of Insertion by the Translocatable Tetracycline-Resistance Element Tn10

Genetic analysis of 131 independent transpositions of the tetracycline-resistance element Tn10 from a single site in phage P22 into the histidine operon of Salmonella typhimurium reveals that Tn10 insertions are not randomly distributed along this chromosomal target. The insertions occur in 22 different "clusters"; insertions within each cluster are very tightly linked in recombination tests. Tn10 insertions are not evenly distributed among the identified clusters. The existence of these clusters suggests that this chromosomal target contains particular genetic signals that guide Tn10 to particular preferred positions for insertion. Insertions within each cluster occur in both orientations with roughly equal frequency.--The relationship among different insertions within each cluster has been examined. The resolution of genetic mapping places an upper limit of about 50 basepairs on the distance between different insertions within a cluster. Different insertions within a cluster usually have the same reversion frequency; however, heterogeneity in reversion frequency has been detected in at least two clusters. For most clusters, the available data are consistent with the simple possibility that all insertions within a cluster are at identical positions; however, the data do not exclude other possibilities.     

Value of 1-alpha-hydroxy vitamin D3 in treatment of primary hyperparathyroidism before parathyroidectomy.

The postoperative course of six patients with primary hyperparathyroidism and obvious radiological evidence of bone disease pretreated with 1-alpha-hydroxy vitamin D3 (1 alpha HCC) was indistinguishable from that of six patients with a similar clinical and radiological picture who were not pretreated. 1alphaHCC may increase the hypercalcaemia in some cases and cannot be recommended for the routine preparation of such patients for surgery.     

Transdetermination of Drosophila imaginal discs cultured in vitro

Imaginal discs of Drosophila melanogaster undergo transdetermination when cultured in vivo in the abdominal cavity of adult female hosts. We report here that leg discs cultured in vitro, in a recently developed system, also undergo transdetermination. Whether cultured in vivo or in vitro, leg discs produce a similar range of specific transdetermined structures. Moreover, in comparison to discs cultured in vivo, the discs cultured in vitro exhibit a similar correlation between the amount of growth and the total frequency of transdetermination.     

Protoplast induction inMicrasterias andCosmarium

Summary Protoplasts of the desmidsMicrasterias angulosa, M. denticulata, M. thomasiana andCosmarium turpinii were obtained by incubating cells in Waris' liquid medium + 0.3 M mannitol + 2% Cellulysin for 1–3 hours. One osmotically fragile protoplast was formed at the isthmus from the joint contents of both semicells. The resultant protoplasts were bright green and remained so for more than 5 days in the osmotically protective medium. The protoplast yield was better than 80%. The empty cell walls were not digested by the Cellulysin or by autolytic enzymes.     

The zinc content of yeast alcohol dehydrogenase

Analyses for zinc in high specific activity preparations of yeast alcohol dehydrogenase (YADH) indicate a metal content of 1.8–1.9 moles of zinc per mole of enzyme subunit. This zinc content is observed for YADH prepared from Bakers yeast by recrystallization from Am₂SO₄ containing 1 mM EDTA, followed by chromatography on DE-52 and Sephadex-G-200. YADH obtained from Boehringer-Mannheim is characterized by a variable specific activity: preparations with Sp. Ac. = 380–400 U/mg contain 1.8–1.9 moles of zinc per mole of subunit. Dialysis of YADH against EDTA (pH 8.5, 25°, under N₂) reduces the specific activity and zinc content in an approximately linear fashion down to a Sp. Ac. = 150 U/mg, consistent with the preferential loss of a single, weakly bound zinc per subunit which is essential for catalytic activity. Dialysis of YADH against 1 mM ZnCl₂ (pH 6.5–8.5, 25°, under N₂) does not lead to an increase in the zinc content of the enzyme, indicating that under these conditions zinc does not bind adventitiously to YADH. Dialysis against 50 mM CoSO₄ (pH 5.5, 25°, under N2, 60–90 hr) leads to an exchange of ≈ 40% of the enzyme-bound zinc by cobalt. Our preparations of YADH are consistently characterized by a zinc content of ≈ 2 per subunit and we are unable to reduce the zinc content of YADH by dialysis against EDTA without a concomitant loss in enzyme activity, in contrast to reports of one zinc per subunit [Veillon, C. and Sytkowski, A.J., BBRC $\text{67}$: 1499 (1975); Vallee, B.L. and Hoch, F.L., Proc. Nat. Acad. Sci. USA $\text{41}$: 327 (1955)]. The findings reported here, together with the observed structural similarities between YADH and horse liver alcohol dehydrogenase [Jornvall, H., Woenckhaus, C. and Johnscher, G., Eur. J. Biochem. $\text{53}$: 71 (1975)], suggest a role for zinc at both a structural and catalytic site in YADH.     

Non-accidental injury in children: what we do in Derby.

A scheme for dealing with cases of non-accidental injury in children in the Derby clinical area has been operating since 1971. A stable team of doctors, policemen, and social workers deal with each case. The parents are told at once that battering is suspected, and the police and social services department co-operate closely in establishing the facts, supporting the family, and protecting the child. A psychiatric assessment of the parents may help social workers decide on the long-term care of the child, and the forensic physician is invaluable if the case has to go to court. The team has made three recommendations about prevention and management of these cases: a specialist social service team should be set up to deal with these children and regain the skills and knowledge lost when children''s departments were abolished in 1971; babies should be routinely weighed naked in infant welfare clinics; and juvenile courts should be able to order a psychiatric report on the parents in care proceedings.