Search

Risk-perception theory, derived largely from studies of technological risk assessment by Slovic and associates (Slovic, 1987; Slovic, Fischhoff, & Lichtenstein, 1986), may assist in understanding the risks seen to be associated with health-related behaviors. Risk perceptions, and their relationship to different stages of the acquisition of smoking behavior, were examined in a sample of 205 Australian high school students who were in Grades 10 and 11, and had an average age of 15 years. Current smokers differed from experimenters, ex-smokers, and never smokers on a number of factors that are argued to underlie perceptions of risk: They perceived less personal risk, less severe health consequences, greater benefits relative to risks, found it more difficult to picture harmful consequences to themselves, and perceived smoking to be less avoidable. Implications for understanding and for dealing with the initiation and maintenance of smoking behavior in adolescence are discussed.

The density of binding sites for kainic acid was measured both in fresh slices and in the particulate fraction of the homogenate from various zones of the CNS of goldfish. Binding in the homogenate fraction was always found higher than in the corresponding slices, which should be representative of receptors located on the outer surface of the cellular membrane. The hypothesis is discussed that the sites demonstrated by homogenization are located in the intracellular compartment.

Binding of [3H]kainic acid to the synaptosomal-mitochondrial fraction (P2) of the goldfish brain was studied. Specific binding to this fraction represents about half of the total binding capability of the homogenate particulate material and is enriched in synaptic membranes; it is greater by about two orders of magnitude than those given for rat brain and pigeon optic tectum membranes. Association of the ligand-site complex has a time constant lower than 1 min and the same is true for the main component of the dissociation process. The binding equilibrium is apparently not affected by substances contained in the fraction material. The analysis of the dose-response data showed a main receptor population (B max = 139 pmol/mg protein) which displayed positive cooperativity (nH = 1.29). The same behaviour was shown by washed membranes from the same fraction but, in this case, the affinity for the ligand was lower (apparent affinity constants: K'D = 0.28 nM for the intact fraction and K'D = 0.38 nM for membranes). A smaller population of sites with higher affinity was also detected both in the intact fraction and in membranes. Among the substances tested as displacers of kainic acid from the synaptosomal sites, the most effective were quisqualate and L-glutamate. Folic acid and its dihydro and tetrahydro derivatives were half as potent as glutamate whereas methyltetrahydrofolic acid and folinic acid had a very weak action. The difference between these sites and those detected on rat brain membrane preparations is discussed.

A quantitative study of the kinetics of electron transfer under coupled conditions in photosynthetic bacteria has so far been prevented by overlap of the electrochromic signals of carotenoids and bacteriochlorophyll with the absorbance changes of cytochromes and reaction centers. In this paper a method is presented by which the electrochromic contribution at any wavelength can be calculated from the electrochromic signal recorded at 505 nm, using a set of empirically determined polynomial functions. The electrochromic contribution to kinetic changes at any wavelength can then be subtracted to leave the true kinetics of the redox changes. The corrected redox changes of the reaction center measured at 542 and 605 nm mutually agree, thus providing an excellent test of self-consistency of the method. The corrected traces for reaction center and of cytochrome b-566 demonstrate large effects of the membrane potential on the rate and poise of electron transfer. It will be possible to study the interrelation between proton gradient and individual electron reactions under flash or steady-state illumination.